Yeon June Kang

Evaluation of Optical Properties for Development of Ultrahigh-Resolution Flexible Contact Endoscope

In this study, a new flexible contact endoscope that is similar to a fiber-optic ultrathin endoscope is examined. Using a new optical design with a 0.23 pitch gradient index lens and an ultrathin fiber-optic image guide, we have obtained 228 line pairs/mm ultrahigh-resolution images. The resolution and magnification of the obtained images are measured and analyzed. Also, the relationship between magnification and the working distance from the target to the gradient index (GRIN) lens using GRIN lenses of different pitch lengths is determined. Finally, we have taken an image of red blood corpuscles of 6–9 µm average size.

A methodolgy for evaluating the structure-borne road noise prior to a prototype vehicle using direct force measured on a suspension rig

Numerous previous studies have been conducted on quantifying road noise through transfer path analysis (TPA) using the matrix inversion and the dynamic stiffness methods. However, the matrix inversion method is a calculation that always contains error, even when treated with the best condition number found by trial and error iteration to match the calculation SPL (sound pressure level) to measured SPL. Furthermore, the caveat of the dynamic stiffness method is that it requires accurate dynamic stiffness value up to the frequency range of interest, which, in reality, is rarely available and is challenging to obtain. Therefore, TPA using these two methods is only possible when a complete vehicle is available. For the sake of cost and time reduction, circumventing these limitations is crucial within the vehicle production period. The main focus of the present study is to directly obtain the operational forces at the suspension mounting points neglecting the effect of the vehicle body through a special suspension rig. The suspension rig is verified through a comparative analysis with the actual baseline vehicle measurement up to 250 Hz. In addition, an example approach for finding suspensions NVH performance improving factor using the rig benchmarking technique is introduced.

Estimation of body input force transmission change due to parts’ modification using the impedance method under rolling excitation

This study aims to estimate the change in suspension to body input force transmission due to the softening of the connecting elastomer under rolling excitation. In this respect, the suspension coupled to a vehicle body via an elastomer bushing is modeled using point impedance. A numerical study is performed for achievable force reduction due to a softened bush under the influence of different impedance combinations for the suspension and the vehicle body. Following a numerical study, the proposed model is validated through empirical testing of McPherson strut type suspension in the lateral arm Y direction and multilink type rear suspension in the front mount X direction, which represent extremely stiff and extremely soft coupling cases for the suspension type, respectively. Due to the difficulties in measuring road-induced operational forces within an actual vehicle, a validation test is performed using a previously developed rig that enables direct measurement of the force without modifying the structure of the suspension. Additionally, the rig-measured force, which is potentially misleading due to the large deviation in stiffness between the rig and an actual vehicle, is investigated under varying combinations of suspension and bush stiffness.

A validation study of the detachable shell dyno excitation method for structure-borne road noise evaluation

Road-induced noise within a vehicle is always a relative quantity of its excitation. Therefore, automotive NVH engineers strive to keep the excitation as precise and reproducible as possible when it comes to road noise measurement. To achieve this purpose, a dyno excitation method using precision CNC-milled detachable shell is proposed and its proper operational condition for road noise evaluation is investigated in this article. The proposed dyno excitation method not only enables a highly reproducible matching excitation to the actual proving ground excitation up to 500 Hz, but also circumvents typical unfixed phase relation of the road noise input problem by applying symmetric excitation surfaces between the left and right wheel about the longitudinal axis. Additionally, the ini¬,uence of the roller diameters on this excitation method is experimentally examined.