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Analysis and attenuation of impulsive sound pressure in large caliber weapon during muzzle blast
Hafizur Rehman,Seung Hwa Hwang,Berkah Fajar,정한식,정효민 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.10
Due to the supersonic speed at which propellant gas flows through the gun barrel, a high intensity impulsive sound pressure is created,which has negative effects in many respects. Therefore, the high pressure waves generated due to muzzle blast flow of tank gun during firing is a critical issue to examine. The purpose of this paper is to study and analyze this high pressure impulsive sound, generated during the blast flow. The large caliber 120 mm K1A1 tank gun has been selected especially for this purpose. An axisymmetric computational domain has been constructed by employing Spalart Allmaras turbulence model to evaluate pressure and sound level in the tank gun using Computation Fluid Dynamics technique. Approximately 90% of pressure and 20 dB of sound level have been attenuated due to use of the three baffle silencer at the muzzle end of the gun barrel in comparison to the tank gun without silencer. Also, the sound pressure level at different points in the ambient region shows the same attenuation in the results. This study will be helpful to understand the blast wave characteristics and also to get a good idea to design silencer for large caliber weapon system.
Dispersion Behavior of Al₂O₃-H₂O Nanofluids with Dependence of Time
하피줘 라흐만(Hafizur Rehman),여철모(Chul-Mo Yeo),정현권(Hyun-Gweon Jeong),정효민(Hyomin Jeong),정한식(Hanshik Chung) 대한설비공학회 2011 대한설비공학회 학술발표대회논문집 Vol.2011 No.7
Nanofluids are kind of engineering material, with a new challenge for thermal sciences provided by nanotechnology. Nanofluids are being investigated for numerous applications, including cooling process, manufacturing process, chemical process pharmaceutical process and medical treatment process etc. Nanofluids are basically the suspension of solid nanoparticles with size typically 1- 100 ㎚ in base fluid. In current research, Alumina size less than 50㎚ has been used. The tested fluids have been prepared by dispersing Al₂O₃ into DI water at three different conditions by using 1%wt, 3%wt. and 5%wt. concentrations of alumina without using any surfactant. To ensure the best dispersion and stability of alumina nanoparticles in DI water ultrasonicator with 47㎑ frequency and dispersion time until 3hrs has been used. Particles sedimentation test of these different condition nanofluid samples has been critically observed until 30days. As per result, after 30 days approximately 28% particles sedimentation of Al₂O₃ nanofluid with ultrasonicator dispersion time 3hrs recorded in 3%wt and 21% recorded in 5%wt concentration. Also particle size system (PSS) result of 3%wt and 5%wt concentration of Al₂O₃ nanofluid with dispersion time 3hrs achieved as 46nm and 60nm respectively. The present research will be helpful to investigate the dispersion behavior of water-based Al₂O₃ nanofluid with changing rate of time and also helpful to select different conditions for making Al₂O₃ nanofluid without using surfactants or any other surface additives to use further in heat transfer processes.