In three-dimensional (3D) blood flow simulations, lumped parameter models (0D) are often used to model the neglected parts of the downstream circulatory system. We consider two 3D-0D coupling approaches in which a fra...
详细信息
In three-dimensional (3D) blood flow simulations, lumped parameter models (0D) are often used to model the neglected parts of the downstream circulatory system. We consider two 3D-0D coupling approaches in which a fractional-step projection scheme is used in the fluid. Our analysis shows that explicit approaches might yield numerical instabilities, particularly in the case of realistic geometries with multiple outlets. We introduce and analyze an implicitly 3D-0D coupled formulation with enhanced stability properties and which requires a negligible additional computational cost. We also address the extension of these methods to fluid-structure interaction problems. The theoretical stability results are confirmed by meaningful numerical experiments in patient specific geometries coming from medical imaging.
The linear and geometrically nonlinear (large amplitude) dynamical response of a thin plate in contact with water on one or both sides has been experimentally studied, considering different filling levels. The free li...
详细信息
The linear and geometrically nonlinear (large amplitude) dynamical response of a thin plate in contact with water on one or both sides has been experimentally studied, considering different filling levels. The free liquid surface is free to slosh and the water is delimited by practically rigid walls, except for the thin plate. An experimental method for monitoring and measuring the free surface waves of the fluid has been also used in order to analyze the behavior of the liquid free surface during the nonlinear vibration of the plate forced by harmonic excitation. The plate deflection due to hydrostatic pressure plays a significant role in changing the plate nonlinearity, but tests with liquid on both sides eliminating this effect have been also presented. For excitation in the frequency neighborhood of the fundamental mode of the plate, the oscillation of the free surface of the liquid is characterized by a very large 1/2-subharmonic component. (C) 2013 Elsevier Ltd. All rights reserved.
In this paper, the performance of the incompressible SPH (ISPH) method and an improved weakly compressible SPH (IWCSPH) method for free surface incompressible flows are compared and analyzed. In both methods, the Navi...
详细信息
In this paper, the performance of the incompressible SPH (ISPH) method and an improved weakly compressible SPH (IWCSPH) method for free surface incompressible flows are compared and analyzed. In both methods, the Navier-Stokes equations are solved, and no artificial viscosity is used. The ISPH algorithm in this paper is based on the classical SPH projection method with common treatments on solid boundaries and free surfaces. The IWCSPH model includes some advanced corrective algorithms in density approximation and solid boundary treatment (SBT). In density approximation, the moving least squares (MLS) approach is applied to re-initialize density every several steps to obtain smoother and more stable pressure fields. An improved coupled dynamic SBT algorithm is implemented to obtain stable pressure values near solid wall areas and, thus, to minimize possible numerical oscillations brought in by the solid boundaries. Three representative numerical examples, including a benchmark test for hydrostatic pressure, a dam breaking problem and a liquid sloshing problem, are comparatively analyzed with ISPH and IWCSPH. It is demonstrated that the present IWCSPH is more attractive than ISPH in modeling free surface incompressible flows as it is more accurate and more stable with comparable or even less computational efforts. Copyright (c) 2013 John Wiley & Sons, Ltd.
We investigated a flexible wing that can function as a folding fan by vibrating smoothly on a heated surface, and the effects of this vibration on heat transfer. For flexible up-down vibrations of the wing in a pulsat...
详细信息
We investigated a flexible wing that can function as a folding fan by vibrating smoothly on a heated surface, and the effects of this vibration on heat transfer. For flexible up-down vibrations of the wing in a pulsating flow, we propose a novel milli-scale flexible wing shape with a relatively large body and a narrow connecting leg. The shape was optimized such that its deformation became much larger at a low air flow. We performed two-way fluid-structure interaction analyses to predict performance, and an experimental validation was also conducted. The details of flow, heat transfer, and structural deformation are summarized qualitatively. Our results show that the heat transfer coefficient of a heated surface with a single flexible wing was approximately 11.3 % greater than that of a flat plate.
This paper proposes a new practical and efficient procedure to investigate the seismic response of gravity dams that (1) avoids the finite or boundary element discretization of the impounded reservoir;(2) can be appli...
详细信息
This paper proposes a new practical and efficient procedure to investigate the seismic response of gravity dams that (1) avoids the finite or boundary element discretization of the impounded reservoir;(2) can be applied using standard finite-element software not necessarily including fluid-structure interaction capabilities;and (3) accounts for dam and foundation flexibility, water compressibility, and reservoir bottom wave absorption. The proposed technique consists of modifying the original input ground acceleration to obtain a new accelerogram that directly accounts for the complex effects of fluid-structure interaction. This new accelerogram can then be applied to a dam or dam-foundation system without the impounded reservoir. The exact and simplified formulations of the proposed method are developed, and its efficiency is validated through examples of dam-reservoir systems with different geometries. Very satisfactory agreement is obtained when comparing the results to more advanced finite-element solutions including fluid-structure interaction capabilities. The new procedure enhances the efficiency of seismic assessment of gravity dams by reducing the modeling and computational burden associated with reservoir discretization while keeping the main advantages of conventional solid finite-element software in conducting dynamic analyses and providing the resulting stresses, strains, force distributions, and other dam response indicators.
Hydrodynamic impacts of free surface waves are a widely known issue in coastal and ship engineering. They can result in severe damage to important industry facilities (e.g. offshore wind turbines) or means of transpor...
详细信息
Hydrodynamic impacts of free surface waves are a widely known issue in coastal and ship engineering. They can result in severe damage to important industry facilities (e.g. offshore wind turbines) or means of transport (e.g. oil tankers). This kinds of damage give rise to different difficulties due to economic losses and environmental pollution. On that account, the present paper deals with a special feature of a protective mechanism for offshore structures. We develop a numerical multiregional wave-structure impact model of a damping element prototype. The investigated prototype consists essentially of an elastic cover that is attached to the cylindrical mono-pile foundation at wave level. The chamber between the flexible structure and the mono-pile is filled with a liquid. A prototype of the damping element has been constructed as a mono-pile structure test object. In order to measure the hydrodynamic loads on the test object, we placed piezoelectric sensors on the stagnation points of the mono-pile. The multiregional simulation model created is able to imitate the wave impact and its consequences. These implications include the deformation and oscillation of the elastic shell, the resultant force affecting the pile and the dissipation power of the damping fluid. The dissipation power can be understood as the crucial factor preventing the shell from oscillating over long periods of time. It enables us to state the mechanical energy that is transfered due to the wave's impact on the damping fluid region.
The transient analysis was carried out to investigate the dynamic stress and vibration of volute casing for a large double-suction centrifugal pump by using the transient fluid-structure interaction theory. The flow p...
详细信息
The transient analysis was carried out to investigate the dynamic stress and vibration of volute casing for a large double-suction centrifugal pump by using the transient fluid-structure interaction theory. The flow pulsations at flow rate ranging from 60% to 100% of the nominal flow rate (Q(d)) were taken as the boundary conditions for FEM analysis of the pump volute casing structure. The results revealed that, for all operating conditions, the maximum stress located at the volute tongue region, whereas the maximum vibration displacement happened close to the shaft hole region. It was also found that the blade passing frequency and its harmonics were dominant in the variations of dynamic stress and vibration displacement. The amplitude of the dominant frequency for the maximum stress detected at 0.6 Q(d) was 1.14 times that at Q(d), lower than the related difference observed for pressure fluctuations (3.23 times). This study provides an effective method to quantify the flow-induced structural dynamic characteristics for a large-scale double-suction pump. It can be used to direct the hydraulic and structural design and stable operation, as well as fatigue life prediction for large-scale pumps.
In this article we describe a stable partitioned algorithm that overcomes the added mass instability arising in fluid-structure interactions of light rigid bodies and inviscid compressible flow. The new algorithm is s...
详细信息
In this article we describe a stable partitioned algorithm that overcomes the added mass instability arising in fluid-structure interactions of light rigid bodies and inviscid compressible flow. The new algorithm is stable even for bodies with zero mass and zero moments of inertia. The approach is based on a local characteristic projection of the force on the rigid body and is a natural extension of the recently developed algorithm for coupling compressible flow and deformable bodies [1-3]. The new algorithm advances the solution in the fluid domain with a standard upwind scheme and explicit time-stepping. The Newton-Euler system of ordinary differential equations governing the motion of the rigid body is augmented by added mass correction terms. This system, which is very stiff for light bodies, is solved with an A-stable diagonally implicit Runge-Kutta scheme. The implicit system (there is one independent system for each body) consists of only 3d + d(2) scalar unknowns in d = 2 or d = 3 space dimensions and is fast to solve. The overall cost of the scheme is thus dominated by the cost of the explicit fluid solver. Normal mode analysis is used to prove the stability of the approximation for a one-dimensional model problem and numerical computations confirm these results. In multiple space dimensions the approach naturally reveals the form of the added mass tensors in the equations governing the motion of the rigid body. These tensors, which depend on certain surface integrals of the fluid impedance, couple the translational and angular velocities of the body. Numerical results in two space dimensions, based on the use of moving overlapping grids and adaptive mesh refinement, demonstrate the behavior and efficacy of the new scheme. These results include the simulation of the difficult problems of shock impingement on an ellipse and a more complex body with appendages, both with zero mass. (C) 2013 Elsevier Inc. All rights reserved.
In this paper, the free vibration, deterministic vibration and random vibration characteristics of transversely isotropic Magneto-Electro-Elastic (MEE) rectangular plates in contact with fluid are investigated. The ma...
详细信息
In this paper, the free vibration, deterministic vibration and random vibration characteristics of transversely isotropic Magneto-Electro-Elastic (MEE) rectangular plates in contact with fluid are investigated. The mathematical formulation on the determination of added virtual mass for water-contacting MEE rectangular plates with uniform thickness is performed. Based on the recently proposed differential equation governing the dynamical responses of the MEE rectangular plates, a fluid-structure interaction model is established and analyzed. First of all, the added virtual mass incremental (AVMI) factor of the system is calculated by using the proposed approach and the added virtual mass can then be obtained, furthermore, the natural frequencies of the MEE rectangular plates in contact with fluid are also investigated. Then the forced vibration and random vibration behaviors of the system are determined. It is noted that the vibration characteristics based on the proposed method are very useful for those engineers and researchers who are engaged in the vibration analysis and design of the MEE plate in contact with fluid. (C) 2013 Elsevier Ltd. All rights reserved.
The paper presents a method to experimentally characterize the significance of hydroelasticity for slamming loaded marine panels. The methodology is based on a large number of systematical experiments of slamming load...
详细信息
The paper presents a method to experimentally characterize the significance of hydroelasticity for slamming loaded marine panels. The methodology is based on a large number of systematical experiments of slamming loaded panels from which semi-empiric expressions for the pressure distributions are derived. Finite element simulations are used to obtain rigid/quasi-static reference solutions. Hydroelastic effects are quantified by comparing deflections and strains from experiments with the corresponding non-hydroelastic reference solutions. The study shows that the largest hydroelastic effects appear to be a time-lag effect, which however does not seem to affect the structural response magnitudes dramatically. The most significant hydroelastic effects can be expected to be close to the panel supports for very flexible structures or sandwich constructions. The results are also discussed with reference to classification rules which indicate that hydroelastic effects are small in the design of conventional ship hull structures. (C) 2013 Elsevier Ltd. All rights reserved.
暂无评论