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15 June 2011, Volume 33 Issue 3
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    2011, 33(3):  84-86.  doi:10.6052/1000-0879-lxysj2011-038
    Abstract ( 1939 )   PDF (602KB) ( 524 )  
    Thomas Young was a polymath scholar, and his research interest covered optics, acoustics, hydrodynamics, medicine, strength of materials, archaeology, language, assurance, etc. However, his contributions to mechanics didn't draw a lot of attentions of his contemporary scientists due to some reasons. These contributions include mechanics of materials, hydrodynamics of blood, energy, impact dynamics, surface wetting mechanics, structural analysis of engineering materials, etc. He was a pure natural philosopher, and at the same time he combined his theory with the engineering applications, with the spirit of engineering science being realized.
    2011, 33(3):  110-110.  doi:10.6052/1000-0879-lxysj2011-055
    Abstract ( 2046 )   PDF (676KB) ( 657 )  
    2011, 33(3):  67-69.  doi:10.6052/1000-0879-lxysj2011-024
    Abstract ( 1319 )   PDF (380KB) ( 575 )  
    2011, 33(3):  11-14.  doi:10.6052/1000-0879-lxysj2011-123
    Abstract ( 1567 )   PDF (626KB) ( 957 )  
    The brachistochrone with consideration of viscous resistance may be an issue in engineering situations. A generalized variational principle with constraints removed is deduced first, and it is also applicable to other forms of resistance and optimization of systems with multiple degrees of freedom. We then obtain the ordinary differential equations describing the functions of the brachistochrone with viscous resistance, whose solution is reduced to roulette when the viscous resistance is neglected. The effects of the resistance on the brachistochrone are quantitatively analyzed on the basis of numerical computations by using MATLAB. When the viscous resistance is not very large, the brachistochrone becomes more concave. With the increase of the resistance, the brachistochrone will become flatter. A very large resistance will finally lead to a straight-line brachistochrone.
    2011, 33(3):  7-10.  doi:10.6052/1000-0879-lxysj2011-035
    Abstract ( 1004 )   PDF (655KB) ( 428 )  
    Surfactant is an important factor that causes sloshing damping. In the present paper, the theory of sloshing damping caused by surfactant is analyzed, and the calculation formula is derived. Then a numerical calculation method of surfactant sloshing damping is proposed on the basis of FEM. The calculated value is compared with the theoretical and experimental value, and the effectiveness of the numerical method is verified.
    Around the mechanics
    2011, 33(3):  1-6.  doi:10.6052/1000-0879-lxysj2011-197
    Abstract ( 1595 )   PDF (1378KB) ( 1089 )  
    Low-thrust optimization and design of spacecraft trajectory for deep space exploration is a global optimization problem with large numbers of local solutions. The strategy of trajectory design consists of global optimization and local optimization as a whole. As a concept design, the goal of global optimization is to approximately determine exploration sequences and node times after simplifying spacecraft trajectory generated by low thrust. Local optimization is generally cataloged as direct methods, indirect methods, and hybrid methods. Direct methods convert the continuous optimal control problem into a parameter optimization problem through discretization. Indirect methods are involved in solving two- or multi-point boundary-value problems satisfying the first-order necessary conditions derived from the calculus of variations and the maximum principle. Hybrid methods partly utilize the conditions derived by indirect methods, and then as what direct methods do, resort to parameter optimization. This paper surveys the state of the art in low-thrust trajectory optimization, and describes the benefits and deficiencies of the newest and most popular methods.
    2011, 33(3):  15-19.  doi:10.6052/1000-0879-lxysj2010-516
    Abstract ( 1102 )   PDF (1278KB) ( 400 )  
    Touchdown zone (TDZ) is one of the locations vulnerable to fatigue damage. The fatigue life prediction is difficult, which would greatly depend on model experiments. As a result, based on the related theoretical research, a SCR fatigue life test system for the TDZ is designed to simulate the actual working condition of riser. This system has considered the variation and combination of tension, bending, internal and external pressure, pipe-soil interaction and other factors. The test system can be used for carrying out deepwater riser fatigue experiments, studying the fatigue failure mechanism of SCR in the TDZ, and predicting its fatigue life accurately.
    2011, 33(3):  20-24.  doi:10.6052/1000-0879-lxysj2010-454
    Abstract ( 1397 )   PDF (743KB) ( 506 )  
    A beam-column theory is proposed for bent housing positive displacement motor (PDM) assemblies with medium-short radius ($K=1^\circ$/m$ \sim 3^\circ$/m) of building capability. According to the conditions of continuity at the support and the boundary of the bottom hole assembly (BHA), the mechanical models of PDM building assemblies in horizontal wells of medium-short radius are established based on the non-uniform stiffness beam-column theory and the application of equivalent load to beam-column with initial bent angles. Furthermore, the side force of the drill bit can be caculated and is used to predict the building capability of bent housing PDM assemblies. %This method can be used for bent housing PDM design and well-path control.
    2011, 33(3):  25-29.  doi:10.6052/1000-0879-lxysj2010-317
    Abstract ( 1200 )   PDF (1072KB) ( 495 )  
    In order to study the partial-wear between rod and tubing in the mechanical production, the buckling deformation and the contact of tubing with inner rod and outer casing are considered, and the variable cross-section of structure and the annular clearance with the tubing and rod are assumed, the tubing post-buckling and the contact with casing and rod are simulated by using the nonlinear finite element method of large displacement with contact, and the initial displacement of tubing is obtained from the multi-band instability wave superposition value based on structure stability analysis. This method can be used in the post-buckling and contact analysis of compressional tubing in the vertical well, which would provide some guidance for the rod and tubing partial-wear analysis and preventive measure development.
    2011, 33(3):  30-33.  doi:10.6052/1000-0879-lxysj2010-220
    Abstract ( 1175 )   PDF (1125KB) ( 397 )  
    For the flying-panel in double parallel ERAs, the interaction between jet and double parallel ERAs can be devided into two phases. Before the collision with the middle panel, the jet can be considered to interact with two single ERAs. But after collision, the jet is considered to interact with a single ERA. Based on the movement of the flying-panel, the collision time of the middle panel can be obtained. Results of the simulation and experiment are in good agreement.
    2011, 33(3):  34-37.  doi:10.6052/1000-0879-lxysj2010-445
    Abstract ( 1069 )   PDF (743KB) ( 503 )  
    The secondary deformation of steel reinforced concrete (SRC) columns is much smaller than that of RC columns because of the use of section steel, and the current bias distance increase coefficient in Chinese design code is not suitable for composite columns. On the basis of theoretical analysis, two methods for calculating the bias distance increase coefficient are proposed, and formula about the coefficient is obtained by using the eccentricity increase method with the ultimate curvature as the main parameter based on the mechanical characteristics of SRC columns. Other $\eta $ expressions are summarized, and an example is presented with the maximum error of less than 10{\%} between the suggested and other available formulas, which thus indicates that the proposed formula has a high precision.
    2011, 33(3):  38-41.  doi:10.6052/1000-0879-lxysj2010-388
    Abstract ( 890 )   PDF (960KB) ( 393 )  
    Based on the model of atom lattice, the variation of atom vibration frequency and radiation against the distance between atoms is studied in this paper. The infrared radiation characteristics and influencing factors and the deformation range are analysed and discussed in the elastic stage of the solid materials. The theoretical results are compared with the infrared radiation fields of the elastic-solid materials in the experiments. The results in those infrared increased temperature zones and infrared decreased temperature zones agree well with the test results, therefore, the microscopic mechanism of the infrared radiation characteristics for solid materials in the process of primary loading in room-temperature is confirmed.
    2011, 33(3):  42-45.  doi:10.6052/1000-0879-lxysj2010-415
    Abstract ( 1268 )   PDF (770KB) ( 458 )  
    Based on the ANSYS finite element model, this paper studies the external tendon and the key technologies of the external prestressed reinforcement. The conclusions are as follows. To a rational function position of the external tendon, the original structure's stress condition must be complied as far as possible to ensure the safety performance of the reinforcement. The reinforcement tendon should use the replacement principle of equivalent area, for the reasonable construction process. The strength tendon's junction device must keep the principle of ``conformation, thin, strong''. The engineering disposal of longitudinally and staggered layout for the external tendon in reinforcement engineering, which will promote the integral structure ductility.
    2011, 33(3):  46-49.  doi:10.6052/1000-0879-lxysj2010-510
    Abstract ( 1036 )   PDF (1099KB) ( 404 )  
    In order to quantitatively assess the residual strength of the aging aircraft with widespread corrosion damages the equivalent crack size technique is used to simulate the surface corrosion pits as initial surface cracks on corrosion structure, where a hypothetical initial surface crack with the same life as the corrosion pit is used. Thus the analysis of the corrosion structure with numerous pits becomes a problem of multiple surface cracks. Then, the parameter finite element method and the cycle-by-cycle iterative algorithm are used to compute the stress intensity factor, crack extension directions, and crack-growth increments. When the stress intensity factor history is obtained using the crack-growth increment and stress intensity factors, the fatigue life of the structure under fatigue loading is estimated through cycle-by-cycle damage accumulation. The result provides a guidance for fatigue life prediction of an aircraft structure with widespread corrosion pits in complicated environments.
    2011, 33(3):  50-55.  doi:10.6052/1000-0879-lxysj2010-396
    Abstract ( 1223 )   PDF (1049KB) ( 486 )  
    The modern model validation considers uncertainty and the modeling error. In order to study modeling and validation criterions in the model validation course, in this paper, the normal distribution and nonparametric kernel density estimate (KDE) are adopted to test the uncertain modeling by an example of the Sandia's structural dynamics challenge problem. At the same time, two validation criterions are adopted for model validation to obtain a better model. It is shown that by combining two validation criterions in the processes of model validation, better results can be expected.
    2011, 33(3):  56-58.  doi:10.6052/1000-0879-lxysj2010-459
    Abstract ( 1127 )   PDF (648KB) ( 458 )  
    This paper studies the computational efficiency and accuracy of the eight-node hexahedral combined hybrid element (CHH (0-1)), and the reliability of data from ANSYS software. The bending plate model is taken as a test problem to be solved by CHH (0-1) element, 8-node brick element and 20-node brick element in ANSYS software, respectively. A comparison of the displacement and stress results shows that the so-called 8-node brick element in ANSYS software is the Wilson brick element actually, which gives reliable displacement results, but its computational accuracy for stress is poor. The 20-node brick element is very time-consuming and the computational accuracy of stress results is not so good. But CHH (0-1) element can achieve a high-precision for both displacement and stress with less cost.
    2011, 33(3):  59-62.  doi:10.6052/1000-0879-lxysj2010-370
    Abstract ( 1058 )   PDF (694KB) ( 398 )  
    This paper discusses the principle and the structure of a new frame beam testing device, which can produce axial restraints and rotational restraints at beam ends to effectively simulate the actual mechanical state of frame beams. Some reinforced concrete frame beams were tested using this device. Test results are confirmed by the results of theoretical analysis and verify a good stability and reliability of the testing device.
    2011, 33(3):  63-66.  doi:10.6052/1000-0879-lxysj2010-458
    Abstract ( 1124 )   PDF (1238KB) ( 550 )  
    The numerical simulation of uniform flow past a golf ball with diameter of 42.6\,mm and with well-distributed pits is carried out by using the large eddy simulation (LES) method, based on the Smagorinsky---Lilly subgrid scale model. The results show that the detached point of the ball's wake is farther than that for a ball of smooth sphere and the drag on the golf ball is smaller. Consider the uniform flow past a golf ball with the effect of clockwise and anticlockwise rotations with a speed of 100\,rad/s. The results show that the wake structure is more uneven, which would result in the pressure perpendicular to the flow direction. The magnitude of pressure has nothing to do with the direction of the rotation and the drag coefficient is larger than that of a non-rotation golf ball. Rotation has an important influence on the pressure.
    2011, 33(3):  70-72.  doi:10.6052/1000-0879-lxysj2010-501
    Abstract ( 1172 )   PDF (1048KB) ( 541 )  
    2011, 33(3):  73-74.  doi:10.6052/1000-0879-lxysj2010-488
    Abstract ( 994 )   PDF (537KB) ( 661 )  
    2011, 33(3):  75-76.  doi:10.6052/1000-0879-lxysj2010-016
    Abstract ( 1979 )   PDF (495KB) ( 618 )  
    In terms of the three typical proofs for the Nanson’s formula nowadays in literatures, the paper evaluates the three proofs with their characteristics from a point of view of both mathematical deduction and limpiditazation of mechanical concepts, pointing out respectively for each proof the advantages and disadvantages together with the spots where improvements for the proofs may be made. Accordingly, the paper puts forward an improved and comprehensible proof for the formula. Also, the paper proposes an argumentation that a proof for a mechanical problem should reflect the intrinsic law of mechanics.
    2011, 33(3):  77-79.  doi:10.6052/1000-0879-lxysj2010-391
    Abstract ( 903 )   PDF (528KB) ( 469 )  
    Self-exited vibration may be regard as the most severe and damaging behavior for the mechanism systems. Generally, it is reduced by adding lubricants. In this paper, the non-solution condition in the planar translational joint is investigated under the assumptions that the body is rigid and the clearance in the joint is infinitesimal small. The condition may be regard as one inducement to the self-excited vibration, and it may be applied to every translational joint in the mechanism systems.
    2011, 33(3):  80-81.  doi:10.6052/1000-0879-lxysj2010-447
    Abstract ( 1224 )   PDF (461KB) ( 353 )  
    The teaching reforms of basic mechanics is promotd based on organizing and coaching of the mechanics competition. Aiming at improving students' mechanics quality and innovation ability and surrounding how to innovate basic mechanics teaching mode, the basic porfermence, practical effect and innovation achievements on promoting the teaching reforms of basic mechanics based on mechanics competition are introduced from stimulate student, reforming teaching test and promoting mechanic course construction.
    2011, 33(3):  82-83.  doi:10.6052/1000-0879-lxysj2010-448
    Abstract ( 2093 )   PDF (417KB) ( 596 )  
    2011, 33(3):  97-101.  doi:10.6052/1000-0879-lxysj2010-149
    Abstract ( 1316 )   PDF (1518KB) ( 560 )  
    It be Introduced that Dujiangyan Irrigation Project and the methods of diverting water and scouring sediment in Dujiangyan, and the principle of these methods be analyzed. Understands of Li Bing advanced ideas of flood control as well as may obtain inspiration in Li Bing advanced ideas.
    2011, 33(3):  103-105.  doi:10.6052/1000-0879-lxysj2010-520
    Abstract ( 1537 )   PDF (989KB) ( 467 )  
    2011, 33(3):  106-109.  doi:10.6052/1000-0879-lxysj2010-508
    Abstract ( 1230 )   PDF (1256KB) ( 507 )