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Active vibration reduction for lightweight structures has attracted more and more attention in automotive industries. In this paper, reduced-order controllers are designed based on H∞ techniques to realize vibration reduction. A finite element model of piezo-based smart structure is constructed from which a nominal model containing 5 modes and validation model containing 10 modes are extracted. A mixed-sensitivity robust H∞ controller is firstly designed based on the nominal structural model. Considering the ease of controller deployment, an order reduction for the controller is then exploited using balanced truncation method. The effectiveness of the reduced-order controller is finally verified on the validation model via system simulations.

Certification of vehicle noise emissions for passenger vehicles, motorcycles and light trucks is achieved by measuring external sound levels according to procedures defined by international standards such as ISO362. The current procedure based on a pass-by test during wide-open throttle acceleration is believed far from actual urban traffic conditions. Hence a new standard pass-by noise certification is being evaluated for implementation. It will put testing departments through their paces with requirements for additional testing under multiple ‘real world’ conditions. The new standard, together with the fact that most governments are imposing lower noise emission levels, make that most of the current models do not meet the new levels which will be imposed in the future. Therefor automotive manufacturers are looking for new tools which are giving them a better insight in the Pass-by Noise contributors.

This paper presents a new time-domain source contribution analysis method for in-room pass-by noise. The core of the method is a frequency-domain ASQ model (Airborne Source Quantification) representing each noise generating component (engine, exhaust, left and right tyres, etc.) by a number of acoustic sources. The ASQ model requires the measurement of local FRF's and acoustic noise transfer functions to identify the operational loads from nearby pressure indicator responses and propagate the loads to the various target microphones on the sides of the vehicle. Once a good ASQ model is obtained, FIR filters are constructed, allowing a time-domain synthesis of the various source contributions to each target microphone. The synthesized target response signals are finally recombined into a pass-by sound by taking into account the speed profile of the vehicle.

Despite the fact that Transfer Path Analysis (TPA) is a well known and widely used NVH tool it still has some hindrances, the most significant being the huge measurement time to build the full data model. For this reason the industry is constantly seeking for faster methods. The core concepts of a novel TPA approach have already been published in a paper at the ISMA 2008 Conference in Leuven, Belgium. The key idea of the method is the use of parametric models for the estimation of loads. These parameters are frequency independent as opposed to e.g. the classical inverse force identification method where the loads have to be calculated separately for each frequency step. This makes the method scalable, enabling the engineer to use a simpler model based on a small amount of measurement data for quick troubleshooting or simply increase accuracy by a few additional measurements and using a more complex model.

This paper presents an on-line, order-based roughness approach for vehicle engine sounds. This new algorithm reconstructs the sound envelope per critical band in an analytical way from the order amplitudes, phases and frequencies. The most time-demanding operations of the classical roughness models are no longer needed, rendering the algorithm extremely fast and applicable in real-time. Another interesting characteristic of this new algorithm is the unique link which is established between the roughness and the engine order components of the sound. Sound engineers can easily identify which order components need to be modified to reduce a roughness problem.

15 years of NVH applications make Transfer Path Analysis appear a commodity tool. This is however not the case. Required insight in the application constraints makes TPA remain an expert approach. This paper reviews past progress in TPA methodology and its limitations. It then introduces a number of innovative approaches addressing these, opening new application fields. This includes speed improvement (Fast TPA), structural modeling integration (Modal Contribution Analysis), CAE integration (Hybrid TPA), sound quality interpretation (TPA-sound synthesis) and supporting better exploitation of operational data (Operational Path Analysis). An outlook is given to the next challenge, the application to transient problems.

While CAE methods allow improving nominal product design using virtual prototypes, uncertainty and variability in properties and manufacturing processes lead to scatter in actual performances. Uncertainty must hence be incorporated in the CAE process to guarantee the robustness and reliability of the design. This paper presents an overview of uncertainty-based design in automotive and aerospace engineering. Fuzzy methods take uncertainty into account, whereas reliability analysis and a reliability-based design optimization framework can deal with variability. Key enabling technologies to alleviate the computational burden, such as workflow automation, substructuring and design of experiments, are discussed, and industrial applications are presented.

A key element to bring research advances on intelligent materials to industrial use is that the product CAE models must support such solutions. This involves modeling capabilities for intelligent material systems, sensor and actuator components, control systems as well as their integration in system-level application designs. The final result will then be a multi-attribute optimization approach integrating noise and vibration performance with reliability, durability and cost aspects. As no single integrated solution will fulfill all requirements of the various material and control approaches, the focus of the research is on the use, combination and extension of existing codes and tools.

This paper discusses the requirement for CAE methods to properly take into account the variabilities and uncertainties that characterizes design input properties without leading to oversized structures. Optimizing the structural behaviour while taking into account expected variability and uncertainty in the structure and its model, requires the adoption of a reliability-based design optimization approach. This paper starts with an overview of the problem of simulation uncertainty. The key focus is then on the description of the most commonly used methods and enabling tools for reliability analysis and reliability based design optimization. The theory is illustrated by real automotive design problems.

Due to the trend to build more vehicle models on a common platform, body development is very often on the critical path in the automotive development process. While the virtual assessment of attributes like crash, structural rigidity or production feasibility is common practice today, it is done less systematically for NVH and durability. They are traditionally only considered close to the availability of prototypes. Performance issues discovered at this stage will lead to additional design cycles which conflicts with the need to further shorten the total development time. The process proposed in this paper results in a better initial design by doing more NVH analysis in the pre-CAD phase and a reduced number of iteration cycles required for NVH and durability engineering by iterating much faster to the final design. Mesh morphing and beam concept analysis make it possible to evaluate and optimize functional performance characteristics based upon predecessor FE models.

Aircraft noise modeling aims to provide designers with computational tools that allow exploring the design parameters domain early in the design and development process. A number of modeling techniques are available for acoustics and vibration prediction, but in order to define objective targets for sound quality perception, dedicated tools are still needed to correlate structural models and design modifications with human perception of sounds. This paper presents a model-based sound synthesis concept for interior and exterior aircraft noise that allows interactive, real-time sound reproduction and replay. The proposed approach is presented through two application cases: jet flyover noise and turboprop interior noise.

This paper presents the results of an experimental test campaign carried out on a city bus powered by serial hybrid power train. The driveline system combines an Internal Combustion Engine with a battery pack and two electric motors. Tests were aimed at identifying the salient signal characteristics of the noise spectra recorded during operating conditions and to assess the acoustic comfort in the passenger compartment. Transfer Path Analysis technique was applied to identify airborne and structure borne vibro-acoustic loads, to measure transfer functions linking source locations to target locations and to estimate the internal vibro-acoustic comfort in operating conditions.

The paper will introduce some recent advances in vibration testing and modal analysis of airplanes. Recently, a very promising parameter estimation method became available, that has the potential to become the new standard. The main advantage of this so-called PolyMAX method is that it yields extremely clear stabilization diagrams even for broadband and high-order analyses. The method will be applied to two aircraft cases: a Ground Vibration Test using broadband shaker excitation on a small composite aircraft and in-flight data using natural turbulences as excitation. These two data sets allow illustrating both the classical Frequency Response Function based as well as the operational output-only modal analysis process.

Friction-induced vibration is a serious problem in many industrial applications containing systems with rotating and/or sliding parts. Brake noise is a typical example. The critical element in the noise generation process is the combination of friction-induced loads with the dynamics of the braking system. In the present paper, a detailed experimental and numerical study of a specific low-frequency brake squeal problem is made on a simplified brake noise test rig. First, the signal and spatial characteristics of the noise were analyzed by spectral and acoustic holography techniques. A parametric study of influence factors as brake pressure, rotation speed, etc. was made. Operational deformation analysis during squeal confirms the dominant modal behavior of the components, implying the critical role of the assembly structural dynamics.

Traditionally, vibration analysis in operating conditions (on the road or on a bench) had to be combined with experimental modal analysis in controlled laboratory conditions in order to understand the modal behaviour of the structure. This requires additional measurements, costs and time. However, in many applications, the real operating conditions may differ significantly from those applied during the modal test and hence the vibration modes from the modal test might not be representative for the active modes in operation conditions. The need for a capability of doing a modal analysis on data from operating conditions is obvious. Over the last years, several modal parameter estimation techniques have been proposed and studied for modal parameter extraction from output-only data. Each method needs to make a number of assumptions and has some limitations.

One of the scientific fields where, for already more than 20 years, system identification plays a crucial role is this of structural dynamics and vibro-acoustic system optimization. The experimental approach is based on the “Modal Analysis” concept. The present paper reviews the test procedure and system identification principles of this approach. The main focus though is on the real problems with which engineers, performing modal analysis on complex structures on a daily basis, are currently confronted. The added value of several new testing approaches (laser methods, smart transducers…) and identification algorithms (spatial domain, subspace, maximum likelihood,..) for solving these problems is shown. The discussed elements are illustrated with a number of industrial case studies.

Traditionally, vibration analysis in operating conditions (on the road or on a bench) had to be combined with experimental modal analysis in controlled laboratory conditions in order to understand the modal behaviour of the structure. This requires additional measurements, costs and time. However, in many applications, the real operating conditions may differ significantly from those applied during the modal test and hence the vibration modes from the modal test might not be representative for the active modes in operation conditions. The need for a capability of doing a modal analysis on data from operating conditions is obvious. Over the last years, several modal parameter estimation techniques have been proposed and studied for modal parameter extraction from output-only data. Each method needs to make a number of assumptions and has some limitations.

This paper discusses a road noise analysis application on a passenger car. It involves a study of the interior noise in the car, which is explained in function of the energy transfer paths from the suspension into the car body. For this, multiple reference transfer path analysis is used. A link is made between specific characteristics of this energy transfer and the operational analysis of the measurements on the suspension during road tests, as well as the acoustical modes of the cavity. The operational data are correlated with modal analysis results on the suspension, explaining certain problems occurring during running condition.

Optimal design changes to solve vibration induced fatigue failures can only be derived by including structural dynamics considerations into the fatigue lifetime calculation process. Such an integrated design approach to resonance fatigue problems has been developed within the EC Esprit Project 2486 DYNAMO. Also an integration of crack initiation and crack growth calculations has been realised. This integrated dynamic analysis/fatigue analysis procedure is demonstrated in the paper by means of a resonance fatigue problem of a car.