Acta Mechanica Sinica
     Acta Mechanica Sinica
  Acta Mechanica Sinica--2014, 30 (6)   Published: 20 November 2014
Preface: Aerodynamics, dynamics and control of animal (insects, birds and bats) flight Hot!
Sun Mao
Effects of aspect ratio on flapping wing aerodynamics in animal flight Hot!
Jun-Jiang Fu, Csaba Hefler, Hui-He Qiu, Wei Shyy

Morphology as well as kinematics is a critical determinant of performance in flapping flight. To understand the effects of the structural traits on aerodynamics of bioflyers, three rectangular wings with aspect ratios (AR) of 1, 2, and 4 performing hovering-like sinusoidal kinematics at wingtip based Reynolds number of 5 300 are experimentally investigated. Flow structures on sectional cuts along the wing span are compared. Stronger K-H instability is found on the leading edge vortex of wings...

Aerodynamic interaction between forewing and hindwing of a hovering dragonfly Hot!
Zheng Hu, Xin-Yan Deng

The phase change between the forewing and hindwing is a distinct feature that sets dragonfly apart from other insects. In this paper, we investigated the aerodynamic effects of varying forewing-hindwing phase difference with a 60° inclined stroke plane during hovering flight. Force measurements on a pair of mechanical wing models showed that in-phase flight enhanced the forewing lift by 17% and the hindwing lift was reduced at most phase differences. The total lift of both wings was also ...

Dynamic performance and wake structure of flapping plates with different shapes Hot!
Gao-Jin Li, Nan-Sheng Liu, Xi-Yun Lu

The dynamic performance and wake structure of flapping plates with different shapes were studied using multi-block lattice Boltzman and immersed boundary method. Two typical regimes relevant to thrust behavior are identified. One is nonlinear relation between the thrust and the area moment of plate for lower area moment region and the other is linear relation for larger area moment region. The tendency of the power variation with the area moment is reasonably similar to the thrust behavior an...

Power regulation of kinematic control inputs for forward flying Drosophila Hot!
Kenneth MacFarlane, Imraan Faruque, J. Sean Humbert

The choices of insect wing kinematic programs is not well understood, particularly the mechanism by which an insect selects a distortion to achieve flight control. A methodology to evaluate prospective kinematic control inputs is presented based on the reachable states when control actuation was constrained to a unit of power. The method implements a computationally-derived reduced order model of the insect's flight dynamics combined with calculation of power requirement. Four kinematic input...

Effects of wing deformation on aerodynamic performance of a revolving insect wing Hot!
Ryusuke Noda, Toshiyuki Nakata, Hao Liu

Flexible wings of insects and bio-inspired micro air vehicles generally deform remarkably during flapping flight owing to aerodynamic and inertial forces, which is of highly nonlinear fluid-structure interaction (FSI) problems. To elucidate the novel mechanisms associated with flexible wing aerodynamics in the low Reynolds number regime, we have built up a FSI model of a hawkmoth wing undergoing revolving and made an investigation on the effects of flexible wing deformation on aerodynamic per...

Dynamic flight stability of a model dronefly in vertical flight Hot!
Chong Shen, Mao Sun

The dynamic flight stability of a model dronefly in hovering and upward flight is studied. The method of computational fluid dynamics is used to compute the stability derivatives and the techniques of eigenvalue and eigenvector used to solve the equations of motion. The major finding is as following. Hovering flight of the model dronefly is unstable because of the existence of an unstable longitudinal and an unstable lateral natural mode of motion. Upward flight of the insect is also unstable...

Underlying principle of efficient propulsion in flexible plunging foils Hot!
Xiao-Jue Zhu, Guo-Wei He, Xing Zhang

Passive flexibility was found to enhance propulsive efficiency in swimming animals. In this study, we numerically investigate the roles of structural resonance and hydrodynamic wake resonance in optimizing efficiency of a flexible plunging foil. The results indicates that (1) optimal efficiency is not necessarily achieved when the driving frequency matches the structural eigenfrequency; (2) optimal efficiency always occurs when the driving frequency matches the wake resonant frequency of the ...

Preface: Current research progress on mechanics of high speed rail Hot!
Yujie Wei
Numerical simulation and control of welding distortion for double floor structure of high speed train Hot!
Wen-Chao Dong, Shan-Ping Lu, Hao Lu, Dian-Zhong Li, Li-Jian Rong, Yi-Yi Li

The welding heat source models and the plastic tension zone sizes of a typical weld joint involved in the double floor structure of high speed train under different welding parameters were calculated by a thermal-elastic-plastic FEM analysis based on SYSWELD code. Then, the welding distortion of floor structure was predicted using a linear elastic FEM and shrinkage method based onWeld Planner software. The effects of welding sequence, clamping configuration and reverse deformation on welding ...

Development of a simulation model for dynamic derailment analysis of high-speed trains Hot!
Liang Ling, Xin-Biao Xiao, Xue-Song Jin

The running safety of high-speed trains has become a major concern of the current railway research with the rapid development of high-speed railways around the world. The basic safety requirement is to prevent the derailment. The root causes of the dynamic derailment of highspeed trains operating in severe environments are not easy to identify using the field tests or laboratory experiments. Numerical simulation using an advanced train-track interaction model is a highly efficient and low-cos...

Analysis of vibration and frequency transmission of high speed EMU with flexible model Hot!
Zun-Song Ren, Guang Yang, Shan-Shan Wang, Shou-Guang Sun

When the operation speed of the high-speed train increases and the weight of the carbody becomes lighter, not only does the sensitivity of the wheel/rail contact get higher, but also the vibration frequency range of the vehicle system gets enlarged and more frequencies are transmitted from the wheelset to the carbody. It is important to investigate the vibration characteristics and the dynamic frequency transmission from the wheel/rail interface to the carbody of the high-speed electric multi...

Energy harvester array using piezoelectric circular diaphragm for rail vibration Hot!
Wei Wang, Rong-Jin Huang, Chuan-Jun Huang, Lai-Feng Li

Generating electric energy from mechanical vibration using a piezoelectric circular membrane array is presented in this paper. The electrical characteristics of the functional array consisted of three plates with varies tip masses are examined under dynamic conditions. With an optimal load resistor of 11 kΩ, an output power of 21.4mW was generated from the array in parallel connection at 150 Hz under a pre-stress of 0.8N and a vibration acceleration of 9.8m/s2. Moreover, the ...

Influences of aerodynamic loads on hunting stability of high-speed railway vehicles and parameter studies Hot!
Xiao-Hui Zeng, Han Wu, Jiang Lai, Hong-Zhi Sheng

The influences of steady aerodynamic loads on hunting stability of high-speed railway vehicles were investigated in this study. A mechanism is suggested to explain the change of hunting behavior due to actions of aerodynamic loads: the aerodynamic loads can change the position of vehicle system (consequently the contact relations), the wheel/rail normal contact forces, the gravitational restoring forces/moments and the creep forces/moments. A mathematical model for hunting stability incorpora...

Theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains Hot!
Ning Zhu, Shou-Guang Sun, Qiang Li, Hua Zou

One of the major problems in structural fatigue life analysis is establishing structural load spectra under actual operating conditions. This study conducts theoretical research and experimental validation of quasi-static load spectra on bogie frame structures of high-speed trains. The quasistatic load series that corresponds to quasi-static deformation modes are identified according to the structural form and bearing conditions of high-speed train bogie frames. Moreover, a force-measuring fr...

Sand particle dislodgement in windblown sand
Tian-Li Bo, Zheng Li, Xiao-Jing Zheng
The incipient motion of sand particle from sand bed plays a very important role in the prediction of windblown sand. In this paper, we proposed a new method for predicting the incipient motion of sand particle based on wind speed fluctuation as follows, when the wind speed is larger than the critical wind speed, if the total impulse on sand particle is larger than the critical impulse, incipient motion of sand particle would take place, otherwise if not. Furthermore, from the analysis of entrain...
Evaluation of strongly singular domain integrals for internal stresses in functionally graded materials analyses using RIBEM
Hai-Feng Peng, Jian Liu, Qiang-Hua Zhu, Ch. Zhang
An accurate evaluation of strongly singular domain integral appearing in the stress representation formula is a crucial problem in the stress analysis of functionally graded materials using boundary element method. To solve this problem, a singularity separation technique is presented in the paper to split the singular integral into regular and singular parts by subtracting and adding a singular term. The singular domain integral is transformed into a boundary integral using the radial integrati...
The Mexican hat effect on the delamination buckling of a compressed thin film
Yin Zhang, Yun Liu
Because of the interaction between film and substrate, the film buckling stress can vary significantly, depending on the delamination geometry, the film and substrate mechanical properties. The Mexican hat effect indicates such interaction. An analytical method is presented, and related dimensional analysis shows that a single dimensionless parameter can effectively evaluate the effect.
Stability analyses of the mass abrasive projectile high-speed penetrating into concrete target. Part I: Engineering model for the mass loss and nose-blunting of ogive-nosed projectiles
Hao Wu, Xiao-Wei Chen, Li-Lin He, Qin Fang
The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator, obviously reducing the penetration efficiency of penetrator. Provided that the work of friction between projectile and target is totally transformed into the heat to melt penetrator material at its nose surface, an engineering model is established for the mass loss and nose-blunting of the ogive-nosed proj...
Stability analyses of the mass abrasive projectile high-speed penetrating into concrete target. Part II: Structural stability analyses
Hao Wu, Xiao-Wei Chen, Qin Fang, Li-Lin He
The initial oblique and attacking angles as well as the asymmetrical nose abrasion may lead to bending or even fracture of a projectile, and the penetration efficiency decreases distinctly. The structural stability of a high-speed projectile non-normally penetrating into concrete and the parametric influences involved are analyzed with the mass abrasion taken into account. By considering the symmetrical or asymmetrical nose abrasion as well as the initial oblique and attacking angles, both the a...
A local pseudo arc-length method for hyperbolic conservation laws
Xing Wang, Tian-Bao Ma, Hui-Lan Ren, Jian-Guo Ning
A local pseudo arc-length method (LPALM) for solving hyperbolic conservation laws is presented in this paper. The key idea of this method comes from the original arc-length method, through which the critical points are bypassed by transforming the computational space. The method is based on local changes of physical variables to choose the discontinuous stencil and introduce the pseudo arc-length parameter, and then transform the governing equations from physical space to arc-length space. In or...
Design of low-energy transfer from lunar orbit to asteroid in the Sun-Earth-Moon system
Ya-Min Wang, Dong Qiao, Ping-Yuan Cui
Asteroid exploration trajectories which start from a lunar orbit are investigated in this work. It is assumed that the probe departs from lunar orbit and returns to the vicinity of Earth, then escapes from the Earth by performing a perigee maneuver. A low-energy transfer in Sun-Earth- Moon system is adopted. First, the feasible region of lowenergy transfer from lunar orbit to perigee within 5 000 km height above the Earth surface in Sun-Earth-Moon system is calculated and analyzed. Three transfe...
Blended skip entry guidance for low-lifting lunar return vehicles
Zong-Fu Luo, Hong-Bo Zhang, Guo-Jian Tang
A skip entry guidance algorithm blending numerical predictor-corrector and nominal trajectory tracking is presented for lunar return vehicles. The guidance is decoupled into longitudinal and lateral channels. A piecewise bank-vs-energy magnitude profile and a sign profile are adopted in the skip phase. A magnitude parameter is used to adjust the predicted downrange, and a pseudo-crossrange at the beginning of the final phase is selected as the lateral control variable. Prediction biases of both ...
Dynamical analysis and performance evaluation of a biped robot under multi-source random disturbances
Chun-Biao Gan, Chang-Tao Ding, Shi-Xi Yang
During bipedal walking, it is critical to detect and adjust the robot postures by feedback control to maintain its normal state amidst multi-source random disturbances arising from some unavoidable uncertain factors. The radical basis function (RBF) neural network model of a five-link biped robot is established, and two certain disturbances and a randomly uncertain disturbance are then mixed with the optimal torques in the network model to study the performance of the biped robot by several eval...
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