30톤 추력급 터보펌프 터빈의 구조 강도 및 진동 해석을 통한 안정성 예측

ABSTRACTIn this study, a locking-free six-node triangular shell element is proposed to nonlinear analysis of shell structures under the effects of both thermal and mechanical loads. Total Lagrangian formulation is used to consider large deflections and rotations. Besides, mixed interpolation of tensorial components is applied in the relations to deviate shear and membrane locking. The effects of temperature on the nonlinear deflections of shells are studied in several numerical examples. Moreover, analytical solution will be proposed for large deflection analysis of cantilever and simply supported beam under the thermal loads. To validate the proposed formulation, the finite element analysis results are compared by analytical solutions. Based on the obtained results of linear and nonlinear problems, it will be depicted that the authors’ scheme is capable for thermomechanical analysis of shell structures accurately.

During the development stage of a liquid rocket engine structural analyses are needed for increasing structural reliability and identify necessary design changes. These analyses need enormous efforts for detail modeling and cause large computational cost. With increasing computational power, the modeling can be more detailed than in the past. In this study, non-linear static structural and free vibration analyses taking into account the static loading as preloading are performed for a 750 kN class liquid rocket engine system. The finite element (FE) structural analyses are performed using the general purpose commercial code, Abaqus 2016. The effects of the static loadings on stress distributions and the free vibration results are analyzed. Additionally a simple kinematic model using rigid body elements is made up to investigate the elasticity effects on the rotation angles due to engine gimbaling. The strains measured from a ground firing test are converted to equivalent stresses to be compared with the FE analysis results. And a certain leakage problem solved using the FE analysis results is also presented.

Nonlinear static analysis of cable-stayed bridge structures

In this work, we describe the formulation and implementation for stress-based hybrid elements for conducting non-linear analysis of elastic structures. The motivation behind developing these elements is that they should be as simple to use as standard displacement-based isoparametric brick elements, but at the same time, be relatively immune to the shortcoming that these elements suffer from, namely, ‘locking’ problems which occur when they are used to model plate/shell geometries, almost incompressible materials or when the elements are distorted, and so on. The formulation is based on a two-field mixed variational principle. Numerical examples are presented to demonstrate the excellent performance of the proposed elements on a variety of challenging problems involving very large deformations, buckling, mesh distortions, almost incompressible materials, etc. Copyright © 2006 John Wiley & Sons, Ltd.

Multidisciplinary design optimization based on independent subspaces (MDOIS), which is a multidisciplinary design optimization (MDO) algorithm, has been recently proposed. Since MDOIS is relatively simple compared with other MDO algorithms, it is easy to apply MDOIS to practical engineering problems. In this research, an MDO problem is defined for the design of a belt-integrated seat (BIS) while considering crashworthiness. The crash model consists of an airbag, a BIS, an energy-absorbing steering system, and a safety belt. It is found that the current design problem has two disciplines - structural non-linear analysis and occupant analysis. The interdisciplinary relationship between the disciplines is identified. Interdisciplinary variables between the two disciplines are stiffness of the seat back frame and the belt load. The interdisciplinary relationship is addressed in the system analysis step in MDOIS. Prior to each independent subspace design, values of interdisciplinary variables at a given design point are determined in the system analysis step. The determined values are passed to corresponding subspaces, and the subspaces treat the received values of the interdisciplinary variables as constant parameters throughout the subspace design. For the present example, the belt load is passed to the structural analysis subspace and the stiffness of the seat back frame is passed to the occupant analysis subspace. Determined design variables in each subspace are passed to the system analysis step. In this way, the design process iterates until the convergence criterion is satisfied. As a result of the design, the weight of the BIS and the head injury criterion (HIC) of an occupant are reduced while the specified constraints are satisfied. Since the system analysis cannot be formulated in an explicit form in the current example, an optimization problem is formulated to solve the system analysis. The results from MDOIS are discussed.

The article presents a finite element based study of linear and geometrically non-linear progressive failure analysis of thin walled composite aerospace structures subjected to combined in-plane and out-of-plane loading which are typically encountered in thin walled aerospace structures. Different ply and constituent based failure criteria and material property degradation schemes have been coded into a PCL code in Nastran. As case studies, progressive failure analyses of sample composite laminates with cut-outs under combined loading are executed to study the effect of geometric non-linearity on the first ply failure and progression of failure. Different ply and constituent based failure criteria and different material property degradation schemes are also compared in terms of predicting the first ply failure and failure progression. For mode independent failure criteria, a method is proposed for the determination of separate degradation factors for fiber and matrix failures which are assumed to occur simultaneously. The results of the present study, show that under combined out-of-plane and in-plane loading, depending on the load case linear analysis can significantly underestimate or overestimate the failure progression compared to geometrically non-linear analysis even at low levels of out-of-plane loading.

Static and dynamic physically non-linear analysis of concrete structures using a hybrid mixed finite element model

Nonlinear structural analysis, which can account for geometrical or material nonlinearities beyond the scope of linear methods, typically incurs high computational costs. Recent advances have shown that quantum computers can accelerate various numerical simulations. Although quantum acceleration of linear structural analysis via the Quantum Linear System Algorithm (QLSA) has been studied, its application to nonlinear structural analysis remains unexplored. Here, we introduce our proposed quantum algorithm for accelerating nonlinear structural analysis, summarizing its key features and performance results from our recent study.

Purpose – The purpose of this paper is to present an efficient smoothed particle hydrodynamics (SPH) method particularly adapted for the geometrically nonlinear analysis of structures. Design/methodology/approach – In order to resolve the inconsistency phenomenon which systematically occurs in the standard SPH method at the domain’s boundaries of the studied structure, the classical kernel function and its spatial derivatives were modified by the use of Taylor series expansion. The well-known tensile instabilities inherent to the Eulerian SPH formulation were attenuated by the use of the Total Lagrangian Formulation (TLF). Findings – In order to demonstrate the effectiveness of the present improved SPH method, several numerical applications involving geometrically nonlinear behaviors were carried out using the explicit dynamics scheme for the time integration of the PDEs. Comparisons of the obtained results using the present SPH model with analytical reference solutions and with those obtained using ABAQUS finite element (FE) commercial software, show its good accuracy and robustness. Practical implications – An additional application including a multilayered composite structure and involving buckling and delamination was investigated using the present improved SPH model and the results are compared to the FE results, they confirmed both the efficiency and the accuracy of the proposed method. Originality/value – An efficient 2D-continuum SPH model for the geometrically nonlinear analysis of thin and thick structures is proposed. Contrarily to the classical SPH approaches, here the constitutive material relations are used to link naturally the stresses and strains. The Total Lagrangian approach is investigated to alleviate the tensile instabilities problem, allowing at the same time to avoid the updating procedure of the neighboring particles search and therefore reducing CPU usage. The proposed approach is valid for isotropic and multilayered composites structures undergoing large transformations. CPU time savings and better results with the new 2D-continuum SPH formulation compared to the classical continuum SPH. The explicit dynamic scheme was used for time integration allowing a fast resolution algorithm even for highly nonlinear problems.

This paper discusses implementation and adaptivity of the Discontinuous Galerkin (DG) finite element method as applied to linear and non-linear structural dynamic problems. By the DG method, both displacements and velocities are approximated as piecewise bilinear functions in space and time and may be discontinuous at the discrete time levels. Both implicit and explicit iterative algorithms for solving the resulted system of coupled equations are derived. They are third-order accurate and, while the implicit procedure is unconditionally stable, the explicit one is conditionally stable. An h-adaptive procedure based on the Zienkiewicz–Zhu error estimate using the SPR technique is applied. Numerical examples are presented to show the suitability of the DG method for both linear and non-linear structural dynamic analysis. Copyright © 1999 John Wiley & Sons, Ltd.

While exact solutions for linear static analysis of most frame structures can be obtained by the finite element method, it is very difficult to obtain exact solutions for free vibration and harmonic analyses for non‐trivial cases. This paper presents a study on new finite element formulation and algorithms for exact solutions of undamped axial vibration problems of elastic bars. Appropriate shape functions are constructed by using the homogeneous governing equations, and based on the new shape functions, a novel element is formulated. An iterative procedure is proposed for determining both the exact natural frequency values and the corresponding vibration mode shapes. Exact solutions can also be obtained for undamped harmonic response analyses by using the new element, as its stiffness and mass matrices are exact for a specified frequency. Illustrative examples are presented to demonstrate the effectiveness of the proposed element and algorithm. Copyright © 2007 John Wiley & Sons, Ltd.

This paper gives a general overview of the analysis of offshore structures under fire loads. Attention is drawn to the different requirements of component fire testing, which may give misleading emphasis to certain types of analysis. It is shown that the basis of structural behaviour under fire loading is the change in material properties. However, it is the effects of thermal strains which are most likely to promote structural instability, leading to collapse. Non-linear structural analysis has ban USCXI to illustrate fire loading effects, but it is likely that the offshore design industry will employ linear elastic structural analysis in many designs. The design of seeondary structures to reskt fire loadings is discussed. INTRODUCTION The design of steel offshore structures to resist fire loadings is a new technology. Analytical techniques are not particularly well developed [1,2] or understood by either practicing engineers who develop the designs or safety specialists, who overview the design process. What is well understood is the technology of fire component testing [3,4], and it is this knowledge which is perhaps misleading the development of the analysis of steel structures under fire loadings. Recent research into structural fire performance has concentrated on the numerical simulation of furnace fire tests. Whereas such work [5] can lead to economies in component testing programs it does little to increase the fundamental understanding of full-scale structures in real fires. Offshore fires involve a hydrocarbon inventory, and embrace jet, pool and running liquid fire types. The description and calculation of fire loadings is not addressed in this paper. Material Behaviour The behaviour of steel structures under fire loading conditions is determined largely by temperature related material properties. Foundation data is available from a number of sources [6,7,8,9]. It is conventional to split the material properties into two groups. These are then termed the thermal and the mechanical material properties. Thermal properties are:specific heat,thermal conductivitycoefficient of thermal expansion.The mechanical properties are:yield stress (Fy),Youngs modulus (E),Shear modulus (G). Almost without exception, the material properties of steel vary to a greater or lesser extent with temperature. The stress-strain behaviour of a typical structural steel is shown in Figure 1. Note the loss of a sharp yield point and the drop in performance between 400 deg C and 750 deg C. When a steel type has been given enhanced properties by heat treatment, then the properties are likely to fall-back to those associated with the chemical composition when a threshold temperature of about 600 deg C is attained in a fire. By contrast the material properties associated with microstructure and hence chemical composition are both enduring and pertinent to fire conditions. In Figure 2 the behaviour of Austenitic stainless steel, low carbon structural steel and 'fire-resisting' steel are compared. In the range 600 deg C to 800 deg C the stainless steel retains more of its basic strength.

FEPACS (Finite Element Package for linear static, dynamic and instability Analysis of Composite Structures under hygro-thermo-mechanical loads) incorporates a complete library of consistent and correct 1-, 2- and 3-dimensional linear and quadratic general purpose finite elements. In this paper, we shall discuss the finite element technology that has gone into the package as well as its present modelling and solution capabilities. We shall also discuss briefly recent developments toward enhancing the package: Robust composite elements based on aC 0-continuous higher order transverse deformation plate/beam theory, and nonlinear element technology and solution strategies. Finally, we shall also briefly touch upon several satellite application modules that are in different stages of planning/development to aid FEPACS: damage assessment/prediction,expert-like advisors for solid modelling and finite element modelling/analysis, pre-/post-processing for FEPACS applications, structural optimisation and related finite element algorithms, and finally, a frontal solution module for FEPACS to enhance its feasibility for vectorisation/parallelisation.

This comprehensive textbook combines classical and matrix-based methods of structural analysis and develops them concurrently. It is widely used by civil and structural engineering lecturers and students because of its clear and thorough style and content. The text is used for undergraduate and graduate courses and serves as reference in structural engineering practice. With its six translations, the book is used internationally, independent of codes of practice and regardless of the adopted system of units. Now in its seventh edition: the introductory background material has been reworked and enhanced throughout, and particularly in early chapters, explanatory notes, new examples and problems are inserted for more clarity., along with 160 examples and 430 problems with solutions. dynamic analysis of structures, and applications to vibration and earthquake problems, are presented in new sections and in two new chapters the companion website provides an enlarged set of 16 computer programs to assist in teaching and learning linear and nonlinear structural analysis. The source code, an executable file, input example(s) and a brief manual are provided for each program.

The article presents a modified finite element (FE) based algorithm for non linear analysis of 2D beam structures, which takes into account the influence of the shear forces.The method proposed enables using complex materials with nonlinearities without the need of implementing advanced constitutive models in FE routines.It can be directly inte grated with commonly available FE software for linear analysis of beam structures, so its functionality can be easily extended also with material nonlinearities.The presented approach adopts the generalized constitutive law algorithm to iteratively modify the stiffness of beam element.To address an influence of a shear stiffness, a Timoshenko beam element was used.The methodology was implemented and its performance was verified on several numerical examples.For validation, the displacements and the ultimate loads were compared with the values from a commercial FE software.The results shown a good correlation between the ref erence model and the method proposed.