Cetin Yilmaz

INERTIAL AMPLIFICATION INDUCED PHONONIC BAND GAPS IN SC AND BCC LATTICES

This paper investigates effects of inertial amplification mechanisms on the phononic band structure of infinitely periodic simple cubic (SC) and body centered cubic (BCC) lattices. First, these three-dimensional lattices are formed using mass and spring elements. Then, dispersion curves of these lattices are obtained. Consequently, inertial amplification mechanisms are embedded around each spring in these lattices and their dispersion curves are calculated again. When compared to the cases in which inertial amplification was not used, phononic band gaps are obtained at much lower frequencies.Copyright

The effect of the folding rear-seat aperture in the acoustic response of a sedan car

The coupled vibro-acoustic response of a sedan is analysed, and the effect of the folding rear-seat aperture is studied. First, a simplified model of an acoustic cavity that consists of two adjacent boxes connected by an aperture is modelled. An analytical solution is proposed to calculate the acoustic eigenfrequencies of the simplified model. Then, the uncoupled acoustic eigenfrequencies of the actual cavity (where the trunk cavity and the cabin cavity are connected through an aperture) are computed. It is shown that the planar acoustic eigenfrequencies of the sedan can be calculated approximately using the analytical solution proposed. To clarify the effect of the folding rear-seat aperture further, the coupled vibro-acoustic response of the sedan is analysed using different case studies. It is observed that the booming noise is highly correlated with the calculated uncoupled planar acoustic eigenfrequencies.

Reducing Tire-Induced Noise and Vibration2

Abstract Tire-induced noise and vibration spans a wide range of frequencies, depending on, among other attributes, tread design, road surface, and vehicle speed. Vehicle designers are faced with th...

Reducing force transmission through exhaust mounts of a vehicle

Under the excitation of an engine, an exhaust system vibrates, and the vibrational energy is transmitted to the vehicle body through the exhaust mounts. The transmitted energy makes contribution to the vibration of the body, which in turn increases the overall vehicle noise level. Noise contributed by the exhaust can be eliminated up to a certain level by reducing the force transmitted through the exhaust mounts. In this study, an objective function, which represents the force transmitted through the exhaust mounts, is defined. The aim is to minimise the transmitted force to achieve better vibration isolation. First, structural dynamic analysis of the vehicle exhaust system is evaluated using computational and experimental procedures. The finite element model of the exhaust system is complemented and validated by following an experimental modal analysis procedure. In the correlation procedure, it is observed that boundary conditions of the exhaust system have significant effects on the results. Hence, the definitions and the assumptions of boundary conditions are studied in detail to achieve a better correlation between the computational and the experimental models. Then, the validated computational model is used for optimisation studies. Moreover, a mass is attached to the exhaust system to reduce the forces transmitted to the vehicle body. For the optimisation problem, the stiffness and the location of exhaust mounts and the weight and the location of hanging mass are defined as design variables. Significant improvements are achieved compared to the initial design.

Topologically optimised flexure hinge based XY stage

The purpose of this study is to develop a millimeter scale two degree of freedom planar actuation mechanism (XY stage) with flexure hinges that can generate micrometer scale motion at high frequencies. To amplify the micro scale motion in X and Y directions, two identical levers are used. According to the analytical and computational results, a prototype is developed for validation. Piezoelectric actuators are used in the system because of their compactness and large force capacity. The levers in the XY stage are topologically optimized so that the first resonance frequency of the system is maximized, which enlarges the operation range of the system.

Fabrication of steel displacement amplifiers integrated to microfluidic channels

A flexure mechanism consisting of steel thin film displacement amplifier and trapping fingers inside a microfluidic channel actuated by hand or a simple mechanical tool is realized for biology and cell analysis. Unlike pneumatic, electromagnetic, electrostatic, ultrasonic or other actuation methods in microfluidic devices, this mechanism does not require any power supply or large actuators for operation. This steel mechanism is fabricated via electrochemical and wet etching of 50-μm-thick stainless steel film. It is integrated to a microfluidic channel formed between 125-μm-thick polyethylene naphthalate (PEN) films for the first time in this work.

Active Noise Control in a Duct With Flow

Active noise control in a one dimensional acoustic duct, in which fluid medium inside the duct has a mean flow velocity, is studied. The acoustic duct model with general boundary conditions is solved in Laplace domain and infinite dimensional system transfer functions are obtained. For controller designs, appropriate microphone, and noise canceling source locations are determined. Low order finite dimensional transfer function approximations of actual system transfer functions are obtained. It is found that, in a selected frequency range, approximations represent actual system in a satisfactory way. By using approximated system transfer functions, finite dimensional, low order, optimal H2 and H1 controllers are synthesized via linear matrix inequalities method. Closed loop frequency response and time domain simulations show that the controllers successfully suppress unwanted sound, which propagates along the duct. [DOI: 10.1115/1.4026410]