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Ocean waves represent a substantial renewable energy source, prompting this study's exploration of harnessing this potential via multi-point floating absorbers equipped with hydraulic Power Take-Off (PTO) systems. The study's primary motivation is to comprehensively model a Wave Energy Converter (WEC), including the hydraulic PTO system's control mechanism and protection system. To optimize the WEC design, we first investigate the hydrodynamic parameters of the floating absorber, employing potential flow theories and assessing the effects of varying the diameter-to-draft ratio. Our research involves analyzing Response Amplitude Operators (RAOs) and hydrodynamic forces for different ratios to identify the most effective design, followed by using computed wave forces as inputs for PTO simulations in MATLAB/SimScape to determine the unit parameters. The analysis of RAOs and wave-exciting forces reveals that diameter-to-draft ratios between 0.67 and 1.0 yield the best WEC performance, offering promising recommendations. In the final step, we compare the performance of single and multi-point absorber system simulations, assessing factors such as pressure drop, flow rate, and power output at the hydraulic motor. This comparison concludes that multi-point absorbers generate a more stable power output than their single-absorber counterparts.

Nowadays, Plastics are widely used mainly as packaging. With the increasing use of plastic, the amount of plastic waste was increasing. Plastic was a material that was difficult to decompose naturally so that plastic waste will continue to accumulate. This condition will disturbance the environment. In other conditions, energy needs, especially fuel oil, are increasing but the availability of crude oil was limited. This condition requires alternative fuels to maintain the availability of fuel oil for the needs of industry, vehicles and households. Both of these conditions can be related to convert plastic waste into fuel oil through the pyrolysis process. Pyrolysis of plastic waste can be done as thermally and catalytically. The thermal plastic pyrolysis process can be carried out at temperatures between 300-500degC and pyrolysis time between 30-60 minutes. The results of pyrolysis of plastic waste produce fuel oil which can be used as fuel in industries such as boilers. Yield of pyrolysis plastic polypropylene (PP) was higher than plastic polyethylene (PE). The physical properties of oil plastic pyrolysis PE and PP like gasoline but the flash point was lower than gasoline.

The aims of the study were to characterize and investigate the ammonium adsorption kinetic and isotherm of the natural zeolites from Lampung. Characterization of the natural zeolite was performed by using X-Ray Diffraction (XRD), nitrogen-physisorption, Scanning Electron Microscope (SEM) and X-Ray Fluorescence (XRF). According to XRD analysis, the natural zeolites were identified as clinoptilolite dominant phase with some impurities i.e. mordenite and quartz. The surface area calculated by BET model was 45 m2/g. The SEM images showed the irregular morphology shape. The XRF analysis revealed that the ratio Si/Al was 6.2. Ammonium sorption experiment was performed by using 100 ppm of ammonium solution in the batch reactor with variation on natural zeolite mass loading and adsorption time. Ammonium adsorbed onto the zeolites was increased with the adsorption time and mass loading. The kinetic models, i.e. Lagergren's 1st order, Pseudo 2nd order, Elovich, Intraparticle diffusion, and isotherm models, i.e., Langmuir, Langmuir-Vageler, Freundlich, Temkin were fitted with the ammonium adsorption kinetic data by using non-linear regression analysis in MATLAB.

Exfoliation of pencil graphite core throughout electrolysis process is considered as one of the simple and friendly method to synthesis graphene from graphite. In this research, sodium sulphate (Na2SO4) was used as an electrolyte to investigate the effect on pencil graphite core with different grades for exfoliation process. Pencil graphite core was applied as both anode and cathode electrodes and exposed in 0.1 mol of Na2SO4 solution and followed with sonication in DMF solution. The morphology of exfoliated graphite was characterized by FESEM and TEM image. It was found that higher pencil grade produced more exfoliated powder as compared to lower grade pencil, and morphology investigation revealed that the exfoliated powder can produced graphene in nanoplatelet forms.

In oil and gas pipelines and offshore structure, inhibitors have been considered to be the first choice to reduce corrosion rate. There are many corrosion inhibitor compositions available in the market. To produce the best corrosion inhibitor requires many experimental data which is not efficient. These experiments used response surface methodology (RSM) to select corrosion inhibitor compositions. The experiments investigated effects of corrosion inhibition on corrosion rate of low carbon steel in 3% NaCl solution with different concentrations of selected main inhibitor compositions which are ethyl acetate (EA), ethylene glycol (EG) and sodium benzoate (SB). Corrosion rate were calculated using linear polarization resistance (LPR). All of the experiments were set in natural conditions at pH 7. MINITAB(r) version 15 was used for data analysis. It is shown that a quadratic model is a representative model can predict best corrosion inhibitor composition comprehensibly.

In this work, the morphology of ZrO2 thin film from dip coating process on mild steel has been investigated. Mild steel was dip-coated on solution made of zirconium butoxide as a precursor, ethanol as solvent, acetylacetone as chelating agent and water for hydrolysis. Number of dipping was adjusted at 3, 5 and 7 times. The dipped sample then annealed at 350degC for two hours by adjusting the heating rate at 1degC/min respectively. The optical microscope showed that micro-cracks were observed on the surface of the coating with its concentration reduced as dipping sequence increased. The XRD result showed that annealing process can produce polycrystalline tetragonal-ZrO2. Meanwhile, SEM image showed that the thicknesses of the ZrO2 coatings were in between 400-600 nm. The corrosion resistance of uncoated and coated substrates was studied by polarization test through potentio-dynamic polarization curve at 1mV/s immersed in with 3.5% NaCl. The coating efficiency was improved as the number of layer dip coated increased, which showed improvement in corrosion protection.

The demand for increasing efficiency has led to the development and construction of higher operating temperature power plant. This condition may lead to more severe thickness losses in boiler tubes due to excessive corrosion process. Hence, the research to improve the corrosion resistance of the current operated material is needed so that it can be applied for higher temperature application. In this research, the effect of chromizing process on the oxidation behaviour of T91 steel was investigated under steam condition. In order to deposit chromium, mixture of chromium (Cr) powder as master alloy, halide salt (NH4Cl) powder as activator and alumina (Al2O3) powder as inert filler were inserted into alumina retort together with the steel sample and heated inside furnace at 1050degC for ten hours under argon gas environment. Furthermore, for the oxidation process, steels were exposed at 700degC at different oxidation time (6h-24h) under steam condition. From FESEM/EDX analysis, it was found that oxidation rate of pack cemented steel was lower than the un-packed steel. These results show that Cr from chromizing process was able to become reservoir for the formation of Cr2O3 in high temperature steam oxidation, and its existence can be used for a longer oxidation time.

Corrosion control using inhibitor is an effective method to protect carbon steel from corrosion. Due to environmental toxicity of chemical inorganic corrosion inhibitors (synthetic), green inhibitors are potentially to develop. In atmospheric conditions, green vapour corrosion inhibitors are the best solutions to replace the uses of inorganic corrosion inhibitors. This research used chemical acid extraction from the key lime (citrus aurantiifolia) leaves and seeds. They are used as the main ingredients to produce this effective green corrosion inhibitor. The experiments investigated effects of corrosion inhibition on corrosion rate of low carbon steel in 3% NaCl solution using both fog salt chamber and electrochemical cell. Using salt fog chamber to represent atmospheric conditions, and corrosion rates are evaluated visually and calculated using weight loss methods. Corrosion rate on electrochemical cell were calculated using linear polarization resistance (LPR) methods. All of the experiments were set in natural conditions at pH 7. Using weight loss for three days exposure time, the efficiency of the inhibitor reached 82.39%.

Wetting and spreading of molten brazing filler material are important factors that influence the brazing ability of a joint to be brazed. Several investigations into the wetting ability of a brazing filler alloy and its spreading area in the molten state, in addition to effects of brazing temperature on the contact angle, have been carried out. Generally, the composition of copper-based filler and temperature affect spreading of molten brazing filler material during brazing. Wetting by and interfacial reactions of the molten brazing filler material with the metallic substrate, especially, affect strongly the spreading of the filler material. In this study, the effects of filler composition and brazing temperature on the spreading of molten brazing filler metallic alloys were investigated. MBF 2005 (Cu, 5.7wt.%Ni, 9.7wt.%Sn, 7.0wt.%P), MBF 2002 (Cu, 9.9wt.%Ni, 4.0wt.%Sn, 7.8wt.%P) and VZ 2250 (Cu, 7.0wt.%Ni, 9.3wt.%Sn, 6.3wt.%P) alloys were used as brazing filler materials. Pure copper block and a rectangular plate were employed as the base metal. Brazing filler material and metallic base plate were first washed with acetone. Brazing was performed at 750degC and 800degC under Ar gas for 30 minutes using an electrically heated furnace, after which, the original spreading area, defined as the sessile drop area, and the apparent spreading area were both evaluated. It was observed that the spreading area and wetting angle influenced by the composition of copper-based filler.