Stefan Ringwelski

Modeling of a fluid-loaded smart shell structure for active noise and vibration control using a coupled finite element-boundary element approach

A recently developed approach for the simulation and design of a fluid-loaded lightweight structure with surface-mounted piezoelectric actuators and sensors capable of actively reducing the sound radiation and the vibration is presented. The objective of this paper is to describe the theoretical background of the approach in which the FEM is applied to model the actively controlled shell structure. The FEM is also employed to model finite fluid domains around the shell structure as well as fluid domains that are partially or totally bounded by the structure. Boundary elements are used to characterize the unbounded acoustic pressure fields. The approach presented is based on the coupling of piezoelectric and acoustic finite elements with boundary elements. A coupled finite element–boundary element model is derived by introducing coupling conditions at the fluid–fluid and fluid–structure interfaces. Because of the possibility of using piezoelectric patches as actuators and sensors, feedback control algorithms can be implemented directly into the multi-coupled structural–acoustic approach to provide a closed-loop model for the design of active noise and vibration control. In order to demonstrate the applicability of the approach developed, a number of test simulations are carried out and the results are compared with experimental data. As a test case, a box-shaped shell structure with surface-mounted piezoelectric actuators and four sensors and an open rearward end is considered. A comparison between the measured values and those predicted by the coupled finite element–boundary element model shows a good agreement.

Noise Reduction Potential of an Engine Oil Pan

Considering automobiles with internal combustion engines, the power train represents one of the main noise sources, especially during idling and slow driving speeds. One major contributor to the overall power train noise emission is the engine oil pan. The objective of this paper is to evaluate the noise reduction potential of an oil pan with a combined use of passive and active methods. The passive approach is best suited for a frequency range above 1,000 Hz and is implemented in this study using different substitute materials. Active noise control techniques are efficient in a frequency range below 1,000 Hz. In the present study piezoceramic patches are used as actuators as well as sensors. By means of FE simulations a smart system is designed to reduce passively and actively the structural vibrations and consequently the resulting sound radiation. Therefore, optimal locations of piezoelectric actuators are computed. A control algorithm with respect to a collocated design is used to obtain high active damping effects. With control, attenuations up to 15 dB in vibration level are achieved at the resonance frequency regions of the most dominant modes of the oil pans in laboratory. It is shown that significant reductions up to 4 dB are achieved on the engine test bench in a frequency range up to 1,000 Hz and at engine speeds below 2,000 rpm, where a multi-discrete excitation characteristic exists. Due to the use of a low-mass plastic oil pan, improvements at several engine operating points are measurable. Drawbacks of this material substitution are the higher temperature dependency and the lower electromechanical coupling of the piezoelectric patches due to the elasticity of the plastic ground material. An oil pan made of sheet steel has shown the worst acoustical properties.

NOISE CONTROL OF VEHICLE DRIVE SYSTEMS

The paper presents an overall simulation approach to control the noise emission of car engines at a very early stage of the design process where no real prototypes are available. The suggested approach combines different physical models and couples different software tools such as multi-body analysis, fluid dynamics, structural mechanics, magneto-electrodynamics, thermodynamics, acoustics and control as well. The general overall simulation methodology is presented first. Then, this methodology is applied to a combustion engine in order to improve its acoustical behavior by passive means, such as changing the stiffness and the use of damping materials to build acoustic and thermal encapsulations. The active control by applying piezoelectric patch actuators at the oil sump as the noisiest part of the engine is discussed as well. The sound emission is evaluated by hearing tests and a mathematical prediction model of the human perception. Finally, it is shown that the presented approach can be extended to electric engines, which is demonstrated at a newly developed electric wheel hub motor.

Analysis and Design of Smart Structures to Control Vibration and Noise

The paper presents an overall analysis and design approach for smart lightweight structures to actively reduce vibration and noise. As smart materials, distributed piezoelectric patches are attached to the structure. The basis of the approach is an overall finite element model, which includes the structure itself, the acoustic fluid, the piezoelectric actuators and sensors as well as the controller. As a test example a smart acoustic box is simulated and the simulation results are compared with measured data. Finally, also industrial applications are briefly presented.Copyright

Active Vibration and Noise Control of a Car Engine: Modeling and Experimental Validation

The paper presents an overall design approach for smart light-weight structures made of metal sheets or fiber reinforced plastics, equipped with thin piezoelectric wafers as actuators and sensors to control vibration and noise. The design process is based on an overall finite element model, which includes the passive structure, the piezoelectric wafers attached to the structure or embedded between the layers of a composite and the controller as well. In active noise control the vibrating structure interacts with the surrounding fluid, which is also included into the overall model. In order to evaluate the quality of the approach, test simulations are carried out and the results are compared with experimental data. As a test case, a smart car engine with surface-mounted piezoelectric actuators and sensors for active noise reduction is considered. A comparison between the measured values and those predicted by the coupled finite element model shows a good agreement.