scholarly journals Design Optimisation of Lower-Bound Buckling Capacities for FRP-Laminated Cylindrical Shells

2012 ◽  
Vol 2012 ◽  
pp. 1-10
Author(s):  
Hongtao Wang ◽  
James G. A. Croll
Keyword(s):  
Lower Bound ◽  
Cylindrical Shells ◽  
Design Parameters ◽  
Design Decision ◽  
Buckling Loads ◽  
Frp Composite ◽  
Elastic Load ◽  
Design Variables ◽  
Mathematical Algorithms ◽  
Parametric Studies

The imperfection sensitive buckling loads of fibre reinforced polymeric (FRP) composite cylindrical shells under axial compression can be optimised with respect to many material and geometric parameters. Current approaches, using mathematical algorithms to optimise the linearised classical critical loads with respect to many design variables, generally ignore the potential reductions in elastic load carrying capacities that result from the severe sensitivities of buckling loads to the effects of initial imperfections. This paper applies a lower-bound design philosophy called the reduced stiffness method (RSM) to the optimisation design of FRP shell buckling. A physical optimisation in terms of parametric studies is carried out for simply supported, 6-ply symmetric, glass-epoxy circular cylindrical shells under uniform axial load. It is shown that under the guidance of RSM, safe lower-bound buckling loads can be enhanced greatly by choosing appropriate combinations of design parameters. It is demonstrated how this approach encourages the delineation of those components of the shell’s membrane and bending stiffness that are important and those that are unimportant within each of the prospective buckling modes. On this basis, it is argued that the RSM provides not only a safe but also a more rational strategy for better design decision making.

Buckling Analysis of Advanced Grid Stiffened Composite Cylinders

2014 ◽  
Vol 875-877 ◽  
pp. 755-762 ◽  
Author(s):  
Kang Hee Lim ◽  
He Wei ◽  
Zhi Dong Guan
Keyword(s):  
Cylindrical Shells ◽  
Computational Cost ◽  
Structure Design ◽  
Grid Structure ◽  
Constant Weight ◽  
Buckling Loads ◽  
Design Variables ◽  
Weight Design ◽  
Composite Cylinders ◽  
Composite Cylindrical Shells

Advanced Grid Stiffened(AGS) composite cylindrical shells are widely used in aerospace industry. This study analyzes the buckling loads for various types of grid structures of AGS composite cylindrical shells. The grid structures are classified as Angle-grid, Iso-grid, Kagome-grid, Ortho-grid, Orthotropic-grid and the characteristics had been analyzed for each grid type. In this study, the various types of grid structure were designed that weight of the whole structure keeps a constant. Under the condition of constant-weight, design variables such as grid angle, number of the grid, h/t ratio of the grid were controlled, and buckling loads of the grid structures were analyzed. The results were analyzed for each type of grid and each design variable of the structures. This study was performed through finite element method and the accuracy of the analysis was verified by previous studies. Finally, buckling modes were analyzed with the thickness of the skin. The selection for the most appropriate design variables had been verified for each grid type and the result can be applied to the optimization of grid structure design, and is also very helpful for reducing the computational cost and obtaining optimization values more accurately.

Design of Flexure Pivot Tilting Pads Gas Bearings for High-speed Oil-Free Microturbomachinery

2006 ◽  
Vol 129 (1) ◽  
pp. 112-119 ◽  
Author(s):  
Kyuho Sim ◽  
Daejong Kim
Keyword(s):  
High Speed ◽  
Hydrodynamic Pressure ◽  
Design Parameters ◽  
Gas Bearings ◽  
Bearing Clearance ◽  
High Speeds ◽  
Radial Stiffness ◽  
Design Variables ◽  
Final Design ◽  
Parametric Studies

This paper introduces flexure pivot tilting pad gas bearings with pad radial compliance for high-speed oil-free microturbomachinery. The pad radial compliance was for accommodation of rotor centrifugal growth at high speeds. Analytical equation for the rotor centrifugal growth based on plane stress model agreed very well with finite element method results. Parametric studies on pivot offset, preload, and tilting stiffness were performed using nonlinear orbit simulations and coast-down simulations. Higher preload and pivot offset increased both critical speeds of the rotor-bearing system and onset speeds of instability due to the increased wedge effect. Pad radial stiffness and nominal bearing clearance were very important design parameters for high-speed applications due to the physically existing rotor centrifugal growth. From the series of parametric studies, the maximum achievable rotor speed was limited by the minimum clearance at the pad pivot calculated from the rotor growth and radial deflection of pads due to hydrodynamic pressure. Pad radial stiffness also affects the rotor instability significantly. Small radial stiffness could accommodate rotor growth more effectively but deteriorated rotor instability. From parametric studies on a bearing with 28.5mm in diameter and 33.2mm in length, optimum pad radial stiffness and bearing clearance are 1-2×107N∕m and 35μm, respectively, and the maximum achievable speed appears 180krpm. The final design with suggested optimum design variables could be also stable under relatively large destabilizing forces.

Optimization of orthotropic girders in cable supported bridges by parametric studies

2019 ◽  
Author(s):  
Mads Baandrup ◽  
Peter Noe Poulsen ◽  
John Forbes Olesen ◽  
Henrik Polk
Keyword(s):  
Boundary Conditions ◽  
Suspension Bridge ◽  
Design Parameters ◽  
Fe Model ◽  
Design Variables ◽  
Gradient Based ◽  
Parametric Studies ◽  
Bridge Girder ◽  
Support Conditions ◽  
Material Utilization

<p>For the last six decades closed-box orthotropic steel girders have been widely used in cable supported bridges due to their simple but useful structural concepts. Several numerical parametric studies were previously carried out in order to investigate inherent fatigue stress problems and in general, to improve the bridge girder designs. However, often such studies have been carried out with over-simplified finite element models, especially where boundary conditions have been challenging. In the present work, an advanced multi-scale FE model of a suspension bridge is established with sophisticated boundary conditions applied to a local parametric sub-model of a bridge girder. Thus, the model accommodates realistic support conditions. With this sub-model, a parametric study of the usual design parameters is carried out with focus on fatigue and a Eurocode stiffness requirement. The study reveals trends and correlations for the varying design parameters. Finally, the parametric sub-model is utilized in an automatic gradient-based optimization of multiple design variables simultaneously with the goal of minimizing weight. The methods allow bridge engineers to push material utilization to its limits by giving new insight into the effect of changing design parameters.</p>

scholarly journals Parametric Analysis on Landing Gear Strut Friction of Light Aircraft for Touchdown Performance

2021 ◽  
Vol 11 (12) ◽  
pp. 5445
Author(s):  
Shengyong Gan ◽  
Xingbo Fang ◽  
Xiaohui Wei
Keyword(s):  
Response Surface ◽  
Energy Absorption ◽  
Landing Gear ◽  
Surface Model ◽  
Absorption Properties ◽  
Surface Method ◽  
Design Variables ◽  
Landing Impact ◽  
Landing Response ◽  
Parametric Studies

The aim of this paper is to obtain the strut friction–touchdown performance relation for designing the parameters involving the strut friction of the landing gear in a light aircraft. The numerical model of the landing gear is validated by drop test of single half-axle landing gear, which is used to obtain the energy absorption properties of strut friction in the landing process. Parametric studies are conducted using the response surface method. Based on the design of the experiment results and response surface functions, the sensitivity analysis of the design variables is implemented. Furthermore, a multi-objective optimization is carried out for good touchdown performance. The results show that the proportion of energy absorption of friction load accounts for more than 35% of the total landing impact energy. The response surface model characterizes well for the landing response, with a minimum fitting accuracy of 99.52%. The most sensitive variables for the four landing responses are the lower bearing width and the wheel moment of inertia. Moreover, the max overloading of sprung mass in LC-1 decreases by 4.84% after design optimization, which illustrates that the method of analysis and optimization on the strut friction of landing gear is efficient for improving the aircraft touchdown performance.

A unified framework for the design of low-complexity wavelet filters

2017 ◽  
Vol 15 (06) ◽  
pp. 1750054 ◽  
Author(s):  
Ameya K. Naik ◽  
Raghunath S. Holambe
Keyword(s):  
Feature Extraction ◽  
Compact Support ◽  
Low Complexity ◽  
Design Parameters ◽  
Unified Framework ◽  
Vanishing Moments ◽  
Wavelet Filters ◽  
Design Variables ◽  
Optimum Filter ◽  
Simulation Results

An outline is presented for construction of wavelet filters with compact support. Our approach does not require any extensive simulations for obtaining the values of design variables like other methods. A unified framework is proposed for designing halfband polynomials with varying vanishing moments. Optimum filter pairs can then be generated by factorization of the halfband polynomial. Although these optimum wavelets have characteristics close to that of CDF 9/7 (Cohen-Daubechies-Feauveau), a compact support may not be guaranteed. Subsequently, we show that by proper choice of design parameters finite wordlength wavelet construction can be achieved. These hardware friendly wavelets are analyzed for their possible applications in image compression and feature extraction. Simulation results show that the designed wavelets give better performances as compared to standard wavelets. Moreover, the designed wavelets can be implemented with significantly reduced hardware as compared to the existing wavelets.

Buckling Design of Axially Compressed Cylindrical Shells Based on Energy Barrier Approach

2021 ◽  
pp. 2150165
Author(s):  
Haigui Fan ◽  
Wenguang Gu ◽  
Longhua Li ◽  
Peiqi Liu ◽  
Dapeng Hu
Keyword(s):  
Experimental Data ◽  
Energy Barrier ◽  
Thin Shell ◽  
Design Method ◽  
Lightweight Design ◽  
Cylindrical Shells ◽  
Design Criterion ◽  
The Other ◽  
Shell Structures ◽  
Buckling Loads

Buckling design of axially compressed cylindrical shells is still a challenging subject considering the high imperfection-sensitive characteristic in this kind of structure. With the development of various design methods, the energy barrier concept dealing with buckling of imperfection-sensitive cylindrical shells exhibits a promising prospect in recent years. In this study, buckling design of imperfection-sensitive cylindrical shells under axial compression based on the energy barrier approach is systematically investigated. The methodology about buckling design based on the energy barrier approach is described in detail first taking advantage of the cylindrical shells whose buckling loads have been extensively tested. Then, validation and discussion about this buckling design method have been carried out by the numerical and experimental analyses on the cylindrical shells with different geometrical and boundary imperfections. Results in this study together with the available experimental data have verified the reliability and advantage of the buckling design method based on energy barrier approach. A design criterion based on the energy barrier approach is therefore established and compared with the other criteria. Results indicate that buckling design based on energy barrier approach can be used as an efficient way in the lightweight design of thin-shell structures.

CAD and Optimization of Helical Torsion Springs

1994 ◽  
Author(s):  
Sayed M. Metwalli ◽  
M. Alaa Radwan ◽  
Abdel Aziz M. Elmeligy
Keyword(s):  
Iterative Process ◽  
Minimum Weight ◽  
Design Parameters ◽  
Optimal Parameters ◽  
Direct Evaluation ◽  
Torsion Spring ◽  
Performance Requirements ◽  
Design Variables ◽  
Method Of Lagrange Multipliers ◽  
Torsion Springs

Abstract The convensional procedure of helical torsion spring design is an iterative process because of large number of requirements and relations that are to be attained once at a time. The design parameters are varied at random until the spring design satisfies performance requirements. A CAD of the spring for minimum weight is formulated with and without the variation of the maximum normal stress with the wire diameter. The CAD program solves by employing the method of Lagrange-Multipliers. The optimal parameters, in a closed form are obtained, normalized and plotted. These explicit relations of design variables allow direct evaluation of optimal design objective and hence, an absolute optimum could be achieved. The comparison of optimum results with those previously published, shows a pronounced achievement in the reduction of torsion spring weight.

A Study on Optimum Design Using Fuzzy Numbers As Design Variables

1995 ◽  
Author(s):  
Masao Arakawa ◽  
Hiroshi Yamakawa
Keyword(s):  
Fuzzy Sets ◽  
Optimum Design ◽  
Fuzzy Numbers ◽  
Fuzzy Optimization ◽  
Design Parameters ◽  
Numerical Examples ◽  
Design Variables ◽  
Conventional Methods

Abstract In this study, we summerize the method of fuzzy optimization using fuzzy numbers as design variables. In order to detect flaw in fuzzy calculation, we use LR-fuzzy numbers, which is known as its simplicity in calculation. We also use simple fuzzy numbers’ operations, which was proposed in the previous papers. The proposed method has unique characteristics that we can obtain fuzzy sets in design variables (results of the design) directly from single numerical optimizing process. Which takes a large number of numerical optimizing processes when we try to obtain similar results in the conventional methods. In the numerical examples, we compare the proposed method with several other methods taking imprecision in design parameters into account, and demonstrate the effectiveness of the proposed method.

Design Sensitivity Analysis of Nonlinear Multidisciplinary Multibody Systems in the MIXEDMODELS Platform

2007 ◽  
Author(s):  
Shilpa A. Vaze ◽  
Prakash Krishnaswami ◽  
James DeVault
Keyword(s):  
Sensitivity Analysis ◽  
Multibody Systems ◽  
Design Sensitivity ◽  
Differential Algebraic Equations ◽  
The State ◽  
Design Sensitivity Analysis ◽  
Design Parameters ◽  
State Variables ◽  
Sensitivity Coefficients ◽  
Design Variables

Most state-of-the-art multibody systems are multidisciplinary and encompass a wide range of components from various domains such as electrical, mechanical, hydraulic, pneumatic, etc. The design considerations and design parameters of the system can come from any of these domains or from a combination of these domains. In order to perform analytical design sensitivity analysis on a multidisciplinary system (MDS), we first need a uniform modeling approach for this class of systems to obtain a unified mathematical model of the system. Based on this model, we can derive a unified formulation for design sensitivity analysis. In this paper, we present a modeling and design sensitivity formulation for MDS that has been successfully implemented in the MIXEDMODELS (Multidisciplinary Integrated eXtensible Engine for Driving Metamodeling, Optimization and DEsign of Large-scale Systems) platform. MIXEDMODELS is a unified analysis and design tool for MDS that is based on a procedural, symbolic-numeric architecture. This architecture allows any engineer to add components in his/her domain of expertise to the platform in a modular fashion. The symbolic engine in the MIXEDMODELS platform synthesizes the system governing equations as a unified set of non-linear differential-algebraic equations (DAE’s). These equations can then be differentiated with respect to design to obtain an additional set of DAE’s in the sensitivity coefficients of the system state variables with respect to the system’s design variables. This combined set of DAE’s can be solved numerically to obtain the solution for the state variables and state sensitivity coefficients of the system. Finally, knowing the system performance functions, we can calculate the design sensitivity coefficients of these performance functions by using the values of the state variables and state sensitivity coefficients obtained from the DAE’s. In this work we use the direct differentiation approach for sensitivity analysis, as opposed to the adjoint variable approach, for ease in error control and software implementation. The capabilities and performance of the proposed design sensitivity analysis formulation are demonstrated through a numerical example consisting of an AC rectified DC power supply driving a slider crank mechanism. In this case, the performance functions and design variables come from both electrical and mechanical domains. The results obtained were verified by perturbation analysis, and the method was shown to be very accurate and computationally viable.

Optimum Design of Anti-Siphon Device used to Prevent Cerebrospinal Fluid from Overdraining

2003 ◽  
Vol 17 (08n09) ◽  
pp. 1374-1380
Author(s):  
Jong Yun Jang ◽  
Chong Sun Lee ◽  
Chang Min Suh
Keyword(s):  
Cerebrospinal Fluid ◽  
Numerical Simulations ◽  
Optimum Design ◽  
Upright Position ◽  
Design Parameters ◽  
Design Variables

The present study investigated design parameters of an anti-siphon device used with shunt valves to treat patients with hydrocephalus. Structural analyses were performed to understand roles of design variables and optimize performance of the diaphragm-type anti-siphon device (hereafter referred to as the ASD). Experiments were performed on the lab-made product and showed good agreements with the numerical simulations. Using the simulations, we were able to design a more physiological ASD which gave equal opening pressures in both supine and upright postures. Tissue encapsulization phenomenon was also simulated and the results indicated underdrainage of CSF in the upright position of the patient.

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