Simulated and Experimental Study of Sediments Sampling Parameters Based on the VOF Method

Sediments in the seabed hold vital clues to the study of marine geology, microbial communities and history of ocean life, and the remote operated vehicle (ROV) mounted tubular sampling is an important way to obtain sediments. However, sampling in the seabed is a particularly difficult and complicated task due to the difficulty accessing deep water layers. The sampling is affected by the sampler’s structural parameters, operation parameters and the interaction between the sampling tube and sediments, which usually results in low volume and coring rate of sediments obtained. This paper simulated the soft viscous seabed sediments as non-Newtonian Herschel-Bulkley viscoplastic fluids and established a numerical model for the tubular sampling based on the volume of fluid (VOF) method. The influence rules of the sampling tube diameter, drainage area rate, penetration velocity, and sediments dynamic viscosity on coring rate and volume were studied. The results showed that coring volume was negatively correlated with all the parameters except the sampling tube diameter. Furthermore, coring rate decreased with increases in penetration velocity, drainage area rate, and sediments dynamic viscosity. The coring rate first increased and then decreased with increasing of the sampling tube diameter, and the peak value was also influenced by penetration velocity. Then, based on the numerical simulation results, an experimental sampling platform was set up and real-world sampling experiments were conducted. The simulation results tallied with the experimental results, with a maximum absolute error of only 4.6%, which verified that the numerical simulation model accurately reflected real-world sampling. The findings in this paper can provide a theoretical basis for facilitating the optimal design of the geometric structure of the seabed sediments samplers and the parameters in the sampling process.

Numerical Simulations of Air Cavities in Inclined Plunging Jets

The dynamic process of circular water jets plunging into a quiescent pool was analyzed in this study based on the RNG k∼ε turbulence model and VOF method. The effects of jet velocity and inclination angles relative to horizontal on the cavity shapes and sizes were analyzed. The simulation successfully captured the formation, development, pinch-off, and disintegration phenomena of cavities. The shape of the cavity is mainly affected by the impact angle, while the impact velocity mainly affects the size of the cavity. The cavity pinch-off initially appears at a certain point in any direction for vertical jets, while the cavity in the opposite direction of flow pinch-off appears before the cavity in the direction of flow for inclined jets. Before cavity pinch-off, the maximum radial and axial sizes of the cavity generally increase with the impact velocity and the time after impingement. The axial penetration velocity of the cavity tip is approximately half of the impact velocity, which is consistent with previous research. Finally, based on the statistics of the cavity sizes, empirical formulas for predicting the maximum radial and axial sizes of the cavity were established.

Oblique Penetration of a Circular Pipe Target by a Prefabricated Fragment

For the oblique penetration of a circular pipe target by a prefabricated fragment, the finite element software LS-DYNA was used to build a computational model for the circular pipe considering the penetration by a cylindrical fragment from different directions. The failure characteristics of the pipe were acquired and the critical penetration velocity was calculated. The relationship between the initial velocity and critical angle of ricochet was found. The experiment was then conducted to verify the results obtained, indicating that the simulation results are in good agreement with the experimental ones. It was shown that the main critical failure pattern of a circular pipe is shear perforation or a penetrating crack. The critical penetration velocity is positively correlated with the direction angle [Formula: see text] and entry angle [Formula: see text]. For entry angles greater than 30∘, the critical penetration velocity increases with an increase in the direction angle, and this effect is stronger for higher direction angles. The critical angle of ricochet is positively correlated with the initial velocity of the fragment. The critical angle of ricochet tends to approach a constant of 60∘ as the initial velocity of the fragment increases.

Hypervelocity penetration of granular silicon carbide from mesoscale simulations

Penetration of gold rods into SiC powder targets at velocities of 1 to 3 km/s are investigated using mesoscale simulations. The range of impact velocities is chosen to coincide with previous penetration experiments and represents a new regime over which to test the applicability of mesoscale simulations of granular materials. Both 2D and 3D geometries of the combined penetrator and powder system are considered. Analysis of the penetration depth histories at various impact velocities shows the penetrator undergoes an initial transient period of rapid deceleration within the first several microseconds before converging to a steady state characterized by jumps in the penetration velocity on the order of a few hundred meters per second. Steady-state penetration velocities obtained from 2D and 3D simulations agree well with one another, but lie below those computed using hydrodynamic theory, which indicates a non-zero strength for the simulated powders over this range of impact velocities. For comparable initial powder densities, 3D simulations predict steady-state penetration velocities in good agreement with those measured in penetration experiments on pre-compacted SiC powder specimens.

Simulating Lateral Drift of a Shaped Charge Jet in ALEGRA

Shaped charge jet (SCJ) research has long been an active area for industrial, academic, and defense organizations. Traditionally, the depth of penetration (DOP) has been one of the most important metrics for the evaluation of shaped charge jet performance, and early 1D analytical penetration models based on hydrodynamic penetration were created with this metric in mind [1]. As the standoff of a shaped charge jet increases, the DOP reaches a maximum and then begins to decrease. A simple 1D hydrodynamic penetration model must account for the totality of the jet material on axis penetrating, and as a result experimental DOP at longer standoffs is lower than the analytical models predicted. Some analytical models reasoned that since a velocity gradient evolves as a SCJ forms, contributions to penetration from jet material below a minimum jet or penetration velocity should be eliminated. These were better able to account for the difference between analytical hydrodynamic and experimental DOPs [2]. The actual difference between analytical hydrodynamic penetration theory and experimentally recorded values is now regarded to be a result of 3D phenomena including particle tumbling and motion transverse to the jet axis known as lateral drift [2]. The origins of these 3D phenomena have been attributed to sources including variability in the uniformity of the explosive charge or the microstructure of the liner [2,3].

Evaluation of protective properties of safety anti-penetration inserts in footwear designed for professional use

In accordance with applicable standards: PN-EN 12568:2011 i PN-EN ISO 20344:2012, anti-penetration inserts and footwear outsole with anti-penetration inserts are tested at penetration velocity (10 ± 3) mm/min, with a test nail of (4.50 ± 0.05) mm in diameter and a conical tip with a truncation of 1 mm and an angle of 30o. This velocity is relatively low compared to penetration velocity when walking vigorously. The diameter of the test nail also exceeds diameters of most nails used in industry. Users’ contact with sharp objects potentially present on the ground at a worksite is usually more dynamic. It is important for footwear and the inserts to ensure workers’ safety. The Footwear Laboratory aimed to determine the effect of penetration velocity and test nail dimensions on the protective capacity of inserts. It also evaluated the quality of these items.

Investigation on penetration model of shaped charge jet in water

To analyze the process of jet penetration in water medium quantitatively, the properties of jet penetration spaced target with water interlayer were studied through test and numerical simulation. Two theoretical models of jet penetration in water were proposed. The theoretical model 1 was established considering the impact of the shock wave, combined with the shock equation Rankine–Hugoniot and the virtual origin calculation method. The theoretical model 2 was obtained by fitting theoretical analysis and numerical simulation results. The effectiveness and universality of the two theoretical models were compared through the numerical simulation results. Both the models can reflect the relationship between the penetration velocity and the penetration distance in water well, and both the deviation and stability of theoretical model 1 are better than 2, the lower penetration velocity, and the larger deviation of the theoretical model 2. Therefore, the theoretical model 1 can reflect the properties of jet penetration in water effectively, and provide the reference of model simulation and theoretical research.