Vibration analysis of super-yachts: Validation of the Holden Method and estimation of the structural damping

The hull excitation generated by marine propellers constitutes one of the most significant vibration sources affecting comfort on passenger ships. Consequently, the evaluation of the propeller-generated excitation through reliable numerical tools during the preliminary stage of ship design is fundamental. The Holden Method (HM) is an empirical tool utilized to calculate the propeller-induced pressure distribution on a ship hull. The present paper validates the HM, which is applied to a twin-screw, 54-m super-yacht. Finite Element Analysis (FEA) is used to benchmark the HM numerical predictions against a set of full-scale vibration measures. The outcomes show that the magnitude of the propeller-induced dynamic excitation predicted by the HM is overestimated. Thereafter, the calibrated propeller-induced forces and the diesel engine excitation are applied to the FE model to perform a series of forced vibration analyses and estimate the global structural damping coefficient of the super-yacht. The study highlights the necessity of developing new empirical methodologies, analogous to the HM, to be applied to modern small luxury vessels.     

不对称船体结构总纵强度计算方法及影响分析

传统的船体结构总纵强度梁理论计算一般是基于对称的船体横剖面,文中提出了不对称船体结构梁理论弯曲正应力的计算方法,并选取样船作为算例,结合有限元计算进行弯曲正应力对比分析,验证梁理论计算的准确性。同时对比将不对称结构视为对称结构时的梁理论计算总纵弯曲正应力,提出不对称结构对总纵强度的影响。     

17000载重吨油船结构疲劳分析的快速估算方法(英文)

Fatigue cracks and fatigue damage have been important issues for ships and offshore structures for a long time.However,in the last decade,with the introduction of higher tensile steel in hull structures and increasingly large ship dimensions,the greater attention should be paid to fatigue problems.Most research focuses on how to more easily access the fatigue strength of ships.Also,the major classification societies have already released their fatigue assessment notes.However,due to the complexity of factors influencing fatigue performances,such as wave load and pressure from cargo,the combination of different stress components,stress on concentration of local structure details,means stress,and the corrosive environments,there are different specifications with varying classification societies,leading to the different results from different fatigue assessment methods.This paper established the Det Norske Veritas(DNV) classification notes "fatigue assessment of ship structures" that explains the process of fatigue assessment and simplified methods.Finally,a fatigue analysis was performed by use data of a real ship and the reliability of the result was assessed.     

张立腿平台浮箱框架结构强度分析方法研究

浮箱是张力腿平台主体结构的组成部分之一,它承受着由平台甲板和立柱传递来的总体载荷以及局部静水载荷。不同的浮箱结构型式会对荷载路径和受力大小产生影响,不同的设计需求会带来不同的结构型式设计。本文介绍 TLP平台浮箱框架的典型结构型式以及基于有限元的强度分析方法,并通过浮箱横向框架有支柱和无支柱2种不同型式的浮箱框架结构案例分析予以阐述。     

Time-domain strip method with memory-effect function considering the body nonlinearity of ships in large waves

A time-domain strip method with memory-effect function considering body nonlinearity is presented. In small waves, results from conventional linear strip theory and the present method for a modified Wigley model were compared with the results of linear theories and with experiments, and they were found to be in good agreement. In large waves, a 716 TEU containership was used to compare time histories of motions and vertical bending moments calculated using the present method with experimental results. The time histories of motion were not strongly distorted, but those of the vertical bending moments were extremely distorted, especially for the fore part, and were far from sinusoidal signals. The time histories of the calculations and the experimental results were found to be, qualitatively and quantitatively, in good agreement. A post-Panamax containership was also used as an example of an up-to-date large bow-flare ship, and the calculated results were also found to be in good agreement with the experimental results.     

基于损失函数法的船舶操纵水动力导数灵敏度分析

船舶操纵水动力导数的灵敏度分析是简化和重建船舶操纵运动数学模型的主要手段。本文使用平方损失函数方法对船舶操纵水动力导数进行灵敏度分析,并基于灵敏度分析结果对Mariner船的操纵运动数学模型进行简化。通过基于简化模型和原始数学模型的操纵运动仿真对比,验证了基于损失函数法的船舶操纵水动力导数灵敏度分析方法的有效性。     

浅谈初稳性高在油船共同结构规范疲劳分析中的应用

对比初稳性高(GM)的取值方法在油船共同结构规范(CSR-OT)和协调版共同结构规范(CSR-H)中的差异,分析初稳性高与船体构件疲劳寿命的关系:初稳性高与船体构件疲劳寿命负相关。统计分析不同船型的实际初稳性高与规范缺省计算值的差异,对于B/D较小的"窄高型"油船,装载手册中经修正的初稳性高与规范缺省计算值的差异较大。通过某"窄高型"巴拿马最大型油船计算案例说明,选择装载手册中经修正的初稳性高可显著提高疲劳寿命计算结果,从而简化节点设计或减小构件尺寸。     

Some aspects of the structural design of a mat foundation for various soil conditions

There are several important structural design parameters in the analysis of a mat type structure for a jackup mobile offshore drilling unit. These consist of dimensions for the mat, soil foundation types, and structural loads. Methods for determining the proper dimension of the mat structure, modeling the structure and its loading cases, modeling the soil conditions and a method for identifying critical load cases for each element and load case is presented. By using a database approach for the finite element output for all of the various loading cases, a rational approach is presented which solves the problem of sorting and analyzing all of the elements and load cases, ensuring that all are included and none of the critical cases are missed.     

Numerical calculation method for the hydroelastic response of a pontoon-type very large floating structure close to a breakwater

This paper presents an effective scheme for calculating the wave-induced hydroelastic response of a pontoon-type very large floating structure (VLFS) when it is near a breakwater. The basic numerical calculation method is the one previously developed by the same author for a VLFS in the open sea (no breakwater), which is expanded to include the effect of the hydrodynamic mutual interaction between the breakwater and the floating structure. The efficiency and accuracy of the proposed method are validated through comparisons with other numerical results and with existing experimental results. After that confirmation, various numerical calculations were conducted, paying special attention to the resonance phenomena which will occur depending on the relation between the wavelength and the clearance between the breakwater and the floating structure. The irregular frequency phenomenon which appears in the calculation of the fluid dynamic problem is discussed in the appendices, including a method for its elimination. Received: October 31, 2000 / Accepted: December 19, 2000     

A multi-criteria decision method for the analysis of the Motorways of the Sea: the application to the case of France and Spain on the Atlantic Coast

Despite European Union (EU) political support to identify the most feasible Motorways of the Sea, the final decision can only be made by Private Shipping Companies, which are operators of a unique stretch of the intermodal chain. This paper provides a multi-criteria decision method to identify the most suitable Motorways of the Sea taking into account the competitiveness of whole intermodal routes versus the alternative of road transport from the loader’s perspective. The analysis is carried out assuming a ‘many-to-many’ transport model. Firstly indexes of time and cost were defined and evaluated for every available route in the model in accordance with a multi-criteria decision matrix. Secondly, through a Monte Carlo simulation a sensitivity analysis was carried out in order to evaluate the influence on the results of the forecast assumed to construct the matrix. The results obtained are not only quantitative, but also qualitative. The development of intermodal routes via Motorways of the Sea is especially relevant for the peripheral EU countries. Due to the relevance of the freight flow between France and Spain and the congestion of their connections through the Pyrenees, the method proposed was applied to the analysis of this particular case     

多浮体耦合的长大过江弯管系统沉放过程动力响应数值仿真分析

过江管道在沉放过程中的动力响应直接影响管道的水下定位、沉放安全性及稳定性等,研究沉放过程中过江管道沉放过程水动力行为具有重要工程价值,可以降低施工风险、提高工程安全可靠性。以南宁市邕江过江管道工程水上施工过程为研究背景,对长大弯曲型管道沉放过程中多个浮体之间的复杂耦合作用、整体沉放系统复杂的动力特性进行了研究。研究应用非线性时域动力分析方法、莫里森水动力理论、水动力多体耦合理论、长大弯管理论等,借助OrcaFlex软件,建立了考虑多体耦合的长大弯曲型过江管道沉放过程水动力数值仿真分析模型。基于数值仿真模型,运用全耦合方法,进行系统时域仿真计算分析,获取了计算工况下沉管过程管道的动力响应和锚索及吊缆的受力时域图像。对影响沉放过程动力表现的关键施工变量,如气囊放气和管道下放的配合、气囊放气时间、吊缆预张力等进行了参数敏感性分析,根据数值模拟结果提出了施工安全性控制技术及施工建议。     

Methodology for global structural load effect analysis of the semi-submersible hull of floating wind turbines under still water,wind, and wave loads

In designing the support structures of floating wind turbines (FWTs), a key challenge is to determine the load effects (at the cross-sectional load and stress level). This is because FWTs are subjected to complex global, local, static, and dynamic loads in stochastic environmental conditions. Up to now, most of the studies of FWTs have focused on the dynamic motion characteristics of FWTs, while minimal research has touched upon the internal load effects of the support structure. However, a good understanding of the structural load effects is essential since it is the basis for achieving a good design. Motivated by the situation, this study deals with the global load effect analysis for FWT support structures. A semi-submersible hull of a 10-MW FWT is used in the case study. A novel analysis method is employed to obtain the time-domain internal load effects of the floater, which account for the static and dynamic global loads under the still water, wind, and wave loads and associated motions. The investigation of the internal stresses resulting from various global loads under operational and parked conditions and the dynamic behavior of the structural load effects in various environmental conditions are made. The dominating load components for structural responses of the semi-submersible floater and the significant dynamic characteristics under different wind and wave conditions are identified. The dynamic load effects of the floating support structure are investigated by considering the influence of the second-order wave loads, viscous drag loads induced global motions, and wind and wave misalignments. The main results are discussed, and the main findings are summarized. The insights gained provide a basis for improving the design and analysis of FWT support structures.     

小开孔球壳强度分析的解析方法

文章基于回转壳的基本微分方程组,建立了一种受静水压力下小开孔球壳强度分析的解析单元法（AEM）。将AEM与传统回转壳方法、有限元法相比,AEM解决了传统回转壳方法计算小开孔应力误差较大的问题,其计算结果和有限元法较一致。该方法可应用于潜艇内部球面舱壁和深海耐压球壳开孔强度计算之中。     

椭圆余弦波浅水变形实用计算法（I）——对《海港水文规范》的一个补充

尽管线性波浪理论不适宜应用在近岸浅水海域,但我国《海港水文规范》中波浪浅水变形的计算方法仍是建立在线性波浪理论的基础上,且没有考虑外界因素（如风和海底摩擦）的影响。为弥补上述不足,基于波浪传播过程中能量守恒的原理建立了一个波浪浅水变形的数值模型,该模型采用椭圆余弦波假定,并考虑了风和海底摩擦对波能的增加和损耗作用。在该数值模型基础上,分析大量工况下的计算结果,提出了便于工程设计初期用于确定近岸波浪要素的浅水变形实用计算方法（PCM）     

正交设计法与回归分析相结合对高速三体船侧体参数优化

基于高速三体船线性兴波阻力离散点源型数值计算方法,用正交设计法初步优选侧体主尺度参数和布局参数,进一步将模长限制的多元正交回归计算方法与正交设计法结合,得到了单位排水量总阻力关于侧体布局和主尺度参数的回归公式,据此探讨了高速三体船侧体布局和主尺度参数优化问题.     

Fatigue life estimation of explosive cladded transition joints with the use of the spectral method for the case of a random sea state

The problem with fatigue lifetime estimation of explosive cladded transition joints under random loading conditions has been described. The paper presents the fatigue test results performed for the random state of tension-compression under a generated spectrum according to the Pierson-Moskowitz model. The obtained spectrum has a non-Gaussian characteristic. The tested material consists out of a transition joint clad with four layers of aluminium alloy A5083, A1050, Titanium Grade 1 and steel Grade D. The material has been tested for the existence of residual stresses after the welding process with the hole drilling method. The welding process has been also simulated with ANSYS and the residual stresses have been generated for the Goldak volumetric distribution. The obtained values of residual stresses comprise to the values of real tests performed for the hole drilling method. The information about the residual stress values have been taken into account in the process of fatigue lifetime estimation in the form of non-zero mean stresses compensation inside the clad. The fatigue life has been calculated with the use of the frequency domain method. The Goodman mean stress compensation model has been used in the process of residual stress compensation. The non-gaussianity has been compensated with the use of the Bracessi formula. The obtained fatigue life assessment results have been compared with stand test results. The calculated results are within the scatter area of 3, but individual scatter values have been calculated for calculated series.