Numerical simulation of fluid-structure interaction of a moving flexible foil

The hybrid Cartesian/immersed boundary method is applied to fluid-structure interaction of a moving flexible foil. A new algorithm is suggested to classify immersed boundary nodes based on edges crossing a boundary. Velocity vectors are reconstructed at the immersed boundary nodes by using the interpolation along a local normal line to the boundary. For eliminating pressure reconstruction, the hybrid staggered/non-staggered grid method is adapted. The deformation of an elastic body is modeled based on dynamic thin-plate theory. To validate the developed code first, free rotation of a foil in a channel flow is simulated and the computed angular motion is compared with other computational results. The code is then applied to the fluid-structure interaction of a moving flexible foil which undergoes large deformation due to the fluid loading caused by horizontal sinusoidal motion. It has been shown that the moving flexible foil can generate much larger vertical force than the corresponding rigid foil and the vertical force can be attributed to the downward fluid jet due to the alternating tail deflection. This paper was recommended for publication in revised form by Associate Editor Haecheon Choi Sangmook Shin received his B.S. and M.S. degrees in Naval Architecture from Seoul National University, Korea in 1989 and 1991, respectively. He received his Ph.D. degree in Aerospace Engineering from Virginia Tech, USA in 2001. He is currently an Assistant Professor at Department of Naval Architecture and Marine Systems Engineering at Pukyong National University in Busan, Korea. His research interests include fluid-structure interaction, unstructured grid method, internal wave, and two-phase flow. Hyoung Tae Kim received the B.S. and M.S. degrees in Naval Architecture from Seoul National University in 1979 and 1981, respectively and the Ph.D. degree in Mechanical Engineering from University of Iowa, U.S.A. in 1989. Dr. Kim is currently a Professor at the Department of Naval Architecture & Ocean Engineering at Chungnam National University, Korea. His research interests are in the area of Ship Hydrodynamics, CFD calculations of turbulent flows around ships and propellers, and human-powered and solar boat design.     

Numerical study on the rotation of an elastic rod in a viscous fluid using an immersed boundary method

We present a three-dimensional computational model based on an immersed boundary (IB) method to study the hydrodynamic features of a solid flexible cylindrical rod in a viscous fluid driven at one side by a tiny motor. The elastic rod is modelled by a number of circular cross-sections with twelve IB points on each cross-section. Three types of elastic links are created from each IB point to obtain an elastic network model of the rod and the first cross-section is modelled as the motor part. The elastic forces are computed based on an elastic energy approach and the motor forces are obtained from the applied angular frequency of rotation of the motor. The Stokes equations governing the fluid are solved on a staggered Cartesian grid system using the fractional-step based finite-volume method. Numerical simulations are performed to demonstrate the three dynamical stages of rod motion-twirling, whirling and overwhirling for different rotational frequency of the motor. It is revealed that for low rotational frequencies, the rod undergoes stable rigid body motion known as twirling. For high rotational frequencies of the motor, it is observed that the rod initially undergoes whirling motion and attains an unstable helical shape. Further, it is noticed that a discontinuous shape transition occurs for the rod and it folds back on itself. This unstable motion is referred to as overwhirling. It is also found that there exists a critical value of angular frequency of rotation of the motor below which the rod is subjected to twirling motion and above which it undergoes overwhirling motion.     

Investigation of liquid-gas interfacial shapes in reduced gravitational environments

The objective of this study was to investigate the liquid-gas interfacial shapes in a low-gravity environment. Experimentally, a free-falling test setup was established to perform drop tests for observing interfacial flow phenomena under reduced-gravity conditions. In the theoretical analysis, the complex two-phase flowfield was simulated by using the transient three-dimensional conservation equations of mass and momentum. The continuous surface force (CSF) model was adopted to treat the surface-tension effect at the liquid-gas boundary. The volume-of-fluid (VOF) method, together with the piecewise linear interface construction (PLIC) technique, was used to describe the liquid-gas interface movements. The predictions were compared with the photographed images of the water-air interface shapes to validate the present computer code. To extend the application to the internal flow study of a ROCSAT-2 propellant tank, 16 numerical experiments were conducted to examine various effects, including liquid-filled ratio, gravity level, surface tension, and contact angle on the equilibrium shape of the pressurized helium gas bubble and the location of the center of mass (CoM).     

New Immersed Boundary Method on the Adaptive Cartesian Grid Applied to the Local Discontinuous Galerkin Method

Currently, many studies on the local discontinuous Galerkin method focus on the Cartesian grid with low computational e ciency and poor adaptability to complex shapes. A new immersed boundary method is presented, and this method employs the adaptive Cartesian grid to improve the adaptability to complex shapes and the immersed boundary to increase computational e ciency. The new immersed boundary method employs different boundary cells(the physical cell and ghost cell) to impose the boundary condition and the reconstruction algorithm of the ghost cell is the key for this method. The classical model elliptic equation is used to test the method. This method is tested and analyzed from the viewpoints of boundary cell type, error distribution and accuracy. The numerical result shows that the presented method has low error and a good rate of the convergence and works well in complex geometries. The method has good prospect for practical application research of the numerical calculation research.     

Optimization design technique for reduction of sloshing by evolutionary methods

The oscillation of a fluid caused by external force, called sloshing, occurs in moving vehicles containing liquid masses, such as trucks, railroad cars, aircraft, and liquid rockets. This sloshing effect could be a severe problem in vehicle stability and control. Therefore, development of efficient and easy method to reduce sloshing effect is positively necessary. In this study, optimization design technique for reduction of the sloshing using evolutionary method is suggested. Two evolutionary methods are employed, respectively, the artificial neural network (ANN) and genetic algorithm (GA). ANN is used for the analysis of sloshing and GA is adopted as optimization algorithm. The considered storage tank for fluid is a rectangular tank. The design variables are width and installation location of the baffle, and sloshing reduction coefficient by baffle is used as an object function in the optimization. As a result of this study, the optimal design for sloshing reduction is presented.     

A numerical study of the fluid flow and heat transfer around a single row of tubes in a channel using immerse boundary method

The analysis of the time-dependent and two-dimensional fluid flow and heat transfer around a single row of tubes in a channel is performed numerically. Due to its fundamental significance and practical importance, aerodynamic and heat transfer characteristics of tube bundle have been paid great attention by many researchers. In the present study, the immersed boundary method is applied by using a Cartesian grid system. Numerical solution for the governing equations of mass, momentum and energy conservation is obtained with the finite volume method. To validate the numerical approach with the immersed boundary method, the results have been compared with published data. The generation and evolution of vortical structures, wake interactions and their effects on the drag, lift and heat transfer are analyzed at different Reynolds numbers. The effect of hydraulic boundary layer development on the fluid flow and heat transfer is also investigated.     

Reduction of sloshing effects in a rectangular tank through an air-trapping mechanism – a numerical study

A 2D rectangular tank subjected to horizontal excitations is used to analyze the effects of sloshing. The tank is fitted with horizontal baffles on two sides to suppress the impact pressure of sloshing by using an air-trapping mechanism. The volume of fluid method is adopted to create sloshing phenomena. Five cases with fixed baffle gaps and various baffle lengths are used to analyze the effects of suppressing the sloshing impact pressure in the tank. The peak pressure values of the cases with baffles are compared with those of the cases without baffles. Results show that the maximum suppression rate achieved is 63.6 % due to air trapping and baffle effects. Baffle ratio (Defined by G/L), a geometrical dimensionless factor, is considered to analyze the effects of baffle length and gap. A baffle ratio of 0.5 results in a 14.2 % reduction in the sloshing impact rate. An increasing amount of air is trapped within the baffle array as BR decreases.     

刚性和柔性储液罐简化模型仿真分析

选取了两种力学模型,刚性理论的Housner模型和柔性理论的Haroun—Housner模型,将Housner模型简化为二质点结构,Hauroun—Housner模型简化为三质点结构,将其和规范算法、有限元算法进行频率对比,误差不足5％。采用Newmark—B法进行弹性时程分析,得到液体各质点的位移时程、罐底剪力时程、倾覆弯矩时程。仿真结果表明：简化模型和有限元、规范算法频率相差很小,水平地震激励后期,晃动质点位移时程相差较大,刚性脉冲质点位移时程几乎一致,罐底剪力和规范算法相差很小,倾覆弯矩相差较大。Housner方法设计的储液罐,液体晃动部分的响应被低估,储液罐工程设计人员及研究人员应予以重视。     

An immersed-boundary finite-volume method for simulation of heat transfer in complex geometries

An immersed boundary method for solving the Navier-Stokes and thermal energy equations is developed to compute the heat transfer over or inside the complex geometries in the Cartesian or cylindrical coordinates by introducing the momentum forcing, mass source/sink, and heat source/sink. The present method is based on the finite volume approach on a staggered mesh together with a fractional step method. The method of applying the momentum forcing and mass source/sink to satisfy the no-slip condition on the body surface is explained in detail in Kim, Kim and Choi (2001, Journal of Computational Physics). In this paper, the heat source/sink is introduced on the body surface or inside the body to satisfy the iso-thermal or iso-heat-flux condition on the immersed boundary. The present method is applied to three different problems : forced convection around a circular cylinder, mixed convection around a pair of circular cylin-ders, and forced convection around a main cylinder with a secondary small cylinder. The results show good agreements with those obtained by previous experiments and numerical simulations, verifying the accuracy of the present method.     

Trajectory coordination planning and control for robot manipulators in automated material handling and processing

Motion coordination planning and control play a crucial role in robot application to Cartesian task operations with taking into account kinematics and dynamics constraints. This paper presents a unified approach to coordination planning and control for robot position and orientation trajectories in Cartesian space. The concept of generalised robot pose is defined as the robot configuration consisting of position and orientation, in which the orientation is described by a vector equivalent to the rotational angular displacement. The robot pose ruled surface is formed as a three-dimensional motion locus of its configuration vector. The unified treatment of the end-effector positions and orientations is based on the robot pose ruled surface concept and used in trajectory interpolations. The coordination planning of pose trajectories for the robot end effector is accomplished by generating and optimising the pose ruled surface under the constraints of kinematics and dynamics performances. The coordination control is implemented through controlling the motion laws of two end points of the orientation vector and calculating the coordinates of instantaneous corresponding points. The simulation experiment using PUMA 560 robot in arc welding and surface finishing processes are carried out to verify the feasibility of the proposed approach and demonstrate the capabilities of generation and control models.     

The vibration performance experiment of Tuned Liquid damper and Tuned Liquid Column damper

Tuned Liquid damper and Tuned Liquid Column are kind of passive mechanical damper which relies on the sloshing of liquid in a rigid tank for suppressing structural vibrations. TLD and TLCD are attributable to several potential advantages —low costs; easy to install in existing structures; effective even for small-amplitude vibrations. In this paper, the shaking table experiments were conducted to investigate the characteristics of water sloshing motion in TLD (rectangular, circular) and TLCD. The parameter obtained from the experiments were wave height, base shear force and energy dissipation. The shaking table experiments show that the liquid sloshing relies on amplitude of shaking table and frequency of tank. The TLCD was more effective control vibration than TLD.     

液罐车流-固耦合分析及优化设计

在液罐车转向的过程中,罐体内液体的晃动会对液罐车产生侧向冲击力和侧倾力矩。以非满载液罐体为研究对象,采用流体体积法(Volume of fluid,VOF)对转向工况下的液体晃动进行数值分析,获得了侧向加速度和充液比对液晃的影响规律。建立液罐车侧向动力学模型,仿真结果表明,充液比为50%~70%时液罐车侧翻阈值较小。对罐体内部结构进行优化设计,设计一种倒V型防波板装置来降低液体对罐壁冲击。研究了9种倒V型防波板在不同充液比时的减晃效果,结果表明,安装三块夹角为150°的V型防波板防晃效果最好。搭建缩比液罐车侧倾台架,利用电动液压缸举升整个钢板平面和滑台以模拟罐车侧倾状态,同时滑台带动罐体向反方向平移,实现质心位置纠正,从而减小液体侧向晃动力与侧倾力矩,提高了液罐车的侧向稳定性。     

Flow response of magnetic fluid surface by pitching motion

This research analyses the dynamic behavior of magnetic fluid that sloshes due to the pitching motion of the container. To analyze the behavior of magnetic fluid, we first analyze the equations that govern magnetic fluid as well as the momentum equation of the sloshing that results from a magnetic field. In each case, we conducted simulation and compared the results from simulation with those from experiments. When sloshing does not occur, the surface of the magnetic fluid rises towards the location of intensity of the magnetic field; in the absence of an additional, external body force, the fluid remains elevated. In case sloshing occurs simultaneously with the application of the magnetic field, the elevation of the surface as a result of the magnetic field is maintained. Further, we can confirm that if the excitation frequency of sloshing is small, the wave motion of the surface is small because the magnetic body force dominates the effect of sloshing. Even if the excitation frequency increases, the wave motion of the fluid surface is smaller than when a magnetic field is not applied. The fluid surface rises in that location where the intensity of the magnetic field is strong. Where the intensity of the magnetic field is weak, the height of the fluid surface is lower than the initial level that obtains in the absence of a magnetic field. Through the study, we can conclude that the sloshing behavior of magnetic fluid is influenced by the magnetic field intensity and distribution.     

装载量与罐式汽车侧倾稳定性关系的分析

在弯道或变道行驶时，由于非满载罐内液体货物的晃动，罐式汽车的侧倾稳定性将低于运输等量固体货物的汽车。本文分析了非满载罐内晃动液体质心位置的变化，通过建立罐式汽车侧翻数学模型，推导出了非满载罐式汽车稳态转向时的侧翻阈值计算公式，表明装载量对罐式汽车侧倾稳定性具有较大影响，并提出了改善罐式汽车侧倾稳定性的方法。     

Hydroelastic vibration of the bottom plate of the cylindrical tank coupled with sloshing

Journal of Mechanical Science and Technology - This study is concerned with the hydroelastic vibration of the flexible bottom plate of a cylindrical tank coupled with sloshing. The cylindrical tank...     

Improvements to the instrumentation of a laboratory demonstration surge tank

The instrumentation described in this paper is designed to provide a relatively cheap and simple method of recording the changing water level during the operation of a laboratory surge tank. The method detects the passage of the water surface past a number of pairs of electrodes fitted into the side of the surge tank. One of each pair is supplied with a low D.C. voltage, so that when the pair is immersed in water, a small current flows. This signal is amplified and encoded before being used by a VELA datalogger acting as a timing device. The data is later transferred to a microcomputer for presentation in graphical and printed form. The method copes accurately both with the initial rapid large change in water level and the subsequent slowly decaying oscillations. It can also be used for automatic calibration of other methods of recording changing water levels.     

Stress Intensity Factors Evaluation for Rolling Contact Fatigue Cracks in Rails

The stress intensity factors (SIFs) for multiple rolling contact fatigue cracks of a network in the Iran railway under vehicle dynamic load are evaluated in this article. Stress intensity factor evaluation under dynamic loading is simulated in three dimensions using a linear elastic boundary element code. For this purpose, a UIC60 rail with accurate geometry using a boundary element method is studied. A three-dimensional model in Franc3D is provided. Finally, the influence of the friction coefficient between the wheel and rail, crack surface friction, trapped fluid, and initial crack length on SIFs are investigated in detail.     

迷宫气封三维非定常流场及转子动特性数值仿真

通过计算流体力学方法,采用近似的解析变换网格,以及混合有限分析格式,对迷宫气封流场进行三维非定常数值求解,进而求得密封气流对转子的气流激振力,获得转子的动特性系数。将计算结果与试验结果以及双控制体计算结果相比较,结果令人满意,说明了该计算程序是正确可靠的。该方法精度较高,适用范围广,可以应用于各种复杂的涡动情况及各种齿型,对气封转子的深入研究有重要意义。计算结果还显示了主刚度、主阻尼对气流进口周向速度不敏感,而交叉刚度对气流进口周向速度非常敏感。由于交叉刚度对转子的稳定性影响相当大,这一点是值得注意和利用的。     

Three-dimensional metacarpophalangeal joint kinematics using two markers on the phalanx

A protocol for analysing three-dimensional metacarpophalangeal (MCP) joint motion in vivo using two markers on the proximal phalanx is described. The analysis uses an assumption that the rotation of the phalanx about its own long axis is zero. In an experimental study 24 volunteers had surface markers applied to the dorsal surfaces of their hands and index and long finger proximal phalanges, with three-dimensional marker positions recorded in two hand and finger postures in an incomplete box design using a test-retest protocol. Kinematic parameters from the optoelectronic system were compared with those obtained from three-dimensional reconstruction of bone landmarks and of the marker positions identified on stereoradiographs. Pronation/supination angles obtained from bone landmarks showed high test-retest variability, reflecting the difficulty in obtaining reliable pronation/supination data in small bones without the use of implanted markers. Changes in MCP joint extension and deviation angles determined using two surface markers agree with those obtained from bone landmarks. The results indicate a reproducible protocol for tracking MCP joint motion using only two phalangeal markers, suggesting that the 'no-rotation assumption' can be applied without affecting measures of extension and deviation motion in the normal joint.