An underwater towed system formerly included a dragging body and a dragging cable. In the past, the dragging body was calculated by the Runge-Kutta method and the dragging cable was calculated by the finite difference method. The distinctive features of our new method are: ( 1 ) our system has two dragging cables; (2) it is more convenient to calculate the dragging body also with the finite difference method. Sections 1,2 and 3 of the full paper explain our new method. The core of section 1 is that we build the three-dimensional equations of motion of each dragging cable according to the d' Alembert theory. The core of section 2 is that we make only some changes in the three-dimensional equations of motion of the buoy taken from some open literature. The core of section 3 is that we use the unified finite difference method to work out the numerical solution of the two-part underwater towed system; we point out that the finite difference method for calculating the whole of two-part underwater towed system produces a different numerical solution from that of one-part underwater towed system. The core of section 4 is that we simulate a certain two-part underwater towed system; the simulation results, given in Figs. 3, 4 and 5, and their analysis show preliminarily that: ( 1 ) the two-part underwater towed system moves steadily in the sea, indicating that the equations of motion we established are correct; (2) the use of a floating body distances the dragging cable away from the submarine, thus ensuring its safety and indicating that the use of the floating body is necessary.%水下双拖系统是海洋工程中非常重要的一种拖曳系统,可以用于潜艇通讯、数据传输、海洋测量等.文章根据达朗伯原理建立了拖曳系统的动力学模型,确定了边界条件,根据动量和动量矩定理建立了浮标运动的数学模型,并基于统一的有限差分数值方法建立了整个拖曳系统的数值解法.最后对典型的水下双拖系统进行了仿真计算,结果显示:水下双拖系统运动稳定,说明建立的动力学模型的正确性,及其数值算法的稳定性;浮体的使用使拖缆远离了艇体,很好地保证了潜艇的安全性,说明了浮体使用的必要性.
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