Water impact of three dimensional wedges using CFD

Nair, Vinod V.,Bhattacharyya, S.K. Techno-Press 2018 Ocean systems engineering Vol.8 No.2

In this paper the results of CFD simulations, that were carried out to study the impact pressures acting on a symmetric wedge during water entry under the influence of gravity, are presented. The simulations were done using a solver implementing finite volume discretization and using the VOF scheme to keep track of the free surface during water entry. The parameters such as pressure on impact, displacement, velocity, acceleration and net hydrodynamic forces, etc., which govern the water entry process are monitored during the initial stage of water entry. In addition, the results of the complete water entry process of wedges covering the initial stage where the impact pressure reaches its maximum as well as the late stage that covers the rebound process of the buoyant wedge are presented. The study was conducted for a few touchdown velocities to understand its influence on the water entry phenomenon. The simulation results are compared with the experimental measurements available in the literature with good accuracy. The various computational parameters (e.g., mesh size, time step, solver, etc.) that are necessary for accurate prediction of impact pressures, as well as the entry-exit trajectory, are discussed.

NUMERICAL SIMULATION OF VERTICAL WATER-EXIT AND WATER-ENTRY OF CAVITATING PROJECTILES

Van-Tu Nguyen,Cong-Tu Ha,Wam-Gyu Park 한국전산유체공학회 2012 한국전산유체공학회 학술대회논문집 Vol.2012 No.11

The present study focuses on the simulation of unsteady ventilated-cavitating flow during the vertical water-exit and water-entry of projectiles with and without exhaust plume. The propulsion exhaust plume gas embedded within the surrounding liquid strongly affects on the wake of flow. For simulation of water-exit and water-entry behavior of the cavitating projectiles which presents aspects of the flow physics such as cavity shape and phase topography of the flow during the processes, a numerical multi-phase homogeneous mixture model is utilized. The model is developed based on the unsteady incompressible Reynolds-averaged Navier-Stokes equations. Preconditioning pseudo-time stepping method is employed to improve the computational efficiency of the model. The results indicate that characteristics of cavity flow induced during water-exit and water-entry primarily depend on the geometry of projectiles and the velocities of flow. In addition, the gas exhaust delays the surface closure of the water-entry cavity that is one of the most important events in later cavity growth.

상품 및 서비스 혁신 : 한국 생수산업의 해외시장진출 전략에 관한 연구

홍성헌 ( Song Hon Hong ) 한국통상정보학회 2010 통상정보연구 Vol.12 No.4

It should be unthinkable to not provide water at survival of any living things. Water is too a basic element for development for a country. Currently, the global market of mineral water is growing rapidly. This study, I conceptualized mineral water as bottled water. In particularly, bottled water has seen huge global growth for the last few years. The annual growth rate of the market in the period 2005-2009 was 5.9%. Following a surge in obesity and subsequent health and wellness trends, many consumers are switching from sugary soft drinks to healthier alternatives. Therefore, the global bottled water market is one area which has big potential for growth, but price competition is getting intensified among multi-national and domestic firms. Korean providers too are faced with strong competition in growing domestic market. The bottled water market has presence of multinational provider like Nestle, Danone and Coca-Cola, which collectively account for 35.1% of the world market share in 2009. On the basis of a market orientation approach, this article looks at changing environments in the world mineral water industry and attempts to describe foreign market entry strategy of the Korean mineral water industry. The market orientation provides strong norms for learning from customers and competitors, is instrumental in creating a superior value for buyers, innovating successfully, and generating excellent firm performance. So firms should consider a strategic planning in basis on market orientation before they enter foreign markets. Some discussions were made about managerial implications for Korean bottled water providers.

Water-Entry Induced Cavity Pressure

Lee, Min-Hyung The Korean Society of Mechanical Engineers 2000 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.14 No.5

The pressure in a water-entry induced cavity, is analyzed up to the closed cavity (bubble). Water-entry is a highly transient phenomenon, and the evolution of the water-entry cavity must be explained by considering the entry speed, shape of the solid body, atmosphere pressure, and cavity pressure as the primary variables. This work is an extension of the cavity dynamics model recently reported by Lee (l997a). To extend the model for a wide range of entry speeds the cavity pressure is calculated from a one-dimensional quasi-steady flow model. The estimation of the cavity pressure allows us to explain the experimentally observed surface closure phenomena at low entry speeds. Predictions for the time of surface closure are compared with the published experimental data.

바이오폴리머를 포함한 모래지반의 흙-습윤 특성곡선 연구

정종원(Jongwon Jung) 한국지반환경공학회 2018 한국지반환경공학회논문집 Vol.19 No.10

흙-습윤 특성곡선은 불포화토에서 물의 흐름, 다상유체에서의 상대투수계수, 그리고 흙의 강성 및 부피 변화를 이해하는데 필수적이다. 바이오폴리머는 미생물에 완전 분해가 가능한 자연에 무해한 친환경 물질이다. 따라서, 치토산, 폴리에틸렌 옥사이드, 잔탄검, 알지네이트염 및 폴리아크릴산 등과 같은 바이오폴리머가 지반복원, 지반성능향상 및 오일생산증진을 위해 연구되어왔다. 폴리아크릴산(polyacrylic acid)은 바이오폴리머의 일종으로, 유체의 흐름 특성 향상을 통하여 오일생산증진 및 지반복원 등의 분야에서 우수한 성능을 보여왔다. 따라서, 본 연구에서는 폴리아크릴산(polyacrylic acid)을 포함한 모래의 흙-습윤 특성곡선의 이해하기 위해서 실내시험을 수행하고, 이론적 모델의 매개변수 변화를 연구하였다. 그 결과, 폴리아크릴산(polyacrylic acid)의 농도가 증가함에 따라, 포화된 모래에 주입되는 공기의 주입 모세관압력이 증가함을 보이고, 높은 모세관압력에서의 잔류 함수비 역시 증가하고 있음을 보였다. 또한, 이론식 모델의 매개변수를 구하였으며, 이를 활용한 흙-습윤 특성곡선이 실내 실험 결과와 잘 일치하고 있음을 보였다. 따라서, 이론적 모델의 매개변수를 알고 있으면, 본 연구에서 활용된 폴리아크릴산(polyacrylic acid)이외의 바이오폴리머를 포함한 모래 지반의 흙-습윤 특성곡선이 예측이 가능함을 설명하였다. Soil-water characteristic curve, which is called soil retention curve, is required to explore water flows in unsaturated soils, relative permeability of water in multi-phase fluids flow, and change to stiffness and volume of soils. Thus, the understanding of soil-water characteristic curves of soils help us explore the behavior of soils inclduing fluids. Biopolymers are environmental-friendly materials, which can be completely degraded by microbes and have been believed not to affect the nature. Thus, various biopolymers such as deacetylated power, polyethylene oxide, xanthan gum, alginic acid sodium salt, and polyacrylic acid have been studies for the application to soil remediation, soil improvement, and enhanced oil recovery. PAA (polyacrylic acid) is one of biopolymers, which have shown a great effect in enhanced oil recovery as well as soil remediation because of the improvement of water-flood performance by mobility control. The study on soil-water characteristic curves of sandy soils containing PAA (polyacrylic acid) has been conducted through experimentations and theoretical models. The results show that both capillary entry pressure and residual water saturation dramatically increase according to the increased concentration of PAA (polyacrylic acid). Also, soil-water characteristic curves by theoretical models are quite well consistent with the results by experimental studies. Thus, soil-water characteristic curves of sandy soils containing biopolymers such as PAA (polyacrylic acid) can be estimated using fitting parameters for the theoretical model.

Numerical investigation of water-entry characteristics of high-speed parallel projectiles

Lu Lin,Wang Chen,Li Qiang,Sahoo Prasanta K. 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1

In this study, an attempt has been made to investigate the water-entry characteristics of the high-speed parallel projectile numerically. The shear stress transport k-u turbulence model and the Zwart-Gerber- Belamri cavitation model based on the Reynolds-Averaged NaviereStokes method were used. The grid independent inspection and grid convergence index is carried out and verified. The influences of the parallel water-entry on flow filed characteristics, trajectory stability and drag reduction performance for different values of initial water-entry speed (v0 ¼ 280 m/s, 340 m/s, 400 m/s) and clearance between the parallel projectiles (Lp ¼ 0.5D, 1.0D, 2.0D, 3.0D) are presented and analyzed in detail. Under the condition of the parallel water-entry, it can be found that due to the intense interference between the parallel projectiles, the distribution of cavity is non-uniform and part of the projectile is exposed to water, resulting in the destruction of the cavity structure and the decline of trajectory stability. In addition, the parallel projectile suffers more severe lateral force that separates the two projectiles. The drag reduction performance is impacted and the velocity attenuation is accelerated as the clearance between the parallel projectiles reduces.

Effect of wettability on the water entry problem of aluminum spheres

Seolha Kim,김동섭,김형모 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.3

We investigated the hydrodynamics of water entry by aluminum spheres varying in wettability, assisted by nano/microscaled surface morphology. A wide range of contact angle (C.A.: 0° £ θ 0 < 170°) on the test spheres was prepared via inexpensive single-step anodization method. The water entry events: Splash and cavity formation, were visualized by a high-speed camera to understand the fast transient features affected by the surface wettability. In terms of hydrodynamics, cavity formation and air entrainment during the water entry were analyzed via dynamic wetting of liquid film flow along the sphere surface. It was confirmed that wettability was a determinant factor of both splash shape and cavity formation, especially in hydrophobic condition (90° £ θ 0 ). Furthermore, the analysis of dynamic contact angle of liquid film front in this study was able to classify the water entry events more detail than previous literature. In addition, we also recorded audio signals to evaluate acoustic pressures produced by the impact between spheres and water pool. The audio signals, which are expected to be proportional to acoustic pressures, differed when hydrophilic and hydrophobic spheres entered water.

Characteristics of the multiphase flow field with super-cavitation induced by successively fired projectiles under-water and cross-medium

Dong-Hui Zhou,Hong-Hui Shi,Hui-Xia Jia 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.1

The multiphase flow field with supercavitation induced by successively fired underwater projectiles is very complicated. It involves the interaction of two or more supercavitating flow fields, which is very different from the supercavitating flow of single underwater projectile. In the paper, the multiphase flow field with supercavitation induced by two successively fired projectiles underwater and cross-media (water-entry and water-exit) was simulated. The interaction effect between supercavities induced by two projectiles was particularly analyzed. The influence mechanism of the supercavity evolution on the motion of two projectiles was also analyzed. The results indicate that, the supercavitating flow fields of two successively fired underwater projectiles interact on each other. The coalescence, separation and collapse of cavities occur during the interaction stage of the supercavitating flow fields, which causes that the second-fired projectile enters the supercavity of the first one. The second-fired projectile can catch up with the first one and then a rear-end collision happens. The collision causes disturbances on the supercavity contour. The impact load of the secondfired projectile during the water-entry period is smaller than that of the first one. The cavities induced by the first- and second-fired projectiles coalesce each other into a cavity, and the second-fired projectile is finally completely wrapped by a supercavity. During the water-entry process, a rear-end collision also happens. In the process of water-exit, the supercavity induced by the first-fired projectile is blocked under the free surface, and then the first-fired projectile flies into the air after throwing off the water layer. Under the influence of the supercavity separated by the first-fired projectile, the second-fired projectile can escape from its own supercavity, and then enter the supercavity of the first-fired projectile. With the supercavity collapse of the first-fired projectile, a new partial cavity generates around the second-fired projectile.

Finding the best combination of numerical schemes for 2-D SPH simulation of wedge water entry for a wide range of deadrise angles

Farsi, Mohammad,Ghadimi, Parviz The Society of Naval Architects of Korea 2014 International Journal of Naval Architecture and Oc Vol.6 No.3

Main aim of this paper is to find the best combination of numerical schemes for 2-D SPH simulation of wedge water entry. Diffusion term is considered as laminar, turbulent, and artificial viscosity. Density filter that seriously affects the pressure distribution is investigated by adopting no filter, first order filter, and second order filter. Validation of the results indicates that turbulent model and first order density filter can lead to more reasonable solutions. This simulation was then conducted for wedge water entry with wide range of deadrise angles including 10 degrees, 20 degrees, 30 degrees, 45 degrees, 60 degrees and 81 degrees, with extreme deadrise angles of 10 degrees, 60 degrees and 81 degrees being considered. Comparison of SPH results with BEM solutions has displayed favorable agreement. In two particular cases where experimental data are available, the SPH results are shown to be closer to the experiments than BEM solution. While, accuracy of the obtained results for moderate deadrise angles is desirable, numerical findings for very small or very large deadrise angles are also very reasonable.

Finding the best combination of numerical schemes for 2-D SPH simulation of wedge water entry for a wide range of deadrise angles

Mohammad Farsi,Parviz Ghadimi 대한조선학회 2014 International Journal of Naval Architecture and Oc Vol.6 No.3

Main aim of this paper is to find the best combination of numerical schemes for 2-D SPH simulation of wedge water entry. Diffusion term is considered as laminar, turbulent, and artificial viscosity. Density filter that se-riously affects the pressure distribution is investigated by adopting no filter, first order filter, and second order filter. Validation of the results indicates that turbulent model and first order density filter can lead to more reasonable solutions. This simulation was then conducted for wedge water entry with wide range of deadrise angles including 10 degrees, 20 degrees, 30 degrees, 45 degrees, 60 degrees and 81 degrees, with extreme deadrise angles of 10 degrees, 60 degrees and 81 degrees being considered. Comparison of SPH results with BEM solutions has displayed favorable agreement. In two particular cases where experimental data are available, the SPH results are shown to be closer to the experiments than BEM solution. While, accuracy of the obtained results for moderate deadrise angles is desirable, numerical findings for very small or very large deadrise angles are also very reasonable.