Shell Stiffeners Research Articles

Research on Optimization method of power flow of cylindrical shell stiffener based on BESO

In order to establish a method for topological optimization of the power flow response of a cylindrical shell stiffener structure based on BESO, this paper will combine the BESO topology optimization theoretical and the power flow response theory , and take the overall minimization of the power flow of the cylindrical shell stiffener structure as the optimization goal. Then an iterative optimization algorithm for the layout of the stiffener structure on the cylindrical shell surface can be established. The plate-beam coupling structure is used to simulate the cylindrical shell stiffener structure, a finite element model of the cylindrical shell stiffened is established and solved to obtain the power flow sensitivity of the finite element. This is used as an iterative criterion for the layout of the stiffener on the surface of the cylindrical shell structure optimize. Through the analysis of numerical examples, it is obtained that the optimization of the rib layout can better reduce the overall power flow response of the structure, which also verifies the feasibility of the optimization method.

Optimization of cylindrical shells stiffened by rings under external pressure including their post-buckling behaviour

Optimization of a simply supported cylindrical shell stiffened by inner rings is considered in this paper. The shell is loaded by external pressure. The first critical buckling load is maximized. A material volume and a slope of a post-critical path are assumed as optimization constraints. The inner rings are made from the material obtained from the shell by decreasing its thickness. This way the volume of the material remain constant. The structure is modelled and solved by the finite element method (FEM). The linear and nonlinear stability analyses are done in the ANSYS software. An effect of geometric imperfections on a shape of equilibrium path is discussed. The optimization was performed numerically using the modified particle swarm optimization method (MPSO). The results are compared with a reference cylindrical shell with no rings. The single ring placed in the middle of the shell is good enough for stabilization of a post-buckling path for a shorter shell, regardless of its thickness. It is necessary to use three rings optimally distributed along the shell length, for a longer shell. The additional optimization profit was obtained by varying internal diameters of the rings. The proposed concept of shell stiffening by inner rings eliminates a major disadvantage of smooth cylindrical shells, namely an unstable post-buckling path.

LNG내부탱크 Stiffener 판재 비용의 최소화 분석 연구

Abstract - The analysis of the cost optimization and the total demand weight of 9% Ni-steel plates for installing shell stiffeners in the side wall of the large capacity LNG storage tank are carried out in order to reduce the costs of the plates for stiffeners. This study can be possible for developing the calculation program which evaluates the bill-of-material for stiffeners to reduce the manual calculation time of tank designer, and to enable the est imation of weight and cost for vari-ous plate width. The results show that the demand weight and co st are reduced as the plate width is wider. Nevertheless, both the weight and the cost with plate width for stiffeners should be com-pared and evaluated to obtain the optimum cost time to time because of various cost incremental factors of plates such as transportation and handling cost, etc.Key words : stiffener, LNG storage tank, plate width, plate weight, plate cost 1) I. 서 론 LNG는 편리하고 저렴하면서 깨끗하여 국내 주요 에너지원으로 자리를 확고히 하고 있다. 도시가 † Corresponding author:yunsangkook@daum.net Copyright ⓒ 2014 by The Korean Institute of Gas

Buckling of Cylindrical, Thin Wall, Trailer Truck Tanks and ASME Section XII

New hazmat (hazardous material) and nonhazmat transport tanks will be constructed to the rules of the ASME Code Section XII (ASME Boiler and Pressure Vessel Code, American Society of Mechanical Engineers, 3 Park Avenue, New York, NY 10016-5990). The criteria and basis to design these tanks have been questioned and a full scale buckling test has been performed to evaluate maximum allowable over-the-road loadings and required design details. This paper summarizes the results of this testing and provides comparisons with classical Code buckling criteria, Code Case 2286-2 (ASME Code Case 2286-2, Cases of ASME Boiler and Pressure Vessel Code, Case 2286-2, “Alternative Rules for Determining Allowable Compressive Stresses for Cylinders, Cones, Spheres, and Formed Heads”) and other methods for such evaluations. The objective is to provide the ASME Section XII committee with a basis for establishing buckling design criteria and shell stiffening details for both hazmat and nonhazmat transport tanks.

Influence of the Stiffeners on the Vibration Characteristics of a Stiffened Plate and Shell Coupled Structure

A coupled vibration model of a stiffened cylindrical shell with a stiffened interior plate is established based on the receptance method to get the stiffeners' influence on the plate-shell coupled structure's vibration characteristics. Numerical analysis on how an increase of the plate's and the shell's stiffener number affect the combination's vibration is carried out. It shows that the amplitudes of both the plate's and the shell's acceleration levels would reduce and peaks of their vibration curves would shift to the higher frequency range as stiffeners on the plate increases. And increase of the shell's stiffener number has little impact on the plate's acceleration level curve except for some peaks, but it would reduce the shell's acceleration level.

Thermal Analysis on the Shell Stiffeners of Double Steel Wall LNG Storage Tank

Shell stiffeners are used effectively to prevent preferential local buckling of LNG tank shell. In this paper, Finite element method (FEM) is applied to pay attention to the thermal analysis on the shell stiffeners of double steel wall LNG storage tank. The structural requirements according to British Standard 7777-2:1993 has been considered and then some dimensional adjustments of shell stiffeners are made to evaluate their influence on the thermal field of double steel wall LNG storage tank. Temperature distributions and heat flux of different dimensional shell stiffeners are presented. Though the analysis of results, it puts forward the conclusion that the dimensional design of shell stiffeners used in double steel wall LNG storage tank shall take not only the structural design requirements but also the thermal design ones into consideration in order to finally save cost in both construction and normal operation.

Linear static analysis of composite hat-stiffened laminated shells using finite elements

Analysis of composite stiffened panels used in aerospace, ship and other engineering structures by the method of finite elements has been presented. The formulation presented is based on the concept of equal displacements at the shell–stiffener interface. An eight-noded isoparametric shell element is used in association with three-noded curved beam element for the formulation of the stiffened panel element. First-order shear deformation theory is used in the present study. The stiffness matrix of the stiffener is computed first irrespective of its position within the plate/shell element. The stiffness matrix so computed for the stiffener is then transferred to that of the plate/shell element nodes depending on its position and orientation within the element before assembling the element stiffness matrix. A generalised formulation for the hat-shaped stiffener is presented. The investigation is restricted to linear static analysis of composite stiffened panels and parametric studies have been made to study the various aspects of laminated composite shell with open and closed shaped stiffeners.

FINITE ELEMENT TRANSIENT DYNAMIC ANALYSIS OF LAMINATED STIFFENED SHELLS

The present work describes the transient dynamic response of unstiffened/stiffened composite plates/shells using finite element method. Composite panels find wide applications in aerospace, marine and other engineering because of its high strength to weight ratios. These structures are often subjected to air-blast loading, underwater shock etc., which requires a thorough dynamic response analysis under such loading. A modified approach of shell and stiffener modelling is adopted here using an eight-noded isoparametric quadratic element for the shell and a three-noded curved stiffener element for the stiffeners on the concept of equal displacements at the shell–stiffener interface. The present formulation obviates the need for imposing the mesh line along the stiffeners; rather it accommodates the stiffeners elegantly anywhere placed arbitrarily inside the element with computational efficiency. Newmarks method for direct time integration has been adopted for the solution of the governing equation for undamped motion. The transient dynamic response of stiffened and unstiffened structures subjected to various kinds of time variant loading has been studied and the results are compared with the published ones.

Optimal 3D stiffener design with frequency considerations

In this paper, a new method to design the lay-out of shell stiffeners is introduced. This new approach has been derived from a two-phase, spherical micro-inclusions model and resulted in very simple closed-form expressions for the effective material properties. The ‘relaxed’ topology optimization problem can then be solved by general mathematical programming tools. It is very common to experience eigenvalue switch-over when solving topology optimization problems with frequency design considerations. An incremental objective function formulation with two strategies was studied to reduce the oscillation of optimization solutions. Design examples are presented and discussed. © 1997 Elsevier Science Limited.

Post-buckling Behavior of Stiffened Cross-Ply Cylindrical Shells

The post-buckling of stiffened, cross-ply laminated, circular determine the effects of shell lamination scheme and stiffeners on the reduced load-carrying capacity. The effect of geometric imperfection is also included. The analysis is based on the layerwise shell theory of Reddy, and the “smeared stiffener” technique is used to account for the stiffener stiffness. Nu cylinders under uniform axial compression is investigated to merical results for stiffened and unstiffened cylinders are presented, showing that imperfection-sensitivity is strictly related to the number of nearly simultaneous buckling modes.

Analysis of laminated shells with laminated stiffeners using rectangular shell finite elements

A finite element analysis of laminated shells reinforced with laminated stiffeners is described in this paper. A rectangular laminated anisotropic shallow thin shell finite element of 48 d.o.f. is used in conjunction with a laminated anisotropic curved beam and shell stiffening finite element having 16 d.o.f. Compatibility between the shell and the stiffener is maintained all along their junction line. Some problems of symmetrically stiffened isotropic plates and shells have been solved to evaluate the performance of the present method. Behaviour of an eccentrically stiffened laminated cantilever cylindrical shell has been predicted to show the ability of the present program. General shells amenable to rectangular meshes can also be solved in a similar manner.

A laminated anisotropic curved beam and shell stiffening finite element

The details of development of the stiffness matrix of a laminated anisotropic curved beam finite element are reported. It is a 16 dof element which makes use of 1-D first order Hermite interpolation polynomials for expressing it's assumed displacement state. The performance of the element is evaluated considering various examples for which analytical or other solutions are available.

A variable thickness, curved beam and shell stiffening element with shear deformations

AbstractA family of 2‐D and 3‐D superparametric curved beam elements are introduced as a special form of general 2‐D and 3‐D isoparametric continuum elements. Each beam ‘subelement’ is rectangular incross section, however several elements may be offset and overlayed for the analysis of structural members of quite general section properties. A number of examples are presented in order to illustrate the validity and range of application of the element.

Effect of Plane-Symmetric Mass Loading on the Response of Ring-Stiffened Cylindrical Shells

An analytical study of the in vacuo vibrations of a simply supported, mass-loaded thin cylindrical shell that is reinforced by equally spaced ring stiffeners is presented. Four masses are attached to each stiffening ring in a plane-symmetric fashion. The rotatory inertia of the masses is taken into account, but similar effects for the shell and ring stiffeners are neglected. Lagrange's equations are used to derive the dynamic equations of the shell structure and the Jacobi iteration method is employed to find the natural frequencies and corresponding mode shapes. Results are given for various values and angular position of the masses. When the value of the masses is allowed to become zero, the results for the ring-stiffened shell are in close agreement with those of previous investigators. Modal analysis is used to obtain the response of the structure to two different types of excitation: (1) a band of uniform internal pressure applied as a pulse in time, (2) a pressure wave that strikes the shell transversely. Numerical results are not presented for these two cases. [The investigation was supported by the U. S. Office of Naval Research.]