• 한국구조물진단유지관리공학회 논문집
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• 제20권6호
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• pp.98-105
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• 2016

본 연구에서는 반구형과 평탄형의 비상체를 이용하여 일반콘크리트와 섬유보강콘크리트에 충격시험을 진행한 후 파괴깊이와 형태, 파괴직경, 배면의 인장변형을 평가하였다. 선단면적이 작을수록 충격력의 집중에 의해 파괴깊이는 크고 표면파괴 직경은 작게 되는 것으로 확인되었다. 반면에 선단면적이 클수록 파괴깊이는 작지만 표면파괴직경은 크게 되었다. 일반콘크리트와 섬유보강 콘크리트에서 유사한 표면파괴와 배면변형이 발생하였으나 인장변형의 크기는 일반콘크리트에 비해 섬유보강 콘크리트가 작은 것으로 나타났다. 또한, 비상체의 선단형상에 따른 표면관입의 형태와 배면의 인장변형 사이에 직접적인 연관이 있는 것으로 사료된다. 따라서 콘크리트의 배면박리한계두께 예측 시에는 표면관입깊이뿐만 아니라 배면의 변형거동 또한 고려할 필요성이 있을 것으로 사료된다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2015년도 추계 학술논문 발표대회
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• pp.30-31
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• 2015

High velocity impact of projectile generate local failure such as penetration, scabbing, perforation on concrete. It has been reported that local failure is affected by such as nose shape, mass of projectile. In this study, comparing and weighing the impact failure properties of concrete by high velocity impact test that using spherical nose and flat nose type projectile. As a result, It was considered that scabbing of Flat nose projectile reduced more than spherical nose projectile by dispersion of impact force.

• 대한기계학회논문집A
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• 제28권10호
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• pp.1566-1573
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• 2004

When a projectile travels at high speed underwater, supercavitating flow arises, in which a huge cavity is generated behind the projectile so that only the nose, i.e., the cavitator, of the projectile is wetted, while the rest of it should be surrounded by the cavity. In that case, the projectile can achieve very high speed due to the reduced drag. Furthermore if the nose of the body is shaped properly, the attendant pressure drag can be maintained at a very low value, so that the overall drag is also reduced dramatically. In this study, shape optimization technique is employed to determine the optimum cavitator shape for minimum drag, given certain operating conditions. Shape optimization technique is also used to solve the potential flow problem fur any given cavitator, which is a free boundary value problem having the cavity shape as unknown a priori. Analytical sensitivities are derived for various shape parameters in order to implement a gradient-based optimization algorithm. Simultaneous optimization technique is proposed for efficient cavitator shape optimization, in which the cavity and cavitator shape are determined in a single optimization routine.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1876-1881
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• 2003

When a projectile travels at high speed underwater, supercavitating flow arises, in which a huge cavity is generated behind the projectile so that only the nose, i.e., the cavitator, of the projectile is wetted, while the rest of it should be surrounded by the cavity. In that case, the projectile can achieve very high speed due to the reduced drag. Furthermore if the nose of the body is shaped properly, the attendant pressure drag can be maintained at a very low value, so that the overall drag is also reduced dramatically. In this study, shape optimization technique is employed to determine the optimum cavitator shape for minimum drag, given certain operating conditions. Shape optimization technique is also used to solve the potential flow problem for any given cavitator, which is a free boundary value problem having the cavity shape as unknown a priori. Analytical sensitivities are derived for various shape parameters in order to implement a gradient-based optimization algorithm. Simultaneous optimization technique is proposed for efficient cavitator shape optimization, in which the cavity and cavitator shape are determined in a single optimization routine.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년도 제30회 춘계학술대회논문집
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• pp.82-85
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• 2008

수중에서 발사체가 고속으로 주행할 때 발사체의 머리 즉, 캐비테이터 만이 물과 접촉한 상태에서 커다란 공동이 발생하여 몸체 전체를 뒤덮는 초공동현상이 발생한다. 초공동 상태에서는 발사체는 저항이 감소되어 매우 빠른 속도를 낼 수 있게 된다. 더욱이 캐비테이터가 적합한 형상을 가지게 되면 매우 낮은 압력저항을 유지하고 전체적인 저항도 획기적으로 줄일 수 있기 때문에 본 연구에서는 주어진 작용환경 하에서 저항을 최소화 하기위한 최적의 캐비테이터 형상최적설계 문제를 고려하였다. 그리고 효율적인 캐비테이터 형상최적화를 위해 공동과 캐비테이터 형상을 하나의 죄적화로 변환한 동시최적화기법을 수행하였다.

• Steel and Composite Structures
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• 제22권4호
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• pp.777-796
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• 2016

In this paper, the behavior of woven E-glass fabric composite laminate was experimentally investigated under quasi-static indentation and high velocity impact by flat-ended, hemispherical, conical (cone angle of $37^{\circ}$ and $90^{\circ}$) and ogival (CRH of 1.5 and 2.5) cylindrical perforators. Moreover, the results are compared in order to explore the possibility of extending quasi-static indentation test results to high velocity impact test results in different characteristics such as perforation mechanisms, performance of perforators, energy absorption, friction force, etc. The effects of perforator nose shape, nose length and nose-shank connection shapes were investigated. The results showed that the quasi-static indentation test has a great ability to predict the high velocity impact behavior of the composite laminates especially in several characteristics such as perforation mechanisms, perforator performance. In both experiments, the highest performance occurs for 2.5 CRH projectile and the lowest is related to blunt projectiles. The results show that sharp perforators indicate lower values of dynamic enhancement factor and the flat-ended perforator represents the maximum dynamic enhancement factor among other perforators. Moreover, damage propagation far more occurred in high velocity impact tests then quasi-static tests. The highest damage area is mostly observed in ballistic limit of each projectile which projectile deviation strongly increases this area.

• 대한건축학회논문집:구조계
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• 제35권2호
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• pp.13-20
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• 2019

This study was conducted in order to validate the nose shape factors of projectile in existing impact formulas for high-strength concrete in the event of collision with high-speed projectiles. In order to conduct the high-speed impact experiment, specified concrete strengths of 35, 100, and 120 MPa were prepared and tested in collision with both conical and hemispherical projectiles. The results showed that the measured penetration depth did not decrease linearly as concrete strength increased. Comparing the ratio penetration depth to the kinetic energy of the conical and hemispherical projectiles, the difference in the ratios for high strength concrete was observed to decline as concrete strength increased. However, in the modified NDRC and the Hughes formulas, the difference in the predicted penetration depth of the conical and hemispherical projectiles was constant despite increasing concrete strength. The modified NDRC and Hughes formulas should be improved upon so as to be applied to high strength concrete.

• 한국시뮬레이션학회논문지
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• 제29권3호
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• pp.49-55
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• 2020

발사체의 사거리 증대는 중요한 성능개선 목표 중 하나이다. 일반적으로 발사체 비행탄두의 형상은 공기역학 및 구조적인 요소를 복합적으로 고려하여 선정한다. 몸체, 탄두부 및 탄미부 형상의 선정은 공기역학적 설계에 중요한 영향을 미친다. 발사체 비행탄두 형상의 주요 설계 요소는 공기역학적 항력이다. 공기역학적 항력은 발사체의 운동과 반대 방향으로 작용하는 공기역학적 힘이다. 준실험적 기법을 이용하여 탄두부, 탄미부 및 몸체 형상이 발사체의 공기역학적 특성에 미치는 영향을 분석하기 위한 연구를 수행하였다. 여러 가지 비행탄두 형상 변수에 대한 연구를 수행하였으며, 최대 사거리 성능 분석에는 탄도 모사분석 모델을 사용하였다. 발사체 비행탄두 형상 최적화를 이용한 사거리 증대 가능성을 분석하고, 형상 변수 최적화에 의한 사거리 증대 효과를 확인하였다.

• Structural Engineering and Mechanics
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• 제60권5호
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• pp.829-849
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• 2016

In this paper, experimental as well as numerical analysis of Glass Fiber Reinforced Polymer (GFRP) laminated composite has been presented under ballistic impact with varying projectile nose shapes (conical, ogival and spherical) and incidence velocities. The experimental impact tests on GFRP composite plate reinforced with woven glass fiber ($0^{\circ}/90^{\circ}$)s are performed by using pneumatic gun. A three dimensional finite element model is developed in AUTODYN hydro code to validate the experimental results and to study the ballistic perforation characteristic of the target with different parametric variations. The influence of projectile nose shapes, plate thickness and incidence velocity on the variation of residual velocity, ballistic limit, contact force-time histories, energy absorption, damage pattern and damage area in the composite target have been studied. The material characterization of GFRP composite is carried out as required for the progressive damage analysis of composite. The numerical results from the present FE model in terms of residual velocity, absorbed energy, damage pattern and damage area are having close agreement with the results from the experimental impact tests.

• Advances in aircraft and spacecraft science
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• 제9권2호
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• pp.119-130
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• 2022

Supersonic projectiles like rockets, missiles, or aircraft find various applications in the field of defense. The shape of the wings is mainly designed as wedge shape or delta wings for supersonic vehicles. The study of supersonic flows over the wedges and flat plate delta wings around the large scale of incidence angle is considered in the supersonic projectile. In the present paper, the prime attention is to study the pressure at the nose of the plane wedge over the various Mach number and the various angles of incidence. Ghosh piston theory is used to obtain the pressure distribution analytically, and the results are compared with CFD analysis results. The wedge angle and Mach number are the parameters considered for the research work. The range of wedge angle is 50 to 250, and Mach number is 1.5 to 4.0 are considered for the current research work. The analytical results show excellent agreement with the CFD results. The results show that both the parameters wedge angle and Mach number are influential parameters to vary the static pressure. The static pressure increases with an increase in Mach number and wedge angle.