大庆地区东西剖面油气的应力圈闭初探

以大庆地区地质资料为基础，应用弹性力学问题的有限单元法．计算大庆地区东西剖面的应力场，分析多个指标的分布特点及其所指示的应力圈闭和流体活动特点，为今后油田的勘探和开发提供新依据。     

Lamb波在水下弹性板散射声场仿真实验

利用有限元声场计算软件 COMSOL,仿真实验了 Lamb 波在水下弹性板直角板端反射并发生模态转换时的散射声场,通过对散射声场的分析,结合能量守恒定律,忽略杂散波(如棱角波)近似计算了 Lamb 波在水下弹性板直角板端的模态转换效率,并且与理论值进行了比较。     

水下节流阀砂粒冲蚀数值模拟研究

在海洋油气开发中,水下节流阀作为水下生产系统的重要组成部分,用于调节生产单元的流量,冲蚀是其主要失效因素之一,因此研究水下节流阀冲蚀失效的影响机理尤为重要。以某笼套式角型水下节流阀为研究对象,建立了水下节流阀的三维流体域模型,采用ANSYS Fluent的标准k-ε湍流模型、DPM离散相模型和Generic冲蚀模型进行了不同开度下的流场数值模拟计算和冲蚀分析,研究了流场环境参数对冲蚀的影响。对水下节流阀流场数值模拟结果进行分析,得到了水下节流阀流场内流速、压力的分布规律。对不同开度下水下节流阀的冲蚀数值模拟结果进行分析,发现节流孔处是冲蚀最为严重区域,得到了冲蚀率随开度的变化曲线。对不同流场环境参数下水下节流阀的冲蚀数值模拟结果进行分析,得到了最大冲蚀率和最大冲蚀深度随流场环境参数的变化规律。根据数值模拟的分析及结论可以对水下节流阀结构进行改进,并在油气生产中对流场环境参数进行控制,提高海洋油气开发的经济效益。     

涡激振动对船舷安装的相干声纳条带测深系统测量精度影响分析

相干声纳条带测深系统采用船舷安装时,连接系统水下单元的钢管在水流作用下可能发生共振和频率锁定而剧烈振动,其下端的以换能器为主的系统水下单元也会随之摆动,使数据质量和测量精度受到影响。笔者通过分析在实际工作中遇到的问题发现:连接系统水下单元的钢管越长,钢管越容易在低流速条件下发生共振现象;换能器剧烈摆动会造成大量噪音信号;换能器摆动幅度较大时系统的安装校准会失效。本文通过解析计算得出了在现场操作中不同悬挂长度的钢管发生频率锁定时的控制流速以及换能器最大摆动幅度,认为实际工作中换能器距固定点在1.0m以内是可靠的,并对现场操作中如何减弱和避免涡激振动对系统精度的影响提出建议。     

两层粘性流体中圆柱体受迫振荡数值模拟

研究两层粘性流体中无限长水平圆柱体的受迫振荡问题。在湍流模式下,采用VOF方法追踪两层流体的内界面,基于动网格技术模拟圆柱体的运动边界,对均匀流中横向振荡圆柱体的绕流场进行了数值模拟。计算受迫振荡圆柱体的升力系数、阻力系数随时间的演化曲线和圆柱体的尾涡分布,以及圆柱体的受迫振荡激发两层流体内界面的扰动,并与均匀流体的情况进行了比较分析。研究表明,流体的两层分层效应对受迫振荡圆柱体的升阻力系数和尾涡分布特性都有显著影响,在水下输油气管道涡激振动特性的工程评估中,应考虑流体的密度分层效应。     

水下桩腿长度变化对浮式结构固有频率的影响研究

为了分析带支腿浮式结构水下桩腿处于不同的长度时振动固有频率的变化情况,采用有限元方法和三维线性水弹性理论对一理想的带支腿浮式结构进行研究,分工况计算了3种弹性模态的干、湿固有频率。结果表明对于同一阶弹性模态来说,结构主体平台振型是决定水动力系数大小的主要因素,桩腿水下长度是次要因素,而振型又受到桩腿长度的制约;桩腿水下长度的改变对带支腿浮式结构的干模态固有频率以及湿固有频率都有较明显地调制作用。对于干模态固有频率来说,桩腿关于船身越趋于对称分布时结构的共振频率越高;对于湿固有频率来说,水下桩腿长度地增加有迫使共振频率趋向低频方向移动趋势。     

平转连续梁转体系统应力理论计算与数值模拟研究

依据弹性接触理论、材料强度理论,对静力作用下,日照肖家庄地区T型连续梁转体系统上、下转盘和球铰应力进行计算和强度分析,并通过ANSYS通用有限元软件对转体系统进行数值模拟,计算静力作用下转盘和球铰的应力分布。将转盘和球铰应力理论值与ANSYS数值模拟结果进行对比分析研究,得出转体系统中球铰应力分布呈现从球铰中心向球铰边缘逐步增大的规律,在球铰平面半径距离外边缘15%的范围内应为球铰设计重点关注区域。研究发现在理论计算中,采用等效应力计算方法较准确;在ANSYS数值模拟计算中,发现球铰采用SOLID单元计算结果更稳定、准确。     

水下加筋圆柱壳结构声散射特性研究

采用有限元/边界元(FEM/BEM)方法对水下加筋圆柱壳结构的声散射特性进行分析。考虑入射声场激发弹性结构振动产生二次辐射声场,总声场为入射场与散射场之和。基于Mindlin理论建立结构受迫振动的有限元模型,考虑入射声场为简谐激励,采用模态叠加法求出结构振动表面速度。根据声学边界元相关理论,利用有限元方法计算得出的弹性结构表面动力相应,可求出弹性结构的散射声场。研究结果表明,在同一波数下,不加筋结构后向散射强于加筋结构;加筋结构的散射指向性图案分叉较为明显;同种结构在波数增加的时候后向散射强度逐渐增大,前向散射强度逐渐减弱。     

均匀流场中并列圆柱涡激振动的现状与预测

并列圆柱体在均匀流场中的涡激振动十分复杂，但又广泛存在于实际工程之中。当两柱在流体激励作用下产生振动时，由于同时存在着流固耦合作用和柱间干扰作用，而使周围流场变得更加复杂。本文对并列刚性和弹性圆柱的流场分类，Ｓｔｒｏｕｈａｌ数及流体载荷等问题进行了综述，在此基础上提出了进一步研究的建议。     

单元升降式网箱强度校核

随着近海渔业的枯竭,海洋养殖业逐渐向深远海发展,但深远海养殖易受极端天气影响,本文基于海洋采油平台设计了一种八边形单元升降式网箱,为降低极端天气对养殖效益的影响提供了可能。针对单元升降式网箱结构安全性问题,本文基于ANSYS/Mechanical建立了单个单元网箱和四单元网箱在水面和水下两种状态的分析模型,通过相位角搜索程序确定不同状态下的工况,最终计算出两组网箱在两种状态下的应力和变形情况,完成对网箱强度的校核。仿真计算结果表明：单元升降式网箱可以通过下降到水面以下的方式有效应对极端天气;支撑桩腿与套筒之间的连接处是单元升降式网箱的结构薄弱处。单元升降式网箱为模块化、高效益化、灵活化深海养殖提供了一种解决方案。     

A study of transient responses of a submerged spherical shell under shock waves

Based on a procedure which couples the finite element method with the doubly asymptotic approximation, this work addresses the problem of the transient responses of a submerged spherical shell subjected to strong, plane, incident shock waves, in which elastoplastic material behavior is considered. Simulation results indicate that the procedure adopted shows good agreement with related literature, which considered linear elastic behavior of the shell. Also presented herein are the time histories of surface pressure, radial velocity and von Mises stress of the shell. Moreover, deformation diagrams and spreading of the plastic zone of the shell are described as well.     

Vibration of a thin-walled prolate dome under external water pressure

The paper reports on a theoretical and an experimental investigation carried out on a thin-walled hemi-ellipsoidal prolate dome in air and also under external water pressure. The investigation found that there was good correlation between experiment and theory. The theoretical investigation was carried out using the finite element analysis to model both the structure and the fluid. The theoretical investigation used two different programs, one of which was the giant computer program ANSYS and the other was an in-house program developed by Ross. For the shell structure, the ANSYS program used 2 different doubly curved thin-walled shell elements, while the in-house program used a simpler axisymmetric thin-walled shell element. This axisymmetric element allowed a sinusoidal variation of the displacements in the circumferential direction, thus, decreasing preparation and computational time. Agreement between the 3 different finite elements was found to be good. This was found particularly encouraging for the in-house software, as it only took a few hours to set up the computer model, and a few seconds to analyse the vessel, whereas the ANSYS software took several weeks to set up the computer model, and several minutes to analyse the shell dome. The ANSYS software, however, did have the advantage in producing excellent graphical displays in both the pre-processing and post-processing modes.     

Hydroelastic vibration of a cantilever cylindrical shell partially submerged in a liquid

The dynamic characteristics of a circular cylindrical shell in contact with a liquid are theoretically studied. The cantilevered cylindrical shell with open ends is partially submerged in a liquid which is unbounded in the radial direction, but bounded by a rigid and flat bottom. Since the liquid is assumed to be incompressible and inviscid, the liquid motion can be described as the velocity potentials written in terms of the appropriate Bessel functions for both the inner and the outer liquid regions. The compatibility of the dynamic displacement along the contacting surfaces between the shell and liquid leads the resulting equations, satisfying both the shell and liquid motions, which are solved by using the collocation method. Finally, the Rayleigh–Ritz method is applied to extract the wet natural frequencies and the mode shapes of the liquid-coupled system. The validity of the theoretical method is established with the aid of a commercial finite element computer code. In order to evaluate the dynamic characteristics of the liquid-coupled system, the effects of the submerged depth and the axial gap between the bottom end of the shell and the bottom surface of the liquid are demonstrated.     

Postbuckling Analysis for Offshore Pipelines with Residual Stresses

Based on the finite displacement theory of elastic shells, the postbuckling behaviour of submarine pipelines with residual stresses is investigated by using a new finite element formula. The corresponding complementary energy functional is first constructed, and then a geometrical stiffness matrix suitable for the postbuckling of a cylindrical shell is derived. In this matrix the effects of initial stresses and harmonic coupling terms have been considered. The formulation presented in this paper can be used to solve a significant class of problems in the analysis of elastic shells.     

A refined analytical analysis of submerged pipelines in seabed laying

The paper analyzes the elastic deflection of submerged pipelines laid with a stinger by taking into account the overall effects of the ovalization of the cross section. The analysis is performed by means of a singular perturbation technique and the analytical solution obtained is shown to offer different advantages over the finite element method. Two examples demonstrate the effectiveness of the procedure by means of a comparison with results from other less refined analytical solutions and from the commercial finite element code .     

Optimization of buoyancy of an articulated stinger on submerged pipelines laid with a barge

An analytical method is presented for finding the elastic deflection of submerged pipelines laid with an articulated stinger in which the buoyancy of each element is adjustable. The computer time required for the method is much less than that for the finite element method, so that optimization of the laying parameters can be performed in a large region using mathematical programming. A practical example shows the efficiency of the proposed method.     

The role of submerged berms on the momentary liquefaction around conventional rubble mound breakwaters

Berms deployed at the toe of conventional rubble mound breakwaters can be very effective in improving the stability of the armor layer. Indeed, their design is commonly tackled by paying attention to armor elements dimensioning. Past research studies showed how submerged berms can increase the stability of the armor layer if compared to straight sloped conventional breakwaters without a berm. To fill the gap of knowledge related to the interaction between breakwaters with submerged berm, waves and soil, this research aims to evaluate how submerged berms configuration influences the seabed soil response and momentary liquefaction occurrences around and beneath breakwaters foundation, under dynamic wave loading. The effects of submerged berms on the incident waves transformation have been evaluated by means of a phase resolving numerical model for simulating non-hydrostatic, free-surface, rotational flows. The soil response to wave-induced seabed pressures has been evaluated by using an ad-hoc anisotropic poro-elastic soil solver. Once the evaluation of the seabed consolidation state due to the presence of the breakwater has been performed, the dynamic interaction among water waves, soil and structure has been analyzed by using a one-way coupling boundary condition. A parametric study has been carried out by varying the berm configuration (i.e. its height and its length), keeping constant the offshore regular wave condition, the berm and armor layer porosity values, the water depth and the elastic properties of the soil. Results indicate that the presence of submerged berms tends to mitigate the liquefaction probability if compared to straight sloped conventional breakwater without a berm. In addition, it appears that the momentary liquefaction phenomena are more influenced by changing the berm length rather than the berm height.     

Three-dimensional analysis of wave attenuation by a submerged, horizontal, bottom-mounted, flexible shell

The effectiveness of a submerged, bottom-mounted, flexible breakwater is investigated numerically. The structure is a horizontal, hemicylindrical shell filled with water. Potential flow is considered, and steady-state motions caused by monochromatic waves are studied. The three-dimensional response to normal and oblique waves is determined using the finite element method and a boundary integral method. Results are presented for a shell with a length of 150 m and a radius of 4 m, situated in water having a mean depth of 6 m. They indicate that the structure is effective in reducing the incident wave intensity over a wide range of frequencies.     

Parametric Analysis of A Submerged Cylindrical Shell Subjected to Shock Waves

In this study,an FEM-SBFEM(scaled boundary finite element method)coupling procedure proposed by Fan et al.(2005)is adopted to obtain the dynamic responses of a submerged cylindrical shell subjected to plane step or exponential acoustic shock waves.The coupling procedure can readily be applied to three-dimensional problem,however for clarity,the problems to be presented are limited to two-dimensional domain.In the analyses,the cylindrical shell is modeled by simple beam elements(using FEM),while the effects of the surrounding infinite fluid is modeled by the SBFEM.In it,no free surface and seabed are involved.Compared with Fan and his co-authors' works,the FEM-SBFEM coupling procedure is further verified to be feasible for shock waves by benchmark examples.Furthermore,parametric studies are performed and presented to gain insight into effects of the geometric and material properties of the cylindrical shell on its dynamic responses.