Fabricating Process and Mechanical Properties of Elastomeric Mount

This paper presents the fabricating process of elastromeric mount and their mechanical properties results. Four types of rubber were used to fabricate elastromeric mounts. They are from types of natural rubber (SMR CV-60), synthetic rubber, ekoprena and pureprena. SMR CV-60 is conventional rubber normal grades products from natural rubber. Synthetic rubber is rubber products from petroleum. Ekoprena and pureprena are advance rubber products from natural rubber. Before fabricate elastromeric mount, the rubber compound is designed based on actual mount such as shear modulus, hardness and static stiffness. A few processes have done to make the elastomeric mount such preparation of raw materils, mixing and curring process. Cured compound rubber and elastromeric mount were tested in the laboratory in order to determine their mechanical properties such as hardness, tensile strenght, compression set, static stiffness and dynamic stiffness. The results from static tests showed that elastomeric mount from SMR CV-60 rubber, ekoprena and purepena closed to actual mount except elastomeric mount from synthetic rubber

Investigation on Natural Waste Fibers from Dried Paddy Straw as a Sustainable Acoustic Absorber

The use of synthetic materials as acoustic absorbers is still applied extensively in building industry. These non-biodegradable materials do not only cause pollution to the environment, but also contribute significantly in increasing the CO2 causing the effect of global warming. Therefore researchers have now driven their attentions to find sustainable and eco-friendly materials to be an alternative sound absorber. This paper discusses the use of natural fibers from dried paddy straw as a fibrous acoustic material. Since this is one of common natural waste materials found across South East Asia, the usage will also minimize the production cost. A panel sound absorber from paddy straw is fabricated and its acoustic properties are investigated through experiment. Good acoustic performance is found particularly above 2000 Hz and is comparable against that from the classical synthetic absorber

THE CONTRIBUTION OF MOMENT EXCITATION ON THE UNCERTAINTY IN THE VIBRATION INPUT POWER TO A STRUCTURE

In structural dynamic systems, there is inevitable uncertainty in the input power from a source to a receiver. Apart from the non-deterministic properties of the vibration source and receiver, there is also uncertainty in the excitation. This comes from the uncertainty of the forcing location on the receiver, its relative phase, its amplitude distribution at multiple contact points and also the spatial separation of these points. Moreover, the uncertainty becomes more significant as only translational force is considered while the moment excitation is often excluded in the calculation. This paper investigates the effect of moment excitation on the uncertainty in the vibration input power to a structure. Quantification of the uncertainty using possibilistic and probabilistic approaches are made. These provide the maximum and minimum bounds and the statistics of the input power, respectively. Expressions for the bounds, mean and variance are presented as well as the frequency band-averaged results

Experimental Investigation on the Effect of Liquid Fill Level in a Container to Liquid Sloshing

Liquid sloshing is any motion of free liquid surface inside its container. Sloshing may generate hydrodynamics loads that can be dangerous to structural integrity and stability of moving containers. In this study, liquid sloshing in containers with 50% and 90% fill level were investigated. The containers with liquid inside were excited sinusoidally by using an electrodynamics shaker while the free liquid surface level change was captured by using high speed camera. The free liquid surface amplitude difference obtained for containers with 50% and 90% fill level were compared. Results show that sloshing is more vigorous in containers with 50% fill level compared to 90% fill level. Liquid transportation should be done at an almost full fill level to minimize sloshing

Dried Paddy Straw Fibers as an Acoustic Absorber: A Preliminary Study

The use of synthetic materials as acoustic absorbers is still applied extensively in building industry. These non-biodegradable materials do not only cause pollution to the environment, but also contribute significantly in increasing the CO2 causing the effect of global warming. Therefore researchers have now driven their attentions to find sustainable and eco-friendly materials to be an alternative sound absorber. This paper discusses the use of natural fibers from dried paddy straw as a fibrous acoustic material. Since this is one of common natural waste materials found across South East Asia, the usage will also minimize the production cost. A panel sound absorber from paddy straw is fabricated and its acoustic properties are investigated through experiment. Good acoustic performance is obtained and is comparable against that from the classical synthetic absorber

On a Simple Technique to Measure the Airborne Noise in a Motor Vehicle using Source Substitution

From various methods of measuring noise of a motor vehicle, there is a lack application on how to obtain the ‘pure’ airborne noise in a vehicle cabin as an important measure to improve the noise control treatment. This project proposes a technique in separating airborne and structure-borne noise in a motor vehicle using sound source substitution method. A cone loudspeaker was used as the substitution source and the overall transmission loss was measured to achieve this purpose. It is found that the structure-borne noise is dominant at low frequencies and airborne noise dominates at high frequency. The intersection frequency between the two is roughly 400 Hz

Radiation efficiency of unbaffled and perforated plates near a rigid reflecting surface

The accurate prediction of sound radiation from plate-like structures remains a challenging problem. Although the case of a plate set in a rigid baffle can be solved analytically, when the plate radiates sound into free space the problem is more difficult to solve; nevertheless, several approaches have been proposed to determine the sound radiation from an unbaffled plate. The present study extends the consideration to the situation of an unbaffled plate which is located close to a rigid reflecting surface. For this purpose, Laulagnet’s model for the radiation efficiency of an unbaffled plate is extended by modifying the Green’s function to include an image source due to the reflecting surface. The results show that, depending on the distance between the plate and the rigid surface, the radiation efficiency is considerably reduced at low frequencies. Additional reduction of sound radiation can be achieved by introducing perforation to the plate. However, at higher frequencies, the radiation efficiency is amplified relative to that for the plate in the absence of the rigid surface, both with and without perforation. These results have also been validated experimentally

Determination of Vibration Strength of a Small Structure-Borne Source Using a High Mobility Reception Plate

This paper presents the characterization of vibration strength obtained from reception plate method by applying the mobility concepts. It describes a laboratory-based measurement procedure, which determines the strength of a vibration source in terms of the total squared free velocity of the source. The source used in the experiment is the small electric fan motor installed on high mobility aluminum panel in order to neglect the influence of the source mobility. The complexity of the mobilities at the contact points are reduced using the single value of effective mobility. The aim is to validate the data obtained from the reception plate method with one from the direct measurement. A good agreement is found between the two results

Application of Micro-perforated Panel (MPP) in a Vehicle Vabin: Overcoming the ‘Mass-Air-Mass’ Resonance

One of the most considerable aspects of a vehicle design judged by the customers is the noise level inside the cabin. The conventional method is the use of absorbent materials as the noise absorber e.g. foam and other porous materials. These materials are usually made from synthetic and are therefore not environmentally friendly. Moreover, they can be easily dirty or damage and give bad odour due to smoke or moist. Since the microperforated panel (MPP) has been investigated to have a good performance as the sound absorber, there is a feasibility to implement such a panel inside a vehicle cabin. The MPP which is constructed from a solid panel will provide a hygienic and a non-abrasive material. Its optically attractive surface will also enhance the art in the cabin interior. This paper is the preliminary study to investigate the performance of a double-leaf solid and microperforated partition (SMPP) in terms of its sound transmission loss (STL). The mathematical model for the STL is derived. The result shows that the performance substantially improves at the troublesome frequency the so-called mass-air-mass resonance which occurs in the conventional double-leaf partition. This is important particularly for the noise source predominant at low frequencies. This can also be controlled by tuning the hole size and number as well as the air gap between the panels

Employing the micro-perforated panel in the vehicle cabin: Is this possible?

The micro-perforated panel (MPP) has been developed as a sound absorber which replaces the classical synthetic fibrous material. Known as the ‘hygenic’ acoustic material, its optical surface also makes it attractive enhancing the art of a room interior. This paper discusses the possibility to apply the MPP which substitutes the solid panel at the inner side on the double-leaf partition of vehicle structures to control sound absorption in the vehicle cabin. Having known as an important part of modern lightweight structures such as aircraft fuselages, train walls, car doors, windows and lightweight partition walls in buildings, the double-leaf partition has poor noise insulation at low frequencies due to the coupling between the partition masses and the air between them. The presence of the micro holes adds additional damping which breaches this coupling and increases the sound transmission loss. This can be controlled by tuning the properties of the MPP, i.e. the hole diameter, the perforation ratio and the cavity gap. The solid-MPP (SMPP) system therefore provides double functions simulatenously, i.e. as sound absorber and noise barrier. Derivation of the mathematical model for the transmission loss of the SMPP subjected to oblique and diffuse field incidence of acoustic loading is presented