轴力作用下X型焊接管节点热点应力的分布规律

海洋平台中的焊接管节点的疲劳寿命是由热点应力的大小和分布决定.热点应力的大小决定了管节点在疲劳失效前所能承受的循环荷载的次数,而热点应力的位置则决定了疲劳裂纹的萌生位置和扩展方式.文中采用有限元方法分析了承受轴向拉力作用的X型焊接管节点在焊缝周围的热点应力的分布情况,通过对112个X节点进行的模型分析,研究了节点几何参数对热点应力大小和分布规律的影响.     

轴力作用下X型焊接管节点热点应力的分布规律

海洋平台中的焊接管节点的疲劳寿命是由热点应力的大小和分布决定。热点应力的大小决定了管节点在疲劳失效前所能承受的循环荷载的次数,而热点应力的位置则决定了疲劳裂纹的萌生位置和扩展方式。文中采用有限元方法分析了承受轴向拉力作用的X型焊接管节点在焊缝周围的热点应力的分布情况,通过对112个X节点进行的模型分析,研究了节点几何参数对热点应力大小和分布规律的影响。     

轴向载荷下多平面DT型管节点 应力集中系数研究

应力集中系数对于海洋平台结构中管节点的疲劳寿命评估至关重要。文章以多平面DT型管节点为研究对象,采用有限元方法分析了轴向载荷作用下沿其弦管—撑管相贯线焊缝的应力集中系数分布。在保证计算精度的前提下尽量减少网格数量,采用分区网格划分方法进行管节点建模。基于有限元分析结果,研究了不同几何形状参数对应力集中系数分布变化规律的影响,拟合得到一组应力集中系数参数公式,并通过两种相对误差验证了该参数公式的有效性。     

轴向载荷下多平面DT型管节点应力集中系数概率模型研究

应力集中系数作为一个随机变量,对管节点及导管架平台的疲劳可靠性评估结果有着重要影响。文章以多平面DT型管节点为研究对象,建立了352个几何参数不同的三维管节点有限元模型,并分析了沿弦管-撑管焊缝处的应力集中系数分布。采用密度直方图描述最大应力集中系数统计样本的特征,利用疲劳可靠性分析中常用的几种概率分布进行拟合。各个概率模型中的参数通过极大似然估计方法得到。根据卡方检验的结果对比发现,Birnbaum-Saunders分布是最适合的概率模型。因此,文中提出一组适用于描述在轴向载荷即单向轴向和平衡轴向载荷作用下多平面DT型管节点弦管侧和撑管侧最大应力集中系数分布的概率模型,对今后导管架式海洋平台结构的疲劳可靠性分析具有重要意义。     

海洋平台T型管节点应力集中系数研究

以具有代表性的海洋平台形管接头为例,采用有限元方法,研究接头处的应力集中系数分布.分析支管6个自由度的约束条件和受载方式,基于ABAQUS计算管节点在各种载荷下的应力分布,尤其关注几何学上的最危险地带——管筒十字交叉点处的应力集中系数,并根据6种基本情况下T形管节点的有限元计算结果,得到管节点所受到的应力最大、结构强度...     

轴力作用下T节点焊缝周围的平均应力分布

平均应力模型法是评价海洋平台中管节点疲劳寿命的一种方法,这种方法认为节点的疲劳寿命是由热点应力幅值和焊缝周围的应力分布确定的。管节点焊缝周围应力分布通过一个平均应力分布参数AVS描述。本文研究了轴力作用下T节点的AVS大小,通过对127个不同几何参数的T节点模型的计算,调查了几何参数对AVS的影响,提出了用于计算AVS的参数方程,从而完善了传统的平均应力模型,为轴力作用下T节点的疲劳寿命计算提供了一种快速而高效的方法。     

轴力作用下KT型管节点的应力集中系数分析

为研究平衡的轴向载荷作用下几何参数对KT型管节点应力集中的影响,通过ABAQUS软件建立81个不同几何参数的KT型管节点模型进行数值分析,获得不同参数对应力集中系数大小和分布的影响规律。结果与规范公式进行对比,验证了数模结果的准确性。对KT型管节点,参数γ、τ、θ对SCF数值大小的影响十分显著,参数β对SCF分布的影响最为显著;热点应力的位置并不是固定不变的,几何参数改变其位置有可能会转移。     

典型船舶焊接接头应力集中系数有限元分析

利用MSC/Patran and MSC/Nastran对焊接中常见的对接接头焊趾处的应力集中系数进行有限元建模和计算,在分析有限元计算结果的基础上,提出比较完整的估算焊接接头应力集中系数公式。     

轴向荷载作用下K型管节点焊缝周围应力分布的参数公式

应用分区产生网格的方法产生了K型节点的有限元模型,计算了在轴向荷载作用下K型节点焊缝周围的热点应力分布情况,并与相关试验结果进行对比分析,验证了所提出的有限元模型的可行性和准确性。通过对1152个K节点模型分析,研究了几何参数对K型节点焊缝周围热点应力分布的影响,发现在几何参数取不同值时热点应力的分布随几何参数的变化发生改变,而且热点应力的位置也随着几何参数的变化在冠点和鞍点之间移动。并在此几何参数分析的基础上,提出了K型节点焊缝周围应力集中系数分布的参数公式,并对参数公式进行了误差分析。对于绝大多数K节点模型,拟合得到的参数公式所计算的焊缝周围应力分布结果是精确可靠的,所以提出的参数公式为工程中K节点疲劳设计和分析提供了参考方法。     

对接接头缺口应力集中系数不确定性分析

目的以典型对接接头为研究对象进行参数化建模,建立焊缝几何形状存在不确定性的有限元模型,来研究焊缝几何存在不确定性的对接接头焊趾处缺口应力集中系数$ Kmathrm{_t} $, 并统计分析其分布规律。方法首先,对以往采用的网格尺寸和单元类型进行改进,通过有限元网格敏感性分析,研究不同类型的单元以及网格尺寸对$ Kmathrm{_t} $的影响;其次,沿对接接头焊缝法向提取节点应力,通过绘制应力分布图,确定焊趾处最大应力集中所在部位;然后,通过引入控制点描述对接焊缝几何形状的变化来真实反映焊缝几何形状的不确定性,结合实际测量的焊缝形状数据的分布规律,随机抽样得到大量的焊缝几何参数数据;最后,基于缺口应力法计算$ K_{mathrm{t}} $,并对其进行统计分析,探究对接接头在焊缝几何参数存在不确定性时$ Kmathrm{_t} $的分布规律。结果结果表明,$ Kmathrm{_t} $的分布满足正态分布。结论通过探究焊趾处的应力分布,对于分析疲劳强度和提高疲劳寿命预测精度具有重要意义。     

Stress concentration factors at welds in pipelines and tanks subjected to internal pressure and axial force

In this paper, analytical expressions for stress concentration factors in pipes subjected to internal pressure and axial force are derived for a number of design cases based on classical shell theory. The effect of fabrication tolerances in simple butt welds is assessed. Analyses based on classical mechanics are compared with results from axisymmetric finite element analyses for verification of the presented methodology. Stress concentration factors are presented for circumferential butt welds in pipes welded together from pipes with different thicknesses, welds at buckling arrestors, welds at flanged connections in pipelines, and welds at ring stiffeners on the inside and the outside of the pipes. It also includes stress concentration factors at end closures in pipes for gas storage. Larger pipes are fabricated from plates with a longitudinal weld. This fabrication process introduces out-of-roundness in the pipes. The actual out-of-roundness is a function of internal pressure. An analytical expression for the bending stress in the pipe wall due to this out-of-roundness is presented. The derived stress concentration factors can be used together with a hot spot stress S–N curve for calculation of fatigue damage.     

圆柱壳在径向冲击载荷作用下的动力响应

利用Hamilton原理得出轴向压力和径向冲击载荷作用下圆柱壳位移的运动微分方程,推导方程的解析解。通过数值计算,分析圆柱壳的位移随时间变化曲线,位移的幅频曲线以及应变随时间变化曲线和幅频曲线。数值计算结果表明,圆柱壳的径向和轴向位移要远大于周向位移;简谐激励频率为285 Hz,1 060 Hz,1 152 Hz,2 444 Hz,2 640 Hz,2 763 Hz,4 074 Hz时,径向位移幅值取值最大;简谐激励频率为285 Hz时轴向位移幅值取值最大;简谐激励频率为4 074 Hz时轴向应变幅值取得最大值;简谐激励频率为5 586 Hz,5 762 Hz,6 285 Hz时,周向应变幅值取值最大。     

Hydroelastic analysis of a rectangular plate subjected to slamming loads

A hydroelastic analysis of a rectangular plate subjected to slamming loads is presented. An analytical model based on Wagner theory is used for calculations of transient slamming load on the ship plate. A thin isotropic plate theory is considered for determining the vibration of a rectangular plate excited by an external slamming force. The forced vibration of the plate is calculated by the modal expansion method. Analytical results of the transient response of a rectangular plate induced by slamming loads are compared with numerical calculations from finite element method. The theoretical slamming pressure based on Wagner model is applied on the finite element model of a plate. Good agreement is obtained between the analytical and numerical results for the structural deflection of a rectangular plate due to slamming pressure. The effects of plate dimension and wave profile on the structural vibration are discussed as well. The results show that a low impact velocity and a small wetted radial length of wave yield negligible effects of hydroelasticity.     

Review of empirical and semi-empirical Y factor solutions for cracked welded tubular joints

The practical use of fracture mechanics has been established for use on large turbine and electric generator rotor components used in the atomic power generation and the aircraft industry. Application areas in the offshore industry have also been identified. Fracture mechanics is currently used at the design stage of offshore facilities. It provides the basis for fatigue life prediction, steel selection and tolerance setting on allowable weld imperfections. Fracture mechanics is also used during the operational stage of a structure to make important decisions on inspection scheduling and repair strategies and as a tool for establishing limits on operational conditions. Linear elastic fracture mechanics relies on the use of the stress intensity factor concept. The stress intensity factor is a very important fracture mechanics parameter. Therefore, the accuracy of any fracture mechanics model for the prediction of fatigue crack growth in offshore structures for example will depend very much on the accuracy of the stress intensity factor solution used. Several empirical and semi-empirical solutions have been developed over the years with varying degrees of accuracy. This paper presents a review of some of these methods and attempts to assess their accuracy in predicting Y factors for welded tubular joints by comparing predicted results with experimental data obtained from fatigue tests conducted on large scale welded tubular joints. The experimental results were conducted under simulated service conditions, using a jack-up offshore standard load history (JOSH). A comparison between the experimental and predicted results shows that there may be other factors, which influence fatigue crack growth under variable amplitude conditions. Some of these factors have been identified and discussed in this paper.     

On stress concentration factors for tubular Y- and T-Joints in frame structures

This paper is written as a result of some years experience with fatigue analysis of offshore jacket structures where the connections are made as tubular joints. The hot spot stresses at the tubular joints in such analysis are normally derived based on parametric equations for stress concentration factors. These stress concentration factors are normally related to the axial force in the brace. It is observed that the hot spot stresses at the crown positions of the tubular joint in some cases are significantly affected by the local loading on the chord and the bending moment in the chord. In order to use the existing formulae in these cases some engineering effort is required to derive correct hot spot stress. This work can be avoided by using the nominal stress in the chord as the basis for calculating the hot spot stress at the crown position instead of using the axial force in the brace as basis for the analysis. This also extends the validity of the equations for stress concentration factors for T- and Y- joints in design standards. The proposed modification makes it also simpler to include the effect of joint flexibility in a proper way. The basis for a proposed revision of the equations for stress concentration factors for these joints is presented in this paper. It is considered that this modification leads to minor changes of the computer code, but that it will save analysis work for engineers and reduce the possibility of calculating incorrect fatigue lives in tubular frame structures.     

遭受沉底爆炸载荷作用下的圆柱结构冲击损伤计算

论述了圆柱结构对水下爆炸的冲击损伤计算方法与数值模拟算法。简要介绍了试验工况、计算模型、计算条件等,对沉底状态下圆柱结构遭受沉底水下爆炸作用下的实际损伤与仿真结果进行了对比,研究了冲击毁伤与载荷强度、炸药之间的关系,并应用圆柱壳屈曲理论讨论计算圆柱结构冲击响应的方法,提出了应用表面平均总压力来表征爆炸载荷强度,为今后的潜艇结构抗冲击试验方案设计提供参考。     

Nonlinear analysis of short concrete-filled double skin tube columns subjected to axial compressive forces

Proper material constitutive models for concrete-filled double skin tube (CFDST) columns with circular cross-section and subjected to axial compressive forces are proposed and verified against experiment data using the nonlinear finite element program Abaqus. It is shown that CFDST columns can provide a good confining effect for concrete core, especially when the diameter-to-thickness ratios of both the outer and the inner tubes are small. In addition, empirical equations are proposed to predict the lateral confining pressure of the concrete core for CFDST columns. Finally, the axial strengths of the CFDST columns calculated by the proposed formulations are compared with AISC formulations against the experimental data. It has been shown that the proposed formulations are better than the AISC formulations.