Institute of Dynamics and Vibration Research

Hannover, Germany

Institute of Dynamics and Vibration Research

Hannover, Germany
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Willeke S.,Von Karman Institute for Fluid Dynamics | Willeke S.,Institute of Dynamics and Vibration Research | Verstraete T.,Von Karman Institute for Fluid Dynamics
Proceedings of the ASME Turbo Expo | Year: 2015

This paper addresses the optimization of a two-dimensional U-bend passage of an internal serpentine cooling channel for reduced total pressure loss by means of a steepest-descent method. A steady-state incompressible flow is considered at a Reynolds number of 40,000 based on the bulk vel°City at the domain inlet. The two-equation k-e model is used for primal turbulence modeling. After only 30 design iterations, the gradient-based optimization results in a reduction of total pressure loss by 46% compared to the baseline geometry. To obtain the required objective gradients efficiently, a continuous adjoint approach is implemented in the OpenFOAM environment. Adjoint governing equations and boundary conditions are derived from state equations for steady-state, incompressible, turbulent flows under the assumption of frozen turbulence. Two different methods are proposed for modifying the shape of internal and external curves defining the duct geometry. The first method makes use of direct displacement of boundary grid points, allowing for a wide design space. The second, novel parameterization utilizes a projection of the surface sensitivities to an underlying Bezier curve. In this case, the Bezier control points are used as design variables. A comparison of both methods demonstrates a slightly lower performance improvement by the Bezier-based approach due to the reduced design freedom. This approach has, however, several practical advantages. Previous studies already addressed this optimization problem using gradient-free methods, but were limited in the degrees of freedom given to the shape variation. The present gradientbased optimization allows for a much larger design space and hence is used to compare the different methodologies. It shows that both optimizations result in similar shapes, although the gradient-based method allows for a slightly larger reduction in pressure loss due to the wider design space, while converging faster towards the optimum. © Copyright 2015 by ASME.

Han X.,Institute of Dynamics and Vibration Research | Neubauer M.,Institute of Dynamics and Vibration Research | Wallaschek J.,Institute of Dynamics and Vibration Research
2011 IEEE International Conference on Mechatronics and Automation, ICMA 2011 | Year: 2011

This review collects and presents the prototype control laws of synchronized switching damping technique, shortly SSD. SSD control law is an algorithm, which processes on the motion of the structure to determine the timing and synchronously trigger the switch device. Since the original control law consisting of triggering switch on each extremum of displacement is only optimal in the harmonic excitation and there is not a almighty algorithm which is able to deal with variant excitations, so different control laws were proposed. In this paper, according to different purpose, analyse the corresponding control laws. The advantages and disadvantages of each strategy are evaluated and conclusions are drawn regarding the relevant merits. © 2011 IEEE.

Neubauer M.,Institute of Dynamics and Vibration Research
Proceedings of Forum Acusticum | Year: 2014

In vibration control with piezoceramics, a high coupling of the piezoelement with the structure is desired. A high coupling improves the damping performance of passive techniques like shunt damp-ing. The coupling can be influenced by a the material properties of the piezoceramics, but also by the placement within the structure and the size of the transducer. Detailed knowlegde about the vibration behavior of the structure is required for this. This paper presents an in-depth analysis of the optimal shape of piezoelectric elements. General results for one-dimensional, but inhomogeneos strain distribution are provided. These results are applied to the case of a longitudinal transducer and a bending bimorph. It is obtained that for maximum coupling, only a certain fracture of the volume should be made of piezoelectric material.

Twiefel J.,Institute of Dynamics and Vibration Research | Westermann H.,Institute of Dynamics and Vibration Research
Journal of Intelligent Material Systems and Structures | Year: 2013

Various energy harvesting systems have been proposed in the last years. The use of ambient energy, such as vibration energy, has evoked great interests. Most vibration-based converters generate the maximum power only when the generator is excited at its resonance frequency. To overcome this limitation, researchers focus on strategies for increasing the working bandwidth of an energy harvester. Due to the amount of different approaches for broadband energy harvesting, we suggest a categorization. This review presents a classification of the current techniques. Every technique has its own benefits and drawbacks and is suitable for different applications. This review presents the categorization and describes each conversion technique. Typical research approaches are shown to get a better understanding of the energy harvesting techniques. The advantages and drawbacks are presented, and the suitability is shown for each category. © The Author(s) 2013.

Mojrzisch S.,Institute of Dynamics and Vibration Research | Twiefel J.,Institute of Dynamics and Vibration Research
Archive of Applied Mechanics | Year: 2015

This article presents the measurement of the first-order frequency response function (FRF) for a piezoelectric ceramic ring at high vibration amplitudes. Due to the softening-type nonlinearity of piezoelectric materials, the maximum of the FRF is bended toward lower frequencies. Therefore, at high vibration amplitudes the vibration amplitude can become unstable, and this results in the occurrence of the jump phenomena. However, as we drive the piezoelectric ring by phase feedback control of the electric current, the vibration amplitude is stabilized and the whole FRF can be obtained. In addition to the frequency shift induced by the nonlinear behavior, there is an additional frequency change induced by the heat generated in the piezoelectric material. Both effects are investigated experimentally around the first radial mode of the piezoelectric ring. Moreover, the phase-controlled forced excitation driving method is presented, and its implementation is described in detail. © 2015 Springer-Verlag Berlin Heidelberg

Schwarzendahl S.M.,Institute of Dynamics and Vibration Research
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Structural vibrations can be reduced by shunted piezoelectric elements. The passive piezoelectric damper considered here, consists of a piezoelectric element connected to a host structure and shunted by an inductor-resistor network. The paper gives an in depth analysis on the tuning of the inductor and resistor parameters of the electric network with regard to different optimization goals. The calculations are based on a 2-degree-of-freedom model of the host structure and the shunted piezoelectric element. Three optimization goals are studied: The objective of eigenvalue optimization is to get both pairs of eigenvalues to be equal. Then the damping ratio of the host structure is maximized, leading to a minimized decay time of the free vibration. In the H 2 optimization the total vibration energy within the host system is minimized, leading to optimal results in case of a broad-band excitation. In the H∞ optimization the objective is to minimize the maximum amplitude of the host structure over the whole frequency spectrum. Analytical solutions for these optimization goals are already known in the special case of a host structure without damping. In the more general case of a viscously damped host structure analytical solutions for the eigenvalue and H 2 optimization goal are derived. In case of the H∞ optimization goal an analytical solution cannot be found and perturbation theory is used to calculate an analytical approximation. The approximation is compared to the numerical solution in order to check its accuracy. © 2012 SPIE.

Schwarzendahl S.M.,Institute of Dynamics and Vibration Research | Han X.,Institute of Dynamics and Vibration Research | Neubauer M.,Institute of Dynamics and Vibration Research | Wallaschek J.,Institute of Dynamics and Vibration Research
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Shunted piezoceramics can be used to dissipate vibration energy of a host structure and therefore reduce vibration amplitudes. The piezoceramic converts a portion of the mechanical energy into electric energy which is then dissipated in an electric network. One semi-active control technique is the synchronized switch damping on inductance (SSDI), which has a good damping performance and can adapt to a wide range of excitation frequencies. In the standard SSDI a switch is closed during maximum deformation for one half of the electrical period time. This results in an inversion of the electrical charge. For the rest of the half-period the switch is opened and the charge remains constant. This results in a nearly rectangular voltage signal, which is in antiphase with the deformation velocity. In case of multimodal excitation, more sophisticated switching laws are developed with the aim to extract vibration energy from higher modes (i.e. Richard). This paper describes a novel multimodal switching law for vibration damping. An observer is designed to obtain an estimation of the first two vibration modes, which are used to determine the switching times. In simulations the increase in energy dissipation is evaluated and compared to the standard SSDI technique. With the new switching algorithm an improvement in energy dissipation is observed. The theoretical results are validated by measurements carried out on a clamped-free beam. The location of the piezoceramics is chosen to optimize the electro-mechanical coupling with the first vibration mode of the beam. The modal observer is realized in a realtime environment. Measurements show a good agreement with the theoretical results. © 2010 SPIE.

Neubauer M.,Institute of Dynamics and Vibration Research | Schwarzendahl S.M.,Institute of Dynamics and Vibration Research | Wallaschek J.,Institute of Dynamics and Vibration Research
Journal of Vibroengineering | Year: 2012

Recently, novel damping devices based on shunted piezoceramics have been investigated. Piezoceramics are therefore embedded into the mechanical structure and convert some part of the kinetic vibration energy into electrical energy. Subsequently, this energy is dissipated in the electrical network that is connected at the electrodes of the piezoceramics. The network is designed with the aim to maximize the dissipation, which results in a damping effect on the mechanical system. Alternatively, the converted energy can be stored and utilized to power electronic devices like sensors for health monitoring, called Energy Harvesting. In both cases, the converted energy and the damping performance depend on the so called generalized electromechanical coupling coefficient K. It is therefore crucial to maximize this factor. Besider the piezoelectric material properties, the coupling coefficient also depends on the vibration mode of the piezoceramics. Only for a constant mechanical strain distribution in the whole volume the generalized coupling coefficient K is equal to the material coupling k. In all other cases, K is smaller than k. This publication presents a general derivation of the generalized coupling coefficient K for an arbitrary, uniaxial deformation of the piezoceramics, which is based on the potential energy stored in the piezoceramics. The general result is applied to a piezoelectric bending bimorph and verified by a finite element model. © VIBROENGINEERING.

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