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Acta Mechanica Sinica
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15 February 2012, Volume 34 Issue 1
Around the mechanics
ACCOMMODATION THEORIES AND MECHANICAL PROPERTIES OF HUMAN LENS
SONG Fan, ZHAO Xiyu, DU Ruiqi, WEI Jiachen, XU Xianghong
2012, 34(1): 1-9. doi:
As the core component of optical system, human lens accommodation is realized through the cooperation of ciliary, zonular and lens itself. Ciliary dragging the connected zonular leads to the lens deformation change which finally alters optical power. Through this process, light can focus on the retina and result in visual sense. Actually, lens accommodation is a mechanical process that affects visual quality and the prevalent eye degenerative diseases-presbyopia. This paper illustrates various lens accommodation theories as well as their developments, and also summarizes the mechanical properties of lens.
REVIEW ON COMPUTATIONAL EXPLOSION MECHANICS
NING Jianguo, WANG Meng
2012, 34(1): 10-19,69. doi:
Exact solution of explosion problem cannot be achieved in most cases because of its strong nonlinearity. And data gained from experiments are very limited because explosion is a strong physical course finished in short duration. Simulation of explosion mechanics and related research has greatly promoted rapid development of both explosion mechanics and weaponry. This paper mainly reviews on explosion mechanics, dynamic constitutive model of material and related engineering applications.
SIMULATION BASED ON DISCRETE ELEMENT METHOD AND EXPERIMENT ON FLOW AND PACKING BEHAVIOR OF PARTICLES
LI Wanyi, ZENG Pan, LEI Liping, LIN Dachao
2012, 34(1): 20-26. doi:
The particle flow and packing is an important issue in engineering. In this paper, a series of experiments are designed to measure the physical parameters of particles, such as density, restitution coefficient, friction coefficient and stiffness coefficient. With the hoisting bucket of the blast furnace top in view, the flow behavior of mono-sized particles is simulated by discrete element method (DEM). Results show that the force distribution in the discrete particles is non-uniform, and the strong force chains are parallel to the surface of the left inferior part of the hoisting bucket. A hoisting bucket experimental model with adjusting devices is established for experiments. It is shown that experimental results agree well with DEM results.
SIZE-DEPENDENCE OF SHEAR MODULUS OF A DRYING PARTICULATE FILM FABRICATED BY CONTROLLED VERTICAL DRYING DEPOSITION
CAO He, LAN Ding, WANG Yuren
2012, 34(1): 27-30. doi:
In our previous work, we reported that the initial crack spacing depends on the colloidal particle size. However, crack patterns must be related to the mechanical properties of the drying films, which has not been sufficiently explored. The fracture theories for drying colloidal films and the crystal fracture theory are used in this paper to study of a drying film formed by the controlled vertically drying deposition. We found that the shear modulus also depends on colloidal particle size. Further more, comparing our results with the variation of the dry particulate film's shear modulus, a remarkable discrepancy is found for this size-dependant behavior while the particle radius decreases. This remarkable discrepancy shows that the mechanical behaviors of drying particulate films are determined not only by the structure of the solid part but also by the liquid part.
THE FORMATION OF WIND PROFILE IN ENVIRONMENT SIMULATION LABORATORY
ZENG Bo, ZHANG Hongyan, MENG Qinglong
2012, 34(1): 31-34. doi:
The numerical simulation and the experimental test are used to investigate the formation of the wind profile of the neutral atmospheric surface layer by screens in the environment simulation laboratory. Taking the screen layout program with variations of porosity of screens as a guide, 30 meshes and 16 meshes with fixed porosity of screens with respective heights of four screen layer collocations are selected. The complex screens are simplified as the porous media model and the k-
varepsilon model in using the software Fluent. The results show that the screens can be simulated with the porous media and the wind profile can be formed by the compounding of fixed porosity screens in a short experimental section. The simulation results agree well with those of experiment.
STUDY ON THE AIRCRAFT INTEGRATED CHARACTERS WITH DIFFERENT HEIGHT WINGLETS
ZHANG Jianjun, QIAN Guangpin, YANG Shipu, SI Jiangtao
2012, 34(1): 35-38,30. doi:
This paper considers the wingbody shape with two different types of winglets (the blended winglet and shark winglet) by discretized Reynolds average Navier-Stokes equation and the aero-structure coupled equation. The impact of the different heights of the winglet on the lift-drag ratio, the displacement of the wing pressure center, the weight and the flutter character is studied. The results show that the weight increase of the aircraft structure is smaller than the weight increase of effective loads and that the flutter velocity decrease is adjustable within the safety range. Therefore, it is suggested that the selection of the winglet height should have a priority over the lift-drag ratio character during the trade off between aero and weight & flutter in order to have a good drag reduction.
ANALYTICAL SOLUTION FOR BENDING OF SIMPLY SUPPORTED FUNCTIONALLY GRADED BEAM SUBJECTED TO UNIFORM PRESSURE
LI Huadong, ZHU Xi, MEI Zhiyuan, ZHANG Yingjun
2012, 34(1): 39-47. doi:
Based on the semi-inverse stress function method, an analytical solution is obtained for bending of simply supported functionally graded beam subjected to uniform pressure with arbitrary property distribution across the thickness, including explicit analytical expressions of the stress, strain and displacement. Firstly, the system of partial differential equations for the stress function is established based on the fundamental equations for plane stress states, and the expressions of streses are obtained according to the boundary conditions for stresses. Then, the distributions of strains and displacements are obtained according to the constitutive relations of functionally graded materials and displacement boundary conditions. Finally, the proposed solution is validated by comparing the degenerated results for a homogeneous isotropic beam to the classic elastic solution. The distributions of stresses and displacements obtained in this paper are for the functionally graded beam whose material properties obey a power law distribution of the constituent volume fraction, and the effects of top-bottom surfaces'Young's modulus ratio λ and volume fraction exponent n on the variation of the stresses and displacements of the functionally graded beam are discussed.
COMPUTER SIMULATION OF DEFLECTION CURVE SHAPE FOR THE SLENDER, FLEXIBLE, COMPRESSED BAR AFTER BUCKLING
PAN Wenbo, LI Yinshan, LI Tong, LI Xinye
2012, 34(1): 48-51. doi:
A Maple code is developed for the slender, flexible, compressed post-buckling bar. Its deformation curve shape is numerically simulated. Simulations and detailed solutions are given for two cases---the maximum deflection and the closing deflection curve after buckling. Mechanical character of instability after buckling is analyzed and computed. Analysis expression is given; the geometric features of the curve in the equilibrium case after buckling is analyzed and computed. The results indicate that the maximum deflection after buckling and the closing deflection curve are two completely different buckling states.
THE UNCERTAIN MODELING AND VALIDATION FOR A CANTILEVER WITH FLEXIBLE ROOT
CHEN Xueqian, XIAO Shifu, LIU Xin'en, WANG Yujun
2012, 34(1): 52-56. doi:
There are some flexibility and uncertainty in the root of a cantilever with bolt joints. The dynamic equation and the approximate result of the cantilever with flexible parameters are presented in the paper. At the same time, in order to study the uncertainty modeling, the translation and rotation flexible parameters are chosen as the uncertain parameters. Then the flexible parameters are identified according to some modal test results. The mean and standard deviations of flexible parameters are obtained by analyzing the identified results subjected to the normal distribution assumption. The mathematical models of the uncertain parameters varying with the pre-torque are built. The models are validated by other modal test results, and the applicable ranges of the models are obtained according to the results.
PRIMARY RESONANCE OF BEAMS ON ELASTIC FOUNDATIONS SUBJECTED TO LATERAL LOADS
WANG Lianhua, MA Jianjun, LIU Qijian
2012, 34(1): 57-61. doi:
The nonlinear vibration of finite-length beams on the Winkler foundation subjected to the lateral loads is investigated. Based on the Winkler foundation model and the Euler-Bernoulli beam theory, the nonlinear in-plane motion equation of the finite-length beam on the Winkler foundation is obtained. The approximate solution of the finite-length beam for the case of the primary resonance is obtained by the Galerkin method and the method of multiple scales. To illustrate the characteristics of the primary resonance, the effects of major parameters on the frequency-response curves of the beam on the elastic foundation are studied, such as, the slenderness ratio, the stiffness coefficient of the foundation, the amplitude of the excitation and the damping coefficient. Comparing with the non-resonant response of the beam, the effect of the primary resonance on the actual dynamic response is analyzed. The numerical results show that the frequency-response curves of the beam have jump and delay; the damping term plays a very important role in the primary resonance of the beam, the primary resonance significantly increases the amplitude of the steady state response.
APPLICATION OF SYMBOLIC COMPUTATION IN NATURAL VIBRATION ANALYSIS OF CABLES AND SUSPENDERS
LIU Zhijun, RUI Xiaoting, YANG Haigen
2012, 34(1): 62-65. doi:
A sufficiently high computational accuracy is achieved by symbolic computation to obtain a high precision solution for the frequency equation and the numerical calculation for mode functions of cables and suspenders fixed at one or two ends. Based on practical examples, the influence of boundary conditions on vibration modes of cables and suspenders is comparatively analyzed.
NONLINEAR DYNAMIC MODEL ON STEEL-WIRE ISOLATOR
BAN Shuhao, LI Xiaoyan, JIANG Xuedong, HU Aiping
2012, 34(1): 66-69. doi:
A nonlinear dynamic model for the isolation system of steel-wire isolators is constructed with the introduction of a softened frequency coefficient based on static mechanical properties for steel-wire isolators. The dynamic responses to impulse and random vibrations of this system are investigated with the nonlinear dynamic model. The simulated results are discussed. The theoretical analyses and simulated results show that the nonlinear dynamic model with the softened frequency coefficient has a better isolation effect compared to the linear Hookean spring model.
TOPOLOGICAL OPTIMIZATION FOR CONVEYOR LINK PLATE OF STRICKLE RECLAIMER WITH STRESS CONSTRAINTS UNDER MULTIPLE LOADING CASES
HUANG Fei, PENG Gaoming, HE Hao, SHI Limin
2012, 34(1): 70-74. doi:
The ICM method is used to build topological optimization model for conveyor link plate of cantilever strickle reclaimer. A multiple-level and load magnification strategy was introduced to solve ill loading problem, which often occurs in topological optimization with stress constraint for continuum structure in multiple loads. Element's live and death method in ANSYS software associated with ICM method and multiple-level strategy are used to kill, reserve and resurge element. At last, topological optimization for conveyor link plate was accomplished, and light weight design was achieved through APDL in ANSYS.
MECHANICAL BEHAVIOR OF COMPOSITE REPAIRED COMPONENTS UNDER CORROSION ENVIRONMENT
WANG Haowei, LIU Yuanhai, LIU Chengchen
2012, 34(1): 75-79,74. doi:
The center cracked LY12CZ aluminum alloy plates were adhesively bonded with composite patches, and the tensile strength, the fatigue life and the crack growth during fatigue under air environment and accelerated pre-corrosion environment were investigated experimentally. The experimental results show that both the static strength and the fatigue life of the repaired aluminum substrates are significantly increased for the bonded composite patches, and the short-term pre-corrosion environment does not have a notable effect on the mechanical performance of composite repaired components. Also, a simple fatigue crack growth life prediction model, based on Paris formula and Rose's analytical solution, is proposed to predict the fatigue behavior of the repaired plates under air and pre-corrosion environments. The result shows a good quantitative agreement with experimental data.
COMBINATORIAL OPTIMAL ALGORITHM FOR SENSOR ARRANGEMENT IN STRUCTURAL HEALTH MONITORING SYSTEM
LU Lingling, WANG Xi, HUANG Chenguang
2012, 34(1): 80-84,51. doi:
In this paper, we present an effective optimization method of sensor arrangement for monitoring the dynamic response of thin flexible structures like plates and shells. The proposed method consists of genetic algorithm, modal kinetic energy and modal assurance criterion. A simplified wing structure is used to evaluate the effectiveness of the method. The numerical analysis and experimental results demonstrate that the proposed optimization algorithm can be used to determine effectively sensor arrangements. Firstly, the modal kinetic energy algorithm is used to catch the degree of freedom of the dynamic response of the structure with a large amplitude, and effectively improves the signal-noise ratio during the health monitoring. Secondly, the combination of genetic algorithm and modal assurance criterion can effectively ensure the independence of modal shapes, and provide more modal information of the structure, such as the modal frequency and the modal shape. The damage detection and the estimation of the residual life are more accurate and effective by using the proposed optimization method.
A PRELIMINARY STUDY OF A NOVEL TWO-DIMENSION ELECTROMAGNETIC PARTICLE VELOCITY GAUGE UNDER DIVERGENT WAVE
WU Zutang, LI Jin, WANG Zhanjiang, ZHANG Jingsen, HUANG Xiaofei
2012, 34(1): 85-88,61. doi:
To study the electromagnetic test technique for the two-dimension particle velocity under divergent waves, a novel two-dimension electromagnetic particle velocity gauge configuration is designed based on the magnetic characteristic of Helmholtz coil under a pulse current. Its performance is verified through a comparison of the electromagnetic measurement between one-dimension and two-dimension particle velocities in PMMA. The experiment shows that it is efficient for the propagation measurement of divergent waves in an inhomogeneous medium even with interfaces, grooves and joints.
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