Entry Velocity Research Articles

Acute effects of different loading protocols upon performance and kinematics of 180 degrees change of direction

ABSTRACT This study examined the acute effects of different loading protocols on 180° change of direction (COD) performance in eleven male handball players. Participants performed a 10-0-5 COD test under seven conditions: without an external load, and with 3, 6, and 9 kg loads applied under two modes—assisted into the COD and resisted out of it and resisted into the COD and assisted out of it. While total COD time was not affected (p = 0.098; η2 = 0.16), significant phase effects were observed (p < 0.001; η2 ≥ 0.55). Loading protocols significantly influenced velocity, acceleration, and their distances from COD (p < 0.001; η2 ≥ 0.37). Significant phase effects were observed for all step kinematic variables (p ≤ 0.037; η2 ≥ 0.67), except contact time, and significant interaction (phase*condition) effects for all variables (p ≤ 0.004; η2 ≥ 0.08), except for step frequency. Assisted-resisted protocols increased deceleration demands through higher COD entry velocities, displaying fewer but longer steps in the acceleration phase and greater steps taken during the deceleration phase. Resisted-assisted protocols decreased deceleration demands due to lower COD entry velocities, displaying shorter, but more steps taken in the acceleration phase, and fewer steps taken in the deceleration phase. These findings suggest that assisted-resisted and resisted-assisted loading protocols can be used to selectively overload specific phases of COD performance.

Numerical Study of Air Cushion Effect in Notched Disk Water Entry Process Using Structured Arbitrary Lagrangian–Eulerian Method

This paper presents a novel numerical investigation into the air cushion effect and impact loads during the water entry of notched discs, utilizing the Structured Arbitrary Lagrangian–Eulerian (S-ALE) algorithm in LS-DYNA. Unlike prior studies that focused on smooth or unnotched geometries, the present study explores how varying notch parameters influence the fluid–solid coupling process during high-speed water entry. The reliability and accuracy of the computational method are validated through grid independence verification and comparisons with experimental data and empirical formulas. Systematic analysis of the effects of notch size, water entry velocity, and entry angle on the evolution of the free surface, impact loads, and structural responses uncovers several novel findings. Notably, increasing the notch diameter significantly enhances the formation and stability of the air cushion, leading to a considerable reduction in peak impact loads—a phenomenon not previously quantified. Additionally, higher water entry Froude numbers are shown to accelerate air cushion compression and formation, markedly affecting free surface morphology and force distribution. The results also reveal that varying the water entry angle alters the air cushion’s morphological characteristics, where larger angles induce a more pronounced but less stable air cushion, influencing the internal structural response differently across regions.

Dynamic fluid-structure interaction between the projectile and the light-thin ice under the motion state in the polar environment

The interaction between projectiles and ice during water entry is crucial for advancing polar resource exploration and military operations in polar regions. This study introduces a fluid-structure interaction (FSI) model to simulate the dynamics between projectiles and light-thin ice under a motion state, validated through laboratory experiments. It examines the cavity evolution patterns during water entry and analyzes the motion states and dynamic characteristics of both the projectile and the floating ice. The influence of the horizontal-to-vertical velocity ratio (u*) and the initial pitch angle (φ) on the water entry process and collision dynamics has also been considered. The results reveal that as the projectile approaches the floating ice, it generates a wave-making effect, impacting the formation of the water entry splash crown and the deflection motion of the ice. Additionally, the hydrodynamic force acting on the projectile increases by 40 % compared to free water entry conditions. After the collision between the projectile and the light-thin ice, the pinch-off characteristics of the water entry cavity alter. This collision influences the motion state and dynamic characteristics of the projectile, while the ice experiences both collision and hydrodynamic forces, leading to passive motion. With an increasing water entry velocity ratio, the light-thin ice forms an expanding cavity during passive water entry, affecting the cavity pinch-off of the projectile. When u* > 1, the projectile exhibits circuitous motion post-collision with the ice. Variations in water entry angles of the projectile alter the collision mode between the projectile and the ice, resulting in changes to their motion states and dynamic characteristics. A critical pitch angle exists during the cavity pinch-off process.

Numerical investigation on the slamming loads of a truncated trimaran hull entering regular waves

For ship slamming, waves can disturb the water entry progress and thus affect the slamming load characteristics. This paper studied the slamming loads of a trimaran entering regular waves based on the CFD method. The results of a trimaran model impacting calm water and wedge impacting waves are used to verify the present method. The free surface evolution and load characteristics of the trimaran model considering wave effects are discussed. The results showed that the position at which the structure touches the wave surface depends on the formation, deformation and escape of bubble flows, which cause obvious asymmetrical flow. The enclosure of the air cavity induces a step increase in pressure, and the pressure peak appears when the bubble fully escapes. Three typical positions, wave crest, wave cross and wave through, are chosen to explore the influence of waves on slamming loads. The impact load shows a 98% difference at different wave locations. In ship load forecasting, the position of the waves relative to the hull is noteworthy. The influence of the water entry velocity on the slamming load is further discussed. Bubble retention related to the water entry velocity is the key factor affecting the peak load.

Study on water entry impact characteristics and parameter influence analysis of the vehicle passing through the thin crushed ice zone in a polar environment

The problem of water entry in polar environments holds significant research value for polar resource exploration and military applications. This study uses computational fluid dynamics and the discrete element method (CFD-DEM) to investigate the complex process of a vehicle entering water through a thin crushed ice zone. Experimental data validates the efficiency of the coupling algorithm. The primary focus of this study is to investigate the influence of crushed ice shapes, arrangement patterns, coverage densities, and sizes within thin crushed ice zones on the process of water entry. A comprehensive analysis is carried out to assess how the characteristic parameters of different thin crushed ice zones affect the dynamic behavior of the vehicle during water entry and the movements of the crushed ice. Concurrently, the influence of different velocities of the vehicle on the water entry process through a specific thin crushed ice zone is analyzed. The results show that when the crushed ice is in a regular arrangement, it exhibits a circular immersion phenomenon and a cross-shaped passive movement trend. The arrangement patterns, coverage densities, and sizes of the crushed ice have different effects on the water entry process. Of these factors, the complexity of the influence of crushed ice sizes on the water entry process stands out. Meanwhile, the water entry velocity plays a crucial role in determining the relative significance of the hydrodynamic force and the collision force of crushed ice on the total resistance of the vehicle during water entry. These insights provide valuable guidance for the planning and execution of missions in polar regions.

Cosmogenic radionuclides in meteorites from the Otway Massif blue ice area, Antarctica: An unusual, well‐preserved H5 chondrite strewn field

AbstractThe US Antarctic Search for Meteorites (ANSMET) discovered a dense cluster of 88 ordinary chondrites with a total mass of more than 100 kg on a blue ice area (BIA) of 1.6 × 0.3 km2 near the Otway Massif, Grosvenor Mountains, Antarctica. The larger masses (weighing up to 29 kg) were found at one end of an oval‐shaped pattern and the smaller masses (50–200 g) at the other end. We measured concentrations of the cosmogenic radionuclides 10Be (half‐life—1.36 × 106 year) and 36Cl (3.01 × 105 year) in the metal fraction of 17 H chondrites, including 14 fragments of this cluster, to verify the hypothesis that this meteorite cluster on the Otway Massif BIA represents a meteorite strewn field produced by the atmospheric breakup of a single meteoroid. The 10Be and 36Cl concentrations confirm that 10 out of 14 H chondrites from different locations within this small area are paired fragments of the same meteorite fall, while the four other H chondrites represent two additional—smaller—falls. The radionuclides suggest a pre‐atmospheric mass of 200–400 kg for the large pairing group, suggesting that 25%–50% of the meteoroid survived atmospheric entry. Based on the distribution of the paired H chondrites and evidence of their common cosmic‐ray exposure history in space, we conclude that most of the 88 meteorites within this small area represent a meteorite strewn field. The small size of the strewn field suggests that the meteoroid entered at a steep angle (&gt;60°), while the low amount of fusion crust on most meteorite surfaces most likely indicates atmospheric break up at low altitude, while additional fragmentation of a large surviving fragment may have occurred during impact on the ice. This well‐documented strewn field provides a good opportunity to apply model simulations of the atmospheric fragmentation of this object as a function of entry angle, velocity, and meteoroid strength. Cosmogenic 14C analyses in two members of the Otway Massif pairing group yield a terrestrial age of 15.5 ± 1.5 kyr, which represents the time elapsed since this meteorite fell on Earth. The excellent preservation of an Antarctic meteorite strewn field suggests that the Otway Massif BIA represents a relatively stagnant blue ice field.

Positively Charged Microparticle in Plasma with High-Energy Electron Beam

The processes of recharging, heating and evaporation of a positively charged microparticle (MP) introduced into the plasma with an injected high-energy electron beam are considered. It is assumed that the MP is charged outside the plasma and then introduced into the plasma by an accelerating field, where plasma and beam electrons hitting the MP heat and evaporate it. In addition to introducing the MP into the plasma, the positive MP charge provides an additional source of energy needed to heat and evaporate it. Using the OML theory, the system of current and energy balance equations was numerically solved and the conditions, under which the MP is heated to the boiling point of its substance, resulting in its intense evaporation, were determined. The influence of the energy of the electron beam on the process of MP recharging, as well as on the rate of its heating and evaporation, has been studied. An estimate of the particle entry velocity into the plasma has been made; the distances at which its recharging, heating to the boiling point and complete evaporation occur are determined. The work is carried out in order to creating plasma of a given elemental composition.

Revealing the Relationship between Critical Inlet Velocity and a Double-Layer Oxide Film Combined with Low-Pressure Casting Technology

In the context of low-pressure casting, an excessive inlet velocity may result in the introduction of an oxide film and air into a liquid metal, leading to the formation of a two-layer film structure within the casting. Such defects can significantly degrade the mechanical properties of the castings. In order to optimize the advantages of low-pressure casting, an empirically designed equation for the inlet velocity was formulated and the concept of critical inlet velocity was further refined. A comprehensive numerical simulation was conducted to meticulously analyze the liquid metal spreading phase within the cavity. Subsequently, low-pressure casting experiments were carried out with actual castings of an A357 alloy, using two different entrance velocities—one critical and the other exceeding the critical entrance velocity. Tensile test specimens were extracted from the castings for the comparative evaluation of mechanical properties. It was observed that the average tensile strength of specimens cast at the critical inlet velocity exhibited a notable 16% enhancement. In contrast, specimens cast at velocities exceeding the critical inlet velocity manifested the presence of double oxide film defects. This evidence suggests that casting at a velocity faster than the critical inlet velocity leads to the formation of double oxide film defects, which in turn reduces the mechanical properties of the castings.

A coupled smoothed particle hydrodynamics–peridynamics model for two-dimensional hydroelastic water entry

In this paper, a numerical model coupling the smoothed particle hydrodynamics (SPH) with peridynamics (PD) is developed to solve the problem of the hydroelastic water entry. By combining the geometric nonlinear peridynamics with the weakly compressible SPH, the proposed model can efficiently simulate the nonlinear deformation of the structure and the deformation of a fluid free surface. The transmission of information between the fluid and solid phases is implemented by a dummy particle boundary treatment method. By simulating benchmark tests, the ability of the proposed model to solve nonlinear fluid–structure coupling problems is verified. In order to improve the computational efficiency, the graphics processing unit parallel acceleration scheme is applied to the SPH-PD model. Compared with the serial scheme, the speedup effect of the parallel scheme in large-scale computation is verified. As an application of the numerical model, the water entry of the flexible panel at a constant entry velocity is studied. The mechanism of hydroelastic effect is explained by analyzing the variations in the fluid pressure field, slamming force, and panel deformation during water entry. In addition, the influences of plate rigidity, impact velocity, and deadrise angle on the hydroelastic effect are investigated.

Transient cold-front-water through y-shaped aluminium ducts: nature of turbulence, non-equilibrium thermodynamics, and velocity at the converged and diverged outlets

Abstract The interaction between water motion efficiency, outlet control mechanisms, and energy dynamics management hinges significantly on turbulence characteristics. However, understanding the influence of input velocities and duct features on outlets remains elusive. This study employs the realizable k − ɛ viscous model and Reynolds-averaged Navier–Stokes equations (RANS equations) to explore transient water dynamics encountering a cold front through ducts leading to convergence or divergence. Using Ansys Fluent 2023R2 and the waterlight workflow, meticulous meshing of the ducts is executed to capture flow intricacies accurately. Grid independence, suitable boundary conditions, and solver settings are carefully considered to ensure reliable results for investigating four key research questions. Duct bending introduces non-uniformities in velocity distribution, impacting exit velocity and altering flow characteristics and turbulence. In Case III, centrifugal forces from a 90° bend result in higher outlet velocities at the convergent exit and secondary flow patterns like swirls and vortexes. Additionally, entrance velocities influence Reynolds numbers, affecting mixing, heat transfer coefficients, and flow regimes, thereby optimizing thermal conductivity. This comprehensive investigation sheds light on optimizing water dynamics and energy management across various duct configurations, offering valuable insights into efficient flow control and thermal performance enhancement.

Study on the free surface evolution and slamming pressure of curved-wedge water entry using a Riemann-smoothed particle hydrodynamics method

The present study aims to provide a deep understanding of curved wedge water entry. It involves a numerical simulation investigation into the kinematic and dynamic properties of water entry for two curved wedges with deadrise angles of 25° and 35°. The meshless Riemann-smoothed particle hydrodynamics (SPH) model embedded with an acoustic damper is developed to simulate these violent water entries. The validation of the Riemann-SPH accuracy is confirmed through comparison with experimental data, and subsequently, we make a systematical simulation study on curved wedge water entry, including a comparative study of free surface evolution and pressure distribution at different curvatures and drop heights. Furthermore, the kinematics analysis of velocity and displacement of curved wedges and time domain characteristics of slamming pressure loads on both sides of the wedge are investigated. It is revealed that the pressure distribution is symmetrical, with high-pressure regions forming near the bottom of the wedge and gradually propagating outward. The free surface profiles are symmetrical, with deeper depressions formed by sharper wedges. The entry depth and velocity are correlated with the initial theoretical entry velocity, and the rate of speed decline varies with the curvature of the wedge. The slamming pressure loads exhibit distinct time-domain patterns, with lower pressure loads by sharper wedges.

Study on Water Entry of a 3D Torpedo Based on the Improved Smoothed Particle Hydrodynamics Method

The water entry of a torpedo is a complex nonlinear problem, involving transient impact, free surface deformation, droplet splashing, and fluid–structure coupling, which poses severe challenges to traditional mesh methods. The meshless smoothed particle hydrodynamics (SPH) method shows unique advantages in capturing the complex features of the water entry of the torpedo at different entry angles. However, it still suffers from some inherent shortcomings, such as low surface discretization accuracy, poor discretization flexibility, and low calculation efficiency. In this study, an improved adaptive SPH algorithm is proposed to investigate the water entry of the torpedo accurately and efficiently. This method integrates meshless point generation and adaptive techniques simultaneously. The numerical results demonstrate that when the torpedo vertically enters the water at different velocities, the induced impact loads acting on the head of the torpedo fluctuate significantly with two peak values in the initial stage and thereafter stabilize in a later stage. The impact load acting on the torpedo, the entry depth of the torpedo, the splash height of the droplets, and the size of the cavity generated around the torpedo increase with the increment in the entry velocity. When the torpedo enters the water at different entry angles under the same initial entry velocity, both the vertical and the horizontal movements of the torpedo are observed, which results in more complex variations in parameters along the x- and y-axes. The findings and the corresponding numerical method in this study can provide a certain basis for the future designs of the entry trajectory and the structural bearing capacity of torpedoes.

CFD Air Flow Evaluation of Finned Tube Evaporator for Refrigerated Display Cabinet Application

This study is aimed to develop a simulation to improve the performance of the finned tube evaporator which is applied to the refrigerated display cabinet. CFD model was developed to be able to analyse the characteristics of air flow inside the fin gap and air side heat transfer coefficient. Geometry of the model of overall finned tube evaporator is considered covering two aluminium wavy fins with an air flow in between, combination of staggered cooper tubes with refrigerant flow inside. Fin gap is designed 4 mm to anticipate frost on the fin surface that can block air flow. Turbulence models used in the study is the realizable k-ε turbulence which had the best performance turbulence model and it was validated with secondary data from previous studies and shows the lowest error only 5.9 %. The use of CFD was found to be sufficiently representative of the heat transfer characteristics of evaporators, and acted as an effective simulation tool to determine the heat transfer coefficient in order to improve efficiency in terms of improved design. The characteristics of air flow between the fin gap and around the tube was obtained various and complex. In the case study the entry velocity of 1.7 m /s at the highest turbulence condition of the first row can reach speeds of 2.75 m/s. Hight turbulence regime in flow can indicate higher the heat transfer coefficient of the evaporator.

Numerical Study of Plasma Characteristics Under Magnetohydrodynamic Flow Control in Mars Entry

Magnetohydrodynamic flow control is an active thermal protection method for atmospheric entry vehicles. This study examined the plasma characteristics under magnetohydrodynamic flow control and its thermal protection ability at multiple altitudes (20–60 km) on a typical direct Mars entry path using numerical simulation considering the Hall effect. The simulation considered a spherical-conical capsule with an entry velocity of 8 km/s at an altitude of 60 km, equipped with a dipole magnet generating a magnetic field of approximately 0.3 T at the stagnation point of the capsule. The results showed that magnetohydrodynamic flow control can mitigate convective aerodynamic heating at high altitudes (45 km or more), where the high electrical conductivity of the plasma creates strong magnetohydrodynamic interaction. In contrast, at low altitudes (35 km or less), magnetohydrodynamic flow control is ineffective owing to low electrical conductivity. The high electrical conductivity at high altitudes is attributed not only to large flight velocities under low atmospheric pressures but also to the enlargement of the shock layer owing to the strong magnetohydrodynamic interaction, which expands the ionization progression area. Furthermore, the results indicated that considering the Hall effect in the numerical modeling of magnetohydrodynamic flow control in Mars direct entry is essential.

Experimental and Numerical Prediction of Slamming Impact Loads Considering Fluid–Structure Interactions

Slamming impacts on water are common occurrences, and the whipping induced by slamming can significantly increase the structural load. This paper carries out an experimental study of the water entry of rigid wedges with various deadrise angles. The drop height and deadrise angle are parametrically varied to investigate the effect of the entry velocity and wedge shape on the impact dynamics. A two-way coupled approach combing CFD method software STAR-CCM+12.02.011-R8 and the FEM method software Abaqus 6.14 is presented to analyze the effect of structural flexibility on the slamming phenomenon for a wedge and a ship model. The numerical method is validated through the comparison between the numerical simulation and experimental data. The slamming pressure, free surface elevation, and dynamic structural response, including stress and strain, in particular, are presented and discussed. The results show that the smaller the inclined angle at the bottom of the wedge-shaped body, the faster the entry speed into the water, resulting in greater impact pressure and greater structural deformation. Meanwhile, studies have shown that the bottom of the bow is an area of concern for wave impact problems, providing a basis for the assessment of ship safety design.

The impact of mechanical ventilation on Sfax City's greenhouse microclimate

The greenhouse serves as an enclosed structure designed to create a conducive environment for agricultural productivity, irrespective of the challenges posed by seasonal variations. Recognizing the contemporary complexities in agricultural management, our research endeavors involve the development of a comprehensive numerical model and the establishment of an experimental setup to delve into the nuanced impact of mechanical ventilation. Specifically, the study investigates the influence of four different entrance velocity values on airflow dynamics within agricultural greenhouses. The results illuminate the direct correlation between inlet velocity and various crucial variables, including temperature distribution, velocity field distribution, DO irradiation distribution, and static pressure distribution. Notably, at Vint = 12 m.s-1, the maximum temperature remains below Tmax = 307 K, while at Vint = 3 m.s-1, it reaches Tmax = 327 K. This underscores the pivotal role of accurate modeling and control for the optimal management of agriculture in the central region of Tunisia, particularly in Sfax.

Validation of a CFD model for cell culture bioreactors at large scale and its application in scale-up

Among all the operating parameters that control the cell culture environment inside bioreactors, appropriate mixing and aeration are crucial to ensure sufficient oxygen supply, homogeneous mixing, and CO2 stripping. A model-based manufacturing facility fit approach was applied to define agitation and bottom air flow rates during the process scale-up from laboratory to manufacturing, of which computational fluid dynamics (CFD) was the core modeling tool. The realizable k-ε turbulent dispersed Eulerian gas-liquid flow model was established and validated using experimental values for the volumetric oxygen transfer coefficient (kLa). Model validation defined the process operating parameter ranges for application of the model, identified mixing issues (e.g., impeller flooding, dissolved oxygen gradients, etc.) and the impact of antifoam on kLa. Using the CFD simulation results as inputs to the models for oxygen demand, gas entrance velocity, and CO2 stripping aided in the design of the agitation and bottom air flow rates needed to meet cellular oxygen demand, control CO2 levels, mitigate risks for cell damage due to shear, foaming, as well as fire hazards due to high O2 levels in the bioreactor gas outlet. The recommended operating conditions led to the completion of five manufacturing runs with a 100% success rate. This model-based approach achieved a seamless scale-up and reduced the required number of at-scale development batches, resulting in cost and time savings of a cell culture commercialization process.

Research of Slamming Load Characteristics during Trans-Media Aircraft Entry into Water

The trans-media aircraft water entry process generates strong slamming loads that will seriously affect the stability and safety of the aircraft. To address this problem, we design a fixed-wing aircraft configuration and employ numerical simulations with the volume of fluid (VOF) multiphase flow model, standard k-epsilon turbulence model, and dynamic mesh technique. We explore the characteristics of aircraft subjected to bang loads under different conditions. The results show the following: the pressure load on the aircraft surface increases with higher water entry velocity; larger entry angles lead to more drastic changes in the aircraft’s drag coefficient, demonstrating strong nonlinear characteristics; the greater the angle of attack into the water, the greater the pressure load on the root underneath the wing, with little effect on the pressure load on the head; and the water entry drag coefficient and average pressure load follow an increasing order of conical head, hemispherical head, and flat head. These findings provide theoretical references for studying the load characteristics during trans-media water entry of various flying bodies and optimizing fuselage structural strength.

Vertical water entry of a cylinder considering wind and linearly sheared flow effect: A numerical investigation

Objects entering water is a complex multiphase flow event that exhibits nonlinear and transient characteristics. This study examines the impact cavities, multiphase flow characteristics, and motion behaviors of a cylinder during vertical water entry, considering different flow and entry velocities. A three-dimensional model was carried out using OpenFOAM® framework, taking into account the effects of wind and linearly sheared flow through newly customized initial and boundary conditions. The overset mesh technique was applied to capture the water entry trajectories of the moving cylinder. Numerical results for the cavity evolution and cylinder motion behaviors were validated against published laboratory tests. The cavity closure patterns were classified into four categories based on the evolution characteristics, which were found to be more complex than those observed under calm water and uniform current conditions. Furthermore, the rapid closure of the splash dome results in a unique cavity flow phenomenon, which creates a suction air channel. The velocities of the flow and water entry have a noticeable impact on the closure modes and time of the cavity. This, accordingly, affects the motion characteristics of the cylinder, as well as the evolution of the velocity field, pressure field, and vortex structures.

Flow behavior over well-escape weirs

ABSTRACT Weirs play an important role in controlling and managing water in irrigation canal networks through several functions, such as discharge measurements, water distribution, and lowering the water level. Weirs also play a crucial role in protecting canals from flooding, which might cause the earthen banks to collapse, by eliminating surplus water at the ends of the canals. Over the previous decades, the flow over the traditional sharp-crested weirs was extensively investigated by many researchers; however, the well-escape weirs have not received sufficient attention. These types of weirs were mostly constructed in the form of vertical wells that may be circular or rectangular in shape, and water may flow through the entire perimeter of the weir or part of the perimeter. In the present research, the effect of the well-escape-weir shape on the characteristics of flow over the weir was studied. A set of models were constructed in different shapes, circular and square, and the entire perimeter of the weir or part of the perimeter is working as the weir crest length. The discharge passing over the unit length of the weir crest (q) is investigated and compared for the circular and square weirs of various crest lengths and positions. The results indicated that the discharge capacity of the circular weirs increases by a rate ranging between 7.5% and 15% more than that of the square weirs at the same head. Also, results indicated that the discharge coefficient of the circular weirs increases by a rate ranging between 9.3% and 10.3% more than that of the square weirs. This behavior can be attributed to the interference between the orthogonal water nappes at the corners of the square models. In addition, the flow direction has little effect on the discharge coefficient at small discharges, and this effect becomes more obvious at higher discharges. Additionally, the well-escape weirs of the upstream crest have a slightly higher discharge capacity than those of the downstream crest due to the effect of the approach velocity, which increases the water entrance velocity at the upstream crest. The results of flow patterns around the weir showed that the locations of maximum flow velocities (u, v, w) are mostly near the weir crest and depend entirely on the crest length and position.