• Structural Engineering and Mechanics
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• 제46권5호
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• pp.595-613
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• 2013

A new effective model for calculation of the equivalent uniform blast load for non-uniform blast load such as close-in explosion of a one-way square and rectangle reinforced concrete slab is proposed in this paper. The model is then validated using single degree of freedom (SDOF) system with the experiments and blast tests for square slabs and rectangle slabs. Test results showed that the model is accurate in predicting the damage level on the tested RC slabs under the given explosive charge weight and stand-off distance especially for close-in blast load. The results are also compared with those obtained by conventional SDOF analysis and finite element (FE) analysis using solid elements. It is shown that the new model is more accurate than the conventional SDOF analysis and is running faster than the FE analysis.

• 대한기계학회논문집
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• 제18권2호
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• pp.251-259
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• 1994

Nearfield acoustic holography is known as a powerful tool to study sound radiation from a structure. In this work, the so called backward propagation of sound pressure field is studied to obtain the structure velocity distribution. The results, which were obtained using FFT algorithms, are presented for a finite plate excited at the frequencies above and below coincidence. These results illustrate the effect of stand-off distance and noise. An optimum cutoff frequency in wavenumber domain was suggested to reduce the effects of evanescent wave in the backward propagation. The experimental results were also included for a plate to demonstrate the effectiveness of the suggested cutoff frequency. The optimum cutoff frequency to exclude the unwanted noise in the process of reconstruction of the velocity field gives the good results in both simulations and experiments.

• 한국기계가공학회지
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• 제8권4호
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• pp.14-19
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• 2009

Micro fluid channels are machined on quartz glass using powder blasting, and the machining characteristics of the channels are experimentally evaluated. The powder blasting process parameters such as injection pressure, abrasive particle size and density, stand-off distance, number of nozzle scanning, and shape/size of the required patterns affect machining results. In this study, the influence of the number of nozzle scanning, abrasive particle size, and blasting pressure on the formation of micro channels is investigated. Machined shapes and surface roughness are measured, and the results are discussed. Through the experiments and analysis, LOC are ettectinely machined on quartz glass using powder blasting.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2011년도 정기 학술대회
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• pp.152-155
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• 2011

최근 폭발 등 극한하중에 대한 관심의 증대와 함께 방폭 및 연쇄붕괴방지를 위한 연구가 활발히 진행되고 있다. 이에, 본 연구에서는 폭발하중하의 강구조물의 손상도와 저항성능을 수치적으로 평가하고자 하였다. 이를 위해 구조물의 폭발피해경감을 위해 가장 중요한 구조부재인 기둥을 대상으로 폭발물과 구조물과의 이격거리를 달리하여 폭발하중을 적용하였다. 유한요소해석을 수행한 결과를 토대로 기둥의 손상도와 잔여압축강도를 비교하고 관계를 도출하였다. 본 연구의 목적은 폭발에 의해 기둥이 손상된 경우 구조물 전체의 연쇄붕괴저항성능에의 손상된 기둥의 기여도를 평가하는 것이다.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.425-435
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• 2017

In this work, an overview of flow diagnosis in a shock tunnel is made by means of using established techniques that are easy to setup, economical to arrange, and simple to measure. One flow condition was considered having Mach number of 6 at the nozzle-exit, regarded as freestream. Measured aerothermodynamic data such as shock wave speed, wall static and total pressures, surface heat flux, and shock stand-off distance ahead of test model showed good agreement with calculation. This study shows an overall procedure of flow diagnosis in a shock tunnel in a single manuscript. Outcomes are thought to be useful in the field of education and also in a preliminary stage of high-speed vehicle design and tests, that need to be performed within a short time with decent accuracy.

• 화약ㆍ발파
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• 제23권4호
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• pp.45-55
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• 2005

일반적 의미의 성형폭약이라 함은 폭약 중에 빈공간이 존재하여 표면쪽으로 개방되어 있는 한덩이의 고폭약을 말한다. 이런 이유로 절단 단면의 형상은 주로 V 자형을 이루고 있으며 보통 V자의 뽀족한 부분이 기폭부분이 된다. 성형폭약은 그 생김새를 기준으로 크게 2가지로 나눌 수가 있는데 원뿔형과 선형이 그것이다. 원뿔형 성형폭약은 그 초기 발전단계부터 군용 대장갑용으로 명성을 떨쳤으며 현재에도 많은 연구가 진행되고 있는 상태이다. 이에 비해 선형 성형폭약은 철구조물 해체나 여러 용도의 민간/상업용 절단도구로 많이 쓰이고 있는데 두 번의 세계전쟁을 치루며 엄청난 규모의 물질적 인적 지원을 바탕으로 발전한 원뿔형 성형폭약에 비해서 턱없이 연구실적이 부족한 상태이다. 이 논문에서는 일반적인 선형 성형폭약의 관통력에 대한 연구가 아닌 기능적 측면에 대한 연구결과를 서술하며, 기능적 측면상 중요한 몇 개의 항목에 대한 수량화, 정의 및 연구가 이루어진다. 그 항목으로는 발전거리(run up distance), 이격거리(stand off distance), 기폭위치에 따른 절단모양, 파편 분간 형상 등이 있으며 각 항목에 대한 하류 항목들은 본문에서 다루어진다. 모든 실험은 University of Missouri-Rolla, Rock Mechanics and Explosives Research Center 에서 이루어 졌으며 대부분의 실험은 500grain/ft 선형성형폭약을 사용하여, 기폭 후 철제목표물을 관통한 형상 및 관통 단면을 관찰하는 형식으로 이루어졌다.

• 대한기계학회논문집B
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• 제20권3호
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• pp.1106-1113
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• 1996

The phase criterion of the feedback cycle of low-speed edgetones has been obtained using the jet-edge interaction model which is based on the substitution of an array of dipoles for the reaction of the wedge to the impinging jet. The edgetone is produced by the feedback loop between the downstream-convected sinuous disturbance and upstream-propagating waves generated by the impingement of the disturbance on the wedge. By estimation of the phase difference between the downstream and the upstream disturbances, the relationship between the edge distance and the wavelength is obtained according to the phase-locking condition at the nozzle lip. With a little variation depending on the characteristics of jet-edge interaction, the criterion can be approximated as follows: h/.LAMBDA. + h/.lambda. = n - 1/4, where h is the stand-off distance between the nozzle lip and the edge tip, .LAMBDA. is the wavelength of downstream-convected wave, .lambda. is the wavelength of the upstream-propagating acoustic wave and n is the stage number for the ladder-like characteristics of frequency. The present criterion has been confirmed by estimating wavelengths from available experimental data and investigating their appropriateness. The above criterion has been found to be effective up to 90.deg. of wedge angle corresponding to the cavitytones.

• 한국의류산업학회지
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• 제14권1호
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• pp.136-143
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• 2012

The purpose of this study was to investigate the influence of physical functions of elderly people on their clothing behavior and to provide basic information about manufacturing comfortable apparels for the elderly. A total of 219 people, with ages between 60s and 70s, participated in the survey and in the experiment to correlate their tendency of wearing clothes with the state of their physical functions. About 78.5% of the elderly showed eyesight deterioration in the subjective evaluation. Elders in their 60s raised their arms higher up in overhead reach, and showed shorter distance between middle fingertips in behind back stretch and in back scratch than elders in their 70s. Also, the former stretched farther to the floor in standing trunk flexion, and maintained more steady in one leg stand and in tandem stance than the latter. The narrower the movement range of the upper limb joints was, the more the elderly preferred upper garments with full front opening to those with half or no opening. The more inflexible the upper limbs and waist and the more unbalanced the body was, the more likely the elderly put on pants while sitting on the floor. The time taken to button up the shirt and to put on and take off pants showed a positive correlation with the overhead reach, the behind back stretch, the back scratch and the standing trunk flexion, whereas the former showed a negative correlation with the one leg stand and the tandem stance.

• Structural Engineering and Mechanics
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• 제63권3호
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• pp.347-359
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• 2017

Blast resistant gates are required to be lightweight and able to mitigate extreme loading effect. This may be achieved through innovative design of a gate and its supporting frame. The first is well covered in literature while the latter is often overlooked. The design of supporting frame depends mainly on the boundary conditions and corresponding reaction forces. The later states the novelty and the aim of this paper, namely, the analysis of reaction forces in supporting structure of rectangular steel gates subjected to "far-field explosions". Flat steel plate was used as simplified gate structure, since the focus was on reaction forces rather than behaviour of gate itself. The analyses include both static and dynamic cases using analytical and numerical methods to emphasize the difference between both approaches, and provide some practical hints for engineers. The comprehensive study of reaction forces presented here, cover four different boundary conditions and three length to width ratios. Moreover, the effect of explosive charge and stand-off distance on reaction forces was also covered. The analyses presented can be used for a future design of a possible "blast absorbing supporting frame" which will increase the absorbing properties of the gate. This in return, may lead to lighter and more operational blast resistant gates.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2004년도 춘계 학술대회논문집
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• pp.113-118
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• 2004

This paper presents a two-dimensional edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle by the finite difference lattice Boltzmann method (FDLBM). We use a new lattice BGK compressible fluid model that has an additional term and allow larger time increment comparing the conventional FDLBM, and also use a boundary fitted coordinates. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of $\alpha=23^0$. At a stand-off distance $\omega$, the edge is inserted along the centreline of the jet, and a sinuous instability wave with real frequency f is assumed to be created in the vicinity of the nozzle and th propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations result from periodically oscillation of jet around the edge. That pressure fluctuations propagate with the sound speed. Its interaction with the wedge produces an irrotational feedback field which, near the nozzle exit, is a periodic transverse flow producing the singularities at the nozzle lips. The lattice BGK model for compressible fluids is shown to be one of powerful tool for computing sound generation and propagation for a wide range of flows.