均匀流场中含自由液面的陷落腔脉动压力分布研究

在有自由液面的情况下,针对横剖面为圆形的陷落腔模型,在均匀流场条件下,开展水动力实验研究,模拟了大量的工况,测量了腔体壁面的流体脉动压力.本文分析了模型所受的脉动压力随傅汝德数在不同腔体位置的变化趋势,并讨论了晃荡现象对压力分布的影响.实验时发现,傅汝德数小于0.35的工况有明显的晃荡现象发生,而傅汝德数小于0.35的工况的脉动压力系数也明显大于其他工况,且变化剧烈.本文认为,流体剪切层自持振荡与腔内液体深度驻波振荡共振是产生晃荡现象的原因,本文实验中Fr≤0.35的工况对应的流速正是达到以上两种振荡频率耦合所需要的流速.本文对工程应用中的腔体尺度和形式的设计有一定的指导意义.     

有自由液面的陷落式圆腔流噪声实验研究

采用基于经验模态分解(EMD)的本征模态函数(IMF)分析法和对比实验法研究了有自由液面的陷落式圆腔的流噪声,实验流速为0.4m/s~2.0m/s,间隔0.2m/s。实验发现当流速为0.4m/s~0.6m/s时,腔内液体有明显的振荡现象,其表现形式为液体沿腔内深度方向的大幅上下运动,称为“活塞(Piston)”现象。当流速大于等于0.8m/s时,腔内无振荡现象出现。通过对背景噪声和腔流噪声的本征模态函数作对比分析,得到了腔内流噪声的特性。     

Robust aspects in dependable filter design for alignment of a submarine inertial navigation system

The strapdown inertial navigation system (SINS) is able to provide continuous estimates of a vehicle??s velocity, position and attitude. As a rule, the SIMS component known as a high accuracy strapdown inertial measurement unit (SIMU) is an exceptionally expensive system. Less expensive SIMUs comprised of low cost sensors suffer from degraded performance, but this can be compensated for, in part, by addition of a velocity data recorder (VDR) to accompany the SINS. In this configuration, the need frequently arises to align the SINS of a submarine to in order to avoid a long run-up of the inertial system before a start command is issued. This in-motion alignment (IMA) can be accomplished by integrating SINS data with some external aiding source, such as the VDR, by using some form of measurement matching method. Accordingly, this paper demonstrates a consistent IMA scheme for a low-cost SIMU using a robust Kalman/ $ H_{\infty } $ filter structure. An error model of the SINS is derived in which the state vector includes attitude, velocity, position and sensor errors. Velocity information from the VDR is used as a measurement to the proposed filter. All significant equations concerning navigation are presented in conjunction with argument. Results show the advantages of the approach and emphasize diverse aspects of the SINS.     

Simulator training for maritime complex tasks: an experimental study

Training simulators are largely deployed to provide operators working within complex systems to instil adequate skills to handle normal and abnormal situations. Improved technology and higher computation power have significantly increased the use of training simulators in the training programs. The goal of this pilot study is to determine the design of training in order to prepare for complex tasks within the maritime domain. In this experimental study, students are trained to perform docking operations when ocean currents with increasing complexity are introduced in the training program. The effect of the training is evaluated by comparing two groups: one trained with homogenous currents and the other with heterogeneous currents. Objective performance measures are used to analyse the participants’ performance. The results indicate that when the participants were exposed to tasks with gradually increasing complexity, they performed better as compared to those who were exposed to complex tasks too early in the training. The results suggest that even though the technology and computational power provide for new possibilities in training simulators, new features that make the tasks more complicated should not be included too early in the training without sufficient investigation. It is also found that increasing functional fidelity of the simulation during training has resulted in the improved performance of the participants during the complex tasks (docking operations), as compared to those training with the highest fidelity from the beginning.     

Consistency in the development of performance assessment methods in the maritime domain

The maritime industry is considered to be a backbone of the global economy. It is therefore imperative to ensure that maritime operations run safely and efficiently. Assessment of maritime performance is necessary for designers and engineers to be able to pinpoint the weakest links in the system and make impactful system improvements. The current article presents a systematic quantitative literature review of research on performance assessment in the maritime industry with the goal of establishing an understanding of accuracy and consistency in the development of methods used to assess performance. The review focuses on four major segments within the industry—port logistics, ship handling, safety and environmental research—and investigates their uses in developing accurate and consistent performance assessment methods. After the completion of an exclusion process, 62 articles published in a wide range of academic journals were used in the analysis. Two important conclusions were drawn from the analysis. First, performance assessment is generally consistent throughout the maritime industry; most papers used accurate and consistent approaches to develop the methods (n?=?43). A subsequent bivariate analysis revealed a call for increased attention to the development of assessment methods within the maritime segment of ship handling. The current study suggests and discusses certain directions with regard to assessment research in the maritime industry.