Characteristics of secondary droplets produced by the impact of drops onto a smooth surface

This work investigates the splashing behaviors of droplets impacting on solid surfaces and mainly focuses on the characteristics of secondary droplets. According to the experimental results, two different splashing patterns, corona splash and levitating-lamella breakup, are observed. A new breakup mode, named rim-segmenting, is found during the levitating-lamella breakup. In particular, the detailed information of the splashing secondary droplets, including the size, velocity, angle, and total volume of the splashing secondary droplets is obtained from the experimental data. The size distribution of the splashing secondary droplets obeys the gamma distribution function. The average diameter and splashing angle of the secondary droplets are mainly related to the Reynolds number Re, and can be expressed as functions of Re. High impact velocity and liquid viscosity will result in a wider size distribution range of splashing secondary droplets. We also put forward an empirical model to predict the total splashing volume, which is consistent with the experimental data both in this work and previous studies. This work is believed to provide insights on the prediction of the characteristics of splashing secondary droplets.

Meteoroids as Source for Mercury’s exosphere

<p>The study of the meteoroid environment for particles with masses in the 1 μg - 10 g range is relevant to planetary science, space weathering of airless bodies and their upper atmospheric chemistry. For the case of airless bodies as Mercury, meteoroids hit their surfaces directly, producing impact debris and contributing to shape their thin exospheres.</p> <p>Mercury is a unique case in the solar system: absence of an atmosphere and the weakness of the intrinsic magnetic field. The Hermean exosphere is continuously eroded and refilled by interactions between plasma and surface, so the environment is considered as a single, unified system surface- exosphere-magnetosphere. The study of the generation mechanisms, the compositions and the configuration of the Hermean exosphere will provide crucial insight in the planet status and evolution. A global description of planet’s exosphere is still not available: missions visited Mercury and added a consistent amount of data, but still the actual knowledge about the morphology of this tenuous atmosphere is anyway poor. The ESA BepiColombo mission will study Mercury in details, by orbiting around the planet from 2025. For this reason, it is important to study the planet exospheric density and to develop a modelling tool ready for testing different hypothesis on the release mechanisms and for interpreting future observational data.</p> <p>In this work we focus the attention on one of the processes responsible of the Mercury’s Ca exosphere formation: micro-meteoroids impact vaporization (MMIV) from the planetary surface. <span lang="EN-US">A prototype of the Virtual Activity (VA) SPIDER (Sun-Planet Interactions Digital Environment on Request) services is used as a Monte Carlo three-dimensional model of the Hermean exosphere to simulate the bombardment of Mercury’s surface by micrometeorites from different sources, as Jupiter Family Comets (JFCs), Main Belt Asteroids (MBA), Halley Type and Oort Cloud Comets (HTCs and OCCs), and to analyze particles ejected. </span>We study how the impact vapor varies with heliocentric distance and the high impact velocity of these particles makes them critical for the morphology of Mercury exosphere, demonstrating a persistent enhancement of dust/meteoroid at dawn, which should be responsible of the dawn–dusk asymmetry in Mercury’s Ca exosphere.</p> <p> </p> <p><sub>The <em>Sun Planet Interactions Digital Environment on Request (SPIDER) Virtual Activity of the Europlanet H2024 Research Infrastucture is funded by the European Union's Horizon 2020 research </em></sub></p> <p><sub><em>and innovation programme under grant agreement No 871149.</em></sub></p>

Axial Force Coefficient of APFSDS Projectile

Armor-piercing ammunition is primarily used to combat against heavy armored targets (tanks), but targets can be light armored vehicles, aircraft, warehouse, structures, etc. It has been shown that the most effective type of anti-tank ammunition in the world is the APFSDS ammunition (Armor Piercing Fin Stabilized Discarding Sabot). The APFSDS projectile flies to the target and with his kinetic energy acts on the target, that is, penetrates through armor and disables the tank and his crew. Since the projectile destroys target with his kinetic energy, then it is necessary for the projectile to have the high impact velocity. The decrease in the velocity of a projectile, during flight, is mainly influenced by aerodynamic forces. The most dominant is the axial force due to the laid trajectory of the projectile. By knowing the axial force (axial force coefficient), it is possible to predict the impact velocity of the projectile, by external ballistic calculation, in function of the distance of the target, and to define the maximum effective range from the aspect of terminal ballistics. In this paper two models will be presented for predicting axial force (the axial force coefficient) of an APFSDS projectile after discarding sabot. The first model is defined in STANAG 4655 Ed.1. This model is used to predict the axial force coefficient for all types of conventional projectiles. The second model for predicting the axial force coefficient of an APFSDS projectile, which is presented in the paper, is the CFD-model (Computed Fluid Dynamics).

Drone Launched Short Range Rockets

A concept of drone launched short range rockets (DLSRR) is presented. A drone or an aircraft rises DLSRR to a release altitude of up to 20 km. At the release altitude, the drone or an aircraft is moving at a velocity of up to 700 m/s and a steep angle of up to 68° to the horizontal. After DLSRRs are released, their motors start firing. DLSRRs use slow burning motors to gain altitude and velocity. At the apogee of their flight, DLSRRs release projectiles which fly to the target and strike it at high impact velocity. The projectiles reach a target at ranges of up to 442 km and impact velocities up to 1.88 km/s. We show that a rocket launched at high altitude and high initial velocity does not need expensive thermal protection to survive ascent. Delivery of munitions to target by DLSRRs should be much less expensive than delivery by a conventional rocket. Even though delivery of munitions by bomber aircraft is even less expensive, a bomber needs to fly close to the target, while a DLSRR carrier releases the rockets from a distance of at least 200 km from the target. All parameters of DLSRRs, and their trajectories are calculated based on theoretical (mechanical and thermodynamical) analysis and on several MatLab programs.

Universal rescaling of drop impact on smooth and rough surfaces

The maximum spreading of drops impacting on smooth and rough surfaces is measured from low to high impact velocity for liquids with different surface tensions and viscosities. We demonstrate that dynamic wetting plays an important role in the spreading at low velocity, characterized by the dynamic contact angle at maximum spreading. In the energy balance, we account for the dynamic wettability by introducing the capillary energy at zero impact velocity, which relates to the spreading ratio at zero impact velocity. Correcting the measured spreading ratio by the spreading ratio at zero velocity, we find a correct scaling behaviour for low and high impact velocity and, by interpolation between the two, we find a universal scaling curve. The influence of the liquid as well as the nature and roughness of the surface are taken into account properly by rescaling with the spreading ratio at zero velocity, which, as demonstrated, is equivalent to accounting for the dynamic contact angle.

Characterizing the Importance of Free Space in the Numerical Human Body Models

The geometric fidelity of the inner organs on finite-element model (FEM) of the human body and the choice to use discontinuous mesh engender the appearance of empty spaces that do not reflect the real-life situation of human body cavities. The aim of this study is to assess the influence of these empty spaces on the behavior of a simplified FEM built with three different structures in interaction which properties are relevant with the abdominal cavity. This FEM is made up of a large sphere (peritoneum) containing two hemispheres (liver and spleen). The space between peritoneum and inner organs was defined with two different approaches and assessed under impact conditions. The first is a meshfree space (Mfs) approach, e.g., consider the space as a perfect gas. The second approach, meshed space (MS), entailed adding volumetric elements in the empty space. From each approach, one optimal configuration was identified regarding the recorded force versus compression, the mobility of inner organs, and the space incompressibility. This space has a considerable influence on the behavior of the FEM and mainly on the applied loadings of inner organs (difference reaching 70% according to the configuration). For the first approach, the incompressible gas is designated because it guarantees space incompressibility (vf/vi = 1) and inner organs loading with the lowest delay (for high impact velocity: Peak force = 89 N, compression 47%). For the second approach, the discontinuous volumetric mesh is preferred because it promotes space incompressibility (vf/vi = 0.94) and acceptable force reaction (for high impact velocity: Peak force = 97 N, compression 49%). The current study shows the importance of this space on the human FEMs cavities behavior and proposes two configurations able to be used in a future study including detailed FEM.