Non-Probabilistic Robust Equilibrium Optimization of Complex Uncertain Structures

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Jin Cheng ◽  
Zhenyu Liu ◽  
Yangming Qian ◽  
Zhendong Zhou ◽  
Jianrong Tan
Keyword(s):  
Structural Performance ◽  
Equilibrium Strategy ◽  
Optimization Approach ◽  
Performance Indices ◽  
Final Design ◽  
Uncertain Structure ◽  
The Rich ◽  
Uncertain Structures ◽  
Robust Equilibrium ◽  
Nested Genetic Algorithm

Abstract Robust optimization of complex uncertain structures usually involves multiple conflicting and competing structural performance indices. Present approaches for achieving the final design of such an optimization problem always involve a decision-making process, which is a demanding task that requires the rich experience and expert skills of designers. To overcome the difficulty, an interval robust equilibrium optimization approach is proposed to find the optimal design of complex uncertain structure based on the robust equilibrium strategy for multiple conflicting and competing structural performance indices. Specifically, a new concept of closeness and crossing coefficient between interval boundaries (CCCIBs) is proposed at first, based on which the tri-dimensional violation vectors of all interval constraints can be calculated and the feasibility of a design vector can be assessed. Then, the robust equilibrium assessment of multiple objective and constraint performance indices is investigated, based on the results of which the feasible design vectors can be directly ranked according to the robust equilibrium strategy for all structural performance indices. Subsequently, the algorithm for the robust equilibrium optimization of complex uncertain structures is developed by integrating the Kriging technique and nested genetic algorithm. The validity, effectiveness, and practicability of the proposed approach are demonstrated by two illustrative examples.

Development and Assessment of a Total Resistance Optimized Bow for the AE 36

1994 ◽  
Vol 31 (02) ◽  
pp. 149-160
Author(s):  
Donald C. Wyatt ◽  
Peter A. Chang
Keyword(s):  
Experimental Data ◽  
Optimization Procedure ◽  
Wave Resistance ◽  
Scale Model ◽  
Optimization Approach ◽  
Nonlinear Constraints ◽  
Total Resistance ◽  
Hull Form ◽  
Final Design ◽  
Resistance Data

A numerically optimized bow design is developed to reduce the total resistance of a 23 000 ton ammunition ship (AE 36) at a speed of 22 knots. An optimization approach using slender-ship theory for the prediction of wave resistance is developed and applied. The new optimization procedure is an improvement over previous optimization methodologies in that it allows the use of nonlinear constraints which assure that the final design remains within practical limits from construction and operational perspectives. Analytic predictions indicate that the AE 36 optimized with this procedure will achieve a 40% reduction in wave resistance and a 33% reduction in total resistance at 22 knots relative to a Kracht elliptical bulb bow design. The optimization success is assessed by the analysis of 25th scale model resistance data collected at the David Taylor Research Center deepwater towing basin. The experimental data indicate that the optimized hull form yields a 51% reduction in wave resistance and a 12% reduction in total resistance for the vessel at 22 knots relative to the Kracht bulb bow design. Similarly encouraging results are also observed when comparisons are made with data collected on two other conventionally designed AE 36 designs.

Improving the Flutter Margin of an Unstable Fan Blade

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Sina Stapelfeldt ◽  
Mehdi Vahdati
Keyword(s):  
Steady Flow ◽  
Leading Edge ◽  
Measured Data ◽  
Optimization Approach ◽  
Speed Range ◽  
Final Design ◽  
Flutter Boundary ◽  
Fan Blade ◽  
Flutter Margin ◽  
Stagger Angle

The aim of this paper is to introduce design modifications that can be made to improve the flutter stability of a fan blade. A rig fan blade, which suffered flutter in the part-speed range and for which good quality measured data in terms of steady flow and flutter boundary is available, is used for this purpose. The work is carried out numerically using the aeroelasticity code AU3D. Two different approaches are explored: aerodynamic modifications and aero-acoustic modifications. In the first approach, the blade is stabilized by altering the radial distribution of the stagger angle based on the steady flow on the blade. The re-staggering patterns used in this work are therefore particular to the fan blade under investigation. Moreover, the modifications made to the blade are very simple and crude, and more sophisticated methods and/or an optimization approach could be used to achieve the above objectives with a more viable final design. This paper, however, clearly demonstrates how modifying the steady blade aerodynamics can prevent flutter. In the second approach, flutter is removed by drawing bleed air from the casing above the tip of the blade. Only a small amount of bleed (0.2% of the total inlet flow) is extracted such that the effect on the operating point of the fan is small. The purpose of the bleed is merely to attenuate the pressure wave that propagates from the trailing edge to the leading edge of the blade. The results show that extracting bleed over the tip of the fan blade can improve the flutter margin of the fan significantly.

Improving the Flutter Margin of an Unstable Fan Blade

2018 ◽  
Author(s):  
Sina Stapelfeldt ◽  
Mehdi Vahdati
Keyword(s):  
Steady Flow ◽  
Leading Edge ◽  
Measured Data ◽  
Optimization Approach ◽  
Speed Range ◽  
Final Design ◽  
Flutter Boundary ◽  
Fan Blade ◽  
Flutter Margin ◽  
Stagger Angle

The aim of this paper is to introduce design modifications which can be made to improve the flutter stability of a fan blade. A rig fan blade, which suffered from flutter in the part-speed range and for which good quality measured data in terms of steady flow and flutter boundary is available, is used for this purpose. The work is carried out numerically using the aeroelasticity code AU3D. Two different approaches are explored; aerodynamic modifications and aero-acoustic modifications. In the first approach, the blade is stabilized by altering the radial distribution of the stagger angle based on the steady flow on the blade. The re-staggering patterns used in this work are therefore particular to the fan blade under investigation. Moreover, the modifications made to the blade are very simple and crude and more sophisticated methods and/or an optimization approach could be used to achieve the above objectives with a more viable final design. This paper, however, clearly demonstrates how modifying the steady blade aerodynamics can prevent flutter. In the second approach, flutter is removed by drawing bleed air from the casing above the tip of the blade. Only a small amount of bleed (0.2% of the total inlet flow) is extracted such that the effect on the operating point of the fan is small. The purpose of the bleed is merely to attenuate the pressure wave which propagates from the trailing edge to the leading edge of the blade. The results show that extracting bleed over the tip of the fan blade can improve the flutter margin of the fan significantly.

Design and Development of XY Micro-Positioning Stage Using Modified Topology Optimization Technique

2014 ◽  
Vol 592-594 ◽  
pp. 2220-2224 ◽  
Author(s):  
T. Ramesh ◽  
Ramalingam Bharanidaran ◽  
V. Gopal
Keyword(s):  
Finite Element Method ◽  
Topology Optimization ◽  
Compliant Mechanism ◽  
Optimization Technique ◽  
Optimization Techniques ◽  
Structural Performance ◽  
Interpolation Function ◽  
Positioning Stage ◽  
Final Design ◽  
Node Connectivity

XY positioning stages are fundamental components during precision manipulation of micro sized objects. A compliant mechanism based mechanism is the appropriate choice for the design of XY stage. Topology optimization techniques are utilized to design the compliant mechanism. During the process of topology optimization, senseless regions are appearing from the manufacturability perspective. Senseless regions are staircase boundaries and node to node connectivity which is impossible to manufacture. Interpolation function is included in the topology optimization to minimize the effect of senseless regions. However topologically developed design is post processed to attain the manufacturability. Structural performance of the post processed final design is validated through Finite Element Method (FEM) and experimental technique.

An Optimization Approach Toward a Robust Design of Six Degrees of Freedom Haptic Devices

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Aftab Ahmad ◽  
Kjell Andersson ◽  
Ulf Sellgren
Keyword(s):  
Design Optimization ◽  
Robust Design ◽  
Degrees Of Freedom ◽  
Design Parameters ◽  
Manufacturing Cost ◽  
Optimization Approach ◽  
Performance Indices ◽  
New Approach ◽  
Haptic Devices ◽  
Six Degrees Of Freedom

This work presents an optimization approach for the robust design of six degrees of freedom (DOF) haptic devices. Our objective is to find the optimal values for a set of design parameters that maximize the kinematic, dynamic, and kinetostatic performances of a 6-DOF haptic device while minimizing its sensitivity to variations in manufacturing tolerances. Because performance indices differ in magnitude, the formulation of an objective function for multicriteria performance requirements is complex. A new approach based on Monte Carlo simulation (MCS) was used to find the extreme values (minimum and maximum) of the performance indices to enable normalization of these indices. The optimization approach presented here is formulated as a methodology in which a hybrid design-optimization approach, combining genetic algorithm (GA) and MCS, is first used. This new approach can find the numerical values of the design parameters that are both optimal and robust (i.e., less sensitive to variation and thus to uncertainties in the design parameters). In the following step, with design optimization, a set of optimum tolerances is determined that minimizes manufacturing cost and also satisfies the allowed variations in the performance indices. The presented approach can thus enable the designer to evaluate trade-offs between allowed performance variations and tolerances cost.

A Novel Method for Load Bounds Identification for Uncertain Structures in Frequency Domain

2018 ◽  
Vol 15 (06) ◽  
pp. 1850051 ◽  
Author(s):  
Z. C. He ◽  
X. Y. Lin ◽  
Eric Li
Keyword(s):  
Least Squares ◽  
Frequency Domain ◽  
Interval Uncertainty ◽  
Uncertain Parameters ◽  
Interval Extension ◽  
Uncertain Structure ◽  
Novel Method ◽  
Uncertain Structures ◽  
Derivatives Of ◽  
Least Squares Approach

A novel method for load bounds identification for uncertain structures is proposed in the frequency domain. The uncertain parameters are assumed to locate in their intervals and only their bounds rather than their precise information are needed. To quantitatively describe the effect of the interval uncertainty on the load identification in the frequency ranges, the interval extension is then introduced in the frequency response function (FRF)-based least squares approach. Therefore, the load bounds are determined through the summation of the two separate parts including the midpoint part and the perturbed part of the load. The midpoint part is computed by using the Moore–Penrose pseudo-inversion and the perturbed part is transformed into the first derivatives of the midpoint load with respect to the uncertain parameters by applying the truncated total least squares (TTLS). Two numerical examples are investigated to validate that the proposed method is very effective to predict the load bounds for the uncertain structure in frequency domain.

scholarly journals Geometry analysis and optimal design of Geneva mechanisms with curved slots

2004 ◽  
Vol 218 (4) ◽  
pp. 449-459 ◽  
Author(s):  
J-J Lee ◽  
K-F Huang
Keyword(s):  
Optimal Design ◽  
Structural Performance ◽  
Design Parameters ◽  
Performance Indices ◽  
Mathematical Expressions ◽  
Crank Angle ◽  
Conjugate Surfaces ◽  
Geometry Analysis ◽  
Maximum Contact ◽  
Roller Radius

A systematic procedure is proposed for the design of Geneva mechanisms with curved slots. Based on the theory of conjugate surfaces, mathematical expressions for the slot profile, pressure angle and cutter's location for manufacturing are presented. In addition, to evaluate the combined kinematics and structural performance of the mechanism, the maximum contact stress and degree of wear are established as the performance index. Effects of variations in various design parameters on the values of the performance indices are investigated. Using the indices as the objective function, the optimum design that takes into account the initial crank angle, offset and roller radius is performed.

The Perturbation Method for Stability Analysis of Uncertain Structures

2013 ◽  
Vol 367 ◽  
pp. 302-307
Author(s):  
Chang Rui Ji ◽  
Zao Ni
Keyword(s):  
Stability Analysis ◽  
Eigenvalue Problem ◽  
Perturbation Method ◽  
Stability Problem ◽  
Upper Bounds ◽  
Lower And Upper Bounds ◽  
Interval Mathematics ◽  
Stiffness Matrices ◽  
Uncertain Structure ◽  
Uncertain Structures

This paper is concerned with the structural stability problem involving uncertain-but-bounded parameters, specified as bounds on these parameters. This produces interval stand and geometry stiffness matrices, and the problem is transformed into a interval buckling eigenvalue problem in interval mathematics. The perturbation method is proposed to determine the lower and upper bounds on the buckling eigenvalues and due to uncertain-but-bounded parameters. Moreover, the critical load of the uncertain structure can be obtained. The effectiveness of the presented method was demonstrated by comparison with conventional stability theory, using a typical numerical example.

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