纳米碳纤维混凝土力学性能的试验研究

纳米碳纤维作为一种新型材料,具有高强度,高弹性模量等力学上的优异特性.通过单轴抗压试验和劈裂试验,测试了掺加3种类型纳米碳纤维的普通混凝土和自密实混凝土的基本力学性能,并讨论其最优掺量.实验结果表明:适当掺量且纤维分散良好的纳米碳纤维混凝土28 d抗压强度和劈裂强度均有不同程度的提高,表明纳米碳纤维对于混凝土材料力学性...     

一种提高分裂阵频域波束形成测向分辨力的方法

为了提高声呐系统对目标方位的分辨能力,本文提出一种分裂阵频域波束形成方法,即超波束互谱测向法。通过将超波束方法得到的方位谱加权到互谱方法得到的波束形成结果上,从而得到最终的波束输出结果。超波束互谱测向方法的优点是既能够降低主瓣宽度,抑制旁瓣,提高测向分辨力;又能够保留相位信息,为后续谱分析应用提供参考。实验室水池测试结果表明,利用阵元间距为0.016 m的16元均匀直线阵,对于37.5 kHz的声信号,采用超波束互谱方法进行波束形成与单纯采用互谱方法进行波束形成相比较,在0°和60°方位上的波束主瓣宽度分别减小了3.8°和6.9°,旁瓣幅度降低超过30 dB,测向分辨力得到明显提高,从而验证采用超波束互谱测向方法提高测向分辨力的可行性和有效性。     

制动盘的纵波模态对制动尖叫声影响研究

针对钳盘式制动器产生的制动尖叫声问题,对制动盘模态进行分析可知,即使制动盘纵波压缩模态频率在两个相邻模态频率中间,纵波压缩模态也可能被激发而产生制动尖叫声.提出了改变制动盘摩擦部分和帽子部分模态动态耦合的措施,并对改进后制动器进行了有限元分析和台架试验,结果表明,改进后制动器尖叫声的声压级和发生制动尖叫的次数都比改进前显著降低.     

混合动力汽车功率分配装置的功率传动分析

针对混合动力汽车功率分配装置这一关键部件,分析了以行星齿轮机构为核心的功率分配装置的动力学特性,得出了动力学方程,详细讨论了在各种驱动模式下的功率分配传动过程和效率,其结果可作为下一步混合电动汽车整车能量优化控制研究的基础.     

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针对商业网点的交通方式构成特性,首先分析了影响交通方式选择的因素,在北京市商业网点的调查数据基础上,利用人工神经网络强大的非线性映射能力和泛化功能,建立了公交出行比例预测的神经网络模型,并定量的分析了影响因素值的改变对公交比例的影响,预测了在不同策略下商业网点公交出行比例的变化情况。     

基于巢式Logit模型的航空港集疏运方式选择研究

为研究航空旅客出行方式选择行为,在航空港集疏运系统需求描述的基础上,介绍并运用巢式Logit模型原理,以广州白云国际机场为实例,建立适用于白云机场集疏运系统的方式选择模型(NL模型),分析确定各相关影响因素项的影响机理,运用最大似然估计法对虚拟选择枝的共性和相异部分的参数进行修正和标定,从而获取各种集疏运方式的选择概率.结合调查选取的20份样本数据,运用模型编程计算得出私人小汽车、出租车、机场巴士、城际巴士和城市轨道共5种集疏运方式的方式选择概率分布结果,结果显示私人小汽车和出租车二者占比大于45%,机场巴士和城际巴士占比约40%,城市轨道仅占比15%.因此,为大力发展城市的公共交通,需要对白云机场提出具有参考性集疏运系统改进方案,为今后航空港集疏运系统的发展和航空旅客交通方式选择行为研究提供一定的借鉴.      

基于TMD的钢弹簧浮置板轨道结构改进研究

为提升钢弹簧浮置板轨道低频域制振性能,应用有限元方法建立地铁车辆-钢弹簧浮置板轨道耦合动力学模型,对带凸台的常规钢弹簧浮置板轨道进行结构改进设计。参考某地铁实际线路,基于TMD定点理论以及多自由度系统等价质量识别法,通过对无凸台钢弹簧浮置板轨道进行模态分析和谐响应分析,确定钢弹簧浮置板凸台下减振元件的最优刚度、最优阻尼;然后基于车辆-钢弹簧浮置板轨道耦合动力学模型,研究列车动荷载作用下钢弹簧浮置板轨道改进前后低频域制振效果。结果表明:改进后的钢弹簧浮置板轨道能够有效地抑制轨道板固有频率附近频段的低频振动;合理的TMD参数匹配能够有效地控制列车动荷载下钢弹簧浮置板基频范围内的低频振动及对应频段钢弹簧支反力向周围基础的传递。     

Moving towards more eco-efficient tourist transportation to a resort destination: The case of Whistler, British Columbia

Transportation is not only a key component of the tourism value chain, but it is also a critical management consideration in shaping tourism's environmental footprint. Transportation consumes the greatest portion of the energy used in the tourism system. Most of this consumption is associated with travel to and from the destination. Despite this situation, scant research has addressed ways in which destinations can play a role in reducing this energy use challenge. Strategies such as shifting visitors to more energy-efficient modes have the potential to improve the eco-efficiency of tourist transportation. Using a case study of transportation management options and visitor responses in Whistler, British Columbia, Canada, this paper examines visitor reactions to a range of transportation strategies designed to shift skiers from private to public modes of transport. Respondents completed an online survey employing both traditional and stated choice questioning methods to examine tourists' transportation choice behaviour. Long-haul tourists were the most likely to shift transport modes based on the management options offered to them. Destination management strategies for moving this target group to public modes of transportation are described.     

Natural vibration characteristics of short-span submarine power cables with bending stiffness and sag

Based on a continuum model that governs the dynamics of submarine power cables, analytical solutions of the natural frequencies and modal shapes for free spanning cables are derived. The effects of sag, axial and bending stiffness are all included. The cable sag calculation has considered the effects of bending stiffness on the static profile. The accuracy of the derived solutions is validated by the results from a laboratory experiment. The applicable ranges of these solutions and that of Ricciardi (Ricciardi and Saitta, 2008) [15] are determined. Also, the effects of static profile, boundary conditions and non-dimensional parameters (ξ and λ²) on the cable natural frequencies and modal shapes are discussed. The results show that the static profile and boundary conditions have significant effects on the modal properties for free spanning submarine power cables. It must be noted that, for lower ξ values, the frequencies of the symmetric modes show a non-monotonic dependence on bending stiffness. The single-degree-of-freedom approach is adopted to further analyze the mechanisms of the non-monotonic behavior.     

大容量UPS电源车厢体骨架改进前后强度对比分析

大容量UPS电源车在首次设计制作中,发生骨架强度不够、厢体变形的情况,在对厢体骨架进行加固后,厢体再未发现变形情况,针对此次厢体变形整改情况建立加强前和加强后厢体骨架模型,运用ANSYSWorkbench对厢体骨架进行预应力模态分析,通过分析有限元仿真结果,对比厢体骨架在方案改进前后的应力和应变,得出厢体改进的可行性....