会计信息失真的经济分析及其对策研究

产权各行为主体的利益冲突、激励与约束机制不对称以及委托-代理关系带来的会计信息失真,明晰产权、加强会计规范建设、理顺各方的利益关系以及强化契约关系有利于提高会计信息质量     

基于有限元的缸孔变形量分析

在发动机工作过程中,缸套的变形直接影响到气缸套与活塞环间的间隙以及缸套与缸盖间的密封性,从而导致机油消耗增加、产生窜漏、增加损耗和燃油消耗。为了避免这些问题,文章采用有限元方法重点分析预紧力作用下的气缸套失圆问题。结果表明,发动机第1缸和第4缸的变形量过大。通过增加壁厚很好地解决了此问题,说明有限元分析可以在设计初期解决缸孔变形的问题。     

预防上层建筑变形的技术与工艺措施

本文简要介绍了船舶上层建筑的分段制作、装配和整体预制，分析了上层建筑变形产生的原因，最后从设计到施工全过程详细介绍了预防上层建筑产生变形的技术和工艺措施。     

高速铁路接触网非工作支平腕臂变形原因分析及措施

时速300km及以上的高速铁路接触网采用铝合金腕臂,实际工程应用中出现了非工作支平腕臂变形现象,有必要分析其原因并采取措施。以某高速铁路为例,结合接触网主要技术参数,从铝合金热处理、应力释放、工差配合、施工工序等理论方面分析可能导致腕臂变形的原因;将变形腕臂模型化为简支梁结构,校验腕臂的强度;建立转换柱的几何模型,采用ANSYS有限元分析方法,计算关键节点的变形量。采用上述两种方法校验的结果表明:设计采用的结构能满足腕臂挠度不大于1%的要求。为了加强铝合金腕臂的整体强度,避免由于材料加工制造、施工安装等方面原因造成腕臂挠度超标现象,结合现场试验,采取增设腕臂支撑措施。     

Verification of a simplified analytical method for predictions of ship groundings over large contact surfaces by numerical simulations

In this paper, a verification is presented of a simplified analytical method for the predictions from numerical simulations of structural performance during ship groundings over seabed obstacles with large contact surfaces and trapezoidal cross-section. This simplified analytical method was developed by Lin Hong and Jørgen Amdahl and calculates grounding characteristics, such as resistance and distortion energy, for double-bottomed ships in shoal grounding accidents. Two finite-element models are presented. One was built for a hold, and the other was built for a hold and a ship hull girder and also considers sectional properties, ship mass, added mass and the hydrodynamic restoring force. The verification was completed by comparing horizontal and vertical resistances and the distortion energy between seven numerical-simulation cases and a set of corresponding cases computed by a simplified analytical method. The results show that the resistances obtained by the simplified analytical method are close to the mean values of the resistance curves obtained by numerical simulations. The comparisons prove that the energy dissipation-prediction capability of the simplified analytical method is valuable. Thus, the simplified analytical method is feasible for assessing ship groundings over seabed obstacles with large contact surfaces and trapezoidal cross-section. Furthermore, studies of the influence of ship motion during groundings ascertained that ship motion affects structural performance characteristics. Resistances are lessened at the end of the grounding due to the reduction of indentations caused by heave and pitch motions of the ship hull girder. Finally, a new method for predicting the structural performance of the time-consuming complete-ship model by applying a combination of normal numerical simulations and ship-motion calculations is proposed and proven.     

Influence of the welding sequence on residual stress and distortion of fillet welded structures

T-joints are one of the most common welded joints used in the construction of offshore structures, including ships and platforms. In the present study, a sequentially coupled thermo-mechanical finite element model that considers temperature-dependent material properties, high temperature effects and a moving volumetric heat source was used to investigate the effect of welding sequence on the residual stresses and distortions in T-joint welds. The parameters of Goldak's double ellipsoidal heat source model were predicted using a neural network. The numerical models were successfully validated by the experimental tests. The results show that the welding sequences have significant effects on the residual stresses and distortions, both in the magnitude and distribution mode. The optimization of the welding sequences should be investigated numerically or experimentally before the construction welded structure.     

浅析黄土高边坡变形破坏的基本形式及其机理

本文对黄土高边坡变形破坏的基本形式及其机理进行了分析,指出其破坏形式有坡面冲刷、坡面剥落掉块、坡体湿陷变形、崩塌、滑塌、泥流等几种。黄土高边坡变形破坏模式主要有滑塌、滑坡的破坏模式;崩塌破坏模式和坡面破坏模式等三种。     

Plastic mechanism analysis of structural performances for stiffeners on bottom longitudinal web girders during a shoal grounding accident

A theoretical model is introduced in this paper for structural performance of stiffeners on double-bottom longitudinal girders in a shoal grounding accident. Major emphasis is placed on establishing the characteristic deformation mechanism of stiffeners and identifying major energy dissipation patterns. Numerical simulations using the LS-DYNA nonlinear finite-element program were carried out to examine thoroughly the progressive deformation process during sliding deformation. Stiffener deformations were observed to fall into two categories: stiffeners fully contacted with the indenter, and stiffeners subjected to indirect deformation due to energy transfer from attached girders. Grounding performance of stiffeners is substantially influenced by that of the attached plating, and therefore a review of the existing deformation models of longitudinal girders (i.e. Simonsen 1997, Midtun 2006 and Hong 2008) was included. Hong's model of bottom girders was found not capable of representing the effects of stiffeners, and a new model of girders was thus developed. Based on observation of the numerical deformation process and the new analytical girder model, a kinematically admissible model of stiffeners on bottom longitudinal girders was built. Using the methods of plastic mechanism analysis, simplified analytical expressions for energy dissipation by girder-attached stiffeners, both fully contacted and noncontacted, were formulated, and equations for grounding resistance were subsequently obtained. The theoretical expressions agree favorably with results from nonlinear finite-element simulations and capture two significant characteristics of the problem: that energy varies little with indentation for stiffeners that fully contacting the indenter, and that energy is independent of slope angle for indirectly deformed stiffeners. The proposed theoretical model helps to predict analytically shoal grounding performance of stiffeners on longitudinal girders with reasonable accuracy.     

变速箱齿轮齿形齿向渗碳淬火热处理变形测量方法

本文论述了变速箱齿轮的齿形、齿向渗碳淬火热处理变形规律的试验及测量方法，为进一步的变形精度控制提供依据。