86m沿海甲板运输船总纵强度校核外文翻译资料

Longitudinal strength of

a high-speed ferry

T.E. Schellin , A.Perez de Lucas

Abstract

The longitudinal strength of the high-speed ferry was investigated by subjecting the shiprsquo;s hull girder to long-term loads obtained from a frequency-domain panel code. Prior to the statistical analysis, linearly computed transfer functions were corrected for nonlinear effects, yielding two sets of transfer functions valid for different wave amplitudes. One set corresponded to the hogging condition; the other set, to the sagging condition. Two regular equivalent design waves were specified that resulted in loads representing the most severe global design load conditions. The still-water loading condition, yielding a still-water vertical bending moment in hogging, was superimposed on the wave-induced loads to obtain the total (design) loads in hogging. For the sagging condition only, additional impact-related loads were superimposed to obtain the total (design) loads in sagging. A finite element model of the shiprsquo;s structure was subjected to pressure distributions according to the two regular design waves. For comparison with classification society rule values, a simple beam theory strength analysis of the shiprsquo;s midship section was performed first, and then another finite element analysis was carried out, whereby the imposed loads were tuned to the rule values of vertical bending moments. Rule-based magnitudes of nominal maximum longitudinal stress deviated significantly (25–39%) from comparable stresses obtained by the panel code based finite element analysis. However, stresses obtained from the rule-based finite element analysis agreed more favorably, especially in hogging. In the uppermost deck, for example, the panel code based compressive stress was only 9% larger than the comparable stress from the rule-based finite element analysis.

1.Introduction

Under the European research project WAVELOADS (advanced methods to predict wave-induced loads for high-speed ships) practical tools were developed to compute wave-induced global loads on high-speed monohulls. Two alternative numerical methods were investigated. One method was based on a linear three-dimensional radiation/diffraction Green function formulation in the frequency domain that accounts for forward speed effects ([1]). The other method was based on a nonlinear time domain strip theory, taking into account the most dominant nonlinearities associated with the vertical responses (i.e.[12]).The research work also encompassed model tests of three fast monohulls in a seakeeping laboratory to obtain the necessary experimental data to validate the numerical methods and to test the limits of their application regarding the speed of advance. [2] presented a summary of the project results. Their results also include the specification of global design loads based on first principles as well as a structural strength analysis of a high-speed ferry, one of the ships investigated under the project. The strength analysis of this ferry is presented in this paper.

The gross global load effects of waves are reflected by the bending moments they cause on the shiprsquo;s hull. Thus, in this study the midship vertical bending moment was considered to be the most important global load parameter. A finite element model of the shiprsquo;s structure was constructed to perform a longitudinal strength analysis. Pressures resulting from the seakeeping analysis were transformed to nodal forces and then applied to the finite element model, thereby simulating the corresponding pressure distribution of two equivalent regular design waves for the hogging and sagging conditions. These design waves represented the most severe global hull structural response.

From a practical standpoint, it was advantageous to use the frequency-domain technique to compute the wave-induced hydrodynamic pressures. The resulting pressures were inte-grated to obtain transfer functions of the vertical midship bending moments, and these bending moments were then statistically analyzed to obtain long-term (design) loads. The frequency domain technique used ([3,4]) was a panel method that relies on the zero-speed Green function, which meant that computations were performed according to the so-called encounter-frequency approach.

The application of this linear method is restricted to small amplitude waves, resulting in equal magnitudes of vertical bending moment in the hogging and sagging conditions. Unrealistic wave-induced loads may result if major nonlinea-rities, such as the effects due to bow and stern flare, are not accounted for. Therefore, the linearly computed, wave-induced hydrodynamic pressures were corrected for nonlinear effects according to the procedure developed by [5] and applied by, e.g.,[6]. This procedure was first proposed by [7] and further extended by [8]. The correction yielded two sets of transfer functions. One set corresponded to the hogging condition; the other set, to the sagging condition. The resulting transfer functions were valid only for specific wave amplitudes.

Although nonlinear wave-induced global load effects were considered, a linear analysis was used to select the equivalent regular design waves. The justification for this approach was based on the study by [9]. They demonstrated that critical wave episodes that produce the largest linear responses can be expected to also produce the largest nonlinear responses.

The numerically predicted wave-induced global loads were compared to results from classification society rule values, here calculated according to the requirements of [10] Rules for High-Speed Craft.

2.Ship particulars and wave climate

The high-speed ferry represents current trends for new-buildings of fast passenger carrying monohulls in that it features high speed, small draft, light weight, and aluminum construction. Main particulars of the ship are listed in Table 1; a b

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高速渡轮的纵向强度

T.E. Schellin , A.Perez de Lucas

摘要

通过对船舶的船体梁从频域的面板代码获得的长期荷载，对高速渡轮的纵向强度进行了研究。在此之前的统计分析，线性计算的传递函数因非线性效应得到修正，2组传递函数服从于不同的波振幅。一组对应于中拱状态；另一组对应于中垂状态。这2个正则等价设计波，导致荷载表现出最严重的整体设计负载条件。静水荷载条件服从中拱静水垂直弯矩叠加波浪载荷得到作用于中拱的总（设计）荷载作用。对于中垂的条件，附加的冲击载荷进行叠加，以获得中垂的总（设计）荷载作用。船体结构的有限元模型根据这两个正则设计波进行压力分布。相比较于船级社的规范值，首先用一个简单的梁理论强度分析船中截面，然后再进行有限元分析，从而施加的荷载被调整到纵向弯矩的规则值。基于规则的最大纵向应力的大小显著偏离（25-39%）基于面板代码为基础的有限元分析的相当应力的值。然而，特别对于中拱来说，基于规则的有限元分析得到的应力更容易被接受。例如，在最上面的甲板，基于压应力的面板代码只基于规则的有限元分析得到的相当应力大9%。

1. 简介

欧洲研究项目（高速船舶预测波浪载荷的先进方法）实用工具被应用于计算在高速单体船上波浪引起的整体荷载。研究了两种不同的数值方法。一种方法是基于一种已成为正向速度效应的频域中的线性三维辐射/衍射格林函数公式（[1]）。另一种方法是基于一个非线性时间域切片理论，考虑到最占主导地位的非线性关联与垂直响应（例如[12]）。研究工作还包括在耐波性实验室的三个单体船的模型试验，以获得必要的实验数据来验证数值方法和测试他们关于前进速度的应用的限制。[2]中给出了项目结果的总结。他们的研究结果还包括基于第一原理和在该项目下研究的船只之一的高速渡轮的结构强度分析的整体设计荷载的规范。这艘渡轮的强度分析将在本文中展现出来。

波浪的总荷载效应由它们在船体上产生的弯矩所反映。因此，在本研究中船中截面的纵向弯矩被认为是最重要的整体荷载参数。构建船体结构的有限元模型来进行纵向强度分析。从耐波性分析中产生的压力转换为节点力，然后应用到有限元模型，从而模拟分布于中拱和中垂的两个等效正则设计波的对比压力。这些设计波代表了最严重的整体船体结构响应。

从实际的角度来看，它对使用频域的技术来计算波浪引起的动水压力是有利的。由此产生的压力进行合成来获得船中截面弯矩的传递函数，而这些弯矩进行统计分析以获得长期（设计）荷载。频域方法（[3,4]）是一种依赖于零航速格林函数的面元法，这意味着这个计算是根据所谓的遭遇频率法进行的。

这种线性方法的应用受到小振幅波的限制，导致在中拱和中垂的垂直面的弯矩相等。主要的非线性机构可能会导致产生偏离实际的波浪载荷，例如船头和船尾的外倾的影响，至今没有定论。因此，线性计算，波浪引起的动水压力由根据[5]和[6]等开发的程序的非线性影响进行了校正。本程序是由[7]和进一步扩展[8]首次提出的。修正了两组传递函数。一组对应于中拱状态；另一组对应于中垂状态。由此产生的传递函数针对特定的波振幅是有效的。

虽然考虑了非线性波引起的整体负荷效应，但是线性分析被用来选择等效正则设计波。这种做法的理由是基于[9]的研究。它们表明产生最大线性响应的临界波也可以如预期的产生最大的非线性响应。

数值预测的波引起的整体负荷与船级社规范值的结果相比较，这里根据高速渡轮规则[10]的要求进行计算。

1. 船舶情况与波浪细节

高速渡轮展现出快速客运单体船的新趋势，它具有高速度、小吃水、重量轻、铝结构的特点。船舶的主要详情见表1，船体图见图1。该船是专为开放海域服务而设计，即，在的一个有效波浪高度不大于4米、平均每年不超过10%的海域里进行巡航模式运行。根据船级社的规定，这一限制定义了船舶重心的垂直加速度的设计，并对应于在预期的最严重的海上条件下最高平均1%的垂直加速度。

表1.高速渡轮的主要详情

假定这艘船在西地中海的海上作业。相应的波浪数据，根据上述开放的海上服务限制进行调整，总结见表2。这些波的数据是根据短期海上状态发生的概率给定的，这以有效波浪高度和零交叉波期间为特征（[11]）。

图1.高速渡轮的船体

表2. OC 3服务约束运作下的西地中海波浪数据

1. 有限元模型

纵向结构强度评估采用通用有限元程序MAESTRO7.1系统程序veristar部分。为了这个目的，有限元网格构建使高速渡轮的结构理想化。

有限元模型，关于船舶中心线对称，理想化整个船体的主承载结构。该模型包括约22500个节点和15900个单元。结构部分包括底板、框架，梁、柱、板、板单元。所有的加筋板和纵向梁采用四节点正交异性壳四边形单元模拟，而用两节点梁单元代表横梁。柱子采用双节点偏心梁单元来模拟。灯泡的框架以等截面及同性质的L型梁为模型。完整的有限元模型见图2。

图2.船体结构的有限元模型

结构模型由两个子结构组成，贯穿整个船的长度。子结构1（框架6和54之间）包含九个模块；子结构2（框架54和106之间）包含六个模块。（船尾垂线位于框架0处，船头垂线位于框架99处。）通常，模块定义与两个舱壁之间。三个模块定义了船尾垂线和框架12之间的结构。四个模块位于框架12和30之间，包括车辆坡道和轮机室。七个模块定义船头垂线以上的结构，最后一个模块定义了超出该位置的结构。甲板被定义为整个船的长度，并增加了一个甲板桥以接近船舶结构的上部。

边界条件被指定来约束模型的移动。这意味着某些节点的一些运动必须被限制。在底部，位于框架0处的中心节点被固定；在龙骨处，位于框架79处的中心节点被限制为垂直移动；在甲板3处，位于框架0处的中心节点被限制为横向移动。所有其他节点在整个平面内自由移动。所有质量和荷载是平衡的，直到在模型边界处的反力达到可以接受的最低值。

1. 静水荷载和波浪荷载

在NAPA软件的帮助下，获得了在静水中的船舶静态平衡垂向加载的情况。静态载荷包括浮力和重力，或在满载条件下的重量。纵向载荷分布使船体梁在中拱状态受到垂直静水弯矩如图3所示。在船中截面，位于船尾垂线42.3米处，由此产生的静水弯矩是MSWZ40935kN/m。

图3.纵向重量分布和静水垂直弯矩

对于动水载荷计算被视为一个刚体的船舶，即，不考虑船体的伸展性。船体被浸湿的表面被细分为数量有限的小表面板。在这些面板上的压力近似于船体上分布的压力。为了推算波引起的压力的波形，输入数据也要包括设计水线以上的表面板。足够的精确度是由将船体离散为5650个平面三角形和四边形表面板来实现的；其中的1636个表面板是位于设计水线以下的。这些表面面板被位于面板顶点的5815个节点所定义。

1. 规则设计波

在最严重的整体（设计）荷载条件下，对船体梁的强度进行了分析。对于高速渡轮来说这些条件发生在迎浪时。指定了两个所谓的等效规则设计波，一个是中拱，与波峰位于船的中部，一个是中垂，与波峰靠近船的末端。在规律的迎浪中，为了等效设计波对应于线性计算，选择112.8米的长度，导致了最大的波浪弯矩。

波动幅度取决于为动态平衡船舶定位而指定的动水压力。平衡是通过求解运动方程和利用新发现的加速度来调整惯性力实现的。由此产生的压力分布定义了整体波浪作用的设计载荷，当作用于船体上时，使船中剖面遭受中拱和中垂的垂向波浪弯矩。

图4.规则头波中的波动幅值与垂直弯矩对比

由于波浪引起的动水压力取决于波幅，因此产生的波浪弯矩取决于波幅。确定两个等效设计波的振幅的过程必须考虑到这一函数关系。按照图4展示的，这个过程包括增加波幅直至达到设计弯矩的目标值。对于中拱，通过在中拱将静水弯矩加到设计波浪弯矩上以获得这个目标值；对于中垂，通过在中垂将静水弯矩以及砰击引起的弯矩加到设计波浪弯矩上，见表3。这导致设计波振幅在中拱达到6.12米，在中垂达到5.15米。

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