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241.
Athanasios A. Pallis 《WMU Journal of Maritime Affairs》2007,6(1):3-20
Throughout Europe, a number of maritime interests have re-targeted their lobbying structures and strategies aiming to influence
the development of the maritime related European Union (EU) policies. The paper examines these maritime interests’ mobilisation
in the making of the Common EU Maritime Transport Policy (CMTP). First, it provides a review of the role of these interest
groups and the implications of the observed collective interests’ representation. Then, with the contribution a data-set of
replies to a questionnaire distributed to all the interest groups that are involved in EU maritime affairs, the paper analyses
the variety of interest groups representing the maritime sector in EU affairs. The focus is on the structures (i.e. membership
numbers and types, location, internal structures, budget) and the lobbying practices of the 37 identified EU level maritime
related organisations. The paper also presents an evaluation of the most positive and most negative parameters of the ‘EU
environment’ and the ‘economic environment’ that assist, or undermine, the governability cohesiveness of this collective action.
This study provides information on whether and under what conditions maritime interests are able to form comprehensive EU-level
organisations capable of representing their members and their interests in the EU policy making process 相似文献
242.
An efficient method for calculation of the slamming pressures on ship hulls in irregular waves is presented and validated
for a 290-m cruise ship. Nonlinear strip theory was used to calculate the ship–wave relative motions. The relative vertical
and roll velocities for a slamming event were input to the slamming calculation program, which used a two-dimensional boundary
element method (BEM) based on the generalized 2D Wagner formulation presented by Zhao et al. To improve the calculation efficiency,
the method was divided into two separate steps. In the first step, the velocity potentials were calculated for unit relative
velocities between the section and the water. In the next step, these precalculated velocity potentials were used together
with the real relative velocities experienced in a seaway to calculate the slamming pressure and total slamming force on the
section. This saved considerable computer time for slamming calculations in irregular waves, without significant loss of accuracy.
The calculated slamming pressures on the bow flare of the cruise ship agreed quite well with the measured values, at least
for time windows in which the calculated and experimental ship motions agreed well. A simplified method for calculation of
the instantaneous peak pressure on each ship section in irregular waves is also presented. The method was used to identify
slamming events to be analyzed with the more refined 2D BEM method, but comparisons with measured values indicate that the
method may also be used for a quick quantitative assessment of the maximum slamming pressures. 相似文献
243.
Forng-Chen Chiu Wen-Chuan Tiao Jenhwa Guo 《Journal of Marine Science and Technology》2007,12(4):203-217
It is well known that the hydrodynamic responses of a high-speed vessel traveling in regular head waves of even moderate wave
height can show significant nonlinear behavior, and so linear statistical techniques become insufficient for predicting the
statistics of responses in irregular waves. On the other hand, it has been shown that an approximate third-order Volterra
model is applicable to handling the statistics of some nonlinear seakeeping problems, such as motions and vertical hull girder
loads. In the present study, the focus is on the nonlinear behavior of the pressure responses of the hull surface, especially
on the pressures acting on alternately wet and dry areas near the waterline and on the bow zone with high deadrise angles
that may be subject to slight impact and water pile-up effects. To clarify the validity of applying Volterra modeling to this
problem, a series of experiments in regular and irregular head waves were carried out, and approximate third-order and fifth-order
Volterra models with the proposed algorithm for finding frequency response functions (FRFs) were applied as a means of validation.
In the present article, the first part of the validation was performed using experimental data in regular waves. It was confirmed
that the third-order Volterra model has adequate accuracy to simulate deterministically the variation of pressure responses
in regular waves of different wave steepness up to a wave amplitude to wavelength ratio of 0.01 even for the highly nonlinear
pressures acting on the above-mentioned areas of the hull surface. 相似文献
244.
245.
246.
HANBing ZHAOGuo-liang 《船舶与海洋工程学报》2004,3(1):24-27
The course-keeping control of underactuated hovercraft with two aft propellers was considered. The control of the heading error and cross-track error was accomplished by the yaw torque merely in this case. The hovercraft dynamic model is nonlinear and underactuated. At first the Controllability of course-keeping control for hovercraft was proved, then a course-keeping control law was derived that keeps hovercraft heading constant as well as minimizes the lateral movement of hovercraft. The proposed law guarantees heading error and sway error all converge to zero exponentially. Simulation tests were carried out to illustrate the effectiveness of the proposed control law. For further research, the disturbance influence would be considered in the dynamic equations. 相似文献
247.
Chang Doo Jang Jong Jin Jung Alexander A. Korobkin 《Journal of Marine Science and Technology》2007,12(2):95-101
This article describes an estimation method for the hull girder response of a ship due to springing. The linear and nonlinear
springing effects on the hull girder are evaluated. Previous studies on the springing response focused mainly on the symmetric
response, or vertical response. In this article, however, the springing analysis is extended to asymmetric responses, or horizontal
and torsional responses. The Timoshenko beam model was used to calculate the hull girder response and the quadratic strip
method was employed to calculate hydrodynamic forces and moments on the hull. To remove irregular frequencies, a rigid lid
was adopted on the hull free surface level and hydrodynamic coefficients were interpolated for asymptotic values. Applications
to two ships for the symmetric and asymmetric responses were carried out and the effect of springing responses is also discussed. 相似文献
248.
Sales tax measures passed at the local level and dedicated to transportation projects have become increasingly popular in
the United States. While revenues from fuel taxes stagnate, growth of local transportation sales taxes (LTSTs), most approved
in local elections, has led to a gradual shift of the financial base for transportation projects away from user fees and toward
broader-based taxes. In this study, the relationship between voter support and the social, political, and geographic characteristics
of the voters is explored. Using precinct-level voting data and census demographic data for three local transportation sales
tax elections in Sonoma County, in the San Francisco Metropolitan area of California, regression models were constructed to
analyze this relationship. In addition, the relationship between the outcomes of the three measures was explored to better
understand which transportation projects might have garnered more support for the successful measure. It was found that the
closer voters lived to the transportation projects to be funded, the greater their support. Higher incomes were also positively
related to support, controlling for other variables. Political leanings were found to affect support, with the direction of
the effect dependent upon the project list in each measure’s expenditure plan. Finally, it appears that the latest measure,
which passed successfully, benefited greatly from its multi-modal expenditure plan. 相似文献
249.
WAN De-Cheng 《船舶与海洋工程学报》2007,6(2):51-58
In this paper, an efficient multigrid fictitious boundary method (MFBM) coupled with the FEM solver package FEATFLOW was used for the detailed simulation of incompressible viscous flows around one or more moving NACA0012 airfoils. The calculations were carried on a fixed multigrid finite element mesh on which fluid equations were satisfied everywhere, and the airfoils were allowed to move freely through the mesh. The MFBM was employed to treat interactions between the fluid and the airfoils. The motion of the airfoils was modeled by Newton-Euler equations. Numerical results of experiments verify that this method provides an efficient way to simulate incompressible viscous flows around moving airfoils. 相似文献
250.
LIU Sheng FANG Liang 《船舶与海洋工程学报》2007,6(3):62-67
Given the uncertainty of parameters and the random nature of disturbances that effect a ships course, a robust course controller should be designed on the basis of rudder/flap vector control. This paper analyzes system uncertainty, and the choice of weighting functions is also discussed. When sea waves operate on a ship, the energy-concentrating frequency varies with the angle of encounter. For different angles of encounter, different weighting functions are designed. For the pole of a nominal model existing in an imaginary axis, the bilinear-transform method is used. The "2-Riccati" equation is adopted to solve the H∞ controller. A system simulation is given, and the results show that, compared with a PID controller, this system has higher course precision and more robust performance. This research has significant engineering value. 相似文献