2012年01期 (共 篇) 引用文章 全选
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This paper presents a canonical Hamiltonian model of liquid sloshing for the container coupled with spacecraft. Elliptical shape of rigid body is considered as spacecraft structure.Hamiltonian system is an important form of mechanical system. It mostly used to stabilize the potential shaping of dynamical system. Free surface movement of liquid inside the container is called sloshing.If there is uncontrolled resonance between the motion of tank and liquid-frequency inside the tank then such sloshing can be a reason of attitude disturbance or structural damage of spacecraft.Equivalent mechanical model of simple pendulum or mass attached with spring for sloshing is used by many researchers.Mass attached with spring is used as an equivalent model of sloshing to derive the mathematical equations in terms of Hamiltonian model.Analytical method of Lyapunov function with Casimir energy function is used to find the stability for spacecraft dynamics.Vertical axial rotation is taken as the major axial steady rotation for the moving rigid body.
Multi-modes control method for spacecraft formation establishment and reconfiguration near the libration points
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This paper studies Multi-modes control method for libration points formation establishment and reconfiguration. Firstly,relations between optimal impulse control and Floquet modes are investigated.Method of generating modes is proposed.Characteristics of the mode coefficients stimulated at different time are also given.Studies show that coefficients of controlled modes can be classified into four types,and formation establishment and reconfiguration can be achieved by multi-impulse control with the presented method of generating modes. Then,since libration points formation is generally unstable,mutli-modes keeping control method which can stabilize five Floquet modes simultaneously is proposed.Finally,simulation on formation establishment and reconfiguration are carried out by using method of generating modes and mutli-modes keeping control method. Results show that the proposed control method is effective and practical.
+ 摘要浏览:203 全文浏览：11 全文下载：8
Numerical simulations and experimental research are both carried out to investigate the controlled effect of spanwise oscillating Lorentz force on a turbulent channel flow.The variations of the streaks and the skin friction drag are obtained through the PIV system and the drag measurement system,respectively.The flow field in the near-wall region is shown through direct numerical simulations utilizing spectral method.The experimental results are consistent with the numerical simulation results qualitatively,and both the results indicate that the streaks are tilted into the spanwise direction and the drag reduction utilizing spanwise oscillating Lorentz forces can be realized.The numerical simulation results reveal more detail of the drag reduction mechanism which can be explained,since the spanwise vorticity generated from the interaction between the induced Stokes layer and intrinsic turbulent flow in the near-wall region can make the longitudinal vortices tilt and oscillate,and leads to turbulence suppression and drag reduction.
+ 摘要浏览:107 全文浏览：56 全文下载：12
This paper presents a fundamental gaskinetic study on high speed rarefied jets expanding into vacuum from a cluster of planar exits.Based on the corresponding exact expressions for one planar jet,this paper straightforwardly derives the combined multiple jet flowfield solutions of density and velocity components,however,for the combined temperature and pressure solutions,extra attention shall be practiced.Several direct simulation Monte Carlo simulation results are provided and they validate these analytical solutions of rarefied planar jet flows.
+ 摘要浏览:109 全文浏览：4 全文下载：5
This paper develops a hypersonic aerothermal simulation method for missile slot flow.The finite volume method of structure grid solver is developed for solving Euler and Navier-Stokes equations. The solver includes Park's two temperature model and the air multi-species reaction model.The second-order accuracy TVD numerical method was deduced to compute the hypersonic aeroheating which improves the computational efficiency.Computational results are given to show the high accuracy comparing to the existing experimental data.
+ 摘要浏览:110 全文浏览：65 全文下载：12
Particle based methods can be used for both the simulations of solid and fluid phases in multiphase medium,such as the discrete-element method for solid phase and the smoothed particle hydrodynamics for fluid phase.This paper presents a computational method combining these two methods for solid-liquid medium.The two phases are coupled by using an improved model from a reported Lagrangian-Eulerian method.The technique is verified by simulating liquid-solid flows in a two-dimensional lid-driven cavity.
+ 摘要浏览:114 全文浏览：57 全文下载：10
This paper establishes the velocity field and the adequate shear stress corresponding to the motion of an Oldroyd-B fluid between two infinite coaxial circular cylinders by means of finite Hankel transforms.The flow of the fluid is produced by the inner cylinder which applies a time-dependent longitudinal shear stress to the fluid. The exact analytical solutions,presented in series form in terms of Bessel functions,satisfy all imposed initial and boundary conditions.The general solutions can be easily specialized to give similar solutions for Maxwell,second grade and Newtonian fluids performing the same motion.Finally,some characteristics of the motion as well as the influence of the material parameters on the behavior of the fluid motion are graphically illustrated.
+ 摘要浏览:147 全文浏览：52 全文下载：11
The turtle shell is an amazing structure optimized through the long-term evolution by nature.This paper reports the experimental study on the mechanical property at different levels and locations,and the microstructure of the shell from Trachemys scripta (Red-ear turtle) living in South China.
+ 摘要浏览:108 全文浏览：49 全文下载：9
Tbis letter reviews the adhesive and frictional properties of the first mushroom-shaped adhesive microstructure (MSAMS),which has come a long way from inspiration by the attachment devices evolved in beetles to a large-scale industrial production.It was shown to have an that about twice higher pull-off force compared to a smooth control made from the same material measured on smooth substrates.Pull-off forces measured underwater are even higher than those in air.Moreover,it retained adhesive performance over thousands of attachment cycles and initial adhesive capability could be recovered by washing after being contaminated.In shearing,MSAMS exhibits reduced and stabilized friction in comparison with a smooth control,which demonstrated pronounced stick-slip motion,and shows zero pull-off force in a sheared state,allowing the adhesion to be switched on and off.The presence of a fluid in the contact zone showed adhesion enhancement on both smooth and rough substrates.All these features lead us to conclude that MSAMS may have practical potential in a variety of applications.
+ 摘要浏览:100 全文浏览：26 全文下载：6
Anal fistula is one of the three greatest anorectal diseases with a high prevalence. The traditional treatments(e.g.,surgery) for fistula have limitations due to damage to the internal anal sphincter of patients.With recent advances in biomaterials,treatments based on biomaterial filling (e.g.,scleraprotein injection,fistula plug) have emerged as novel therapies for fistula.The anal fistula plug (e.g.,based on small intestinal submucosa (SIS)) has attracted increasing attention because of short term heaiing rate and biocompatibility.However,challenges remain for this method such as plug falling as observed in clinics.To address this,this paper analyzes the case of SIS falling under physiological condition from mechanical point of view using ANSYS simulation. It then proposes three new geometrical structures for fistula plug and compares their mechanical behavior (e.g.,axial stress,reaction of constraint) with that of clinically used structure (cone shape). Based on the simulation,it optimizes the geometric parameters of fistula plug.The approach developed here can help to improve the design of fistula plug for better clinical treatments.
+ 摘要浏览:105 全文浏览：18 全文下载：4
This paper proposes a 3-dimensional coarse grain model of microtubules and treats the tubulin monomer as a sphere of multiple patches,with parameters chosen to yield experimental values of bending and stretching stiffness.The model has demonstrated the ability to produce the bistability of tubulin sheets,elastic deformation near the tip,and cracking and peeling of protofilaments.This model is expected to take into account the structural and mechanical aspects underlying the physical mechanism of polymerization/depolymerization and dynamic instability of microtubules.
Mechanical properties of crosslinks controls failure mechanism of hierarchical intermediate filament networks
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Intermediate filaments are one of the key components of the cytoskeleton in eukaryotic cells,and their mechanical properties are found to be equally important for physiological function and disease.While the mechanical properties of single full length filaments have been studied,how the mechanical properties of crosslinks affect the mechanical property of the intermediate filament network is not well understood.This paper applies a mesoscopic model of the intermediate network with varied crosslink strengths to investigate its failure mechanism under the extreme mechanical loading.It finds that relatively weaker crosslinks lead to a more flaw tolerant intermediate filament network that is also 23％ stronger than the one with strong crosslinks.These findings suggest that the mechanical properties of interfacial components are critical for bioinspired designs which provide intriguing mechanical properties.
+ 摘要浏览:119 全文浏览：31 全文下载：8
Self-assembled nanostructures of lipids and nanoparticles hold great promise for applications in such fields as nanomedicine.This paper uses the self-consistent field theory to investigate the self-assembly behavior of lipid molecules and nanoparticles with different shapes in an aqueous solution. It is found that the lipid molecules can form monolayered and bilayered nanostructures around the nanoparticles with different shapes (e.g.,triangular,square,hexagonal and octangular).With decreasing the size of nanoparticles or increasing the number of polygon edges,the shape of lipid layers will approach an approximately spherical shape.These findings may help to predict and design novel drug delivery nanocarriers.
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Volumetric elastic modulus (VEM) is an important parameter in biophysics and biomechanics of plants for in particular understanding cell growth. This paper proposes a new relation that can be used for precisely determining VEM.With the aid of this relation,it shows that the exponential approximation of the pressure-volume relationship adopted in most of the literatures in this field may lead to serious errors on VEM.
+ 摘要浏览:97 全文浏览：11 全文下载：3
This paper aims at developing a stochastic-elastic model of a soft elastic body adhering on a wavy surface via a patch of molecular bonds.The elastic deformation of the system is modeled by using continuum contact mechanics,while the stochastic behavior of adhesive bonds is modeled by using Bell's type of exponential bond association/dissociation rates.It is found that for sufficiently small adhesion patch size or stress concentration index,the adhesion strength is insensitive to the wavelength but decreases with the amplitude of surface undulation,and that for large adhesion patch size or stress concentration index,there exist optimal values of the surface wavelength and amplitude for maximum adhesion strength.
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+ 摘要浏览:101 全文浏览：50 全文下载：10
It is very important to measure local deformations for an in-depth understanding of mechanical properties and fracture mechanism of structural and functional materials.In this paper,different types of model grid fabrication methods and many types of electron Moiré methods using an electron beam drawing system,a scanning electron microscope or a focus ion beam are reported,together with their applications in the measurement of deformations occurring in various engineerings and materials science research.