拖下水·滑下水·自己下水

看过电视剧《杨乃武与小白菜》,笔者觉得最不是滋味的就是冤案昭雪后,“老佛爷”怪罪小白菜的那句独白:“你坏了我一百多文官。”“老佛爷”的意思,杨案中那胡审乱批被罢职的京浙百官都是小白菜拖下水的。其实,稍知剧情者都知道,小白菜何其冤也?！ 作为历史人物,谁也不知道“老佛爷”是否说过这句话。

万吨级下水驳船

对于大型深水导管架的海上安装，当其吊重超过现有浮吊起重能力时，采用导管架从驳船上滑移下水是一种提高浮吊利用率、通常也是唯一可行的导管架安装方法，承担这种作业的驳船必须是具有特殊装备和功能的下水驳船。

深水导管架安装研究

对于大型深水导管架的海上安装,当其吊重超过现有浮吊起重能力的情况下,采用导管架从驳船上滑移下水是一种提高浮吊利用效率,通常也是唯一可行的安装方法,目前该技术代表了国际先进的深水导管架施工方法。本文介绍了该方法的特点、关键技术、主要施工过程及所需的设备设施。

小学自然教学的教学模式——学习刘默耕小学科学教育思想之一

一种教学思想要转化成教育实践,必须用相应的教学方式来实施,这些方式带有这种教学思想的明显特征,人们就把这些方式叫做“模式”。那么,刘默耕的小学科学教育思想在自然教学中所采用的模式又是什么呢? 我们先来看刘默耕是怎样认识“模式”的。他认为,教学模式不应该是一成不变的固定程序,而应该“根据当时的教材内容、学生状况、当时周围的条件来定”,“各种方法都是为达到目的而用的”。(本组文章中刘默耕的话均引自《刘默耕小学自然课改革探索》一书)“

Design of novel sliding-mode controller for high-velocity AUV with consideration of residual dead load

This work focuses on motion control of high-velocity autonomous underwater vehicle(AUV).Conventional methods are effective solutions to motion control of low-and-medium-velocity AUV.Usually not taken into consideration in the control model,the residual dead load and damping force which vary with the AUV’s velocity tend to result in difficulties in motion control or even failure in convergence in the case of high-velocity movement.With full consideration given to the influence of residual dead load and changing damping force upon AUV motion control,a novel sliding-mode controller(SMC)is proposed in this work.The stability analysis of the proposed controller is carried out on the basis of Lyapunov function.The sea trials results proved the superiority of the sliding-mode controller over sigmoid-function-based controller(SFC).The novel controller demonstrated its effectiveness by achieving admirable control results in the case of high-velocity movement.

Nonlinear trajectory tracking control of a new autonomous underwater vehicle in complex sea conditions

Autonomous underwater vehicles (AUVs) navigating in complex sea conditions usually require a strong control system to keep the fastness and stability. The nonlinear trajectory tracking control system of a new AUV in complex sea conditions was presented. According to the theory of submarines,the six-DOF kinematic and dynamic models were decomposed into two mutually non-coupled vertical and horizontal plane subsystems. Then,different sliding mode control algorithms were used to study the trajectory tracking control. Because the yaw angle and yaw angle rate rather than the displacement of the new AUV can be measured directly on the horizontal plane,the sliding mode control algorithm combining cross track error method and line of sight method was used to fulfill its high-precision trajectory tracking control in the complex sea conditions. As the vertical displacement of the new AUV can be measured,in order to achieve the tracking of time-varying depth signal,a stable sliding mode controller was designed based on the single-input multi-state system,which took into account the characteristic of the hydroplane and the amplitude and rate constraints of the hydroplane angle. Moreover,the application of dynamic boundary layer can improve the robustness and control accuracy of the system. The computational results show that the designed sliding mode control systems of the horizontal and vertical planes can ensure the trajectory tracking performance and accuracy of the new AUV in complex sea conditions. The impacts of currents and waves on the sliding mode controller of the new AUV were analyzed qualitatively and quantitatively by comparing the trajectory tracking performance of the new AUV in different sea conditions,which provides an effective theoretical guidance and technical support for the control system design of the new AUV in real complex environment.

A space-saving steering method for underwater gliders in lake monitoring

An increasing number of underwater gliders have been applied to lake monitoring. Lakes have a limited vertical space. Therefore, good space-saving capacity is required for underwater gliders to enlarge the spacing between monitoring waypoints. This paper presents a space-saving steering method under a small pitch angle （SPA） for appearance-fixed underwater gliders. Steering under an SPA increases the steering angle in per unit vertical space. An amended hydrodynamic model for both small and large attack angles is presented to help analyze the steering process. Analysis is conducted to find the optimal parameters of net buoyancy and roll angle for steering under an SPA. A lake trial with a prototype tiny underwater glider （TUG） is conducted to inspect the applicability of the presented model. The trial results show that steering under an SPA saves vertical space, unlike that under a large pitch angle. Simulation results of steering are consistent with the trial results. In addition, multiple-waypoint trial shows that monitoring with steering under an SPA covers a larger horizontal displacement than that without steering.

Steering control for underwater gliders

Steering control for an autonomous underwater glider （AUG） is very challenging due to its changing dynamic char- acteristics such as payload and shape. A good choice to solve this problem is online system identification via in-field trials to capture current dynamic characteristics for control law reconfiguration. Hence, an online polynomial estimator is designed to update the yaw dynamic model of the AUG, and an adaptive model predictive control （MPC） controller is used to calculate the optimal control command based on updated estimated parameters. The MPC controller uses a quadratic program （QP） to compute the optimal control command based on a user-defined cost function. The cost function has two terms, focusing on output reference tracking and move suppression of input, respectively. Move-suppression performance can, at some level, represent energy-saving performance of the MPC controller. Users can balance these two competitive control performances by tuning weights. We have compared the control performance using the second-order polynomial model to that using the filth-order polynomial model, and found that the tbrmer cannot capture the main characteristics of yaw dynamics and may result in vibration during the flight. Both processor-in-loop （PIL） simulations and in-lake tests are presented to validate our steering control performance.