固定式起重机的支撑圆筒在地震载荷下的动态特性研究

从港口反馈的信息表明,固定式起重机支撑圆筒的抗弯刚度相对较弱,在承受动载荷（货物突然起升、卸载、回转等）时,其顶端容易产生较大幅度的振动。对起重机在回转机构制动冲击载荷下和起升冲击载荷下的动态特性的研究,为振动控制和结构优化设计工作提供了很大的帮助,而对地震载荷下的起重机动力学问题的研究很少见,本文对此作初步探讨。     

Numerical study on the effect of current profiles on vortex-induced vibrations in a top-tension riser

In this paper, numerical simulations of vortex-induced vibrations in a vertical top-tension riser with a length-to-diameter ratio of 500 using our in-house code viv-FOAM-SJTU are presented. The time-dependent hydrodynamic forces on two-dimensional strips are obtained by solving the Navier-Stokes equations, which are, in turn, integrated into a finite-element structural model to obtain the riser deflections. The riser is discretized into 80 elements with its two ends set as pinned and 20 strips are located equidistant along the risers. Flow and structure are coupled by hydrodynamic forces and structural displacements. In order to study the effects of the shear rate, of the current profiles on the vortex-induced vibrations in the riser, vibrations, with varying shear rates, in both the in-line and cross-flow directions, are simulated. In addition to the time domain analysis, spectral analysis was conducted in both the temporal and spatial domains. Multi-mode vibration characteristics were observed in the riser. The relationship between dominant vibration mode number and the shear rate of current profiles is discussed. In general, the overall vibrations in the riser pipe include contributions from several modes and each mode persists over a range of shear rates. Moreover, the results suggest that with a larger shear rate the position of the maximum in-line time-averaged displacement will move closer to the end where the largest velocity is located.     

定子绕组等效模型对电机热计算结果影响研究

在电机热计算中,由于定子绕组结构比较复杂,一般对其进行相应的等效简化处理,但对相关处理方法的理论支撑及对温升计算结果的影响很少进行深入研究。本文主要针对定子绕组常用的两种等效形式进行相关研究,首先对不同模型进行理论分析,再通过三维仿真计算,对不同形式的温升结果进行评估和对比,得到相关的结论,可用于指导提高电机热计算的准确度。根据仿真结果可知,绝缘材料对定子绕组的散热影响较大,将全部绕组等效为一个整体分布在槽中间,绝缘均匀分布在其周围的假设所得结果最接近实际情况。     

三相三重斩波电路的建模和仿真研究

阐述了三相三重斩波电路的工作原理,并且给出其在MATLAB/Simulink中的仿真模型和仿真结果,仿真结果表明其输出电流为单个斩波电路平均电流的三倍,而且其电流脉动频率为单个斩波电路的三倍。     

地层注浆加固对隧道与地下水相互作用过程中的“双赢”影响效应分析

目前山岭隧道大多采用的"半包"防水方式,可较为有效地降低衬砌背后水压荷载作用,但同时造成地下水资源的大量流失。文章通过建立隧道瞬态渗流模型,分析了"半包"防水条件下隧道施工及运营过程中隧道排水流量及水位变化规律,以及运营过程中衬砌背后水压力分布规律;研究了帷幕注浆和径向注浆两种方式不同工况下不同注浆范围及参数对排水流量、水位变化及衬砌水压荷载的影响效应。数值分析结果和工程实践表明,地层注浆加固既可降低衬砌背后水压荷载,又可减少地下水资源流失量,从而可以实现隧道与地下水相互作用过程中的"双赢"影响效应。文章最后对"半包"防水条件下仰拱是否设置排水系统进行了分析探讨。     

多目标模糊决策在软土地基加固方案中的应用

针对软土地基加固方案的影响因素具有模糊性这一特点,运用模糊数学理论,对定性指标量化,利用层次分析法确定评价因素的权重,提出采用模糊综合评价法对加固方案选优,并结合实例进行验证分析。