Papers by Keyword: Water Impact

Abstract: Aiming to evaluate the resistance of High Performance Concrete (HPC) against the abrasion erosion due to the continual impact of water and water borne materials, six HPC mixtures reinforced with different fibers and fiber combinations were prepared and tested experimentally in this study. All mixtures share the same contents of all materials, while the types and combinations of fibers used were different among the mixtures. All mixtures included a total of 2.5% volumetric content of fibers. The mixture S6 included pure 6 mm micro-steel fiber (S6), S15 mixture included pure 15 mm micro-steel fiber (S15), while the S6-S15 mixture included 1.25% of each of S6 and S15. S6-PP and S15-PP included 2.0% of S6 or S15, respectively, in combination with 0.5% of polypropylene fiber (PP), while the sixth mixture included 1.0% S6, 1.0% S15 and 0.5% PP. The impact abrasion test was conducted on 200×200 mm plat targets with 50 mm thickness that were fixed perpendicular to a water jet with a high speed of 20 m/s. The results revealed that all HPC mixtures exhibited much higher abrasion resistance than normal concrete. The results also showed that the S15 mixture was the one with highest abrasion resistance with an abrasion loss of only approximately 20 grams after 12 hours testing.

Abstract: An experimental program was directed in this study to evaluate the abrasion resistance of reactive powder concrete (RPC) under direct normal impact of water jet. Abrasion and compressive strength specimens were cast from six RPC mixtures using different single and hybrid distributions of 6 mm-length and 15 mm-length micros-steel fibers and 18 mm-length polypropylene fiber. Fixed mix proportions were used for the six RPC mixtures and with fixed total volumetric fiber content of 2.5%. In addition to the RPC mixtures, a normal concrete mixture was prepared for comparison purposes. All specimens were cured in the same conditions and tested at an age of 28 days. The test results showed that abrasion weight losses increase with time at rates that are independent of fiber type and fiber distribution. The results also showed that all RPC mixtures exhibited significantly lower abrasion losses than normal concrete. The lowest percentage abrasion weight losses were recorded for the mixture with pure 15 mm micro-steel, where after 12 testing hours, it was 0.41% of the total weight before testing. On the other hand, the mixture with pure 6 mm micro-steel fiber exhibited the highest percentage abrasion weight loss (0.98%) among the six RPC mixtures. Another conclusion is that the inclusion of polypropylene fiber to compose hybrid fiber distribution with micro-steel fiber led mostly to lower abrasion losses.

Abstract: It is significant for the phenomena of bouncing on water to analyze the ditching procedure of any kind of aircraft. The SPH method is employed to achieve a numerical simulation in the architecture of LS-DYNA and PrePost programs. The water domain is modeled by SPH and the boundary condition is discussed too. Through a set of contrastive analysis of different boundary conditions, some constructive suggestions of establishing the boundary conditions are given to deeply simulate aircraft ditching in the future.

Abstract: The aim of this work is to investigate the hydroelastic responses of rectangular, clamped light weight pyramidal sandwich plate structures with imperfection (LWPSPS-IM) subjected to water impact via analytical prediction and numerical simulation. Firstly, the characteristics of impact pressure and structure deformation are computed by using FEM program LS-DYNA based on the proposed 3D multi-physics computational model. Numerical results show that the impact pressure of total fluid-solid interaction (FSI) surface for LWPSPS-IM is lower than that of the perfect LWPSPS. In the theoretical approach, a novel analytical method is proposed to calculate the elastic constants of LWPSPS-IM. Then an engineering estimation model to predict the maximum deformation of LWPSPS-IM is developed, in which the total deformation is divided into two parts, i.e. local field deformation and global field deformation and they are both computed using analytical approach. Good agreement between the numerical results and ones obtained from the proposed analytical model is achieved.

Abstract: The outcomes of a research focusing on water modeling and Fluid-Structure Interaction by ALE and SPH in LSTC/LS-Dyna971 are presented in this paper. Firstly the water impact behaviors of a rigid wedge are modeled with water region by ALE and SPH. The size of fluid elements plays critical role to the numerical results, so three different cases varied in mesh or particle spacing both in ALE and SPH methods are detailed discussed. The numerical results are compared both one to the others and to the experimental and theoretical results in terms of vertical velocity and slamming force, which can be concluded that the more elements modeled in the simulation, the better approximation with the experiment results. An additional discussion of propagation of pressure wave by SPH and CPU time are also presented.

Abstract: The impact on water of aeronautical structures is likely to turn into a tragic event. In view of this, it is essential to develop new solutions to design worthy structure that can assure best behavior. The Smoothed Particles Hydrodynamics (SPH) is a mesh-free interpolation method which is a recent numerical analysis technique. One example of water impact based on SPH is presented here, which aims at an accurate numerical simulation of Fluid-Structure Interaction(FSI) in free surface flow context. The example describes a rigid sphere impacting onto water, presenting the global impact behavior as well as comparing the impact coefficient with analytical and experimental results. The SPH method is proved to be a reliable and efficient numerical tool.

Abstract: Numerical simulations of two-dimensional cylinder free droping into water are presented based on volume of fluid (VOF) method and dynamic mesh technique. Solutions with a time-accurate finite-volume method (FVM) were generated based on the unsteady compressible ensemble averaged Navier-Stokes equations for the air and the unsteady incompressible ensemble averaged Navier-Stokes equations for the water. Computed pressure histories of the cylinder were compared with experimentally measured values. The performance of various turbulence models for pressure prediction was assessed. The results indicate that Realizable k-epsilon model with Enhanced Wall Treatment is the best choice for engineering practice.

Abstract: The paper presents a fluid structure interaction based numerical study of impact loading for a hemispherical structure upon water and a space capsule water landing. The study has a strong relevance in the determination of the crashworthiness of aerospace structures upon water impact loading. Finite element based numerical techniques have been used for the analysis of the underlying transient dynamic and fluid-structure interaction. Smoothed Particle Hydrodynamics (SPH) and Arbitrary Lagrange-Eulerian (ALE) methods have been used to simulate the behaviour of the fluid (water) under impact conditions. The accelerations and velocities of the impacting objects have been validated with by experimental measurements and analytical results. Numerical analyses showed a strong potential for the use of developed computational fluid structure interaction models for analyses of water impact loading related problems.