近水面状态有限长圆柱壳振动特性分析

基于波传播方法和镜像法,建立了近水面状态圆柱壳-声场耦合模型,并采用数值方法求解耦合系统的特征方程,得到了近水面状态圆柱壳的模态频率。理论分析结果与现有实验测量结果及有限元仿真结果的良好吻合验证了本文理论方法的有效性。数值分析表明:自由液面的存在使得水下圆柱壳结构的模态频率较对应模态下理想全浸没状态结构的模态频率明显增大;随着潜深的增加,自由液面对水下圆柱壳模态频率的影响逐渐减小,当潜深大于4倍壳体半径时,自由液面的影响可以忽略。

近水面状态有限长圆柱壳受迫振动的输入功率流和声辐射特性

基于声固耦合模型,采用波传播方法分析近水面状态有限长圆柱壳受迫振动的输入功率流和声辐射特性,并考虑了自由液面的影响。通过与有限元仿真结果进行对比分析,验证了该方法的正确性。当圆柱壳接近自由液面时,自由液面的存在致使水下圆柱壳输入功率流和声辐射特性的峰值频率向高频偏移,且响应幅值也略有增大。随着潜深的增大,自由液面对圆柱壳输入功率流特性的影响逐渐减小。当潜深大于5倍半径时,自由液面对耦合系统输入功率流的影响可以忽略,但其对耦合系统声辐射特性的影响不可忽略。

基于数据驱动的水面艇航行状态检测与诊断

水面无人艇是一种自主规划、自主航行的小型水面舰艇,多用于执行各种危险的作战任务,现已被各国广泛应用于军事领域.为保证水面艇在工作过程中的安全性和可靠性,讨论了基于数据驱动的方法应用于水面艇航行状态检测与诊断的优势,分析了基于PCA、SVM、BP神经网络3种方法的应用效果,提出了可行的检测与诊断方法,可为研究人员的相关工作提供参考.

论《72年国际海上避碰规则》在水面船舶与潜艇间避碰方面的适用性及对策

随着海上船舶密度不断增大,航行环境越来越复杂。船舶与潜艇海上相遇的机会明显增多,船舶与潜艇避碰问题愈来愈显重要。要达到安全避让的目的,就有个相互熟悉了解的问题。由于潜艇的特殊结构、机动性能差和强调行动隐蔽。

Transition of super-hydrophobic states of droplet on rough surface

Twelve samples with periodic array square pillars microstructure were prepared on the silicon wafer by plasma etching techniques, on which space b of the square pillars increased from 5 to 60 μm. In order to study the effect ofb on the wettability of the rough surface, the effects of apparent contact angle （CA） and sliding angle （a） of the droplet on the rough surface were measured with the contact angle meter. The results show that the experimental values of CA well agree with the classical wetting theory and a decreases with the increase of b. Two drop shapes exist on the samples＇ surface, corresponding to the Cassie state and the Wenzel state respectively. The contact state in which a drop would settle depends typically on the size of b. On the role of gravitation, the irreversible transition of a drop from Cassie state to Wenzel state should occur at a certain space of the square pillars. Since the transition has implications on the application of super-hydrophobic rough surfaces, theoretically, the prediction of wetting state transition on square pillar array micro-structured surfaces provides an intuitionistic guidance for the design of steady superhydrophobic surfaces.

Steering Vibrational Population Transfer via Double-∑-Type Laser Scheme

The vibrational state-selected population transfer from a highly vibrationally excited level to the ground level is of great importance in the preparation of ultra-cold molecules. By using the time-dependent quantum-wave-packet method, the population transfer dynamics is investigated theoretically for the HF molecule. A double-E-type laser scheme is proposed to transfer the population from the ｜v=16〉 level to the ground vibrational level ｜v=0〉 on the ground electronic state. The scheme consists of two steps： The first step is to transfer the population from ｜v=16〉 to ｜v=7〉 via an intermediate level ｜v=11〉, and the second one is to transfer the population from ｜v=7〉 to ｜v=0〉 via ｜v=3〉. In each step, three vibrational levels form a E-type population transfer path under the action of two temporally overlapped laser pulses. The maximal population-transfer efficiency is obtained by optimizing the laser inten- sities, frequencies, and relative delays. Cases for the pulses in intuitive and counterintuitive sequences are both calculated and compared. It is found that for both cases the population can be efficiently （over 90%） transferred from the ｜v=-16〉 level to the ｜v=0〉 level.

Trajectory planning and tracking control for underactuated unmanned surface vessels

The trajectory planning and tracking control for an underactuated unmanned surface vessel(USV) were addressed.The reference trajectory was generated by a virtual USV,and the error equation of trajectory tracking for underactuated USV was obtained,which transformed the tracking and stabilization problem of underactuated USV into the stabilization problem of the trajectory tracking error equation.A nonlinear state feedback controller was proposed based on backstepping technique and Lyapunov's direct method.By means of Lyapunov analysis,it is proved that the proposed controller ensures that the solutions of closed loop system have the ultimate boundedness property.Numerical simulation results are presented to validate the effectiveness and robustness of the proposed controller.

Influence of laser geometric morphology type on Si C surface wettability

To obtain effective surface morphology to control surface wettability, this work investigated the influence of protuberant and concave morphology, which are respectively represented by circle-dimpled and micro-square-convex morphology, on surface wettability. The geometric morphologies were processed on silicon carbide （SIC） surfaces by a laser-marking machine, and surface wettability was monitored by the measurement of contact angles using the sessile drop method. Correlation analysis between contact angles and morphology parameters was conducted to determine the extent of influence. The results showed that the circle-dimpled diameter had a signific^mt influence on surface wettability, whereas grooved width did not. Additionally the depth of dimples and grooves exerted less influence on controlling wetting behaviors. In addition, surface wettability transformed from a superhydrophilic state to a hydrophobic state on micro-square-convex surfaces; contact angles on cir- cle-dimpled surfaces showed a relatively slow transformation, though the surface wettability also underwent the state change.

Peach skin effect:a quasi-superhydrophobic state with high adhesive force

The surface of a peach is known to exhibit spe- cial wettability and adhesion behaviors. We disclose that the peach surface is covered with long and short indumentums. The long indumentums are covered mainly with hydrophobic wax molecules, while the short indumentums are coated mostly with hydrophilic polysaccharides. Thus, the peach surface exhibits a quasi-superhydrophobic property and high adhesive force. A water droplet on the surface of a peach is a quasi-sphere, which is unable to roll off even when the peach is turned upside down. This is defined as the peach skin effect. We present that the quasi-superhydrophobic state with high adhesive force is attributed to the special coexisting Wenzel＇s and Cassie＇s state for water droplets, thus creating the strong interaction between the water droplet and surface.

An experimental investigation of tribological performance of triangular textures in water lubrication regime

Surface texturing has been considered as an effective approach to improve the tribological performances.Based on the consideration of enhancing the tribological performance,the experiments are carried out to investigate tribological performance of triangular textures in water lubrication.The textures are generated by the Nd:YAG laser marking system,with an area density of 20%and a depth of 7 m and are distributed uniformly on the surface of the SiC rings.Compared with the circular textures,the triangular textures have obvious tribological anisotropy.The triangular textures in clockwise direction show the best friction reduction effect among the three textures.The friction reduction mechanisms of the triangular textures in clockwise direction are also analyzed and discussed.