Kesan lapisan berliang dan nisbah keluasan plat berlubang terhadap ciri akustik serabut sabut kelapa sebagai bahan penyerap bunyi

Penyelidikan ini dilakukan untuk mengkaji ciri akustik serabut sabut kelapa yang berpotensi digunakan sebagai bahan penyerap bunyi. Untuk meningkatkan ciri akustik serabut sabut kelapa pada frekuensi rendah, lapisan berliang digunakan di bahagian depan atau belakang bertujuan untuk meningkatkan nilai galangan permukaan. Bahan selanjutnya dilapisi dengan plat berlubang dengan nisbah keluasan yang berbeza. Sampel diuji mengikut piawaian antarabangsa ASTM E 1050-98 untuk menentukan pekali penyerapan bunyi. Daripada hasil uji kaji, plat 1 mm berlubang yang diperbuat daripada kepingan aluminium yang melapisi serabut sabut kelapa, didapati bahawa nilai maksimum pekali penyerapan bunyi berada pada frekuensi antara 2750 Hz hingga 2825 Hz iaitu dengan nilai 0.97. Nilai nisbah keluasan plat berlubang memberikan pengaruh penurunan pekali penyerapan bunyi pada frekuensi tinggi. Penurunan nilai pekali penyerapan bunyi terjadi apabila plat berlubang mempunyai nilai nisbah keluasan di bawah 0.22. Akan tetapi, penggunaan plat berlubang boleh meningkatkan prestasi penyerapan bunyi serabut sabut kelapa pada frekuensi rendah. Kesepakatan yang baik diperoleh daripada keputusan uji kaji dan analisis dengan pendekatan rangkaian elektrik setara yang digunakan untuk menghitung nilai pekali penyerapan bunyi. Ini menunjukkan bahawa pendekatan rangkaian elektrik setara boleh digunakan untuk merancang dan mengoptimumkan ciri akustik serabut sabut sebagai bahan penyerap buny

A machine component monitoring system using audio acoustic signals.

The main objective of this study is to develop a new type of machine-component monitoring system which is non-intrusive and non-contact in nature. Moreover, the design of the system to be developed must be robust enough for it to be implemented in an industrial environment. Therefore, this study was initiated to overcome some of the problems that were encountered using the well-established vibration method. For instance, vibration measurement of a machine component is dependent on the quality of contact between an accelerometer with a vibrating surface. Vibration measurement of a machine component is also affected by the vibration of other machine components near the vicinity, in addition to the presence of power-supply-line frequency and its harmonics. On the other hand, the application of a desirable non-intrusive and a non-contact nature of sound pressure measurement method is difficult to carry out if the background sound level is high. This is because sound pressure measurement is dependent on the characteristics of a sound field where a measurement is carried out. For these reasons, air-particle acceleration signals were utilised in the study. Air-particle acceleration is a vector quantity and measurement of vector property can improve the signal-to-noise ratio of the measured signal, even in a noisy environment.A dedicated test rig was constructed to carry out the experiments and to test the hypothesis. Rolling element bearings were used for the experiment because of the many different types of defect that can develop in them, such as inner race, rolling element and outer race defects. Moreover, the dynamic behaviour of bearings are well understood and can be compared with experimental results obtained from the study. Several different methods of analysis were used in the study including statistical, spectral, cepstral and wavelet transform methods. The results from using air-particle acceleration signals were compared with results obtained from utilising sound pressure and vibration signals. These results showed that the performance from using air-particle acceleration signals were superior to the performance from using sound pressure signals. Results from the analysis of air-particle acceleration signals can clearly indicate the presence of a defective component in the test-bearing. This is so even when the overall background noise was 14dB higher than the overall noise level emitted by the test-bearing. Moreover, the sensitivity of the measurement of air-particle acceleration signal to indicate the presence of a defective bearing was similar to the sensitivity when using conventional vibration equipment.Applications of artificial neural networks were also included for automatic identification of defect signals. The multilayer perceptron network was chosen and tested to classify the bearing signals because of the suitability of this type of network to be used for pattern recognition. Finally, a new type of machine-component monitoring system using air-particle acceleration signal was successfully developed and tested in industry

Application of Acoustic Emission Technique to Monitor the Viscosity of Single Grade Diesel Engine Lubricant Oil.

This paper presents an investigation of the capability of the acoustic emission (AE) technology in the processes of monitoring and detecting the variation of diesel engine lubricant viscosity via in-situ operation. The investigations were conducted on an 8.5-hp single cylinder of four strokes with a water cooling diesel engine. One single grade engine lubricant oil condition has been put to the test; namely, SAE 40. The lubrication condition in the diesel engine was successfully monitored based on the AE signatures generated by the interaction between the piston surface and the layer of the lubricant during the time that the engine was in operation. The generated AE signatures were captured using an AE wide band transducer that was bonded outside the engine block and located at the lower part of the bottom dead centre (BDC). The captured waveform signatures were then analysed using the MATLAB software. The results of the experimental works show that the statistical analysis parameters including the root-mean-square (rms), maximum amplitude and AE energy values are capable of distinguishing the variant of the viscosity. The AE technique can assist the owner of the diesel engine in determining the diesel engine lubricant oil condition before replacing it

The Design And Simulation Of Flow Mode Electrorheological Damper

Electrorheological (ER) Damper Is A Damper That Utilizes Electrorheological Fluid As The Working Fluid. By Changing The Strength Of Applied Electric Field To The Fluid, The Flow Resistance Of The Fluid Changes And Hence The Damping Characteristic Could Be Adjusted. This Paper Provides Theoretical Formulation To Calculate The Damping Constant Of Semi-Active Flow Mode ER Damper. The Formula Is Developed By Analyzing Fluid Velocity Profile That Flows In Electrode Gap. From The Simulation, It Shows That Electric Field Strength Gives Severe Effect To The Damping Level Of The Damper. Without Applying Electric Field, A Reduction On The Gap Of Electrode From 3 To 1 Mm Will Increase The Damping Constant Value By A Factor Of Only 27, While With A 3 Kvmm–1 Electric Field Being Applied, The Increase Is By A Factor Of 595

Hubungan kelikatan minyak enjin terhadap usia guna serta suhu

Kelikatan minyak enjin bergred tunggal mengalami perubahan apabila berlakunya perubahan pada suhu dan tekanan. Namun begitu, secara realiti kelikatan minyak enjin juga mengalami perubahan terhadap usia guna. Oleh itu, kajian ini memperkenalkan satu hubungan kelikatan minyak enjin terhadap perubahan suhu serta usia guna. Hubungan ini berasaskan kepada persamaan matematik empirik yang melibatkan teori pelincir Newtonan dan bukan Newtonan. Hubungan yang baru ini dikenali sebagai model kelikatan matematik (ηmath). Dalam model ini, kelikatan minyak enjin dipengaruh oleh dua faktor iaitu faktor suhu (ks) dan faktor masa (km). Nilai kedua-dua faktor ini bergantung kepada formula bahan tambah minyak enjin tersebut. Analisis reologi meter likat telah digunakan untuk mendapatkan nilai kedua-dua faktor ini. Hasil kajian menunjukkan kelikatan minyak enjin mengalami penurunan apabila usia guna meningkat. Ini dibuktikan melalui model kelikatan matematik (ηmath) dan juga analisis reologi meter likat

Utilisation of indigenous resources for acoustical applications / Valliyappan D. Natarajan and Mohd Jailani Mohd Nor

This paper presents the development of novel sound absorbing materials based on natural indigenous resources particularly that of fibrous nature. Coir fiber in the form of stitched mat, which is porous and fuzzy, was utilized as the main sound absorbing component. Composite panels support the coir mat laterally. The panels were made from oil palm frond fibre (OPF) and rice husk (RH) bounded in either unsaturated polyester (UP) or polypropylene (PP) matrix. The acoustical properties of the composite structures were determined in an impedance tube based on the two-microphone transfer function method in the frequency range of 125Hz to 4000Hz. Overall results indicate that the coir mat-composite panel structure is a potential absorbent-barrier with not less than 50% of sound absorption. General improvements were achieved in the absorption properties over the entire frequency range using the more flexible RH-PP panel while superior low frequency absorption was attained using panel made of 50% volume fraction of OPF I RH mixture in UP. The product of this research offers exceptional cost-performance balance to the existing, relatively expensive noise control industry while reducing waste disposal problems in the plantation industry

EVALUATION OF SEAT VIBRATION SOURCES IN DRIVING CONDITION USING SPECTRAL ANALYSIS

Seat vibration is one of the major causes of discomfort in moving vehicle. Tyre, engine, drivetrain and aerodynamic forces excite the cabin and interior through various pathways. In this paper, the contributions of tyre and engine vibration to seat excitations are studied. Virtual Source Analysis (VSA) is implemented to decompose the source signals into incoherent phenomena. Studying these phenomena (virtual sources) shows the amount and frequency bands that physical sources affect the seat vibration as the response channel. Experiment is conducted while riding on smooth and bumpy roads. Road roughness is characterized using International Roughness Index (IRI). VSA technique approve that tyre is the main source of seat vibration for the moving vehicle. Seat vibration has significant values below 400 Hz and tyre is found to be the dominant source of excitations for both smooth and bumpy roads. For smooth road, strong engine harmonics below 200 Hz also has some involvements. But in bumpy road, tyre vibration rise up and become the dominant broadband source of excitations. Tyre damper and engine mount Frequency Response Function (FRF) analysis show that these parts are designed to be highly efficient below 1400 Hz and 200 Hz, respectively. These ranges are identical with those that were found as the critical operational frequency spans in VSA

A preliminary study of sound absorption using multi-layer coconut coir fibers

Acoustic treatment using absorbing materials are widely used to reduce reverberation properties of closed spaces and to increase the transmission loss properties of multi-layer sound absorption panels. Natural fibers such as coconut coir fiber have high potential to be used as acoustic materials. As the natural fibers are agriculture waste, manufacturing natural product is therefore an economic and interesting option. This paper discusses the sound absorption using multi-layer coconut fiber as absorbing material component. The effect of micro-perforated plate and air-spaces layers towards the sound absorption of the multi-layer construction was also investigated in this paper. Acoustic absorption coefficient is the main parameter to be estimated in this research. Computer simulation using WinFLAGTM program was done to calculate the acoustic absorption coefficients. Simulation indicated that multi-layer coconut coir fibers and air-spaces could increase the acoustic absorption coefficient. All simulation results obtained are based on diffused sound incidence situation