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591.
This paper investigates mathematical modelling of response amplitude operator(RAO) or transfer function using the frequency-based analysis for uncoupled roll motion of a floating body under the influence of small amplitude regular waves. The hydrodynamic coefficients are computed using strip theory formulation by integrating over the length of the floating body. Considering sinusoidal wave with frequency( ω) varying between 0.3 rad/s and 1.2 rad/s acts on beam to the floating body for zero forward speed, analytical expressions of RAO in frequency domain is obtained. Using the normalization procedure and frequency based analysis, group based classifications are obtained and accordingly governing equations are formulated for each case. After applying the fourth order Runge-Kutta method numerical solutions are obtained and relative importance of the hydrodynamic coefficients is analyzed. To illustrate the roll amplitude effects numerical experiments have been carried out for a Panamax container ship under the action of sinusoidal wave with a fixed wave height. The effect of viscous damping on RAO is evaluated and the model is validated using convergence, consistency and stability analysis. This modelling approach could be useful to model floating body dynamics for higher degrees of freedom and to validate the result. 相似文献
592.
A pneumatic launcher is theoretically investigated to study its natural transverse vibration in water. Considering the mass effect of the sealing cover, the launcher is simplified as a uniform cantilever beam with a top point mass. By introducing the boundary and continuity conditions into the motion equation, the natural frequency equation and the mode shape function are derived. An iterative calculation method for added mass is also presented using the velocity potential function to account for the mass effect of the fluid on the launcher. The first 2 order natural frequencies and mode shapes are discussed in external flow fields and both external and internal flow fields. The results show good agreement with both natural frequencies and mode shapes between the theoretical analysis and the FEM studies. Also, the added mass is found to decrease with the increase of the mode shape orders of the launcher.And because of the larger added mass in both the external and internal flow fields than that in only the external flow field, the corresponding natural frequencies of the former are relatively smaller. 相似文献
593.
In this paper an analytical solution for the stability of the fully developed flow drive in a magneto-hydro-dynamic pump with pulsating transverse Eletro-magnetic fields is presented. To do this, a theoretical model of the flow is developed and the analytical results are obtained for both the cylindrical and Cartesian configurations that are proper to use in the propulsion of marine vessels. The governing parabolic momentum PDEs are transformed into an ordinary differential equation using approximate velocity distribution. The numerical results are obtained and asymptotic analyses are built to discover the mathematical behavior of the solutions. The maximum velocity in a magneto-hydro-dynamic pump versus time for various values of the Stuart number, electro-magnetic interaction number, Reynolds number, aspect ratio, as well as the magnetic and electrical angular frequency and the shift of the phase angle is presented. Results show that for a high Stuart number there is a frequency limit for stability of the fluid flow in a certain direction of the flow. This stability frequency is dependent on the geometric parameters of a channel. 相似文献
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在短波信道探测中,收发系统的本振频差对多普勒频移的测量至关重要.针对短波信道探测系统中IC-725A短波电台原有本振频偏较大的问题,采用锁相环(PLL)频率合成技术,利用铷时钟提供基准参考频率,对IC-725A短波电台的本振信号源进行高稳定度改进.给出PLL中鉴相器(PD)、环路低通滤波器(LF)的设计方案,并用电路实现.研究并给出一种在不影响电台总体性能的情况下将PLL输出的高稳定度本振信号注入到电台中的方法.实验测试结果表明,改造后两部IC-725A短波电台的本振信号的频差在10-4 Hz数量级,完全能满足短波信道探测对电台本振频率精度的要求. 相似文献
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为提高车辆获取位置信息的准确性,基于RFID(射频识别)技术提出一种车辆位置信息辅助系统,在本系统中,将RFID标签铺设至路面上,为装有RFID读卡器车辆提供准确的道路和位置信息系统.根据标签中提供的位置信息,利用车间通信,并依据车辆的运行状态,让无RFID车辆同时能够计算出自身的位置,达到信息扩散与共享的效果.本文结合8种不同的道路状况,进行仿真实验.结果表明:本系统能够在不同的道路状况下良好运行,实现位置信息的扩散与共享. 相似文献
599.
以泰州大桥为对象,分析了整体结构温度变化对于三塔两跨悬索桥结构静动力特性的影响.从Euler-Bernoulli梁出发,导出了杆件单元的内力变化后的动力特性分析等效刚度表达式.通过温度变化后大跨桥梁的静力分析,得到构件单元内力增量,计算等效刚度,进而计算温度变化后的动力特性.利用ANSYS的二次开发功能,编制了相应的宏命令和分析模块,分析了结构整体温度变化对大桥动力特性的影响.结果表明:环境温度变化对于泰州大桥结构静动力特性影响明显,温度的变化与大桥自振频率的变化呈反比关系.在进行大跨桥梁试验模态分析,以及结构损伤识别等研究中应考虑环境温度的影响. 相似文献
600.