Shakedown limit loads for elbows under internal pressure and cyclic in-plane bending

This paper presents elastic, shakedown and plastic limit loads for 90° elbows under constant internal pressure and cyclic in-plane bending, via finite element (FE) analysis. Effects of the elbow geometry (the bend radius to mean radius ratio and the mean radius-to-thickness ratio) and of the large geometry change are systematically investigated. By normalizing the in-plane bending moment by the plastic limit load solution of Calladine, the shakedown diagram is found to be close to unity up to a certain value of normalized pressure (normalized with respect to the limit pressure) and then to decrease almost linearly with increasing normalized pressure. The value up to which shakedown limit loads remain constant depends on the elbow geometry and the large geometry change effect. Effects of the elbow geometry and the large geometry change on shakedown diagrams are discussed.     

Limit loads for thin-walled piping branch junctions under internal pressure and in-plane bending

The present work presents plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on detailed three-dimensional (3-D) finite element (FE) limit analyses using elastic–perfectly plastic materials. To assure reliability of the FE limit loads, modelling issues are addressed first, such as the effect of kinematic boundary conditions and branch junction geometries on the FE limit loads. Then the FE limit loads for branch junctions under internal pressure and in-plane bending are compared with existing limit load solutions, and new limit load solutions, improving the accuracy, are proposed based on the FE results. The proposed solutions are valid for ratios of the branch-to-run pipe radius and thickness from 0.4 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 10.0 to 20.0.     

Limit loads for piping branch junctions under internal pressure and in-plane bending—Extended solutions

The authors have previously proposed plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on finite element (FE) limit loads resulting from three-dimensional (3-D) FE limit analyses using elastic–perfectly plastic materials [Kim YJ, Lee KH, Park CY. Limit loads for thin-walled piping branch junctions under internal pressure and in-plane bending. Int J Press Vessels Piping 2006;83:645–53]. The solutions are valid for ratios of the branch-to-run pipe radius and thickness from 0.4 to 1.0, and for the mean radius-to-thickness ratio of the run pipe from 10.0 to 20.0. Moreover, the solutions considered the case of in-plane bending only on the branch pipe. This paper extends the previous solutions in two aspects. Firstly, plastic limit load solutions are given also for in-plane bending on the run pipe. Secondly, the validity of the proposed solutions is extended to ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0. Comparisons with FE results show good agreement.     

Limit loads for pipe bends under combined pressure and in-plane bending based on finite element limit analysis

Approximate plastic limit load solutions for pipe bends under combined internal pressure and bending are obtained from detailed three-dimensional (3-D) FE limit analyses based on elastic-perfectly plastic materials with the small geometry change option. The FE results show that existing limit load solutions for pipe bends are lower bounds but can be very different from the present FE results in some cases, particularly for bending. Accordingly closed-form approximations are proposed for pipe bends under combined pressure and in-plane bending based on the FE results.     

Analysis and experiments on the plastic limit pressure of elbows

This paper discusses the plastic limit pressure of elbows without defects and with local thinned area in the extrados. Finite element analysis (FEA) and experiments have been used. The results of FEA show that the limit load of elbows under internal pressure increases with increasing wall thickness and bend radius of the elbow. The results are consistent with the calculated results by the Goodall formula, the maximum error is 6.58%. By data fitting of FEA, an empirical formula for the limit load of elbows with local thinned area in the extrados has been proposed, which is validated by experiments.     

Effects of attached straight pipes on finite element limit analysis for pipe bends

The effect of the length of an attached straight pipe on the plastic limit load of a 90° pipe bend under combined pressure and bending is quantified, based on finite element (FE) limit analyses using elastic–perfectly plastic materials with the small geometry change option. Systematic FE limit analyses of pipe bends with various lengths of the attached pipe are performed. It is shown that the effect of the length of the attached straight pipe on plastic limit loads can be significant, and the limit loads tend to decrease with decrease of the length of the attached straight pipe. In the limiting case of no attachment, the limit loads are found to be close to existing analytical solutions.     

Modeling of the fluid structure interaction of a human trachea under different ventilation conditions

This work is focused on the analysis of the response of the tracheal wall to different ventilation conditions. Thus, a finite element model of a human trachea is developed and used to analyze its deformability under normal breathing and mechanical ventilation. The geometry of the trachea is obtained from computed tomography (CT) images of a healthy man. A fluid structure interaction approach is used to analyze the deformation of the wall when the fluid (in this case, air) moves inside the trachea. A structured hexahedral-based grid for the tracheal walls and an unstructured tetrahedral-based mesh with coincident nodes for the fluid are used to perform the simulations with the finite element-based commercial software code (ADINA R & D Inc.). The tracheal wall is modeled as a fiber reinforced hyperelastic solid material in which the anisotropy due to the orientation of the fibers is introduced. Deformation of the tracheal walls is analyzed under different conditions. Normal breathing is performed assuming a sinus shape of the pressure at the inlet and air speed at the outlet based on real data which represent the inspiration and the expiration processes respectively. Mechanical ventilation is simulated as smooth square shape velocity airflow considering positive values of pressure using data from a mechanical ventilation machine. Deformations of the tracheal cartilage rings and of the muscle membrane, as well as the maximum principal stresses in the wall, are analyzed. The results show that, although the deformation and stresses are quite small for both conditions, forced ventilation does not exactly imitate the physiological response of the trachea, since with always positive pressure values the trachea does not collapse during mechanical breathing.     

Simplified fitness-for-service assessment of pressure vessels and piping systems containing thermal hot spots and corrosion damage

Fitness-for-service (FFS) assessment is a quantitative engineering evaluation of operational components. In the context of pressure vessels and piping systems FFS assessment is performed periodically to ensure the operational safety and structural integrity. In this paper, a simplified method is developed for Level 2 FFS assessment (as described in API 579) of pressure vessels and piping systems containing thermal hot spots or corrosion damage. The method is based upon variational principles in plasticity, the m_α-tangent method (an extension of the m_α method), the concept of decay length and reference volume. The use of the m_α-tangent method extends the range of applicability to components and structures experiencing significant stress gradients in and around the damaged spot. The method is shown to provide a reasonably accurate estimate of the remaining strength of ageing pressure components. The method is demonstrated through an example, and the results are compared with Level 3 inelastic finite element analyses.     

Stress distributions in a horizontal pressure vessel and the saddle supports

This paper presents analysis results of stress distributions in a horizontal pressure vessel and the saddle supports. The results are obtained from a 3D finite element analysis. A quarter of the pressure vessel is modeled with realistic details of saddle supports. In addition to presenting the stress distribution in the pressure vessel, the results provide details of stress distribution in different parts of the saddle separately, i.e. wear, web, flange and base plates. The effect of changing the load and various geometric parameters is investigated and recommendations are made for the optimal values of ratio of the distance of support from the end of the vessel to the length of the vessel and ratio of the length of the vessel to the radius of the vessel for minimum stresses both in the pressure vessel and the saddle structure. Physical reasons for favoring of a particular value of ratio of the distance of support from the end of the vessel to the length of the vessel are also outlined.     

正三轮摩托车车架的结构分析及改进

车架可靠性对整车的安全性有着重要的作用。本文应用有限元方法对新开发的正三轮摩托车车架进行了结构分析。实车测试结果与计算结果的对比证明了所建立的车架有限元模型的正确性。分析结果表明：原始设计方案中车架纵梁的强度较弱，需要进行改进。在综合考虑现场工艺条件等问题的基础上，提出了改进方案，从而缩短了新车型的开发时间。     

2D numerical study on the deflection of thin steel plate subjected to gaseous detonation wave interaction

An elaborate numerical study with a validated LS-DYNA® immersed boundary method fluid-solid interaction code is used to characterize the influence of pre-detonation pressure, ignition point location and time duration on plastic deformation of thin steel plates subjected to hydrogen-oxygen gaseous detonation. Simulation relies on the modeling of detonation by chemical reaction kinetic and its propagation by conservative element solution element solver. Immersed boundary method is used to simulate the interface motion between the detonating gas and the deforming plate to facilitate the assessment of fluid pressure distribution on the plate surface. The numerical tool relates the pressure distribution and gaseous detonation parameters to the plate macroscopic deformation by employing multi-species reactive Euler's equations for the gas and assuming a Johnson-Cook material model for the plate. The numerical model simulated the experimental tests and a good agreement between them was obtained where specific features of gas detonation-driven forming were considered. With the confidence of the validation, the numerical model investigated the effects of different parameters such as the gaseous mixture initial temperature and combustion cylinder longitudinal capacity on overpressure-time history and strain-time history. It is demonstrated that the larger longitudinal capacity of combustion cylinder and more distant ignition point location have a great influence on increasing the detonation wave intensity. Eventually, the rate-dependent Johnson-Cook failure criterion was used to assess the failure state of plate under high-intensity detonations.     

Experimental study of low-cycle fatigue of pipe elbows with local wall thinning and life estimation using finite element analysis

Low-cycle fatigue tests were conducted using elbow specimens with local wall thinning. Local wall thinning was machined on the inside of the elbow in order to simulate metal loss from erosion corrosion. The local wall thinning was located in three different areas known as the extrados, crown and intrados. The elbow specimens were subjected to cyclic in-plane bending under displacement control without internal pressure. In addition, three-dimensional elastic-plastic analyses were also carried out using the finite element method. As a result, the crack penetration area and the crack growth direction were successfully predicted by the analyses. The fatigue lives estimated by the analyses were close to those obtained by the experiments.     

Cogging torque reduction by optimal design of PM synchronous generator for wind turbines

In this study, design and optimization of a surface-mounted permanent magnet synchronous generator (PMSG) have been carried out for use in low power wind turbines. In the successive optimization steps based upon the parametric solution method, design parameters of skew, pole embrace, and pole arc offset are chosen to be optimized so that the cogging torque is reduced. Cogging torque is a type of torque ripple coming from the machine design and causes undesired vibration and acoustic noise during the operation of machine. Moreover, although the effect of cogging torque in high power surface-mounted PMSGs is not sensible, it becomes important in low power applications to maintain good dynamical behavior. Analytical and finite element analysis (FEA) are conducted after obtaining the magnet structure that provides minimum cogging torque. Electrical and electromagnetic distributions are presented according to the changes in the corresponding design parameters. While the cogging torque in the initial design is 522.7 mNm, it has been reduced to 49.1 mNm in the optimized generator, which in turn means an improvement of about 90%. The generator under consideration has the specifications of 2.5 kW, 120 V, 14-pole with an inner type-rotor.     

机体刚度对气缸盖—气缸套密封性能的影响

讨论了在某V6缸柴油机进行改进设计时,气缸盖-气缸套之间的密封性能在预紧工况和爆发工况时的工作状况。利用三维有限元分析方法,对两种机体方案的气缸盖-气缸套的密封性能进行分析,得出了预紧工况,爆发工况下密封圈的比压图及接触压力对比曲线,发现改进方案机体两侧刚度分布比较合理,有利于气缸盖一气缸套的密封。     

Buckling of functionally graded plates under thermal,axial, and shear in-plane loading using complex finite strip formulation

A complex finite strip method was used to study the buckling of functionally graded plates (FGPs) under thermal and mechanical (longitudinal, transverse, and shear in-plane) loading. The mechanical characteristics of FGPs were assumed to vary through the thickness, according to power law distribution. The nonlinear temperature distribution in the direction of the plate thickness was assumed according to thermal conduction steady state conditions. In complex finite strip method, the polynomial Hermitian functions were assumed in the transverse direction and the complex exponential functions were used in the longitudinal direction to evaluate the standard and geometric stiffness matrices that have the ability of calculating the critical shear stress in contrast to trigonometric shape functions. The solution was obtained by the minimization of the total potential energy and solving the corresponding eigenvalue problem. In addition, numerical results for FGPs with different boundary conditions were presented and compared with those available in the literature and the interaction curves of mechanical and thermal buckling capacity of FGPs were obtained.     

Parametric investigation of the soil–structure interaction effects on the dynamic behaviour of a shallow foundation supported wind turbine considering a layered soil

The proposed investigation is concerned with influential factors of soil–structure interaction issues for onshore wind turbines. Indeed, the awareness of these aspects encounters hardly a straightforward application in practical regulations and therefore is often neglected. However, with the rapid recent growth, the wind energy installations are expanding into regions where the soil conditions may be unfavorable. A consciousness raising of the significance of interaction between the wind turbine, its foundation and the underlying soil is lacking. This paper aims to fill this research gap. It involves a three‐blade wind turbine grounded on a layered half space. The layered soil is simplified as a horizontal layer over an homogeneous half space. However, the method can consider multilayered soil and different bottom conditions, such as rigid bedrock or flexible half space. The soil–structure system is modeled by means of a coupling between finite element and boundary element method. The analysis is carried out in frequency domain. At the first stage, the only foundation–soil system is investigated, and subsequently, the focus shifts to the whole turbine‐soil assembly. The effects of different parameters are systematically evaluated, in order to provide a range of values for which the soil–structure interaction has to be accounted for. The investigation highlighted the importance of the relative stiffness of structure and soil. Also, the ratio of the layer stiffness to the half space stiffness plays an important role. Copyright © 2014 John Wiley & Sons, Ltd.     

连杆小头油孔对连杆疲劳寿命影响的研究

采用有限元方法对两种不同方案的连杆小头油孔 (单油孔方案和双油孔方案 )进行了分析。通过对其主要考查部位的应力、连杆大头、小头轴孔的纵、横向变形进行对比研究 ,并根据疲劳累积损伤原理对连杆各方案进行疲劳强度校核 ,发现双油孔连杆方案在变形和应力方面都有较好的改善。此外 ,还对双油孔连杆方案的两油孔夹角采用不同的角度 (5 0°和 6 0°)做了有限元分析对比 ,结果表明两油孔夹角为 6 0°时 ,油孔的位置恰好能避开连杆小头的高应力区。建议若条件允许 ,连杆小头最好采用双油孔方案 ,且油孔夹角取 6 0°左右为宜。     

A comparison of plastic collapse and limit loads for single mitred pipe bends under in-plane bending

This paper presents a comparison of the plastic collapse loads from experimental in-plane bending tests on three 90° single un-reinforced mitred pipe bends, with the results from various 3D solid finite element models. The bending load applied reduced the bend angle and in turn, the resulting cross-sectional ovalisation led to a recognised weakening mechanism. In addition, at maximum load there was a reversal in stiffness, characteristic of buckling. This reversal in stiffness was accompanied by significant ovalisation and plasticity at the mitre intersection. Both the weakening mechanism and the post-buckling behaviour are only observable by testing or by including large displacement effects in the plastic finite element solution. A small displacement limit solution with an elastic-perfectly plastic material model overestimated the collapse load by more than 40% and could not reproduce the buckling behaviour.     

A numerical creep analysis on the interaction of twin semi-elliptical cracks

The interaction and coalescence of multiple flaws will significantly influence the service life of components. In this paper, the interaction of two identical semi-elliptical cracks in a finite thickness plate subjected to the remote tension is investigated. The results indicated that interaction of multiple cracks is different between the time-dependent fracture characterized by C^*-integral and linear elastic fracture noted by SIF. The magnifying factors of creep fracture are obviously larger than that of the linear elastic fracture cases. Therefore, the current interaction and coalescence rule developed from linear elastic fracture analysis may lead to a non-conservative result when it is used in the assessment of creep crack. At the end, an empirical equation is developed based on the numerical results.     

The effect of material difference and flange nominal size on the sealing performance of new gasketless flanges

This paper deals with a new seal system between flange joints without using a gasket. This gasketless flange includes a groove and an annular lip that is machined in one of the flange rings which when removed being in contact with the other flange to form a seal line when the flanges are assembled. In this study, firstly, fundamental dimensions are examined for unplasticized polyvinyl chloride (PVC-U JIS) to obtain the best sealing performance. Then, the effects of material difference and flange nominal size upon the sealing performance of the new gasketless flange are investigated for two types of materials, 0.25% carbon steel (S25C JIS) and PVC-U. It is found that the critical internal pressure at which leakage appears is mainly controlled by the maximum stress at the annular lip for each material even if the flange nominal sizes are different. The gasketless flange made by PVC-U shows the higher critical internal pressure compared with the case of S25C if the same clamping forces are applied. The effect of stress relaxation for PVC-U on the sealing performance is also considered. Then, it may be concluded that this PVC-U gasketless flange as well as S25C has good sealing performance.