Parametric survey of upper and lower bound limit internal pressures for single mitred pipe bends of various geometries

Internal pressure limit analysis for cylinder–cylinder intersections forming various geometries of single mitred pipe bends subject to internal pressure was investigated. Lower bound analysis with new formulations of force and moment equilibrium together with a higher number of parameters were utilized which resulted in better stability compared to a previously similar analysis of the same problem. Simultaneously, ABAQUS finite element plastic collapse internal pressures were obtained as upper bounds to this problem. Two sets of results were compared, showing good agreement with each other at most points. However, a discrepancy at a mitre angle of 45 degrees between the two sets of results could not be successfully explained. Apart from the conflicting internal limit pressure at the mitre angle of 45°, it is strongly concluded that the true limit internal pressures are bounded between the two sets of results.     

CRACK ARREST ANALYSIS UNDER CYCLIC THERMAL SHOCK FOR AN INNER-SURFACE CIRCUMFERENTIAL CRACK IN A FINITE-LENGTH THICK-WALLED CYLINDER

This article presents a crack arrest depth analysis under cyclic thermal shock for an inner-surface circumferential crack in a finite-length thick-walled cylinder with rotation-restrained edges. The inside of the cylinder is cooled from a uniform temperature distribution. The effects of heat transfer conditions on the maximum transient stress intensity factor for the problem were investigated with systematical evaluation methods formerly developed. Then, under an assumption of a tentative threshold stress intensity range j K th together with the Paris law, the crack arrest depth under cyclic thermal stress was evaluated. The results suggested the existence of an upper limit for the normalized crack arrest depth, independent of the cylinder material in an engineering sense. Finally, the validity of applying j K max h j K th as a crack arrest criterion under cyclic thermal shock was confirmed by fatigue tests under mechanical loads equivalent to those induced by cyclic thermal shock.     

基于柴油机冷却系统的CFD仿真应用

本文针对我公司某3缸90缸径柴油机可靠性试验后一缸进气门密封带处磨损超差,造成气门下沉量偏大的问题,通过对柴油机冷却系统进行CFD仿真计算分析及试验验证,有效解决了该机上述问题。     

Shakedown analysis of thick-walled cylinders subjected to internal pressure with the unified strength criterion

Most previous studies on shakedown of thick-walled cylinders were based on the assumption that the compressive and tensile strengths of the materials were identical. In this paper the shakedown of an internally pressurized cylinder made of a material with a strength-difference and intermediate principal stress effects is dealt with by using a unified strength criterion which consists of a family of convex piecewise linear strength criteria. Through an elasto-plastic analysis the solutions for the loading stresses, residual stresses, elastic limit, plastic limit and shakedown limit of the cylinder are derived. It is shown that the present solutions include the classical plasticity solutions as special cases and have the ability to account for the strength-difference and intermediate principal stress effects. Finally, the influence of the two effects on the shakedown limit of the cylinder is investigated. The results show that the shakedown limit depends on the two effects and is underestimated if these effects are neglected as in the classical plasticity solution based on the Tresca criterion.     

On the mechanical and thermal transient analysis of cylinder-to-cylinder vessels by a finite plate method

A problem common to the pressure vessel analyst is the evaluation of stresses in nozzle-to-cylinder structures subjected to internal pressure, nozzle axial force and nozzle moments. In this paper, the finite plate method—discussed by Brown³¹ in a paper on nozzle-to-cylinder structures subjected to internal pressure—is extended to include axial force and moments at the nozzle terminus. The purpose is to provide an economical alternative to 3-D geometric analytical and experimental stress analysis of such structures.The finite plate concept explored by Rodabaugh²⁵ as a geometric approximation of a finite region of the cylinder about the nozzle is used as the axisymmetric attachment to the nozzle. The variable plate parameters are the outer radius dimension and the harmonic loading at the outer radius of the plate. The parameters are determined for the pressure problem by utilising the shell solution of stresses about a circular hole in a cylinder as data for matching in the flat plate with a hole solution. The parameters for the axial force and moment loading of the nozzle problem are determined by utilising the cylindrical shell series solution of Bijlaard³² for radial force and moment loading and the series solution for asymmetrically loaded axisymmetric plates. Once the parameters are determined, the structural stresses may be calculated by means of an interfacing numerical axisymmetric geometry, asymmetric loading shell or finite element program.In this paper the theoretical development of the geometric and pressure load parameters is briefly reviewed. The analytical development of the parameters for axial force, inplane moment and out of plane moment is presented in detail. The range of applicability is reviewed for the various types of loading.Examples are presented for nozzle-to-cylinder structures loaded by pressure, axial nozzle force, inplane moment at the nozzle and out of plane loading at the nozzle. Finite plane results are compared with the ORNL model No. 3 data obtained by strain gauge and 3-D finite element methods and loaded by nozzle loads. The finite plate results versus the experimental data obtained by Van Campen²⁷ and 3-D finite element data for internal pressure are briefly discussed. In all instances the data compare favourably at the critically stressed location which is at the nozzle-to-cylinder juncture.A comparison of 3-D finite element, 2-D finite element with the finite plate assumptions and some 2-D finite element nozzle-to-hemisphere data from thermal loading is presented.Finally, some observations were made with respect to the assessment of nozzle loads not analytically treated.     

一起充装台氧气瓶爆炸事故原因分析

针对一起充装台氧气瓶爆炸事故,通过对爆炸气瓶残骸进行化学成分、力学性能、金相组织观察、内壁附着物光谱和能谱分析着重阐述了气瓶爆炸事故的起因。分析认为,由于氮气瓶错装氧气,导致气瓶内部残存烃类油被高压氧气迅速氧化分解放出热量,使瓶内的氧气迅速升温升压,超出气瓶承压极限引起气瓶爆炸。结合实际应用与工作经验,提出了氧气瓶安全使用的建议以及相关措施,对氧气瓶的安全管理具有参考价值和实际意义。     

Application of PET as a non-metallic liner for the 6.8 L type-4 cylinder based on the hydrogen cycling test

This study aims to find the evidence that polyethylene terephthalate (PET) is pertinent, with respect to the risk of thermal degradation during fueling, as a liner material of a type-4 composite cylinder for storing 6.8 L of compressed hydrogen. In particular, one type-4 cylinder with the PET liner of thickness 0.6 mm and one type-3 cylinder for comparison have simultaneously undergone 6 cycles of fast fueling (0.15 MPa/s) and fast defueling (0.55 MPa/s) with hydrogen gas in the range of 2 to 45 MPa. The hydrogen temperatures in cylinders, which were measured by a specially-devised thermocouple inserted in each cylinder, change within the range of ?30.0 to 70.0 ^°C. Although the temperature in the type-4 cylinder rises higher than that in the type-3 cylinder due to the lower heat conductivity of PET, it does not exceed 85 ^°C, which is the limit set by the international standards, EC No. 79. Furthermore, from the measurements of the deformation by the laser displacement sensors, the type-4 cylinder swells less than the type-3 cylinder. The pressure-displacement analysis shows that the deformation of type-4 cylinders occurs reversibly, i.e., defueling makes the cylinder regain its previous shape. In essence, PET is safe against thermal degradation when applied as a liner of a 6.8 L type-4 cylinder for hydrogen storage.     

Design by analysis versus design by formula of high strength steel pressure vessels: a comparative study

A comparative study for design by analysis and design by formula of a cylinder to nozzle intersection has been made using different finite element techniques. The cylinder to nozzle intersection investigated is part of a typical vertical pressure vessel with a skirt support. For the study the commonly used ductile P355 steel alloy and the high strength steel alloy P500 QT were considered. The comparative results clearly show disadvantages in terms of limit load capability when the design-by-formula procedures are used in the design of high strength steel pressure vessels. The FE results also clearly show advantages of the shell to solid sub-modeling technique, as it combines the accuracy of 3D-solid modeling with the affordable computing time of the 3D-shell modeling technique.     

Exact yield hyper-surface for thin pipes

A yield hyper-surface for pipe sections subjected to combinations of normal forces, internal and external pressure, twisting moments, biaxial bending moments and biaxial shearing forces is developed. The formulation is based on the fully plastic capacity of the pipe as determined by the maximum distorsional energy density yield criterion. The solution is obtained by maximizing a lower bound analysis and yields a yield hyper-surface that is exact within the limitations of the formulation. The developments are expressed as universal non-dimensional relationships suitable for limit states design of elevated pipes, submerged pipes, offshore platforms and structural tubular steel members. Previously established interaction relations for bending moments, axial forces and internal pressure are recovered as a special case of the general solution. The merits of using the yield hyper-surface to characterize generalized plastic hinge behavior in elasto-plastic pipe stress analysis are presented.     

A theoretical analysis of the extinction limits of a methane-air opposed-jet diffusion flame

A theoretical analysis is described for a methane-air diffusion flame stabilized in the forward stagnation region of a porous metal cylinder in a forced convective flow. The analysis includes effects of radiative heat loss from the porous metal surface and finite rate kinetics but neglects the effects of gravity. The theoretically predicted extinction limits compare well with experimentally observed extinction limits from the literature.After the predicted limits compared well with the experimental limits, a parametric study of the effect of fuel surface emissivity and Lewis number was conducted with the numerical model. It was found that the computed blowoff limit is independent of radiative heat loss for high fuel blowing velocities but is a strong function of Lewis number. At low fuel blowing velocities, the extinction limit varies with both radiative heat loss and Lewis number. It is discovered, however, that even if thermal losses from the fuel surface are absent, the flame can extinguish at the fuel surface independently of Lewis number due to excessive reaction zone thinning.     

柴油机机体模态分析与结构改进

为降低机体的表面结构振动和噪声辐射,采用ANSYS有限元分析软件建立了495型柴油机机体的有限元模型,对其进行自由模态分析,并对机体进行了试验模态分析。通过有限元结果和试验结果比较,验证了计算模型的准确性。根据模态分析结果,得出机体的固有振动特性。在该模型的基础上,增加了梯形加强板结构,使其固定于机体油底壳法兰底部。计算结果表明,铝制加强板能提高机体裙部刚度,抑制机体裙部的开合振动,有效地提高机体的固有频率。     

Analytical function theory approach to the heat transfer problem of a cylinder in cross-flow at small Péclet numbers

The theory of analytical functions is used to study the heat transfer from a uniformly heated cylinder with large length to diameter ratio in cross-flow, in the limit of small Péclet numbers. The energy conservation equation is solved in Fourier’s space, and inverted by means of the residue theorem to obtain an analytical expression of the average Nusselt number in closed form. The result agrees with other theoretical solutions of the same problem existing in the literature.     

A variable material property approach for solving elastic-plastic problems

The linear elastic solution of a boundary value problem is used as a basis to generate its inelastic solution. The method considers the material parameters as field variables. Their distribution is obtained in an iterative manner using the projection method, the arc-length method, and Nueber's rule. The rate of convergence is compared. The problem of thick-walled cylinder is considered as an example. The method yields the analytical solution in the limiting case if the cylinder is made of non-hardening Tresca material and is under internal pressure. The paper also presents solutions for a Mises solid whose hardening is described by the Ramberg-Osgood formula.     

某发动机工艺缸盖螺栓的设计与验证

针对某发动机由于缸筒变形过大,导致机油耗过高的问题,通过对工艺缸盖的使用分析,介绍了工艺缸盖螺栓的设计过程和验证方法。试验验证表明:最终确定的工艺缸盖螺栓目标轴向力和拧紧规范满足使用要求;解决了发动机缸筒变形问题。     

Experimental studies on temperature rise within a hydrogen cylinder during refueling

In this research, experiments were performed to investigate the thermal behaviors such as temperature rise and distributions inside 35 MPa, 150 L hydrogen storage cylinders during its refueling. The main factors affecting the temperature rise in the fast fill process such as the mass filling rate and initial pressure in the cylinder were considered. The experimental results show that the mass filling rate is a constant when the ratio of the pressure in the tank to the cylinder is higher than 1.7, and the mass filling rate decreases when the ratio is lower than 1.7; the temperature inside the cylinder increases nonlinearly in the filling process and the maximum value of temperature rise at the interface of the cylinder exists in the caudal region; the temperature rise reaches a larger value with a lower initial pressure in the cylinder or a higher mass filling rate. Furthermore, the limit of mass filling rate in the case of different ambient temperature was obtained.     

Inverse Problem of a Piezothermoelastic Cylinder Subject to Transient Heating

An inverse problem of a radially polarized piezoelectric hollow circular cylinder of crystal class 6 mm is investigated. It is assumed that a voltage induced by the action of a time-varying temperature applied to the inner surface of the cylinder is measured on the outer surface. The inverse problem entails a determination of the heating temperature from knowledge of the measured voltage. First, an exact solution to the problem is found by solving the equations of equilibrium and electrostatics for the cylinder subject to the prescribed boundary conditions. Then a least-squares residual method that incorporates Lagrange multipliers for satisfaction of the boundary equations is employed to derive an approximate analytic solution. Both formulations are utilized in order to calculate the unknown heating temperature, and the corresponding temperature, displacement and stress fields in a cylinder of cadmium selenide. Numerical results based upon the least-squares residual formulation are found to compare favorably with those obtained by the exact analysis.     

点燃式液压自由活塞发动机高增压燃烧过程的试验与仿真研究

在快速压缩-膨胀机上进行试验,模拟液压自由活塞发动机(hydraulic free piston engine,HFPE)在不同缸内初始压力下的单次燃烧做功过程,并利用OpenFOAM和CONVERGE三维计算流体力学(computational fluid dynamics,CFD)仿真平台进行增压仿真研究。结果表明:液压自由活塞发动机随着缸内初始压力的增大,相同压缩比下发动机循环周期缩短,活塞在上止点附近停留时间缩短,爆震极限压缩比增大,抗爆能力增强。适当提高缸内初始压力有利于提高指示效率,当缸内初始压力提高至0.15MPa时,发动机指示效率由0.30提高至0.31,但当初始压力达到0.20MPa后,指示效率又降至0.30。针对缸内初始压力进一步增大后出现的效率降低问题,在仿真研究中发现采用多火花塞点火方案,即使在初始压力0.80MPa的条件下也能得到较高的指示效率而不发生爆震。     

Numerical simulation of melting of ice around a horizontal cylinder

The problem of outward melting of ice around a horizontal isothermal cylinder is considered. A numerical model in which natural convection induced in the molten water encompassing density inversion is taken into consideration has been developed. Via finite-difference solution of the melting model, numerical simulation of melting of ice has been performed for the cylinder surface temperature T_i = 4, 6, 8, 9 and 10°C with cylinder radius of 25.4 mm. The results of the present simulation were found qualitatively valid when compared with the existing experimental data.     

Limit and shakedown analysis of nozzle/cylinder intersections under internal pressure and in-plane moment loading

A simple technique called the elastic compensation method developed previously by Mackenzie & Boyle is used in combination with full three-dimensional finite-element analysis to obtain limit and shakedown interaction diagrams for nozzle/cylinder intersections subject to combined internal pressure and in-plane nozzle moment loading. The results are compared with solutions from the literature and also with detailed elasto-plastic thin shell finite-element analysis. It is found that the simple elastic compensation procedure can provide good estimates of plastic failure mechanisms for complex three-dimensional structures. A detailed discussion of various issues which arose relates to finite-element modelling and the measures taken to improve the results are also documented.