共查询到20条相似文献,搜索用时 234 毫秒
1.
2.
3.
基于自适应Backstepping方法的舰船电力系统混沌控制 总被引:1,自引:0,他引:1
将自适应Backstepping方法运用到舰船电力系统的混沌运动的控制中,可以将混沌系统稳定在平衡点,从而达到对船舰电力系统混沌运动的有效控制。根据船舰电力系统应用模型,该文设计了自适应控制器,当舰船电力系统处于混沌运动时该控制器自动开启。数字仿真表明该方法能够达到迅速抑制混沌的目的。 相似文献
4.
5.
6.
7.
为了改进利用传统回声状态网络(Echo Stale Network,ESN)方法预报非线性舰船摇荡时历时预报精度不足的问题,提出将相空间重构和回声状态网络相结合的方法,在依托海军某型舰实船采集摇荡数据的基础上,采用相空间重构技术提取舰船摇荡时历的内部结构信息,获取摇荡时历的相空间特性,对时历数据进行可用性筛选,然后将重构后的数据输入到回声状态网络进行学习训练,用于预报舰船极短期的摇荡姿态。利用实船数据进行不同预报时长条件下的试验仿真,并按照均方误差、均方根误差等误差标准对仿真结果进行误差分析。试验结果表明:所提方法对于舰船摇荡的预报具有精度高及稳定性强的优点,预报值与真实值相比从摇荡值和摇荡相位上都具有较好的精度,证明了该方法的可行性。 相似文献
8.
9.
10.
11.
《Marine Structures》2003,16(4):275-321
Various design loads used in the strength evaluation of ship structures have been introduced currently by classification societies. As most of these design loads have been determined as the standard loads for the sake of convenience, the relationships between the design loads and the sea states actually encountered by ships seem to be weak. Accordingly, it may be difficult to refer and utilize them as the fundamental design concepts for ship designers or the operational guidelines for ship operators. To overcome these difficulties, the authors have developed practical estimation methods of the design loads having transparent and consistent backgrounds to the actual loads acting on primary structural members of tankers. In this paper, the design sea states that closely resemble the actual sea states which are considered as the most severe for hull structures are firstly proposed. Secondly, the practical estimation methods of the design sea states are proposed by parametric studies using the results of series calculation of representative tankers. Thirdly, the practical estimation methods of design regular waves resulting in the same level of stresses with that induced in irregular waves under the design sea states are proposed. Finally, the practical estimation methods of the design loads such as ship motions, accelerations, hull girder bending moments and hydrodynamic pressures that are induced under design regular waves are proposed. 相似文献
12.
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
13.
《船舶与海洋工程学报》2018,(3)
The effect of coupling between sloshing and ship motions in the evaluation of slosh-induced interior pressures is studied. The coupling between sloshing loads and ship motions is modelled through a hybrid algorithm which combines a potential flow solution based on transient Green function for the external ship hydrodynamics with a viscous flow solution based on a multiphase interface capturing volume of fluid(VOF) technique for the interior sloshing motion. The coupled algorithm accounts for full nonlinear slosh forces while the external forces on the hull are determined through a blended scheme of linear radiationdiffraction with nonlinear Froude-Krylov and restoring forces. Consideration of this level of nonlinearities in ship motions is found to have non-negligible effects on the slosh-coupled responses and slosh-induced loads. A scheme is devised to evaluate the statistical measure of the pressures through long-duration simulation studies in extreme irregular waves. It is found that coupling significantly influences the tank interior pressures, and the differences in the pressures between coupled and uncoupled cases can be as much as 100% or more. To determine the RAO over the frequency range needed for the simulation studies in irregular waves, two alternative schemes are proposed, both of which require far less computational time compared to the conventional method of finding RAO at each frequency, and the merits of these are discussed. 相似文献
14.
15.
In order to understand characteristics of low-frequency motions of ships moored inside ports and harbors, analysis on actual cargo handling logbook of stevedoring services company, including events of interruption of cargo handling, and countermeasure for ship mooring problems are investigated by field observations at two ports and numerical simulation on moored ship motions. First model port concerns with interruption of cargo handling due to the low-frequency motions. Second model port relates to a resonant effect of long-period waves or harbor oscillations, and its countermeasure by mooring system. From the investigation, it is confirmed that the low-frequency motions of ships are induced by a resonance between surge motions and long-period waves or harbor oscillations and an asymmetry in the mooring system, and affect safe ship mooring and operation efficiency of cargo handling in ports and harbors significantly. 相似文献
16.
17.
18.
ClassNK has undertaken wide-ranging basic research covering many aspects related to the safety of ship structures, including design loads, structural analysis, strength assessment of buckling, collapse, and fatigue, and rational corrosion margins to develop new design standards which have transparency and consistency. Among the wide-ranging basic research, this article summarizes the results of extensive work on the design loads used for strength assessments of tanker and bulk carrier structures. The main aim of the research was to develop practical estimation methods of design loads with rational technical backgrounds relating to the actual loads acting on the primary structural members of tankers and bulk carriers. During this study, we proposed the following methodology. Design sea states that closely resemble the actual sea states which are considered to be the most severe for hull structures. Find practical estimation methods for the design sea states by parametric studies using the results of series calculations on representative tankers and bulk carriers. Find practical estimation methods for design regular waves which will result in the same level of stresses as those induced in irregular waves under the design sea states. We also briefly introduced some practical estimation methods for the design loads, such as ship motions, accelerations, hull-girder bending moments, and hydrodynamic pressures that are induced under design regular waves. The findings in this study have been summarized and implemented in the new design standards for tanker and bulk carrier structures.Updated from the Japanese original which won the 2003 SNAJ prize (J Soc Nav Archit Jpn 2002; 191:195–207; 2002; 191:208–220; and 2002; 192:723–733) 相似文献
19.
URANS analysis of a broaching event in irregular quartering seas 总被引:1,自引:0,他引:1
Pablo M. Carrica Kwang-Jun Paik Hamid S. Hosseini Frederick Stern 《Journal of Marine Science and Technology》2008,13(4):395-407
Ship motions in a high sea state can have adverse effects on controllability, cause loss of stability, and ultimately compromise
the survivability of the ship. In a broaching event, the ship losses control, naturally turning broadside to the waves, causing
a dangerous situation and possibly capsizing. Classical approaches to study broaching rely on costly experimental programs
and/or time-domain potential or system-based simulation codes. In this paper the ability of Reynolds averaged Navier–Stokes
(RANS) to simulate a broaching event in irregular waves is demonstrated, and the extensive information available is used to
analyze the broaching process. The demonstration nature of this paper is stressed, as opposed to a validated study. Unsteady
RANS (URANS) provides a model based on first principles to capture phenomena such as coupling between sway, yaw, and roll,
roll damping, effects of complex waves on righting arm, rudders partially out of the water, etc. The computational fluid dynamics
(CFD) method uses a single-phase level-set approach to model the free surface, and dynamic overset grids to resolve large-amplitude
motions. Before evaluating irregular seas two regular wave cases are demonstrated, one causing broaching and one causing stable
surf riding. A sea state 8 is imposed following an irregular Bretschneider spectrum, and an autopilot was implemented to control
heading and speed with two different gains for the heading controller. It is concluded that the autopilot causes the ship
to be in an adverse dynamic condition at the beginning of the broaching process, and thus is partially responsible for the
occurrence of the broaching event. 相似文献
20.
This article introduces novel extreme value prediction method that can be used for a variety of offshore engineering applications. First, to demonstrate the novel method, fictitious data from a non-linear Duffing oscillator and measured wave heights were used as examples. The second incident included a container ship that experienced significant deck panel strains while traveling across the Atlantic Ocean in bad weather. The main concern for cargo ship transportation is potential loss of container owing to violent movements. It is challenging to model such a situation because waves and ship motions are both non-stationary and complicatedly nonlinear. Extreme motions greatly increase the role of nonlinearities, activating effects of second and higher order.Furthermore, due to the scaling and the choice of sea state, laboratory testing may also be called into doubt. Therefore, data collected from actual ships during difficult weather voyages offers a special perspective on the statistics of ship motions.This paper aims to highlight an alternative method of extrapolation that is based on intrinsic properties of the data set itself and does not assume any extrapolation functional class. Extreme value predictions typically originate from certain statistical distribution functional classes to fit the data and then extrapolate. Engineering design can make use of the unique extrapolation method that has been proposed. The proposed method's forecast accuracy has been verified in comparison to the Averaged Conditional Exceedance Rate (ACER) extrapolation method. 相似文献