Acta Mechanica Sinica
     Acta Mechanica Sinica
  Acta Mechanica Sinica--2014, 30 (5)   Published: 20 September 2014
THEME ARTICLES ON ORBITS AROUND ASTEROID
Low-thrust trajectory optimization in a full ephemeris model Hot!
Xing-Shan Cai, Yang Chen, Jun-Feng Li
Abstract

The low-thrust trajectory optimization with complicated constraints must be considered in practical engineering. In most literature, this problem is simplified into a two-body model in which the spacecraft is subject to the gravitational force at the center of mass and the spacecraft's own electric propulsion only, and the gravity assist (GA) is modeled as an instantaneous velocity increment. This paper presents a method to solve the fuel-optimal problem of low-thrust trajectory with complica...

Time-optimal rendezvous transfer trajectory for restricted cone-angle range solar sails Hot!
Jing He, Sheng-Ping Gong, Fang-Hua Jiang, Jun-Feng Li
Abstract

The advantage of solar sails in deep space exploration is that no fuel consumption is required. The heliocentric distance is one factor influencing the solar radiation pressure force exerted on solar sails. In addition, the solar radiation pressure force is also related to the solar sail orientation with respect to the sunlight direction. For an ideal flat solar sail, the cone angle between the sail normal and the sunlight direction determines the magnitude and direction of solar radiation pr...

FLUID MECHANICS
Dynamics of low-speed streak evolution and interaction in laminar boundary layer
Si-Chao Deng, Chong Pan, Jin-Jun Wang
Abstract

The present paper presents an experimental effort on the regeneration process of two low-speed laminar streaks in a zero-pressure-gradient laminar boundary layer. Two vertical thin wires separated by a spanwise distance of 30mm are used to introduce disturbances of two rolls of transitional Kármán vortex street to the downstream boundary layer. Both hydrogen bubble visualization and particle image velocimetry (PIV) measurement show that two lowspeed streaks are induced through l...

Transient simulation of a pump-turbine with misaligned guide vanes during turbine model start-up
Ye-Xiang Xiao, Ruo-Fu Xiao
Abstract

Experimental studies of a model pump-turbine S-curve characteristics and its improvement by misaligned guide vanes (MGV) were extended to prototype pump turbine through 3-D transient flow simulations. The unsteady Reynolds-averaged Navier-Stokes equations with the SST turbulence model were used to model the transient flow within the entire flow passage of a reversible pump-turbine with and without misaligned guide vanes during turbine model start-up. The unstable S-curve and its improvement b...

On the horizontal distribution of algal-bloom in Chaohu Lake and its formation process
Yuan-Ying Chen, Qing-Quan Liu
Abstract

Based on the remote sensing images of algae, the present work analyzes the horizontal distribution characteristics of algal blooms in Chaohu Lake, China, which also reveals the frequency of algal blooms under different wind directions. Further, an unstructured-grid, three-dimensional finite-volume coastal ocean model (FVCOM) is applied to investigate the wind-induced currents and the transport process to explain the reason why algal blooms occur at the detected places. We first deduce the pri...

Fully nonlinear modeling of radiated waves generated by floating flared structures
Bin-Zhen Zhou, De-Zhi Ning, Bin Teng, Ming Zhao
Abstract

The nonlinear radiated waves generated by a structure in forced motion, are simulated numerically based on the potential theory. A fully nonlinear numerical model is developed by using a higher-order boundary element method (HOBEM). In this model, the instantaneous body position and the transient free surface are updated at each time step. A Lagrangian technique is employed as the time marching scheme on the free surface. The mesh regridding and interpolation methods are adopted to deal with ...

An experimental research on surface oscillation of buoyant-thermocapillary convection in open cylindrical annuli
Li Zhang, Li Duan, Qi Kang
Abstract

An experiment is carried out on the surface oscillation of buoyant-thermocapillary convection in an open cylindrical annulus. When the radial temperature difference ΔT reaches a critical value ΔTc, a regular oscillation appears and soon disappears on the open surface, which varies when the liquid layer's thickness h and temperature difference ΔT are varied. With growth of ΔT, dominant frequency of the visible osci...

SOLID MECHANICS
Artificial boundary conditions for Euler-Bernoulli beam equation
Shao-Qiang Tang, Eduard G. Karpov
Abstract

In a semi-discretized Euler-Bernoulli beam equation, the non-nearest neighboring interaction and large span of temporal scales for wave propagations pose challenges to the effectiveness and stability for artificial boundary treatments. With the discrete equation regarded as an atomic lattice with a three-atom potential, two accurate artificial boundary conditions are first derived here. Reflection coefficient and numerical tests illustrate the capability of the proposed methods. In particular...

Dislocation stability in three-phase nanocomposites with imperfect interface
Ying-Xin Zhao, You-Wen Liu, Qi-Hong Fang
Abstract

Interface imperfection can significantly affect the mechanical properties and failure mechanisms as well as the strength and toughness of nanocomposites. The elastic behavior of a screw dislocation in nanoscale coating with imperfect interface is studied in the three-phase composite cylinder model. The interface between inner nanoinhomogeneity and intermediate coating is assumed as perfectly bonded. The bonding between intermediate coating and outer matrix is considered to be imperfect with t...

Propagation behavior of elastic waves in one-dimensional piezoelectric/piezomagnetic phononic crystal with line defects
Y. Pang, F.-Y. Jiao, J.-X. Liu
Abstract

Using a stiffness matrix method, we investigate the propagation behaviors of elastic waves in one-dimensional (1D) piezoelectric/piezomagnetic (PE/PM) phononic crystals (PCs) with line defects by calculating energy reflection/transmittion coefficients of quasi-pressure and quasi-shear waves. Line defects are created by the replacement of PE or PM constituent layer. The defect modes existing in the first gap are considered and the influences on defect modes of the material properties and volum...

Theoretical analysis of the sound absorption characteristics of periodically stiffened micro-perforated plates
Hai-An Zhou, Xiao-Ming Wang, Yu-Lin Mei
Abstract

The vibro-acoustic responses and sound absorption characteristics of two kinds of periodically stiffened micro-perforated plates are analyzed theoretically. The connected periodical structures of the stiffened plates can be ribs or block-like structures. Based on fundamental acoustic formulas of the micro-perforated plate of Maa and Takahashi, semi-analytical models of the vibrating stiffened plates are developed in this paper. Approaches like the space harmonic method, Fourier transforms and...

DYNAMICS, VIBRATION, AND CONTROL
Stability and oscillations in a slow-fast flexible joint system with transformation delay
Shan-Ying Jiang, Jian Xu, Yao Yan
Abstract

Flexible joints are usually used to transfer velocities in robot systems and may lead to delays in motion transformation due to joint flexibility. In this paper, a linkrotor structure connected by a flexible joint or shaft is firstly modeled to be a slow-fast delayed system when moment of inertia of the lightweight link is far less than that of the heavy rotor. To analyze the stability and oscillations of the slowfast system, the geometric singular perturbation method is extended, with both s...

Dynamics of a prey-predator system under Poisson white noise excitation
Shan-Shan Pan, Wei-Qiu Zhu
Abstract

The classical Lotka-Volterra (LV) model is a well-known mathematical model for prey-predator ecosystems. In the present paper, the pulse-type version of stochastic LV model, in which the effect of a random natural environment has been modeled as Poisson white noise, is investigated by using the stochastic averaging method. The averaged generalized Itô stochastic differential equation and Fokker-Planck-Kolmogorov (FPK) equation are derived for prey-predator ecosystem driven by Poisson wh...

Coupled lateral-torsional-axial vibrations of a helical gear-rotor-bearing system
Chao-Feng Li, Shi-Hua Zhou, Jie Liu, Bang-Chun Wen
Abstract

Considering the axial and radial loads, a mathematical model of angular contact ball bearing is deduced with Hertz contact theory. With the coupling effects of lateral, torsional and axial vibrations taken into account, a lumped-parameter nonlinear dynamic model of helical gearrotor- bearing system (HGRBS) is established to obtain the transmission system dynamic response to the changes of different parameters. The vibration differential equations of the drive system are derived through the La...

BIO-MECHANICS
Biomechanical and dynamic mechanism of locust take-off
Dian-Sheng Chen, Jun-Mao Yin, Ke-Wei Chen, Zhen Li
Abstract

The biomimetic locust robot hopping vehicle has promising applications in planet exploration and reconnaissance. This paper explores the bionic dynamics model of locust jumping by using high-speed video and force analysis. This paper applies hybrid rigid-flexible mechanisms to bionic locust hopping and studies its dynamics with emphasis laid on the relationship between force and jumping performance. The hybrid rigid-flexible model is introduced in the analysis of locust mechanism to address t...

 
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