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08.01 Vehicle Noise & Vibration, Part 2

Turbulent model validations with CFD/wind tunnel test and application to statistical energy analysis for wind noise prediction
Time: 7:40 pm


Abstract ID: 1330

Wind noise is becoming to have a higher priority in automotive industry. Several past studies investigated whether SEA can be utilized to predict wind noise by applying a turbulent spectrum model as the input. However, there are many kinds of turbulent models developed and the appropriate model for input to SEA is still unclear. Due to this, this paper focuses on clarifying an appropriate turbulent model for SEA simulation. First, the input turbulent pressure spectrum from five models are validated with wind tunnel tests and CFD. Next, a conventional numerical approach is used to validate models from the aspect of response accuracy. Finally, turbulent models are applied to an SEA model developed for a wind tunnel, and the SEA response is validated with test data. From those input/response validations, an appropriate turbulent model is investigated.

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An adjustable bearing seat stiffness element for targeted vibration influencing
Time: 2:00 pm

Author: Carolin Sturm

Abstract ID: 1642

In order to be able to influence the dynamic system behavior in a targeted manner, parameters such as stiffness in the technical system must be adjustable. In high-speed powertrains, the stiffness of the bearing seat, in particular, has an influence on the dynamic characteristics. As part of our research, we developed an adjustable bearing seat stiffness element. The focus of research was on an adjustable, scalable element with a small design space and the same properties over the perimeter. We characterized it statically with the help of a universal testing machine and dynamically using a shaker system. The results are compared with theoretical approaches. The results show that the stiffness is almost linearly adjustable in the load range of 0-100N. The results indicate that the developed element can be used to adjust desired stiffness and thus to influence vibrations in a targeted manner. The findings can be used in the design of high-speed powertrains e.g. in serial products or test benches.

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Silencer for high-frequency turbocharger compressor noise via an acoustic straightener
Time: 3:20 pm

Author: Pranav Sriganesh

Abstract ID: 1917

Decades of successful research and development on automotive silencers for engine breathing systems have brought about significant reductions in emitted engine noise. A majority of this research has pursued airborne noise at relatively low frequencies, which typically involve plane wave propagation. However, with the increasing demand for downsized turbocharged engines in passenger cars, high-frequency compressor noise has become a challenge in engine induction systems. Elevated frequencies promote multi-dimensional wave propagation rendering at times conventional silencer treatments ineffective due to the underlying assumption of one-dimensional wave propagation in their design. The present work focuses on developing a high-frequency silencer that targets tonal noise at the blade-pass frequency within the compressor inlet duct for a wide range of rotational speeds. The approach features a novel “acoustic straightener” that creates exclusive plane wave propagation near the silencing elements. An analytical treatment is combined with a three-dimensional acoustic finite element method to guide the early design process. The effects of mean flow and nonlinearities on acoustics are then captured by three-dimensional computational fluid dynamics simulations. The configuration developed by the current computational effort will set the stage for further refinement through future experiments.

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Innovative elastomeric shear leg mount concepts for quasi-zero stiffness isolation
Time: 3:40 pm

Author: Luke Fredette

Abstract ID: 2184

Passive vibration isolation may be a cost-effective solution to isolate a supported system containing a source and/or receiver from the supporting structure. The standard linear theory suggests a low-stiffness joint to create a mobility mismatch in the transmission path, but this solution may lead to large amplitude motions in the supported system. To achieve both motion control and isolation with the same mount and without compromising either objective, an innovative, nonlinear mount concept is proposed. Taking advantage of geometric nonlinearity for large displacements, a quasi-zero stiffness is generated by exploiting the interaction between the nonlinear mechanisms that govern the motion of a number of inclined shear legs. For example, a three-regime stiffness profile is created, including a medium-stiffness preload regime, a quasi-zero stiffness isolation regime, and a high-stiffness motion control regime. This concept offers significant benefits compared with a more conventional compromise approach in that low-amplitude vibrations are exceptionally isolated while large amplitude transient motions are controlled. Illustrative computational examples will be presented to support the underlying linear and nonlinear design principles. Limiting cases will be discussed as well.

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OTPA method-based contribution analysis of components on the vibration of fuel cell in fuel cell vehicles
Time: 2:40 pm

Author: Zequn Nan

Abstract ID: 2501

Due to the introduction of auxiliary components in fuel cell vehicle powertrains and absence of internal combustion engine, the vibration sources and transfer paths are very different from conventional vehicles. These vibrations interact on the output performance of the fuel cell system. Therefore, it is necessary to investigate the vibration characteristics of the fuel cell system under vehicle operating conditions. IPEK conducted vehicle measurements regarding different driving manoeuvres and environments. In order to quantitatively evaluate contributions of each vibration source on the total vibration of fuel cell, frequency-domain contribution was investigated based on Operational Transfer Path Analysis method with the singular value decomposition as well as principal component. The results of vibration in Z-direction in the vehicle coordinate system show that the hydrogen pump dominantly contributes to the vibration of fuel cell in a wide range of frequency in the majority of the driving manoeuvres. However, the results vary in various driving manoeuvres, environments and frequencies. The Paper will discuss in detail the vibrational contributions in X-, Y- and Z-direction.

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Test bench development and validation for blocked force measurements in six degrees of freedom
Time: 2:20 pm

Author: Martin Burkhardt

Abstract ID: 2561

For transfer path analysis (TPA) methods, the description of the source is essential. The possibilities of source characterization are as different as the TPA methods. For the classical methods, the source is considered in the installed state with feedback from the receiver structure, while for component-based TPA the source is described without feedback from the coupled structure. In addition to TPA, source characterization is also used in the product development process for evaluation or comparisons. Also in these cases, the source must be characterized without feedback from the test structure, which can generally be realized by measuring free velocities or blocked forces. Because of the need of external load to reach the components operating point, force measurements are often used. However, the realization of a reactionless test setup for the measurement of forces poses some challenges. The paper presents a setup that can be used to perform a direct force measurement at a point in six degrees of freedom. The necessary boundary conditions to approximate the idealized blocked force assumption are discussed, the calculation of the blocked force in six degrees of freedom is presented, the structural dynamic response at a reference point is calculated and compared with operational measurements.

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Development of disc spring stack containment methods for vibration isolation
Time: 3:00 pm

Author: Paul Gilmore

Abstract ID: 2865

Cone disc springs exhibit quasi-zero stiffness behavior that is useful in isolating objects from low frequency vibrations.  However, the stroke of a single disc spring is too low for most applications, and springs are stacked to increase the displacement.  A method to contain the isolator stack then becomes critical for practical uses.  Many challenges in developing these containment methods have been identified and can be collectively described as how to appropriately contain the stack without affecting isolation performance.  In this work, three designs are considered: a retaining ring design, tube and shaft design, and zero poisson ratio sleeve design.  Disc spring stacks with containment method are built, and load-deflection curves are measured and compared with standalone stacks.  Under quasi-static compression testing, each containment method has minimal effect on the standalone stack load-deflection curve.  However, significant differences in isolation performance are observed in vibration testing and found to depend on characteristics such as lateral stability, lateral strength, and degrees of freedom.  Lastly, advantages, disadvantages, and appropriate applications for each containment method are summarized.  The conclusions of this work are that containment method is an important variable in the application of disc spring isolators and robust, versatile containment designs have been demonstrated.

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