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排序方式: 共有699条查询结果,搜索用时 31 毫秒
691.
Ming-Hsiung Hsiao 《运输规划与技术》2015,38(8):889-908
This paper examines the relationships among different transportation modes, and between transportation and telecommunications, by applying the structural equation modeling (SEM) technique. For this purpose, we collected and compiled time series data on national travel demand, and socioeconomic and telecommunications conditions in Taiwan, and built national travel demand models using SEM. The estimation results show that the relationship between telecommunications and transportation demand (either car ownership or public transportation) is more complementary than substitutional. Moreover, car ownership is a type of inelastic necessity good, and its relationship with public transportation is more substitutional than complementary. Finally, among the three public transportation modes – rail, bus and domestic air – it is found that air is weakest in terms of competitive power. From the viewpoint of long-term forecasting trends, the bus holds its competitive power in comparison with other public transportation modes and would not be replaced in the future. 相似文献
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为了研究斜拉索在端部激励下的振动机理,考虑了斜拉索垂度、刚度、非线性、空间三维、端部位移等诸多因素,经过一系列精细推导,利用Galerkin多模态截断方法,建立了单自由度斜拉索三维振动的统一方程,并提出了斜拉索三维振动频率分量由各自方向上的固有频率和端部位移激励扰动项组成。斜拉索在考虑三维端部位移理想激励时,采用4~5阶龙格-库塔法编写了端部位移激励与斜拉索固有频率比值以1:1和2:1进行振动的MATLAB数值求解程序。研究表明:当频率比值以1:1振动时,位移响应规律性的拍频消失,转变为拍频叠合的效果,且其振动幅值在时间域上表现出高低起伏的趋势,其位移响应峰值、谷值均呈现出不断增大趋势。此外,斜拉索在端部很小的位移激励下便可产生较大的振动。当频率比值以2:1振动时,其位移响应表现出与一阶强迫共振同样的拍频特征。参数振动位移响应振幅正负值同样出现了偏差值,此条件下,微小的端部位移也能够激起较大的参数振动响应,因此参数振动同强迫振动一样不容忽视。斜拉索在端部位移作用下不仅有频率比为1:1的共振和2:1的参数共振,还发生了1:2的共振,即斜拉索在端部位移激励下具有3个主共振区,分别在频率比值为0.5,1,2周围,1:2共振产生的振幅明显小于1:1共振和2:1参数共振。 相似文献
695.
如果线性有源网络的每一条支路上的物理量都视为独立变量,那么网络成了这些参量的有理函数域F(z)上的网络.文中讨论了F(z)上线性有源网络状态方程存在的条件,推导出状态方程表达式.并用VC与MATLAB语言设计了专门的电网络分析软件,可将所需要分析的电网络通过图形输入及编辑、电路拓扑结构分析和矩阵代数运算,即可得到要求的状态方程。 相似文献
696.
建立SBS改性沥青在老化过程中性能衰变的非线性预测方程,通过薄膜烘箱试验验证了预测方程的可靠性,基于预测方程分析了SBS改性沥青老化过程中性能指标的变化速率。研究结果表明,非线性方程x(t)=(Lx0)/[1+(L-1)e-rt]可用以预测针入度、软化点、延度在SBS改性沥青老化过程中的变化规律;沥青针入度、软化点、延度的变化速率随老化时间的延长而逐渐下降,其中延度指标在老化初期的变化速率下降最快;可通过建立宏观性能指标与红外光谱a1700/a1600的关系方程,进行SBS改性沥青老化程度的预测评估。 相似文献
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Theoretically calculation and laboratory experiments were performed to investigate the horizontal force exerted by internal solitary wave (ISW) on small circular cylindrical structures. Improvement in calculation of drag force and inertia force by introducing two-drag-coefficient method and spatial derivative of velocity into the calculation of force by eigenfunction was made based on systematically study on theoretical foundations. Particle image velocimetry (PIV) method and high precision force sensor were used to measure the velocity and force exerted by ISW, respectively. ISW waveform was traced by analyzing image frames follow grayscale threshold method. For the first time, components of horizontal force were calculated from PIV data, which show good agreement with theoretical one. Moreover, series comparisons between experimental data and calculational results were carried out to examine the proposed method. The results show ideal accuracy of the method and significant improvement comparing to the traditional method. 相似文献
699.
[Objectives]Electromagnetic pulse can seriously affect and even destroy naval shipborne electronic information systems, weapons, equipment and so on. Due to the complexity of the antenna port load circuit, it is necessary to formulate a numerical method which can easily obtain the antenna load current. [Methods]The induced current of the terminal is obtained on the basis of the finite-difference time-domain (FDTD) and Holland model. According to the Thévenin equivalent circuit, the conductor is equivalent to the voltage source to realize decoupling between the conductor and load end, and the load circuit is solved using Simulink software.[Results]Compared with the traditional terminal model, this method is simple and feasible for high-order circuit processing. The effectiveness of the model is verified using non-linear elements and parallel capacitors and resistors as the load respectively. The results show that the calculation results of this method are consistent with those of the traditional methods. Finally, the antenna of the end-connected protect- or is calculated. The results show that the lead inductance caused by the installation of the protector is an important factor affecting the protection performance.[Conclusions]The method proposed in this paper can greatly reduce the simulation complexity of the coupling current of an antenna with a complex load, giving it useful reference value for the field of ship electromagnetic pulse protection design. © 2023 Editorial Department of Chinese Journal of Ship Research. All Rights Reserved. 相似文献