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Technical Paper

Parametric Model Order Reduction for Vibroacoustic Metamaterials based on Modal Superposition

2022-06-15
2022-01-0943
Vibroacoustic Metamaterials (VAMM) have recently shown great potential in the elimination of noise and vibration in targeted and tunable frequency regions. The so-called stop band behavior is mainly driven by small resonance structures on a subwavelength scale. Due to the complex material and geometry composition, stochastic methods for uncertainty quantification, model updating, and optimization are necessary in the design and validation process of VAMM. Those methods require to repeatedly solve Finite Element (FE) models with slightly changed parameters and can become computationally challenging for large numerical models. Hence, the need for Parametric Model Order Reduction (PMOR) techniques arise to reduce the computational burden. For VAMM, consisting of many substructures, common PMOR methods based on Component Mode Synthesis (CMS) can become cumbersome to set up and numerically challenging.
Technical Paper

Hierarchical Bayesian Networks for predicting the structural behavior of coupled systems

2022-06-15
2022-01-0942
Simulations play an important role in the continuing effort to reduce development time. However, to simulate the dynamic behavior of complex engineering systems accurately, large and complex models are necessary. In recent years, the use of data driven models based on machine learning (ML) algorithms have become popular for predicting the structural dynamic behavior of mechanical systems. Due to their advantages in capturing non-linear behavior and efficient calculation, data driven models are used in a variety of fields like uncertainty quantification, optimization problems, and structural health monitoring. However, the black box structure of ML models reduces the interpretability of the results and complicates the decision-making process. Hierarchical Bayesian Networks (HBNs) offer a framework to combine expert knowledge with the advantages of ML algorithms.
Technical Paper

On the Calculation of Modal Damping Ratios

2022-06-15
2022-01-0945
The prediction of the sound characteristic of a drive train in early development stages poses a significant competitive advantage to specifically design the sound of e.g. a vehicle. However, at the state of the art, the structural behavior cannot be predicted with satisfactory accuracy due to the various and sensitive mechanisms which contribute to it. In the case of complex structures like electric motors or even complete drive trains, usually model order reduction and linearization techniques like the modal superposition method are employed to reduce the calculation effort and obtain usable models for transient time domain simulations. The three main force contributions which have to be considered are spring forces, inertia forces and damping forces. The former two arise from the Youngs-Modulus and the mass density. Both material parameters are relatively constant over a wide range of boundary conditions and therefor easy to calculate.
Technical Paper

Acoustic Fluid-Structure Interaction (AFSI) in the car underbody

2022-06-15
2022-01-0937
The turbulent flow around vehicles causes high pressure fluctuations at the underbody, consisting of both hydromechanic and acoustic contributions. This causes vibrations in the underbody structures, which in turn may lead to sound transmission into the passenger compartment, especially at low frequencies. In this contribution we analyse these phenomena by studying the flow, acoustics and structural vibration of the SAE body in a wind tunnel. The excited and vibrating underbody is resembled by an aluminium plate in the underbody of the SAE body which allows for sound transmission into the interior. Different excitation situations are generated by placing obstacles at the underbody in front of the aluminium plate. For this setup we carry out a fully coupled simulation of flow, acoustics and vibration of the plate. The flow and acoustics are computed with a hybrid method (MGLET), which is two way coupled to a simultaneous solution of the structural vibrations.
Technical Paper

Effects of Boundary Layer and Local Volumetric Cells Refinements on Compressor Direct Noise Computation

2022-06-15
2022-01-0934
The use of turbochargers with downsized internal combustion engines improves road vehicles’ energy efficiency but introduces additional sound sources of strong acoustic annoyance on the turbocharger’s compressor side. In the present study, direct noise computation (DNC) is carried out on a passenger vehicle turbocharger compressor. The work focuses on assessing the influence of grid parameters on the acoustic predictions, to further advance the maturity of the acoustic modelling of such machines with complex three-dimensional features. The DES study investigates the influence of the inflation layers characteristics, and of the spatial resolution of the mesh, on the simulated acoustic signatures. In the core mesh, refinements are applied in areas of major acoustic production, to generate cells with sizes proportional to the local Taylor microscale values.
Technical Paper

Validation of Combining Compressible CFD Results with Statistical Energy Analysis for Vehicle Interior Noise Simulation

2022-06-15
2022-01-0936
Already a concern and a main customer satisfaction complaint for many years, wind noise for passenger vehicle is an increasingly important concern as the masking effects of internal combustion engines is phased out for Electric Vehicles which replace engine, intake and exhaust noise with electric component and other accessory noise. Acoustic wind tunnel testing is expensive and time consuming and can generally only provide useful results near the end of the vehicle design process with mature prototypes, and this is at a design phase where changes or countermeasures to reduce wind noise may be difficult or at the least costly. This paper represents a validation case for a production vehicle where a compressible Computational Fluid Dynamics (CFD) model was used to calculate surface pressures on the vehicle.
Technical Paper

Aero-acoustic source terms from Large-Eddy Simulation in turbulent pipe flow

2022-06-15
2022-01-0940
In the acoustic design of electric vehicles, novel simulation technologies for predicting relevant sound sources early in the design state become increasingly important. This requires accurate numerical methods to describe these phenomena. The present study computationally investigates the flow-induced noise from aero acoustic sound sources, generated in turbulent pipe flow. The analysis follows a hybrid approach, where the acoustic sound field is predicted separately from the underlying the turbulent flow field, however supplied with acoustic source terms from an incompressible flow simulation of the considered configuration in the limit of low Mach number. Source terms from for use as input into different acoustic analogies, the Lighthill’s wave equation, the vortex-sound theory, and the Perturbed Convective Wave Equation (PCWE) are computed performing incompressible Direct Numerical Simulation (DNS) and Large-Eddy Simulations (LES) of fully developed pipe flow.
Technical Paper

Using Analytical Techniques to Understand the Impacts Intelligent Thermal Management Has on Piston NVH

2022-06-15
2022-01-0930
In order to align with net-zero CO2 ambitions, automotive OEMs have been developing increasingly sophisticated strategies to minimise the impact that combustion engines have on the environment. Intelligent thermal management systems have a positive impact on friction generated in the power cylinder by improving the warmup rate of cylinder liners and heads. This increase in temperature results in an improved frictional performance and cycle averaged fuel consumption, but also increases the dynamic piston to liner clearance and therefore the propensity for piston slap. In low temperatures this piston slap can substantially decrease the NVH quality to unacceptable levels. Using analytical techniques, it is possible to model the thermo-structural and NVH response of the power cylinder with different warm up strategies.
Technical Paper

Time-Domain Simulation Approach for the Electromagnetically Excited Vibrations of Squirrel-Cage Induction Machine Drives under Pulse-Width Modulated Supply

2022-06-15
2022-01-0932
One key point of the design process of electrified drive trains is the optimization regarding noise, vibration and harshness (NVH). An important task in this regard is to identify NVH related issues in early design phases by means of computer simulations. A main contributor for vibrations and noises are electromagnetically excited forces and torque stemming from the electric motor that propagate to housing and transmission. In our current study we explore the whole multi-physical simulation workflow from electromagnetics and structural dynamics to acoustics. In electromagnetic simulations, forces and torque signals are calculated for specific speed-torque operation points. In order to consider all system non-linearities correctly, time-domain simulations are carried out. The electric motor investigated in this study is a squirrel-cage induction machine. For this machine type, the simulation effort with full transient numerical methods like finite element analysis is very high.
Technical Paper

Energy Harvesting for lightweight design by means of ferroelectret transmission mechanisms arranged in clusters

2022-06-15
2022-01-0949
Aircraft traffic causes a significant amount of greenhouse gas emissions. Since modern aircrafts are highly electrified, the total weight is affected by cables within the components. Piezoelectric energy harvesting appears to be a reasonable option for reducing cables in certain parts of the aircraft and hence reducing fuel consumption. The proposed work covers energy harvesting in lightweight design with transmission mechanisms using so-called ferroelectrets. The energy harvester (EH) design is motivated by a strain-excitation in an aircraft wing caused by a quasi-stationary dynamic pressure. Ferroelectrets are piezoelectric polymers that show a higher ecological compatibility and a much higher structural flexibility than piezoceramics. Furthermore they provide charge constants in the same order of magnitude as piezoceramics.
Technical Paper

Mastering uncertainty in model-based prediction of vibroacoustic vehicle properties

2022-06-15
2022-01-0988
Vibroacoustic properties specify among others the quality of vehicles and contribute to customer satisfaction. In early design phases a finite element analysis is usually carried out to predict and design vibroacoustic properties. Models are simplified to predict vibroacoustic properties with reasonable computational effort. For example, substructures such as seats are reduced to point masses. Especially in the early design phase, this lack of knowledge leads to uncertainty. Uncertainty is only partially taken into account yet, resulting in inaccurate model predictions. This paper proposes a three-part approach, which aims to improve the model-based predictions of the vibroacoustic properties by mastering uncertainty. First, structural uncertainty is also considered in addition to the well-known data uncertainty and model uncertainty.
Technical Paper

Characterization and modelling of mounts for electric powertrains

2022-06-15
2022-01-0986
The topic of this paper is to deal with the filtering of medium and high frequency excitations generated by electrified powertrains. It is now recognized that the whining noise generated by the electromagnetic forces and/or the meshing process of the transmission can propagate to the car-body through the rubber mounts. In the design phase, the prediction of the structure borne contribution requires a good knowledge of the dynamic behavior of the rubber mounts. The main issue is the stiffness of the mounts which cannot be modeled as pure springs. In fact, the dynamic behavior of a mount is governed by the material rheology and its internal resonances. The work presented in this paper propose a simulation workflow for the rubber mounts dynamic model and a methodology for the dynamic stiffness measurement including the sensitivity with the preload and with the amplitude of the excitation. Finally, experimental and digital data are compared to assess the simulation method.
Technical Paper

A Coupled Simulation Approach for the Quantification of Impact Events in Automotive Applications

2022-06-15
2022-01-0985
Squeak and Rattle are the most obnoxious noises, affecting the perceived quality of an automobile interior. Minimizing or eliminating these transient events poses a great challenge in vehicle construction as they are generally discovered late in the product development cycle. Identifying and quantifying these issues at the design and virtual validation stage is of prime importance. Current simulation methodologies estimate the occurrence of these events by measuring the relative displacement between the interacting parts. Solving this problem using linear simulations do not accurately reflect real-world non-linear mechanical behavior and most importantly, quantifying the noise caused by these impact events. Capturing a suitable impact behavior is essential along with the quantification of noise generated by these events is necessary for understanding the severity of the problem.
Technical Paper

An efficient methodology to predict the dynamic instabilities of a frictional system

2022-06-15
2022-01-0984
Stochastic Finite Elements Method (SFEM) is applied in many fields. For instance, in frictional systems, it helps quantify uncertainties due to a generalized lack of knowledge about the involved process and thus, provides a more reliable prediction of the dynamic instabilities. Usually, SFEM is coupled with sensitivity theory to investigate the effect of a given input on the output. However, the available methods which often couple Monte-Carlo (MC) algorithm with the Finite Element (FE) method have a computational cost that scales linearly as a number of stochastic iteration N and input parameters k (i.e., t ~ N k). For an interesting convergence property, the magnitude of N must be on the order of thousands or even millions. Hence, for a frictional system with 5 random variables and requires 15 min of CPU per run, the computational cost will exceed 52 days (!).
Technical Paper

NVH Refinement of Automotive HVAC System

2022-06-15
2022-01-0982
The present day, car performance is more prevailing option to fascinate the buyer in IC and electric passenger vehicle. Acoustic and thermal performance balancing of heating ventilation and air conditioning (HVAC) system within car cabin proves to be critical aspect for automotive OEM. The HVAC system induced noise inside car cabin could be significant discomfort to passengers. For this reason, acoustic quality is becoming increasingly prioritized as a key design issue throughout the entire development process of HVAC system. The paper studies the advancement in using innovative development tools to map the HVAC system noise performance at vehicle level and evaluating at sub component level for noise, vibration and transient flow of refrigerant fluid induced noise with the help of universal buck under controlled condition.
Technical Paper

On the different contributions of mounts and flexible hoses on the structure borne noise of refrigerant compressors

2022-06-15
2022-01-0983
Air conditioning acoustics have become of paramount importance in electric vehicles, where noise from electromechanical components is no longer masked by the presence of the internal combustion engine. The coolant compressor is one of the most important elements in the HVAC systems of a car in terms of vibration and noise generation. The generated structural noise is studied in detail in a prototype installation, and the noise transmission and propagation mechanisms are analyzed and discussed. Through ”in situ” measurements and virtual point transformation the rotor unbalance forces and torques acting within the component are identified. The dynamic properties of the rubber mounts installed between the compressor and its support are identified thanks to matrix inversion methods. To assess the quality of the proposed procedure, the synthesised sound pressure level (SPL) is compared with experimental (SPL) measurements in different operational conditions.
Technical Paper

Analytical and Numerical Models of the Sound Radiated by Fully Clamped Rectangular Vibrating Plates

2022-06-15
2022-01-0973
In the present work, fully clamped rectangular vibrating plates are investigated: the response is calculated under steady-state excitation determined by the application of a harmonic point force, and the consequent sound radiation is evaluated. An isotropic, undamped material was employed, having the mechanical properties (density, Young’s modulus and Poisson’s ratio) of the aluminium. The study is carried out both theoretically and numerically. At first, the analytical solution of the motion equation for a fully clamped plate is calculated by means of a MATLAB implementation. The solution is based on the Principle of Virtual Work, calculating the displacement as a function of the frequency at the nodes of a rectangular mesh. The monopole approximation of the Rayleigh’s integral is then used to estimate the sound radiated in free field condition. The numerical solution is evaluated using COMSOL Multiphysics, employing the Finite Elements Method (FEM).
Technical Paper

Modeling and controling acoustic performance of heterogenous materials made of recycled foams

2022-06-15
2022-01-0961
Recycling channels for foam materials, especially mattress foams, are set up. The foams are generally crushed into flakes and then assembled resulting in heterogeneous materials. These materials are more valuable if their properties are controlled. This work focuses on their acoustical properties. First, the properties of initial foams have to be estimated and the assembling process has to be analyzed in order to model the acoustic behavior of the reconstructed heterogeneous materials. The foams flakes are assembled with a binder and compressed during the manufacturing process. This work presents the methodology set up to predict the sound absorption of such heterogeneous materials based on recycled foams, from the estimation of the raw material properties to the final assembly. First, a large number of foams were measured in order to distinguish categories of materials. The data is stored in a database management software in order to perform some statistical analysis.
Technical Paper

A Trend Line Analysis of the Insertion Loss Test Data and Application to Sound Transmission Loss Simulation

2022-06-15
2022-01-0959
In this paper, an application process is studied at which insertion loss (IL) test data of sound barrier assemblies are utilized for the sound transmission loss (STL) simulation of the trimmed dash structure. The considered sound barrier assemblies were composed of a felt layer, a mass layer, and a decoupler layer. Flat samples of sound barrier assemblies with several different thicknesses were prepared, and ILs of them were measured by using a sound transmission loss facility. Flat samples were assumed to have mass-spring resonance frequencies. The mass was set as the area mass of the sound barrier layer of the felt layer and the mass layer. The spring constant of the decoupler layer was assumed as the multiplication of that of an air spring and a spring correction factor. At the beginning, the spring correction factor was assumed to be 1, and the measured IL data vs frequencies are converted to IL data vs frequency ratios, frequency f over the resonance frequency fres.
Technical Paper

Polyurethane decoupling foam with variable stiffness and thickness: Insulation performance versus their mechanical and transport properties

2022-06-15
2022-01-0957
The polyurethane (PU) foam is widely used in several automotive noise reduction solutions. The insulation performance of decoupling foam depends on its intrinsic properties: the elastic and transport parameters (Biot parameters). When the transport parameters of foam are controlled, the mechanical properties become dominant for its decoupling function. Globally, a soft foam is better to decouple the vibration from the BIW. However, foam with adequate stiffness is also required due to various reasons (mounting, comfort…). In this work, flat samples of PU foam injected on heavy layer were studied at different foam thickness and hardness. Their Insertion Loss (IL) performances were measured through the Small Cabin system, by both Faurecia and Stellantis, with globally good correlation. The Biot parameters of foam (including the Young’s modulus) and the compression load deflection (CLD - stiffness at high compression rate) of all foam samples were also measured or characterized.
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