Forced vibrations of a beam elastically restrained against rotation and carrying a spring–mass system

An exact solution for the title problem is obtained in closed form fashion in the case of a Bernoulli–Euler beam. It is assumed that the exciting force is applied to the mass which is elastically mounted on the beam. The mathematical model constitutes a first order approximation to a motor or engine elastically mounted on a structural element. The operation of the machine generates a transverse, sinusoidally varying force. The problem is of basic interest in mechanical, naval and ocean engineering systems from the point of view of the determination of dynamic displacements and stresses; sound radiation calculations, etc. The present problem arose in connection with the mounting of an engine on a structural beam in a small naval vessel and when excessive vibrational level was noted. This study was undertaken in order to understand the physical problem and to correct the mechanical situation     

西非深水海底管道沉降分析

基于西非深海安哥拉32区块KAOMBO油田实际工程,对海底管道沉降进行了理论分析和数值计算,考虑了极浅层土力学参数的不确定性,认为土体不排水抗剪强度对管道沉降的影响不可忽视,随着土体强度的增加,管道沉降量呈指数衰减,当土体强度达到2.0 k Pa时,管道沉降量趋于一致。同时考虑了管道安装过程中纵横向摆动对管道沉降的影响,引入了动力系数,考虑管道触泥点处应力集中产生的附加沉降,荷载集中系数随管道弯曲刚度和土壤刚度增加而增加,随铺设张力的增加而减小,并区分"轻""重"管道进行了沉降分析,结果与几内亚湾和安哥拉海域实际工程和现场实际观测数据相符。     

Consistent tangent matrices for density‐dependent finite plasticity models

The consistent tangent matrix for density‐dependent plastic models within the theory of isotropic multiplicative hyperelastoplasticity is presented here. Plastic equations expressed as general functions of the Kirchhoff stresses and density are considered. They include the Cauchy‐based plastic models as a particular case. The standard exponential return‐mapping algorithm is applied, with the density playing the role of a fixed parameter during the nonlinear plastic corrector problem. The consistent tangent matrix has the same structure as in the usual density‐independent plastic models. A simple additional term takes into account the influence of the density on the plastic corrector problem. Quadratic convergence results are shown for several representative examples involving geomaterial and powder constitutive models. Copyright © 2001 John Wiley & Sons, Ltd.     

应用人工神经网络计算孤立波爬高

运用附加动量法和自适应学习速率对具有一层隐含层的BP网络进行改进，并由此建立神经网络模型来计算孤立被的爬高。将试验值分别与Synolakis公式以及本文结果进行比较，证实神经网络模型计算方法对于计算孤立波的爬高是合适的。     

Melt–water Accumulation on the Surface of the Greenland Ice Sheet: Effect on Albedo and Mass Balance

Satellite–derived albedo maps of the western part of the Greenland ice sheet (between 64.5 and 70.5 ^∘ N) reveal a north–south extending zone with relatively low albedos at some distance from the ice margin. In the literature it has been hypothesized that this "dark zone" is due to a local maximum in melt–water accumulation on the ice–covered surface. A plausible explanation for this maximum in melt–water accumulation is thatrelative to the situation within the "dark zone", melt–water accumulation is reduced at higher elevations by a smaller melt–water production rate whereas runoff occurs more easily at lower elevations where slopes are generally steeper. For the present paper AVHRR images from eight years (1990–1997) were analysed. The following indications confirming the "melt–water accumulation hypothesis" were found: (1) there is a significant correlation between the annual mean albedo lowering within the "dark zone" and the annual amount of melt as inferred from local mass–balance measurements; and (2) within each summer season the albedo lowering within the "dark zone" seems to respond to the melt–water production rate as inferred from local temperature measurements. The effect of melt–water accumulation on the albedo implies a positive feedback between the albedo and the amount of melt. It is estimated that approximately 40% of the interannual mass–balance variations in the "dark zone" are due to this feedback.     

地震力作用下影响巨子型有控结构的动力参数研究

附加柱刚度与附加阻尼为影响巨子型有控结构抗震性能的两个重要参数。本文基于随机振动理论探讨水平地震作用下附加柱刚度及附加阻尼对巨、子结构动态特性的影响,分析附加阻尼与附加柱间的制约关系,并对比研究传统巨型框架结构、巨子型有控结构安装流体阻尼器前后的响应功率谱变化。结果表明:巨子型有控结构具有极好的抗震性能,安装合理的附加阻尼后,其抗震能力得到进一步提高;附加柱刚度变化不但影响巨、子结构动力响应,而且会导致最优附加阻尼区间迁移。因此,巨子型有控结构具有广阔的发展空间,实际设计中应充分考虑附加柱与附加阻尼的相互影响。     

沙生植物渗透调节物对干旱、高温的响应及其在抗逆性中的作用

在科尔沁沙地选择不同类型沙地优势植物,测定了其在自然脱水、高温处理及复水后叶可溶性糖、可溶性蛋白质和脯氨酸含量的变化。结果表明,在胁迫过程中流动沙地上的沙米、欧亚旋覆花,叶片内可溶性糖积累,尤其是脯氨酸积累较高,处理12h较处理前分别增加了92.87%、10.28倍,可溶性蛋白质含量下降,在胁迫处理后植株枯死;半固定沙地上的差不嘎蒿可溶性糖增加41.57%、脯氨酸含量增加8.95倍、可溶性蛋白质下降15.04%,在两种胁迫处理后依然存活并恢复生长;固定沙地的白草和狗尾草可溶性糖增加89.82%和89.43%,脯氨酸增加2.49倍和2.53倍、可溶性蛋白质增加。因此,如果把胁迫中叶内积累的脯氨酸与胁迫后植株的存活结合起来看,两种胁迫中差不嘎蒿、狗尾草、白草体内积累的脯氨酸起保护性反应,而沙米、欧亚旋覆花的则是受害症状。     

油页岩开发地下水资源影响预测与评价

以吉林省汪清县罗子沟油页岩开发为实例．根据参数的确定、地下水资源的估算、坑道排水量的计算、矿坑排水最大水位降的预测．对矿坑排水量进行评价,再运用地下水资源补给模数、潜水调节量及疏干体积法验证排水量的计算．从而达到研究油页岩的开发对地下水资源的影响和评价的目的。     

Thermal effects on fluid flow and hydraulic fracturing from wellbores and cavities in low-permeability formations

The coupled heat-fluid-stress problem of circular wellbore or spherical cavity subjected to a constant temperature change and a constant fluid flow rate is considered. Transient analytical solutions for temperature, pore pressure and stress are developed by coupling conductive heat transfer with Darcy fluid flow in a poroelastic medium. They are applicable to low permeability porous media suitable for liquid-waste disposal and also simulating reservoir for enhanced oil recovery, where conduction dominates the heat transfer process. A full range of solutions is presented showing separately the effects of temperature and fluid flow on pore pressure and stress development. It is shown that injection of warm fluid can be used to restrict fracture development around wellbores and cavities and generally to optimize a fluid injection operation. Both the limitations of the solutions and the convective flow effect are addressed. Copyright © 1999 John Wiley & Sons, Ltd.