Yuksel Gur

Nonlinear analysis of automotive door weatherstrip seals

Abstract Automotive door system weatherstrip seals play a major role in determining door closing effort, isolating the passenger compartment from water and reducing the wind noise inside the vehicle. Using nonlinear finite element analysis, a seal cross section can be analyzed for compression load deflection (CLD) behavior, contact pressure distribution and aspiration due to a pressure differential across the seal. The seal CLD response, the deformed shape during compression, the contact pressure distribution and the aspiration pressure difference are all important seal performance factors that are considered in door weathership seal design. The analyses described herein and the associated design evaluations can be performed before any prototype hardware is developed if sufficient geometry and material property information is available.

Modeling foam damping materials in automotive structures

Foam damping materials judiciously placed in automotive structures efficiently reduce the vibration amplitudes of large, relatively flat exterior body panels such as the hood, roof, deck lid (trunk) and door skin. These polymer foams (typically epoxy or vinyl) have mechanical properties that depend on the foam homogeneity, degree of expansion, temperature and frequency of excitation. Standard methods for determining true bulk mechanical properties, such as Youngs modulus, shear modulus and damping terms, are discussed along with methods for determining engineering estimates of the properties as used in automotive applications. Characterizing these foam damping materials in a component or full body finite element structural model as discrete springs and dashpots provides an accurate and economical means to include these features. Example analyses of the free vibrations and forced response of a hood are presented accompanied by test data that demonstrate the accuracy of the structural model. A parametric study investigates the effect of foam material stiffness and damping properties on hood vibration amplitudes under dynamic air loading. A methodology is discussed to reduce the hood vibration level under cross-wind conditions to an acceptable level with the use of foam materials.

NVH Performance of Lightweight Glazing Materials in Vehicle Design

Fuel economy and NVH (noise, vibration, and harshness) performance of vehicles are important parameters in a customer’s vehicle purchase decision. Lightweight vehicle designs are necessary to help with fuel economy improvements. In this research work, the weight saving potential and NVH performance of different lightweight glazing materials are investigated to help the lightweight design effort. The lightweight glazing materials included in this study are “Material A”, “Material B”, “Material C” with regular lamination, and “Material C” with acoustic lamination. The results of this research work indicate that the lightweight glazing materials have 30% to 40% weight saving potentials without NVH penalty. These materials have much higher damping properties than conventional tempered glass so they can compensate for the mass reduction influence on vehicle NVH. The tire patch noise reduction, vehicle transparency, and wind noise results of “Vehicle A” tested with different lightweight backlight designs indicate that there is almost no acoustic response difference between the tempered glass and other lightweight alternative backlight designs. Damping loss factor measurements indicate that “Material C” with acoustic PVB (polyvinyl-butyral) has the highest damping loss factor value of 37%. The “Material C” backlight with acoustic PVB is the best among all the lightweight alternatives and brings 29% weight reduction without any NVH degradation. Statistical Energy Analysis (SEA) results also indicate that it is possible to eliminate the NVH degradation by using glazing material having high material damping properties or using laminated panels having damping loss values in the range of 6% to 20%. In this paper, we only address the weight reduction and NVH performance of light weight glazing materials but not the costs or any potential assembly procedure changes.Copyright

Fluid‐loaded elastic slab excited by line and point loads

The plate equations are not sufficient to predict the response for high wave‐number excitations. In order to determine the difference between plate and elastic slab results, and the range of validity of the plate equations, the following problems were solved: an infinite slab excited by a line load and a point load. The space above the slab contains an acoustic medium and below the slab there is a vacuum. It was proven that the point‐loading case was formally identical to the line‐loading case. The only difference was in the use of Hankel transforms instead of Fourier transforms. Full elastic slab equations were solved for this acoustic medium/elastic slab coupling problem with analytical and numerical techniques. Far‐field‐radiated pressure and surface interface displacement results indicated that full elastic slab equations predict lower radiated pressure and higher interface trapped wave amplitude compared to thin plate results for high‐frequency excitations. The upper nondimensional frequency limit fo...

Experimental and numerical techniques for lightweight vehicle sound package development

The use of lightweight structural materials poses great challenge to noise control of a vehicle. A new approach to sound package design in lightweight vehicles was developed to reduce vehicle interior noise level without addition of weight. This new approach relies on lightweight acoustical materials that provide superior sound absorption performance to reduce noise level at the source, e.g., inside engine compartment and near the tires. Vehicle NVH finite element analysis (FEA) models were used to develop the lightweight vehicle’s structural design to bring the lightweight vehicle’s low and mid frequency responses closer the baseline vehicle’s performance. Full vehicle SEA (statistical energy analysis) model was developed to evaluate the high frequency NVH (noise, vibration, and harshness) performance of a vehicle. This correlated SEA model was used for the vehicle sound package optimization studies to develop sound package design to improve lightweight vehicle’s acoustic performance. In this paper, the use of NVH CAE (computer aided engineering) simulations for lightweight vehicle design is presented to highlight the limitation and use of FEA and SEA in lightweight vehicle development.

Vehicle Moonroof Design for Wind Noise

A study was undertaken to address excessive moonroof wind noise in some vehicles. Mathematical models were developed to understand noise generation mechanisms associated with the moonroof system, and these models were used to investigate ways to reduce vehicle interior noise levels. Extensive acoustic & vibration testing was performed on vehicles in the wind tunnel and on the test track. The wind tunnel and test track data were analyzed in a sound quality laboratory for root cause analysis. CFD (computational fluid dynamics) simulations were performed to understand flow behavior over the moonroof in both modes of operations (vented and fully retracted). An experimental moonroof deflector optimization study was developed and conducted to identify the necessary design changes to minimize the vehicle interior noise level for fully retracted condition. Variability studies were also performed on the moonroof flushness, deflector height, and retraction distance. Through extensive analyses, using both experimental and analytical techniques, the main causes of wind noise associated with moonroof system were identified. Vehicle moonroof design recommendations were generated for significant wind noise reductions.Copyright

Vehicle door seal modeler for wind noise

Wind‐noise performance of a passenger vehicle plays a significant role in the customer’s perception of overall vehicle quality. Wind noise aerodynamically generated on the exterior surface of a vehicle can propagate to the vehicle interior through body panels, window glass, and the seal gap between the door and door opening panel. Experimental studies indicate that automotive door seal systems are generally a major contributor to the vehicle wind‐noise performance. Traditionally, automotive door seals are designed using the ‘‘bread board’’ and other ‘‘build and test’’ procedures. Two new finite‐element‐based acoustic‐structure analysis tools have been developed to evaluate the wind‐noise performance of door sealing system. These validated CAE techniques allow the engineer to predict door seal system performance in sound transmission and aspiration leakage before the availability of prototype hardware. These methods combine the separate analysis capabilities of finite‐element analysis for acoustics, rubber...

Analytical prediction of sound transmission through automotive door seal systems

A finite element‐based acoustic‐structure interaction modeling procedure is developed to determine the sound transmission loss characteristics of automotive door seals. The model accounts for the effects of seal system compression, the density and constitutive behavior of the materials used in the seal construction, individual seal cross‐sectional geometry, and spacing between layers of seals. The results of a sensitivity analysis conducted using the modeling procedure reveals that the overall transmission loss of door seal systems is most sensitive to changes in: seal material density, geometry of the seal in the compressed deformed configuration, and geometry of the cavities formed by the space between seals of adjoining layers. An important implication arising from the sensitivity analysis for the design of door systems for closing efforts is that, without changing seal system compression load deflection behavior, the sound transmission characteristics may be altered substantially by changing the spaci...