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1.
A separation distance between adjacent buildings is provided to reduce the risk of pounding of adjacent buildings under seismic excitations. It should be recognized that the evaluation of the critical separation distance is a one-sided barrier crossing problem while the problem of structural design under seismic excitations is a two-sided crossing problem. A procedure for assessing the required separation distance with or without considering possible uncertainty in structural properties was presented based on the reliability methods and random vibration theory. The procedure was used to carry out parametric analyses. It is shown that use of the complete quadratic combination (CQC) rule with the modal responses employed for designing structures may over- or underestimate the critical separation distance, depending on the damping ratios and the closeness of the natural vibration periods of adjacent buildings. This is due to not only one-sided versus two-sided crossing problem but also the approximation in the CQC rule. Further, the effect of the uncertainty in structural properties on the estimated separation is investigated. The results indicate that this uncertainty tends to increase the required critical separation distance. 相似文献
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颗粒尾涡增强湍流的大涡模拟以及气固两相流中湍流变动的数值模拟 总被引:1,自引:0,他引:1
The turbulence enhancement by particle wake effect is studied by large eddy simulation (LES) of turbulent gas flows passing a single particle. The predicted time-averaged and root-mean-square fluctuation velocities behind the particle are in agreement with the Reynolds-averaged Navier-Stokes modeling results and experimental results. A semi-empirical turbulence enhancement model is proposed by the present-authors based on the LES resuits. This model is incorporated into the second-order moment two-phase turbulence model for simulating vertical gas-particle pipe flows and horizontal gas-particle channel flows. The simulation results show that compared with the model not accounting for the particle wake effect, the present model gives simulation results for the gas turbulence modulation in much better agreement with the experimental results. 相似文献
4.
X70管线钢在役焊接局部脆化区的组织及精细结构 总被引:2,自引:0,他引:2
采用焊接热模拟试验研究了X70管线钢在役焊接粗晶区和临界粗晶区的显微组织及其精细结构,并和常规焊接进行了对比.结果表明,X70管线钢在役焊接粗晶区和临界粗晶区的组织在类别上与常规焊接相差不大,主要都是粒状贝氏体和贝氏体铁素体,不同的只是数量的多少和尺寸的大小.透射电镜下,在役焊接和常规焊接的粗晶区与临界粗晶区的主要形貌都是铁素体板条和分布在板条之间或板条基体上的岛状物,铁素体板条的亚结构都是高密度位错.在役焊接粗晶区和临界粗晶区的铁素体板条宽度都比常规焊接的要小,位错密度都比常规焊接的要高. 相似文献
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Harry Bunt 《Computer Speech and Language》2011,25(2):222-245
This paper studies the multifunctionality of dialogue utterances, i.e. the phenomenon that utterances in dialogue often have more than one communicative function. It is argued that this phenomenon can be explained by analyzing the participation in dialogue as involving the performance of several types of activity in parallel, relating to different dimensions of communication. The multifunctionality of dialogue utterances is studied by (1) redefining the notion of ‘utterance’ in a rigorous manner (calling the revised notion ‘functional segment’), and (2) empirically investigating the multifunctionality of functional segments in a corpus of dialogues, annotated with a rich, multidimensional annotation schema. It is shown that, when communicative functions are assigned to functional segments, thereby eliminating every form of segmentation-related multifunctionality, an average multifunctionality is found between 1.8 and 3.6, depending on what is considered to count as a segment's communicative function. Moreover, a good understanding of the nature of the relations among the various multiple functions that a segment may have, and of the relations between functional segments and other units in dialogue segmentation, opens the way for defining a multidimensional computational update semantics for dialogue interpretation. 相似文献
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无线电高度表信号模拟器是无线电高度表进行性能测试和检修时必需的专用仪器。本文设计一种采用C8051F320单片机作为主控制单元(MCU)和PCF8576作为液晶显示器显示驱动芯片的无线电高度表信号模拟器控制/显示模块组件。该控制/显示模块的MCU检测操作键盘的按键操作,向外部的射频信号延时/衰减模块发送相应的模拟高度选择和功率衰减值设置控制信号,同时向显示驱动芯片发送相应的显示控制信号,实现控制和显示功能。实际工程应用表明,该无线电高度表信号模拟器控制/显示模块可靠性好、操作简便、性价比高,具有较高的工程推广应用价值。 相似文献
8.
基于数据可视化技术的逆变器用T型滤波器优化设计方法 总被引:3,自引:1,他引:3
以提高滤波器对非线性负载的适应性和整机功率密度为目的,提出一种用四维可视化技术优化非对称T型滤波器的设计方法。优化目标为降低输出阻抗和提高系统功率因数,取值范围由四维表现图的交域构成;截止角频率等约束条件的选择充分考虑到器件的电流负担和电压应力;整个设计过程在四维表现图、两参数变化的根轨迹和Bode图的可视化条件下进行,便于把握多目标函数的变化趋势,进而综合考虑各方面的因素来确定最优解。实验结果和相关数据表明所设计的低通滤波器达到了带约束条件的多目标优化目的,且该方法也可用于类似的工程优化设计。 相似文献
9.
Guo-hua Qin Wei-hong Zhang 《The International Journal of Advanced Manufacturing Technology》2007,32(1-2):78-91
After being located on a machine bed, a workpiece will be subject to gravity and cutting forces during the machining operation.
In order to keep the locating precision as well as the production safety, it is necessary to maintain the workpiece stability.
In this paper, a linear programming method is proposed for stability analysis of the workpiece. Based on the linear approximation
of the friction cone, a quantitative criterion is established to verify the workpiece stability in association with the rationality
of the clamping sequence, magnitude of clamping forces and clamping placement. This criterion allows designers to plan reasonably
the clamping sequence, magnitude of clamping forces as well as clamping placement. Compared with existing methods, the main
advantage of this approach lies in that the sophisticated computing of contact forces between fixture elements and the workpiece
is avoided. In this work, both friction and frictionless cases can be easily taken into account in stability analysis. Mathematical
formulations of the method are given and some numerical tests are finally demonstrated to validate the proposed method. 相似文献
10.
对TB17钛合金进行了亚β固溶处理(固溶温度800℃-835℃,固溶时间0.5h-9h),采用电子探针分析了Al、Mo、Nb元素在初生α相和β基体中的分布,研究了合金亚β固溶时初生α相析出、元素重分布规律及其对时效次生相的影响。结果表明,合金亚β温度固溶时以晶内析出针状初生α相为主,晶界析出少量片层状初生α相。初生α相析出量随亚β固溶温度升高而降低,固溶温度高于825℃时基本不析出α相。初生α相尺寸随固溶时间延长而增大,固溶时间超过2h后,初生α相析出量达到稳态。Al元素倾向于在初生α相中富集,Mo和Nb元素则倾向于β基体富集。初生α相中心部位Al元素浓度较高,边缘部位较低,而Mo和Nb元素中心部位则浓度较低,边缘部位较高。增加初生α相析出量,会使β基体Al浓度降低,Mo、Nb元素浓度升高。初生α相较少(2%)时初生α相周围的次生α相以针状或片层状形貌为主,远离初生α相区域的次生α相以似网篮结构为主,初生α相较多(10%)时次生α相均以片层状形貌为主。 相似文献