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10 December 2005, Volume 27 Issue 6
Interesting mechanics story
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-188
Abstract ( 1460 )   PDF (2329KB) ( 794 )
The application of X-ray CT technology to rock damage measurement becomes an important part of rock damage mechanics. In this paper, first, the measurement principle, technical specifications and development of the CT machine are described. Secondly, the application of CT technology to rock damage measurement are reviewed. Thirdly, the existing methods of CT analysis, including the statistical frequency method put forward by the author, are discussed. Fourthly, all kinds of damage variables based on mean CT values are analyzed. Finally, the existing problems and future development are pointed out.
2005, 27(6):  0-0.  doi:10.6052/1000-0879-2004-207
Abstract ( 1213 )   PDF (505KB) ( 644 )
To study the variations of airflow in the goaf flow field with various boundary conditions, a finite element numerical model is established to compute the flow pattern of caving goaf based on flow equation for air leakage in heterogeneous porous media. Combined with in-situ cases, the seepage flow patterns of air leakage in goafs with complicated shapes are described, and an accurate graph distribution solution of flow pattern is given. Flow pattern computation is carried out by using a modified function of stream function Laplace equation proposed by the author, and the flow fields of heterogeneous goafs with complicated shapes and along the boundary direction can meet the condition of orthogonality of flow net, and at the same time the orthogonality can be controlled by the precision of split meshes. A conclusion is drawn that the air leakage intensity of goaf along the caving uncompacted zones around solid wall boundary is relatively large, namely, the air leakage intensity of two ends of working face is large, and the flow lines can be extended to the deep parts of goaf.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-326
Abstract ( 1315 )   PDF (898KB) ( 661 )
The inversion of strong scatterer imbedded in the half-space is a practical, but very difficult problem of strong non-linearity. The Born iterative method is only suitable to weakly non-linear problems. Based on DBI(distorted Born iterative) method, an iteration algorithm is proposed for solving this kind of strongly non-linear problems. In the numerical simulation process the moment method is employed for discretization and the resulting ill-conditioned matrix equation is solved through the regularization technique. The numerical results show that this approach can converge fast and achieve a high accuracy.
2005, 27(6):  0-0.  doi:10.6052/1000-0879-2004-352
Abstract ( 1253 )   PDF (750KB) ( 659 )
The stability of frozen soil wall is determined by its applied load and deformation. The unloading process of the frozen soil is taken into account, together with the interaction between the frozen soil wall and the surrounding earth mass. At the same time, the creep displacement is also taken into account in the stability analysis of frozen soil wall. The expressions of the stresses and displacement of frozen soil wall are obtained based on the viscous-elastic-plastic theory. The calculated displacement of the frozen soil wall is well consistent with those measured in-situ.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-361
Abstract ( 892 )   PDF (357KB) ( 694 )
An analysis method for transmission tower with the split rigidity method is proposed, with each section of equivalent flexural rigidity matrix and equivalent shear rigidity matrix being established separately by using the split rigidity method to replace the total rigidity matrix in the space truss analysis method, to obtain the internal force of each section of tower. Using an iterative method, the truss member force of entire tower is obtained. The calculating results agree well with the calculating data by using computer.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-374
Abstract ( 1270 )   PDF (629KB) ( 551 )
Conical tension failure in concrete is a basic failure mode for post-installed anchors in concrete components. Based on theory of elasticity and the failure criterion of concrete, a theoretical formula for the ultimate bonding capacity of expanding anchors is derived and simplified. Parametric analysis on the ultimate strength of the post-anchored concrete of different concrete strengths is carried out and it is found that the projected diameter of the critical cone $R$ is approximately a linear function of the effective depth embedded in the concrete base for anchors. Compared with test results, the predicted values of the ultimate tension capacity of expanding anchors by the simplified formula agree well with the test measurements from different sources, and the accuracy of the method satisfies the requirements of engineering practice.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-380
Abstract ( 1374 )   PDF (574KB) ( 530 )
Roll tensioning is a prestressing procedure commonly used to increase the stability of circular saws. This paper describes how the finite element method can be used to analyze the residual stresses induced by roll tensioning. As the results measured by X-ray disagree with the calculations on the basis of three-region theoretical model, this paper introduces a new model, in which the main parameters affecting roll tensioning include plastic constitutive relationship of the material, structure and rotational speed of roller, applied pressure, tensioning radius, times of tensioning. The results of residual stresses agree with experimental measurements.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-447
Abstract ( 1483 )   PDF (736KB) ( 920 )
Among various types of strain-measurement sensors, the form of double cantilever beam is not in common use. In this paper, the double cantilever beam structure is analyzed, a type of strain sensor based on the double cantilever beam is developed, using the nearly translational movement at the end of the beam under a small displacement. The comparative test result between this sensor and the stain gauge shows that the maximum error is less than 1.7%. This type of sensor can be used extensively in strain-measurement for various structures.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-449
Abstract ( 1163 )   PDF (331KB) ( 527 )
Boiler pressurized combustion is a serious problem, which affects the working safety of the boiler. There are many factors in the problem. A case of pressurized combustion is presented, which is caused by the unsteady shedding flow of separated vortex in the forward and backward facing step flow. Vibration of the wall caused by flow-solid coupling is another important factor causing pressurized combustion. A better result is achieved and electric power is saved with the wall being reinforced and the back facing step eliminated.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-466
Abstract ( 1412 )   PDF (606KB) ( 663 )
A mass-spring-damper model for the structure of bolt-flange is put forward, with viscous damping and coulomb damping. Simulation is carried out with an exponentially decayed pressure pulse acting on the flange. In the simulation the effect of the pre-stress in bolts, the bolt numbers, the damping between flange and bolts is studied. The pre-stress in bolts and the bolt numbers have a great effect on the peak of bolt deformation. The damping has not much effect in this respect.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-476
Abstract ( 1237 )   PDF (668KB) ( 816 )
It is known from the production experience that the rotary kiln's continued down slippage may cause troubles and accidents in the production system. Using elasticity theory and tribology, the kiln axial slippage is analyzed and discussed, and the calculating methods for the kiln slippage velocity and the measures of controlling the kiln axial slippage are proposed.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2004-490
Abstract ( 1452 )   PDF (892KB) ( 637 )
The article establishes an FEM model for reinforced concrete under impact loads. The depth of intruding and the radius of crater are obtained.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2005-009
Abstract ( 1312 )   PDF (735KB) ( 536 )
The element-free Galerkin method is applied to solve the incompressible viscous flows problem, which is described by the Navier-Stokes equation. The discrete formulation of the element-free Galerkin method is obtained by a weighted residual method, and the fractional step method in time domain is adopted. This method is useful because one may use the same moving least-squares(MLS) interpolation functions for both velocity and pressure, and velocity and pressure are solved by independent equations, respectively. The Newton-Raphson iterative method is used for the velocity and pressure in each time step. Finally, the method is applied to the shear-driver cavity flow to verify the validity and accuracy of this study.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2005-071
Abstract ( 1058 )   PDF (595KB) ( 733 )
The process of molten aluminium infiltration with different viscosity in a porous medium under low-pressure is investigated through organic transport material simulation based on the principle of similarity. Experiments indicate that the plane surface of infiltrating liquid advances perpendicularly and conforms to the law of fourth root. At a certain time $t$, the Reynold's number $Re(t)$, the resistance coefficient $\lambda (t)$ and the pressure loss can be calculated by corresponding formulas. It is found that the viscosity changes of molten aluminum in a certain range (5{\%}) have little influence on the infiltration velocity. The filling time in the simulation is compared with that for prototype, and a good agreement is found.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2005-096
Abstract ( 1045 )   PDF (605KB) ( 616 )
According to the field demand of reinforced concrete long picket (post) hoisting, the hoisting plan in double-hoist three-point lifting is analyzed, its mathematical model is established, and some difficult problems are solved.
2005, 27(6):  0-0.  doi:10.6052/1000-0992-2005-345
Abstract ( 1359 )   PDF (2295KB) ( 564 )
The importance of energy for mankind is pointed out and the necessity to find new kinds of energy is discussed. Nuclear energy is the only way to solve this problem, as was forecasted by A. Einstein one hundred years ago, which has opened a new era of nuclear energy, where attention was paid to fission and fusion energy. In this paper, the technology to use nuclear energy is presented with detailed description of the requirement to use fusion energy, its development and the present status, including magnetic confinement and inertial confinement. Now tokamak is the best choice to use fusion energy, so the contribution of ITER is an important step and milestone of the research and development of fusion energy. The strategy in energy development in this century in China is also disscussed in the last part of this paper.