ORCID Profile
0000-0002-8389-7209
Current Organisations
Manmohan Memorial Institute of Health Sciences
,
University Of Strathclyde
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Publisher: Elsevier BV
Date: 05-2023
Publisher: AIP Publishing
Date: 12-2016
DOI: 10.1063/1.4971252
Abstract: A fully nonlinear solution for bi-chromatic progressive waves in water of finite depth in the framework of the homotopy analysis method (HAM) is derived. The bi-chromatic wave field is assumed to be obtained by the nonlinear interaction of two monochromatic wave trains that propagate independently in the same direction before encountering. The equations for the mass, momentum, and energy fluxes based on the accurate high-order homotopy series solutions are obtained using a discrete integration and a Fourier series-based fitting. The conservation equations for the mean rates of the mass, momentum, and energy fluxes before and after the interaction of the two nonlinear monochromatic wave trains are proposed to establish the relationship between the steady-state bi-chromatic wave field and the two nonlinear monochromatic wave trains. The parametric analysis on ε1 and ε2, representing the nonlinearity of the bi-chromatic wave field, is performed to obtain a sufficiently small standard deviation Sd, which is applied to describe the deviation from the conservation state (Sd = 0) in terms of the mean rates of the mass, momentum, and energy fluxes before and after the interaction. It is demonstrated that very small standard deviation from the conservation state can be achieved. After the interaction, the litude of the primary wave with a lower circular frequency is found to decrease while the one with a higher circular frequency is found to increase. Moreover, the highest horizontal velocity of the water particles underneath the largest wave crest, which is obtained by the nonlinear interaction between the two monochromatic waves, is found to be significantly higher than the linear superposition value of the corresponding velocity of the two monochromatic waves. The present study is helpful to enrich and deepen the understanding with insight to steady-state wave-wave interactions.
Publisher: American Society of Mechanical Engineers
Date: 19-06-2016
Abstract: Slug flow in horizontal pipelines and riser systems in deep sea has been proved as one of the challenging flow assurance issues. Large and fluctuating gas/liquid rates can severely reduce production and, in the worst case, shut down, depressurization or damage topside equipment, such as separator, vessels and compressors. Previous studies are primarily based on experimental investigations of fluid properties with air/water as working media in considerably scaled down model pipes, and the results cannot be simply extrapolated to full scale due to the significant difference in Reynolds number and other fluid conditions. In this paper, the focus is on utilizing practical shape of pipe, working conditions and fluid data for simulation and data analysis. The study aims to investigate the transient multiphase slug flow in subsea oil and gas production based on the field data, using numerical model developed by simulator OLGA and data analysis. As the first step, cases with field data have been modelled using OLGA and validated by comparing with the results obtained using PIPESYS in steady state analysis. Then, a numerical model to predict slugging flow characteristics under transient state in pipeline and riser system was set up using multiphase flow simulator OLGA. One of the highlights of the present study is the new transient model developed by OLGA with an added capacity of newly developed thermal model programmed with MATLAB in order to represent the large variable temperature distribution of the riser in deep water condition. The slug characteristics in pipelines and temperature distribution of riser are analyzed under the different temperature gradients along the water depth. Finally, the depressurization during a shut-down and then restart procedure considering hydrate formation checking is simulated. Furthermore, slug length, pressure drop and liquid hold up in the riser are predicted under the realistic field development scenarios.
Publisher: American Society of Mechanical Engineers
Date: 08-06-2014
Abstract: Offshore wind energy development has gained considerable momentum around the world as wind is stronger and steadier offshore compared to land. This has led to a significant increase in production in recent years, especially offshore wind turbine embedded in shallow waters, such as the recent large scale offshore wind farms in the Northern Europe region. Being at the offshore waters, the wind turbines are subjected to harsh environment. The pile supporting the wind turbine must be reliable and able to withstand such sea condition. It is an important part of the design to study the structural behaviour of the piles under the wave loads. Due to the significant capital cost associated with the fabrication of the large circular cylinders, a new recommended innovative design to overcome such problem is to substitute the circular cylinder with a vertical monopile of octagonal cross-sectional shape. This paper describes the development of an efficient numerical model for structural analysis of wave interaction with octagonal pile using a modified semi analytical Scaled Boundary Finite Element Method (SBFEM). In contrast to the existing solutions obtained using the traditional methods such as the Finite Element Method (FEM) which typically suffer from high computational cost and the Boundary Element Method (BEM) which faces limitation from fundamental equations and problems with singularities. The most prominent advantage that SBFEM has over the FEM is in terms of the number of elements used for calculation and hence a reduction in computational time. When compared with BEM, the SBFEM does not suffer from computational stability problems.
Publisher: Cambridge University Press (CUP)
Date: 25-10-2018
DOI: 10.1017/S104161021800145X
Abstract: To investigate whether amnestic mild cognitive impairment (aMCI) identified with visual memory tests conveys an increased risk of Alzheimer’s disease (risk-AD) and if the risk-AD differs from that associated with aMCI based on verbal memory tests. 4,771 participants aged 70.76 (SD = 6.74, 45.4% females) from five community-based studies, each a member of the international COSMIC consortium and from a different country, were classified as having normal cognition (NC) or one of visual, verbal, or combined (visual and verbal) aMCI using international criteria and followed for an average of 2.48 years. Hazard ratios (HR) and in idual patient data (IPD) meta-analysis analyzed the risk-AD with age, sex, education, single/multiple domain aMCI, and Mini-Mental State Examination (MMSE) scores as covariates. All aMCI groups ( n = 760) had a greater risk-AD than NC ( n = 4,011 HR range = 3.66 – 9.25). The risk-AD was not different between visual ( n = 208, 17 converters) and verbal aMCI ( n = 449, 29 converters, HR = 1.70, 95%CI: 0.88, 3.27, p = 0.111). Combined aMCI ( n = 103, 12 converters, HR = 2.34, 95%CI: 1.13, 4.84, p = 0.023) had a higher risk-AD than verbal aMCI. Age and MMSE scores were related to the risk-AD. The IPD meta-analyses replicated these results, though with slightly lower HR estimates (HR range = 3.68, 7.43) for aMCI vs . NC. Although verbal aMCI was most common, a significant proportion of participants had visual-only or combined visual and verbal aMCI. Compared with verbal aMCI, the risk-AD was the same for visual aMCI and higher for combined aMCI. Our results highlight the importance of including both verbal and visual memory tests in neuropsychological assessments to more reliably identify aMCI.
Publisher: Hindawi Limited
Date: 2017
DOI: 10.1155/2017/2541413
Abstract: The time-dependent mixed bioconvection flow of an electrically conducting fluid between two infinite parallel plates in the presence of a magnetic field and a first-order chemical reaction is investigated. The fully coupled nonlinear systems describing the total mass, momentum, thermal energy, mass diffusion, and microorganisms equations are reduced to a set of ordinary differential equations via a set of new similarity transformations. The detailed analysis illustrating the influences of various physical parameters such as the magnetic, squeezing, and chemical reaction parameters and the Schmidt and Prandtl numbers on the distributions of temperature and microorganisms as well as the skin friction and the Nusselt number is presented. The conclusion is drawn that the flow field, temperature, and chemical reaction profiles are significantly influenced by magnetic parameter, heat generation/absorption parameter, and chemical parameter. Some ex les of potential applications of such bioconvection could be found in pharmaceutical industry, microfluidic devices, microbial enhanced oil recovery, modeling oil, and gas-bearing sedimentary basins.
Publisher: Elsevier BV
Date: 05-2019
Publisher: Elsevier BV
Date: 2018
Publisher: American Society of Mechanical Engineers
Date: 19-06-2016
Abstract: Vortex-Induced-Motions (VIM) is a cyclic rigid body motion that is induced by vortex shedding of a large sized floating structure (Spar, Semi-Submersible and Tension-Leg Platform) in deep water. Since the potential impact of VIM on fatigue life of mooring and riser systems can be critical, the study of the VIM phenomenon has drawn considerable attention among offshore engineering community. Despite the effort, there is still lack of understanding the complex fluid-structure interaction phenomenon. To date, it is very much relying on the simplified empirical approach in practical design. Most of the Semi-Submersibles consist of four rounded-cornered rectangular columns. To investigate the flow interaction between each columns can reveal some physics behind the VIM. In this study, flow past four stationary rounded-corner rectangular columns are tested in the circulating channel and numerically simulated by the Star-CCM+ CFD package. Forces on the columns and the flow characteristics behind the structures are present in this study. A 2-D particle imaging velocimetry (PIV) technic has been adopted in present study to obtain the flow characteristics. The aim of this study is to investigate the interactions between four square columns.
Publisher: Elsevier BV
Date: 11-2020
Publisher: Elsevier BV
Date: 02-2018
Publisher: MDPI AG
Date: 10-11-2018
Abstract: In this paper, we report an interesting bubble melt electrospinning (e-spinning) to produce polymer microfibers. Usually, melt e-spinning for fabricating ultrafine fibers needs “Taylor cone”, which is formed on the tip of the spinneret. The spinneret is also the bottleneck for mass production in melt e-spinning. In this work, a metal needle-free method was tried in the melt e-spinning process. The “Taylor cone” was formed on the surface of the broken polymer melt bubble, which was produced by an airflow. With the applied voltage ranging from 18 to 25 kV, the heating temperature was about 210–250 °C, and polyurethane (TPU) and polylactic acid (PLA) microfibers were successfully fabricated by this new melt e-spinning technique. During the melt e-spinning process, polymer melt jets ejected from the burst bubbles could be observed with a high-speed camera. Then, polymer microfibers could be obtained on the grounded collector. The fiber diameter ranged from 45 down to 5 μm. The results indicate that bubble melt e-spinning may be a promising method for needleless production in melt e-spinning.
Publisher: American Society of Mechanical Engineers
Date: 17-06-2018
Abstract: Electricity generation from tidal current can provide a reliable and predictable addition to a reduced carbon energy sector in the future. Following the deployment of the first multi-turbine array, significant cost reduction can be achieved by moving beyond demonstrator projects to large scale tidal turbine arrays. The interactions between multiple turbines installed in close proximity can affect the total electricity generation and thus require knowledge of the resulting flow field within and downstream of the array. Results are presented for experimental and numerical studies investigating the flow field characteristics in terms of velocity deficit and turbulence intensity in a staggered tidal turbine array section. Multiple configuration with varying longitudinal and transverse spacing between devices in a three-turbine array are tested. Comparison between numerical and experimental flow characteristics shows that open source numerical models with dynamic mesh features achieve good agreement and can be used for the investigation of array wake effects. The standard k–ω SST shows good agreement with experiments at reduced computational efficiency compared to higher order turbulence models (RSM). The importance of mixing with ambient flow is highlighted by identifying areas of significantly reduced velocity recovery within closely spaced arrays where ambient flow does not penetrate between adjacent wakes.
Publisher: Oxford University Press (OUP)
Date: 04-03-2017
DOI: 10.1093/MNRAS/STX565
Publisher: Elsevier BV
Date: 12-2017
Publisher: Elsevier BV
Date: 10-2022
Publisher: Elsevier BV
Date: 09-2017
Publisher: SAGE Publications
Date: 2013
Abstract: Chronic kidney disease is a public health problem with an increasing incidence and prevalence, poor outcomes, and high cost. Patient involvement forms the keystone in the management of chronic kidney disease. This study evaluated effects of pharmacist-provided counseling in dialysis patients in terms of their knowledge, attitude, and practice outcomes. A total of 64 patients with chronic kidney disease were enrolled into the prospective, pre–post study based on the inclusion and exclusion criteria. The knowledge, attitude, and practice of patients regarding chronic kidney disease were assessed and recorded via baseline questionnaire. Case group patients were counseled regarding chronic kidney disease, their medication, diet, and lifestyle, and they were also provided with informative leaflet, whereas in the control group patients, the pharmacist did not intervene. After 1-month intervention, knowledge, attitude, and practice scores of patients of both groups were measured using the same knowledge, attitude, and practice questionnaire. Effectiveness of counseling on case group patients was evaluated by comparing the mean knowledge, attitude, and practice scores before and after counseling by paired t-test. Mean knowledge, attitude, and practice scores before intervention were 8.16 ± 4.378, 38.19 ± 3.217, and 6.69 ± 0.896, respectively, and these scores were changed to 13.75 ± 3.510, 38.78 ± 3.035, and 6.91 ± 0.777, respectively, after the intervention ( p 0.05). The pharmacist-provided counseling is effective in improving knowledge, attitude, and practice of patients toward the disease management.
Publisher: Elsevier BV
Date: 07-2008
Publisher: Wiley
Date: 10-05-2018
DOI: 10.1111/JGS.15412
Publisher: Elsevier BV
Date: 11-2018
Publisher: Elsevier BV
Date: 12-2007
Publisher: Springer Science and Business Media LLC
Date: 08-08-2016
Publisher: ASME International
Date: 16-11-2016
DOI: 10.1115/1.4034902
Abstract: A mathematical model describing the homogeneous–heterogeneous reactions in the vicinity of the forward stagnation point of a cylinder immerged in a nanofluid is established. We assume that the homogeneous reaction is given by isothermal cubic autocatalator kinetics, while the heterogeneous reaction is chosen as first-order kinetics. The existence of multiple solutions through hysteresis bifurcations is discussed in detail for the various diffusion coefficients of reactant and autocatalyst.
Publisher: American Society of Mechanical Engineers
Date: 03-08-2020
Abstract: The climate change may affect the long-term wave statistics and consequently affect the cumulative fatigue damage. This paper aims to project the trend of annual fatigue damage of offshore floating structures and to detect the climate change impact on the future fatigue damage by coupling a conventional fatigue design method with climate and wave models. Firstly, climate scenarios are selected to project the global radiative forcing level over decadal or century time scales. Secondly, climate models are used to simulate atmosphere circulations and to obtain the wind field data. Thirdly, wave conditions are simulated by coupling wind driven wave models to climate models. Fourthly, stress analysis and fatigue assessments are conducted to project the annual fatigue damage. At last, control simulations are carried out in order to identify the range of natural variability and to detect the human-induced change. A case study is presented in the Sable field offshore South Africa. The results indicate that the significant wave height is considerably influenced by the human-induced climate change. However, this change induced by human activities is still partially masked by the dominant natural variability. In addition, both the significant wave height and the annual fatigue damage increase over century time-scales.
Publisher: American Society of Civil Engineers (ASCE)
Date: 09-2009
Publisher: American Society of Mechanical Engineers
Date: 09-06-2013
Abstract: This paper presents the results of towing tank tests carried out to predict the wave loads in regular wave conditions on a Deep-V hull form catamaran model. The experiments were carried out at the Newcastle University towing tank using a segmented model of the university’s new research vessel, “The Princess Royal”. The vessel is a twin hull with a Deep-V shape cross-section. The model, ided into two parts at the cross-deck level, was fitted with a 5-axis load cell at the position of the vessel’s centre of gravity in order to measure the motions response and wave loads due to the encountered waves. The longitudinal, side and vertical forces, along with the prying and yaw splitting moments were measured. The results obtained were further compared with those from numerical predictions carried out using a 3D panel method code based on potential flow theory that uses Green’s Function with the forward speed correction in the frequency domain. The results highlight reasonable correlations between the measurements and the predictions as well as the need for a proper understanding of the response of the multihull vessels to the wave-induced loads due to the non-linearity that have been observed in the experimental measurements of wave loads.
Publisher: Elsevier BV
Date: 03-2017
Publisher: Elsevier BV
Date: 08-2014
Publisher: ASMEDC
Date: 2009
Abstract: In this paper, scaled boundary finite-element method (SBFEM) is extended to study wave interaction with two adjacent rectangular cylinders. In addition to the advantages in accurate and efficient representation of singularities and unbounded domains, the modified SBFEM shows distinct capability in dealing with wave diffraction including adjacent multiple structure interactions. Comparisons of wave runup and wave forces on each cylinder of the two adjacent offshore caissons with traditional panel method demonstrate a high accuracy achieved with excellent computational efficiency. Detailed results and discussion of the spacing effect on the hydrodynamics of the two cylinder system are presented. Design recommendations are made based on the maximum wave forces on both caissons.
Publisher: Elsevier BV
Date: 09-2014
Publisher: Springer Science and Business Media LLC
Date: 04-2018
Publisher: Public Library of Science (PLoS)
Date: 08-06-2015
Publisher: Elsevier BV
Date: 04-2015
Publisher: ASMEDC
Date: 2010
Abstract: In this paper, wave diffraction by a harbour is studied by the scaled boundary finite-element method (SBFEM). The semi-analytical approach, with the combined advantages of both finite-element and boundary-element methods, is based on linear wave theory and is applicable to harbours of circular arc profile. The whole solution domain is ided into one unbounded subdomain and one bounded sub-domain by the profile of the harbour. The effects of the incident wave angle and the opening angle of the harbour are discussed. Discretising only the circumference of the harbour, the current semi-analytical SBFEM model exhibits excellent computational accuracy and efficiency. The technique can be extended to solve more practical wave-structure interaction problems with increased complexity.
Publisher: Elsevier BV
Date: 2020
Publisher: Elsevier BV
Date: 08-2014
Publisher: Elsevier BV
Date: 09-2019
Publisher: Cambridge University Press (CUP)
Date: 31-07-2018
DOI: 10.1017/JFM.2018.526
Abstract: Direct numerical simulations are performed for the uniform flow around an inclined circular disk. The diameter–thickness aspect ratio ( $\\unicode[STIX]{x1D712}=D/t_{d}$ ) of the disk is 50 and the inclination angle ( $\\unicode[STIX]{x1D6FC}$ ) is considered over the range of $0^{\\circ }\\leqslant \\unicode[STIX]{x1D6FC}\\leqslant 80^{\\circ }$ , where $\\unicode[STIX]{x1D6FC}=0^{\\circ }$ refers to the condition where the flow is normal to the disk. The Reynolds number ( $\\mathit{Re}$ ), based on the short axis of projection in the streamwise direction, is defined as $\\mathit{Re}=U_{\\infty }D\\cos \\unicode[STIX]{x1D6FC}/\\unicode[STIX]{x1D708}$ , where $U_{\\infty }$ is the velocity of the flow and $\\unicode[STIX]{x1D708}$ is the kinematic viscosity. $\\mathit{Re}$ is investigated over the range of 50 ${\\leqslant}\\mathit{Re}\\leqslant$ 300. In the considered $\\mathit{Re}$ – $\\unicode[STIX]{x1D6FC}$ parametric space, five states are observed and denoted as: (I) steady state (SS) (II) periodic state (PS) (III) periodic state with a low frequency modulation (PSL) (IV) quasi-periodic state (QP) and (V) chaotic state (CS). Both $\\mathit{Re}$ and $\\unicode[STIX]{x1D6FC}$ affect the bifurcation mechanism. The bifurcating sequence occurring at $\\unicode[STIX]{x1D6FC}=0^{\\circ }$ is generally observed over the whole $\\mathit{Re}$ – $\\unicode[STIX]{x1D6FC}$ space, although it is advanced at small $\\unicode[STIX]{x1D6FC}$ and delayed at large $\\unicode[STIX]{x1D6FC}$ . The advancement of thresholds for different states is due to the effects introduced by inclination, which tend to select the plane of symmetry for the wake in order to regulate the wake and intensify some flow features. Nevertheless, the bifurcations are still in the dominant position when leading a state without stable symmetry, i.e. the planar symmetry could not be recovered by small $\\unicode[STIX]{x1D6FC}$ . These phenomena are further discussed with respect to the vortex shedding patterns behind the disk. Furthermore, for any fixed disk, the wake behaviour is only associated with that found in the steady vertical state of a freely falling disk. The fully coupled fluid–body system is fundamentally different from the fixed cases.
Publisher: ASME International
Date: 02-2004
DOI: 10.1115/1.1643085
Abstract: Spar platforms with cylindrical shape and constant cross-section area may experience resonant heave motions in sea states with long peak periods, which are probably excessive for riser integrity due to its low d ing and relatively low natural heave period. Changes to hull shape and cross-section that produce more benign heave behavior were discussed by some researchers in the past. In this study, the viscous d ing of spar structures is explicitly calculated, and incorporated to the potential solution. It is concluded that the heave resonant response can be considerably reduced by alternative hull shapes via increased d ing mechanism and the natural heave period being kept outside the range of the wave energy.
Publisher: American Society of Mechanical Engineers
Date: 09-06-2013
Abstract: Traditional offshore wind turbines are normally supported by circular monopiles which are fabricated by rolling thick plates and welding them longitudinally. Due to the significant capital cost associated with the fabrication of such large circular cylinders, a new recommended innovative design to overcome such problem is introduced by replacing the circular cylinder with a vertical pile of octagonal cross-sectional shape. An efficient and very accurate semi-analytical/numerical solution based on the Scaled Boundary Finite Element Method (SBFEM) is developed to calculate the wave diffraction forces acting on the octagonal cylinders where no fundamental solutions known exist. Compared to the traditional Boundary Element Method (BEM), the SBFEM is free from the irregular frequency difficulty which means that it does not suffer from computational stability problems at sharp corners. The SBFEM solution also exhibits an enormous reduction of elements used to calculate the wave diffraction compared to the Finite Element Method (FEM), hence, a significant reduction in computational time. The SBFEM computation of the diffraction force demonstrates highly accurate results with a small number of surface elements. The presented method shows significant advantages, and is suitable for engineering applications especially the wave-structure interaction in the practical design.
Publisher: MDPI AG
Date: 31-05-2023
DOI: 10.3390/JMSE11061154
Abstract: The peridynamic (PD) theory is based on nonlocal mechanics and employs particle discretization in its computational domain, making it advantageous for simulating cracks. Consequently, PD has been applied to simulate ice damage and ice–structure interaction under various conditions. However, the calculation efficiency of PD, similar to other meshless methods, is constrained by the number of particles and the inherent limitations of the method itself. These constraints hinder its potential for further development in the field of ice−structure interaction. This study aims to explore the computational efficiency of various methods that can be employed to improve the computational cost of PD in ice–structure interactions. Specifically, we analyze the computational efficiency of three different methods (the MPI parallelization, the updated link−list search method, and the particle−pair method) and their collaborative calculation efficiency to reduce simulation time. These methods are employed to calculate ice–ship interaction, and their coupled efficiency is studied. Furthermore, this study discusses the computation strategy to improve efficiency on using the PD method to calculate ice–structure interaction. The present work provides scholars who employ PD to calculate ice–structure interaction or ice damage with a referential discussion plan to achieve an efficient numerical computation process.
Publisher: AIP Publishing
Date: 06-2019
DOI: 10.1063/1.5097929
Abstract: The Boundary Integral Method (BIM) has been widely and successfully applied to cavitation bubble dynamics however, the physical complexities involved in the coalescence of multiple bubbles are still challenging for numerical modeling. In this study, an improved three-dimensional (3D) BIM model is developed to simulate the coalescence of multiple cavitation bubbles near a rigid wall, including an extreme situation when cavitation bubbles are in contact with the rigid wall. As the first highlight of the present model, a universal topological treatment for arbitrary coalescence is proposed for 3D cases, combined with a density potential method and an adaptive remesh scheme to maintain a stable and high-accuracy calculation. Modeling for the multiple bubbles attached to the rigid boundary is the second challenging task of the present study. The effects of the rigid wall are modeled using the method of image thus, the boundary value problem is transformed to the coalescence of real bubbles and their images across the boundary. Additionally, the numerical difficulties associated with the splitting of a toroidal bubble and self-coalescence due to the self-film-thinning process of a coalesced bubble are successfully overcome. The present 3D model is verified through convergence studies and further validated by the purposely conducted experiments. Finally, representative simulations are carried out to elucidate the main features of a coalesced bubble near a rigid boundary and the flow fields are provided to reveal the underlying physical mechanisms.
Publisher: Elsevier BV
Date: 10-2021
Publisher: Elsevier BV
Date: 11-2014
Publisher: American Society of Mechanical Engineers
Date: 09-06-2019
Abstract: Leading-edge tubercles have been investigating widely on the performance of foils in the last decade. In this study, the biomimetic tubercle design has been applied to the corner shape on a deep-draft semi-submersible. A numerical study on flow over a deep-draft semi-submersible (DDS) with a biomimetic tubercle corner shape was carried out to investigate the corner shape effects on the overall hydrodynamics and motion responses. The hydrodynamic performance of the biomimetic tubercle corner is compared with a traditional round corner design platform. It is demonstrated that, as the corner shape design changed, the motion responses alter drastically. In addition, the flow patterns were examined to reveal some insights into fluid physics due to the biomimetic tubercle corner design. The comprehensive numerical results showed that the three-dimensional effect, which causes spanwise flow, can be reduced by a continuous spanwise (column-wise) variation of the shear-layer separation points.
Publisher: American Society of Mechanical Engineers
Date: 08-06-2014
Abstract: An accurate prediction of the global response of a floating production and storage offloading (FPSO) system under harsh environmental conditions is of great importance in order to achieve the reliability and safety operation of the whole system. FPSOs may be subjected to significant resonant oscillations in the horizontal plane due to low frequency (LF) wave effects and wind excitation forces. These characteristics may contribute to the increase in surge due to the low level of viscous hull d ing. Additionally, it has been observed that when the water depth increases, the coupled effects (d ing, inertia and restoring force) contributions from mooring lines and risers increases. This paper investigates the LF response behavior of a deepwater FPSO unit in the Gulf of Mexico by carrying out a coupled analysis based on a nonlinear time domain analysis. A 3D model based on boundary integrated element method is used to investigate the hydrodynamic behaviour of the floater as well as a 3D finite element model for each of the slender elements representing the mooring lines and risers. The LF motions of a FPSO with a typical arrangement of catenary mooring lines and steel catenary risers is studied for surge, sway and yaw mainly. The hydrodynamic characteristics of the FPSO are studied through both Newman’s approach and the full Quadratic transfer function. The coupling effect of the floater and mooring/riser systems is examined by comparing the tensions in mooring lines/risers and the global responses of the system in six degree of freedom. The nonlinearity of the hydrodynamics of wave-vessel interaction and the dynamic contribution of mooring lines and risers are investigated with storm and hurricane events for a particular location in deep water Gulf of Mexico (GOM).
Publisher: Emerald
Date: 30-12-2020
Abstract: The purpose of this paper is to investigate the immiscible two-layer heat fluid flows in the presence of the electric double layer (EDL) and magnetic field. The effects of EDL, magnetic field and the viscous dissipative term on fluid velocity and temperature, as well as the important physical quantities, are examined and discussed. The upper and lower regions in a horizontal microchannel with one layer being filled with a nanofluid and the other with a viscous Newtonian fluid. The nanofluid flow in the lower layer is described by the Buongiorno’s nanofluid model with passively controlled model at the boundaries. An appropriate set of non-dimensional quantities are used to simplify the nonlinear systems. The resulting coupled nonlinear equations are solved by using homotopy analysis method. The present work demonstrates that increasing the EDL thickness and Hartmann number can restrain the fluid flow. The Brinkmann number has a significant role in the enhancement of heat transfer. It is also identified that the influence of EDL effects on microflow cannot be ignored. The effects of viscous dissipation involved in the heat transfer process and the body force because of the EDL and the magnetic field are considered in the thermal energy and momentum equations for both regions. The detailed derivation procedure of the analytical solution for electrostatic potential is provided. The analytical solutions can lead to improved understanding of the complex microfluidic systems.
Publisher: Elsevier BV
Date: 08-2019
Publisher: Elsevier BV
Date: 05-2022
Publisher: Elsevier BV
Date: 07-2022
Publisher: American Society of Mechanical Engineers
Date: 03-08-2020
Abstract: Sea-keeping model tests of ships based on transient waves have been widely applied over the past several decades. In order to obtain response litude operators (RAOs) of a ship, most of the post-processing of the experimental data uses the fast Fourier transform (FFT) to obtain the wave spectrum and the corresponding response spectrum. However, for transient waves related model tests, FFT may produce larger errors due to its characteristics. Hilbert-Huang transform (HHT) is a newly developed signal analysis tool which is suitable for nonlinear and non-stationary data. The application of HHT to the post-processing of the experimental data of sea-keeping model tests of ships has not yet been investigated. In this study, the transient wave packets satisfying a Gaussian wave spectrum were generated in a large towing tank to conduct the sea-keeping model tests of a drilling ship under the condition of head waves, oblique waves and beam waves, respectively. Then the marginal Hilbert spectrum (MHS) in the framework of HHT is introduced to obtain the motion and the acceleration RAOs the drilling ship. In order to demonstrate the effectiveness of the approach, the results based on FFT and regular waves are also presented. It is found that in most cases, in comparison to that by means of FFT, the RAOs of the ship based on the transient Gaussian wave packets by means of MHS agree better with the results based on regular waves, especially for roll motion with significant nonlinear characteristics. Due to the advantages of HHT, the MHS approach employed in this study is expected to play a vital role in more sea-keeping related model tests of ships.
Publisher: Elsevier BV
Date: 03-2010
Publisher: American Society of Mechanical Engineers
Date: 09-06-2019
Abstract: The spatial localized influence of wind on wave induced load on a flexible cylinder has been assessed throughout a test series conducted in a wave-wind-current flume at Newcastle University. The tests are motivated from other experimental and numerical investigations showing air flow separation on the leeward side of steep waves that can lead to added wind energy transfer, which could suggest an increase in the impulsive wave loading. The waves are generated as focused waves, resulting in a plunging breaker, leading to an impulsive wave load. The test model was equipped with a load cell measuring the connection load. Due to the flexibility of the cylinder, the measured force response shows oscillations and dynamic lification of the load. The maxima of the force responses are compared for the tests with and without wind. Another measure for comparison is the local and short-lived impulse, which is responsible for the lification. This impulsive load is estimated from the load cell and acceleration measurements. For the tests in this study, the introduction of wind over the breaking waves does for some cases lead to a slight increase in the peak of the impulsive load and thereby the load response, although large scattering is present. Further investigations are needed to verify this effect. Some differences in the time series of the free surface elevation are observed when wind is present, but the maximum of the surface elevation does not change notably, and the slope is only minimally changed, meaning that this should not give basis for the differences in the loads.
Publisher: American Society of Mechanical Engineers
Date: 17-06-2018
Abstract: A numerical study on flow over a stationary deep-draft semi-submersible (DDS) with various corner shapes was carried out to investigate the corner shape effects on the overall hydrodynamics. Three models based on a typical DDS design with different corner shapes were numerically investigated under 45° incidence. The present numerical model has been validated by an experimental test carried out in a circulating water channel. It is demonstrated that, as the corner shape design changed, the hydrodynamic characteristics alter drastically. In addition, the flow patterns were examined to reveal some insights of the fluid physics due to the changing of different corner shape designs. The detailed numerical results from the geometric study will provide a good guidance for future practical designs.
Publisher: Springer International Publishing
Date: 03-04-2020
Publisher: American Society of Mechanical Engineers
Date: 08-06-2014
Abstract: The roll d ing coefficient is a crucial parameter for several design and operational aspects of FPSOs. The accurate prediction of the coefficient is not a trivial task and generally performed experimentally. A polynomial linearization of the decay test data has been widely applied in the offshore industry. However, research has indicated that for FPSOs with rectangular cross section and attached bilge keels, this methodology may lead to inaccurate d ing coefficients. This paper presents a study on the experimental determination of roll d ing coefficients for FPSOs, obtained by free decay tests. For this purpose model tests are executed in the towing tank of the Marine Hydrodynamic Laboratory at Newcastle University. The model is based on the design of a purposely build FPSO, as typically applied in the central North Sea sector. The cross section of the FPSO is boxed shaped with a characteristic knuckle shaped bilge. The tests are conducted using three different bilge keel arrangements. The parametric change in bilge keel size results in the variation of the flow characteristics around the bilge knuckle. The d ing coefficients are then established from the decay test data using a polynomial approach, a bi-linear approach and a hyperbolic approach. A comparison between the d ing evolutions obtained with the different methodologies is performed for each bilge keel configuration. Further, a numerical model of the FPSO is created using DNVs Sesam software. With the established d ing coefficients, d ing matrices are manually defined as an input to Sesam and roll transfer functions are numerically established. The computational determined transfer functions are then compared against the RAOs obtained from the model tests in regular waves to determine the most appropriate methodology. The d ing coefficient for the bare hull is well established by all three proposed methodologies. However, with the attached bilge keels the bi-linear and the hyperbolic methodologies produce d ing coefficients reflecting the experimental results more accurately than the polynomial approach, indicating that the recently developed hyperbolic method is a valid alternative, and in certain cases, is more suitable to determine the roll d ing coefficient. The experimental measurements could serve as a benchmark for further research and contribute to the practical application of FPSO roll d ing determination.
Publisher: Springer Science and Business Media LLC
Date: 26-09-2018
Publisher: Elsevier BV
Date: 09-2021
Publisher: AIP Publishing
Date: 03-2019
DOI: 10.1063/1.5079315
Abstract: The flooding of a damaged ship in waves is a complex process, often coupled with the internal and external liquid motion together with the ship hull motion. Paramount to the operation safety, in order to improve the prediction accuracy of ship motion during the flooding process, the strip theory is applied to study the dynamic response of the damaged ship in beam seas a smoothed particle hydrodynamics (SPH) model is developed to consider the coupling effects of various factors including internal sloshing of intact cabins and damaged cabins and external waves. The numerical wave tank with a perfectly matched layer absorbing boundary condition is established and validated by the experimental results. The detailed sensitivity study is carried out focusing on the effects of damaged opening sizes, the relative position of opening, and the incident wave and the liquid loading conditions on the dynamic response of the damaged ship in regular beam waves. It is observed that the flooding process was slowed down and interrupted by the water exchanges at the damaged opening due to the dynamic motion. Compared with the opening facing the incident wave, the back one endangered the ship pronouncedly with large litude and frequency roll motion. It is also revealed that the liquid tank in the damaged ship imposes a significant influence on its rolling response. It is further demonstrated that the present SPH model is capable of handling the nonlinear phenomenon in a flooding process of a damaged ship.
Publisher: Cambridge University Press (CUP)
Date: 12-01-2017
DOI: 10.1017/JFM.2016.800
Abstract: Direct numerical simulations of the flow induced by a circular disk oscillating sinusoidally along its axis are performed. The aspect ratio ( $\\unicode[STIX]{x1D712}=\\text{diameter}/\\text{thickness}$ ) of the disk is 10. The Reynolds number ( $\\mathit{Re}$ ), based on the maximum speed and the diameter of the disk, is in the range of $50\\leqslant \\mathit{Re}\\leqslant 800$ . The Keulegan–Carpenter number ( $KC$ ) is in the range of $1\\leqslant KC\\leqslant 24$ . Five flow regimes are observed in the considered $\\mathit{Re}$ – $KC$ space: (I) axisymmetric flow (AS), (II) planar symmetric flow in the low- $KC$ region (PSL), (III) azimuthally rotating flow in the low- $KC$ region (ARL), (IV) planar symmetric flow in the high- $KC$ region (PSH) and (V) azimuthally rotating flow in the high- $KC$ region (ARH). The critical boundaries between different flow regimes are identified based on the evolutions of the magnitude and direction of transverse force acting on the disk. For the non-axisymmetric flow regimes, the flow is one-sided with respect to the axis of the disk and is associated with a non-zero mean value of the transverse force acting on the disk.
Publisher: Wiley
Date: 2009
DOI: 10.1002/FLD.2080
Publisher: Elsevier BV
Date: 11-2023
Publisher: ASME International
Date: 21-05-2018
DOI: 10.1115/1.4040049
Abstract: Dynamic position (DP) control and pipeline dynamics are the two main parts of the deepwater S-lay simulation model. In this study, a fully coupled analysis tool for deepwater S-lay deployment by dynamically positioned vessels is developed. The method integrates the major aspects related to numerical simulation, including coupled pipeline motion and roller contact forces. The roller–pipe interaction is incorporated in the S-lay pipeline model using a contact search method based on a lumped-mass (LM) formulation in global coordinates. A proportional-integration-differentiation (PID) controller and a Kalman filter are applied in the vessel motion equation to calculate the thrust allocation of the DP system in time domain. Numerical simulation results showed that the dynamic effects add a significant contribution to the tension, but have little influence on the maximum pipe stress and strain. The dynamic response of the coupled S-lay and DP pipeline deployment system increases the demand on the tensioner load carrying capability as well as the maximum DP thruster power.
Publisher: Elsevier BV
Date: 2017
Publisher: Springer Science and Business Media LLC
Date: 24-05-2018
Publisher: Elsevier BV
Date: 06-2017
DOI: 10.1016/J.APPET.2017.03.005
Abstract: Consuming a healthy diet forms an important component of diabetes management however, adhering to a healthy diet is challenging. Dietary behaviour is often guided by socio-cultural, environmental and emotional factors, and not necessarily by physical and nutritional needs. This study explored Nepalese patients' perceptions of the impact of diet, diet management requirement for diabetes and how Nepalese food culture in particular influenced diet management. Interviews were conducted with Nepalese participants with type 2 diabetes in Sydney and Kathmandu and data was thematically analysed. Diet was recognized as a cause of, and a key treatment modality, in diabetes. Besides doctors, participants in Nepal received a large amount of dietary information from the community. Dietary changes formed a major component of lifestyle modifications adopted after diagnosis, and mostly consisted of removal of foods with added sugar and foods with high total sugar content from the diet, and a reduction in overall quantity of foods consumed. Perceived dietary restriction requirements created social and emotional discomfort to patients. Most participants perceived the Nepalese food culture as a barrier to effective diet management. Meals high in carbohydrates, limited food choices, and food preparation methods were identified as barriers, particularly in Nepal. In Australia, participants reported greater availability and easier access to appropriate food, and healthier cooking options. The socio-cultural aspects of food behaviour, mainly, food practices during social events were identified as significant barriers. Although diet was acknowledged as an important component of diabetes care, and most adopted changes in their diet post-diagnosis, effective and sustained changes were difficult to achieve. Future public health c aigns and education strategies should focus on improving diet knowledge, awareness of food options for diabetes, and effective dietary management.
Publisher: Elsevier BV
Date: 09-2017
Publisher: Elsevier BV
Date: 02-2016
Publisher: Elsevier BV
Date: 11-2007
Publisher: SAGE Publications Ltd
Date: 2023
Publisher: American Society of Civil Engineers (ASCE)
Date: 11-2016
Publisher: Informa UK Limited
Date: 25-02-2017
DOI: 10.1080/13557858.2017.1294659
Abstract: To explore anti-diabetic medication taking behaviour in Nepalese patients with type 2 diabetes and investigate the factors impacting medication taking in this population. Face-to-face interviews (n = 48) were conducted with Nepalese patients with type 2 diabetes in Sydney (Australia) and Kathmandu (Nepal). All interviews were audio-recorded, transcribed verbatim and thematically analysed. Participants' medication adherence was also assessed quantitatively using the summary of diabetes self-care activity (SDSCA) questionnaire. The medication taking behaviour of Nepalese participants aligned with the Stages of Change Model, with some notable patterns of behaviour. Most participants initiated and implemented anti-diabetic medications soon after obtaining their prescription. However, a few, delayed initiation and/or ceased medications after initiation to recommence later. Nonetheless, upon recommencement, participants persisted fairly well with their medications. The self-reported medication adherence was high (97.3%). Although some participants expressed adherence as a challenge at the start of therapy, medication taking on a day-to-day basis was not reported as difficult. Factors such as participants' reluctance towards using medications and preference for natural methods of treatment, together with inadequate understanding about diabetes and treatment resulted in the delay in initiating therapy, and contributed to cessation of therapy. On the other hand, ooccasional non-adherence in daily medication taking was mostly related to inconsistency in meal practices and forgetfulness. Encouragement from doctors and increased awareness about the disease and treatment facilitated medication adherence, including initiation of therapy. This study demonstrates that Nepalese patients are likely to delay or cease anti-diabetic medications until they fully accept and acknowledge the benefits and necessity of medications for effective diabetes management. Thus, educating patients about the need for medications, as well as implementing strategies to address patients' psychological resistance towards medications will be essential for effective medication management.
Publisher: American Society of Mechanical Engineers
Date: 19-06-2016
Abstract: This paper describes an open source numerical investigation into slugging flow in a typical two-dimensional pipeline-riser for the first time. CFD tools Gmsh, OpenFOAM and ParaView are employed for mesh generation, numerical simulation and post process respectively. Original OpenFOAM solver ‘twoPhaseEulerFoam’ is used to simulate the gas-liquid flow in the system consisting of inclined pipeline and vertical riser. By comparing the numerical results of slugging phenomena and pressure fluctuation periods to previous experimental observations, it can be confirmed that it is possible to carry out such simulations in a complete open source way. Based on case studies, pressure fluctuation features in a typical single slugging cycle is also discussed in details. Furthermore, temperature variation of the internal flow due to air compressibility is found to have similar fluctuation period as that of pressure. In the end, the impacts of fluid properties on system pressure variations are discussed too. To future numerical investigations of subsea pipeline-riser induced slugging, present work is a basis for further open source solvers development.
Publisher: Elsevier BV
Date: 08-2021
Publisher: Elsevier BV
Date: 11-2022
Publisher: OTC
Date: 20-03-2018
DOI: 10.4043/28426-MS
Abstract: An excellent vortex suppression device, in the form of an antinode fairing is presented towards reducing the Vortex Induced Vibration of structural members exposed to flow. An analytical procedure is also developed to optimise the depth and location of the fairings along the members. Two newly developed fairing sections are tested on cylindrical legs of a Jackup model and the results are qualitatively compared with the expected behaviour, particularly the effect of selected fairlead depth and location. A simplified mathematical model is developed based on the principle of conservation of energy, which could be used to decide the optimum location and depth of the vortex suppression devices for the cylinders undergoing Vortex Induced Vibration in a uniform flow. Based on the mathematical studies, modal antinodes are found as the optimum locations for the installation of the fairings and accordingly two compact leg fairing designs have been developed for practical applications. Those are based on NACA0018 profiles but with reduced L/B ratios of around 2.40 and 3.00. The tests with scaled down Jackup models with cylindrical legs demonstrated that both the fairing designs could reduce Vortex Induced Vibration litudes significantly, by around 80%. The weathervaning stability of both the fairing designs were also found to be satisfactory. From the mathematical studies and test results, it is inferred that fairings contribute to the reduction of Vortex Induced Vibration in three ways reduction of excitation force, disruption of vortex synchronisation and the increase in fluid d ing. Fairings are also found not to have significant bearing on the drag coefficient of the structure. The fairing design with the lesser L/B ratio of 2.40 is found to be an optimal solution for vortex suppression, when the structure is not sensitive to drag forces. However, fairings are found to initiate galloping responses at higher flow speeds above the lock-in range and hence it is recommended that the same shall be of the detachable type for cylinders exposed to large flow speed variations. The mathematical approach presented will enable practicing engineers to design and optimise antinode fairings for structures experiencing Vortex Induced Vibration. The two fairing section offsets presented may be readily used by Industry for practical applications.
Publisher: Elsevier BV
Date: 04-2014
Publisher: Elsevier BV
Date: 03-2020
Publisher: Springer Science and Business Media LLC
Date: 11-02-2021
DOI: 10.1038/S41467-020-20877-8
Abstract: Metabolite levels in urine may provide insights into genetic mechanisms shaping their related pathways. We therefore investigate the cumulative contribution of rare, exonic genetic variants on urine levels of 1487 metabolites and 53,714 metabolite ratios among 4864 GCKD study participants. Here we report the detection of 128 significant associations involving 30 unique genes, 16 of which are known to underlie inborn errors of metabolism. The 30 genes are strongly enriched for shared expression in liver and kidney (odds ratio = 65, p-FDR = 3e−7), with hepatocytes and proximal tubule cells as driving cell types. Use of UK Biobank whole-exome sequencing data links genes to diseases connected to the identified metabolites. In silico constraint-based modeling of gene knockouts in a virtual whole-body, organ-resolved metabolic human correctly predicts the observed direction of metabolite changes, highlighting the potential of linking population genetics to modeling. Our study implicates candidate variants and genes for inborn errors of metabolism.
Publisher: American Geophysical Union (AGU)
Date: 09-2006
DOI: 10.1029/2005JC003149
Publisher: Elsevier BV
Date: 09-2018
Publisher: Elsevier BV
Date: 02-2003
Publisher: ASMEDC
Date: 2011
Abstract: Wave-structure interaction in ocean engineering is a major source of unsteady loading and vibration of offshore structures including platforms, risers and long cables. Many efforts focus on vertical structures in which solution procedures can usually be simplified in the plane of mean free surface as the variable in the direction of gravity can be separated. In this paper, wave interaction with an infinite long horizontal elliptical cylinder is solved by a semi-analytical method, namely, the scaled boundary finite-element method (SBFEM). The solution domain is ided into two bounded domains and two unbounded domains with parallel side-faces. The governing partial differential equation (Helmholtz equation) is weakened and transformed to ordinary matrix differential equations in radial direction and are then solved analytically by SBFEM.
Publisher: ASME International
Date: 24-03-2005
DOI: 10.1115/1.1951780
Abstract: Nonlinear roll d ing has a profound influence on ship motions and stability in ocean waves. In this study, an experimental investigation is conducted on the nonlinear roll d ing of a ship in regular and irregular waves. The random decrement method, previously used in linear roll d ing prediction, is extended to nonlinear roll d ing estimation in the data process. The accuracy of the nonlinear roll d ing obtained by using the random decrement method is found to be dependent on the values of the threshold and segment number.
Publisher: Elsevier BV
Date: 02-2020
Publisher: Elsevier BV
Date: 03-2023
Publisher: American Society of Mechanical Engineers
Date: 05-06-2022
Abstract: The operation and maintenance (O& M) of an offshore wind turbine consumes large percentage of cost in the whole life of the offshore wind project. In most maintenance strategies, the service operation vessels (SOV) are widely employed in the maintenance activities. So far, the SOVs are large vessels to satisfy the requirement of equipment and functions. Some regular inspections for the wind farm are carried out by remotely operated underwater vessels (ROV). The offshore support vessel can be smaller in regular inspections. An attempt of small service operation vessel with ROV operating regular inspections is discussed in present research. The single point mooring method between offshore wind turbine and offshore support vessel is applied in the case. The relative distance between the vessel and the tension in the connecting lines are discussed under different environmental conditions. The numerical results are validated by the full-scale measurements on the vessel. It is found that the tension in the connecting lines is highly determined by the wind and wave directions. The wind-wave misalignments are also considered in the present study. It is found that the wind-wave misalignment may lead the sharp increase of relative distance and tension in connecting lines between offshore wind turbine and support vessel.
Publisher: ASME International
Date: 18-03-2014
DOI: 10.1115/1.4026586
Abstract: A series of two-dimensional model tests has been conducted to study the coupling between global roll motions of a floating liquefied natural gas (FLNG) vessel and internal sloshing. The model of the FLNG is allowed to move freely in roll under the excitations of an initial heel angle, band-limited waves, and regular waves. To clarify the coupling effects, the FLNG vessel in different filling conditions is ballasted in fresh water and equivalent steel ballast weights, respectively. Time series of both the internal sloshing and the global motions of the vessel are measured. Statistical and spectral analyses have been carried out on the measured data. Sloshing oscillations in different surface modes have been observed. Asymmetry of the internal wave profile relative to still-water surface is also observed. Attempts are made to clarify the influences of the internal sloshing on the global roll motions through the comparison of the experiment results between the liquid and steel ballasting cases. The coupling phenomenon is found to be sensitive to the period and height of excitation waves. Further discussion has been made on the experiment results, and some conclusions regarding the coupling mechanism between global motions and internal sloshing are drawn based on the present study.
Publisher: American Society of Mechanical Engineers
Date: 19-06-2016
Abstract: This paper aims to analyze the hydrodynamics of a floating offshore wind turbine (FOWT) in waves. Instead of modeling the incident random wave with the traditional wave spectrum and superposition theory, an impulse response function method was used to simulate the incident wave. The incident wave velocity was evaluated by a convolution of the wave elevation at the original point and the impulse response function in the domain. To check the validity of current wave simulation method, the calculated incident wave velocities were compared with analytical solutions they showed good agreement. The developed method was then used for the hydrodynamic analysis of the substructure of the FOWT. A direct time-domain method was used to calculate the wave-rigid body interaction problem. The proposed numerical scheme offers an effective way of modeling the incident wave by an arbitrary time series.
Publisher: American Society of Mechanical Engineers
Date: 08-06-2014
Abstract: The vortex-induced vibration (VIV) phenomenon is result of fluid-structure interaction which occurs in many engineering fields. The study of VIV of a circular cylinder is of practical importance (such as in marine cables and flexible risers in petroleum production). In this paper, one classical phenomenological VIV model — the motion of the cylinder is modeled by a simple linear equation, and the fluctuating nature of the vortex wake oscillation is modeled by a van der Pol oscillator, is analyzed. Firstly, the homotopy analysis method (HAM), a powerful technique for highly nonlinear problems, is developed to solve the coupled fluid-structure dynamical system with the convergence of the homotopy series solutions being demonstrated. Based on the HAM solutions, some properties of the fully nonlinear classical coupled VIV model are presented. All the results proved that the proposed HAM scheme has potential to be an effective analytic technique to study the VIV problems.
Publisher: AIP Publishing
Date: 02-2020
DOI: 10.1063/1.5131325
Abstract: A comprehensive numerical study on flow-induced motions (FIMs) of a deep-draft semi-submersible, a typical multiple cylindrical structure in offshore engineering, was carried out to investigate the energy transformation of the vortex shedding process. In addition, the corner shape effect on the flow characteristics, the hydrodynamic forces, and the FIM responses are presented for a multiple cylindrical structure with various corner shapes (sharp, rounded, and chamfered) under 45° current incidence. Different energy transformations, hydrodynamic characteristics, and FIM responses were observed due to the slight variation of the corner shape. The galloping at 45° incidence for a square-section shape column was observed when the corner shape modified as a chamfered corner. A “re-attached vortex shedding” phenomenon is discovered when the “lock-in” happened for a chamfered corner design. Further insights of the fluid physics into the flow characteristics due to the difference of the corner shape are revealed. In addition, the energy transformation and the mechanism for reducing the hydrodynamic forces and the FIM responses are analyzed.
Publisher: Frontiers Media SA
Date: 27-02-2023
DOI: 10.3389/FENRG.2023.1127957
Abstract: Bolted ring flange connections are widely utilized in offshore wind turbines to connect steel tubular segments. After the massive production and installation of offshore wind turbines in the past decade, flatness ergence is regarded as one of the most important initial imperfections for the fatigue design of flange connections. Offshore wind turbines are subjected to wind, wave, and current loads. This initial imperfection may alter the structural response and accelerate the fatigue crack growth. This paper aims to analyse the impact of the initial flatness ergence on the structural response of flange connections and evaluate its consequences on fatigue damage. Two different offshore wind turbines with fixed foundations and floating foundations are modelled to simulate their global responses to environmental loads. Based on a superposition method, local finite-element models of flange connections are established with three types of flatness ergence. Using the same bolt pretension and external loads from global modelling, the impact of these geometric imperfections is further examined by comparing the structural responses of flanges under different radial and peripheral opening lengths. Then, the fatigue assessments on flange connections in both fixed wind turbines and floating wind turbines are conducted, and the impacts of initial flatness ergence on these two different wind turbines are analysed.
Publisher: American Society of Mechanical Engineers
Date: 19-06-2016
Abstract: Tidal currents at many locations around the world have great potential to be used as a large scale renewable energy resource in the future. For large tidal turbine arrays to be commercially viable, the interactions of large devices operating in a confined operating environment need to be understood to optimise the layout of arrays to maximise electricity generation. This study presents results from a comprehensive experimental investigation of the flow field characteristics within tidal turbine arrays across a number of array layout configurations and current velocities. Up to four small scale turbines were placed in a circulating water channel to investigate the effects of changing array configuration and wake interaction on the flow velocity and turbulence characteristics in small array layouts. Detailed account of the resulting flow field characteristics has been taken by particle image velocimetry measurements at a number of locations within the wake of the array thus providing a large set of instantaneous flow recordings for further analysis of flow features and wake characteristics. Results are shown for experimental studies of single, three and four turbine arrays and some preliminary comparison between experimental measurements and numerical results are made.
Publisher: Elsevier BV
Date: 11-2007
Publisher: American Society of Civil Engineers (ASCE)
Date: 03-2016
Publisher: Elsevier BV
Date: 05-2023
Publisher: Elsevier BV
Date: 12-2021
Publisher: Elsevier BV
Date: 04-2003
Publisher: Elsevier BV
Date: 06-2022
Publisher: ASMEDC
Date: 2008
Abstract: In this paper, the scaled boundary finite-element method (SBFEM) proposed for interaction of wave and circular cylinder [Tao et al, 2007] is modified and applied to wave diffraction by a vertical square caisson. By introducing a virtual circular cylinder surrounding the square caisson, the whole fluid domain is ided into one unbounded subdomain and four bounded subdomins. The corresponding boundary value problems in bounded and unbounded domains are solved by the SBFEM using different base solutions. Comparisons to the previous BEM solutions demonstrate the excellent computation accuracy and efficiency of the present SBFEM approach, as well as the benefit of not suffering from the difficulties of irregular frequency and singularity problems, which are often encountered by BEM. The method can be extended to solve more complex wave-structure interaction problems resulting in direct engineering applications.
Publisher: Elsevier BV
Date: 09-2021
Publisher: Elsevier BV
Date: 07-2017
Publisher: Public Library of Science (PLoS)
Date: 24-02-2015
Publisher: ASMEDC
Date: 2009
Abstract: In this paper, the hydroelastic response of a circular plate excited by plane incident waves is studied using the scaled boundary finite-element method (SBFEM), a novel semi-analytical approach with the combined advantages of both finite-element and boundary-element methods. The governing sixth-order partial differential equation is decomposed into three Helmholtz-type equations and solved semi-analytically by matching the boundary conditions at the edge of the plate. Discretising only the circumference of the plate, the current SBFEM model exhibits excellent computational accuracy and efficiency. The technique can be extended to solve more complex wave-structure interaction problems resulting in direct engineering applications.
Publisher: Elsevier BV
Date: 06-2021
Publisher: Springer Science and Business Media LLC
Date: 16-08-2022
Publisher: Informa UK Limited
Date: 09-2016
DOI: 10.2147/PPA.S113467
Publisher: Elsevier BV
Date: 10-2000
Publisher: Springer Science and Business Media LLC
Date: 24-03-2009
Publisher: Springer Science and Business Media LLC
Date: 06-10-2021
Publisher: Springer Science and Business Media LLC
Date: 06-2021
Publisher: American Society of Mechanical Engineers
Date: 09-06-2019
Abstract: Plunging breakers, unlike non-breaking waves, impose additional slamming load on the offshore structures. This additional slamming load is considered an extreme event and is one of the most devastating forces that an offshore structure could encounter during its operational lifecycle. Whilst there are design guidelines for offshore structures pertaining to breaking waves, however it is limited to only cylindrical shape. The amount of slamming load contribution by the plunging jet is also dependent on the cross section geometries of the offshore structures. Different geometries would give rise to different air entrainment phenomenon during wave breaking and therefore affecting the slamming load contributions. In this research, JONSWAP spectrum was used to create plunging breakers via the focusing method at Newcastle University’s Wind Wave and Current tank. The crux of this research is to investigate the wave-breaking impact load on cylindrical structures with different cross section geometries commonly used in the offshore industry.
Publisher: American Society of Mechanical Engineers
Date: 09-06-2019
Abstract: A simple mathematical model is developed based on the single-degree-of-freedom analogy and principle of conservation of energy evaluating various modes of Vortex-Induced-Vibration (VIV) of a jack-up with cylindrical legs in regular waves. Similar to uniform current, mass ratio, d ing ratio and mode factor are found to be the important parameters controlling the cross-flow VIV and radius of gyration also for the yaw VIV. Criteria for the initiation of the mentioned VIV modes are developed for the cases of a single 2D cylinder experiencing planar oscillatory flow, four rigidly coupled 2D cylinders in rectangular configuration experiencing planar oscillatory flow and jack-up experiencing regular waves. The newly developed VIV model is validated by a set of experiments conducted in a wind, wave and current flume. The importance of mass d ing parameter is further demonstrated in suppressing VIV in regular waves. The mathematical method will equip engineers to consider the effect of VIV due to regular waves in jack-up designs.
Publisher: MDPI AG
Date: 29-07-2020
Abstract: Healthcare professionals’ level of engagement in diabetes care and their perceptions of challenges to effective diabetes care are key indicators impacting diabetes management. This study investigated diabetes-related healthcare services provided in Nepal, and explored healthcare professionals’ opinions of the barriers to, and strategies for, effective diabetes care. In-depth face-to-face interviews were conducted with thirty healthcare professionals providing healthcare or medication-related services to patients with type 2 diabetes within Kathmandu Valley. Interviews were audio-recorded, transcribed verbatim and thematically analysed. Participants were physicians, dieticians, nurses and pharmacy staff. Diabetes care services varied between healthcare institutions, between healthcare professionals and between patients, with the overall patient-care model reported as sub-optimal. Diabetes related services were mostly limited to physician-patient consultations. Only a few hospitals or clinics provided additional diabetes education classes, and in idual dietician or nurse consultations. Limited collaboration, large patient-load and workforce shortages (particularly lack of diabetes educators) were reported as major issues affecting diabetes care. Regulatory measures to address healthcare system barriers were identified as potential facilitators for effective diabetes management. Whilst the findings are specific to Nepal, there are lessons to be learnt for other healthcare settings as the fundamental barriers to optimal diabetes care appear to be similar worldwide.
Publisher: Elsevier BV
Date: 11-2007
Publisher: ASMEDC
Date: 2007
Abstract: The scaled boundary finite-element method (SBFEM) is a novel semi-analytical approach, with the combined advantages of both finite-element and boundary-element methods. The basic idea behind SBFEM is to discretize the surface boundary by FEM and transform the governing partial differential equations to ordinary differential equations of the radial parameter. The radial differential equation is then solved analytically. It has the inherent advantage for solving problems in unbounded medium with discretization to the interface only. In this paper, SBFEM is applied to solve the wave diffraction by a circular cylinder. The final radial matrix differential equation is solved fully analytically without adoption of any numerical scheme. Comparisons to the previous analytical solutions demonstrate the excellent computation accuracy and efficiency of the present SBFEM approach. It also revealed the great potential of the SBFEM to solve more complex wave-structure interaction problems.
Publisher: Springer Singapore
Date: 06-10-2020
Publisher: Elsevier BV
Date: 07-2020
Publisher: ASMEDC
Date: 2005
Abstract: Hydroelastic response of VLFS under inhomogeneous sea environment is an important issue in offshore engineering applications. The most typical inhomogeneous ocean environment in offshore engineering is the inhomogeneity caused by the uneven sea bottom. In this paper, the hydroelastic response of VLFS due to the variation of water depth is studied experimentally and numerically. Experiments were performed in the state key laboratory of ocean engineering at Shanghai Jiao Tong University (SJTU). Different shoals were set on the bottom of the wave basin to simulate the uneven sea bottom. The cases tested in the Lab were studied by extending the traditional hydroelastic method in constant water depth to the varied water depth. Comparisons between the experimental measurements and the numerical results show good agreement. It is found that the inhomogeneous ocean environment has some effect on the hydroelastic response of VLFS.
Publisher: American Society of Mechanical Engineers
Date: 08-06-2014
Abstract: Floating Liquefied Natural Gas (FLNG) facilities, which are a new type of floating platform, have been developed as an alternative to long pipelines for the exploitation of stranded offshore fields. FLNG vessels will be subjected to very complicated and onerous sea states in some regions and very severe motion responses must be avoided. The vessel motion can induce internal tank sloshing, which can in turn affect the global motion response of the vessel. This coupling response is of great importance for the safe design and operation of FLNG facilities in real sea states. This paper investigates the coupling effect between FLNG roll motions and sloshing. Model tests are carried out for a section of an FLNG vessel containing a tank excited in roll by band-limited white noise waves. During the model tests, the FLNG model is ballasted with fresh water and equivalent steel ballast weights respectively, to quantify the coupling effects due to the internal sloshing. Time histories of the global motions and the internal sloshing oscillations have been measured. Statistical and spectral analyses have been carried out on the measured data. The response litude operators are obtained using measured motion spectra ided by the excitation wave spectrum. The influence of the internal sloshing on the global motions has been illustrated through the comparison of the experimental results between the liquid and solid (steel) ballast weight cases. Based on the experimental results, some conclusions regarding the coupling mechanism between FLNG motions and sloshing are drawn.
Publisher: Elsevier BV
Date: 07-2014
Publisher: American Society of Mechanical Engineers
Date: 05-06-2022
Abstract: The deployment of offshore wind turbines has focused primarily on shallow seas (such as the North Sea, Chinese coastal waters, and the New England coast) using bottom fixed foundations. However, much of the world’s offshore wind resource lies in deeper waters where bottom-fixed foundations are not suitable, and floating platforms must be utilised. To date, the majority of floating concepts have been developed to support a single wind turbine. This leads to a high capital cost for each in idual platform and consequently a high levelised cost of energy. The W2Power platform (developed by EnerOcean S.L, Spain) currently supports a pair of 6 MW wind turbines on outward-leaning towers. The design significantly reduces the cost per installed MW, increases the structure’s natural period, added mass, and radiation d ing. The platform, patented in 2009, was the world’s first twin-turbine platform and the first to be demonstrated at sea (2019). This paper presents the hydrodynamics of a 1:40 scale model of the W2Power platform using the well-known OrcaFlex software. The analysis has been carried out under extreme and operational conditions, and the resulting hydrodynamic loads and motion response are presented. The mooring system was found to be sensitive to wave direction, particularly when propagating along the current direction. Furthermore, the results showed advantages in the hydrodynamic responses for the W2Power platform as an innovative floating system.
Publisher: Elsevier BV
Date: 02-2016
Publisher: Elsevier BV
Date: 2016
Publisher: ASMEDC
Date: 2002
Abstract: A production spar designed for West African (WA) offshore conditions must consider possible resonance with long period swell, which might result in large litude heave oscillations. Preliminary study of a classic spar with diameter of 39 m (128 ft) and draft 198 m (650 ft) for a WA application led the authors to believe that excessive heave response of 5.2 m (17 ft) may occur at the natural period of 28 seconds. This led the team to investigate the possibility of adding a heave plate (circular disk) at the base of the spar to control the response to within 3.1 m (10 ft), which is the limit set by a typical compensation system. Important design issues arose with regards to the geometry of the plate, i.e. diameter and thickness. Numerical simulations and model testing were used to identify the influence of a heave plate on the heave response of the spar. Heave response for various diameters and thickness were investigated. Comparison of added mass and d ing values were found to be in reasonable agreement. Issues such as effect of a centerwell and moorings, plate cutouts for ease of transportation were also investigated. Discussion of the experimental results and comparison with numerical simulations are presented in this paper, and some recommendations are made on optimum heave plate geometry.
Publisher: ASMEDC
Date: 2011
Abstract: This paper presents the results of experiments carried out to determine the motion/seakeeping behavior of a deep-vee hull form catamaran in regular sea condition. A deep-vee catamaran model for the Newcastle University’s new RV replacing the old RV Bernicia was used for the motion measurements. The experiments were performed in the university’s towing tank. The results obtained were validated using a 3D panel method in frequency domain. A comparison of these results with the motion characteristics of the NPL (National Physical Laboratory) round bilge hullform based catamaran of similar geometrical properties revealed that the deep-vee hull forms possess significantly better seakeeping capabilities than a round bilge hull form.
Publisher: Springer Science and Business Media LLC
Date: 05-07-2021
DOI: 10.1186/S12913-021-06681-0
Abstract: Cardiovascular diseases (CVDs) are the leading cause of deaths and disability in Nepal. Health systems can improve CVD health outcomes even in resource-limited settings by directing efforts to meet critical system gaps. This study aimed to identify Nepal’s health systems gaps to prevent and manage CVDs. We formed a task force composed of the government and non-government representatives and assessed health system performance across six building blocks: governance, service delivery, human resources, medical products, information system, and financing in terms of equity, access, coverage, efficiency, quality, safety and sustainability. We reviewed 125 national health policies, plans, strategies, guidelines, reports and websites and conducted 52 key informant interviews. We grouped notes from desk review and transcripts’ codes into equity, access, coverage, efficiency, quality, safety and sustainability of the health system. National health insurance covers less than 10% of the population and more than 50% of the health spending is out of pocket. The efficiency of CVDs prevention and management programs in Nepal is affected by the shortage of human resources, weak monitoring and supervision, and inadequate engagement of stakeholders. There are policies and strategies in place to ensure quality of care, however their implementation and supervision is weak. The total budget on health has been increasing over the past five years. However, the funding on CVDs is negligible. Governments at the federal, provincial and local levels should prioritize CVDs care and partner with non-government organizations to improve preventive and curative CVDs services.
Publisher: Springer Science and Business Media LLC
Date: 09-03-2016
Publisher: Elsevier BV
Date: 04-2004
Publisher: Elsevier BV
Date: 12-2016
Publisher: MDPI AG
Date: 08-03-2022
DOI: 10.3390/JMSE10030388
Abstract: The decarbonisation of waterborne transport is arguably the biggest challenge faced by the maritime industry presently. By 2050, the International Maritime Organization (IMO) aims to reduce greenhouse gas emissions from the shipping industry by 50% compared to 2008, with a vision to phase out fossil fuels by the end of the century as a matter of urgency. To meet such targets, action must be taken immediately to address the barriers to adopt the various clean shipping options currently at different technological maturity levels. Green hydrogen as an alternative fuel presents an attractive solution to meet future targets from international bodies and is seen as a viable contributor within a future clean shipping vision. The cost of hydrogen fuel—in the short-term at least—is higher compared to conventional fuel therefore, energy-saving devices (ESDs) for ships are more important than ever, as implementation of rules and regulations restrict the use of fossil fuels while promoting zero-emission technology. However, existing and emerging ESDs in standalone/combination for traditional fossil fuel driven vessels have not been researched to assess their compatibility for hydrogen-powered ships, which present new challenges and considerations within their design and operation. Therefore, this review aims to bridge that gap by firstly identifying the new challenges that a hydrogen-powered propulsion system brings forth and then reviewing the quantitative energy saving capability and qualitive additional benefits of in idual existing and emerging ESDs in standalone and combination, with recommendations for the most applicable ESD combinations with hydrogen-powered waterborne transport presented to maximise energy saving and minimise the negative impact on the propulsion system components. In summary, the most compatible combination ESDs for hydrogen will depend largely on factors such as vessel types, routes, propulsion, operation, etc. However, the mitigation of load fluctuations commonly encountered during a vessels operation was viewed to be a primary area of interest as it can have a negative impact on hydrogen propulsion system components such as the fuel cell therefore, the ESD combination that can maximise energy savings as well as minimise the fluctuating loads experienced would be viewed as the most compatible with hydrogen-powered waterborne transport.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Longbin Tao.