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RISS 인기검색어
- 검색키워드
- 저자 : Nachiketa Tiwari (검색결과 2 건)
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Simulation and experimental investigation of a ballistic compression soft recovery system
Girijesh Mathur,Nachiketa Tiwari 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.1
A soft recovery system is used to arrest a supersonic object over a limited distance in a controlled manner. This may be achieved through ballistic compression of gas. This work explains the motion of a supersonic object passing through a ballistic compression decelerator i.e., pressurized gas column initially sandwiched between two diaphragms. The accompanying mechanics is complex and includes diverse effects such as separation of shock from the supersonic object, travelling shocks, shock reflections, creation of a new shock, emergence and dissolution of contact discontinuities and expansion waves, and shock-shock interactions. In this work, these phenomena have been numerically and experimentally studied. While the method of characteristics was used to solve Euler’s equations in continuous regions, jump conditions derived from control volume considerations were used to obtain solutions across discontinuities. In this way, a duly validated finite difference method computer program was developed to analyze the problem. Finally, simulation predictions were validated by conducting experiments on a 7.62 mm soft recovery system tube. Our results showed that, an object having an entry velocity of 880 m/s, left the SRS with a velocity that was lower by 47 % from simulation predictions. Further analysis showed that friction between the object and tube was a major contributor to this gap. Post accounting for friction, the difference between numerical analysis and experimental data got reduced to about 5 % at most locations, and to 17 % at the end of the SRS. We attribute this residual difference between observations and simulations to build up of pressure at a location post passage of shock by it. Our 2-D finite volume study results, which are consistent with earlier research, as well as with our experimental data, show that such a phenomenon is prominent particularly in narrow tubes due to development of significantly thick turbulent boundary layers.
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Vijaya Kumar Narne,Nachiketa Tiwari 한국언어재활사협회 2021 Clinical Archives of Communication Disorders Vol.6 No.2
Purpose: The Long-Term Average Speech Spectrum (LTASS) and Dynamic Range (DR) of speech strongly influence estimates of Speech Intelligibility Index (SII), gain and compression required for hearing aid fitting. It is also known that acoustic and linguistic characteristics of a language have a bearing on its LTASS and DR. Thus, there is a need to estimate LTASS and DR for Indian languages. The present work on three Indian languages fills this gap and contrasts LTASS and DR attributes of these languages against British English. Methods: For this purpose, LTASS and DR were measured for 21 one-third octave bands in the frequency range of 0.1 to 10 kHz for Hindi, Kannada, Indian English and British English. Results: Our work shows that the DR of Indian languages studied is 7–10 dB less relative to that of British English. We also report that LTASS levels for Indian languages are 7 dB lower relative to British English for frequencies above 1 kHz. Finally, we observed that LTASS and DR attributes across genders were more or less the same. Conclusions: Given the evidence presented in this work that LTASS and DR characteristics for Indian languages analyzed are markedly different than those for BE, there is a need to determine Indian language specific SII, as well as gain and compression parameters used in hearing aids.
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