Specific Kinetic Energy Research Articles

A Residual Thermodynamic Analysis of Turbulence – Part 1: Theory

A new theoretical groundwork for the analysis of wall-bounded turbulent flows is offered, the application of which is presented in a parallel paper. First, it is proposed that the turbulence phenomenon is connected to the onset of an irreversible process – specifically the action of a slip flow – by which a new fundamental model can be derived. Fluid cells with specific dimensions – of length connected with the local slip length and thickness connected with the distance between two parallel slipping flows – can be hypothetically constructed, in which a specific kinetic energy dissipation can be considered to occur. Second, via a maximum entropy production process a self-organized grouping of cells occurs – which results in the distinct zones viscous sublayer, buffer layer, and the log-law region to be built up. It appears that the underlying web structure may take the form of either representing a perfect web structure without any visible swirls, or a partially defect web structure where unbalanced forces may result in the generation of apparent swirls – which in turn might grow into larger turbulent eddies. Third, on the transition from laminar to turbulent flows, a nominal connection between the onset of a turbulent wall boundary layer (in a pipe flow), the Reynolds number as well as the wall surface roughness can be derived.

Experimental and numerical study of tantalum‑tungsten alloy rod penetrator impacting thick armor plate

To study the penetration ability of tantalum‑tungsten alloy rod penetrator into armor plate and clarify its deformation and failure behavior in the process of penetration, the experimental and numerical study of tantalum‑tungsten alloy rod penetrator penetrating armor plate was carried out in this paper. The results show that the penetration efficiency of tantalum‑tungsten alloy rod penetrator and tungsten alloy rod penetrator into 30CrMnMoRE armor plate is equivalent in the range of impact velocity from 1100 m/s to 1700 m/s, whereas the penetration efficiency per unit specific kinetic energy of tantalum‑tungsten alloy rod penetrator is higher than that of tungsten alloy rod penetrator when the impact velocity is greater than 1500 m/s. The ultimate penetration velocity of tantalum‑tungsten alloy rod penetrator with length-to-diameter ratio of 6.25 and diameter of 8 mm to 30CrMnMoRE armor plate with the thickness of 60 mm is about 1695 m/s. At the moment of impacting the target plate, the velocity of the head of the tantalum‑tungsten alloy rod penetrator decreases sharply, but the velocity at the rear of the penetrator remains basically unchanged. In the process of penetration, the head of the penetrator deforms and flows outward under the huge impact pressure, and finally, the length of the penetrator is shortened to zero, forming a barrel-like structure, but the barrel structure still has a certain penetration ability. This study can help to further understand the flow characteristics and penetration ability of tantalum‑tungsten alloy rod penetrator in high-speed penetration.

Influence of wind and light on the floating and sinking process of Microcystis

The vertical migration and accumulation of Microcystis colonies is a critical process in algal bloom formation. This work explored the effect of wind and light intensity on the vertical migration of Microcystis colonies. The wind-driven currents, light-driven changes in mass density of colonies, and the effect of colony size was coupled to simulate the vertical motion of colonies via Ansys Fluent and MATLAB. Results showed that light causes Microcystis to exhibit a ‘day-sinking and night-floating’ (d-n) phenomenon, however, wind weakens the phenomenon by forming a turbulent drag force that inhibits the vertical movement of Microcystis. This study proposed a kinetic ratio-based method, that there is a specific equilibrium turbulent kinetic energy and when turbulent kinetic energy of the water body is greater than the equilibrium turbulent kinetic energy, the d-n phenomenon does not occur. For Lake Taihu, the wind-driven turbulent kinetic energy is usually greater than the equilibrium turbulent kinetic energy. Therefore, Microcystis colonies may not exhibit the d-n phenomenon. Our findings provide a new theoretical basis for current process-based models in simulating algal blooms in large shallow lakes.

Experimental research on damage characteristics of multi-spaced plates with long rods of steel and W-Zr reactive material at hypervelocity impact

The damage or penetration research of the long rods has attracted more and more attention from scholars worldwide. In this article, the dynamic compression tests of W-Zr reactive material are performed. Six experiments of the long rods impacting the multi-spaced plates at hypervelocity are carried out on a two-stage light gas gun. Two kinds of long rods, inert 40CrNi2MoA steel and W-Zr reactive material, are used. The initial impact speed ranges from 2040 m/s to 3200 m/s. According to results, W-Zr reactive material reacts at the strain rate of 2200 s−1 and higher, whose strength limit is related to the strain rate. The long rods can produce debris clouds when hitting the multi-spaced plates at the speed of 2040 m/s and higher, causing large perforation and great damaged area in the subsequent plates. The perforations and damaged areas of the multi-spaced plates depend on the specific kinetic energy of the long rods. The violent reaction behavior of the W-Zr reactive material helps to cause large perforation and damaged area of the subsequent plates than inert materials. It proves that the damage ability of the W-Zr reactive material is stronger than that of the inert material with a similar density.

Effect of sphere radius and bullet hitting location on the ballistic performance of alumina ceramic tile

Designers in the defense industry aim to increase the protectiveness of armors while decreasing their weight. On-body armors, composites, and ceramics are widely used due to their lightweight, high hardness, and reduction in blunt trauma. Ceramic armor materials are usually used as the front face for their capability to erode or break up the projectile. There exist various parameters affecting the performance of ceramic armors, and one of these parameters is surface profile. It is a compelling parameter due to its ability to yaw the projectile, causing a reduction of projectile penetration capacity. This study aims to compare alumina ceramic tiles with different surface profiles in terms of their specific kinetic energy absorption (SKEA). Although experimental results are necessary due to an armor system’s acceptance, numerical results lead to a better understanding of surface profiling. In this study, LS-DYNA software is used for ballistic impact simulations to explore the effect of surface profiling. In the simulations, a steel projectile with varying velocities penetrates a ceramic tile. Johnson-Cook material model is used for the projectile, whereas Johnson- Holmquist material model is used for ceramic tiles. For the modeling of ceramic tile, smoothed particle hydrodynamics (SPH) is used to capture fractures and debris. In this study, the finite element (FE) model that simulates a projectile impacting a flat ceramic tile is generated and validated with the experimental results available in the literature. Then, surface profiled ceramic tiles having spherical surface profile with different radius values are analyzed, and their SKEA values are compared. It is found that surface profiling can increase the SKEA value up to 56% when the bullet hits the gap between four spheres. The worst ballistic performance of surface profiled tiles occurs when the bullet hits the top of the sphere; however, even the worst performance increases the SKEA value by 21%.

Нелинейные эффекты при распылении арсенида галлия и кремния кластерными ионами висмута

An experimental study on the influence of the energy and the number of atoms in the bombarding ions Bin+ (n = 1-4) on the sputter yield of GaAs was carried out. It was shown that the specific sputter yield Ysp nonadditively increase with an increasing of n and specific kinetic energy Esp per an atom in the bombarding ion, and the efficiency of energy transfer from bombarding ions to target atoms also increases with an increasing of n. A comparison was made with the previously obtained results for Si targets.

Nonlinear effects in the sputtering of gallium arsenide and silicon by bismuth cluster ions

An experimental study on the influence of the energy and the number of atoms in the bombarding ions Bin+ (n=1-4) on the sputter yield of GaAs was carried out. It was shown that the specific sputter yield Ysp non-additively increases with increasing n and specific kinetic energy Esp per an atom in the bombarding ion, and the efficiency of energy transfer from bombarding ions to target atoms also increases with increasing n. A comparison was made with the previously obtained results for Si targets. Keywords: ion sputtering, non-additivity factor, cluster ions, bismuth.

Evaluation of detonation performance and working capacity of explosives by optimized VLW EOS

Detonation performance is fundamental to the power evaluation of high explosives (HEs). This paper assesses the detonation performance (including detonation velocity D, detonation pressure P, detonation heat Q, specific kinetic energy Ek, detonation products, working capacity, etc.) of HEs by an optimized method. Firstly, “exp-six” intermolecular potential function was used to optimize the theoretical VLW (Virial-Wu) EOS (equation of state), which exhibits a good precision in calculations of detonation performance. Then, the detonation performance of three new HEs (LLM-105, FOX-7, and TKX-50) was calculated and compared with traditional HEs (TATB, HMX, and CL-20). The results indicate that, for D and P, LLM-105, FOX-7, and TKX-50 are superior to TATB, but inferior to HMX and CL-20 except for D of TKX-50. The descending order for Q and Ek is CL-20, HMX, TKX-50, FOX-7, LLM-105, and TATB. By analyzing detonation product components, more gaseous products with a higher proportion of heavy and medium molecules favor better detonation performance. Finally, the JWL (Jones-Wilkins-Lee) EOS was fitted by theoretically acquired isentropic expansion process of detonation products and cylinder test was simulated by the hydrodynamic program LS-DYNA. An increasing sequence of working capacity is TATB, LLM-105, FOX-7, TKX-50, HMX and CL-20.

Numerical Study of Heat Transfer to Supercritical Water in an Inclined Tube

A numerical study is conducted to investigate heat transfer characteristics of supercritical water flowing upward in an inclined smooth tube under uniform heating conditions. In this study, model verification was performed under the conditions of low heat flux and high heat flux to ensure the accuracy of experimental data. Inner wall temperature and heat flux distribute non-uniformly on the circumference due to the influence of natural convection. The increase of heat flux enhances the non-uniform circumferential distribution, while the increase of mass flux reduces the non-uniform circumferential distribution. Heat transfer of upward vertical and inclined flows is compared under low and high heat flux conditions. Radial distributions of fluid temperature, density, specific heat capacity, velocity, and turbulent kinetic energy are presented and analyzed. The analysis shows that the increase of heat flux reduces radial turbulence and heat-absorbing capacity of the boundary fluid, while increases radial temperature and density gradient. Three dimensionless buoyancy parameters are used to evaluate the buoyancy effect of inclined flow.

Influence of shaped charge structure parameters on the formation of linear explosively formed projectiles

The research of LEFP (linear explosive forming projectile) is of great value to the development of new warhead due to its excellent performance. To further improve the damage ability of the shaped charge warhead, a special shell overhanging structure was designed to increase the charge based on the traditional spherical charge, in which case the crushing energy of LEFP could be guaranteed. LS-DYNA was used to simulate different charge structures obtained by changing the number of detonation points, the length of shell platform, the radius of curvature and the thickness of liner. The RSM (response surface model) between the molding parameters of LEFP and the structural parameters of charge was established. Based on RSM model, the structure of shaped charge was optimized by using multi-objective genetic algorithm. Meanwhile, the formation process of jet was analyzed by pulsed X-ray photography. The results show that the velocity, length-diameter ratio and specific kinetic energy of the LEFP were closely related to the structural parameters of the shaped charge. After the optimization of charge structure, the forming effect and penetration ability of LEPP had been significantly improved. The experimental data of jet velocity and length were consistent with the numerical results, which verifies the reliability of the numerical results.

IWC Analysis of Turbulent Plume Fires

Plumes fires are characterized by a turbulent nature with a large number of different scales. LES is used to solve the largest structures and to model the smallest ones. Grid size and time steps become decisive to place a limit between solved and modelled turbulence. A spectral analysis, both in frequency and wavenumber domain of the specific turbulent kinetic energy is an instrument to check for the information investigated. Unfortunately, the spectra in the wavenumber domain can be difficult to achieve adequately, because the specific turbulent kinetic energy values should be available in many points. This issue can be overcome by identifying a correlation law between frequencies and wavenumbers. An approach to identify this correlation law can be to adopt the IWC method. Here, for a test case of a turbulent reacting plume of burning propane, specific turbulent kinetic energy is analysed both in frequency and wavenumber and a correlation law between them is identified by using the IWC method. A study has been performed to evaluate the grid dependency of the specific turbulent kinetic energy spectra, by assessing the extension of the Kolmogorov power law region. The correlation results are discussed and compared with the Taylor’s hypothesis.

Effect of Impact Cavity Shape Induced by Supersonic Oxygen Jet on the Dynamic Characteristics of Molten Bath in Converter

The cavity shape formed by the impinging of the supersonic oxygen jet on liquid metal surface is of importance to the converter steelmaking process. This work adopts the volume of fluid (VOF) model to numerically study the behavior of four‐nozzle supersonic jet impinging on molten steel bath in a 100 ton converter. First, the model is validated by comparing the jet velocity with that obtained from the literature. After validation, the dynamic interaction between supersonic jet and molten bath is studied. Moreover, the effects of lance height and operating pressure on the impact cavity depth and diameter are investigated. Compared with operating pressure, lance height shows a larger influence on altering the cavity dimensions. To quantitatively describe the profile of the scattered cavities, a dimensionless number called the modified cavity shape index (I cm) is put forward, which has a significant influence on the velocity distribution and specific kinetic energy of molten bath. The modified cavity shape index is found to be a function of the specific kinetic energy. With the modified cavity shape index ranging from 1.47 to 1.72, the dynamic flow of the molten bath becomes beneficial to the stirring and mixing of the molten bath.

Analytical and Numerical Simulation of Asymmetric Converging Flow of Gas Under Drill Bits in Reverse Circulation Gas Drilling

Abstract Reverse circulation gas drilling has been considered to solve engineering problems such as formation water influx, wellbore instability, and excess gas requirement in gas drilling. The performance of reverse circulation gas drilling depends to a large extent on the structure design of the drill bit. An analytical model and a numerical model were developed in this study to simulate the asymmetric converging flow of gas under the drill bit for reverse circulation gas drilling. The two models were compared and applied to the evaluation of a drill bit structure design for bottom hole cleaning capacity of gas flow. It was found that the pressure, velocity, and specific kinetic energy given by the analytical model are slightly lower than that given by the numerical model. The relative difference between the gas flowrates given by the analytical model and the numerical model is less than 5%. For the drill bit structure design considered in this study, the gas flow energy between the short blades is much higher than that between the long blades. A gas injection rate of 10 m3/min (360 ft3/min) is expected to clean the drill cuttings between the short blades, while a gas flowrate of 28 m3/min (990 ft3/min) is required to clean the drill cuttings between the long blades. Although the numerical model gives more accurate result than the analytical model in predicting hydraulics parameters, the analytical model is recommended for evaluating drill bit structure design because of its simplicity and conservativeness.

Analysis of specific kinetic energy for the Birikh–Ostroumov shear diffusion flow

The article presents a new exact solution for stratified steady-state shear diffusion flows of a viscous fluid in an infinite horizontal layer with impenetrable boundaries. The announced exact solution belongs to the Ostroumov–Birikh family. Two components of the velocity vector depend on the vertical (transverse) coordinate. The concentration field and the pressure field are described by linear forms relative to horizontal (longitudinal) coordinates, with coefficients depending on the third coordinate. The components of the velocity field and the shear stress field are analyzed in detail, and the behavior of the specific kinetic energy is studied. It is shown that this exact solution is capable of describing the stratification of the shear stress field and the nonmonotonic behavior of flow velocity. The relation of flow velocities and shear stresses to the distribution of specific kinetic energy is revealed.

Sputtering of silicon by atomic and cluster bismuth ions: An influence of projectile nuclearity and specific kinetic energy on the sputter yield

An influence of the specific kinetic energy Esp and nuclearity n of Bin+ (n = 1–4) projectiles on the sputter yield of Si was studied by means of the volume loss method. It was found that the specific sputter yield Ysp exhibited non-additive increase with an increasing of n and Esp values. As a non-additivity k-factor, the slope of the straight line approximating Ysp(n) dependences at the same specific energy was proposed to use. For Bin+ (n = 1–4) projectiles at Esp = 10 keV at−1 the k-factor was equal to 0.41 ± 0.08. In addition, it was ascertained that the efficiency of energy transfer from projectiles to target atoms increased with an increase in the projectile nuclearity, e.g., it was 2.8 times greater for Bi3+ bombarding ions as compared with Bi+ ones.

Paths not taken – The Gossamer roadmap’s other options

Highly efficient low-thrust propulsion is increasingly applied beyond commercial use, also in mainstream and flagship science missions, in combination with gravity assist propulsion. Another recent development is the growth of small spacecraft solutions, not in size but in numbers and individual capabilities.Just over ten years ago, the DLR-ESTEC Gossamer Roadmap to Solar Sailing was set up to guide technology developments towards a propellant-less and highly efficient class of spacecraft for solar system exploration and applications missions: small spacecraft solar sails designed for carefree handling and equipped with carried application modules.Soon, in three dedicated Gossamer Roadmap Science Working Groups it initiated studies of missions uniquely feasible with solar sails such as Displaced L1 (DL1) space weather advance warning and monitoring, Solar Polar Orbiter (SPO) delivery to very high inclination heliocentric orbit, and multiple Near-Earth Asteroid (NEA) rendezvous (MNR). Together, they demonstrate the capability of near-term solar sails to achieve at least in the inner solar system almost any kind of heliocentric orbit within 10 years, from the Earth-co-orbital to the extremely inclined, eccentric and even retrograde. Noted as part of the MNR study, sail-propelled head-on retrograde kinetic impactors (RKI) go to this extreme to achieve the highest possible specific kinetic energy for the deflection of hazardous asteroids.At DLR, the experience gained in the development of deployable membrane structures leading up to the successful ground deployment test of a (20 m)2, i.e., 20 m by 20 m square solar sail at DLR Cologne in 1999 was revitalized and directed towards a 3-step small spacecraft development line from as-soon-as-possible sail deployment demonstration (Gossamer-1) via in-flight evaluation of sail attitude control actuators (Gossamer-2) to an envisaged proving-the-principle flight in the Earth-Moon system (Gossamer-3). First, it turned the concept of solar sail deployment on its head by introducing four separable Boom Sail Deployment Units (BSDU) to be discarded after deployment, enabling lightweight 3-axis stabilized sailcraft. By 2015, this effort culminated in the ground-qualified technology of the DLR Gossamer-1 deployment demonstrator Engineering Qualification Model (EQM). For mission types using separable payloads, such as SPO, MNR and RKI, design concepts can be derived from the BSDU characteristic of DLR Gossamer solar sail technology which share elements with the separation systems of asteroid nanolanders like MASCOT. These nano-spacecraft are an ideal match for solar sails in micro-spacecraft format whose launch configurations are compatible with ESPA and ASAP secondary payload platforms.Like any roadmap, this one contained much more than the planned route from departure to destination and the much shorter distance actually travelled. It is full of lanes, narrow and wide, detours and shortcuts, options and decision branches. Some became the path taken on which we previously reported. More were explored along the originally planned path or as new sidings in search of better options when circumstance changed and the project had to take another turn. But none were dead ends, they just faced the inevitable changes when roadmaps face realities and they were no longer part of the road ahead. To us, they were valuable lessons learned or options up our sleeves. But for future sailors they may be on their road ahead.

The antesonic condition for the explosion of core-collapse supernovae – II. Rotation and turbulence

ABSTRACT In the problem of steady free fall on to a standing shockwave around a central mass, the ‘antesonic’ condition limits the regime of stable accretion to $c_T^2/v_\mathrm{esc}^2\le 3/16$, where cT is the isothermal sound speed in the subsonic post-shock flow, and vesc is the escape velocity at the shock radius. Above this limit, it is impossible to satisfy both the Euler equation and the shock jump conditions, and the system transitions to a wind. This physics explains the existence of a critical neutrino luminosity in steady-state models of accretion in the context of core-collapse supernovae. Here, we extend the antesonic condition to flows with rotation and turbulence using a simple one-dimensional formalism. Both effects decrease the critical post-shock sound speed required for explosion. While quite rapid rotation is required for a significant change to the critical condition, we show that the level of turbulence typically achieved in supernova simulations can greatly impact the critical value of $c_T^2/v_\mathrm{esc}^2$. A core angular velocity corresponding to a millisecond rotation period after contraction of the proto-neutron star results in only a ∼5 per cent reduction of the critical curve. In contrast, near-sonic turbulence with specific turbulent kinetic energy $K/c_T^2=0.5-1$, leads to a decrease in the critical value of $c_T^2/v_{\rm esc}^2$ by ∼20 to 40 per cent. This analysis provides a framework for understanding the role of post-shock turbulence in instigating explosions in models that would otherwise fail and helps explain why multidimensional simulations explode more easily than their one-dimensional counterparts.

Investigation of the operation of vibration-centrrifugal installation for automobile parts machining

The scheme of vibration-centrifugal installation, providing the increase of productivity and efficiency of machine parts vibration treatment is presented in this paper. The influence of the treated environment on the technological vibration treatment process and determination of its optimal parameters is investigated on the basis of mathematical modeling. Graphical dependences of specific kinetic energy on the crank rotational velocity at different values of the fork rotational velocity are presented. Effective ways of technological process parameters optimization and new ways of its development are identified.

NEUTRON DEPTH PROFILE CALCULATIONS USING ARTIFICIAL NEURAL NETWORKS

Neutron depth profiling (NDP) is a non-destructive technique used for identifying the concentration of impurity isotopes below the sample surface. NDP is carried out by detection of the emitted charged particles resulting from bombarding the sample with neutrons. NDP specifies the isotopic concentration versus the sample depth for a few micrometers below the surface. The sample is bombarded inside a research reactor using a thermal neutron beam. Charged particles like alpha particles or protons are produced from the neutron induced reactions in the sample. Each neutron isotopic interaction produces a certain Q, indicating a specific kinetic energy for the emitted charged particle. As the charged particle travels through the sample to eject the surface, it loses energy to atoms (electrons) on its path. The charged particle energy loss holds information regarding the number of atoms by which the emitted particle passed, thus indicating its original depth. The purpose of this work is to check the capability of Artificial Neural Networks (ANNs) in predicting the boron concentration profile across a boro-silicate sample of thickness 3.5 μm divided into 10 layers. Each layer included different boron concentration than the other. Also, the boron concentration had the values {0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1}. Training, validation, and test data were generated synthetically using MCNP6 in which the boron concentrations varied in the layer number from one sample to another. MCNP6 model consisted of a silicon barrier detector, boro-silicate sample, chamber body and an idealized thermal neutron source. The detector, sample, and the source were located in a voided chamber. The samples were irradiated with a 0.025 eV monoenergetic thermal neutron beam from a monodirectional disk source. To cover the whole area of the samples, the thermal neutron beam had a radius of 3 cm. The silicon detector active volume was modelled as a 100 μm thick and 3 cm radius facing the sample directly. The sample, beam, and the detector were placed on the same axis. Ten ANN regression models were developed, one for each layer boron concentration prediction where the input for each model was the alpha spectrum read by the detector, while the output was the boron concentration for each layer. Results showed regression values higher than 0.94 for all of the developed models. ANNs proved its capability of predicting the boron profile form the alpha spectrum read by the detector regarding neutron depth profiling in a boro-silicate samples.

A Different Interpretation on Magnetic Surfaces Generated by Special Magnetic Curve in Q2 ⊂ E 3 1

By thinking the magnetic flow connected by the Killing magnetic field, the magnetic field on the setting out particle orbit is investigated in 𝐐2 ⊂ 𝐸31 . Clearly, dealing with the Killing magnetic field of 𝛼 -magnetic curve, the rotational surface generated by 𝛼 -magnetic is expressed in 𝐐2 ⊂ 𝐸31, and the variant kinds of axes of rotation in lightlike cone 𝐐2 ⊂ E31 is given. Furthermore, the specific kinetic energy, specific angular momentum and conditions being geodesic on rotational surface generated by α-magnetic curve are expressed with the help of Clairaut's theorem.