Journal of Engineering and Technological Sciences
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Noise Attenuation of a Duct-resonator System Using Coupled Helmholtz Resonator - Thin Flexible Structures
Get PDFSeveral studies have been devoted to increasing the attenuation performance of the Helmholtz resonator (HR). One way is by periodic coupling of HRs in a ducting system. In this study, we propose a different approach, where a membrane (or a thin flexible structure in general) is added to the air cavity of a periodic HR array in order to further enhance the attenuation by utilizing the resonance effect of the membrane. It is expected that three attenuation mechanisms will exist in the system that can enhance the overall attenuation, i.e. the resonance mechanism of the HR, the Bragg reflection of the periodic system, and the resonance mechanism of the membrane or thin flexible structure. This study found that the proposed system yields two adjacent attenuation peaks, related to the HR and the membrane respectively. Moreover, extension of the attenuation bandwidth was also observed as a result of the periodic arrangement of HRs. With the same HR parameters, the peak attenuation by the membrane is tunable by changing its material properties. However, such a system does not always produce a wider attenuation bandwidth; the resonance bandwidths of both mechanisms must overlap
Application of Nonlinear Finite Element Analysis on Shear-Critical Reinforced Concrete Beams
Get PDFThis paper presents the application of a smeared fixed crack approach for nonlinear finite element analysis of shear-critical reinforced concrete beams. The experimental data was adopted from tests undertaken on twelve reinforced concrete beams by Bresler and Scordelis in 1963, and from duplicate tests undertaken by Vecchio and Shim in 2004. To this end, all beams were modeled in 3D using the software package ATENA-GiD. In the modeling, the nonlinear behaviors of the concrete were represented by fracture-plastic constitutive models, which were formulated within the smeared crack and crack/crush band approaches. The applicability of nonlinear analysis was demonstrated through accurate simulations of the full load-deflection responses, underlying mechanisms, crack patterns, and failure modes of all 24 beams. Detailed documentation of the results is presented to demonstrate the potential and practical value of nonlinear finite element analysis in providing an informed assessment of the safety and performance of reinforced concrete structures
An Analytical and Experimental Evaluation of a Heat Sink Under Constant Heat Flow and Forced Convection Heat Transfer
Get PDFIn this study, the exact transient differential equation was used to calculate the convection heat loss in a heat sink with a rectangular cross section fin. The result of the analytic solution was compared to the result from experiments conducted on a standard heat sink. The experiments were performed at a constant heat flow of 9000 W/m2 and a low airflow rate ranging from 12 to 100 cm3/s in seven steps. The comparative results showed that while there was good agreement between the experimental result and the exact solution, the average error ratio increased with an increase of the airflow rate. However, the maximum average error ratio between the experimental result and the exact solution did not exceed 6.4%. The maximum temperature distribution in the heat sink was obtained at a time of 900 s in all experiments
The Effect of Thermal Ageing on the Mechanical Properties of Natural Rubber-based Compounds Used for Rubber Bearings
Get PDFMolecular changes due to high temperatures, sunlight, and oxygen, deteriorate the physical properties of rubber compounds, yielding additional crosslinks and molecular chain breakdown. Since oxidative degradation is the most important factor that determines the durability of rubber components, this study evaluated the mechanical behavior of rubber compounds exposed to accelerated thermal ageing. Therefore, three carbon black-reinforced natural rubber-based compounds typically used for rubber bearings were exposed to thermal oxidation and their mechanical properties under typical loading states were assessed through standardized tests. Significant differences were found due to thermal ageing in the compressive modulus, compression set, and creep compliance in compression, exhibiting a stiffening effect caused by additional crosslinks. However, no significant differences were observed in hardness, which is a superficial measurement and a typical test in the rubber industry to characterize rubber compounds. Therefore, the assessment of ageing in rubber bearings should not be limited to a hardness test, which is required in design standards but also addresses compressive, cyclic, and transient tests. The results obtained in this study can be considered in the design process of rubber bearings by limiting the allowable compressive stress and creep deflection due to ageing effects
Bayah Natural Zeolites to Upgrade the Quality of Bio Crude Oil from Empty Fruit Bunch Pyrolysis
Get PDFCurrently, the fuel oil for transportation and industry is produced mostly from fossil fuels. Because fossil fuels are a limited resource, biomass could be an alternative resource. Empty fruit bunch (EFB) is biomass waste from fresh fruit bunch processing in palm oil mills. EFB can be converted to bio-crude oil through pyrolysis at temperatures from 400 to 600 °C. The quality of bio-crude oil must be upgraded due to its high oxygen content. Esterification of bio-crude oil potentially improves the quality of bio-crude oil by using zeolite as catalyst. The purpose of this research was to investigate the properties of Bayah natural zeolites for upgrading the quality of bio-crude oil from EFB pyrolysis. Bayah natural zeolite was activated using various NaOH concentrations. Characterization of the natural zeolites was performed by using X-ray diffraction (XRD), scanning electron microscope-energy dispersive X-ray (SEM-EDX), and nitrogen physisorption. The optimum ratio of Si/Al of the modified Bayah natural zeolites was 3.91. The surface area of the parent was initially 19 m2/g and increased significantly to 150 m2/g after treatment with 0.4 M NaOH solution. The application of the activated zeolites for bio-crude oil esterification successfully decreased the total acid number
Pollution Load Allocation on Water Pollution Control in the Citarum River
Get PDFThe Citarum River is a strategic river in Indonesia, but has poor water quality. The existing pollution control program has no impact on the river's water quality, because it uses a regulatory approach and prioritizes industrial sources. To improve the quality of the river, every pollutant source needs to reduce the pollution load discharged into the river based on the ability of the river to receive pollution. The purpose of this study was to measure pollution load allocation based on the total maximum daily load (TMDL) of the river. The results show that non-point sources contribute the highest pollution load (85%) compared with point sources (15%). The results of the measurement of pollution load allocation showed that the highest contribution of pollution load was from domestic waste (83.5%), followed by industrial waste (6.6%). The target of pollution load reduction for domestic sources is 81.8%, and for industries is 79.5%. The improvement of river water quality should be started at tributaries and domestic sources. This study can be used by local governments to develop water pollution control programs, for instance as a basis for determining the wastewater discharge permit of pollutant sources and permit trading
Effectiveness Analysis of Canal Blocking in Sub-peatland Hydrological Unit 5 and 6 Kahayan Sebangau, Central Kalimantan, Indonesia
Get PDFThe height of canal blocking has a significant influence on re-wetting peatland, depending on the canal’s distance. An effective canal in good condition has to raise the groundwater table to -0.4 m below ground level according to the Indonesian Ministry of Environment and Forestry (MENLHK). The effectiveness of different canal blockings was modeled by Freewat software with variation of canal distance (200 m, 250 m, 300 m, 350 m, and 400 m) and blocking height (0.2 m, 0.3 m, 0.4 m, 0.5 m, 0.6 m). This simulation was carried out using recharge and evapotranspiration data covering 20 years. The input of the conductivity value was done using 50 m/day according to the calibration. From the modeling, 0.6 m high canal blockings give a satisfactory result at every canal distance. The study took place during the annual dry season, when recharge was almost zero and average evapotranspiration was 6 mm/day. Adjusting the canal blocking to a maximum of 0.6 m and the canal distance to 400 m, the groundwater table slowly rose 0.38 m and it took 30 days to reach full-re-wetting capacity. This study revealed that the effectiveness of canal blocking is directly related to evapotranspiration and recharge, which has a positive correlation with the groundwater rise and the re-wetting period