An experimental study of wave-in-deck loading and its dependence on the properties of the topside structure

This paper concerns the largest and arguably the most threatening wave loading component experienced by a broad range of offshore structures. It arises when an incident wave crest exceeds the elevation of the underside of the deck structure, leading to direct wave-in-deck (WID) loading. The extent of this loading may be limited to the partial submergence of some of the lowermost deck beams, or could involve the large-scale inundation of the entire deck area. Either way, very large loads can arise which must be taken into account when assessing the reliability of the structure. In an earlier contribution Ma and Swan (2020) provided an extensive laboratory study exploring the variation of these loads with the properties of the incident wave. The present paper describes a second stage of this experimental study in which the variation of the WID loads with the properties of the topside structure is addressed. Specifically, it considers the porosity, position and orientation of the topside relative to the incident wave conditions, and seeks to explore both the variations in the maximum load and the loading time–history resulting from these changes.Given the highly transitory nature of a WID loading event, coupled with the fact that the problem is governed by flow conditions at, or very close to, the instantaneous water surface, the loading process is driven by an exchange of momentum from the wave crest to the topside structure. A recently developed WID load model, based on exactly these arguments (Ma and Swan 2020), is used alongside the laboratory data to provide a break-down of the load into its component parts. This provides an enhanced physical understanding of the resulting load time–history. The first part of the study is based upon an idealised generic topside structure, allowing a systematic variation in key parameters, particularly porosity. The second part addresses a realistic topside structure demonstrating the practical relevance of earlier work. Taken together, the analysis clearly establishes the importance of the topside porosity, clarifies the spatial effects associated with the evolution of a large ocean wave beneath the plan area of a structure and explains the unexpected occurrence of impact-type loading on topside structures having a high porosity. Most importantly, the paper highlights those properties of a topside structure which must be incorporated if the WID loads are to be accurately predicted.     

Active response control of an offshore structure under wave loads using a modified probabilistic neural network

Offshore structures are subjected to wave, wind, and earthquake loads. The failure of offshore structures can cause sea pollution as well as loss of property and life. Therefore, the safety of such structures is an important issue. The reduction of the dynamic response of an offshore structure subjected to wind-generated random ocean waves is another critical problem with regard to the serviceability, fatigue life, and safety of the structure. In this article, the responses of offshore structures under random ocean waves are controlled using a modified probabilistic neural network (MPNN). As a more advanced method, it uses the global probability density function (PDF) produced by summing the heterogeneous local PDFs automatically determined from the individual standard deviation of each variable. The state vectors in a state-space model of a structure and the resulting control forces made by a linear quadratic regulator algorithm were used to generate the training patterns for the MPNN and a conventional multilayer perceptron (MLP). The results were compared with those produced by back-propagation based on the MLP. The proposed MPNN method shows good results not only in controlling the responses but also in terms of the computation time.     

基于压缩感知的正交偶极子阵列信号参数估计

[目的]针对传统的极化敏感阵列的波达方向(DOA)估计算法运算复杂度高、实时性差的问题,提出基于压缩感知的正交偶极子极化敏感阵列结构.[方法]将数据压缩思想应用于阵列结构设计,压缩接收信号矢量维度,减少射频前端链路数量,以控制系统的复杂度,使阵列结构设计具有高度的灵活性.基于结构降维多重信号分类(MUSIC)算法;首先...     

应用两步回归迭代算法校正数字式磁罗经误差

基于椭圆假设的参数估计目前是解决数字式磁罗经误差校正问题的较为先进的方法，然而对该方法中的非线性参数估计问题采取了扩展卡尔曼滤波的办法来解决，这造成误差在测量过程中的发散。提出了两步回归迭代算法来解决此问题的思路，即把待估计的非线性参数组合成线性参数，用卡尔曼滤波进行状态估计后，通过Causs-Newton法解得原非线性参数。实验结果证明了新方法的优越性。     

UKF和PF融合算法在动力定位船舶状态估计中的应用研究

针对船舶动力定位状态估计时使用扩展卡尔曼滤波导致模型失配而产生滤波精度不高甚至滤波发散的问题,设计一种融合无迹卡尔曼滤波和粒子滤波的动力定位船舶状态估计算法.该算法以粒子滤波作为整体框架,运用无迹卡尔曼滤波对粒子状态的每次更新进行最优化估计,从而最优化了每个粒子的状态,再根据每个粒子的重要性分布,得出船舶复合运动中的低频状态.Matlab仿真结果表明,该方法能够从含有高频和噪声干扰的测量信息中估计出的船舶低频运动状态,相比于直接使用UKF,该方法的滤波精度更高,滤波性能也比较稳定.     

基于决策树的模糊序贯最小优化分类器的人脸识别

序贯最小优化算法是一种SVM s(Support VectorM ach ines)训练算法,该算法将一个大型QP(Quadratic Programm ing)问题分解为一系列最小规模的QP子问题,从而避免了多样本情形下的数值解不稳定及耗时问题,同时也不需要大的矩阵存储空间。本文在模糊支持向量机的基础上,提出了基于决策树的模糊序贯最小优化算法并对它进行了分析和研究,在对人脸图像进行独立成分分析后,用该算法进行多类人脸识别。通过在ORL人脸库上的实验结果表明,在样本类别较少的条件下,该算法可以取得较好的效果。     

SPSM and its application in cylindrical shells

In naval architectures, the structure of prismatic shell is used widely. But there is no suitable method to analyze this kind of structure. Stiffened prismatic shell method (SPSM) presented in this paper, is one of the harmonic semi-analytic methods. Theoretically, strong stiffened structure can be analyzed economically and accurately. SPSM is based on the analytical solution of the governing differential equations for orthotropic cylindrical shells. In these differential equations, the torsional stiffness, bending stiffness and the exact position of each stiffener are taken into account with the Heaviside singular function. An algorithm is introduced, in which the actions of stiffeners on shells are replaced by external loads at each stiffener position. Stiffened shells can be computed as non-stiffened shells. Eventually, the displacement solution of the equations is acquired by the introduction of Green function. The stresses in a corrugated transverse bulkhead without pier base of an oil tanker are computed by using SPSM.     

Analysis of the continuous berth allocation problem in container ports using a genetic algorithm

The optimal usage of berths plays a key role in raising the efficiency of container terminals. The berth allocation problem in a container terminal is defined as the feasible allocation of berths to incoming ships such that the total time that elapses between the arrival of the ships to their exit from their berths is minimized. In the transportation literature, the latter problem is usually formulated as a mixed integer programming model. Optimization methods, like the branch and bound algorithm, are efficient ways to solve this model but become absolutely unusable when the size of the problem increases. An advanced search method such as GA may be suited to such a situation. In this paper, a genetic-based algorithm is proposed for the problem. Computational results for two test problems (a small and a large-sized problem) are also presented. The results from the small test are also compared with the results obtained from the branch and bound algorithm.     

Structural behaviour of a high tensile steel deck using trapezoidal stiffeners and dynamics of vehicle–deck interactions

As an early part of a large design and fabrication-oriented project FasdHTS funded by the GROWTH programme of the European Commission, an exotic concept ship was designed in very high tensile steel (EHS690) with the purpose of finding out consequences for design and production. The project has already produced a considerable bank of knowledge for design and shipyard production in this material.This paper presents analysis and discussions on static and dynamic behaviour of a high tensile steel deck designed with trapezoidal stiffeners. First, a finite element model of the deck structure is created. The influence of support condition for the longitudinal girders, and the contact area between the vehicle tyre and panel were analysed. The results from modal analysis of the structure under different load conditions are presented. The different load conditions comprise the unloaded and loaded deck, and the load type, i.e. cargo loads or vehicle loads (car loads or truck loads). From the frequency response analysis under harmonic excitation, it shows how the locations and numbers of cars parked on the deck influence the dynamic response of the structure. Furthermore, by studying the car–deck interaction, it is found that the effects of normal cargo loads are quite different from the vehicle loads due to the spring/damping effects of the vehicles. It is suggested that the carloads have a similar mechanism to that of tuned mass dampers. Finally, two transient analyses of the structure due to excitations transferred from deck supports and lorry braking-induced loading are performed. It is suggested that the deck structure and vehicle design could have more interactions with each other.     

海上风力发电机组支撑结构动力响应特性研究

支撑结构设计是大型海上风电机组设计的重要部分。文章分析了海上风电机组的各种环境载荷,并以3MW风力机组为例计算其所受环境载荷,包括作用在支撑结构顶端的由风机叶轮转动引起的水平轴向力、作用在塔筒上的风载荷以及作用在基础上的海流、海浪载荷,并采用非线性弹簧来模拟基础与海底土层之间的相互作用。在考虑风轮影响情况下,利用有限元法对支撑结构进行了模态分析。最后,分析了环境载荷作用下支撑结构的动态响应。计算结果表明,在对海上风力发电机组进行动态响应计算时,环境载荷之间的相互耦合作用不能忽略。     

两级交变载荷下船体结构典型节点疲劳试验研究

江海直达船属于浅吃水大型宽船,往复航经江段和海段,其疲劳问题不容忽视。将江段和海段载荷简化为小和大2级交变载荷,选取较为典型的船底纵骨贯穿横舱壁节点,通过对比试验探讨2级交变载荷对该船疲劳寿命的影响。试验结果表明,在试验工况下,变幅载荷中的大载荷是导致裂纹扩展的主要因素,小载荷的参与会降低大载荷作用下裂纹扩展的速率。采用等效应力法对变幅载荷下节点的疲劳寿命进行评估,发现采用Miner准则所得结果偏保守,采用均方根法所得结果偏危险,采用修正的Miner准则所得结果精度较高,推荐采用该方法评估2级交变载荷下船体结构典型节点的疲劳寿命。     

A second order volume of fluid （VOF） scheme for numerical simulation of 2-D breaking waves

Among all environmental forces acting on ocean structures and marine vessels, those resulting from wave impacts are likely to yield the highest loads. Being highly nonlinear, transient and complex, a theoretical analysis of their impact would be impossible without numerical simulations. In this paper, a pressure-split two-stage numerical algorithm is proposed based on Volume Of Fluid (VOF) methodology. The algorithm is characterized by introduction of two pressures at each half and full cycle time step, and thus it is a second-order accurate algorithm in time. A simplified second-order Godunov-type solver is used for the continuity equations. The method is applied to simulation of breaking waves in a 2-D water tank, and a qualitative comparison with experimental photo observations is made. Quite consistent results are observed between simulations and experiments. Commercially available software and Boundary Integral Method (BIM) have also been used to simulate the same problem. The results from present code and BIM are in good agreement with respect to breaking location and timing, while the results obtained from the commercial software which is only first-order accurate in time has clearly showed a temporal and spatial lag, verifying the need to use a higher order numerical scheme.     

基于二进制粒子群算法的母联闭合型电网重构策略

为解决母联闭合型电网发生故障时的电网重构问题,提出一种基于二进制粒子群算法的电网重构策略.根据深水半潜平台电网特殊的网络架构和电气特性,建立以最大程度恢复重要负载供电为目标,以电网结构和系统容量为约束条件的母联闭合型电网故障恢复模型.为提升求解效率,为该模型设计基于二进制粒子群算法的两阶段优化求解流程,并将求解结果与混...     

First year ice interactions on Molikpaq: Measurements and experiments

The Molikpaq is a steel mobile arctic structure which has been used for exploration of hydrocarbon reserves on the Canadian Beaufort shelf. In early 1986, the Molikpaq experienced numerous interactions with various ice features at Amanuligak I-65. An extensive ice loads investigation program was conducted as a joint industrial project. Ishikawajima-Harima Heary Industries (IHI) has proposed a method to estimate the global ice load on an arctic structure by utilizing results from ice tank experiments. Experiments were conducted in the IHI ice model tank using a model of the Molikpaq. A comparison between the measured ice loads and the estimated ice loads was made and it was found to be in fair agreement, in spite of some uncertainties involved in both the measured and the estimated ice loads. In this paper, instrumentation which the Molikpaq employed in the investigation program is briefly introduced. Failure modes of ice features observed in the program are also mentioned. The basic idea behind the dual parameters testing and estimating method (DuPTEM) is described. The model experiments and the results are then outlined. The comparison between the measured and estimated ice loads is shown. Finally, uncertainties in both the estimated and the measured ice loads are discussed.     

Combining low- and high-frequency loads acting on large floating structures

Loads acting on large floating structures usually consist of high-frequency and low-frequency loads. The high-frequency loads are associated with the hydroelastic behavior of the structure and excitation of the natural frequency modes. The low-frequency loads are associated with the body motion of the structure and the wave profile. In design analysis, extreme values of these loads must be combined taking into consideration the correlation between them. This paper discusses a methodology for combining the extreme loads, and proposes a simple formulation suitable for use in reliability analysis. A proposed load combination factor K was found to depend on the correlation coefficient of the two loads, the ratio of their standard deviations and the frequency content of the processes from which the loads are determined. The correlation coefficient was found to depend on the complex frequency response functions of the loads and the input wave spectrum. The paper also discusses characteristic extreme values of slightly nonlinear loads acting on large floating structures.Extreme loads may be based on a storm condition with a specified return period. Since very large floating structures are expected to have a long operational lifetime, the return period must be selected carefully. The paper discusses a method for selecting return periods based on the expected operational life of the structure and encounter probability.     

多Agent的船舶电力系统网络重构技术

Reconfigurability of the electrical network in a shipboard power system (SPS) after its failure is central to the restoration of power supply and improves survivability of an SPS. The navigational process creates a sequence of different operating conditions. The priority of some loads differs in changing operating conditions. After analyzing characteristics of typical SPS, a model was developed used a grade III switchboard and an environmental prioritizing agent (EPA) algorithm. This algorithm was chosen as it is logically and physically decentralized as well as multi-agent oriented. The EPA algorithm was used to decide on the dynamic load priority, then it selected the means to best meet the maximum power supply load. The simulation results showed that higher priority loads were the first to be restored. The system satisfied all necessary constraints, demonstrating the effectiveness and validity of the proposed method.     

基于对称分量法的谐波抑制分析

由于谐波问题日益严重以及电能质量日趋重要,因此谐波治理非常关键。提出谐波异地并联补偿的算法,来解决敏感负荷的电压畸变问题。经算例验证,该异地并联补偿算法在补偿点有较好的谐波抑制效果,算法简单,易于实现,克服了谐波源不可观测的缺点,并且在电网三相不对称状态下仍然有效。     

自适应网格交互多模型不敏粒子滤波算法

将一种变结构多模型算法——自适应网格交互多模型(AGIMM)算法和不敏粒子滤波(UPF)算法相结合,提出了自适应网格交互多模型不敏粒子滤波算法(AGIMMUPF).该算法通过自适应网格实现了模型自适应,从而以较小的模型集合覆盖了目标大范围的机动,并以此来克服固定结构交互多模型粒子滤波(IMMPF)算法存在的缺陷,同时各模型滤波算法采用不敏粒子滤波(UPF)算法,使重要性密度函数融合了最新量测信息,更好地逼近真实状态的后验概率分布.通过计算机仿真证明,提出的算法可以有效提高IMMPF的费效比.     

Maritime accident risk estimation for sea lanes based on a dynamic Bayesian network

ABSTRACT

The safety of maritime transportation has become increasingly important with the development of international economics and trade. This paper introduces a dynamic Bayesian network (DBN) model to facilitate the estimation of the dynamic emergency risk in sea lanes. The DBN model is a novel model that can efficiently represent and infer complex stochastic knowledge. To construct this model, available data, which were collected from emergency investigation reports by the International Maritime Organization (IMO), are employed in conjunction with expert knowledge to develop and demonstrate a BN; an evidence theory approach is applied to calculate the prior probability with the help of historical data; the conditional probability is learned by the expectation maximization (EM) algorithm; and the transition probability is obtained by a Markov model. Finally, the Viterbi algorithm is adopted to estimate emergency risk. The emergencies that occurred in the Indian Ocean from 2009 to 2018 were used as a case study for risk estimation. Sensitivity analysis was conducted to identify significant influential factors. The results show that the sea lane risk in the Indian Ocean fluctuates within a small range, presenting an overall downward trend over time. These findings provide a reference for maritime stakeholders to make proper decisions.     

Multi-objective topology and size optimization of high-speed vehicle-passenger catamaran structure by genetic algorithm

Ship structural design has become recently an ever more important and difficult task, because it should always take into account several estimation criteria which are a crucial element of shipyard management, as the hull structural strength is one of the most important factors of overall ship safety, and the total cost of structural materials used for the construction of a ship is a significant part of her total construction cost. Simultaneously, a complete definition of the optimal structural design requires a formulation of size-topology-shape-material optimization task unifying the optimization problems from these four areas and giving an effective solution of this problem. So far, a significant progress towards a solution of this problem has not been achieved. An objective of the underlying paper was to develop an evolutionary algorithm for multi-objective optimization of both topology and scantlings of structural elements of large spatial sections of ships. In the paper an evolutionary algorithm where selection takes place based on the scalar objective function is proposed and applied to solve the problem of structural elements weight and cleaned and painted surface area on a high-speed vehicle-passenger catamaran structure with several design variables, such as plate thickness, scantlings of longitudinal stiffeners and transverse frames, and spacing between longitudinal and transversal members. The results of numerical experiments with the use of the developed algorithm are presented. They show that the proposed genetic algorithm can be an efficient multi-objective optimization tool for simultaneous design of the topology and sizing of ship structures.