scholarly journals A Computational Method for Analyzing the Biomechanics of Arterial Bruits

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Chi Zhu ◽  
Jung-Hee Seo ◽  
Hani Bakhshaee ◽  
Rajat Mittal
Keyword(s):  
Shear Wave ◽  
Sound Propagation ◽  
Acoustic Method ◽  
Longitudinal Component ◽  
Transverse Component ◽  
Computational Method ◽  
Surrounding Tissue ◽  
Immersed Boundary ◽  
Flow Solver ◽  
Epidermal Surface

A computational framework consisting of a one-way coupled hemodynamic–acoustic method and a wave-decomposition based postprocessing approach is developed to investigate the biomechanics of arterial bruits. This framework is then applied for studying the effect of the shear wave on the generation and propagation of bruits from a modeled stenosed artery. The blood flow in the artery is solved by an immersed boundary method (IBM) based incompressible flow solver. The sound generation and propagation in the blood volume are modeled by the linearized perturbed compressible equations, while the sound propagation through the surrounding tissue is modeled by the linear elastic wave equation. A decomposition method is employed to separate the acoustic signal into a compression/longitudinal component (curl free) and a shear/transverse component (divergence free), and the sound signals from cases with and without the shear modulus are monitored on the epidermal surface and are analyzed to reveal the influence of the shear wave. The results show that the compression wave dominates the detected sound signal in the immediate vicinity of the stenosis, whereas the shear wave has more influence on surface signals further downstream of the stenosis. The implications of these results on cardiac auscultation are discussed.

scholarly journals Longitudinal Component Properties of Circularly Polarized Terahertz Vortex Beams

2021 ◽  
Vol 9 ◽  
Author(s):  
Miao Wang ◽  
Xinke Wang ◽  
Peng Han ◽  
Wenfeng Sun ◽  
Shengfei Feng ◽  
...  
Keyword(s):  
Spot Size ◽  
Longitudinal Component ◽  
Transverse Component ◽  
Quarter Wave Plate ◽  
Phase Plate ◽  
Vortex Beam ◽  
Circularly Polarized ◽  
Left Hand ◽  
Quarter Wave ◽  
Focusing Properties

A circularly polarized vortex beam possesses similar focusing properties as a radially polarized beam. This type of beam is highly valuable for developing optical manufacturing technology, microscopy, and particle manipulation. In this work, a left-hand circularly polarized terahertz (THz) vortex beam (CPTVB) is generated by utilizing a THz quarter wave plate and a spiral phase plate. Focusing properties of its longitudinal component Ez are detailedly discussed on the simulation and experiment. With reducing the F-number of the THz beam and comparing with a transverse component Ex of a general circularly polarized THz beam, the simulation results show that the focal spot size and intensity of its Ez component can reach 87 and 50% of Ex under a same focusing condition. In addition, the experimental results still demonstrate that the left-hand CPTVB can always maintain fine Ez focusing properties in a broad bandwidth, which manifest the feasibility of this class of THz beams.

An Aid to Learn Computational Fluid Dynamics: Immersed-Boundary-Based Simulation of 2D Flow

Volume 1 ◽  
2004 ◽  
Author(s):  
Sungsu Lee ◽  
Kyung-Soo Yang ◽  
Jong-Yeon Hwang
Keyword(s):  
Complex Geometry ◽  
Mass Conservation ◽  
Computational Method ◽  
Staggered Grid ◽  
Navier Stokes ◽  
Immersed Boundary ◽  
Step Method ◽  
Fractional Step Method ◽  
Navier Stokes Equation ◽  
Finite Volume Approach

Development of geometry-independent computational method and educational codes for simulation of 2D flows around objects of complex geometry is presented. Referred as immersed boundary method, it introduces virtual forcing to governing equations to represent the effect of physical boundaries. The present method is based on a finite-volume approach on a staggered grid with a fractional-step method to solve Navier-Stokes equation and continuity equation. Both momentum and mass forcings are introduced on and inside the object to satisfy no-slip condition and mass conservation. Since Cartesian grid lines in general do not coincide with the immersed boundaries, several interpolation schemes are employed. Several examples are simulated using the method presented in this study and the results agree well with other results. Both user-friendly preprocessor with GUI and FORTRAN-based solver are open to the public for educational purposes.

Shear-Wave Elastographic Values of Benign and Malignant Breast Lesions and Surrounding Tissue

2011 ◽  
Vol 37 (8) ◽  
pp. S45-S46 ◽  
Author(s):  
G. Ivanac ◽  
A. Hrkac Pustahija ◽  
R. Huzjan Korunic ◽  
B. Brkljacic
Keyword(s):  
Shear Wave ◽  
Surrounding Tissue ◽  
Breast Lesions ◽  
Malignant Breast

Effect of Uvula Length on Airflow and Pressure Oscillation in a Human Pharynx Model

2019 ◽  
Author(s):  
Xuanming Zhao ◽  
Junshi Wang ◽  
Pan Han ◽  
Jinxiang Xi ◽  
Haibo Dong
Keyword(s):  
Aerodynamic Force ◽  
Pressure Oscillation ◽  
Magnetic Resonance Images ◽  
Immersed Boundary ◽  
Pressure Oscillations ◽  
Flow Solver ◽  
Pharyngeal Airway ◽  
Aerodynamic Pressure ◽  
Fast Fourier Transform Analysis ◽  
Original Length

Abstract Unsteady uvula motions and the resultant pressure oscillations within the pharyngeal airway are critical for the pathology of snoring and sleeping apnea. In this paper, an immersed-boundary-method based direct numerical simulation flow solver was adopted to simulate the unsteady flows in an anatomically accurate pharynx model reconstructed from human magnetic resonance images (MRI) with prescribed uvula oscillation and airway obstruction. In order to study the influence of uvula length on the aerodynamics of pharyngeal airflow, simulations were conducted using various uvula models with scaled uvula lengths at 25%, 50%, 75%, and 100% of the original length, respectively. Analyses of vortex dynamics, pressure oscillations, and the aerodynamic force of uvula were conducted. It was found the length of uvula had significant impacts on vortex development as well as aerodynamic pressure/force. Shorter uvula induced weaker pressure oscillations and fewer vortices in the airway. Further fast Fourier transform analysis of pressures from different pressure probes showed higher-order harmonic waves other than the base frequency of uvula motion. This study is expected to bring understanding of snoring and sleep apnea and provide guidance for surgery.

scholarly journals The role of tissue elasticity in the differential diagnosis of benign and malignant breast lesions using shear wave elastography

BMC Cancer ◽  
2020 ◽  
Vol 20 (1) ◽  
Author(s):  
Hui Yang ◽  
Yongyuan Xu ◽  
Yanan Zhao ◽  
Jing Yin ◽  
Zhiyi Chen ◽  
...  
Keyword(s):  
Logistic Regression ◽  
Regression Analysis ◽  
Shear Wave ◽  
Logistic Regression Analysis ◽  
Diagnostic Performance ◽  
Shear Wave Elastography ◽  
Surrounding Tissue ◽  
Breast Lesions ◽  
Tissue Elasticity ◽  
Malignant Breast

Abstract Background Elastography is a promising way to evaluate tissue differences regarding stiffness, and the stiffness of the malignant breast lesions increased at the lesion margin. However, there is a lack of data on the value of the shear wave elastography (SWE) parameters of the surrounding tissue (shell) of different diameter on the diagnosis of benign and malignant breast lesions. Therefore, the purpose of our study was to evaluate the diagnostic performance of shell elasticity in the diagnosis of benign and malignant breast lesions using SWE. Methods Between September 2016 and June 2017, women with breast lesions underwent both conventional ultrasound (US) and SWE. Elastic values of the lesions peripheral tissue were determined according to the shell size, which was automatically drawn along the edge of the lesion using the following software guidelines: (1): 1 mm; (2): 2 mm; and (3): 3 mm. Quantitative elastographic features of the inner lesions and shell, including the elasticity mean (Emean), elasticity maximum (Emax), and elasticity minimum (Emin), were calculated using an online-available software. The receiver operating characteristic curves (ROCs) of the elastographic features was analyzed to assess the diagnostic performance, and the area under curve (AUC) of each elastographic feature was obtained. Logistic regression analysis was used to predict significant factors of malignancy, permitting the design of predictive models. Results This prospective study included 63 breast lesions of 63 women. Of the 63 lesions, 33 were malignant and 30 were benign. The diagnostic performance of Emax-3shell was the highest (AUC = 0.76) with a sensitivity of 60.6% and a specificity of 83.3%. According to stepwise logistic regression analysis, the Emax-3shell and the Emin-3shell were significant predictors of malignancy (p < 0.05). The AUC of the predictive equation was 0.86. Conclusions SWE features, particularly the combination of Emax-3shell and Emin-3shell can improve the diagnosis of breast lesions.

A sparsity-based adaptive filtering approach to Shear Wave Splitting

2021 ◽  
Author(s):  
Hamzeh Mohammadigheymasi ◽  
Mohammad Reza Ebrahimi ◽  
Graça Silveira ◽  
David schlaphorst
Keyword(s):  
Frequency Domain ◽  
Shear Wave ◽  
Adaptive Filtering ◽  
Elastic Anisotropy ◽  
Real Data ◽  
Shear Wave Splitting ◽  
Transverse Component ◽  
Time Frequency ◽  
Regularized Inversion ◽  
Wave Splitting

&lt;p&gt;Shear wave splitting analysis is a frequently used tool to study elastic anisotropy from the lower mantle to the crust. Several methods have been developed to evaluate the splitting parameters, &amp;#934; (fast axis) and &amp;#948;t (delay time), including the correlation of wave components, minimization of covariance matrix eigenvalues, and minimizing energy on the transverse component. Despite massive progress in introducing sophisticated methods, still fundamental problems, related mainly to noisy data, interfering phases, length of the analyzed waveform, and stability and reliability of results, remain. This study presents a sparsity-based adaptive filtering method to magnify the SKS waveforms and suppress the unwanted noise and interfering phases. The study is an extension of Jurkevics (1988), computing the semi-minor and semi-minor axis of the polarized motion in the time-frequency domain using a regularized inversion-based approach imposing a sparsity constraint. Afterward, the elliptical particle motion caused by the split shear waves and correspond to high semi-minor amplitude is derived in the time-frequency domain. The information is used to design an adaptive filter in the time domain to amplify the SKS phase and suppress the noise and other phases having non-elliptical polarization. The regularized inversion-based approach enables obtaining a sparse time-frequency semi-minor map while handling noise problems in the time-frequency decomposition. Conducting synthetic simulations, we show that the proposed method increases the signal-to-noise ratio of the SKS phase in radial and transverse components, giving a better estimation of anisotropy parameters in the presence of noise and other interfering phases. Future work involves implementing the processing algorithm on real data recorded in S&amp;#227;o Tom&amp;#233; and Pr&amp;#305;&amp;#769;ncipe, Madeira, and Canary islands. This research contributes to the FCT-funded SHAZAM (Ref. PTDC/CTA-GEO/31475/2017) and SIGHT (Ref. PTDC/CTA-GEF/30264/2017) projects.&lt;/p&gt;

Hemodynamics in the Left Atrium and Its Effect on Ventricular Flow Patterns

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Vijay Vedula ◽  
Richard George ◽  
Laurent Younes ◽  
Rajat Mittal
Keyword(s):  
Left Atrium ◽  
Pulmonary Veins ◽  
Mitral Annulus ◽  
Flow Patterns ◽  
Immersed Boundary ◽  
Flow Solver ◽  
Tomographic Images ◽  
Computed Tomographic ◽  
Circulatory Flow ◽  
The Right

In the present study, we investigate the hemodynamics inside left atrium (LA) and understand its impact on the development of ventricular flow patterns. We construct the heart model using dynamic-computed tomographic images and perform simulations using an immersed boundary method based flow solver. We show that the atrial hemodynamics is characterized by a circulatory flow generated by the left pulmonary veins (LPVs) and a direct stream from the right pulmonary veins (RPVs). The complex interaction of the vortex rings formed from each of the PVs leads to vortex breakup and annihilation, thereby producing a regularized flow at the mitral annulus. A comparison of the ventricular flow velocities between the physiological and a simplified pipe-based atrium model shows that the overall differences are limited to about 10% of the peak mitral flow velocity. The implications of this finding on the functional morphology of the left heart as well the computational and experimental modeling of ventricular hemodynamics are discussed.

Dynamic pitching of an elastic rectangular wing in hovering motion

2012 ◽  
Vol 693 ◽  
pp. 473-499 ◽  
Author(s):  
Hu Dai ◽  
Haoxiang Luo ◽  
James F. Doyle
Keyword(s):  
Three Dimensional ◽  
Immersed Boundary ◽  
Mass Ratio ◽  
Flow Solver ◽  
Thin Walled Structures ◽  
Insect Wings ◽  
Passive Deformation ◽  
Comparable Magnitude ◽  
Wing Deformation

AbstractIn order to study the role of the passive deformation in the aerodynamics of insect wings, we computationally model the three-dimensional fluid–structure interaction of an elastic rectangular wing at a low aspect ratio during hovering flight. The code couples a viscous incompressible flow solver based on the immersed-boundary method and a nonlinear finite-element solver for thin-walled structures. During a flapping stroke, the wing surface is dominated by non-uniform chordwise deformations. The effects of the wing stiffness, mass ratio, phase angle of active pitching, and Reynolds number are investigated. The results show that both the phase and the rate of passive pitching due to the wing flexibility can significantly modify the aerodynamics of the wing. The dynamic pitching depends not only on the specified kinematics at the wing root and the stiffness of the wing, but also greatly on the mass ratio, which represents the relative importance of the wing inertia and aerodynamic forces in the wing deformation. We use the ratio between the flapping frequency, $\omega $, and natural frequency of the wing, ${\omega }_{n} $, as the non-dimensional stiffness. In general, when $\omega / {\omega }_{n} \leq 0. 3$, the deformation significantly enhances the lift and also improves the lift efficiency despite a disadvantageous camber. In particular, when the inertial pitching torque is assisted by an aerodynamic torque of comparable magnitude, the lift efficiency can be markedly improved.

Application of an Immersed Boundary Method to Flow in Cerebral Aneurysms and Porous Media

2010 ◽  
Author(s):  
Julia Mikhal ◽  
David J. Lopez Penha ◽  
Steffen Stolz ◽  
Bernard J. Geurts
Keyword(s):  
Poiseuille Flow ◽  
Stokes Equations ◽  
Spatial Arrangement ◽  
Computational Method ◽  
Implicit Time ◽  
Immersed Boundary ◽  
Time Stepping ◽  
Flow Through ◽  
Masking Function ◽  
Ib Method

We present the development and application of an immersed boundary (IB) method for the simulation of incompressible flow inside and around complex geometrical shapes and cavities. The IB method is based on a volume-penalization method that is applied throughout the domain, rendering the velocity in stationary solid parts negligibly small, while the flow in the open parts of the domain is governed by the Navier-Stokes equations. The flow solver is based on a skew-symmetric finite-volume discretization in combination with explicit time-stepping for the convective and viscous fluxes, and implicit time-stepping for the IB forcing term. The complex domain is characterized in terms of a so-called ‘masking function’ which equals unity in the solid parts and zero in the open parts of the domain. The focus is on the accuracy with which gradients of the solution close to solid walls can be approximated using the IB methodology. We investigate this for flow through a model of an aneurysm as may develop in the circle of Willis in a human brain, and to flow in a structured porous medium composed of a regular spatial arrangement of square rods. The shear stress acting on the vessel walls in case of flow through an aneurysm, and the permeability of the porous material, are analyzed. The computational method converges as a first order method for Poiseuille flow, with a considerable influence derived from the precise definition of the masking function near solid-fluid interfaces. We identify the best masking function strategy and show that for plane Poiseuille flow even second order convergence may be obtained. Qualitatively reliable results are obtained already at modest resolutions of 8–16 grid cells across a characteristic opening in the flow domain, e.g., the vessel diameter or the size of the gap between individual square rods.

Effects of Tail Geometries on the Performance and Wake Pattern in Flapping Propulsion

2016 ◽  
Author(s):  
Geng Liu ◽  
Haibo Dong
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Computational Study ◽  
Hydrodynamic Performance ◽  
Immersed Boundary ◽  
Caudal Fin ◽  
Flow Solver ◽  
Wide Range ◽  
Wake Patterns ◽  
Caudal Fin Shape

Swimming fishes exhibit remarkable diversities of the caudal fin geometries. In this work, a computational study is conducted to investigate the effects of the caudal fin shape on the hydrodynamic performance and wake patterns in flapping propulsion. We construct the propulsor models in different shapes by digitizing the real caudal fins of fish across a wide range of species spanning homocercal tails with low aspect ratio (square shape used by bluegill sunfish, rainbow trout, etc.) or high aspect ratio (lunate shape adopted by tuna, swordfish, etc.), and even heterocercal caudal fin adopted by sharks. Those fin models perform the same flapping motion in a uniform flow to mimic fish’s forward swimming. We then simulate the flow around the flapping fins by an in-house immersed-boundary-method based flow solver. According to the analysis of the hydrodynamic performance, we have found that the lunate shape model (high aspect-ratio) always generates a larger thrust compared to other models. The comparison of the propulsive efficiency shows that the large aspect ratio fins (tuna and shark) have a higher efficiency when the Strouhal number (St) is in the range of steady swimming (0.2<St<0.4), while the lower aspect ratio caudal fins (catfish, trout, etc.) are more efficient when St>0.4, in which the fish is accelerating or maneuvering. Finally, the 3D wake patterns of those propulsors are analyzed in detail.

Sign in / Sign up

Export Citation Format

Share Document