Hydraulic turbines include stationary and rotating components. The interaction of the components, mainly between the runner blades and distributor vanes, is critical when the frequency of the rotor-stator interaction ...
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Hydraulic turbines include stationary and rotating components. The interaction of the components, mainly between the runner blades and distributor vanes, is critical when the frequency of the rotor-stator interaction (RSI) approaches the runner natural frequency. This causes resonance in the turbine runner and the premature failure of the blades. Several turbines have experienced such problems in the last few years. The studies indicated that the added mass effect causes change in natural frequency of the runner. In the critical conditions, when the runner natural frequency is close to the RSI frequency, hydrodynamic damping is an important parameter in controlling turbomachinery blade-forced response. A reliable technique that can predict/estimate the change in the runner natural frequency due to added mass has yet to be developed. This paper reviews the investigations conducted on fluidstructureinteraction (FSI) focusing on the role of hydrodynamic damping during resonance, RSI and added mass effect. In specific, the review includes: (1) role of boundary layer to improve the damping effect, (2) how nearby structure and submergence level changes the damping effect, (3) dependency on mode-shape, (4) how freestream velocity and vortex shedding helps to increase damping, (5) damping during cavitation, (6) damping variation with respect to a dimensionless beta parameter and (7) damping effect during rotation. In the summary, need for the future study of FSI within the field of hydropower and how damping is important in avoiding the catastrophic failures in the early life of hydraulic turbines is discussed. 2017 Elsevier Ltd. All rights reserved.
We study a nonlinear fluid-structure interaction (FSI) problem between an incompressible, viscous fluid and a composite elastic structure consisting of two layers: a thin layer (membrane) in direct contact with the fl...
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We study a nonlinear fluid-structure interaction (FSI) problem between an incompressible, viscous fluid and a composite elastic structure consisting of two layers: a thin layer (membrane) in direct contact with the fluid, and a thick layer (3D linearly elastic structure) sitting on top of the thin layer. The coupling between the fluid and structure, and the coupling between the two structures is achieved via the kinematic and dynamic coupling conditions modeling no-slip and balance of forces, respectively. The coupling is evaluated at the moving fluid-structure interface with mass, i.e., the thin structure. To solve this nonlinear moving-boundary problem in 3D, a monolithic, fully implicit method was developed, and combined with an arbitrary Lagrangian-Eulerian approach to deal with the motion of the fluid domain. This class of problems and its generalizations are important in e.g., modeling FSI between blood flow and arterial walls, which are known to be composed of several different layers, each with different mechanical characteristics and thickness. By using this model we show how multi-layered structure of arterial walls influences the pressure wave propagation in arterial walls, and how the presence of atheroma and the presence of a vascular device called stent, influence intramural strain distribution throughout different layers of the arterial wall. The detailed intramural strain distribution provided by this model can be used in conjunction with ultrasound B-mode scans as a predictive tool for an early detection of atherosclerosis (Zahnd et al. in IEEE international on ultrasonics symposium (IUS), pp 1770-1773, 2011).
In this paper, we numerically investigate the impact of body shape and wing orientation upon the flow induced drag forces experienced by a body in its steady state. The current study focuses on simple toy models but d...
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In this paper, we numerically investigate the impact of body shape and wing orientation upon the flow induced drag forces experienced by a body in its steady state. The current study focuses on simple toy models but derives its motivations from previous reported work on wind-induced drag on birds in flight most of which are experimental in nature. Our numerical results show that body shape/eccentricites, wing length and orientation are all important in determining the forces experienced by a body in a flow. Their geometries and specific features are key to determining the optimal mode of locomotion which is determined by looking at the relationship between drag force, bending behavior versus flow and geometric parameters.
A robust immersed boundary-lattice Boltzmann method(IB-LBM)is proposed to simulate fluid-structure interaction(FSI)problems in this *** with the conventional IB-LBM,the current method employs the fractional step techn...
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A robust immersed boundary-lattice Boltzmann method(IB-LBM)is proposed to simulate fluid-structure interaction(FSI)problems in this *** with the conventional IB-LBM,the current method employs the fractional step technique to solve the lattice Boltzmann equation(LBE)with a forcing ***,the non-physical oscillation of body force calculation,which is frequently encountered in the traditional IB-LBM,is suppressed *** is of importance for the simulation of FSI *** the meanwhile,the no-slip boundary condition is strictly satisfied by using the velocity correction ***,based on the relationship between the velocity correction and forcing term,the boundary force can be calculated accurately and easily.A few test cases are first performed to validate the current ***,a series of FSI problems,including the vortex-induced vibration of a circular cylinder,an elastic filament flapping in the wake of a fixed cylinder and sedimentation of particles,are *** on the good agreement between the current results and those in the literature,it is demonstrated that the proposed IB-LBMhas the capability to handle various FSI problems effectively.
We study the existence of weak solution for unsteady fluidstructureinteraction problem for shear-thickening flow. The time dependent domain has at one part a flexible elastic wall. The evolution of fluid domain is g...
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We study the existence of weak solution for unsteady fluidstructureinteraction problem for shear-thickening flow. The time dependent domain has at one part a flexible elastic wall. The evolution of fluid domain is governed by the generalized string equation with action of the fluid forces. The power-law viscosity model is applied to describe shear-dependent non-Newtonian fluids.
In this study, we perform a series of aero-thermo-mechanical analyses to predict the running-tip clearance and the effects of impeller deformation on the performance using a centrifugal compressor. During operation, t...
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In this study, we perform a series of aero-thermo-mechanical analyses to predict the running-tip clearance and the effects of impeller deformation on the performance using a centrifugal compressor. During operation, the impeller deformation due to a combination of the centrifugal force, aerodynamic pressure and the thermal load results in a non-uniform tip clearance profile. For the prediction, we employ the one-way fluid-structure interaction (FSI) method using CFX 14.5 and ANSYS. The predicted running tip clearance shows a non-uniform profile over the entire flow passage. In particular, a significant reduction of the tip clearance height occurred at the leading and trailing edges of the impeller. Because of the reduction of the tip clearance, the tip leakage flow decreased by 19.4%. In addition, the polytrophic efficiency under operating conditions increased by 0.72%. These findings confirm that the prediction of the running tip clearance and its impact on compressor performance is an important area that requires further investigation.
Objective: Varicose vein has become enlarged and twisted and, consequently, has lost its mechanical strength. As a result of the varicose saphenous vein (SV) mechanical alterations, the hemodynamic parameters of the b...
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Objective: Varicose vein has become enlarged and twisted and, consequently, has lost its mechanical strength. As a result of the varicose saphenous vein (SV) mechanical alterations, the hemodynamic parameters of the blood flow, such as blood velocity as well as vein wall stress and strain, would change accordingly. However, little is known about stress and strain and there consequences under experimental conditions on blood flow and velocity within normal and varicose veins. In this study, a three-dimensional (3D) computational fluid-structure interaction (FSI) model of a human healthy and varicose SVs was established to determine the hemodynamic characterization of the blood flow as a function of vein wall mechanical properties, i.e. elastic and hyperelastic. Methods: The mechanical properties of the human healthy and varicose SVs were experimentally measured and implemented into the computational model. The fully coupled fluid and structure models were solved using the explicit dynamics finite element code LS-DYNA. Results: The results revealed that, regardless of healthy and varicose, the elastic walls reach to the ultimate strength of the vein wall, whereas the hyperelastic wall can tolerate more stress. The highest von Mises stress compared to the healthy ones was seen in the elastic and hyperelastic varicose SVs with 1.412 and 1.535MPa, respectively. In addition, analysis of the resultant displacement in the vein wall indicated that the varicose SVs experienced a higher displacement compared to the healthy ones irrespective of elastic and hyperelastic material models. The highest blood velocity was also observed for the healthy hyperelastic SV wall. Conclusion: The findings of this study may have implications not only for determining the role of the vein wall mechanical properties in the hemodynamic alterations of the blood, but also for employing as a null information in balloon-angioplasty and bypass surgeries.
A numerical assessment on the solution performance of adaptive finite element methods for fluid-structure interaction (FSI) is presented in this paper. The partitioned-based approach involving separate fluid and struc...
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A numerical assessment on the solution performance of adaptive finite element methods for fluid-structure interaction (FSI) is presented in this paper. The partitioned-based approach involving separate fluid and structure solvers is considered for adaptive finite element computation with triangular mesh. The performance of the hp-adaptivity, in which error in energy norm is reduced by way of mesh refinement (h) and polynomial order extension (p), is of particular interest. In addition, parallel solution process based on the domain decomposition method is also assessed due to the complexity of two way coupling scheme. Based on its numerical convergence, the hp-adaptive procedure for the FSI problem is shown to yield the fastest convergence as generally expected. Moreover, our domain decomposition parallelization scheme shows reduction in the computation time by up to order 2. Subsequently, the convergence performance is highly dependent on the aspect ratios of the triangular elements. The solution performance strongly suggests the viability of the parallel hp-adaptive method in partitioned-based FSI formulation.
Building off of previous analytical results for recasting fluid-structure interaction into an optimal control setting, an a priori error estimate is given for the optimality system by means of BRR theory. The converge...
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Building off of previous analytical results for recasting fluid-structure interaction into an optimal control setting, an a priori error estimate is given for the optimality system by means of BRR theory. The convergence of the steepest descent method is proven in a discrete setting for a sufficiently small time step and mesh size. A numerical study is included supporting the theoretical rate of convergence over a single time step. Additional results demonstrate optimal convergence in space and time over several time steps. (C) 2016 Elsevier Inc. All rights reserved.
3D printed hair-like micro-structures have been previously demonstrated in a novel micro-fluidic flow sensor aimed at sensing air flows down to rates of a few milliliters per second. However, there is a lack of in-dep...
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3D printed hair-like micro-structures have been previously demonstrated in a novel micro-fluidic flow sensor aimed at sensing air flows down to rates of a few milliliters per second. However, there is a lack of in-depth understanding of the structural response of these `micro-hairs' under a fluid flow field. This paper demonstrates the use of lattice Boltzmannmethods (LBM)to understand this structural response towards a better optimization of the micro-hair flow sensors designed to suit the end applications' needs. The LBM approach was chosen as an efficient alternative to simulate Navier-Stokes equations for modeling fluid flow around complex geometries primarily for improved accuracy and simplicity with lesser computational costs. As the spatial dimensions of the sensor's flow channel are much larger in comparison to the actual micro-hairs (the sensing element), a multidimensional approach of combining two-dimensional (D2Q9) and three-dimensional (D3Q19) lattice configurations were implemented for improved computational speeds and efficiency. The drag force on the micro-hairs was estimated using the momentum-exchange method in the D3Q19 configuration and this drag force is transferred to the structural analysis model which determines the micro-hair deformation using Euler-Bernoulli beam theory. The entirety of the LBM fluid-structure interaction (FSI) model was implemented within MATLAB and the obtained results are compared against the numerical model implemented on a commercially available software package.
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