Wouter Dehandschutter

A subspace algorithm for the identification of discrete time frequency domain power spectra

In this paper we present a new subspace algorithm for the identification of multi-input multi-output linear discrete time systems from measured power spectrum data. We show how the state space system matrices can be determined by taking the inverse discrete Fourier transform of the given data and applying the result to a new realization algorithm. Special attention is paid to ensure the positive realness of the identified power spectrum. The computational speed is improved by applying a Lanczos algorithm. The algorithm is illustrated with two practical examples.

Active Control of Structure-Borne Road Noise Using Vibration Actuators

Structure-borne road noise is generated by road induced excitation forces. The control approach presented here relies on the use of vibration actuators to modify the vibration behavior of the car body such that its noise radiation efficiency is decreased (Active Structural Acoustic Control-ASAC). The controller is optimized using laboratory experiments and numerical tools to simulate the performance a complete vehicle control set-up. Road tests yield a 6.9 dB noise reduction in the frequency range 75-105 Hz at the error microphone and 6.1 dB noise reduction at the passengers ear.

Parameter identification for LMS CDTire

This paper discusses the parameter identification procedure for the LMS comfort and durability tyre (LMS CDTire) model. CDTire is a family of three models (namely CDTire 20, CDTire 30 and CDTire 40) based on a macroscopic physical description of tyres, which is a compromise between scope of applicability and speed. The ‘macroscopic description’ implies that the actual model contains elements representing, for example, the ‘belt’, but not individual cords of the belt layers. Therefore, model parameters such as the belt bending stiffness essentially have to be determined by testing the whole tyre in a number of different ways instead of assembling mechanical properties of all the individual elements of a tyre such as cord stiffness. The considered tests are standard tyre tests that can be performed by most tyre test facilities. The parameter identification process is explained in a generic way with exemplary focus on one specific identification subtask, as the complete process description would go beyond the scope of this article. Furthermore, some of the strategic decisions made in the build-up of the parameter identification process are highlighted. Together with a more involved discussion on some numerical aspects of the tyre test rig simulations, the choice of optimization algorithms is explained. The technical discussion is complemented with some results obtained with this parameter identification procedure on a 205/55 R16 non-commercial passenger car tyre.

Design of an active noise control system using a distributed actuator

A distributed acoustic actuator for active noise control, consisting of a piezoelectric PVDF film, bonded at each side of a carrier structure, is simulated and built. The piezoelements are driven in anti-phase, resulting in a bending motion of the actuator, and thus in the necessary out-of-plane displacement for sound radiation.An analytical model for the acoustic actuator is derived, relating the actuators displacement to the applied voltage, taking into account the influence of the piezoelectric film on the actuators stiffness. The model is used to optimise the specifications for the piezoelectric film and the carrier structure, resulting in the highest sound power output in a frequency range from 30–500 Hz.An analytical model for the behaviour of a double panel partition is derived. The analytical model is combined with the model for the acoustic actuator, describing an actively controlled double panel partition with a distributed acoustic actuator integrated in the cavity. A controller is added to the system to control the sound power transmitted through the double panel partition. Simulation results show that a substantial increase of transmission loss can be achieved in the low frequency region (30–500 Hz) with this configuration.

Active structural and acoustic control of structure-borne road noise in a passenger car

Within the Brite-Euram Project “Anrava” several active control systems have been evaluated in order to reduce the road noise generated inside the cabin of a mid size station wagon during driving condition on different road surfaces. Different control strategies (feedforward with local and global control, pure feedback) and different approaches (active structural acoustic control and active noise control) have been tested on the car in laboratory conditions and the control performances have been evaluated. The final control strategies that have been selected based on the results of this study, are based on an adaptive feedforward control algorithm: six accelerameters provide the reference signals and 4 microphones placed inside the cabin give the error feedbacks. Two control configurations, each using a different kind of control source, have been retained : a structural acoustic control system which works with 6 inertial shakers positioned at the main vibration transmission paths of the car suspension, an anti-noise system with 4 loudspeakers inside the cabin. The paper describes the approaches utilised to design the different control systems and presents the results obtained during laboratory and road tests, comparing them with the performances predicted by numerical simulations.

Experimental H/sub /spl infin// control to improve an industrial off-line tracking control scheme on an automotive suspension test rig

This paper discusses the improvement of the tracking accuracy on an automotive suspension test rig by extending the available industrial off-line controller with a H/sub /spl infin// feedback controller. To reach a prescribed accuracy level in a bandwidth between 0 and 20 Hz, the off-line controller needs 7 iterations on a 2-axial durability suspension test rig to determine the correct control inputs. The extended scheme employs H/sub /spl infin// control techniques to achieve the same result in only 3 iterations. This approach takes forward the process of durability testing to a point where the required accuracy can be achieved in significantly less time.

Real-time enhancement of reference signals for feedforward control of random noise due to multiple uncorrelated sources

The problem envisaged in this paper is the optimization of the reference set for broadband feedforward control of sound and vibration in the presence of multiple, uncorrelated primary sources. A real-time algorithm is presented that generates a set of orthogonal virtual references out of a given set of reference signals. The algorithm is based on recursive singular value decomposition (SVD) techniques. The technique simplifies controller design in the sense that primarily, comparable control performance can be achieved using a reduced set of virtual references instead of the extensive original reference set. Hence, controller dimensions (and, thus, the memory requirements for implementation) and the computational burden reduce accordingly. Second, it is shown that convergence speed of the adaptive filtered-X LMS feedforward control algorithm is enhanced. The technique is applied to active control of structure-borne road noise inside a car cabin. Time domain simulation of a control configuration, utilizing either an extensive set of original references as well as a reduced virtual reference set, shows that in the frequency ranges of interest, a set of four virtual references yields the same noise reductions as the original set of 12 references.

Active control of sound transmission through an industrial sound encapsulation

In this paper, an active control system is developed to enhance the sound transmission loss of a sound encapsulation at low frequencies. The sound encapsulation is used to shield a noise source, such as an air compressor. The control systems comprise two control loudspeakers and two error microphones. The Filtered‐X LMS adaptive feedforward control algorithm is used to drive the signals at the error microphones to a minimum. The reference signal for the control algorithm is taken from the noise source, i.e., the tacho signal of the compressor. This study deals with the optimization of the location of control sources and error sensors in view of the achieved control performance. From this perspective it is important to note that minimizing the sound‐pressure level at the error microphones, which are constrained to be located inside the sound encapsulation, does not necessarily reduce the acoustic intensity measured in the far field of the encapsulation (or at least, not to the same degree). Relevant issues which are considered are: the coupling of control sources with the acoustic modes of the enclosure, changes to the interior sound field due to active control, etc.

The reduction of structure‐borne road noise by active noise and vibration control

In this work, the feasibility of active structural and acoustic control of structure‐borne rolling noise in a passenger car is demonstrated. A full vibroacoustical analysis of the demonstrator vehicle was carried out, in order to characterize fully the on‐road behavior (coherence analysis, operational force analysis, and transfer path analysis), as well as to derive the necessary input/output models. The results of these analyses have been used as input for the actuator design and the control configuration determination (reference signals, actuator number and location, feedback signal determination). Different control configurations have been investigated and tested by means of numerical simulations and laboratory tests. Two control configurations, each using a different kind of control source, have been retained: a structural acoustic control system which works with six inertial shakers positioned at the main vibration transmission paths of the car suspension, and an antinoise system with four loudspeake...