A new type of microperforated panel absorber (MPA) that has holes of multiple sizes instead of uniform size is experimentally investigated. The objective of this research is to obtain a wide band sound absorber that is thin, durable, clean, and healthy. The first step of this research is to investigate the performance of MPA having two different sizes and the same numbers of holes. The investigation is then extended to a combination of three and four different sizes of holes with various spatial arrangements and various densities or percentages of each size of holes on panels. The hole diameters vary between 0.4 mm and 1 mm and the cavity depths vary between 10 mm and 15 mm. The results show that a multi-size MPA enhances the absorption rate and widens the effective frequency band. This study also proves that a multi-size MPA when compared with a uniform size MPA has better sound absorption characteristics with respect to the absorber thickness and absorption bandwidth. These results make it possible to build thin, single layer sound absorbers that are effective in wide frequency bands and have the advantage of being tunable.
This research was conducted to analyze the alkali treatment in improving the quality of coir fiber. Study coir fiber done by specifying the physical characteristics and methods of making specimen, mechanical treatment and testing the tensile strength of single fiber. Determine the characteristics physical of the fiber is done by observing and measuring the diameter of the fiber directly, testing the density and moisture content testing. Chemical treatment is done by the method of alkali. Single coir fibers for the treatment carried out using NaOH 5%. Alkali solution set with a variation of the submersion of 0, 1, 2, 3, and 4 hours. Single fiber tensile strength testing is done according to standard ASTM C1557-2003. Tensile tests showed that an alkali treatment can increase the tensile strength of single fiber of 27.9% in immersion lye for 2 hours compared without soaking and increase the elongation of over 20% compared without soaking.
A theoretical method is presented for calculating the absorption coefficient of a multi-leaf microperforated panel absorber. In this work, the possibility of using multi-leaf type of microperforated panels without solid backing panel is investigated. The number of panels varies from 2 to n (≥2). The sound absorption coefficient is calculated based on electro-acoustic analogy by taking the sound transmission coefficient due to the absence of solid backing panel into consideration. The optimum performance of leaf microperforated panel absorber is also investigated as the function with respect to the design parameters such as perforation ratio, diameter of holes and distance between panels. The numerical results show that the configuration of leaf of microperforated panels can increase absorption coefficient at low frequency region. This fact will give an advantage to the multi-leaf microperforated panel over conventional microperforated panel arrangements. That is, to solve the problem of quite narrow frequency band absorption effect, especially in mid-high frequency region corresponding to their resonant frequencies, that the conventional microperforated panel arrangements inherently possess. Experiment results are also presented that show a reasonable agreement with the theoretical results. Some feasible application ideas of the multi-leaf type of arrangement are also presented.
The goal of this research was to gather knowledge and to analyze the problem of excessive vibration level of Gas Turbine Generator (GTG) 100 MW system installed in cogeneration power plant in Sumatra Island, Indonesia which supports one of biggest oil and gas industries in Indonesia. The case research related to vibration problem were presented to diagnosis the main causes of excessive vibration that occur in the gas turbine generator during operation. Vibration analysis is one of the most important activities in predictive maintenance. Vibration monitoring system and machinery diagnostic technical specification are presented. The vibration data of this research were collected using online vibration monitoring system Bently Nevada 3500 series and system 1® display software at different bearing locations during transient (shutdown & start-up and steady state (on-line) condition. Assessment on overall vibration levels shall refer to Original Equipment Manufacturer (OEM) alert & danger set points, as well as relevant ISO 20816-2 standard. Finally, recommendation of reducing excessive vibration level is provided to ensure safe and reliable operation of the GTG unit.
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