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The aim of the present work is to investigate whether the degree of freedom (DOF) of a floating body has a notable effect on the maximum impact pressure due to green water on deck. The analysis is carried out for a box-shaped floating structure with a deckhouse, using experimental and numerical means to model the green water load. Green water on deck and impact on the deckhouse is generated by the impingement of a focusing wave group on a floating structure. Computations are performed using a two-dimensional constrained interpolation profile-based model solving the Navier–Stokes (N–S) equations with free surface boundary condition to deal with nonlinear water–structure interactions. The free surface is captured by a volume of fluid (VOF)-type tangent of hyperbola for interface capturing/slope weighting (THINC/SW), which is more accurate than the original THINC scheme. The verifications of the simulation through a series of model-to-model comparisons are performed in a two-dimensional glass-wall wave tank. Experimental water surface elevations, body motions and impact pressure are compared satisfactorily with the computed results for different DOFs cases. As a result, the peak impact pressure due to green water decreases rapidly with the increasing DOF. 相似文献
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An extension of the Tail-Equivalent Linearization Method (TELM) to the frequency domain is presented. The extension defines the Tail-Equivalent Linear System in terms of its frequency-response function. This function is obtained by matching the design point of the nonlinear response with that of the linearized response, thus guaranteeing the equivalence of the tail probability of the latter and the first-order approximation of the tail probability of the nonlinear response. The proposed approach is particularly suitable when the input and response processes are stationary, as is usually the case in the analysis of marine structures. When linear waves are considered, the Tail-Equivalent Linear System possesses a number of important properties, such as the capability to account for multi-support excitations and invariance with respect to scaling of the excitation. The latter property significantly enhances the computational efficiency of TELM for analysis with variable sea states. Additionally, the frequency-response function of the Tail-Equivalent Linear System offers insights into the geometry of random vibrations discretized in the frequency domain and into the physical nature of the response process. The proposed approach is applied to the analysis of point-in-time and first-passage statistics of the random sway displacement of a simplified jack-up rig model. 相似文献
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Maintenance is playing an important role in integrity management of marine assets such as ship structures, offshore renewable energy platforms and subsea oil and gas facilities. The service life of marine assets is heavily influenced by the involvement of numerous material degradation processes (such as fatigue cracking, corrosion and pitting) as well as environmental stresses that vary with geographic locations and climatic factors. The composition of seawater constituents (e.g. dissolved oxygen, salinity, temperature content, etc.) is one of the major influencing factors in degradation of marine assets. Improving the efficiency and effectiveness of maintenance management strategies can have a significant impact on operational availability and reliability of marine assets. Many research studies have been conducted over the past few decades to predict the degradation behaviour of marine structures operating under different environmental conditions. The utilisation of structural degradation data – particularly on marine corrosion – can be very useful in developing a reliable, risk-free and cost-effective maintenance strategy. This paper presents an overview of the state-of-the-art and future trends in asset maintenance management strategies applied to corroded steel structures in extreme marine environments. The corrosion prediction models as well as industry best practices on maintenance of marine steel structures are extensively reviewed and analysed. Furthermore, some applications of advanced technologies such as computerized maintenance management system (CMMS), artificial intelligence (AI) and Bayesian network (BN) are discussed. Our review reveals that there are significant variations in corrosion behaviour of marine steel structures and their industrial maintenance practices from one climatic condition to another. This has been found to be largely attributed to variation in seawater composition/characteristics and their complex mutual relationships. 相似文献
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加筋圆柱壳体支撑结构振动传递特性试验研究 总被引:3,自引:0,他引:3
支撑结构型式和布置位置对加筋圆柱壳体内振动传递特性具有重要影响。文中设计了加筋圆柱壳体试验模型装置,内含壳体支撑结构、平台支撑结构和舱壁支撑结构,开展了加筋圆柱壳体模型的振动模态试验和传递特性试验。以振动传递函数为评价指标,研究了不同频率下支撑结构至加筋圆柱壳体表面的振动传递特性,得出振动传递特性在低频时很大程度上受到壳体结构振动模态的影响。提出等效振动传递函数概念,分析了支撑结构的型式及布置对加筋圆柱壳体传递特性的影响。试验研究结果有助于控制动力机械设备的中低频振动传递,对加筋圆柱壳体内支撑结构的声学设计具有参考价值。 相似文献
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为解决含内部结构的水下圆柱壳振动声辐射快速预报问题,提出一种解析-数值混合方法.将整个结构分为水下圆柱壳和内部结构两部分,采用轴对称边界元法得到圆柱壳表面声阻抗,结合Flügge壳体理论,建立水下圆柱壳的数理模型;采用有限元法建立内部结构的动力学模型.根据圆柱壳与内部结构接触点的位移协调和内力平衡条件,建立整个结构的动力学方程,求解方程得到壳体表面振动速度,再采用边界元法得到声场中任意一点的辐射声压.通过与数值软件计算结果对比,验证了本文方法的正确性.本文方法在改变内部结构进行多方案对比分析时具有显著的计算速度优势. 相似文献
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船舶的研发与设计过程非常的浩大而复杂,为了提高船舶的研发效率,同时减少船舶制造过程的下水实验次数,船舶工业领域投入大量精力研制船舶模拟控制平台。通过模拟各种海况,在实验室模拟和仿真船舶在海洋中的姿态和运动,从而降低开发成本和周期。本文对船舶六自由度模拟控制器平台进行系统的运动学分析,并基于运动模型设计船舶模拟控制器的仿真系统,进行船舶横摇角度的仿真分析。 相似文献
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ANSYS在港工结构中的应用 总被引:1,自引:1,他引:0
分析港工结构的受力特点和作用机理,指出现有常规计算软件的不足,对常用的ANSYS单元和建模技巧进行归纳整理,综合介绍ANSYS在港工结构中的应用. 相似文献
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采用能量法分析了流场中环肋圆柱壳的自由振动问题,讨论肋骨布置型式、流场压力对环肋圆柱壳自由振动频率的影响,给出了附加质量和振动波数之间的关系曲线. 相似文献
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WANG Bai-he HUANG Jian-guo 《船舶与海洋工程学报》2007,6(4):13-17
A classical time-varying signal,the multi-component Chirp signal has been widely used and the ability to estimate its instantaneous frequency(IF) is very useful. But in noisy environments,it is hard to estimate the IF of a multi-component Chirp signal accurately. Wigner distribution maxima(WDM) are usually utilized for this estimation. But in practice,estimation bias increases when some points deviate from the true IF in high noise environments. This paper presents a new method of multi-component Chirp signal IF estimation named Wigner Viterbi fit(WVF) ,based on Wigner-Ville distribution(WVD) and the Viterbi algorithm. First,we transform the WVD of the Chirp signal into digital image,and apply the Viterbi algorithm to separate the components and estimate their IF. At last,we establish a linear model to fit the estimation results. Theoretical analysis and simulation results prove that this new method has high precision and better performance than WDM in high noise environments,and better suppression of interference and the edge effect. Compared with WDM,WVF can reduce the mean square error(MSE) by 50% when the signal to noise ration(SNR) is in the range of -15dB to -11dB. WVF is an effective and promising IF estimation method. 相似文献
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轴系纵振对双层圆柱壳体水下声辐射的影响研究 总被引:7,自引:1,他引:7
采用有限元/边界元方法(FEM/BEM)对推进轴系纵振引起的双层圆柱壳水下辐射噪声特性进行研究.使用ANSYS有限元软件建立了流固耦合的有限元模型,计算了流-固耦合状态下结构振动位移响应.利用边界元技术对结构水下辐射噪声特性进行研究,并对推力轴承的布置位置和结构进行了改变,从而改变了激振力的大小及传递途径,对轴系纵振引起的结构水下辐射噪声起到了一定的改善. 相似文献
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对于水下结构,流体对结构模态频率的影响主要体现在预应力效应与流固耦合效应两方面.为研究水下壳结构固有频率对这2种效应的敏感度,本文首先计算某水下壳体在空气中的模态,然后研究壳结构在不同水深工作产生的静水压对其固有频率的影响,最后使用声固耦合的方法计算了流固耦合效应下的壳体湿模态.计算结果表明:流固耦合效应占主导因素,但随着壳体工作水深(预应力)的增大,预应力效应对水下壳体频率的影响也逐渐显著.因而,在开展水下结构动力学设计时,不仅要重点考虑流固耦合效应对结构固有频率的影响,还应关注结构实际工作环境下的应力状态,分析其对结构固有频率的影响. 相似文献
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轴系整体减振系统横向低频振动传递特性研究 总被引:1,自引:0,他引:1
为降低螺旋桨传递至艇体的振动,利用轴系整体减振系统对各轴承及主辅机进行弹性支撑,通过改变桨-轴-艇体的振动传递路径使振动能量衰减,从而实现减振降噪的目的。提出了轴系整体减振系统的概念,建立了桨轴系统的力学模型,采用解析法和有限元法分析了系统横向振动的动态特性。以轴承处位移响应和力传递率为指标,对比分析了传统支撑和弹性支撑两种不同方式的隔振效果。结果表明,轴系整体弹性支撑下的轴承处位移响应小于传统支撑方式,在15~100 Hz内整体弹性支撑方式的隔振效果提高了10.9 dB,低频减振效果明显,验证了整体减振系统设计方法的可行性,为潜艇艉部耦合系统减振降噪的设计提供了一种新方法。 相似文献