Effects of Magnetic Shear on the Resistive Wall Mode Instability in a Cylindrical Model

The linear evolution of a resistive wall mode(RWM)with magnetic shears was analytically studied in a cylindrical geometry.The incompressible magnetohydrodynamic(MHD)equations were solved by the Fourier analysis method,and various equilibrium magnetic fields were considered.The shear in the magnetic field had an unstable effect on the linear evolution of the RWM.The linear growth rate increased obviously with increase of the magnetic shear rate for higher magnetic shears.Slow plasma rotation could stabilize the RWM with low magnetic shears,but the plasma rotation could not stabilize the RWM with high magnetic shears.The stabilizing effects of the wall conductivity on the RWM are more efficient for lager magnetic shear.

AXISYMMETRIC PROBLEMS OF CYLINDRICAL SHELLS WITH VARIABLE WALL THICKNESS

The purpose of this paper is to give the general solutions for axisymmetric eylindrical shells with paraholically varying wall thickness.

STUDY ON LOCATION OF HOT SPOT AT TUBE WALL FOR FIRED CYLINDRICAL FURNACE COMBUSTION

Based on the analysis of heat radiation intensity from flame, a new mathematical model ofthe tube-wall temperatmp of heated tubes is developed by taking down-fired, upright-tube cylindricalfurnace for example. The proposed mathematical model can be employed to indicate both the positionand size of the hot spot at fire-facing wall of heated tube of combustion chamber, and is characteristicof simplicity and efficiency If coupled with thermoelectric couple or infrared viewer, the presentedlocation method of combustion hot spot can offer engineers very valuable proposal to keep furnacerunning more safely The same is true for any other type of tubular furnaces.

THEORY OF THICK-WALLED SHELLS AND ITS APPLICATION IN CYLINDRICAL SHELL

In this paper, a theory of thick-walled shells is established by means of Hellinger-Reissner's variational principle, with displacement and stress assumptions. The displacements are expanded into power series of the thickness coordinate. Only the first four and the first three terms are used for the displacements parallel and normal to the middle surface respectively. The normal extruding and transverse shear stresses are assumed to be cubic polynomials and to satisfy the boundary stress conditions on the outer and inner surfaces of the shell. The governing equations and boundary conditions are derived by means of variational principle. As an example, a thick-walled cylindrical shell is disscussed with the theory proposed. Furthermore, a photoelastic experiment has been carried out, and the results are in fair agreement with the computations.

Elastic Buckling of Bionic Cylindrical Shells Based on Bamboo

High load-bearing efficiency is one of the advantages of biological structures after the evolution of billions of years. Biomimicking from nature may offer the potential for lightweight design. In the viewpoint ofrnechanics properties, the culm of bamboo comprises of two types of cells and the number of the vascular bundles takes a gradient of distribution. A three-point bending test was carried out to measure the elastic modulus. Results show that the elastic modulus of bamboo decreases gradually from the periphery towards the centre. Based on the structural characteristics of bamboo, a bionic cylindrical structure was designed to mimic the gradient distribution of vascular bundles and parenchyma cells. The buckling resistance of the bionic structure was compared with that of a traditional shell of equal mass under axial pressure by finite element simulations. Results show that the load-bearing capacity of bionic shell is increased by 124.8%. The buckling mode of bionic structure is global buckling while that of the conventional shell is local buckling.

矩形大开孔外压薄壁圆柱壳结构稳定性研究

以含矩形大开孔的薄壁圆柱壳结构为研究对象,利用ANSYS Workbench软件对其进行了屈曲分析,研究了不同的几何影响因素和材料参数与其临界失稳载荷和屈曲行为的关系。结果表明:结构的临界失稳载荷主要影响因素为壳体的径厚比;在弹性模量不变的情况下,临界失稳载荷与材料的屈服强度近似为线性关系;径厚比和材料参数的改变并不会改变结构的屈曲行为和趋势。

内压薄壁圆柱壳电阻凸焊接头疲劳寿命研究

为提高凸焊接头在使用过程中的安全性能,笔者采用有限元法和等效结构应力法,对内压薄壁圆柱壳电阻凸焊接头疲劳寿命预测方法进行了研究。提出了一种考虑预压载荷对圆柱壳形状影响的建模方法,计算了不同预压载荷下的筒体变形和凸焊接头疲劳寿命。研究结果表明薄壁圆柱壳在凸焊接头处的变形对凸焊接头疲劳寿命有显著影响。建议在制造中采取措施减小焊接过程对圆柱壳在开孔区的变形的影响,从而使凸焊接头获得较高的疲劳寿命。

Radial envelope forming mechanism and process design method for cylindrical rings with thin wall and high web ribs

Cylindrical rings with thin wall and high web ribs(CRTWHWR)are widely used as the key load bearing structures such as rocket body and space station cabin in aerospace field.However,it is still difficult to efficiently manufacture CRTWHWR with high performance because of their extreme geometry with thin-walled skins,high web ribs and large size.In this paper,a novel radial envelope forming process is put forward to efficiently achieve the plastic forming of CRTWHWR with high performance.Firstly,the principle of radial envelope forming process is clarified.Then,an efficient design method for the tool motion and geometry is proposed based on the reverse envelope principle,i.e.,CRTWHWR is adopted to reversely envelope the tool and thus the tool which does not interfere with CRTWHWR can be efficiently obtained in a single operation.Finally,a reasonable 3D FE model of the radial envelope forming process of CRTWHWR is established and the radial envelope forming mechanism of CRTWHWR is comprehensively revealed.Through the FE simulation and experiments with material of plastic mud,a typical CRTWHWR with diameter of 300 mm,axial height of 192 mm,the maximum rib height of 25 mm,the minimum rib thickness of 3 mm and skin thickness of 5 mm is radial envelope formed,i.e.,the ratio of the maximum rib height to the minimum rib thickness reaches 8.33,the ratio of the maximum rib height to skin thickness reaches 5 and the ratio of diameter to the minimum rib thickness reaches 100.The above results verify that the proposed radial envelope forming process has great potentials in efficiently manufacturing CRTWHWR with extreme geometry.

高温合金薄壁圆筒焊接变形控制研究

为解决某型号航空发动机产品焊接加工难题,进行了Inconel 718高温合金薄壁圆筒零件焊接变形控制工艺研究。通过分析薄壁筒体焊接变形的原因,采取合理的接头设计、焊接工装设计、优化焊接工艺和焊后热处理及热处理防变形工装等措施,产品焊缝质量满足I级要求,焊缝圆度变形控制在0.2 mm以内。最终通过了验证,较好地控制了高温合金薄壁圆筒产品焊接变形,焊缝质量优良,可为相关薄壁圆筒产品焊接提供技术支持。

Experimental and Numerical Assessment on Seismic Performance of Earth Adobe Walls

Earth buildings are common types of structures in most rural areas in all developing countries.Catastrophic failure and destruction of these structures under seismic loads always result in loss of human lives and economic losses.Wall is an important load-bearing component of raw soil buildings.In this paper,a novel approach is proposed to improve the strength and ductility of adobe walls.Three types of analyses,material properties,mechanical properties,and dynamic properties,are carried out for the seismic performance assessment of the adobe walls.These performed studies include that,material properties of the earth cylinder block,mechanical properties of adobe walls under quasi-static loads,and dynamic performance of adobe walls excited by seismic waves.On investigation of material properties,eighteen cylindrical specimens with a diameter of 100 mm and a height of 110 mm were divided into three groups for compressive,tensile,and split pull strength tests,respectively.The results of the three groups of tests showed that the yield strength ratios of compressive,tensile,and shear strength were about 1:0.3:0.2.In order to study the performance of structural components,three 1/3 scale model raw soil walls with a dimension of 1,200 mm in width,1,000 mm in height,and 310 mm in thickness were tested under cyclic loading.The average wall capacity of the wall obtained by the test was about 13.5 kN and the average displacement angle was about 1/135.The numerical simulation experiment is used to explore the mechanism of structural failure.A three-dimensional finite element model is established by choosing the material parameters based on the above test outcomes.The accuracy of the numerical simulation experiment is verified by simulation and comparison of the above quasi-static test results.Further,the collapse process of raw soil wall under a seismic wave is simulated for exploring the response and damage mechanism of structure.Based on those systematically analyzed,some useful suggested guidelines are provided for improving the seismic performance of raw soil buildings.

小样本数据下圆柱薄壳初始缺陷不确定性量化的极大熵方法

具有不确定性特征的初始缺陷被认为是导致薄壳结构实际临界载荷值与理论解不相符并呈现分散特征的主要原因.对实际薄壳结构初始缺陷的建模至少需要考虑两个方面的不确定性量化,一是对缺陷分布形式和幅值等固有随机性的量化,二是对小样本量和不准确测量所导致缺陷统计量的不确定性的量化.本文在利用随机场的Karhunen-Loeve展开法对薄壳初始几何缺陷建模的基础上,提出一种基于极大熵原理的缺陷建模方法.首先,采用极大熵分布来估计Karhunen-Loeve随机变量的概率密度函数,以适应不能使用高斯随机场进行缺陷随机场建模的情况.随后,通过将经典的等式约束极大熵模型扩展为区间约束极大熵模型,实现对实际工程中仅能获得少量薄壳结构几何缺陷样本数据所导致的认知不确定性的量化.最后,将所提方法用于对国际缺陷数据库的A-Shell进行缺陷建模和临界载荷预测.研究表明,所提基于区间约束极大熵原理的随机场建模方法在能够有效表征实测数据高阶矩信息的同时,还具备量化小样本数据导致的认知不确定性的能力,并且高斯随机场模型和基于等式约束极大熵原理的随机场模型是本文所提建模方法的两种特殊情况.

腐蚀减薄柱形壳轴压屈曲特性研究

本文对不锈钢局部减薄缺陷柱形壳在轴向压力下的屈曲性能进行研究。对完好柱壳和4种外表面局部腐蚀而导致壁厚减薄的柱壳,进行几何测量、轴压试验和数值计算。5种类型柱壳的位移载荷曲线、临界载荷和失稳模式通过轴压实验获得;非线性数值分析中采用弧长法获得平衡曲线、极限载荷和柱壳后屈曲模式。在数值分析和试验的基础上,对局部减薄柱形壳屈曲问题进行研究,其中对比了减薄位置差异和减薄形状差异对柱形壳屈曲的影响。结果表明,柱形壳对腐蚀减薄形状和腐蚀减薄位置都具有敏感性,尤其对于柱壳周向长方形缺陷形状的敏感性更强。

含初始缺陷不锈钢柱壳的多模态屈曲特性

以海洋平台圆柱壳桩腿为研究对象,研究不锈钢柱壳在受到局部腐蚀和未受到腐蚀两种情况下的屈曲特性,其中用柱壳局部区域均匀减薄模拟桩腿腐蚀。对一组未减薄的完好柱壳和一组经过减薄加工的腐蚀柱壳进行初始缺陷测量、轴压试验和数值分析。通过试验获得柱壳临界屈曲载荷。对柱壳进行线性屈曲分析,得到柱壳前50阶模态缺陷和屈曲特征值。采用Riks弧长法对赋予初始缺陷幅值的柱壳前50阶模态缺陷进行非线性屈曲分析,得到柱壳的平衡曲线、临界载荷。在此基础上,研究初始缺陷对受到局部腐蚀和未受到局部腐蚀不锈钢柱壳屈曲的影响,并在多模态缺陷条件下对其最差阶模态进行探究。结果表明:与未受到腐蚀的柱壳相比,受到腐蚀的柱壳对初始缺陷的敏感性更低,对不同模态缺陷的敏感性更低;对于未受腐蚀的普通不锈钢柱壳而言,最差的模态缺陷并不是通常认为的第1阶,也有可能出现在高阶模态中。

基于高速摄影的直角壁面附近柱形空泡动力学行为研究

本文基于高速摄影实验,对直角壁面附近的柱形空泡动力学行为进行了研究。空泡由激光聚焦诱导产生,形成于具有较小间距的两片平行玻璃板之间的液体环境中,从而具有了较为明显的柱形特征。通过改变柱形空泡距离直角壁面顶点的无量纲距离l*和位置角度θ,分别探究了对称和非对称处柱形空泡的完整溃灭行为及变化趋势,并揭示了柱形空泡与直角壁面的相对位置对柱形空泡泡壁变形、形心移动距离及方向等泡动力学特性的影响。研究发现:在第一周期溃灭过程中,柱形空泡远离直角壁面一侧的泡壁将会出现凹陷,并且逐渐发展直至将柱形空泡分为两部分;当空泡位于对称位置时,随着无量纲距离l*的逐渐增大,柱形空泡表面凹陷程度逐渐减弱,且空泡在溃灭阶段的形心移动距离逐渐减小;当空泡位于非对称位置时,随着空泡位置角度θ的减小(对θ<45°的情况而言),柱形空泡形心的移动方向由指向壁面顶点逐渐变为指向下壁面。

弹性边界功能梯度石墨烯增强薄壁圆柱壳的振动特性

基于一阶剪切变形理论、Halpin-Tsai微观力学模型和Rayleigh-Ritz法分析FG-GPLRC圆柱壳振动特性。为满足复杂的使役环境,引入人工弹簧技术,分析GPLs质量分数、分布模式和层数等参数对壳体结构振动特性的影响,探究弹性边界条件下周向波数、轴向半波数和固有频率之间的规律。研究结果表明,GPLs作为增强体可以显著提高基体的力学性能;分布模式对薄壁圆柱壳的固有频率有重要影响,GPL-X分布模式的固有频率最高;固有频率随层数的增加变化趋势减小。

一种5m级大型薄壁筒类零件加工工艺方案研究

针对大型薄壁产品在机械加工过程中的吊装、转运、装夹工序中的划伤,研究了加工工艺,采用型面吻合高阻尼支撑块技术,有效解决了5 m级贮箱吊装磕碰的难题。通过重型整体气动夹紧工装增加该薄壁筒类零件的强度,减少刀具在加工中的自激振动,实现了零件的可靠装夹,保证了零件机械加工的高精度要求。

等离子体处理对CFRP筒状件内壁活化效果的影响

为解决碳纤维增强树脂基复合材料(CFRP)筒状件内壁表面化学惰性较高导致与金属涂层结合强度差的问题,采用射频辉光放电对其内表面进行活化处理来提高其表面活性。通过接触角测试和红外光谱分析,探究等离子体处理气压、射频电源功率、处理时间和离子种类对活化效果的影响。结果表明,经射频辉光放电等离子体处理后CFRP筒状件内壁表面等离子体活化效果明显,表面能显著提高。其他工艺参数相同情况下,活化效果随气压增大先提升后降低,随射频电源功率和处理时间的增大而提高,以氧等离子体活化效果最佳。其中,在处理气压0.5 Pa、射频电源功率500 W、处理时间60 min、氧等离子体条件下效果最为显著,水和二碘甲烷的接触角分别由71.29°、49.36°降低到4.93°、5.39°,表面能从38.85 mJ·m^(-2)提升到74.73 mJ·m^(-2)。通过红外光谱分析,经等离子体处理后的CFRP中C-H和C≡C等非活性键被打断,带有C=O的醛基和羧基活性基团增多,浸润性大幅提高。活化后的CFRP基体与金属薄膜的膜基结合力由不足0.1 MPa提升至0.49 MPa。研究通过射频辉光放电对CFRP筒状件内壁表面进行活化处理,为制备高结合强度的金属涂层打下基础。

国内外标准中立式圆筒形储罐罐壁开口许用外载荷计算讨论

对立式圆筒形储罐的罐壁开口许用外载荷计算,主要涉及到API 650—2018“Welded Tanks for Oil Storage”和GB 50341—2014《立式圆筒形钢制焊接油罐设计规范》这2个标准。从适用范围、计算方法、制造商和采购方工作范围、计算算例、有限元方法说明、补强类型以及相关数值来源等方面对2个标准的条文异同进行对比分析,可为标准的准确使用提供帮助。

大型圆形深基坑设计分析研究

大型圆形地下结构方案是一种能够结合基坑体系的结构性能,力学上较合理的地下结构形式,近年来在大型地下工程中得到了广泛的应用。某圆形水池工程中无扶壁无圈梁一次性开挖14 m的大型圆形地下连续墙围护结构,对圆形基坑工程的设计思路及分析方法进行了综合的阐述。为了综合考虑圆形基坑的空间效应,本文采用三种不同的计算方法对圆形围护结构的变形及内力进行对比分析,结果显示二维环形墙等效弹簧刚度法可以较为简单的考虑环形结构的三维效应,但内力结果力学意义不明确,仅可作为初步估算方法;三维m法和三维连续介质有限元分析方法能够比较清楚的描述圆形结构的三维效应,且三维连续介质有限元法能够考虑结构与土体的相互作用,通过与实测的监测结果对比,能够较好的模拟基坑开挖引起围护结构的变形与应力和周围土体的变形。

圆型基坑的变形特点及主要影响因素分析

圆形基坑多为应用于特殊场合的超深基坑,上海某圆形基坑的施工监测资料显示,圆形基坑的变形规律与条形基坑差异很大,对圆形基坑的水平位移、土压力监测资料进行了分析,并通过应用中厚壳理论对基坑变形和内力作的有限元模拟,认为圆形基坑以承受环向轴压为主,与主要承受经向弯矩的条形基坑有本质区别。同时,对混凝土轴向受压、槽段间泥浆受压、环向不均匀荷载等主要变形因素也进行了探讨,指出在设计和施工阶段应对不均匀荷载予以密切关注。