Structure design and traction trafficability analysis of multi-posture wheel-legs bionic walking wheels for sand terrain

Nowadays, the existing walking wheels still have problems with the wheel-legs structure and the traction trafficability on the loose sand. It is commonly believed that African ostrich (Struthio camelus) is a kind of bipedal species with superior running performance on the sandy environment. Being enlightened by this, four bionic walking wheels (herringbone wheel, in-line wheel, V-shaped wheel and combination wheel) were designed and tested by imitating the structure and posture of ostrich’s feet travelling on sand. The results showed that when the wheel load was 20, 30 and 50N respectively and the slip ratio was less than 35%, the herringbone wheel had better traction trafficability than that of other wheels. When the wheel load was 30, 50 and 70N and the slip ratio was more than 35%, the in-line wheel had better performance than that of other wheels. It was shown in this thesis that the bionic walking wheels designed with the multi-posture wheel-legs and the simple structure could reduce the soil resistance and the disturbance to sand, thereby achieving a superior performance of traveling on sand. In addition, a new idea and research method for designing of walking mechanism on soft terrain has been provided in this thesis.     

Direct computation of thermodynamic properties of chemically reacting air with consideration to CFD

This paper details a two‐equation procedure to calculate exactly mass and mole fractions, pressure, temperature, specific heats, speed of sound and the thermodynamic and jacobian partial derivatives of pressure and temperature for a five‐species chemically reacting equilibrium air. The procedure generates these thermodynamic properties using as independent variables either pressure and temperature or density and internal energy, for CFD applications. An original element in this procedure consists in the exact physically meaningful solution of the mass‐fraction and mass‐action equations. Air‐equivalent molecular masses for oxygen and nitrogen are then developed to account, within a mixture of only oxygen and nitrogen, for the presence of carbon dioxide, argon and the other noble gases within atmospheric air. The mathematical formulation also introduces a versatile system non‐dimensionalization that makes the procedure uniformly applicable to flows ranging from shock‐tube flows with zero initial velocity to aerothermodynamic flows with supersonic/hypersonic free‐stream Mach numbers. Over a temperature range of more than 10000 K and pressure and density ranges corresponding to an increase in altitude in standard atmosphere of 30000 m above sea level, the predicted distributions of mole fractions, constant‐volume specific heat, and speed of sound for the model five species agree with independently published results, and all the calculated thermodynamic properties, including their partial derivatives, remain continuous, smooth, and physically meaningful. Copyright © 2003 John Wiley & Sons, Ltd.     

Data processing methodology in the characterization of the mechanical properties of terrain

The methodology for processing load-sinkage and shear test data obtained using the bevameter is examined. A weigthed least squares technique is proposed for deriving terrain values from experimental data. To streamline data processing time, a portable automatic data processing unit for the bevameter has been developed. The basic features and functions of the unit are described. The automatic data processing unit, together with associated bevameter, has undergone extensive field trials. They have been employed to measure the properties of various types of natural terrain. The results indicate that this new system can provide a basis for the development of a reliable, convenient and standardized technique for identifying terrain properties in relation to off-road mobility.     

Mechanical properties of double-stranded DNA biofilm with Gaussian distribution简

In microcantilever-based label-free biodetection technologies, deflection changes induced by adsorptions of double-stranded DNA （dsDNA） molecules on Au-layer surface are greatly affected by the mechanical, thermal and electrical properties of DNA biofilm. In this paper, the elastic properties of dsDNA biofilm are studied. First, the Parsegian＇s empirical potential based on a mesoscopic liq- uid crystal theory is employed to describe the interaction energy among coarse-grained DNA cylinders. Then, con- sidering a Gaussian distribution of DNA interaxial distance, the thought experiment method is used to derive an analyti- cal expression for Young＇s modulus of DNA biofilm with a stochastic packing pattern for the first time. Results show that Young＇s modulus of DNA biofilm is on the order of 10 MPa. These findings could provide a simple and effective method to evaluate the mechanical properties of soft biofilm on snbstrate.     

Pressure distribution in the neighborhood of a growing fracture with a constant wedge force

Exact solutions of the problem of the pressure field in the neighborhood of a hydraulic fracture developing in accordance with a square root law in a permeable porous medium with a constant wedge force acting on the fracture edges are constructed. A particular case admitting a self-similar formulation and an exact solution and, as a result, the fairly complete investigation, is considered. The solution constructed holds for an arbitrary self-similar pressure distribution over the fracture edges. The problem considered reduces to the solution of a mixed boundary-value problem for the Helmholtz equation. The solution found can be useful both in itself and for testing more universal numerical algorithms.     

Mechanical properties in relation to vehicle mobility of Sepang peat terrain in Malaysia

An analytical framework for determining the mechanical properties of peat and predicting the tractive performance of tracked vehicle is presented. It takes into account the load-sinkage and shearing characteristics of peat as well as all major design parameters of tracked vehicle. An experimental study on the mechanical properties of peat soil was conducted at Sepang area, Selangor, Malaysia. The stiffness values of surface mat and underlying weak peat deposit from load-sinkage test were determined by specially made bearing capacity apparatus. The mean values of surface mat stiffness before and after drainage were found to be 31 and 45.62 kN/m³, respectively and the mean values of underlying peat stiffness before and after drainage were found to be 252 and 380.20 kN/m³, respectively. The mean value of the internal frictional angle, cohesiveness and shear deformation modulus of the peat soil sample were determined using a direct shear box apparatus in the laboratory. The mean values of internal friction angle, cohesiveness and shear deformation modulus before and after drainage were found to be 22.80° and 24.31°, 2.63 and 2.89 kN/m², and 1.21 and 1.37 cm, respectively.     

Analysis of deadweight oscillation in a deadweight force machine using a build-up system

This paper describes a build-up system that measures the deadweight oscillation in a deadweight force machine. When a build-up system is calibrated using a deadweight machine, the oscillating signal components of force transducers in the build-up system are strongly related to the motion of deadweight. The authors have, therefore, proposed a model based on the analysis of oscillating signals of force transducers to measure the deadweight oscillation. The analysis of the force transducer signals and the displacement sensor signals shows the validity of the proposed model. The authors have also investigated the behavior of deadweight motion for a deadweight force machine of 498 kN using the proposed model.     

Development of a machine integrated strain-based contact force sensor for pad foot soil compactors

An investigation was undertaken to explore the use of measurable pad strains on a non-vibratory pad foot roller to provide real time continuous evidence of compaction and contact force. Individual pads were instrumented with strain gages in a pattern chosen based on pad finite element analysis (FEA). Different pad–soil contact stress distributions were modeled to simulate a range of soil conditions. The FEA revealed that the contact stress distribution has a significant influence on the observed pad strain field, suggesting soil specific interpretation of pad strains in order to determine contact force. Results from uniaxial laboratory testing of pad loading on dry sand verified the FEA, i.e., experimental strains generally matched within 15% of FEA strains. The contact stress distribution was measured using tactile pressure sensors and found to be moderately parabolic. A soil specific empirical calibration factor relating vertical sidewall strains to contact force was determined. Field testing was performed on the dry sand with multiple instrumented pads installed on a Caterpillar CP56 roller. Pad strain magnitudes increased up to 250% during compaction from repeated passes of the roller. Using the empirical calibration factor, the estimated contact force was shown to increase with compaction, represented by the independently-measured soil unit weight.     

Mechanical properties of unidirectional nanocomposites with non-uniformly or randomly staggered platelet distribution

Unidirectional nanocomposite structures with parallel staggered platelet reinforcements are widely observed in natural biological materials. The present paper is aimed at an investigation of the stiffness, strength, failure strain and energy storage capacity of a unidirectional nanocomposite with non-uniformly or randomly staggered platelet distribution. Our study indicates that, besides the volume fraction, shape, and orientation of the platelets, their distribution also plays a significant role in the mechanical properties of a unidirectional nanocomposite, which can be quantitatively characterized in terms of four dimensionless parameters associated with platelet distribution. It is found that, compared with other distributions, stairwise and regular staggering of platelets produce overall the most balanced mechanical properties, which might be a key reason why these structures are most widely observed in nature.     

Fourier-transform moiré method with consideration of misalignment

We have previously proposed a moiré method using the Fourier transform of a fringe or grating line pattern recorded by a TV camera. It performs automated and accurate analysis of displacement, strain, strain rate and height distributions. In the method, the direction of the grating lines before deformation must co-incide with the direction of the scanning lines of the TV camera. In this paper, the method is extended to include the case of misalignment in which the direction of the grating lines is different from that of the scanning lines of the TV camera. By using this method, positioning of the TV camera is simplified because it does not require precise alignment of the TV camera. This method is useful to analyze fringe patterns with carrier fringes that are introduced to aid in the interpolation of brightness distribution.     

Digital solution of temperature distribution in an electrical machine using network analogy

An analytical method which predicts the temperature rise of the rotor and stator packets, and the associated endwindings of an induction motor is presented. The method also enables the prediction of the temperature rise of the coolant at discrete points in its flow path through the motor.     

横向力作用下悬臂梁固定端应力分布研究

在弹性力学Hamilton体系中,利用解析法,考虑圣维南原理所覆盖的解,对横向力作用下悬臂梁固定端应力分布问题进行研究,并对计算结果进行分析。研究结果表明,辛体系解析法采用对偶的二类变量求解,能很好地处理各种复杂边界条件,并且对此类问题的分析具有优越性,计算精度较高。该方法对其他边界问题的研究也具有指导意义。     

Slip-based experimental studies of a vehicle interacting with natural snowy terrain

As longitudinal slip affects vehicle–pavement interactions on roads and hard surfaces, so too does it play an important role in interactions between vehicles and soft terrains, including snow. Although many slip-based models have been developed recently for tire–snow interactions (e.g., [1] and references cited therein), these models have only been partially validated, due to a lack of relevant experimental data. This paper presents comprehensive data from tests that were performed using a newly-developed test vehicle traversing natural snowy terrain, over a wide range of values for longitudinal slip, vertical load and torque via an effective accelerate/brake maneuver. Drawbar pull, motion resistance, wheel states and tire stiffness were presented as a function of slip; tire sinkage was obtained using a laser profilometer; strength and depth of snow were found using a snow micropenetrometer. The effects of the rear tire going over snow compacted by the front tire were also studied. The maximum traction force normalized by the vertical load is found to be ≈0.47, maximum motion resistance normalized by the vertical load is ≈0.4. Comparison of the trend and order-of-magnitude of test results with those from existing slip-based numerical model [1] shows good comparison in motion resistance, tire sinkage, and longitudinal stiffness, but indicates that a better traction model is needed to improve the comparison.     

A new car-following model with consideration of inter-vehicle communication

In this paper, we construct a new car-following model with inter-vehicle communication (IVC) to study the driving behavior under an accident. The numerical results show that the proposed model can qualitatively describe the effects of IVC on each vehicle’s speed, acceleration, movement trail, and headway under an accident and that the new model can overcome the full velocity difference (FVD) model’s shortcoming that collisions occur under an accident, which illustrates that the new model can better describe the driving behavior under an accident than the FVD model.     

Non-propagating solitary waves with the consideration of surface tension

In this paper, the governing equation for the non-propagating solitary waves, similar to the cubic Schrödinger equation, is derived by the multiple scales with the consideration of surface tension. The non-propagating solitary wave solution is given. It is explained by the capillary-gravity wave theory that the crests are sharpened and the troughs are flattened in the transversal harmonic of the non-propagating solitary waves. On σ～kh plane, two parameter regions are obtained in which the non-propagating solitary wave can occur, but all existing experimental parameters are in region 1 (Fig. 1).     

D型战斗部破片飞散性及威力场快速计算

破片威力场的快速计算是实现战斗部对目标快速评估的关键之一,本文中分别对型面宽度为90°、120°和150°三种D型战斗部的破片飞散规律进行实验和数值模拟研究,考察型面宽度和起爆模式对破片威力场的影响规律。结果表明:三种结构中包含90%破片的方位角分别为21.16°、23.88°和30.08°;偏心线起爆和双端面偏心起爆,在20°方位角内破片总能量分别是周向均匀战斗部中心起爆能量的3.4倍和3.3倍;基于三种典型型面的破片威力场公式,通过构建二次插值函数获得其他型面战斗部的破片分布,为D型战斗部破片威力场的快速计算提供了一种有效方法。     

Decay rates in nano tubes with consideration of surface elasticity

In the present paper we examine the Saint-Venant end effect in the nano tubes via a continuum mechanics with consideration of surface elasticity. The Saint-Venant end effect is quantitatively described by the decay rate. By analytically solving an axial-symmetric torsion in a circular cross-section tube configuration, we demonstrate that the decay rate decreases as the radius of the nano wire/tube decreases with consideration of the surface effect.     

A new car-following model with consideration of anticipation driving behavior

A new anticipation driving car-following (AD-CF) model is presented based on the effect of traffic anticipation in the real world. The model??s linear stability condition was obtained by applying the linear stability theory. Additionally, a modified Korteweg?Cde Vries (mKdV) equation was derived via nonlinear analysis to describe the propagating behavior of traffic density wave near the critical point. Good agreement between the simulation and the analytical results shows that the stability of traffic flow can be enhanced when the driver??s anticipation effects are considered.