Gunther Steenackers

Development of an adaptive response surface method for optimization of computation-intensive models

In general, optimization techniques involve numerous repeated objective function evaluations. As a consequence, optimization times can become very large depending on the complexity of the model to be optimized. This manuscript describes the development of an adaptive response surface method for optimization of computation-intensive models, capable of reducing optimization times. The response model to be optimized is not built from a pre-defined number of design experiments but is adapted and refined during the optimization routine. Different approximation models are applicable in combination with the developed optimization technique. The proposed optimization technique is evaluated on a standard test problem as well as a finite element model design optimization with multiple parameters.

Reliability‐based design optimization of computation‐intensive models making use of response surface models

Design optimization can be very time-consuming depending on the complexity of the model to be optimized. This manuscript describes the development of an adaptive response surface method for reliability-based design optimization of computation-intensive models, capable of reducing optimization times significantly. The method applied in this paper makes use of adaptive response surfaces for the elements of the considered objective function and probabilistic constraints. Because the optimization takes place on the response surface and not on the complex model itself, the number of function evaluations is reduced significantly. Higher order response models are used in combination with the adaptive approach. Additionally, the order of the interpolating functions can increase during successive iteration steps before the optimized design parameter values are achieved. The response model to be optimized is not built from a pre-defined number of design experiments, as is done usually, but is adapted and refined during the optimization routine. The proposed optimization technique is evaluated on a finite element reliability-based design optimization with multiple parameters. Copyright

Bias-specified robust design optimization: A generalized mean squared error approach

The primary goal of robust design is to determine the best design points by minimizing variability of the performance of a manufacturing process and minimizing deviation of the performance from a target value of interest. In this paper, a generalization and improvement of the robust optimization approach, based on the mean squared error, is suggested and applied. The constraint on the process bias is further relaxed. Different response surface functions are evaluated and compared. As an example, different optimization approaches are illustrated with a numerical test case. The results are explained and discussed.

Robust optimization of an airplane component taking into account the uncertainty of the design parameters

A slat track, structural component of an aircraft wing that transfers the aerodynamical loads, excited by operational forces can result in excessive displacement levels if not properly designed. The design parameter values are not always precisely known but can contain a level of uncertainty to some extent due to, for example dimensional variation. During the different optimization approaches, the slat track geometry is optimized in order to limit the maximum vertical displacement, taking into account the variability of the design parameters. Application and comparison of different optimal, robust and generalized optimization approaches is presented and applied on the slat track finite element model, making use of mean and variance response functions to model the uncertainty on the finite element displacement values. Next to validating different objective function statements, a comparison is also made on the level of accuracy and practicability concerning the different response function models, based on regression techniques and Monte Carlo simulations, optimization and transmissibilities and regressive techniques and vibration reduction over a frequency range. Copyright

A study on the bandwidth characteristics of pleated pneumatic artificial muscles

Pleated pneumatic artificial muscles have interesting properties that can be of considerable significance in robotics and automation. With a view to the potential use of pleated pneumatic artificial muscles as actuators for a fatigue test bench high forces and small displacements, the bandwidth characteristics of a muscle-valve system were investigated. Bandwidth is commonly used for linear systems, as the Bode plot is independent of the amplitude of the input signal. However, due to the non-linear behaviour of pleated pneumatic artificial muscles, the systems gain becomes dependent on the amplitude of the input sine wave. As a result, only one Bode plot is insufficient to clearly describe or identify a non-linear system. In this study, the bandwidth of a muscle-valve system was assessed from two perspectives: a varying amplitude and a varying offset of the input sine wave. A brief introduction to pneumatic artificial muscles is given. The concept of pleated pneumatic artificial muscles is explained. Furthermore, the different test methods and experimental results are presented.

Development of an Equivalent Composite Honeycomb Model: A Finite Element Study

Finite element analysis of complex geometries such as honeycomb composites, brings forth several difficulties. These problems are expressed primarily as high calculation times but also memory issues when solving these models. In order to bypass these issues, the main goal of this research paper is to define an appropriate equivalent model in order to minimize the complexity of the finite element model and thus minimize computation times. A finite element study is conducted on the design and analysis of equivalent layered models, substituting the honeycomb core in sandwich structures. A comparison is made between available equivalent models. An equivalent model with the right set of material property values is defined and benchmarked, consisting of one continuous layer with orthotropic elastic properties based on different available approximate formulas. This way the complex geometry does not need to be created while the model yields sufficiently accurate results.

Determining the Power Flow in a Rectangular Plate Using a Generalized Two-Step Regressive Discrete Fourier Series

The evaluation of structural power flow (or structural intensity (SI)) in engineering structures is a field of increasing interest in connection with vibration analysis and noise control. In contrast to classical techniques such as modal analysis, the SI indicates the magnitude and direction of the vibratory energy traveling in the structures, which yields information about the positions of the sources/sinks, along with the energy transmission path. In this paper, a new algorithm is proposed to model operational deflection shapes (ODS). The model is a two-dimensional Fourier domain model that is estimated by using a weighted nonlinear least-squares method. From the wave number-frequency domain data thus obtained, the spatial derivatives that are necessary to determine the structural power flow are easily computed. The proposed method is less sensitive to measurement noise than traditional power flow estimation techniques. A numerical model of a simply supported plate excited by two shakers, phased to act as an energy source and sink, is used as a simulation case. Measurements are executed on a clamped plate excited by an electromagnetic shaker in combination with a damper.

Ultrasonic characterization of materials by means of under water Laser Doppler Vibrometer measurements of continuous waves

Pulse signals are widely use for several ultrasonic testing. They indeed allow an easy estimation of the delays occurring in echo and transmission measurements and give the possibility to filter the noise (i.e undesired reflections occurring in the surface of the transducers) applying a window in the time domain. However their high crest factor makes these signals unsuitable to test attenuating materials. For this reason this paper proposes a new method, based on continuous waves, for ultrasonic characterization of materials. A a wave propagation model in the frequency domain is presented, to determine simultaneously acoustic velocity, mass density, and thickness of two Plexiglas plates, during transmission experiments. The Ultrasonic waves are captured by a Scanning Laser Doppler Vibrometer (SLDV) in order to guarantee a large number of spatial points, acquired with a high resolution.