ORCID Profile
0000-0002-1247-6896
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UNSW
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Turbulent Flows | Interdisciplinary Engineering | Computational Fluid Dynamics | Biomechanical Engineering
Publisher: AIP Publishing
Date: 11-2011
DOI: 10.1063/1.3659892
Abstract: A viscous flow past three filaments in side-by-side arrangement is studied by a numerical simulation and is accompanied by a previously established linear stability analysis. Other than the coupling modes reported previously, which include the in-phase mode, symmetrical mode, and out-of-phase mode, three additional modes are identified in the nonlinear regime by systematically varying the separation distance between the filaments. These modes are the half-frequency mode, irrational-frequency mode, and erratic flapping state. The dynamic characteristics of each mode at the saturated state is described, including the flapping litude, frequency, drag force, and mechanical energy of the filaments. Four typical vortex structures are observed in the wake of the filaments and are described as the coalesced vortices, symmetrical vortices, erratic vortices, and independent vortex streets. The vortex structures are closely related to the coupling modes and the dynamic characteristics of the filaments. As the Reynolds number is increased or as the bending rigidity is reduced, the filaments gain more energy and ordering of the coupling modes may change.
Publisher: IEEE
Date: 10-2013
Publisher: SAGE Publications
Date: 12-05-2020
Abstract: The sound generated by two tandem arranged flexible wings in forward flight is numerically studied by using an immersed boundary method, at a Reynolds number of 100 and Mach number of 0.1. Three distinct cases are studied, encompassing a single wing and two tandem wings flapping in phase and out of phase. The sound generation of flapping wings is systematically studied by varying the wing flexibility (represented by the frequency ratio [Formula: see text]), structure-to-fluid mass ratio ([Formula: see text]), the phase difference (φ), and the gap ([Formula: see text]) between the two flapping wings. The results show that there is a direct correlation between the wing flexibility and sound generation for all cases considered. Specifically, for wings of low mass ratios ([Formula: see text]), an increase in flexibility resulted in a decrease in sound generation. For wings of high mass ratios ([Formula: see text]), an increase in flexibility resulted in higher sound output. The introduction of a second wing flapping in-phase resulted in an increase in aerodynamic features and sound generation, while the introduction of a second wing flapping out-of-phase experiences a decrease in sound output when compared to the in-phase case. In both cases, the effect of the wing flexibility on the sound production is similar to that of the single wing. An increase in flexibility is also found to have an impact on the plane of maximum sound pressure. For ex le, increasing flexibility resulted in a rotation of the plane of maximum sound pressure counter-clockwise relative to those at lower frequency ratios. Flexible wings with a structure-to-fluid mass ratio of unity and medium flexibility (i.e. [Formula: see text] and [Formula: see text]) are found to generate lower sound with high aerodynamic performance conserved.
Publisher: Elsevier BV
Date: 04-2019
Publisher: The Company of Biologists
Date: 15-07-2016
DOI: 10.1242/JEB.140475
Abstract: Fishes may exploit environmental vortices to save in the cost of locomotion. Previous work has investigated fish refuging behind a single cylinder in current, a behavior termed the Kármán gait. However, current-swept habitats often contain aggregations of physical objects, and it is unclear how the complex hydrodynamics shed from multiple structures affect refuging in fish. To begin to address this, we investigated how the flow fields produced by two D-shaped cylinders arranged in tandem affect the ability of rainbow trout (Oncorhynchus mykiss) to Kármán gait. We altered the spacing of the two cylinders from l/D of 0.7 to 2.7 (where l=downstream spacing of cylinders and D=cylinder diameter) and recorded the kinematics of trout swimming behind the cylinders with high-speed video at Re=10,000–55,000. Digital particle image velocimetry showed that increasing l/D decreased the strength of the vortex street by an average of 53% and decreased the frequency that vortices were shed by ∼20% for all speeds. Trout were able to Kármán gait behind all cylinder treatments despite these differences in the downstream wake however, they Kármán gaited over twice as often behind closely spaced cylinders (l/D=0.7, 1.1, and 1.5). Computational fluid dynamics simulations show that when cylinders are widely spaced, the upstream cylinder generates a vortex street that interacts destructively with the downstream cylinder, producing weaker, more widely spaced and less-organized vortices that discourage Kármán gaiting. These findings are poised to help predict when fish may seek refuge in natural habitats based on the position and arrangement of stationary objects.
Publisher: American Physical Society (APS)
Date: 06-07-2012
Publisher: AIP Publishing
Date: 15-07-2013
DOI: 10.1063/1.4813006
Abstract: The interaction between flag/flags and fluid is studied numerically and the time-average flow in the wake is analyzed. It is found that a zero-mass flag in uniform flow can not exhibit sustained flapping which only occurs when the mass is involved, while multiple zero-mass flags with small separation settle into sustained flapping state. Furthermore, the nonzero mass is an essential condition for flag/flags to establish the sustained flapping in the case of convectively instable wake, while it is an unnecessary condition for the case of the absolutely instable wake.
Publisher: World Scientific Pub Co Pte Ltd
Date: 12-2013
DOI: 10.1142/S0219519413400137
Abstract: In order to explore the kinetic characteristics of planktonic microorganisms and nanometer biological motors, a mathematical model is developed to estimate the hydrodynamic force in the migration of micro- and nano-swimmers by using the Laplace transformation and linear superposition. Based on the model, it is found that a micro- and nano-swimmer will enjoy a positive propulsive force by improving frequencies or generating traveling waves along its body if it is not time reversible. The results obtained in this study provide a physical insight into the behaviors of the micro- and nano-swimmer at low Reynolds numbers, and the corresponding quantitative basis can also be potentially used in the design of nanorobot and nanosized biomaterials.
Publisher: Elsevier BV
Date: 09-2015
Publisher: Elsevier BV
Date: 02-2014
Publisher: Springer Science and Business Media LLC
Date: 15-03-2014
Publisher: Informa UK Limited
Date: 12-01-2022
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2014
Publisher: Elsevier BV
Date: 05-2022
Publisher: American Society of Mechanical Engineers
Date: 07-07-2013
Abstract: In this paper, we describe a three-dimensional (3D) computational approach for computing the fluid–structure interaction (FSI) encountered in biological and biomedical flows. The approach combines a Cartesian grid based immerse-boundary method for the viscous incompressible flow and a finite-element method for the solid body mechanics. The separate subroutines of the finite-element method can handle general 3D bodies as well as thin-wall structures such as frames, membranes, and plates. Furthermore, both geometric nonlinearity due to large displacements and large rotations and material nonlinearity due to hyperelasticity have been incorporated. The flow and the solid body are meshed separately, and as the body deforms, no mesh regeneration is needed. The FSI solver has been validated against previous numerical and experimental studies. Applications in insect flight and vocal fold vibration have been demonstrated.
Publisher: Elsevier BV
Date: 2020
Publisher: Informa UK Limited
Date: 21-11-2012
DOI: 10.1080/10255842.2012.729581
Abstract: To study the behaviour of a haemocyte when crossing a stenotic capillary, the immersed boundary-lattice Boltzmann method was used to establish a quantitative analysis model. The haemocyte was assumed to be spherical and to have an elastic cell membrane, which can be driven by blood flow to adopt a highly deformable character. In the stenotic capillary, the spherical blood cell was stressed both by the flow and the wall dimension, and the cell shape was forced to be stretched to cross the stenosis. Our simulation investigated the haemocyte crossing process in detail. The velocity and pressure were anatomised to obtain information on how blood flows through a capillary and to estimate the degree of cell damage caused by excessive pressure. Quantitative velocity analysis results demonstrated that a large haemocyte crossing a small stenosis would have a noticeable effect on blood flow, while quantitative pressure distribution analysis results indicated that the crossing process would produce a special pressure distribution in the cell interior and to some extent a sudden change between the cell interior and the surrounding plasma.
Publisher: AIP Publishing
Date: 04-2022
DOI: 10.1063/5.0085021
Abstract: This paper presents a numerical study on the aerodynamic performance of three-dimensional flapping wings hovering in ultra-low-density fluid by using an immersed boundary method with a focus on the effects of compressibility on force production and flapping efficiency. Simulations are conducted by varying Mach number, aspect ratio, stroke litude, and flexibility of the wing. It is found that the lift coefficient and efficiency of rigid wings are reduced by up to 10.6% and 10.7%, respectively, when the Mach number is increased from 0.2 (weakly compressible) to 0.9 (highly compressible). To achieve sufficient lift force in the ultra-low-density atmosphere, three main strategies including varying the aspect ratio, stroke litude, and flexibility of wings are explored. It is found that a wing with high aspect ratio, small and fast stroke motion, and moderate flexibility is able to generate a high lift. An optimized flexible wing according to the aforementioned analysis is further proposed and simulated, which shows 38.3% and 20.8% enhancements of the mean lift coefficient and efficiency, respectively. The present study shows that the flapping aerial vehicle in ultra-low-density atmosphere is highly feasible from the aerodynamic point of view.
Publisher: World Scientific Pub Co Pte Lt
Date: 12-2010
DOI: 10.1142/S1793524510001069
Abstract: A nonlinear dynamic model of microbial growth is established based on the theories of the diffusion response of thermodynamics and the chemotactic response of biology. Except for the two traditional variables, i.e. the density of bacteria and the concentration of attractant, the pH value, a crucial influencing factor to the microbial growth, is also considered in this model. The pH effect on the microbial growth is taken as a Gaussian function G 0 e -(φ- φ c ) 2 /G 1 , where G 0 , G 1 and φ c are constants, φ represents the pH value and φ c represents the critical pH value that best fits for microbial growth. To study the effects of the reproduction rate of the bacteria and the pH value on the stability of the system, three parameters a, G 0 and G 1 are studied in detail, where a denotes the reproduction rate of the bacteria, G 0 denotes the impacting intensity of the pH value to microbial growth and G 1 denotes the bacterial adaptability to the pH value. When the effect of the pH value of the solution which microorganisms live in is ignored in the governing equations of the model, the microbial system is more stable with larger a. When the effect of the bacterial chemotaxis is ignored, the microbial system is more stable with the larger G 1 and more unstable with the larger G 0 for φ 0 φ c . However, the stability of the microbial system is almost unaffected by the variation G 0 and G 1 and it is always stable for φ 0 φ c under the assumed conditions in this paper. In the whole system model, it is more unstable with larger G 1 and more stable with larger G 0 for φ 0 φ c . The system is more stable with larger G 1 and more unstable with larger G 0 for φ 0 φ c . However, the system is more unstable with larger a for φ 0 φ c and the stability of the system is almost unaffected by a for φ 0 φ c . The results obtained in this study provide a biophysical insight into the understanding of the growth and stability behavior of microorganisms.
Publisher: Hindawi Limited
Date: 2016
DOI: 10.1155/2016/7981386
Abstract: An immersed boundary-lattice Boltzmann method is developed for fluid-structure interactions involving non-Newtonian fluids (e.g., power-law fluid). In this method, the flexible structure (e.g., capsule) dynamics and the fluid dynamics are coupled by using the immersed boundary method. The incompressible viscous power-law fluid motion is obtained by solving the lattice Boltzmann equation. The non-Newtonian rheology is achieved by using a shear rate-dependant relaxation time in the lattice Boltzmann method. The non-Newtonian flow solver is then validated by considering a power-law flow in a straight channel which is one of the benchmark problems to validate an in-house solver. The numerical results present a good agreement with the analytical solutions for various values of power-law index. Finally, we apply this method to study the deformation of a capsule in a power-law shear flow by varying the Reynolds number from 0.025 to 0.1, dimensionless shear rate from 0.004 to 0.1, and power-law index from 0.2 to 1.8. It is found that the deformation of the capsule increases with the power-law index for different Reynolds numbers and nondimensional shear rates. In addition, the Reynolds number does not have significant effect on the capsule deformation in the flow regime considered. Moreover, the power-law index effect is stronger for larger dimensionless shear rate compared to smaller values.
Publisher: International Academy Publishing (IAP)
Date: 05-2010
Publisher: ASME International
Date: 10-2013
DOI: 10.1115/1.4025330
Abstract: Human vocal folds experience flow-induced vibrations during phonation. In previous computational models, the vocal fold dynamics has been treated with linear elasticity theory in which both the strain and the displacement of the tissue are assumed to be infinitesimal (referred to as model I). The effect of the nonlinear strain, or geometric nonlinearity, caused by finite displacements is yet not clear. In this work, a two-dimensional model is used to study the effect of geometric nonlinearity (referred to as model II) on the vocal fold and the airflow. The result shows that even though the deformation is under 1 mm, i.e., less than 10% of the size of the vocal fold, the geometric nonlinear effect is still significant. Specifically, model I underpredicts the gap width, the flow rate, and the impact stress on the medial surfaces as compared to model II. The study further shows that the differences are caused by the contact mechanics and, more importantly, the fluid-structure interaction that magnifies the error from the small-displacement assumption. The results suggest that using the large-displacement formulation in a computational model would be more appropriate for accurate simulations of the vocal fold dynamics.
Publisher: AIP Publishing
Date: 2015
DOI: 10.1063/1.4905537
Abstract: The numerical study on the power extraction performance of a flapping foil with a flexible tail is performed in this work. A NACA0015 airfoil is arranged in a two-dimensional laminar flow and imposed with a synchronous harmonic plunge and pitch rotary motion. A flat plate that is attached to the trailing edge of the foil is utilized to model a tail, and so they are viewed as a whole for the purpose of power extraction. In addition, the tail either is rigid or can deform due to the exerted hydrodynamic forces. To implement numerical simulations, an immersed boundary-lattice Boltzmann method is employed. At a Reynolds number of 1100 and the position of the pitching axis at third chord, the influences of the mass and flexibility of the tail as well as the frequency of motion on the power extraction are systematically examined. It is found that compared to the foil with a rigid tail, the efficiency of power extraction for the foil with a deformable tail can be improved. Based on the numerical analysis, it is indicated that the enhanced plunging component of the power extraction, which is caused by the increased lift force, directly contributes to the efficiency improvement. Since a flexible tail with medium and high masses is not beneficial to the efficiency improvement, a flexible tail with low mass together with high flexibility is recommended in the flapping foil based power extraction system.
Publisher: Cambridge University Press (CUP)
Date: 07-09-2021
DOI: 10.1017/JFM.2021.710
Abstract: The nonlinear dynamics of a two-sided collapsible channel flow is investigated by using an immersed boundary-lattice Boltzmann method. The stability of the hydrodynamic flow and collapsible channel walls is examined over a wide range of Reynolds numbers $Re$ , structure-to-fluid mass ratios $M$ and external pressures $P_e$ . Based on extensive simulations, we first characterise the chaotic behaviours of the collapsible channel flow and explore possible routes to chaos. We then explore the physical mechanisms responsible for the onset of self-excited oscillations. Nonlinear and rich dynamic behaviours of the collapsible system are discovered. Specifically, the system experiences a supercritical Hopf bifurcation leading to a period-1 limit cycle oscillation. The existence of chaotic behaviours of the collapsible channel walls is confirmed by a positive dominant Lyapunov exponent and a chaotic attractor in the velocity-displacement phase portrait of the mid-point of the collapsible channel wall. Chaos in the system can be reached via period-doubling and quasi-periodic bifurcations. It is also found that symmetry breaking is not a prerequisite for the onset of self-excited oscillations. However, symmetry breaking induced by mass ratio and external pressure may lead to a chaotic state. Unbalanced transmural pressure, wall inertia and shear layer instabilities in the vorticity waves contribute to the onset of self-excited oscillations of the collapsible system. The period-doubling, quasi-periodic and chaotic oscillations are closely associated with vortex pairing and merging of adjacent vortices, and interactions between the vortices on the upper and lower walls downstream of the throat.
Publisher: Elsevier BV
Date: 05-2023
Publisher: World Scientific Pub Co Pte Ltd
Date: 12-2013
DOI: 10.1142/S0219519413400125
Abstract: A self-propelled fish swimming in viscous fluid is investigated by solving the incompressible Navier–Stokes equations numerically with the space-time finite element method to understand the mechanisms of aquatic animal locomotion. Two types of propulsion strategies, undulatory body and traveling wave surface (TWS), are considered. Based on the simulations, we find that by performing lateral undulation, the fish is able to move forward with a reverse von Kármán vortex street in its wake. In addition, there is no vortex street in the wake of the fish using TWS. In this case, the thrust of the fish is generated by the jets outside the boundary layer and the high pressure on the leeward side of the traveling wave. The results obtained in this paper will be of help in understanding of the propulsive performance of aquatic animal locomotion.
Publisher: American Physical Society (APS)
Date: 03-08-2010
Publisher: World Scientific Pub Co Pte Lt
Date: 2013
DOI: 10.1142/S1793524512500611
Abstract: A two-dimensional red blood cell (RBC) membrane model based on elastic and Euler–Bernoulli beam theories is introduced in the frame of immersed boundary-lattice Boltzmann method (IB-LBM). The effect of the flexible membrane is handled by the immersed boundary method in which the stress exerted by the RBC on the ambient fluid is spread onto the collocated grid points near the boundary. The fluid dynamics is obtained by solving the discrete lattice Boltzmann equation. A "ghost shape", to which the RBC returns when restoring, is introduced by prescribing a bending force along the boundary. Numerical ex les involving tumbling, tank-treading and RBC aggregation in shear flow and deformation and restoration in poiseuille flow are presented to verify the method and illustrate its efficiency. As an application of the present method, a ten-RBC colony being compressed through a stenotic microvessel is studied focusing the cell–cell interaction strength. Quantitative comparisons of the pressure and velocity on specified microvessel interfaces are made between each aggregation case. It reveals that the stronger aggregation may lead to more resistance against blood flow and result in higher pressure difference at the stenosis.
Publisher: MDPI AG
Date: 04-04-2018
DOI: 10.3390/APP8040559
Publisher: IOP Publishing
Date: 16-11-2022
Abstract: Fish are observed to school in different configurations. However, how and why fish maintain a stable schooling formation still remains unclear. This work presents a numerical study of the dense schooling of two free swimmers by a hybrid method of the multi-agent deep reinforcement learning and the immersed boundary-lattice Boltzmann method. Active control policies are developed by synchronously training the leader to swim at a given speed and orientation and the follower to hold close proximity to the leader. After training, the swimmers could resist the strong hydrodynamic force to remain in stable formations and meantime swim in desired path, only by their tail-beat flapping. The tail movement of the swimmers in the stable formations are irregular and asymmetrical, indicating the swimmers are carefully adjusting their body-kinematics to balance the hydrodynamic force. In addition, a significant decrease in the mean litude and the cost of transport is found for the followers, indicating these swimmers could maintain the swimming speed with less efforts. The results also show that the side-by-side formation is hydrodynamically more stable but energetically less efficient than other configurations, while the full-body staggered formation is energetically more efficient as a whole.
Publisher: MDPI AG
Date: 22-02-2021
Abstract: The dynamic behaviours of a filament in a viscoelastic uniform flow were investigated by an immersed boundary-lattice Boltzmann method. The effects of the Reynolds numbers (Re, ranging from 10 to 200) and the Weissenberg number (Wi, ranging from 0 to 1.2) on the filament flapping motion and the drag and lift coefficients on the filament were studied. It was found that a higher inertial effect (larger Re) promotes the flapping motion of the filament. In addition, the major effect of the viscoelasticity of the Giesekus fluid is to decrease the critical Reynolds number for the flapping motion of the filament and to promote the flapping motion. The drag coefficient on the filament in a Giesekus uniform flow decreases with the increase of Wi at low Re (Re ), and experiences oscillations with similar litudes at all Wi at a sufficiently high Re (Re ). In contrast, the viscoelasticity of the FENE-CR fluid increases the critical Reynolds number at lower Wi (Wi .8), and shows little influence on the critical Reynolds number at higher Wi (Wi≥0.8). In addition, the viscoelasticity of the FENE-CR fluid hinders the flapping motion of the filament, and increases the drag coefficient on the filament at low Re (Re ).
Publisher: Elsevier BV
Date: 12-2023
Publisher: AIP Publishing
Date: 2022
DOI: 10.1063/5.0070450
Abstract: The influences of serrated trailing edge on the aerodynamic and aeroacoustic performance of a flapping wing during hovering flight are investigated using a hybrid framework of an immersed boundary Navier–Stokes solver for the flow field and the Ffowcs Williams–Hawkings (FW–H) analogy for the sound field. A rigid rectangular wing with an aspect ratio of 2 undergoes pitching and stroke motions at a Reynolds number (Re) of 310 and a Mach number (M) of 0.012. Simulations are conducted by varying the dimensionless wavenumber k* from 2π to 10π and wave litude 2h* from 0.25 to 1.0. We find that at k*=8π and 2h*=1.5 (D4), the average sound power level is reduced by up to 6.8 dB within the Strouhal number (St) between 2.0 and 4.0 compared to that of a plain trailing edge while the lift coefficient is maintained. The directivity at St = 0.2, St = 0.4, St = 2.2, and St = 2.4 is discussed. It is found that the serrations of D4 do not affect the directivity for the first two frequencies and significantly reduce the magnitude of the directivity for the last two frequencies. The serrations of D4 considerably alter the flow field near the wing surface and reduced the surface pressure fluctuations near the wing tip, leading to the noise reduction. The lift coefficient of D4 is not significantly changed, because the reduction in the pressure-contributed lift is compensated by an increase in the shear stress-contributed lift. The serrations with higher 2h* and k* have larger shear stress-contributed lift.
Publisher: World Scientific Pub Co Pte Lt
Date: 16-05-2012
DOI: 10.1142/S1793524511001647
Abstract: The analytical solutions of non-Fourier Pennes and Chen–Holmes equations are obtained using the Laplace transformation and particular solution method in the present paper. As an application, the effects of the thermal relaxation time τ, the blood perfusion w b , and the blood flow velocity v on the biological skin and inner tissue temperature T are studied in detail. The results obtained in this study provide a good alternative method to study the bio-heat and a biophysical insight into the understanding of the heat transfer in the biotissue.
Publisher: MDPI AG
Date: 17-01-2022
Abstract: This work presents a numerical study of the collective motion of two freely-swimming swimmers by a hybrid method of the deep reinforcement learning method (DRL) and the immersed boundary-lattice Boltzmann method (IB-LBM). An active control policy is developed by training a fish-like swimmer to swim at an average speed of 0.4 L/T and an average orientation angle of 0∘. After training, the swimmer is able to restore the desired swimming speed and orientation from moderate external perturbation. Then the control policy is adopted by two identical swimmers in the collective swimming. Stable side-by-side, in-line and staggered formations are achieved according to the initial positions. The stable side-by-side swimming area of the follower is concentrated to a small area left or right to the leader with an average distance of 1.35 L. The stable in-line area is concentrated to a small area about 0.25 L behind the leader. A detailed analysis shows that both the active control and passive self-organization play an important role in the emergence of the stable schooling formations, while the active control works for maintaining the speed and orientation in case the swimmers collide or depart from each other and the passive self-organization works for emerging a stable schooling configuration. The result supports the Lighthill conjecture and also highlights the importance of the active control.
Publisher: Springer Science and Business Media LLC
Date: 30-12-2014
Publisher: IEEE
Date: 10-2013
Publisher: MDPI AG
Date: 07-02-2021
Abstract: Due to rising human infertility, sperm motility has been an important subject. Among the hundreds of millions of sperms on the journey up the oviducts, only a few excellent travelers will reach the eggs. This journey is affected by many factors, some of which include sperm quality, sperm density, fluid rheology and chemotaxis. In addition, the sperm swimming through different body tracks and fluids involves complex sperm flagellar, complex fluid environment, and multi-sperm and sperm-wall interactions. Therefore, this topic has generated substantial research interest. In this paper, we present a review of computational studies on sperm swimming from an engineering perspective with focus on both simplified theoretical methods and fluid–structure interaction methods. Several open issues in this field are highlighted.
Publisher: Springer Science and Business Media LLC
Date: 17-03-2009
Publisher: AIP Publishing
Date: 09-2022
DOI: 10.1063/5.0101584
Abstract: This paper presents a study on streamline penetration, velocity error, and consequences of a fluid–structure interaction (FSI) solver based on the feedback immersed boundary method (IBM). In the FSI solver, the fluid dynamics is solved by the lattice Boltzmann method the solid structure deformation is solved by the finite difference method and the finite element method for two- and three-dimensional cases, respectively and the feedback IBM is used to realize the interaction between the fluid and the structure. The IBM is implemented in non-iterative and iterative ways. For the non-iterative version, two types of integration are discussed: without and with velocity prediction step. Five benchmark cases are simulated to study the performance of the three implementations: a uniform flow over a cylinder, flow-induced vibration of a flexible plate attached behind a stationary cylinder in a channel, flow through a two-dimensional asymmetric stenosis, a one-sided collapsible channel, and a three-dimensional collapsible tube. Results show that both the IBM with prediction step, the iterative IBM, and one iteration IBM with proper feedback coefficients can suppress the spurious flow penetration on the solid wall. While the velocity error does not significantly affect the force production and structure deformation for external flows, reducing it significantly improves the prediction of the force distribution and structure deformation for internal flows. In addition, the iterative IBM with smaller feedback coefficient has better numerical stability. This work will provide an important guideline for the correct use of the feedback IBMs.
Publisher: MDPI AG
Date: 20-04-2021
Abstract: Cardiovascular disease is one of the world’s leading causes of morbidity and mortality. Fractional flow reserve (FFR) was proposed in the 1990s to more accurately evaluate the functional severity of intermediate coronary stenosis, and it is currently the gold standard in cardiac catheterization laboratories where coronary pressure and flow are routinely obtained. The clinical measurement of FFR relies on a pressure wire for the recording of pressures however, in computational fluid dynamics studies, an FFR is frequently predicted using a wire-absent model. We aim to investigate the influence of the physical presence of a 0.014-inch (≈0.36 mm) pressure wire in the calculation of virtual FFR. Ideal and patient-specific models were simulated with the absence and presence of a pressure wire. The computed FFR reduced from 0.96 to 0.93 after inserting a wire in a 3-mm non-stenosed (pipe) ideal model. In mild stenotic cases, the difference in FFR between the wire-absent and wire-included models was slight. The overestimation in severe case was large but is of less clinical significance because, in practice, this tight lesion does not require sophisticated measurement to be considered critical. However, an absence of the pressure wire in simulations could contribute to an over-evaluation for an intermediate coronary stenosis.
Publisher: Elsevier BV
Date: 05-2015
Publisher: Springer Science and Business Media LLC
Date: 14-07-2016
Publisher: AIP Publishing
Date: 09-2023
DOI: 10.1063/5.0165614
Publisher: Hindawi Limited
Date: 2016
DOI: 10.1155/2016/9028409
Publisher: Springer Science and Business Media LLC
Date: 23-05-2013
Publisher: Elsevier BV
Date: 03-2019
Publisher: MDPI AG
Date: 21-05-2022
Abstract: Arterial stenosis is a problem of immediate significance, as cardiovascular disease is the number one leading cause of death worldwide. Generally, the study of stenotic flow assumes a smooth, curved stenosis and artery. However, the real situation is unlikely to present an infinitely smooth-surfaced arterial stenosis. Here, the impact of surface roughness on the flow in an arterial stenosis was studied via a computational fluid dynamics analysis. A patient-specific geometry with a smooth surface was reconstructed, and a partially rough model was built by artificially adding random roughness only on the stenotic region of the smooth model. It was found that the flow was oscillatory downstream of the stenosis in the models. A slightly lower velocity near the wall and more oscillatory flows were observed due to the presence of the roughness in the stenotic region. However, the pressure distributions did not vary significantly between the smooth and rough models. The differences in the wall shear metrics were slight in the stenotic region and became larger in the downstream region of the models.
Publisher: Springer Berlin Heidelberg
Date: 2014
Publisher: Elsevier BV
Date: 11-2014
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2015
Publisher: Elsevier BV
Date: 08-2011
Publisher: SAGE Publications
Date: 16-04-2019
Abstract: The immersed boundary method is a methodology for dealing with boundary conditions at fluid–fluid and fluid–solid interfaces. The immersed boundary method has been attracting growing attention in the recent years due to its simplicity in mesh processing. Great effort has been made to develop its new features and promote its applications in new areas. This review is focused on assessing the immersed boundary method fundamentals and the latest progresses especially the strategies to address the challenges and the applications of the immersed boundary method. Various numerical ex les are also presented for demonstrating the capability of the immersed boundary method, including blood flow and blood cells, flapping flag, flow around a hoverfly, turbulence flow over a wavy boundary, shock wave-induced vibration, and acoustic waves scattered by a cylinder and a sphere. The major challenges and several open issues in this field are highlighted.
Publisher: IEEE
Date: 08-2014
Publisher: Elsevier BV
Date: 2013
Publisher: World Scientific Pub Co Pte Lt
Date: 24-08-2015
DOI: 10.1142/S0218202515400084
Abstract: This paper presents a fluid–structure interaction (FSI) solution technique in which the incompressible fluid dynamics involving moving boundaries is solved with the deforming-spatial-domain/stabilized space–time (DSD/SST) method and the structural dynamics is solved with the finite difference (FD) method. The DSD/SST and FD solvers are coupled by an implicit partitioned coupling strategy based on staggered subiterations. Three types of relaxation are applied on the FSI surface velocity and hydrodynamic force. The first one is applied to delay the coupling conditions at the beginning of each simulation the second one is applied to relax the increment during each subiteration and the third one is applied to filter high frequency oscillations between each time step. A pitching plate in a uniform flow is calculated to validate the FSI technique. The present results are in good agreement with data predicted by other methods. In addition, two problems are calculated to demonstrate the capability of this solver: an orbital flow over flapping foil propulsion and energy harvesting and a flexible plate in a cavity excited by an external force.
Publisher: Elsevier BV
Date: 08-2020
Publisher: IEEE
Date: 10-2013
Publisher: Elsevier BV
Date: 2018
Publisher: Springer Science and Business Media LLC
Date: 11-08-2013
Publisher: Elsevier BV
Date: 09-2013
DOI: 10.1016/J.COMPBIOMED.2013.05.023
Abstract: Atherosclerotic plaque can cause severe stenosis in the artery lumen. Blood flow through a substantially narrowed artery may have different flow characteristics and produce different forces acting on the plaque surface and artery wall. The disturbed flow and force fields in the lumen may have serious implications on vascular endothelial cells, smooth muscle cells, and circulating blood cells. In this work a simplified model is used to simulate a pulsatile non-Newtonian blood flow past a stenosed artery caused by atherosclerotic plaques of different severity. The focus is on a systematic parameter study of the effects of plaque size/geometry, flow Reynolds number, shear-rate dependent viscosity and flow pulsatility on the fluid wall shear stress and its gradient, fluid wall normal stress, and flow shear rate. The computational results obtained from this idealized model may shed light on the flow and force characteristics of more realistic blood flow through an atherosclerotic vessel.
Publisher: American Physical Society (APS)
Date: 05-03-2010
Publisher: Elsevier BV
Date: 04-2015
Publisher: Elsevier BV
Date: 12-2018
Publisher: IEEE
Date: 10-2013
Publisher: Elsevier BV
Date: 2016
Publisher: Elsevier BV
Date: 10-2017
Publisher: Elsevier BV
Date: 2012
DOI: 10.1063/2.1202205
Publisher: Elsevier BV
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DOI: 10.1063/2.1202401
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Date: 14-09-2020
DOI: 10.1017/JFM.2020.612
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Date: 03-2020
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Date: 2009
Start Date: 2016
End Date: 2018
Funder: Australian Research Council
View Funded ActivityStart Date: 2020
End Date: 2022
Funder: Australian Research Council
View Funded ActivityStart Date: 06-2016
End Date: 06-2019
Amount: $315,000.00
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End Date: 12-2023
Amount: $535,000.00
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