30 American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) ISSN (Print) 2313-4410, ISSN (Online) 2313-4402 © Global Society of Scientific Research and Researchers http://asrjetsjournal.org/ CAE Methodology for Optimization of Automotive NVH Performance through Wheel Structure Modifications Akbar M. Farahania*, Mahdieh Balaghib a Noise, Vibration and Acoustics (NVA) Research center, School of Mechanical Engineering, University of Tehran, Tehran 1417614418, Iran bDepartment of Industrial Engineering, Islamic Azad University, Arak 38361-1-9131, Iran aEmail: akbar.mazrae@gmail.com bEmail: mahdieh.balaghi@gmail.com Abstract Noise, Vibration and Harshness (NVH) has been considered as one of the biggest challenges in the automotive industry since it is a source of complaints from passengers for decades. A typical automotive wheel has a very important role in optimizing the NVH performance of the vehicle body. An automotive tire is the primary component which is directly in contact with road disturbances. If structural dynamics of the tire is optimized, it can significantly reduce the transmitted noise and vibration to the passenger cabin. Here frequency response analysis is conducted using a developed finite element model of the wheel (tire and rim). The frequency response has been derived using an impulse input force and measuring the acceleration in radial and axial directions. This analysis can give us the resonances and anti-resonances that can be tuned to achieve a desirable performance. Desirable output can be considered as a low noise and vibration inside the automotive cabin to have customer satisfaction. Keywords: NVH optimization; Frequency Response Analysis; Resonance Frequencies; Structural Modification. 1. Introduction Thanks to advancement in CAE methodology, a reliable and simple model can be very useful to predict the behavior (static and dynamics) of a typical system [1,2]. These days CAE has a lot of applications in automotive, aerospace, civil and robotics industries [3]. CAE provides amazing tools to optimize the dynamical performance of the structure in terms of geometry, materials and connections [4-6]. ------------------------------------------------------------------------ * Corresponding author. http://asrjetsjournal.org/ American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 39, No 1, pp 30-37 31 Most recently,Tatari and etc. have shown that a reliable concept model of automotive Body. In-White (BIW) structure can be very beneficial to prevent mode interaction, tune resonance frequencies, and achieve appropriate mode shapes in early design phases [7,8]. The advantage of using a CAE concept model in early design phases is its capability to significantly reduce the time and cost of manufacturing process [9,10]. Another application of a these models is to reduce the structural borne noise in early stage of design process [11]. NVH (Noise, Vibration and Harshness) in the automotive industries is one of the most challenging components in design process since it is directly linked to the passenger satisfaction [12]. There are a lot of complaints from passengers due to the interior noise and vibrations of a vehicle cabin [13]. Generated noise are mostly due to seat structure vibrations and structural BSR (Buzz, Squeak and Rattle) [7], BIW mode interaction [9] and transmitted road disturbance to the automotive body structure through wheel [13] and suspension mechanism [14]. CAE provides an important tool to design the dynamics of the system as close as possible to a desired response [13, 15-16]. Here our focus is on the automotive wheel structure as one of the important sources in the generated noise. A finite element (FE) model of the automotive wheel (developed in Hyperworks) is employed [13] to do a frequency response analysis (FRF) (via MDNastran software) and tune the resonance and anti-resonance frequencies of the wheel. Tuning resonance and anti-resonance frequencies is conducted via some structural modifications to prevent mode interaction and reduce the generated noise. 2. Modeling First a finite element model of the wheel is developed in Hyperworks [13]. All the components (rim, tire and connections) are modeled separately and the assembled to each other. In order to characterize dynamics of the system Frequency Response Function (FRF) has been used. Frequency response is the quantitative measure of the output to the input as Eq. (1). Input force is an impulsive force (containing all frequencies) and acceleration is measured in radial and axial direction. Here we have focused on the ratio of magnitude of the output to that of input. Frequency Response Function (FRF) = magnitude of the out put magnitude of the input = Accelartion Force (1) American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 39, No 1, pp 30-37 32 Figure 1: Finite element of the whole automotive wheel [13] 3. Results Figure 2 illustrates the output acceleration of the rim measured in radial direction versus frequencies up to 1600 Hz. Input force is an impulsive force which swipes all the frequencies. Peaks show the resonance frequencies and relative minimum values show the anti-resonances or nodes which would be stationary points of the structure in the dynamic domain. Table 1 is the values of resonance frequencies. Note that since we have measured the acceleration in radial direction, some frequencies cannot be seen in Table 1 [13]. This is due to the fact that lateral mode shapes (out of plane) do not get activated and measured in radial direction. Figure 2: Frequency response function (FRF) for the rim American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 39, No 1, pp 30-37 33 Table 3: Mode shape and resonance frequencies of the rim [13]. Mode Number Mode Type Frequency (Hz) 7th mode Bending mode 245 8th mode Torsion mode 257 9th mode First triangle mode 685 10th mode Second triangle mode 693 11th mode First rectangular mode 1152 12th mode Second rectangular mode 1178 13th mode Axial mode 1370 High frequency modes - - In the next step, the whole wheel (Tire and rim) gets activated with an impulse force and the response has been measured in radial direction. Figure 3 shows the acceleration versus frequency for the wheel structure. Peaks values demonstrate the resonance frequencies. Table 2 is the values for resonance frequencies of the wheel and also mode shapes. Figure 3: Frequency response function of the rim in radial direction. Table 5: Mode shapes and resonance frequencies of the modeled wheel [13]. Mode number Shape of the mode Resonance Frequency (Hz) 7th mode Axial mode 68 8th mode Twisting mode 93 9th mode Elliptical mode 124 10th mode Triangular mode 152 11th mode Rectangular mode 190 12th mode Pentagonal mode 213 13th mode Hexagonal mode 234 American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 39, No 1, pp 30-37 34 Figure 4: FRF in lateral direction Figure 4 shows the frequency response function of the wheel structure when it is excited in lateral direction. As it was expected, some modes have not been activated when there is a lateral excitation. The modes that have radial motions are missed in lateral excitation. Therefore, in a comprehensive frequency response analysis, a typical structure should be excite in different direction to gain all dynamical properties of the system. 4. Wheel Structure Optimization [18, 19]. As it is shown in Figure 3, the wheel has two resonance frequencies in 213 and 234 Hz. Now CAE methodology can be employed to move resonance frequencies away from the zone of 200 to 250 Hz. Our proposed method is to use o lateral elements as shown in Fig. 5 to reduce the stiffness of the structure and therefore resonance frequencies take place earlier. Fig. 6 illustrates the frequency response function of the wheel structure after modifications. It can be seen that after modification 6th resonance frequency would be lower than 200 Hz and 7th resonance frequency would increase to more than 250 Hz. There is just one local mode after modification and it would not be dangerous since it is not a main mode shape. Figure 5: Modification of the wheel structure American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 39, No 1, pp 30-37 35 It has been shown that tire air has two resonance frequencies less than 500 Hz [17] and the first one happens between 200 to 250 Hz which is significant. Previous studies have shown that when the resonance frequencies of the tire wheel and tire air are close to each other, resonance happens and interior noise cabin will be increased [18, 19]. As it Figure 6: FRF of the whole wheel structure after modification. 5. Conclusion In conclusion, the pneumatic tire forms a vital component of a road vehicle as it interacts with the road to produce the forces necessary for support and movement of the vehicle. Tire as one of the most important components of vehicles requires fulfilling a fundamental set of functions such as: provide load-carrying capacity, cushioning and dampening, stability, reducing noise and vibration, transmit driving and braking torque, resist abrasion, generate steering response, have low rolling resistance, durability throughout the American Scientific Research Journal for Engineering, Technology, and Sciences (ASRJETS) (2018) Volume 39, No 1, pp 30-37 36 expected life span. Therefore NVH performance of the wheel (including tire and rim) is important to be analyzed. Here, as the first step, a finite element model of the wheel has been derived using Hyperworks software. Then, dynamic analysis of the structure is conducted to derive mode shapes and resonance frequencies. 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