水下潜器改进S面控制及控制系统仿真(英文)

S surface controllers have been proven to provide effective motion control for an autonomous underwater vehicle (AUV). However, it is difficult to adjust their control parameters manually. Choosing the optimum parameters for the controller of a particular AUV is a significant challenge. To automate the process, a modified particle swarm optimization (MPSO) algorithm was proposed. It was based on immune theory, and used a nonlinear regression strategy for inertia weight to optimize AUV control parameters. A semi-physical simulation system for the AUV was developed as a platform to verify the proposed control method, and its structure was considered. The simulation results indicated that the semi-physical simulation platform was helpful, the optimization algorithm has good local and global searching abilities, and the method can be reliably used for an AUV.     

白令海潮汐能通量和底边界能耗散

The spatial distribution of the energy flux, bottom boundary layer (BBL) energy dissipation, surface elevation amplitude and current magnitude of the major semidiurnal tidal constituents in the Bering Sea are examined in detail. These distributions are obtained from the results of a three-dimensional numerical simulation model (POM). Compared with observation data from seven stations, the root mean square errors of tidal height are 2.6 cm and 1.2 cm for M₂ and N₂ respectively, and those of phase-lag are 21.8° and 15.8° respectively. The majority of the tidal energy flux off the deep basin is along the shelf edge, although some of this flux crosses the shelf edge, especially in the southeast of the shelf break. The total M₂ energy dissipation in the Bering Sea is 30.43 GW, which is about 10 times of that of N₂ and S₂. The semidiurnal tidal energy enters mainly to the Bering Sea by Samalga Pass, Amukta Pass and Seguam Pass, accounting more than 60% of the total energy entering the Being Sea from the Pacific.     

边界任意弹性约束薄板的横向振动(英文)

This paper presents an analytical study on the influence of edge restraining stiffness on the transverse vibrations of rectangular plate structure. An improved Fourier series method was employed to analyze the transverse vibration of plate structure with general elastically restrained boundary conditions. A linear combination of a double Fourier series and eight auxiliary terms was sought as the admissible function of the flexural displacement of the plate, each term being a combination of a polynomial function and a single cosine series expansion. The auxiliary terms were introduced to ensure and improve the smoothness of the original displacement function and its derivatives at the boundaries. Several numerical examples were given to demonstrate the validity and accuracy of the current solution. The influences of translational and rotational stiffness on the natural frequencies and mode shapes of plate were analyzed by numerical results. The results show that the translational stiffness has bigger influence on the natural frequencies than the rotational stiffness. It is generally well known that little change of the rotational stiffness has little influence on the mode shapes of plate. However, the current work shows that a very little change of rotational stiffness value may lead to a large change of the mode shapes of a square plate structure.     

Optimal scheduling of block lifting in consideration of the minimization of traveling distance while unloaded and wire and shackle replacement of a gantry crane

Nowadays, shipyards are making every effort to efficiently manage their resources such as gantry cranes, transporters, and block stock yards. The scheduling of block lifting for a gantry crane has been manually performed by an expert shipyard manager for many years. Such a practice, however, can lead to an undesirably long time to produce scheduling plans. In addition, the quality of the scheduling plans may not be optimal. To improve the overall process, a block lifting scheduling system for a gantry crane was developed in this study by using optimization techniques. A block lifting scheduling problem was first formulated as a multiobjective optimization problem. For a gantry crane, minimization of the traveling distance while unloaded and wire and shackle replacement between block lifting was considered. An optimization algorithm based on the genetic algorithm was then proposed and implemented so as to solve the problem. To evaluate the efficiency and applicability of the developed system, the system was applied to an actual block lifting scheduling problem in a shipyard. Compared to results achieved by manual scheduling by an expert manager, the results of this work show that blocks can be more efficiently lifted by a gantry crane when the developed system is applied.     

Computational investigation of cavitation on a semi-spade rudder

This article examines noncavitating and cavitating flow fields around a semi-spade rudder in the ship wake and propeller slipstream based on a computational method. The article seeks to explain the erosion that can occur around the gap due to cavitation; such erosion has been reported to occur while a ship is at sea. Another area of research is the effect of the gap size and shape. The effects of erosion-evading devices such as elongated gap edges, an increased edge radius, flow control projections, and vertical and horizontal guide plates were also studied.     

A process-centric ship design management framework

As the concept of concurrent engineering has emerged along with support for optimization techniques, lots of endeavors have been made to apply optimization techniques to real design problems for holistic decision-making. Even if the range of design problems to which optimization is applicable has been extended, most ship designs use an iterative and manual approach due to the difficulties of seamless integration of all related design activities. This paper proposes a process-centric management framework for the preliminary ship design process depending on these approaches. Requirements for the framework are generated based on the features of the ship design process first. The proposed framework consists of both process scheduling and process management parts. Each of these modules is divided into submodules, and the modules and their interactions are elaborated to reflect actual design practice. The designed framework is embodied within a workflow system and its usefulness examined through a pilot project.     

On the financial viability of mass transit development: the case of Hong Kong

Mass transit projects are often a top contender of many cities to meet their increasing demand for travel. Despite the global trend of privatization, mass transit services, as public goods, remain largely being provided and operated by the public sector. Hong Kong is one of the few exceptions that all mass transit services are commercially operated. Both rail and bus services in Hong Kong are reputable for their quality and profitability, often serving as benchmarks for new projects. In this study, we investigate the factors contributing to this success. In particular, we ascertain the quality of transit service provision by the private sector over the past two decades. Then, we conduct an in-depth analysis of the account books of leading railway and bus operators in Hong Kong so as to shed light on their financial viability. Through this study, we hope to present crucial factors for providing financially viable private transit services.     

Exploring passenger anxiety associated with train travel

Although people are often encouraged to use public transportation, the riding experience is not always comfortable. This study uses service items to measure passenger anxieties by applying a conceptual model based on the railway passenger service chain perspective. Passenger anxieties associated with train travel are measured using a modern psychometric method, the Rasch model. This study surveys 412 train passengers. Analytical results indicate that the following service items cause passenger anxiety during trains travel: crowding, delays, accessibility to a railway station, searching for the right train on a platform, and transferring trains. Empirical results obtained using the Rasch approach can be used to derive an effective strategy to reduce train passenger anxiety. This empirical study also demonstrates that anxiety differs based on passenger sex, age, riding frequency, and trip type. This information will also prove useful for transportation planners and policy-makers when considering the special travel needs of certain groups to create a user-friendly railway travel environment that promotes public use.     

Hierarchical ordering of nests in a joint mode and destination choice model

This paper seeks to explore the relationship between mode and destination choice in an integrated nested choice model. A fundamental argument can be made that in certain circumstances, the ordering of choices should be reversed from the usual sequence of destination choice preceding mode choice. This results in a travel demand model where travelers are more likely to change destinations than to change transportation modes. For small and medium size urban areas, particularly in the United States, with less well developed public transit systems that draw few choice riders, this assumption makes much more sense than the traditional modeling assumptions. The models used in the new travel modeling system developed for Knoxville, Tennessee utilize this reversed ordering, with generally good results, which required no external tinkering in the logsum parameters.