Vibration analysis of stepped-pipe strings for mining from deep-sea floors

The present study addresses essentially to the investigation of the longitudinal vibrations of a stepped-pipe string for mining from deep-sea floors. The stepped-pipe string, consisting of four parts having different physical properties in each pipe string segment, is assumed to have two pump modules and a buffer, each of which is equipped with a vibration absorber. Moreover, the pipe string is subjected to external viscous damping because of the surrounding medium. A theoretical analysis has been made for a simplified model of the system, in which it is assumed that both the pump modules and buffer can be considered as concentrated masses, the fluid inside of the pipe string vibrates together with the string, and that the flexible pipe does not affect the vibration of the pipe string. Furthermore, absorbers are modeled as concentrated masses, each of which is attached to pump modules and the buffer by springs and dampers. Applying the method of separation of variables, exact analytical solutions for damped free and forced responses of the system subjected to heave motion of the mining ship are determined with and without absorbers, in which overdamped and underdamped modes are determined and studied separately too. It is important to note that the solutions obtained are expressed in terms of parameters characterizing the physical properties of the system under consideration. Numerical applications show that the attachment of convenient vibration absorbers causes the longitudinal displacements at the certain locations to decrease to very small values, where the vibration absorbers are adjusted to the excitation frequency.     

Exact Bianchi type II, VIII and IX string cosmological models in Saez-Ballester theory of gravitation

Exact Bianchi type II, VIII and IX String cosmological models are obtained in the Saez-Ballester theory of gravitation. Some physical and geometrical properties of the models are studied.     

基于十进制遗传算法的含水层参数的反演

含水层参的反演是一个复杂的非线性优化问题，针对传统二进制遗传算法收敛性能差的缺陷，提出了反演含水层参数的十进制遗传算法.以直线隔水边界附近的井流模型为例，讨论了十进制遗传算法在含水层参数反演中的应用，并与二进制遗传算法的进行比较.结果表明，该方法在含水层参数的反演中不仅是可行的，而且具有较好的确定性和较高的精度;与二进制遗传算法相比，十进制遗传算法的收敛性较好，省时高效，且表示较为自然，容易引入相关领域知识.同时，结合实例的分析结果得出种群的规模对算法的收敛性没有明显的影响。