The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Tayfun E Tezduyar - One of the best experts on this subject based on the ideXlab platform.
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ventricle valve aorta flow analysis with the space time isogeometric discretization and Topology Change
Computational Mechanics, 2020Co-Authors: Takuya Terahara, Kenji Takizawa, Tayfun E Tezduyar, Atsushi Tsushima, Kensuke ShiozakiAbstract:We address the computational challenges of and presents results from ventricle-valve-aorta flow analysis. Including the left ventricle (LV) in the model makes the flow into the valve, and consequently the flow into the aorta, anatomically more realistic. The challenges include accurate representation of the boundary layers near moving solid surfaces even when the valve leaflets come into contact, computation with high geometric complexity, anatomically realistic representation of the LV motion, and flow stability at the inflow boundary, which has a traction condition. The challenges are mainly addressed with a Space–Time (ST) method that integrates three special ST methods around the core, ST Variational Multiscale (ST-VMS) method. The three special methods are the ST Slip Interface (ST-SI) and ST Topology Change (ST-TC) methods and ST Isogeometric Analysis (ST-IGA). The ST-discretization feature of the integrated method, ST-SI-TC-IGA, provides higher-order accuracy compared to standard discretization methods. The VMS feature addresses the computational challenges associated with the multiscale nature of the unsteady flow in the LV, valve and aorta. The moving-mesh feature of the ST framework enables high-resolution computation near the leaflets. The ST-TC enables moving-mesh computation even with the TC created by the contact between the leaflets, dealing with the contact while maintaining high-resolution representation near the leaflets. The ST-IGA provides smoother representation of the LV, valve and aorta surfaces and increased accuracy in the flow solution. The ST-SI connects the separately generated LV, valve and aorta NURBS meshes, enabling easier mesh generation, connects the mesh zones containing the leaflets, enabling a more effective mesh moving, helps the ST-TC deal with leaflet–leaflet contact location Change and contact sliding, and helps the ST-TC and ST-IGA keep the element density in the narrow spaces near the contact areas at a reasonable level. The ST-SI-TC-IGA is supplemented with two other special methods in this article. A structural mechanics computation method generates the LV motion from the CT scans of the LV and anatomically realistic values for the LV volume ratio. The Constrained-Flow-Profile (CFP) Traction provides flow stability at the inflow boundary. Test computation with the CFP Traction shows its effectiveness as an inflow stabilization method, and computation with the LV-valve-aorta model shows the effectiveness of the ST-SI-TC-IGA and the two supplemental methods.
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heart valve isogeometric sequentially coupled fsi analysis with the space time Topology Change method
Computational Mechanics, 2020Co-Authors: Takuya Terahara, Kenji Takizawa, Tayfun E Tezduyar, Yuri Bazilevs, Mingchen HsuAbstract:Heart valve fluid–structure interaction (FSI) analysis is one of the computationally challenging cases in cardiovascular fluid mechanics. The challenges include unsteady flow through a complex geometry, solid surfaces with large motion, and contact between the valve leaflets. We introduce here an isogeometric sequentially-coupled FSI (SCFSI) method that can address the challenges with an outcome of high-fidelity flow solutions. The SCFSI analysis enables dealing with the fluid and structure parts individually at different steps of the solutions sequence, and also enables using different methods or different mesh resolution levels at different steps. In the isogeometric SCFSI analysis here, the first step is a previously computed (fully) coupled Immersogeometric Analysis FSI of the heart valve with a reasonable flow solution. With the valve leaflet and arterial surface motion coming from that, we perform a new, higher-fidelity fluid mechanics computation with the space–time Topology Change method and isogeometric discretization. Both the immersogeometric and space–time methods are variational multiscale methods. The computation presented for a bioprosthetic heart valve demonstrates the power of the method introduced.
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heart valve flow computation with the space time slip interface Topology Change st si tc method and isogeometric analysis iga
2018Co-Authors: Kenji Takizawa, Tayfun E Tezduyar, Takuya Terahara, Takafumi SasakiAbstract:We present a heart valve flow computation with the Space–Time Slip Interface Topology Change (ST-SI-TC) method and Isogeometric Analysis (IGA). The computation is for a realistic heart valve model with actual contact between the valve leaflets. The ST-SI-TC method integrates the ST-SI and ST-TC methods in the framework of the ST Variational Multiscale (ST-VMS) method. The ST-VMS method functions as a moving-mesh method, which maintains high-resolution boundary layer representation near the solid surfaces. The ST-TC method was introduced for moving-mesh computation of flow problems with TC, such as contact between the leaflets of a heart valve. It deals with the contact while maintaining high-resolution representation near the leaflet surfaces. The ST-SI method was originally introduced to addresses the challenge involved in high-resolution representation of the boundary layers near spinning solid surfaces. The mesh covering a spinning solid surface spins with it, and the SI between that mesh and the rest of the mesh accurately connects the two sides. This maintains the high-resolution representation near solid surfaces. In the context of heart valves, the SI connects the sectors of meshes containing the leaflets, enabling a more effective mesh moving. In that context, the ST-SI-TC method enables high-resolution representation even when the contact is between leaflets that are covered by meshes with SI. It also enables dealing with contact location Change or contact and sliding on the SI. With IGA, in addition to having a more accurate representation of the surfaces and increased accuracy in the flow solution, the element density in the narrow spaces near the contact areas is kept at a reasonable level. Furthermore, because the flow representation in the contact area has a wider support in IGA, the flow computation method becomes more robust. The computation we present for an aortic-valve model shows the effectiveness of the ST-SI-TC-IGA method.
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heart valve flow computation with the integrated space time vms slip interface Topology Change and isogeometric discretization methods
Computers & Fluids, 2017Co-Authors: Kenji Takizawa, Tayfun E Tezduyar, Takuya Terahara, Takafumi SasakiAbstract:Abstract Heart valve flow computation requires accurate representation of boundary layers near moving solid surfaces, including the valve leaflet surfaces, even when the leaflets come into contact. It also requires dealing with a high level of geometric complexity. We address these computational challenges with a Space–Time (ST) method developed by integrating three special ST methods in the framework of the ST Variational Multiscale (ST-VMS) method. The special methods are the ST Slip Interface (ST-SI) and ST Topology Change (ST-TC) methods and ST Isogeometric Analysis (ST-IGA). The computations are for a realistic aortic-valve model with prescribed valve leaflet motion and actual contact between the leaflets. The ST-VMS method functions as a moving-mesh method, which maintains high-resolution boundary layer representation near the solid surfaces, including leaflet surfaces. The ST-TC method was introduced for moving-mesh computation of flow problems with TC, such as contact between the leaflets of a heart valve. It deals with the contact while maintaining high-resolution representation near the leaflet surfaces. The ST-SI method was originally introduced to have high-resolution representation of the boundary layers near spinning solid surfaces. The mesh covering a spinning solid surface spins with it, and the SI between the spinning mesh and the rest of the mesh accurately connects the two sides. In the context of heart valves, the SI connects the sectors of meshes containing the leaflets, enabling a more effective mesh moving. In that context, integration of the ST-SI and ST-TC methods enables high-resolution representation even when the contact is between leaflets that are covered by meshes with SI. It also enables dealing with contact location Change or contact and sliding on the SI. By integrating the ST-IGA with the ST-SI and ST-TC methods, in addition to having a more accurate representation of the surfaces and increased accuracy in the flow solution, the element density in the narrow spaces near the contact areas is kept at a reasonable level. Furthermore, because the flow representation in the contact area has a wider support in IGA, the flow computation method becomes more robust. The computations we present for an aortic-valve model with two different modes of prescribed leaflet motion show the effectiveness of the ST-SI-TC-IGA method.
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space time interface tracking with Topology Change st tc
Computational Mechanics, 2014Co-Authors: Kenji Takizawa, Tayfun E Tezduyar, Austin Buscher, Shohei AsadaAbstract:To address the computational challenges associated with contact between moving interfaces, such as those in cardiovascular fluid–structure interaction (FSI), parachute FSI, and flapping-wing aerodynamics, we introduce a space–time (ST) interface-tracking method that can deal with Topology Change (TC). In cardiovascular FSI, our primary target is heart valves. The method is a new version of the deforming-spatial-domain/stabilized space–time (DSD/SST) method, and we call it ST-TC. It includes a master–slave system that maintains the connectivity of the “parent” mesh when there is contact between the moving interfaces. It is an efficient, practical alternative to using unstructured ST meshes, but without giving up on the accurate representation of the interface or consistent representation of the interface motion. We explain the method with conceptual examples and present 2D test computations with models representative of the classes of problems we are targeting.
Xiaozhe Wang - One of the best experts on this subject based on the ideXlab platform.
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online measurement based estimation of dynamic system state matrix in ambient conditions
IEEE Transactions on Smart Grid, 2020Co-Authors: Hao Sheng, Xiaozhe WangAbstract:In this paper, a purely measurement-based method is proposed to estimate the dynamic system state matrix by applying the regression theorem of the multivariate Ornstein-Uhlenbeck process. The proposed method employs a recursive algorithm to minimize the required computational effort, making it applicable to the real-time environment. One main advantage of the proposed method is model independence, i.e., it is independent of the network model and the dynamic model of generators. Among various applications of the estimated matrix, detecting and locating unexpected network Topology Change is illustrated in details. Simulation studies have shown that the proposed measurement-based method can provide an accurate and efficient estimation of the dynamic system state matrix under the occurrence of unexpected Topology Change. Besides, various implementation conditions are tested to show that the proposed method can provide accurate approximation despite measurement noise, missing phasor measurement units (PMUs), and the implementation of higher-order generator models with control devices.
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online measurement based estimation of dynamic system state matrix in ambient conditions
arXiv: Signal Processing, 2019Co-Authors: Hao Sheng, Xiaozhe WangAbstract:In this paper, a purely measurement-based method is proposed to estimate the dynamic system state matrix by applying the regression theorem of the multivariate Ornstein-Uhlenbeck process. The proposed method employs a recursive algorithm to minimize the required computational effort, making it applicable to the real-time environment. One main advantage of the proposed method is model independence, i.e., it is independent of the network model and the dynamic model of generators. Among various applications of the estimated matrix, detecting and locating unexpected network Topology Change is illustrated in details. Simulation studies have shown that the proposed measurement-based method can provide an accurate and efficient estimation of the dynamic system state matrix under the occurrence of unexpected Topology Change. Besides, various implementation conditions are tested to show that the proposed method can provide accurate approximation despite measurement noise, missing PMUs, and the implementation of higher-order generator models with control devices.
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pmu based estimation of dynamic state jacobian matrix
International Symposium on Circuits and Systems, 2017Co-Authors: Xiaozhe Wang, Konstantin TuritsynAbstract:In this paper, a hybrid measurement and model-based method is proposed which can estimate the dynamic state Jacobian matrix in near real-time. The proposed method is computationally efficient and robust to the variation of network Topology. A numerical example is given to show that the proposed method is able to provide good estimation for the dynamic state Jacobian matrix and is superior to the model-based method under undetectable network Topology Change. The proposed method may also help identify big discrepancy in the assumed network model.
Francisco S N Lobo - One of the best experts on this subject based on the ideXlab platform.
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Gravity's Rainbow induces Topology Change
The European Physical Journal C, 2014Co-Authors: Remo Garattini, Francisco S N LoboAbstract:In this work, we explore the possibility that quantum fluctuations induce a Topology Change, in the context of Gravity's Rainbow. A semi-classical approach is adopted, where the graviton one-loop contribution to a classical energy in a background spacetime is computed through a variational approach with Gaussian trial wave functionals. The energy density of the graviton one-loop contribution, or equivalently the background spacetime, is then let to evolve, and consequently the classical energy is determined. More specifically, the background metric is fixed to be Minkowskian in the equation governing the quantum fluctuations, which behaves essentially as a backreaction equation, and the quantum fluctuations are let to evolve; the classical energy, which depends on the evolved metric functions, is then evaluated. Analysing this procedure, a natural ultraviolet (UV) cutoff is obtained, which forbids the presence of an interior spacetime region, and may result in a multipy-connected spacetime. Thus, in the context of Gravity's Rainbow, this process may be interpreted as a Change in Topology, and in principle results in the presence of a Planckian wormhole.
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Gravity’s Rainbow induces Topology Change
The European Physical Journal C, 2014Co-Authors: Remo Garattini, Francisco S N LoboAbstract:In this work, we explore the possibility that quantum fluctuations induce a Topology Change, in the context of Gravity’s Rainbow. A semiclassical approach is adopted, where the graviton one-loop contribution to a classical energy in a background spacetime is computed through a variational approach with Gaussian trial wave functionals. The energy density of the graviton one-loop contribution, or equivalently the background spacetime, is then let to evolve, and consequently the classical energy is determined. More specifically, the background metric is fixed to be Minkowskian in the equation governing the quantum fluctuations, which behaves essentially as a backreaction equation, and the quantum fluctuations are let to evolve; the classical energy, which depends on the evolved metric functions, is then evaluated. Analyzing this procedure, a natural ultraviolet cutoff is obtained, which forbids the presence of an interior spacetime region, and this may result in a multiply connected spacetime. Thus, in the context of Gravity’s Rainbow, this process may be interpreted as a Change in Topology, and in principle it results in the presence of a planckian wormhole.
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planck scale physics and Topology Change through an exactly solvable model
Physics Letters B, 2014Co-Authors: Francisco S N Lobo, Jesus Martinezasencio, Gonzalo J Olmo, D RubieragarciaAbstract:F.S.N.L. acknowledges financial support of the Fundacao para a Ciencia e Tecnologia through an Investigador FCT Research contract, with reference IF/00859/2012, funded by FCT/MCTES (Portugal), and grants CERN/FP/123615/2011 and CERN/FP/123618/2011. G.J.O. is supported by the Spanish grant FIS2011-29813-C02-02, the Consolider Program CPANPHY-1205388, and the JAE-doc program of the Spanish Research Council (CSIC). D.R.G. is supported by CNPq (Brazilian agency) through project No. 561069/2010-7 and thanks the hospitality and partial support of the Theoretical Physics Department of the University of Valencia. This work has also been supported by CNPq through project No. 301137/2014-5.
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phantom stars and Topology Change
Physical Review D, 2008Co-Authors: Andrew Debenedictis, Rerno Garattini, Francisco S N LoboAbstract:In this work, we consider time-dependent dark-energy star models, with an evolving parameter {omega} crossing the phantom divide {omega}=-1. Once in the phantom regime, the null energy condition is violated, which physically implies that the negative radial pressure exceeds the energy density. Therefore, an enormous negative pressure in the center may, in principle, imply a Topology Change, consequently opening up a tunnel and converting the dark-energy star into a wormhole. The criteria for this Topology Change are discussed and, in particular, we consider a Casimir energy approach involving quasilocal energy difference calculations that may reflect or measure the occurrence of a Topology Change. We denote these exotic geometries consisting of dark-energy stars (in the phantom regime) and phantom wormholes as phantom stars. The final product of this topological Change, namely, phantom wormholes, have far-reaching physical and cosmological implications, as in addition to being used for interstellar shortcuts, an absurdly advanced civilization may manipulate these geometries to induce closed timelike curves, consequently violating causality.
Mannque Rho - One of the best experts on this subject based on the ideXlab platform.
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towards the hadron quark continuity via a Topology Change in compact stars
Progress in Particle and Nuclear Physics, 2020Co-Authors: Mannque RhoAbstract:Abstract We construct a generalized effective field theory approach to dense compact-star matter that exploits the Cheshire Cat Principle for hadron–quark continuity at high density, adhering only to hadronic degrees of freedom, hidden Topology and hidden symmetries of QCD. No Landau–Ginzburg–Wilsonian-type phase transition is involved in the range of densities involved. The microscopic degrees of freedom of QCD, i.e., quarks and gluons, possibly intervening at high baryonic density are traded in for fractionalized topological objects. Essential in the description are symmetries invisible in QCD in the matter-free vacuum: Scale symmetry, flavor local symmetry and parity-doubling. The partial emergence of scale symmetry is signaled by a dilatonic scalar in a “pseudo-conformal” structure. Flavor gauge symmetry manifests with the ρ meson mass going toward a Wilsonian RG fixed point identified with the “vector manifestation fixed point (VMFP)” at which the flavor gauge boson mass goes to zero. Parity doubling is to take place as the quasi-nucleon mass converges to the chiral invariant m 0 . The theory with a few controllable parameters accounts satisfactorily for all known properties of normal nuclear matter and makes certain predictions that are drastically different from what is available in the literature. In particular, it provides a topological mechanism, argued to be robust, for the cross-over from soft-to-hard equation of state that predicts the star properties in overall agreement with the presently available data, including the maximum star mass M m a x ∼ 2 . 3 M ⊙ and the recent LIGO/Virgo gravity-wave data. What is most glaringly different from all other approaches known, however, is the prediction for the rapid convergence to a sound velocity of star v s 2 ≈ 1 ∕ 3 (in unit c = 1 ) at a density n ≳ 3 n 0 , far from the asymptotic density ≳ 50 n 0 expected in perturbative QCD. We interpret this to signal the onset of albeit approximate conformal symmetry in dense compact-star matter. We argue that models that properly implement quark degrees of freedom at high densities in the sense of the hadron–quark continuity should, with the parameters fine-tuned, arrive at a qualitatively similar pseudo-conformal structure. The model developed in this paper, if validated by observations, could bring out a new paradigm in nuclear/hadron physics, exploiting ideas ubiquitous in various areas of physics, condensed matter physics, nuclear and particle physics and astrophysics.
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towards the hadron quark continuity via a Topology Change in compact stars
arXiv: Nuclear Theory, 2019Co-Authors: Mannque RhoAbstract:We construct a generalized EFT approach to dense compact-star matter that exploits the CCP for hadron-quark continuity at high density, hidden Topology and hidden symmetries of QCD. No Landau-Ginzburg-Wilsonian-type phase transition is involved. The microscopic DoF of QCD possibly intervening at high baryonic density are traded in for fractionalized topological objects. Essential in the description are symmetries invisible in QCD in the matter-free vacuum: Scale symmetry, flavor local symmetry and parity-doubling. The partial emergence of scale symmetry is signaled by a dilatonic scalar in a "pseudo-conformal" structure. Flavor gauge symmetry manifests with the $\rho$ meson mass going toward a Wilsonian RGFP identified with the VMFP at which the gauge boson mass goes to zero. Parity doubling is to take place as the quasi-nucleon mass converges to the chiral invariant $m_0$. The theory accounts satisfactorily for all known properties of normal nuclear matter and makes certain predictions that are drastically different from what's available in the literature. In particular, it provides a topological mechanism, argued to be robust, for the cross-over from soft-to-hard EoS that predicts the star properties in overall agreement with the presently available data, including the maximum star mass $M_{max}\sim 2.3 M_\odot$ and the recent LIGO/Virgo GW data. What is most glaringly different from all other approaches known, however, is the prediction for the rapid convergence to a sound velocity of star $v_s^2\approx 1/3$ at a density $n\gsim 3 n_0$, far from the asymptotic density $\gsim 50n_0$ expected in pQCD. We interpret this to signal the onset of albeit approximate conformal symmetry in dense compact-star matter. The model developed here could bring out a new paradigm in nuclear/hadron physics, exploiting ideas in condensed matter physics, nuclear and particle physics and astrophysics.
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pseudoconformal equation of state in compact star matter from Topology Change and hidden symmetries of qcd
Science China-physics Mechanics & Astronomy, 2019Co-Authors: H K Lee, Wongi Paeng, Mannque RhoAbstract:We construct a new effective field theory approach to the equation of state (EoS), dubbed pseudo-confomal model “PCM", for nuclear and compact star matter entirely in terms of effective hadron degrees of freedom. The possible transition at $n\!\sim$(2-4)$n_0$ (where $n_0$ is the normal nuclear matter density) from hadron degrees of freedom to strongly-coupled quark degrees of freedom, giving rise to a soft-to-hard Changeover in the EoS that can accommodate the massive stars observed, is effectuated by the Topology Change at $n_{1/2}\mathrel{\rlap{\lower3pt\hbox{\hskip1pt$∼$}}\raise1pt\hbox{$>$}}2n_0$ from skyrmions to half-skyrmions without involving local order-parameter fields. The mechanism exploits possible emergence of hidden scale and local symmetries of QCD at high density, leading to a precocious “pseudo-conformal" sound velocity $v_{\rm~s}^2=1/3$ (in unit of $c=1$) for $n\mathrel{\rlap{\lower3pt\hbox{\hskip1pt$∼$}}\raise1pt\hbox{$>$}}3n_0$. The resulting prediction signals a drastic departure from standard nuclear many-body theory in the density regime involved in the massive stars. We suggest that the tidal deformability implemented in gravitational waves coming from coalescing neutron stars in LIGO/Virgo-type observations could pin down the location of the Topology Change density $n_{1/2}$.
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Scale-Invariant Hidden Local Symmetry, Topology Change and Dense Baryonic Matter II
2017Co-Authors: Wongi Paeng, H K Lee, Thomas T. S. Kuo, Mannque RhoAbstract:Exploiting certain robust topological inputs from the skyrmion description of compressed baryonic matter with a scale-chiral symmetric Lagrangian, we predict the equation of state that is consistent with the properties of nuclear matter at the equilibrium density, supports the maximum mass of massive compact star $\sim 2 M_\odot$ and surprisingly gives the sound velocity close to the "conformal velocity" $1/\sqrt{3}$ at densities $\gtrsim 3 n_0$. At the core of this result is the observation that parity-doubling occurs in the nucleon structure as density goes above $\sim 2n_0$ with a chiral-singlet mass $m_0 \sim (0.6-0.9) m_N$, hinting at a possible up-to-date unsuspected source of proton mass and an emergence at high density of scale symmetry and flavor local symmetry, both hidden in the QCD vacuum.
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Topology Change and tensor forces for the eos of dense baryonic matter
European Physical Journal A, 2014Co-Authors: H K Lee, Mannque RhoAbstract:When skyrmions representing nucleons are put on crystal lattice and compressed to simulate high density, there is a transition above the normal nuclear matter density (n0) from a matter consisting of skyrmions with integer baryon charge to a state of half-skyrmions with half-integer baryon charge. We exploit this observation in an effective field theory framework to access dense baryonic system. We find that the Topology Change involved in the transition implies Changeover from a Fermi liquid structure to a non-Fermi liquid with the chiral condensate in the “melted-off” nucleon. The ∼ 80% of the nucleon mass that remains “unmelted”, invariant under chiral transformation, points to the possible origin of the (bulk of) proton mass that is not encoded in the standard mechanism of spontaneously broken chiral symmetry. The Topology Change engenders a drastic modification of the nuclear tensor forces, thereby non-trivially affecting the EoS, in particular, the symmetry energy, for compact star matter. It brings in stiffening of the EoS needed to accommodate a neutron star of ∼ 2 solar mass. The strong effect on the EoS in general and in the tensor force structure in particular will also have impact on processes that could be measured at RIB-type accelerators.
Kenji Takizawa - One of the best experts on this subject based on the ideXlab platform.
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ventricle valve aorta flow analysis with the space time isogeometric discretization and Topology Change
Computational Mechanics, 2020Co-Authors: Takuya Terahara, Kenji Takizawa, Tayfun E Tezduyar, Atsushi Tsushima, Kensuke ShiozakiAbstract:We address the computational challenges of and presents results from ventricle-valve-aorta flow analysis. Including the left ventricle (LV) in the model makes the flow into the valve, and consequently the flow into the aorta, anatomically more realistic. The challenges include accurate representation of the boundary layers near moving solid surfaces even when the valve leaflets come into contact, computation with high geometric complexity, anatomically realistic representation of the LV motion, and flow stability at the inflow boundary, which has a traction condition. The challenges are mainly addressed with a Space–Time (ST) method that integrates three special ST methods around the core, ST Variational Multiscale (ST-VMS) method. The three special methods are the ST Slip Interface (ST-SI) and ST Topology Change (ST-TC) methods and ST Isogeometric Analysis (ST-IGA). The ST-discretization feature of the integrated method, ST-SI-TC-IGA, provides higher-order accuracy compared to standard discretization methods. The VMS feature addresses the computational challenges associated with the multiscale nature of the unsteady flow in the LV, valve and aorta. The moving-mesh feature of the ST framework enables high-resolution computation near the leaflets. The ST-TC enables moving-mesh computation even with the TC created by the contact between the leaflets, dealing with the contact while maintaining high-resolution representation near the leaflets. The ST-IGA provides smoother representation of the LV, valve and aorta surfaces and increased accuracy in the flow solution. The ST-SI connects the separately generated LV, valve and aorta NURBS meshes, enabling easier mesh generation, connects the mesh zones containing the leaflets, enabling a more effective mesh moving, helps the ST-TC deal with leaflet–leaflet contact location Change and contact sliding, and helps the ST-TC and ST-IGA keep the element density in the narrow spaces near the contact areas at a reasonable level. The ST-SI-TC-IGA is supplemented with two other special methods in this article. A structural mechanics computation method generates the LV motion from the CT scans of the LV and anatomically realistic values for the LV volume ratio. The Constrained-Flow-Profile (CFP) Traction provides flow stability at the inflow boundary. Test computation with the CFP Traction shows its effectiveness as an inflow stabilization method, and computation with the LV-valve-aorta model shows the effectiveness of the ST-SI-TC-IGA and the two supplemental methods.
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heart valve isogeometric sequentially coupled fsi analysis with the space time Topology Change method
Computational Mechanics, 2020Co-Authors: Takuya Terahara, Kenji Takizawa, Tayfun E Tezduyar, Yuri Bazilevs, Mingchen HsuAbstract:Heart valve fluid–structure interaction (FSI) analysis is one of the computationally challenging cases in cardiovascular fluid mechanics. The challenges include unsteady flow through a complex geometry, solid surfaces with large motion, and contact between the valve leaflets. We introduce here an isogeometric sequentially-coupled FSI (SCFSI) method that can address the challenges with an outcome of high-fidelity flow solutions. The SCFSI analysis enables dealing with the fluid and structure parts individually at different steps of the solutions sequence, and also enables using different methods or different mesh resolution levels at different steps. In the isogeometric SCFSI analysis here, the first step is a previously computed (fully) coupled Immersogeometric Analysis FSI of the heart valve with a reasonable flow solution. With the valve leaflet and arterial surface motion coming from that, we perform a new, higher-fidelity fluid mechanics computation with the space–time Topology Change method and isogeometric discretization. Both the immersogeometric and space–time methods are variational multiscale methods. The computation presented for a bioprosthetic heart valve demonstrates the power of the method introduced.
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heart valve flow computation with the space time slip interface Topology Change st si tc method and isogeometric analysis iga
2018Co-Authors: Kenji Takizawa, Tayfun E Tezduyar, Takuya Terahara, Takafumi SasakiAbstract:We present a heart valve flow computation with the Space–Time Slip Interface Topology Change (ST-SI-TC) method and Isogeometric Analysis (IGA). The computation is for a realistic heart valve model with actual contact between the valve leaflets. The ST-SI-TC method integrates the ST-SI and ST-TC methods in the framework of the ST Variational Multiscale (ST-VMS) method. The ST-VMS method functions as a moving-mesh method, which maintains high-resolution boundary layer representation near the solid surfaces. The ST-TC method was introduced for moving-mesh computation of flow problems with TC, such as contact between the leaflets of a heart valve. It deals with the contact while maintaining high-resolution representation near the leaflet surfaces. The ST-SI method was originally introduced to addresses the challenge involved in high-resolution representation of the boundary layers near spinning solid surfaces. The mesh covering a spinning solid surface spins with it, and the SI between that mesh and the rest of the mesh accurately connects the two sides. This maintains the high-resolution representation near solid surfaces. In the context of heart valves, the SI connects the sectors of meshes containing the leaflets, enabling a more effective mesh moving. In that context, the ST-SI-TC method enables high-resolution representation even when the contact is between leaflets that are covered by meshes with SI. It also enables dealing with contact location Change or contact and sliding on the SI. With IGA, in addition to having a more accurate representation of the surfaces and increased accuracy in the flow solution, the element density in the narrow spaces near the contact areas is kept at a reasonable level. Furthermore, because the flow representation in the contact area has a wider support in IGA, the flow computation method becomes more robust. The computation we present for an aortic-valve model shows the effectiveness of the ST-SI-TC-IGA method.
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heart valve flow computation with the integrated space time vms slip interface Topology Change and isogeometric discretization methods
Computers & Fluids, 2017Co-Authors: Kenji Takizawa, Tayfun E Tezduyar, Takuya Terahara, Takafumi SasakiAbstract:Abstract Heart valve flow computation requires accurate representation of boundary layers near moving solid surfaces, including the valve leaflet surfaces, even when the leaflets come into contact. It also requires dealing with a high level of geometric complexity. We address these computational challenges with a Space–Time (ST) method developed by integrating three special ST methods in the framework of the ST Variational Multiscale (ST-VMS) method. The special methods are the ST Slip Interface (ST-SI) and ST Topology Change (ST-TC) methods and ST Isogeometric Analysis (ST-IGA). The computations are for a realistic aortic-valve model with prescribed valve leaflet motion and actual contact between the leaflets. The ST-VMS method functions as a moving-mesh method, which maintains high-resolution boundary layer representation near the solid surfaces, including leaflet surfaces. The ST-TC method was introduced for moving-mesh computation of flow problems with TC, such as contact between the leaflets of a heart valve. It deals with the contact while maintaining high-resolution representation near the leaflet surfaces. The ST-SI method was originally introduced to have high-resolution representation of the boundary layers near spinning solid surfaces. The mesh covering a spinning solid surface spins with it, and the SI between the spinning mesh and the rest of the mesh accurately connects the two sides. In the context of heart valves, the SI connects the sectors of meshes containing the leaflets, enabling a more effective mesh moving. In that context, integration of the ST-SI and ST-TC methods enables high-resolution representation even when the contact is between leaflets that are covered by meshes with SI. It also enables dealing with contact location Change or contact and sliding on the SI. By integrating the ST-IGA with the ST-SI and ST-TC methods, in addition to having a more accurate representation of the surfaces and increased accuracy in the flow solution, the element density in the narrow spaces near the contact areas is kept at a reasonable level. Furthermore, because the flow representation in the contact area has a wider support in IGA, the flow computation method becomes more robust. The computations we present for an aortic-valve model with two different modes of prescribed leaflet motion show the effectiveness of the ST-SI-TC-IGA method.
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space time interface tracking with Topology Change st tc
Computational Mechanics, 2014Co-Authors: Kenji Takizawa, Tayfun E Tezduyar, Austin Buscher, Shohei AsadaAbstract:To address the computational challenges associated with contact between moving interfaces, such as those in cardiovascular fluid–structure interaction (FSI), parachute FSI, and flapping-wing aerodynamics, we introduce a space–time (ST) interface-tracking method that can deal with Topology Change (TC). In cardiovascular FSI, our primary target is heart valves. The method is a new version of the deforming-spatial-domain/stabilized space–time (DSD/SST) method, and we call it ST-TC. It includes a master–slave system that maintains the connectivity of the “parent” mesh when there is contact between the moving interfaces. It is an efficient, practical alternative to using unstructured ST meshes, but without giving up on the accurate representation of the interface or consistent representation of the interface motion. We explain the method with conceptual examples and present 2D test computations with models representative of the classes of problems we are targeting.