We present a sequentially-coupled space-time (ST) computational fluid-structure interaction (FSI) analysis of flapping-wing aerodynamics of a micro aerial vehicle (MAV). The wing motion and deformation data, whether p...
详细信息
We present a sequentially-coupled space-time (ST) computational fluid-structure interaction (FSI) analysis of flapping-wing aerodynamics of a micro aerial vehicle (MAV). The wing motion and deformation data, whether prescribed fully or partially, is from an actual locust, extracted from high-speed, multi-camera video recordings of the locust in a wind tunnel. The core computational FSI technology is based on the Deforming-Spatial-Domain/Stabilized ST (DSD/SST) formulation. This is supplemented with using NURBS basis functions in temporal representation of the wing and mesh motion, and in remeshing. Here we use the version of the DSD/SST formulation derived in conjunction with the variational multiscale (VMS) method, and this version is called "DSD/SST-VMST." The structural mechanics computations are based on the Kirchhoff-Love shell model. The sequential-coupling technique is applicable to some classes of FSI problems, especially those with temporally-periodic behavior. We show that it performs well in FSI computations of the flapping-wing aerodynamics we consider here. In addition to the straight-flight case, we analyze cases where the MAV body has rolling, pitching, or rolling and pitching motion. We study how all these influence the lift and thrust.
In this paper, a rigid thickless lamina is immersed in a quiescent viscous fluid and it undergoes transverse finite amplitude harmonic oscillations near a solid surface. The surrounding flow physics is computed throug...
详细信息
In this paper, a rigid thickless lamina is immersed in a quiescent viscous fluid and it undergoes transverse finite amplitude harmonic oscillations near a solid surface. The surrounding flow physics is computed through the lattice Boltzmann method. In order to account for the presence of the lamina in the lattice fluid background, the Immersed Boundary method is adopted. Several scenarios are investigated by varying the distance between the initial position of the lamina and the solid wall. For a given lamina-solid surface distance, the effect of the Reynolds number is investigated, together with the influence of the Keulegan-Carpenter number. Findings in terms of drag coefficient show that the force exerted by the encompassing fluid upon the lamina is remarkably influenced by the distance from the solid surface, especially for low values of the Reynolds number. Moreover, such results are confirmed by the computation of the hydrodynamic function. In fact, it highlights that the added mass effect and the non-linear damping experienced by the oscillating lamina grow as the above mentioned distance and the Reynolds number reduce. (C) 2014 Elsevier B.V. All rights reserved.
Designing lightweight high-performance materials that can sustain high impulsive loadings is of great interest to marine and civil applications. When designing tough, strong new materials from relatively weak componen...
详细信息
Designing lightweight high-performance materials that can sustain high impulsive loadings is of great interest to marine and civil applications. When designing tough, strong new materials from relatively weak components, mimicking structures from nature can be a highly promising strategy, as illustrated by nacre from red abalone shells. One of nacre's most impressive features is its ability to laterally spread damage and dissipate energy over millimetre length scales at crack tips and other defects. In this work, a composite panel is redesigned to mimic nacre's microstructure. The bio-inspired composite panel and the original composite structure, which have identical areal mass, are subjected to an underwater impulsive loading scenario. Their performances are compared numerically in terms of damage and deflection. A finite element fluid-structure interaction model is developed to capture the water impact on E-glass/vinylester composite facets and to provide insights into the deformation modes and failure mechanisms. Damage and degradation in individual unidirectional composite laminas are simulated using Hashin's composite damage model. The delamination between laminas is modelled by a bilinear cohesive model. Results interpreted from this numerical study will be used as guidance for the future manufacturing and experimental characterisation of bio-inspired composite structures. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.
The magnitudes of the hydrodynamic pressures at the dam-fluid interface depend on the amount of energy transmitted to the fluid by the vibration of the reservoir boundaries. Although the reservoir topology can have a ...
详细信息
The magnitudes of the hydrodynamic pressures at the dam-fluid interface depend on the amount of energy transmitted to the fluid by the vibration of the reservoir boundaries. Although the reservoir topology can have a considerable impact on the amount of generated energy, it has still not been adequately addressed. This article treats an arch dam-fluidinteraction considering a compound wave field of compressive and dilatational waves in a reservoir with a complex topology. A truncation surface was located at a distance beyond which the simulated wave field has only negligible effects.
Offshore pipelines are frequently subjected to accidental impact loads, e.g. from anchors or trawl gear. A lot of parameters including - the pipe geometry, material properties, pipeline content, impact velocity, etc. ...
详细信息
Offshore pipelines are frequently subjected to accidental impact loads, e.g. from anchors or trawl gear. A lot of parameters including - the pipe geometry, material properties, pipeline content, impact velocity, etc. - influence the course of such an impact. Some of these parameters have been studied quite extensively while others not so much. This study presents material and component tests on specimens taken from an X65 offshore pipeline. Empty pipes, as well as open and closed water-filled pipes, are impacted at different velocities. Results in terms of force displacement curves are quite similar for the empty and open water-filled pipes, while the closed water-filled pipes react differently as a consequence of internal pressure build-up during impact. Computer simulations of the component tests are carried out using various numerical techniques for fluid discretisation and for fluid-structure interaction. Numerical results are generally in good agreement with experimental observations and serve as a helpful aid when interpreting results. (C) 2014 Elsevier Ltd. All rights reserved.
A flapping plate flow energy harvester in a viscous uniform flow is simulated using a two-dimensional numerical approach. Our focus is to study the effects of flexibility and active control on the power-extraction cap...
详细信息
A flapping plate flow energy harvester in a viscous uniform flow is simulated using a two-dimensional numerical approach. Our focus is to study the effects of flexibility and active control on the power-extraction capability of the flapping plate, and consequently to find a strategy to increase its power-extraction efficiency. Four typical cases with optimal kinematics predicted by previous studies are presented and discussed: a rigid plate, a flexible plate, a plate with a flexible leading segment and a rigid trailing segment, and a rigid plate with a simple active control on the leading segment. Our simulations show that with the kinematic parameters considered, the plate flexibility cannot significantly improve the power-extraction capability of the plate while the active control on the leading segment of the rigid plate increases the power coefficient by 11.3%. The analysis of flow fields shows that the changes in the power coefficient and drag force are related to the vortex structures and pressure distributions near the plate, as well as the projection area of the plate in the direction of the translational movement. (C) 2014 Elsevier Ltd. All rights reserved.
In this work the problem of a viscoelastic fluid flow in a movable domain is considered. A numerical approximation scheme is developed based on the Arbitrary Lagrangian-Eulerian (ALE) formulation of the flow equations...
详细信息
In this work the problem of a viscoelastic fluid flow in a movable domain is considered. A numerical approximation scheme is developed based on the Arbitrary Lagrangian-Eulerian (ALE) formulation of the flow equations. The spatial discretization is accomplished by the finite element method, and the discontinuous Galerkin method is used for stress approximation. Both first and second order time-stepping schemes satisfying the geometric conservation law (GCL) are derived and analyzed, and numerical experiments that support the theoretical results are presented.
Transient effective flow and force areas of reed valve in a rotary compressor are studied by two three-dimensional fluid-structure interaction (FSI) models. One is the full FSI model, the other one is the simplified F...
详细信息
Transient effective flow and force areas of reed valve in a rotary compressor are studied by two three-dimensional fluid-structure interaction (FSI) models. One is the full FSI model, the other one is the simplified FSI model, in which the discharge port is not covered. It is apparent that two effects have to be considered in the one-dimensional valve model: partly covered discharge port by the cylinder and the roller, and unsteady flow. In an attempt to describe the first effect, comparison of the transient effective flow and force areas between the full FSI model and the simplified FSI model is presented. For the second effect, unsteady flow and force equations are developed and analyzed, and the steady effective flow and force areas are compared with that of the transient. It is found that if these two effects are negligible, the impact velocity of the valve reed impacting on the retainer will be overestimated.
The validation of fluid-structure interaction solvers is difficult since there is a lack of experimental data. Therefore, in this work an aeroelastic experiment is presented. The focus is on the temporal coupling betw...
详细信息
The validation of fluid-structure interaction solvers is difficult since there is a lack of experimental data. Therefore, in this work an aeroelastic experiment is presented. The focus is on the temporal coupling between fluid and structure dynamics. Issues in the spatial coupling are eliminated by using a rigid wing. The wing, with a harmonically actuated 0.2c trailing edge flap, has a degree of freedom in the plunge (vertical) direction. The wing has a chord of 0.5 m and is suspended with springs. The wing motion is constrained by a vertical rail system. For simplicity attached flow is desired and therefore the set angle of attack is alpha=0 degrees. The Reynolds number is approximately Re= 700 000 and the flap deflects over a range of about +/- 2 degrees. The damped natural frequency of the structure expressed as a reduced frequency is about k= 0.194 and measurements are performed for reduced flap frequencies ranging from k= 0.1 to k= 03. Displacements and time dependent aerodynamic forces are measured and for k= 0.198 2-D Ply measurements are performed. The planar Ply measurements are used to intrinsically determine the unsteady loads using Noca's method. As expected the aeroelastic problem shows similarities with a viscously damped mass-damper-spring, meaning the maximum excursion of the wing is found near the system eigenfrequency. The lift is dominated by the flap motion and the effective angle of attack due to the motion introduces phase shifts of the lift signal with respect to the flap phase angle. The experiment has been set up and executed with the necessary precision, but small ambiguities are found in the lift and drag disqualifying the data for validation. Nevertheless the data set provides a clear insight into typical loads and motions and can be used for comparative studies. It can also be used to (re)design future experiments to improve the quality of the data to the desired level of accuracy for validation. (C) 2014 Elsevier Ltd. All rights reserv
This paper investigates the free vibration and stability of a curved rod in flow. The equations of the three-dimensional motions of the rod are derived by the Newtonian approach. The differential quadrature method (DQ...
详细信息
This paper investigates the free vibration and stability of a curved rod in flow. The equations of the three-dimensional motions of the rod are derived by the Newtonian approach. The differential quadrature method (DQM) is introduced to formulate the discrete forms of the governing equations of the inextensible rod with clamped-clamped supports. Based on numerical calculations, the effects of several system parameters, especially the flow velocity, on the natural frequencies and stability of the system are discussed. Buckling and flutter instability are detected as the flow velocity is varied in a certain range. Moreover, a derivation of the generalized slender-body theory for such a deformable curved rod is given in Appendix A. (C) 2014 Elsevier Ltd. All rights reserved.
暂无评论