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Screw extrusion processings are being used in many cases for blending or compounding in order to produce uniform mixtures of more than two different materials. As far as mixing in a single-phase flow is concerned in the single-screw extrusion process a striation thickness can be considered as a mixing measure. In the two-phase immiscible mixing system, however, due to combination of shear rate and interfacial tension on the drop interface, drops easily tend to be in the status of large elongation and eventually breakup under the repetition of the flow with high shear near the barrel surface and low shear near the screw walls. Recently, deformation and breakup mechanism of an immiscible drop were investigated experimentally in a screw channel flow, which mimics the flow in the metering section of section of the single-screw extruder. They presented the flow visualization results of drop deformation patterns and observed the peculiar thread deformation of drop as the comet-like thread. In our research, the numerical simulations by using the commercial software were carried out to understand the drop deformation and breakup mechanism and compared with the experimental results.
The development of new concepts of liners is required in order to effectively neutralize the enemy's attack power concealed in the armored vehicles. A multiple-layer liner is one of possibilities and has a mechanism for explosion after penetrating the target which is known as "Behind Armor Effect." The multiple-layer explosive liner should have sufficient kinetic energy to penetrate the protective structure and explosive material react after target penetration. With this in mind, double-layer liner materials were obtained by cold spray coating methods and these material properties were experimentally characterized and used in this simulation for double-layer liners. In this study, numerical simulations in the three different layer types, i.e., single, A/B, A/B/A in terms of the layer location were verified in terms of finite element mesh sizes and numerical results for the jet tip velocity, kinetic energy, and the corresponding jet deformation characteristics were analysed in detail depending on the structure of layer types.
The development of new concepts of liner is of great importance to effectively neutralize the enemy's attack power concealed in the protective structure or armored vehicles. A double layer liner has a combination of two different materials, one for penetration of target and the other for explosion after penetration. Therefore, it is of great importance to understand the temperature distribution before impact which should be lower than the explosive temperature of pure explosive material of the liner used. In this study, two different liner materials were obtained using cold spray coating and these material properties were characterized by DSC experiments. Numerical computations were done and the effect of temperature distribution and changes over time at each point of the explosive material depending on the layer types of the liner were discussed and analysed in the jet state.
When we develop the tight-fit 2D pattern from the 3D scan data, segmentation of the 3D scan data into several parts is necessary to make a curved surface into a flat plane. In this study, Garland's method of triangle simplification was adopted to reduce the number of data point without distorting the original shape. The Runge-Kutta method was applied to make triangular patch from the 3D surface in a 2D plane. We also explored the detailed arrangement method of small 2D patches to make a tight-fit pattern for a male body. As results, minimum triangle numbers in the simplification process and efficient arrangement methods of many pieces were suggested for the optimal 2D pattern development. Among four arrangement methods, a block method is faster and easier when dealing with the triangle patches of male's upper body. Anchoring neighboring vertices of blocks to make 2D pattern was observed to be a reasonable arrangement method to get even distribution of stress in a 2D plane.
산업 현장이나 학교 기간에서 실험을 하면 비용과 시간이 많이 들기 때문에 CFD를 통해서 교반기의 성능을 분석한다. 성능 분석하기 위해서 가장 중요하는 것 중 하나가 가시화라고 할 수 있다. 교반기의 가시화를 보기 위해서 사용 Software인 Gambit과 Fluent를 이용하였다. 본 논문에서는 유동을 가시화하기 위해 필요한 GUI창에 대한 설명과 lmpeller 회전에 의한 Path line과 단면에 대한 압력분포와 속도분포 그리고 특정 Surface의 유동 분포를 상용 Surface의 유동 분포를 상용 Software Fluent의 Postprocess를 통해 가시화 하는 방법을 설명하였다.
본 논문에서는 산업용 폭약을 이용한 충격고화기술을 ZnO-98%과 Ga2O3-2% 혼합분말에 적용하여 직경 30mm, 두께 6mm인 ZnOGa2O3고화체를 형성시켰다. 고화체의 경도 및 상대밀도는 각각 220~250 Hv, 97%이었으며, 표면에 대한 주사현미경 관찰결과 균열 및 결함은 발생되지 않았으며, 분말입자들은 강한 충격파에 의해 변형되어 서로 결합되었음을 확인하였다. 또한 X-ray 분석결과로부터 입자 간의 격자결합 및 결정자의 변형을 확인 할 수 있었으며, 이러한 격자결합과 결정자의 변형은 높은 전기저항의 원인이 된다는 것을 보여주었다. ZnO-98% and Ga2O3-2% powder were consolidated by shock compaction technique, which uses a high performance explosive. The microstructural and electrical characteristics of ZnOGa2O3 compact with density of 97% and hardness of 220~250 Hv were investigated using SEM (Scanning Electron Microscope) and X-ray diffraction analysis, respectively. In the microstructures of the compact, there were no visible cracks at most of the surface areas, and interparticle bonding between powder particles was confirmed. The broadened peaks were detected due to deformation of crystallited size and high electric resistances were confirmed due to increased grains because of shock energy with a high pressure and high velocity.
In this study we simulated the sleeved projectile which is composed of metal(sleeve) and polymer(core) by using the explicit finite element method. We used the penalty method to consider contact between the sleeve and the core. In simulation, polymeric materials were modeled using viscoelastic constitutive relations with the relaxation time and the shear modulus. We have carried out the numerical simulation for the transient deformation characteristics. The simulation results showed similar behaviors to the well-known experimental ones.
It is of great importance to obtain the uniform layer thickness in the multi-layer co-extrusion processes. In the present study, the three-dimensional numerical simulation was carried out using the open source code named OpenFOAMⓡ to understand the flow characteristics in the multi-layer die. In this numerical study, Multi-thin-layers were successfully computed depending on the number of repeating units. The generation mechanism for the multi-layer was numerically verified by the flow simulation and visualization in the co-extrusion die using OpenFOAMⓡ. The results suggested that the multi-layer has a divided and folded mechanism similar to the stretching and folding in the chaotic flow.
Impregnation of shear-thickening fluid(STF) into high-strength fabrics makes a considerable improvement on the ballistic performance of fabric armors. Understanding dissipation augmentation due to shear thickening effects on yarn-yarn and yarn-projectile friction is of great importance in liquid armor research. This paper takes a shearthickening effect into account in numerical simulations by using a velocity-dependent friction model. Impact simulations were performed to validate the friction model as well as to evaluate the ballistic performance of STF-fabrics. Impact simulations on neat fabrics were also conducted to provide baseline results for comparison.
We present a direct numerical simulation technique and some preliminary results of the capillary spreading of a droplet containing particles on the solid substrate. We used the level-set method with the continuous surface stress for description of droplet spreading with interfacial tension and employed the discontinuous Galerkin method for the stabilization of the interface advection equation. The distributed Lagrangian-multipliers method has been combined for the implicit treatment of rigid particles. We investigated the droplet spreading by the capillary force and discussed effects of the presence of particles on the spreading behavior. It has been observed that a particulate drop spreads less than the pure liquid drop. The amount of spread of a particulate drop has been found smaller than that of the liquid with effectively the same viscosity as the particulate drop.