Noise, vibration and harshness (NVH) issues challenge NVH engineers throughout the entire vehicle development process. It also effects the operation phase of a vehicle. For an efficient and reliable solution, technical expertise covering the entire chain from sound and vibration generation, -transfer and –perception are required- This includes optimal interaction between sophisticated simulation and advanced experimental investigation.
One of VIRTUAL VEHICLE s strength is not only the exceptional testing and validation equipment and processes but also (further) develop best-suited experimental methodologies, testing procedures and reliable test facilities according to the customer’s and partners’ needs.
In a broad variety of challenging R&D projects and services, best possible approaches have been developed for numerous OEMs and TIER 1 and 2 suppliers. For more than 15 years, VIRTUAL VEHICLE successfully operates comprehensive test facilities to investigate and improve the NVH properties of vehicle components and systems in automotive and rail applications.
The increasing complicity in modern powertrains results in highly challenging requirements for test benches and -systems. During early stage of development the powertrain needs to be optimized concerning durability, functionality and efficiency as well as NVH and comfort issues. As many parameters as possible without full vehicle measurements have to be included.
VIRTUAL VEHICLES modern engine test benches verify all necessary and various requirements of OEMs, legislations and customers. Different parameters like operational vibrations, sound radiation as well as efficiency and emission tests are generally measured as a function of torque and rotary speed.
Resonances in components can be determined quickly and reliably by means of experimental vibration testing: The component is excited with a defined excitation by shaker or impulse hammer and the vibration response is recorded at various points using sensors such as accelerometers or laser scanning vibrometers.
PsychoacousticsVIRTUAL VEHICLE is using and further developing technologies for human related sound perception in ongoing research projects to link vehicle measurement results with complex acoustic phenomena and simplified test procedures. The main strength of VIRTUAL VEHICLE is to predict the sound perception and also to avoid customer complaints. In latest projects it has been worked out to implement psychoacoustic metrics into test specifications to prove the quality of automotive components.
Reduction of Disturbing NoiseSeatbelt retractors internal locking mechanism is based on mechanically sensing elements. These can be excited by engine vibrations or when the vehicle is run over rough road tracks and leads to persistent rattle sound, being often rated acoustically annoying in the vehicle. In a three year research project VIRTUAL VEHICLE worked out a functional and comparable test procedure for characterizing rattle noise phenomena. Therefore, the complex in-vehicle situation was modelled on a multi-axial squeak and rattle test bench developed for interfering noise analysis. The results were analysed with customized psychoacoustic metrics. The methodical approach was validate by a round robin test together with industrial partners involved.
NVH optimized operating strategy of a cooling unit for commercial vehicle trailersConflicting requirements related to high fuel economy, excellent thermal efficiency, limited design space and different operating conditions are a real challenge to derive a balanced NVH performance. VIRTUAL VEHICLE developed an acoustic model which is able to predict the sound pressure level at defined assessment positions and therefore allows to optimize the operating strategy and to conclude improvement measures from an NVH point of view. The database for the acoustic model was derived from sound power level measurements using the enveloping surface method. Throughout the comparison of different operating conditions the partial sound power levels for each component and its possible different operating conditions could be calculated.
Trim characterizationWhen it comes to characterization of vibro-acoustic properties the sound insulation materials is a big challenge. Therfore , VIRTUAL VEHICLE has developed a macroscopic approach to describe the dynamic behavior of sound insulation materials:Thisapproach based on surface impedance, which is determined on a tailored test bench using pressure-particle velocity sensors. To account for the mutual interaction of trim with structure and acoustic fluid, the methodology is implemented in a sub-structuring scheme. Integration of the method into existing vehicle NVH development processes is an ongoing research track together with leading automotive OEM and supplier companies.
Flow-induced, low frequency noiseAerodynamic noise is of major importance for vehicle comfort at high driving speeds. To account for the noise generation mechanism in an early design phase, VIRTUAL VEHICLE has developed a forward-coupling strategy. This integrates transient computational fluid dynamics (CFD) analysis with a vibro-acoustic finite element method (FEM) model into one seamless workflow. A particular emphasis has been put on coupling between buffeting noise and vibro-acoustics to account for the effects of mutual interaction between flow and flexible structures. The numerical work has been complemented by experimental campaigns conducted in aero-acoustic wind tunnel and the data gathered has been used for validation.
Orifice noiseTo reduce complexity and improve the stability of the numerical solution of the flow-induced noise a novel method for capturing the effects of vorticity at the trailing edge on the far-field radiation has been developed. Since the vortex-sound interaction is limited to the small region at the sharp edge of the pipe, its effect is described in terms of surface boundary condition enforced at the edge of the pipe. This modification is then implemented in a framework of convected wave equation, which is computationally very efficient to solve and supports convection and refraction of sound in the mean flow.