EFFICIENT METHODS FOR STRUCTURAL OPTIMIZATION WITH FREQUENCY CONSTRAINTS USING HIGHER ORDER APPROXIMATIONS

2008 ◽  
Vol 08 (03) ◽  
pp. 439-450 ◽  
Author(s):  
P. TORKZADEH ◽  
J. SALAJEGHEH ◽  
E. SALAJEGHEH
Keyword(s):  
Optimum Design ◽  
Structural Response ◽  
Higher Order ◽  
Computational Time ◽  
Cross Sectional ◽  
Frequency Constraints ◽  
First Order ◽  
Structural Responses ◽  
Previous Design ◽  
Approximate Function

Presented herein are four different methods for the optimum design of structures subject to multiple natural frequency constraints. During the optimization process the optimum cross-sectional dimensions of elements are determined. These methods are robust and efficient in terms of the number of eigenvalue analyses required, as well as the overall computational time for the optimum design. A new third order approximate function is presented for the structural response quantities, as functions of the cross-sectional properties, and four different methods for the optimum design are defined based on this approximate function. The main features of the proposed function are that only the diagonal terms of higher order derivative matrices are employed, and these derivatives are established by the available first order derivatives. The first order exact derivatives are obtained from a sensitivity analysis at the previous design points. We show that this approximate function creates high quality approximations of the structural responses, such as the frequencies. Examples are presented and the efficiency and quality of the proposed methods are discussed and compared.

Nonlinear Motion Analysis of the Wavestar Wave Energy Converter With a Focus on the Structural Responses

2014 ◽  
Author(s):  
Andrew S. Zurkinden ◽  
Michael S. Jepsen ◽  
Mahdi T. Sichani ◽  
Lars Damkilde
Keyword(s):  
Structural Model ◽  
Structural Response ◽  
Order Theory ◽  
Reactive Control ◽  
Loop Control ◽  
First Order ◽  
First Order Theory ◽  
Nonlinear Motion ◽  
Ansys Apdl ◽  
Structural Responses

The scope of this paper is to connect a nonlinear WEC numerical model with a structural response model. The numerical WEC model takes into account the nonlinear hydrostatic restoring moment of the Wavestar float. A parameterized structural model of the Wavestar arm is developed in ANSYS APDL. Based on the assumption that the structural displacements remain small, linear first order theory is used to calculate the structural response. The section moments and forces are thus superimposed according to the superposition law. The effect of the nonlinear hydrostatic restoring moment on the structural response is investigated. Moreover, an analysis is carried out which shows that reactive control, applied as a closed loop control, increases the section moments and shear forces.

Collapse Analysis of Offshore Platforms Using Constrained New Waves

2014 ◽  
Author(s):  
Mehrdad Kimiaei ◽  
Daud W. Edgarth
Keyword(s):  
Total Duration ◽  
Structural Response ◽  
Computational Time ◽  
Offshore Platforms ◽  
Wave Loads ◽  
Extreme Waves ◽  
Long Duration ◽  
Extreme Response ◽  
Collapse Analysis ◽  
Structural Responses

Traditionally regular deterministic wave theories are employed to estimate wave loads on offshore platforms but they cannot capture random nature of the sea states. Randomly generated sea surfaces will lead to most accurate results for structural responses due to waves but they are usually based on long duration simulations and hence need excessive computational efforts. Constrained NewWaves (CNWs), with significantly shorter computational time, have recently been used successfully for estimating of structural response of offshore platforms due to waves. For extreme waves, as long as there is no indication of major structural nonlinearity in the system, they have shown reasonably accurate results as an alternative for long duration randomly generated sea surfaces. This paper is concerned with using CNWs in collapse analysis of offshore platforms under extreme waves where large geometrical and material nonlinearities are expected. It shows how the plastic level of the response, total duration of the loading, the loading pattern and dynamic characteristics of the platform can influence the extreme response and collapse rates of the offshore platforms.

An Efficient Approximation Method for Structural Synthesis with Reference to Space Structures

1987 ◽  
Vol 2 (3) ◽  
pp. 165-175 ◽  
Author(s):  
E. Salajegheh ◽  
G. N. Vanderplaats
Keyword(s):  
Structural Response ◽  
Optimal Solution ◽  
Cross Sectional ◽  
Non Linear Programming ◽  
Design Variables ◽  
Structural Responses ◽  
Internal Forces ◽  
The Cross ◽  
Nodal Displacements ◽  
Efficient Approximation

A method is presented for the optimum design of structures which is very robust and efficient in terms of the number of required analyses of the structure. Some explicit approximation expressions are generated for the structural response quantities such as nodal displacements, forces and frequencies as functions of the cross-sectional properties. By substituting these expressions into the constraint equations, the design task becomes a non-linear programming problem which is an explicit problem in terms of the design variables. The solution of this problem gives the actual cross-sectional dimensions. The method is an iterative technique and the results indicate that the convergence to the optimal solution results indicate that the convergence to the optimal solution is very rapid. The robustness of the proposed method is due to the generation of explicit approximate relations for the structural response quantities, as in the past the design constraints were approximated. Also a high quality approximation is obtained for the internal forces directly without using the approximate values of the displacements. The quality of approximations is enhanced by expressing the structural responses, in particular, the frequencies with respect to the cross-sectional areas and second moment of inertias instead of using the cross-sectional dimensions. A double-layer grid and a grillage are chosen as test cases, the results of which are presented.

Efficient Optimum Design of Structures with Discrete Design Variables

1993 ◽  
Vol 8 (3) ◽  
pp. 199-208 ◽  
Author(s):  
E. Salajegheh ◽  
G.N. Vanderplaats
Keyword(s):  
Optimum Design ◽  
Main Idea ◽  
Continuous Variable ◽  
Test Cases ◽  
Cross Sectional ◽  
Design Variables ◽  
Discrete Design Variables ◽  
Design Values ◽  
Structural Responses ◽  
Approximate Expressions

A method is presented for optimum design of structures, where some or all design variables can be chosen from a set of prescribed values. The main idea is to reduce the number of structural analyses in the process of optimization. First the structural responses such as forces and displacements are approximated as functions of cross-sectional properties, thus high quality explicit functions are generated for the responses. Employing these approximate expressions in the optimization process, the continuous optimum design can be achieved rapidly. Using the results obtained from the continuous variable optimization and with the help of the approximated responses, a branch and bound method is used to obtain the discrete design values. The results indicate that after the completion of the continuous variable optimization, only one or two extra detailed analyses of the structure is needed to complete the discrete variable optimization. In this work, a dome and a grillage are presented as test cases.

Enhanced Two-Point Exponential Approximation for Structural Optimization

2013 ◽  
Vol 397-400 ◽  
pp. 1021-1024 ◽  
Author(s):  
Tien Tung Chung ◽  
Qi Hong Jiang ◽  
Jia Rong Zhu
Keyword(s):  
Structural Optimization ◽  
Optimum Design ◽  
Approximation Method ◽  
Optimization Problems ◽  
Exponential Approximation ◽  
Design Point ◽  
Optimum Result ◽  
Previous Design ◽  
Approximate Function ◽  
Intervening Variables

This paper proposes a new approximation method called Enhanced Two-Point Exponential Approximation (ETPEA), which is derived based on Two-Point Exponential Approximation (TPEA). In TPEA, when the exponents of intervening variables cannot be calculated by fitting the sensitivities of the previous design point, the accuracy of TPEA is decreased. In such cases, ETPEA uses a substitution function to construct the approximate function, and the optimum result can be improved. Some typical structural optimization problems are tested, and the results indicate that the optimum design can be found accurately and quickly with the new approximation method. It is verified that the new approximation method is also efficient for large structural optimization problems.

Dual systems for all: Higher-order, role-based relational reasoning as a uniquely derived feature of human cognition

2019 ◽  
Vol 42 ◽  
Author(s):  
Daniel J. Povinelli ◽  
Gabrielle C. Glorioso ◽  
Shannon L. Kuznar ◽  
Mateja Pavlic
Keyword(s):  
Temporal Reasoning ◽  
Higher Order ◽  
Important Case ◽  
Human Cognition ◽  
Relational Reasoning ◽  
Dual Systems ◽  
First Order ◽  
Reasoning System ◽  
Role Based

Abstract Hoerl and McCormack demonstrate that although animals possess a sophisticated temporal updating system, there is no evidence that they also possess a temporal reasoning system. This important case study is directly related to the broader claim that although animals are manifestly capable of first-order (perceptually-based) relational reasoning, they lack the capacity for higher-order, role-based relational reasoning. We argue this distinction applies to all domains of cognition.

Challenging the Multidimensional Conception of Perceived Person-Environment Fit

2020 ◽  
pp. 1-9
Author(s):  
Julian M. Etzel ◽  
Gabriel Nagy
Keyword(s):  
Higher Education ◽  
University Students ◽  
Educational Outcomes ◽  
Factor Model ◽  
Higher Order ◽  
Substantial Proportion ◽  
Unique Variance ◽  
First Order ◽  
Person Environment Fit ◽  
Order Factor

Abstract. In the current study, we examined the viability of a multidimensional conception of perceived person-environment (P-E) fit in higher education. We introduce an optimized 12-item measure that distinguishes between four content dimensions of perceived P-E fit: interest-contents (I-C) fit, needs-supplies (N-S) fit, demands-abilities (D-A) fit, and values-culture (V-C) fit. The central aim of our study was to examine whether the relationships between different P-E fit dimensions and educational outcomes can be accounted for by a higher-order factor that captures the shared features of the four fit dimensions. Relying on a large sample of university students in Germany, we found that students distinguish between the proposed fit dimensions. The respective first-order factors shared a substantial proportion of variance and conformed to a higher-order factor model. Using a newly developed factor extension procedure, we found that the relationships between the first-order factors and most outcomes were not fully accounted for by the higher-order factor. Rather, with the exception of V-C fit, all specific P-E fit factors that represent the first-order factors’ unique variance showed reliable and theoretically plausible relationships with different outcomes. These findings support the viability of a multidimensional conceptualization of P-E fit and the validity of our adapted instrument.

Computational Models for Multilayered Composite Shells with Application to Tires

1996 ◽  
Vol 24 (1) ◽  
pp. 11-38 ◽  
Author(s):  
G. M. Kulikov
Keyword(s):  
Type Theory ◽  
Computational Models ◽  
Geometrical Nonlinearity ◽  
Higher Order ◽  
Stress Strain ◽  
Strain Fields ◽  
First Order ◽  
Timoshenko Type ◽  
Joint Influence ◽  
Discrete Layer

Abstract This paper focuses on four tire computational models based on two-dimensional shear deformation theories, namely, the first-order Timoshenko-type theory, the higher-order Timoshenko-type theory, the first-order discrete-layer theory, and the higher-order discrete-layer theory. The joint influence of anisotropy, geometrical nonlinearity, and laminated material response on the tire stress-strain fields is examined. The comparative analysis of stresses and strains of the cord-rubber tire on the basis of these four shell computational models is given. Results show that neglecting the effect of anisotropy leads to an incorrect description of the stress-strain fields even in bias-ply tires.

Analysis and design of thermo-mechanical interfaces

2012 ◽  
Vol 60 (2) ◽  
pp. 205-213
Author(s):  
K. Dems ◽  
Z. Mróz
Keyword(s):  
Optimality Conditions ◽  
Mechanical Loading ◽  
Material Properties ◽  
Structural Response ◽  
External Boundary ◽  
Mechanical Loads ◽  
Internal Interface ◽  
Analysis And Design ◽  
First Order ◽  
Mechanical Nature

Abstract. An elastic structure subjected to thermal and mechanical loading with prescribed external boundary and varying internal interface is considered. The different thermal and mechanical nature of this interface is discussed, since the interface form and its properties affect strongly the structural response. The first-order sensitivities of an arbitrary thermal and mechanical behavioral functional with respect to shape and material properties of the interface are derived using the direct or adjoint approaches. Next the relevant optimality conditions are formulated. Some examples illustrate the applicability of proposed approach to control the structural response due to applied thermal and mechanical loads.

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