Theoretical and Numerical Studies on the Coupling Deformation of Global Lateral Buckling and Walking of Submarine Pipeline

Buckling initiation devices/techniques,including sleepers,distributed buoyancy,snake lay,and residual curvature method(RCM),have recently been widely applied in engineering.These initiated buckles may induce a long pipeline to transform into multiple short pipeline segments,which promote the occurrence of pipeline walking.Thus,a pipeline,which is designed to buckle laterally,may laterally and axially displace over time when subjected to repeated heating and cooling cycles.This study aims to reveal the coupling mechanism of pipeline walking and global lateral buckling.First,an analytic solution is proposed to estimate the walking of pipeline segments between two adjacent buckles.Then,the sensitivity of this method to heating and cooling cycles is analyzed.Results show the applicability of the proposed walking analytical solution of buckling pipelines.Subsequently,an influence analysis of walking on global buckling,including the capacity of buckling initiation,buckling amplitude,buckling mode,and failure assessment of the buckling pipeline,is performed.The results reveal that the effect of walking on the buckling axial force is negligible.However,pipeline walking will aggravate the asymmetry of the pipeline buckling and the failure parameters of the pipeline during the post-buckling.

Controlled buckling of thin film on elastomeric substrate in large deformation

Electronic systems with large stretchability have many applications.A precisely controlled buckling strategy to increase the stretchability has been demonstrated by combining lithographically patterned surface bonding chemistry and a buckling process.The buckled geometry was assumed to have a sinusoidal form,which may result in errors to determine the strains in the film.A theoretical model is presented in this letter to study the mechanics of this type of thin film/substrate system by discarding the assumption of sinusoidal buckling geometry.It is shown that the previous model overestimates the deflection and curvature in the thin film.The results from the model agree well with finite element simulations and therefore provide design guidelines in many applications ranging from stretchable electronics to micro/nano scale surface patterning and precision metrology.

Buckling analysis of shear deformable composite conical shells reinforced by CNTs subjected to combined loading on the two-parameter elastic foundation

The main objective of this study is to investigate the buckling analysis of CCSs reinforced by CNTs subjected to combined loading of hydrostatic pressure and axial compression resting on the twoparameter elastic foundation(T-P-EF).It is one of the first attempts to derive the governing equations of the CCSs reinforced with CNTs,based on a generalized first-order shear deformation shell theory(FSDST)which includes shell-foundation interaction.By adopting the extended mixing rule,the effective material properties of CCSs reinforced by CNTs with linear distributions are approximated by introducing some efficiency parameters.Three carbon nanotube distribution in the matrix,i.e.uniform distribution(U)and V and X-types linear distribution are taken into account.The stability equations are solved by using the Galerkin procedure to determine the combined buckling loads(CBLs)of the structure selected here.The numerical illustrations cover CBLs characteristics of CCSs reinforced by CNTs in the presence of the T-P-EF.Finally,a parametric study is carried out to study the influences of the foundation parameters,the volume fraction of carbon nanotubes and the types of reinforcement on the CBLs.

POSTBUCKLING OF PRESSURE-LOADED SHEAR DEFORMABLE LAMINATED CYLINDRICAL PANELS

A postbuckling analysis is presented for a shear deformable laminated cylindrical panel of finite length subjected to lateral pressure. The governing equations are based on Reddy's higher order shear deformation shell theory with von Krmn_Donnell_type of kinematic nonlinearity. The nonlinear prebuckling deformations and initial geometric imperfections of the panel are both taken into account. A boundary layer theory of shell buckling, which includes the effects of nonlinear prebuckling deformations, large deflections in the postbuckling range, and initial geometric imperfections of the shell, is extended to the case of shear deformable laminated cylindrical panels under lateral pressure. A singular perturbation technique is employed to determine the buckling loads and postbuckling equilibrium paths. The numerical illustrations concern the postbuckling response of perfect and imperfect, moderately thick, cross_ply laminated cylindrical panels. The effects played by transverse shear deformation, panel geometric parameters, total number of plies, fiber orientation, and initial geometric imperfections are studied.

Videometric research on deformation measurement of large-scale wind turbine blades

Utilization of wind energy is a promising way to generate power,and wind turbine blades play a key role in collecting the wind energy effectively.This paper attempts to measure the deformation parameter of wind turbine blades in mechanics experiments using a videometric method. In view that the blades experience small buckling deformation and large integral deformation simultaneously, we proposed a parallel network measurement(PNM) method including the key techniques such as camera network construction,camera calibration,distortion correction,the semi-automatic high-precision extraction of targets,coordinate systems unification,and bundle adjustment,etc. The relatively convenient construction method of the measuring system can provide an abundant measuring content,a wide measuring range and post processing.The experimental results show that the accuracy of the integral deformation measurement is higher than 0.5 mm and that of the buckling deformation measurement higher than 0.1mm.

Finite element analysis of functionally graded sandwich plates with porosity via a new hyperbolic shear deformation theory

This study focusses on establishing the finite element model based on a new hyperbolic sheareformation theory to investigate the static bending,free vibration,and buckling of the functionally graded sandwich plates with porosity.The novel sandwich plate consists of one homogenous ceramic core and two different functionally graded face sheets which can be widely applied in many fields of engineering and defence technology.The discrete governing equations of motion are carried out via Hamilton’s principle and finite element method.The computation program is coded in MATLAB software and used to study the mechanical behavior of the functionally graded sandwich plate with porosity.The present finite element algorithm can be employed to study the plates with arbitrary shape and boundary conditions.The obtained results are compared with available results in the literature to confirm the reliability of the present algorithm.Also,a comprehensive investigation of the effects of several parameters on the bending,free vibration,and buckling response of functionally graded sandwich plates is presented.The numerical results shows that the distribution of porosity plays significant role on the mechanical behavior of the functionally graded sandwich plates。

Role of stress,slenderness and foliation on large anisotropic deformations at deep underground excavations

High stress concentrations around underground excavations can result in significant damage to deep hard-rock mines.These conditions can be the result of stopping activities,blasting,seismicity,or other mining activities.Large anisotropic deformation and excavation closure,especially under high-stress conditions,are expected if the excavation is located in a foliated or thin-bedded rock mass.In this research,the behaviour of excavations under deep and high-stress conditions was investigated and categorised.The main purpose was to enhance the existing knowledge of managing large anisotropic deformations and to help prepare suitable measures for handling such contingencies.Numerical simulations using the distinct element method(DEM)and model calibration were performed to reproduce the anisotropic deformation of an ore drive based on the collected field data.Then,the roles of key factors(i.e.stress ratio,slenderness ratio,foliation orientation,and foliation considering excavation orientation)on the large deformation and damage depth of the excavations were investigated.This study found that increasing both the stress ratio and slenderness ratio induced linear increases in wall closure and damage depth,whereas increasing the foliation angle first increases the deformation and damage depth and then reduces them both before and after 45.The wall closure and damage thickness decreased with increasing orientation intercept.The deformation and damage levels were classified based on these factors.

Stress and buckling analysis of a thick-walled micro sandwich panel with a flexible foam core and carbon nanotube reinforced composite (CNTRC) face sheets

In this paper,the stresses and buckling behaviors of a thick-walled mi-cro sandwich panel with a flexible foam core and carbon nanotube reinforced composite(CNTRC)face sheets are considered based on the high-order shear deformation theory(HSDT)and the modified couple stress theory(MCST).The governing equations of equi-librium are obtained based on the total potential energy principle.The effects of various parameters such as the aspect ratio,elastic foundation,temperature changes,and volume fraction of the canbon nanotubes(CNTs)on the critical buckling loads,normal stress,shear stress,and deflection of the thick-walled micro cylindrical sandwich panel consider-ing different distributions of CNTs are examined.The results are compared and validated with other studies,and showing an excellent compatibility.CNTs have become very use-ful and common candidates in sandwich structures,and they have been extensively used in many applications including nanotechnology,aerospace,and micro-structures.This paper also extends further applications of reinforced sandwich panels by providing the modified equations and formulae.

Application of color structured light pattern to measurement of large out-of-plane deformation

Measurement of out-of-plane deformation is significant to understanding of the deflection mechanisms of the plate and tube structures.In this study,a new surface contouring technique with color structured light is applied to measure the out-of-plane deformation of structures with one-shot projection.Through color fringe recognizing,decoding and triangulation processing for the captured images corresponding to each deformation state,the feasibility of the method is testified by the measurement of elastic deflections of a flexible square plate,showing good agreement with those from the calibrated displacement driver.The plastic deformation of two alloy aluminum rectangular tubes is measured to show the technique application to surface topographic evaluation of the buckling structures with large displacements.

热采水平井出砂段套管变形及屈曲风险分析

针对储层出砂对热采井套管变形及稳定性影响的问题,开展了高温蒸汽对稠油储层岩石性质的影响试验;结合传热及热-固耦合理论,建立二维套管-水泥环-地层和三维套管屈曲模型,分析了注热过程中储层出砂对套管变形及屈曲的作用机理,并对比了不同出砂程度对套管变形和屈曲的影响规律。分析结果表明:储层出砂时,套管同时受热应力及周向非均匀地应力作用而产生内壁屈服,随着出砂区域增大,塑性变形逐渐增大;当出砂加剧导致地层亏空时,出砂段套管受储层岩石支撑作用减弱,注热形成的轴向热应力存在导致套管屈曲的风险;注入蒸汽温度为350℃条件下,地层亏空段小于3 m时套管没有屈曲风险;地层亏空段为4 m时,注热过程中套管轴向力达到临界屈曲载荷4 876.9 kN,对应临界屈曲温度为304.9℃,存在屈曲风险,且随着地层亏空段长度的增加,出砂段套管发生屈曲的临界载荷和对应温度均明显降低,屈曲风险加剧。研究结果可为热采井防砂设计及套管选型提供理论指导。

受外压含缺陷夹层管非线性屈曲分析

为了研究外压作用下夹层管非线性屈曲问题,使用有限元软件ANSYS建立夹层管模型,通过线性屈曲分析获得的屈曲模态制作非线性屈曲的初始缺陷,对受到外压的夹层管进行非线性屈曲分析。研究表明:含有模态缺陷的夹层管在受外压屈曲过程中,会在管径方向产生变形,包括压缩变形和膨胀变形,变形沿轴向传播,压缩变形量始终大于膨胀变形量;使用拐点法,即二者的比值来判定夹层管是否失稳,此方法可以精准判断夹层管失稳外压值,对初始缺陷相同,壁厚比不同的内外管和夹芯层失稳外压进行了分析。研究成果可为夹层管的应用提供借鉴。

基于响应面法的螺杆转子注射成型工艺研究

针对传统金属型螺杆转子制造工艺复杂、加工精度难以控制等问题,提出一种新型螺杆转子注射成型方法,尝试用塑料材质取代金属型螺杆转子。使用Moldflow模流软件对玻纤增强聚酰胺材料的螺杆转子齿面注射成型进行注塑模拟,将缩痕深度和翘曲变形作为质量标准,对影响塑件成型质量的7个工艺参数进行筛选分析,确定了影响2个质量标准的3个工艺参数。采用BBD响应面实验设计方法,研究了熔体温度、保压时间、保压压力等注塑工艺参数对缩痕深度和翘曲变形的影响,获得了最小缩痕深度和最小翘曲变形的多项式回归响应模型。利用回归模型优化的工艺参数组合为熔体温度281.0℃,保压时间18.7 s,保压压力115.7 MPa。数值模拟了最优参数组合,结果表明数值模拟与模型预测值的误差分别为3.75%和0.53%。

某中低速磁悬浮转向机构拉杆的失稳分析

通过有限元分析对某中低速磁悬浮转向机构的拉杆进行了失稳分析,通过理论计算,屈曲分析以及大变形计算方法对拉杆分别进行了临界载荷的计算。在屈曲分析中对比了不同初始载荷对计算结果的影响,在大变形分析中对比了不同的扰动力大小对临界载荷计算的影响。研究结果表明:欧拉公式、屈曲分析以及大变形方法计算所得的临界载荷基本一致;当施加的初始载荷不同时,特征值屈曲分析的临界载荷基本一致;大变形分析中,在不同的扰动作用下,扰动越小,计算所得的临界载荷越接近理论值。

组合碟簧自复位防屈曲支撑滞回性能试验

为控制防屈曲支撑(BRB)的残余变形,采用碟簧自复位系统(DS)和BRB并联形成自复位防屈曲支撑(SBRB)。通过拟静力试验考察组合碟簧刚度、端部连接、复位比率等对SBRB滞回性能的影响。结果表明:与BRB相比,SBRB的残余变形大幅降低;SBRB表现出旗型的滞回曲线,试验后期钢板支撑受拉断裂,其他部件保持完好;SBRB试件中DS部分和BRB部分分别是承载力和累积耗能的主要来源;由于组合碟簧间的摩擦等作用,DS部分的耗能占整个SBRB耗能的23%~36%;其他构造相同时,采用组合碟簧刚度较大的DS部分启动后承载力增幅较多,且DS部分启动力较大的复位比率也较大,残余变形更小。总体上,端部连接形式对残余变形影响不大,刚接SBRB试件因承受额外的端部弯矩,钢板支撑断裂更早,铰接SBRB试件表现出更好的耗能能力。随复位比率增大,SBRB的残余变形逐渐减小,为有效地控制支撑残余变形,同时避免对DS部分要求过高,复位比率宜取0.7~0.9。

麻纤维/聚乳酸包装盒模压成型工艺与性能研究

采用模压成型工艺制备了麻纤维/聚乳酸复合材料包装盒,研究了模压压力、加压速度、模具温度对包装盒的拉伸强度与翘曲变形的影响,分析了产生相应变化的微观机理。实验结果表明,在一定范围内,适当增加模压压力,有利于提高复合材料包装盒的力学强度,降低翘曲变形;增加加压速度,对复合材料包装盒力的学性能的影响不大,但会增加翘曲变形;模具温度为50℃时,包装盒的翘曲变形最小。

基于改进Reddy型三阶剪切变形理论的弹性地基上FG-CNTRC板屈曲无网格分析

针对含碳纳米管转向的Pasternak地基上功能梯度碳纳米管增强复合材料FG-CNTRC(functionally graded carbon nanotube-reinforced composite)板的屈曲问题,提出了一种基于改进Reddy型三阶剪切变形理论TSDT(third-order shear deformation theory)和移动最小二乘近似MLS(moving-least square)的无网格分析模型。该模型避免了无网格法第二类边界条件的施加困难问题,且能够满足中厚/厚板的自由表面条件,无需额外引入剪切修正因子。基于最小势能原理推导了弹性地基上FG-CNTRC板的无网格屈曲控制方程,采用完全转换法处理本质边界条件。通过基准算例验证了本文方法的收敛性及有效性,讨论了碳纳米管的转向角、体积分数、分布形式、地基系数、宽厚比和边界条件等对FG-CNTRC板临界屈曲荷载的影响。

高阶剪切变形理论下Pasternak地基上FG-CNTRC梁自由振动及屈曲分析

功能梯度碳纳米管增强复合材料(functionally graded carbon nanotube-reinforced composite,FG-CNTRC)作为新一代先进复合材料,因其优越的力学性能而被研究者们广泛关注。该研究以Pasternak地基上FG-CNTRC梁为研究对象,基于不同高阶剪切变形理论,将一种具有插值特性的无网格法——稳定移动克里金插值(stabilized moving Kriging interpolation,SMKI)应用于求解Pasternak地基上FG-CNTRC梁的自由振动及屈曲问题。基于稳定移动克里金插值和不同高阶剪切变形理论给出FG-CNTRC梁的位移场,利用Hamilton原理和最小势能原理分别推导了Pasternak地基上FG-CNTRC梁的自由振动和屈曲控制方程。采用MATLAB软件编制了相关程序,将该研究解与解析解或文献解对比,证明了该方法在计算Pasternak地基上FG-CNTRC梁自由振动与屈曲的有效性及准确性。最后,还讨论了不同高阶剪切变形理论、地基系数、碳纳米管体积分数等对其自振频率和屈曲临界荷载的影响。

关于剪切变形对压杆屈曲影响的分析

利用压杆剪应变与轴向应变、弯曲挠度的微分关系建立了压杆弯曲微分方程,推导出了压杆发生弹性失稳时的屈曲载荷公式。计算分析表明:剪切变形对实心等截面压杆屈曲载荷的影响可忽略不计,格缀压杆的屈曲载荷则要考虑剪切变形的影响。同时,还指出有关文献认为深梁在轴力作用下与初等梁一样也有稳定问题这一说法不妥。

薄壁内胆碳纤维全缠绕复合材料气瓶轴向残余变形及屈曲分析

针对钛合金薄壁内胆碳纤维全缠绕复合材料气瓶水压试验后轴向缩短及内胆局部发生屈曲失稳现象,开展了试验研究及有限元分析.结果表明:自紧加卸载后,封头靠近极孔区域沿轴向向内凹陷,封头靠近赤道区域沿径向向外扩张,封头整体沿轴向变短,试验和有限元计算的轴向缩短量为6.15 mm和6.363 mm,误差为3.46%,有限元计算结果与试验结果具有很好的一致性.最后,采用多极孔法优化封头纤维层厚度分布,封头厚度极值降低32.6%,过渡更加均匀,优化后的气瓶沿轴向略有伸长,平均伸长为0.6 mm,采用CT和内窥镜检测,内胆均未出现屈曲失稳,有效地解决了水压试验后轴向缩短及内胆屈曲问题.

中央扣索对悬索桥静动力特性的影响分析

中央扣索是提高悬索桥刚度的有效措施之一,也是悬索桥的重要构件,因此有必要研究中央扣索对悬索桥振动特性、内力、变形的影响。该文以某单跨钢桁梁悬索桥为例,建立2个模型进行对比分析计算。通过分析计算得出,中央扣索增加主桁与主缆、吊索之间的相对纵向刚度,从而使该桥纵飘频率明显增大;在公路-Ⅰ级荷载作用下,主桁沿顺桥向的变形有一定程度的减小,并引起中央扣索区域内弦杆内力和吊索索力突变;对其他截面内力、节点变形基本无影响。