scholarly journals Gelatine cavity dynamics of high-speed sphere impact

2019 ◽  
Vol 880 ◽  
pp. 707-722
Author(s):  
Akihito Kiyama ◽  
Mohammad M. Mansoor ◽  
Nathan B. Speirs ◽  
Yoshiyuki Tagawa ◽  
Tadd T. Truscott
Keyword(s):  
Froude Number ◽  
High Speed ◽  
Cavity Length ◽  
Solid Sphere ◽  
Water Entry ◽  
Cavity Radius ◽  
Surface Textures ◽  
Lower Cavity ◽  
The Impact ◽  
Different Order

We investigate the impact and penetration of a solid sphere passing through gelatine at various impact speeds up to $143.2~\text{m}~\text{s}^{-1}$. Tests were performed with several concentrations of gelatine. Impacts for low elastic Froude number $\mathit{Fr}_{e}$, a ratio between inertia and gelatine elasticity, resulted in rebound. Higher $\mathit{Fr}_{e}$ values resulted in penetration, forming cavities with prominent surface textures. The overall shape of the cavities resembles those observed in water-entry experiments, yet they appear in a different order with respect to increasing inertia: rebound, quasi-seal, deep-seal, shallow-seal and surface-seal. Remarkably, similar to the $We$–$Bo$ phase diagram in water-entry experiments, the elastic Froude number $\mathit{Fr}_{e}$ and elastic Grashof number $\mathit{Gr}_{e}$ (a ratio between gravity and gelatine elasticity) classify all five different phenomena into distinguishable regimes. We find that $\mathit{Fr}_{e}$ can be a good indicator to describe the cavity length $H$, particularly in the shallow-seal regime. Finally, the evolution of cavity shape, pinch-off depth, and lower cavity radius are investigated for different $\mathit{Fr}_{e}$ values.

Experimental Investigation of Water Entry Impact on Hydrophobic Surfaces

2015 ◽  
Author(s):  
Bulent Guzel ◽  
Fatih C. Korkmaz
Keyword(s):  
Experimental Investigation ◽  
Flow Separation ◽  
High Speed ◽  
Water Entry ◽  
Air Entrapment ◽  
Hydrophobic Surfaces ◽  
Blunt Bodies ◽  
Drop Tests ◽  
Set Up ◽  
The Impact

The results of an experimental investigation on hull bottom slamming of three different geometries, sphere, cylinder and wedge, with hydrophobic surfaces are presented. In water entry of blunt bodies, different fluid dynamics phenomena like jet formation, cavity formation, water splashing, flow separation on solid surfaces and air entrapment between solid and liquid surface have been studied for decades. Our study is aimed at understanding and modeling the dynamics of slamming under an extended range of parameters including hydrophobic surfaces. In this study, drop tests have been set up for hull bottom slamming by dropping a body from various heights toward water surface. From digital images captured using a high speed camera, flow separation and water splashing at different velocities are observed and spreading diameters and entrance characteristics are measured during the impact process. At the same time, we measure the pressure distribution on the surface of the bodies during impact via strain gages.

Numerical evaluation of the hydrodynamic impact characteristics of the air launched AUV upon water entry

2020 ◽  
Vol 34 (14) ◽  
pp. 2050149
Author(s):  
Ahmad Zamir Chaudhry ◽  
Guang Pan ◽  
Yao Shi
Keyword(s):  
High Speed ◽  
Impact Load ◽  
Research Work ◽  
Computational Cost ◽  
Water Entry ◽  
Structure Design ◽  
Hydrodynamic Characteristics ◽  
Ale Method ◽  
The Impact ◽  
Selection Of

In this paper, water entry process of air launched AUV is investigated by employing fully coupled finite element method and arbitrary Lagrange–Euler formulation (FEM-ALE) and using penalty coupling technique. Numerical model is established to describe the hydrodynamic characteristics and flow patterns of a high-speed water entry AUV. The effectiveness and accuracy of the numerical simulation are verified quantitatively by the experiments of the earlier study. Selection of suitable advection method and mesh convergence study is carried out during experimental validation process. It is found that appropriate mesh size of impact domain is crucial for numerical simulations and second-order Van Leer advection method is more appropriate for high speed water entry problems. Subsequently, the arbitrary Lagrange–Euler (ALE) algorithm is used to describe the variation laws of the impact load characteristics with water entry velocities, water entry angles and different AUV masses. Dimensionless impact coefficient of AUV at different velocities calculated using ALE method is compared with SPH results. This reveals that ALE method can also simulate the water entry process accurately with less computational cost. This research work can provide beneficial reference information for structure design of AUV and for selection of the water entry parameters.

Rupture of Cavity Film Due to Water Entry of Horizontal Superhydrophobic Circular Cylinders

2013 ◽  
Vol 32 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Y. Ueda ◽  
M. Iguchi
Keyword(s):  
Froude Number ◽  
High Speed ◽  
Water Entry ◽  
Circular Cylinders ◽  
Water Model ◽  
Inertia Force ◽  
Fluid Inertia ◽  
Contact Lines ◽  
Low Froude Number ◽  
High Froude Number

AbstractIn materials refining processes such as steelmaking process, bath-entry of agents such as CaCO3 attracts career gas around their entire surface so that the dispersion in the bath can be inhibited. To shed light on the still vague instant phenomenon, this study employs a water model experiment and carries out the visualization. Therefore, this study visually demonstrates the growth and rupture of air cavity due to water entry of horizontal superhydrophobic circular cylinders with the aid of a high-speed camera. Here, we show that the water entry of the horizontal hydrophobic cylinder forms a film of cavity behind the cylinder whereas a hydrophilic cylinder forms a cavity from both ends of the cylinder. In a high Froude number entry, once the cavity film ruptured on both sides of it, the contact lines of the cavity film abruptly move along the surface of the cylinder. In a low Froude number entry, the influence of weak fluid inertia force makes several ruptures on the cavity film which grow individually and split off the cavity. Of a particular interest is the fact that the multi-rupture regime appeals for the spanwise three-dimensionality on the cavity film against the previous studies within two-dimensional treatment. Furthermore, this report finds the trend for some range of Fr that the nondimensionalized closure depth of the cavity film zc with diameter of the cylinder obeys zc/d ∼ Fr1/3 in the range 4.7 ≤ Fr ≤ 40 although it depends on Fr in the water-entry problem of a hydrophobic sphere.

scholarly journals Numerical simulation of cavitation characteristics in high speed water entry of head-jetting underwater vehicle

2021 ◽  
Vol 39 (4) ◽  
pp. 810-817
Author(s):  
Hairui Zhao ◽  
Yao Shi ◽  
Guang Pan
Keyword(s):  
Numerical Simulation ◽  
High Speed ◽  
Impact Load ◽  
Underwater Vehicle ◽  
Water Entry ◽  
Engineering Practice ◽  
Entry Angle ◽  
Air Jet ◽  
Entry Velocity ◽  
The Impact

Autonomous underwater vehicle will be subjected to a huge impact load during high speed water entry, which will damage the structure and the internal instruments of the vehicle. Therefore, it is of great significance to study the buffer mechanism of the vehicle during the process of water-entry. In this paper, a kind of head-jetting device with disk cavitation is used. The complex cavitation forms, under the three-phase coupling of gas, liquid and solid, in the water entry process of the vehicle on which the device is installed. In this paper, the numerical simulation of high-speed water entry of the vehicle equipped with head jet device is carried out. Through the analysis of water entry cavitation under typical working conditions, the following conclusions are obtained. After the installation of head jet device, the water entry cavity of the vehicle changes gradually from cone to spindle shape. The air jet, compared with that without jet, can promote the formation of water inlet supercavitation, decrease the interaction area between the vehicle and water, and reduce the impact load during water entry. At the same water entry depth, the diameter of cavitation increases with the amount of air jet. The water entry velocity has a great influence on the difference of cavitation shape. The water entry depth closure phenomenon, when the water entry velocity is less than 100 m/s, can be observed in the depth of 3.5 times of the projectile length. The water entry angle has a significant effect on the cavitation shape. The cavity shows obvious asymmetry when the vehicle slants into the water, and the diameter and length of the bubbles decrease with the increase of the water entry angle. The research content of this paper provides technical support for the engineering practice of high-speed water entry and load reduction, and the conclusions are of great significance in related fields.

scholarly journals Effect of Surface Textures and Wettability on Droplet Impact on a Heated Surface

Processes ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 350
Author(s):  
Satoshi Ogata ◽  
Ryo Nakanishi
Keyword(s):  
Stainless Steel ◽  
High Speed ◽  
Liquid Droplet ◽  
Steel Wire ◽  
Heated Surface ◽  
Impact Behavior ◽  
Stainless Steel Surface ◽  
Textured Surface ◽  
Surface Textures ◽  
The Impact

A liquid droplet can hover over a solid surface that is heated above the Leidenfrost point (LFP), at which an insulating vapor layer is formed that acts as a heat transfer barrier. Recent studies have reported that hierarchical micro- and nanoscale textures provide high wettability and significant LFP enhancement. However, such textures are often difficult and expensive to fabricate. Therefore, this study aimed to experimentally demonstrate LFP enhancement through the use of low-cost hierarchical textures. Surface textures were fabricated by coating SiO2 nanoparticles on stainless steel wire meshes. The droplet lifetime method was used to determine the LFP in a temperature range of 200 °C–490 °C. High-speed imaging (4000–23,000 fps) was performed for visualizing the impact behavior of a droplet. The LFP value of the nanocoated mesh surface was found to be greater than 490 °C. This enhanced LFP was 178 °C higher than that of a stainless steel surface and 38 °C higher than that of a single-layer textured surface. Furthermore, with respect to the LFP enhancement, the explosive impact behavior of a droplet can be observed on nanocoated mesh surfaces.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Case study: Prediction and field tests of railway noise and effects of a low-height noise barrier

2020 ◽  
Vol 68 (4) ◽  
pp. 303-314
Author(s):  
Yuna Park ◽  
Hyo-In Koh ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
University of Science and Technology, Transpo ◽  
...  
Keyword(s):  
High Speed ◽  
Field Tests ◽  
Residential Areas ◽  
Railway Systems ◽  
Railway Noise ◽  
Sound Levels ◽  
Noise Barrier ◽  
The Difference ◽  
Reduction Effect ◽  
The Impact

Railway noise is calculated to predict the impact of new or reconstructed railway tracks on nearby residential areas. The results are used to prepare adequate counter- measures, and the calculation results are directly related to the cost of the action plans. The calculated values were used to produce noise maps for each area of inter- est. The Schall 03 2012 is one of the most frequently used methods for the production of noise maps. The latest version was released in 2012 and uses various input para- meters associated with the latest rail vehicles and track systems in Germany. This version has not been sufficiently used in South Korea, and there is a lack of standard guidelines and a precise manual for Korean railway systems. Thus, it is not clear what input parameters will match specific local cases. This study investigates the modeling procedure for Korean railway systems and the differences between calcu- lated railway sound levels and measured values obtained using the Schall 03 2012 model. Depending on the location of sound receivers, the difference between the cal- culated and measured values was within approximately 4 dB for various train types. In the case of high-speed trains, the value was approximately 7 dB. A noise-reducing measure was also modeled. The noise reduction effect of a low-height noise barrier system was predicted and evaluated for operating railway sites within the frame- work of a national research project in Korea. The comparison of calculated and measured values showed differences within 2.5 dB.

The Impact of High-Speed Rail on the Spatial Structure of Chinese Urban Agglomerations

2020 ◽  
Vol 46 (3) ◽  
pp. 379-397
Author(s):  
Chunyang Wang
Keyword(s):  
High Speed ◽  
River Delta ◽  
City Size ◽  
High Speed Rail ◽  
Local Conditions ◽  
Urban Agglomerations ◽  
Large Cities ◽  
Spatial Systems ◽  
Economic Concentration ◽  
The Impact

This paper measures the spatial evolution of urban agglomerations to understand be er the impact of high-speed rail (HSR) construction, based on panel data from fi ve major urban agglomerations in China for the period 2004–2015. It is found that there are signi ficant regional diff erences of HSR impacts. The construction of HSR has promoted population and economic diff usion in two advanced urban agglomerations, namely the Yang e River Delta and Pearl River Delta, while promoting population and economic concentration in two relatively less advanced urban agglomerations, e.g. the middle reaches of the Yang e River and Chengdu–Chongqing. In terms of city size, HSR promotes the economic proliferation of large cities and the economic concentration of small and medium-sized cities along its routes. HSR networking has provided a new impetus for restructuring urban spatial systems. Every region should optimize the industrial division with strategic functions of urban agglomeration according to local conditions and accelerate the construction of inter-city intra-regional transport network to maximize the eff ects of high-speed rail across a large regional territory.

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