In the analysis of flexible flapping wings of insects, the aerodynamic outcome depends on the combined structural dynamics and unsteady fluid physics. Because the wing shape and hence the resulting effective angle of ...
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In the analysis of flexible flapping wings of insects, the aerodynamic outcome depends on the combined structural dynamics and unsteady fluid physics. Because the wing shape and hence the resulting effective angle of attack are a priori unknown, predicting aerodynamic performance is challenging. Here, we show that a coupled aerodynamics/structural dynamics model can be established for hovering, based on a linear beam equation with the Morison equation to account for both added mass and aerodynamic damping effects. Lift strongly depends on the instantaneous angle of attack, resulting from passive pitch associated with wing deformation. We show that both instantaneous wing deformation and lift can be predicted in a much simplified framework. Moreover, our analysis suggests that resulting wing kinematics can be explained by the interplay between acceleration-related and aerodynamic damping forces. Interestingly, while both forces combine to create a high angle of attack resulting in high lift around the midstroke, they offset each other for phase control at the end of the stroke.
The Rayleigh instability (also called the Plateau-Rayleigh instability) of a nanosized liquid propane thread is investigated using molecular dynamics (MD). The validity of classical predictions at small length scales ...
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The Rayleigh instability (also called the Plateau-Rayleigh instability) of a nanosized liquid propane thread is investigated using molecular dynamics (MD). The validity of classical predictions at small length scales is verified by comparing the temporal evolution of liquid thread simulated by MD against classical predictions. Previous works have shown that thermal fluctuations become dominant at small length scales. The role and influence of the stochastic nature of thermal fluctuations in determining the instability at small length scale is also investigated. Thermal fluctuations are seen to dominate and accelerate the breakup process only during the last stages of breakup. The simulations also reveal that the breakup profile of nanoscale threads undergo modification due to reorganization of molecules by the evaporation-condensation process.
The response of cylindrical composite structures subjected to underwater impulsive loads is analyzed. The analysis focuses on the effect of varying structural attributes and material properties on load-carrying capaci...
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The response of cylindrical composite structures subjected to underwater impulsive loads is analyzed. The analysis focuses on the effect of varying structural attributes and material properties on load-carrying capacity, deflection, energy dissipation and damage. The structural designs studied are monolithic composite structures, and sandwich structures with foam cores of different relative densities and different radii. Underwater impulsive loads are generated using a novel experimental setup, and deflection and core compression are characterized using high-speed digital imaging. The experiments are supported by fully dynamic 3D numerical calculations which account for fluid-structure interactions and damage and failure mechanisms in the materials. For the same applied impulse, the monolithic cylindrical sections experience significant warping, delamination and cracking, while sandwich structures experience significantly lower damage. In sandwich structures, as the core density increases, the transmitted impulse and overall damage also increase. Deflection and warping in the impulsively loaded region are influenced by the radius of curvature and material orientation. Results show that cylindrical sandwich structures have superior blast-resistance than cylindrical monolithic structures of equal mass with only relatively minor increases in wall thickness. The experiments, computations and structure-performance relations offer approaches for improving the blast mitigation capabilities of cylindrical composite sections in critical parts of a ship structure like the keel, hull and pipes.
It is now widely recognized that changes in arterial wall properties have a significant impact on hemodynamic indices such as pressure pulse amplification and pulse wave velocity. It is also becoming increasingly evid...
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It is now widely recognized that changes in arterial wall properties have a significant impact on hemodynamic indices such as pressure pulse amplification and pulse wave velocity. It is also becoming increasingly evident that changes in wall mechanics may progress both spatially and temporally (e.g., in age-related arterial stiffening and hypertension). Modeling studies can help delineate how local changes in stiffness affect global hemodynamics. Previously, several modeling studies have investigated blood and pressure in full-body scale arterial trees using one-dimensional formulations. In this paper, we work towards the goal of deepening our understanding of arterial pulse propagation phenomena while incorporating detailed information on localized hemodynamics. To this end, we present the first multi-scale simulation of unsteady blood flow and pressure within a three-dimensional deformable full-body arterial network. This simulation framework builds upon previous advances in fluid-structure interaction, multi-scale outflow boundary conditions, and perivascular tissue support modeling. We consider application examples featuring realistic distributions of spatially and temporally varying mechanical properties. Simulations successfully demonstrate realistic pressure and flow waveforms, regional blood flow distribution, pressure pulse amplification and pulse wave velocity.
In marine applications, composite structures in contact with water are subjected to impacts by projectiles large and small. While the presence of water is known to affect the dynamics of immersed structures, its effec...
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In marine applications, composite structures in contact with water are subjected to impacts by projectiles large and small. While the presence of water is known to affect the dynamics of immersed structures, its effects on the impact dynamics is unclear. This study shows that the contact force history is not affected if the mass of the projectile is large. The opposite is true if the mass of the projectile is small compared to that of the target
We have developed novel numerical methods for fluid-structure and fluid-membrane interaction problems. The basic equation set is formulated in a full Eulerian framework. The method is based on the finite difference vo...
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We have developed novel numerical methods for fluid-structure and fluid-membrane interaction problems. The basic equation set is formulated in a full Eulerian framework. The method is based on the finite difference volume-of-fluid scheme with fractional step algorithm. It is validated through a numerical solution to a deformable vesicle problem, and applied to blood flows including red blood cells (RBCs) and platelets. Further, to gain insight into the mechanism of thrombus formation, a stochastic Monte Carlo model to describe the platelet-vessel wall interaction is incorporated into the Eulerian method. The effect of the RBCs on the platelet motion is discussed.
In this paper we describe a series of experimental tests performed with a 1 :45 scale jacket structure in a water basin. The model structure is assembled on a seismic table that performs a controlled motion, with ampl...
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ISBN:
(纸本)9781880653708
In this paper we describe a series of experimental tests performed with a 1 :45 scale jacket structure in a water basin. The model structure is assembled on a seismic table that performs a controlled motion, with amplitudes and frequencies that could correspond to actual earthquake conditions translated to the scale of the model. The structural response to the imposed displacement is analyzed in terms of the accelerations and reaction forces at the base of the structure, first in air and afterwards in water. The experimental measurements are equally correlated with the computer predictions of dynamic loading that have been obtained with a FEM commercial software - the ADINA.
This paper deals with the simulation of water entry problems using the lattice Boltzmann method (LBM). The dynamics of the free surface is treated through the mass and momentum fluxes across the interface cells. A bou...
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This paper deals with the simulation of water entry problems using the lattice Boltzmann method (LBM). The dynamics of the free surface is treated through the mass and momentum fluxes across the interface cells. A bounce-back boundary condition is utilized to model the contact between the fluid and the moving object. The method is implemented for the analysis of a two-dimensional flow physics produced by a symmetric wedge entering vertically a weakly-compressible fluid at a constant velocity. The method is used to predict the wetted length, the height of water pile-up, the pressure distribution and the overall force on the wedge. The accuracy of the numerical results is demonstrated through comparisons with data reported in the literature.
In this paper, numerical analysis aiming at simulating biological organisms immersed in a fluid are carried out. The fluid domain is modeled through the lattice Boltzmann (LB) method, while the immersed boundary metho...
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In this paper, numerical analysis aiming at simulating biological organisms immersed in a fluid are carried out. The fluid domain is modeled through the lattice Boltzmann (LB) method, while the immersed boundary method is used to account for the position of the organisms idealized as rigid bodies. The time discontinuous Galerkin method is employed to compute body motion. An explicit coupling strategy to combine the adopted numerical methods is proposed. The vertical take-off of a couple of butteries is numerically simulated in different scenarios, showing the mutual interaction that a buttery exerts on the other one. Moreover, the effect of lateral wind is investigated. A critical threshold value of the lateral wind is defined, thus corresponding to an increasing arduous take-off.
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