板翅式换热器封头极限载荷的分析

运用大型有限元分析软件ANSYS,对板翅式换热器封头的承载能力进行了极限分析,研究了同一壁厚下结构形式不同对封头极限载荷的影响。应用ASME锅炉和压力容器标准第八卷第二册中“AD-140设计准则”对在最大允许设计压力作用下的封头最大应力点进行了评定,得到了板翅式换热器不同结构形式封头相应的特点和应用范围,为板翅式换热器封头的设计提供了可行性方法和依据。     

Modifications to the ‘directional simulation in the load space’ approach to structural reliability analysis

‘Directional simulation in the load space (DS-LS)’ is a simulation-based technique used to perform reliability analysis of structures subjected to time-invariant or time-variant random loads. To perform DS-LS a location must first be chosen for an ‘origin of simulation’. The origin may be positioned in either the safe or failure region of the load space, and its precise location (with respect to these regions) influences the DS-LS formulation needed to evaluate reliability correctly. The current formulation requires the origin to be positioned in the safe region. However, even for simple structures, the ‘exact’ location of the safe and failure region is not always known explicitly ‘a priori’. Modifications to allow for the possibility of positioning the origin not only in the ‘safe’ region but in the ‘failure’ region are proposed in this paper. Some numerical examples involving one or more stationary continuous Gaussian loads and the simulation of directions by ‘Monte Carlo’ and ‘the hyperspace division method’ are presented to demonstrate the validity of the proposed formulations. Some comments on convergence are made.     

Calculation of the collapse load of an axially compressed laminated composite stringer-stiffened curved panel–An engineering approach

The effective width method that is widely applied for the analysis of isotropic planar stringer-stiffened panels has been extended to laminated composite stringer-stiffened circular cylindrical panels. The approach was modified and adapted to handle curved composite structures.

Panels stiffened by blade type stiffeners, J-form stiffeners and T-form stiffeners were considered in the present study. Bending buckling of the stiffeners, their torsional buckling, combined bending and torsion buckling and local buckling of the stringers were accounted for in the investigation. Using the proposed extended effective width method, a MATLAB based software code TEW¹ was developed and implemented. To validate this code, predictions obtained by it were compared with experimental results and with finite element calculations. Good agreement between the present proposed method, experiments and finite element simulations was found, thus yielding an efficient, simple to apply and fast engineering code to be used in design and optimization stages.     

An approach to the positioning of FRP provisions in vaulted masonry structures

In the paper, one starts from a theoretical formulation aimed at analysing masonry vaults by selecting, in an inverted approach, families of load shapes that may be equilibrated by sets of admissible solutions, in order to develop an operative method for the positioning of FRP reinforcements in masonry vaulted constructions. On the basis of this premise a strategy is outlined for identifying the areas of the vault to be selected for introducing the FRP provisions. As shown in the numerical investigation, higher intensities of the stress state are then allowed by the introduction of the reinforcement and the local relaxation of some of the constraints of the problem is possible.     

An analytical model for the prediction of load distribution in highly torqued multi-bolt composite joints

This paper presents the development of an enhanced analytical approach for modelling the load distribution in multi-bolt composite joints. The model is a closed-form extension of a spring-based method, where bolts and laminates are represented by a series of springs and masses. The enhancement accounts for static friction effects between the laminates, a primary mechanism of load transfer in highly torqued bolted joints. The method is validated against detailed three-dimensional finite element models and where possible, experimental results. The effect of varying bolt-torque and bolt-hole clearance on the load distribution in a three-bolt, single-lap joint is investigated and the method proves to be robust, accurate and highly efficient. Finally, the method is employed in a parameter study, where increasing bolt torque levels can be used for achieving a more even load distribution in multi-bolt joints.     

考虑载荷作用次数的机械零部件可靠性灵敏度分析方法

 为了研究载荷多次作用时,机械零部件的可靠度及可靠性灵敏度变化规律,从灵敏度角度修改零件的设计参数,降低制造成本,建立一种可靠性模型结合了随机摄动法、Edgeworth级数技术,并考虑了载荷的作用次数．摄动法和Edgeworth级数可以在基本随机参数的前4阶矩已知的情况下,研究具有任意分布参数的机械零件的可靠性灵敏度设计问题,顺序统计量理论考虑了载荷作用次数在可靠度和灵敏度计算中的影响．使用这种模型计算出的可靠度会随着载荷作用次数而变化,这与静态的可靠度计算方法存在差别．以某一型号的螺栓为算例,应用此模型计算了其可靠度、随机变量均值和方差的可靠性灵敏度．由提出的方法得到了可靠度和可靠性灵敏度值及其随载荷作用次数变化的曲线．可靠度及可靠性灵敏度随载荷作用次数变化的规律是：载荷作用次数增加,可靠度值降低,变化趋势单调;载荷作用次数达到最大时,可靠度达到最小;随机变量均值和方差的灵敏度随载荷作用次数变化出现不同的变化趋势,其中螺栓截面直径的均值和方差灵敏度随载荷作用次数的变化最大,随作用次数的增加,螺栓截面直径的参数将对螺栓的可靠性起主要的决定作用．     

基于ARMA模型模拟高架桥的脉动风速时程

强风是高架桥设计与防灾减灾分析的控制性荷载之一.风与高架桥相互作用十分复杂,可以通过风洞试验、现场实测、数值模拟获取可靠的风速(风荷载)数据.尽管如此,时域分析可以使人们更全面地了解高架桥的风振响应特性, 也能更直观地反映高架桥风致振动控制的有效性.因此, 使用线性滤波法即白噪声滤波法(WNFM)中的自回归滑动平均(ARMA)模型模拟高架桥的脉动风速时程.首先, 考虑高架桥脉动风速的时间和空间相关性, 导出自回归(AR)模型阶数与滑动回归(MA)模型阶数不相等时ARMA模型的表达式.接着, 基于Kaimal风速谱,使用ARMA模型来模拟一座实际高架桥的脉动风速时程.最后,通过比较模拟风速功率谱、自相关和互相关函数与目标风速功率谱、自相关和互相关函数的吻合程度, 验证基于ARMA模型模拟高架桥脉动风速时程的可行性.     

More on the ricochet of eroding long rods—Validating the analytical model with 3D simulations

The ricochet of eroding long rods, from inclined steel targets, is investigated by a series of three-dimensional (3D) numerical simulations. These are compared with the predictions of our, previously published, analytical model for ricochet. The agreement between simulation results and model predictions is excellent, strongly enhancing our simple ricochet model. We also highlight several aspects of our model which are derived from its simple closed form. One of these is the fact that ricochet of long rods can take place only at velocities and obliquities which are higher than certain threshold values. Otherwise, the process involves rod bending and sliding along the target impact face.     

An improved damage model using the construction technology of virtual load spectrum and its statistical analysis

In this work, an improved damage model based on construction technology of virtual load spectrum is developed. A predetermined reliability index is used as the termination criterion to calculate the fatigue life, and the results of statistical analysis have shown that the accuracy of fatigue life prediction result has been greatly improved. The model is targeting cyclic loading applications. The main advantage of the model is the use of construction technology of virtual load spectrum for expanding load spectrum and the Monte Carlo method for correcting fatigue damage. Another advantage concerns the link between predetermined reliability criterion and the fatigue life, which puts forward a new method of calculating fatigue life. The convergence proof of the model is presented, and physical experiment data are shown for validation. Several illustrative examples are presented to confirm the accuracy and efficiency of the proposed damage model.     

Continuum topology optimization considering uncertainties in load locations based on the cloud model

Few researchers have paid attention to designing structures in consideration of uncertainties in the loading locations, which may significantly influence the structural performance. In this work, cloud models are employed to depict the uncertainties in the loading locations. A robust algorithm is developed in the context of minimizing the expectation of the structural compliance, while conforming to a material volume constraint. To guarantee optimal solutions, sufficient cloud drops are used, which in turn leads to low efficiency. An innovative strategy is then implemented to enormously improve the computational efficiency. A modified soft-kill bi-directional evolutionary structural optimization method using derived sensitivity numbers is used to output the robust novel configurations. Several numerical examples are presented to demonstrate the effectiveness and efficiency of the proposed algorithm.     

An accurate solution for the responses of circular curved beams subjected to a moving load

In this paper, an accurate and effective solution for a circular curved beam subjected to a moving load is proposed, which incorporates the dynamic stiffness matrix into the Laplace transform technique. In the Laplace domain, the dynamic stiffness matrix and equivalent nodal force vector for a moving load are explicitly formulated based on the general closed‐form solution of the differential equations for a circular curved beam subjected to a moving load. A comparison with the modal superposition solution for the case of a simply supported curved beam confirms the high accuracy and applicability of the proposed solution. The internal reactions at any desired location can easily be obtained with high accuracy using the proposed solution, while a large number of elements are usually required for using the finite element method. Furthermore, the jump behaviour of the shear force due to passage of the load is clearly described by the present solution without the Gibb's phenomenon, which cannot be achieved by the modal superposition solution. Finally, the present solution is employed to study the dynamic behaviour of circular curved beams subjected to a moving load considering the effects of the loading characteristics, including the moving speed and excitation frequency, and the effects of the characteristics of curved beams such as the radius of curvature, number of spans, opening angles and damping. The impact factors for displacement and internal reactions are presented. Copyright © 2000 John Wiley & Sons, Ltd.     

A model to determine the optimal critical level and the monitoring intervals in condition-based maintenance

In condition-based maintenance, a common practice is to record a condition reading at a regular interval, and once the reading is higher than a pre-set critical level, the item monitored is declared faulty and repair or replacement may be initiated. However, surprisingly both in practice and theory, little attention has been paid to whether or not the critical level and the monitoring interval are set in a cost effective way. This paper reports on the development of a model that can be used to determine the optimal critical level and interval in condition-based maintenance in terms of a criterion of interest. The model is established on the basis of the random coefficient growth model where the coefficients of the regression growth model are assumed to follow known distribution functions. A simple example is given in the paper to illustrate the modelling ideas.     

An analytical model to study the effective stiffness of the composites with periodically distributed sphere particles

In order to analytically study the overall elastic stiffness of the composite containing periodically dispersed sphere particles, a new micro-mechanics model is developed in this paper. Three kinds of typical particle packing arrangements in the form of simple cubic lattice, body-centered cubic lattice and face-centered cubic lattice are considered and compared. The special characteristics of regular distribution are fully considered by incorporating the necessary geometrical symmetry conditions into strain Green’s function. It is found that particle arrangement obviously affects the macroscopic elastic response of such the kind of composite. Moreover, most of the predictions by the present model are in good agreement with the FEM computations. The effective Young’s modulus of BCC composite the effective shear modulus of SC composite are not in the range of the Hashin–Shtrikman bounds. The present model is also useful to verify some other numerical results mainly obtained by the unit-cell model, for instance, damage variables, matrix plasticity, etc.     

A decision model to determine the number of shuttles in a tier-to-tier SBS/RS

Shuttle-based storage and retrieval systems (SBS/RSs), which are designed to increase throughput capacity and flexibility, are a type of automated storage and retrieval system used for lightweight loads. SBS/RSs can increase throughput capacity by using multiple shuttles and elevators as storage and retrieval machines (SRMs). They can also facilitate improvements in flexibility since they are able to adjust the number of SRMs according to transaction demands. Thus, determining the number of shuttles is an important issue in tier-to-tier SBS/RSs. In this paper, a decision model to determine the number of shuttles is proposed. The model is based on the travel time model, and it considers parameters such as the physical configuration, velocity profile and the probability that the shuttle operates a dual command. Finally, the throughput capacity from the travel time model is compared with that from a simulation-based approach in order to verify the effects of the model. In addition, a critical discussion regarding the characteristics of the tier-to-tier system is provided.     

Influence of the material properties of a tub on its top load strength

Every time a new package is being developed similar problems have to be faced. These problems involve material and supplier choice, pack requirements, manufacturing performance of the pack, etc. This paper describes a study of the influence of material properties on the top load strength of a tub for frozen products. Additionally, several numerical simulations have been carried out in order to find general guidelines for new packaging developments. Copyright © 1999 John Wiley & Sons, Ltd.     

An analytical model to predict the effective fracture toughness of concrete for three-point bending notched beams

An analytical model to predict the effective fracture toughness of concrete was proposed based on the fictitious crack model. Firstly, the equilibrium equations of forces in the section were formed in combination with the plane section assumption. Then a Lagrange function was presented through the equilibrium equations and the relationship formula between the effective crack length and crack tip opening displacement. Taking into account Lagrange Multiplier Method, the maximum load P_max was obtained, as well as the critical effective crack length a_c. Furthermore, was gained in an analytical manner. Subsequently, some material and structural parameters from other literatures were adopted into the proposed model for the calculation. Compared with the experimental results, most of the calculated values show a good agreement for P_max and a_c. In order to study the influence of the softening curve in the fictitious crack on the calculated fracture parameters, three series of constants determining the shape of the softening curve were chosen in the calculation. The results show that the calculated fracture parameters are not sensitive to the shape of the softening curve. Therefore, only if the elastic modulus E_c and flexural tensile strength f_r were measured, P_max, a_c and can be predicted accurately using the proposed model. Finally, the variations of the calculated fracture parameters with the specimen size and a₀/h (i.e., the ratio of the initial crack length to the depth of the specimen) were studied. It was found that both and the pre-critical crack propagation length Δa_c increase with the specimen size. However, the two parameters increase to the maximums and then decrease gradually with a₀/h. Moreover, the theories of free surface effect were utilized to explain the observed size effects.     

An Algorithm to Compute the Exponential Part of a Formal Fundamental Matrix Solution of a Linear Differential System

In this paper we describe an efficient algorithm, fully implemented in the Maple computer algebra system, that computes the exponential part of a formal fundamental matrix solution of a linear differential system having a singularity of pole type at the origin. Received July 5, 1994; revised version March 21, 1996     

Influence of anisotropy on the limit load of bi-material welded cracked joints subject to tension

A plane-strain upper bound limit load solution for bi-material welded joints subject tension is found. It is assumed that each material obeys Hill's orthotropic yield criterion and one of the principal axes of orthotropy coincides with the tensile direction. A crack of arbitrary length is located at the bi-material interface. The solution is based on a simple discontinuous kinematically admissible velocity field and is an extension of the corresponding solution for the specimen made of isotropic materials. The main purpose of the paper is to demonstrate that the influence of anisotropy on the magnitude of limit loads may be much more significant than other effects.     

An energy-based analytical push-out model applied to characterise the interfacial properties of knitted glass fibre reinforced PET

In this study, the interfacial properties of weft-knitted glass fibre (GF)-polyethylene terephthalate (PET) composites were examined. On thin polished cut-outs of knitted GF/PET composite parts, push-out experiments were carried out at different temperatures using a push-out device set up in a SEM. Load–displacement curves were digitally recorded. FEM results suggested that crack initiation was located at or near the top of the free specimen surface. To interpret the load–displacement curves from the push-out experiments a new energy-based model was proposed. The model follows the principle of minimal energy and includes the effects of friction, Poisson expansion of the fibre, and energy release of the debonded part of the fibre. Crack progression was calculated applying the concept of interfacial surface fracture energy. With the proposed analytical model, the interfacial properties of GF/PET were extracted. The model is compared with existing approaches.