Range Of Velocities Research Articles

The spallation characteristics of polycrystalline aluminum with helium bubbles under a wide range of shock stresses

The spallation behavior of polycrystalline Al with helium (He) bubbles (poly Al–He) under unsupported shock loadings at a wide range of impact velocities was investigated via molecular dynamics simulations. We found that the microstructural features during shock compression and release processes for the poly Al–He are highly analogous to those observed in polycrystalline Al (poly Al), indicating that the bubbles studied here do not have a significant influence on the mechanical deformation before tension. During the tension process, the expansion-merging of He bubbles dominates damage accumulation and leads to the ultimate fracture of the metal, the same as that in a single crystal with He bubbles. The presence of grain boundaries (GBs) does not exhibit an apparent effect on the evolution of He bubbles, resulting in comparable expansion rates for the bubbles in different locations (i.e., near GBs or at grain interiors). Additionally, the nucleation of voids occurs subsequent to bubble expansion due to the much higher critical stress. Voids are preferentially nucleated on GBs when the material is solid and at liquid parts when the material is partially molten, demonstrating that GBs and melting can strongly facilitate void nucleation. However, He bubbles significantly impede void nucleation and growth, resulting in a much smaller quantity and volume of voids formed in the poly Al–He, compared to the poly Al. Furthermore, the critical stress for void nucleation and the spall strength of the metal matrix are reduced by He bubbles.

Experimental investigation of the second-mode internal solitary wave in continuous pycnocline and the applicability of weakly nonlinear theoretical models

The research on the propagation and evolution of the second-mode internal solitary waves(ISWs) is receiving more and more attention. In this study, second-mode internal solitary waves in continuous stratification are physically simulated in a laboratory-stratified fluid flume. Meanwhile, the second-mode ISWs and their induced flow field in the same stratification environment are solved based on the eigenvalue problem of the TG equation (Taylor-Goldstein), combined with the weakly non-linear ISW theoretical models. The experimental and theoretical results show that the symmetry of the second-mode ISW wave-flow field can be improved as the thickness ratio of the upper fluid layer and lower one approaches 1. The ISW speed and horizontal and vertical velocity range values in the continuous pycnocline are positively correlated with the changing ISW amplitude, while only the wavelength is negatively correlated with the iSW amplitude. The waveflow fields of the second-mode ISWs calculated by Korteweg-de Vries (KdV) and extended KdV (eKdV) models in the large amplitude cases are more consistent with the experimental results than those in the small amplitude cases. The two theoretical models used to describe second-mode ISWs can be significantly improved when the thickness ratio of the upper and lower fluid layers approaches 1. In this case, the eKdV model is more applicable than the KdV model.

Design of an Underwater Acoustic Waveform and Integrated System for Communication and Detection

Combining underwater communication and detection can reduce system size and power consumption as well as improve secrecy. This paper presents a waveform that integrates continuous phase modulation (CPM) for data communication with linear frequency modulation (LFM) for detection. It is shown that the velocity ambiguity and range performance with this waveform are similar to those with only LFM. An integrated underwater acoustic system is also proposed to achieve simultaneous communication and detection. A symbol suffix (SS) is introduced into the signal frame at the transmitter and a two-step algorithm is employed at the receiver for frequency and phase offset estimation. Results are presented, showing that this decreases the sensitivity to CPM and reduces the range ambiguity side lobes. Further, the proposed system can effectively recover the data from the received signal. The bit error rate (BER) is shown to be better than that of traditional systems without a symbol suffix. With changes in the signal-to-noise ratio (SNR), the bit error rate (BER) in underwater acoustic environments is comparable to that in an additive white Gaussian noise (AWGN) channel, indicating a significant improvement in communication performance within the underwater acoustic channel.

Effect of Gas Holdup and Gas Velocity on Volumetric Mass Transfer Coefficient in Bubble Column

Bubble columns are widely used in various industrial processes such as wastewater treatment, fermentation, and gas-liquid reactions due to their simplicity and effectiveness in mass transfer operations. In this study, we investigate the influence of gas holdup and gas velocity on the volumetric mass transfer coefficient in a bubble column reactor. The volumetric mass transfer coefficient is a critical parameter that affects the efficiency of gas-liquid mass transfer processes. Through experimental analysis and computational modeling, we systematically examine the relationship between gas holdup, gas velocity, and the volumetric mass transfer coefficient. In this study, volumetric mass transfer coefficient kL.a was calculated using air in water. The data obtained are in the range of superficial gas velocity (0.03-0.2398) m/s for air water system. The experiments were carried out using 0.1 m column diameter with 2 mm hole diameter and 79 holes gas distributor. From the experimental data it was found that kL.a increased with increasing of gas holdup and increasing of superficial gas velocity.

Application of Persistent Scatterer Interferometry to monitor land motion along radar line of sight in landslide-prone areas of Himachal Pradesh, India

Landslides in mountainous regions are often triggered by vertical land movements induced by tectonics or seismic activities, emphasizing the importance of monitoring such motions for early intervention. This study investigates the impact of vertical land motion on landslide-prone districts in Himachal Pradesh, India. We employ Persistent Scatterer InSAR (PS-InSAR) technology to analyse vertical land motion in the region. Utilizing a dataset spanning six years (2017–2023), we provide precise measurements of land movements with millimetre-level accuracy. Our analysis reveals a range of deformation velocities, from −10 mm/year to +5 mm/year, with observed uplift of less than 31 mm and subsidence of up to 60 mm in the study area. These movements are attributed to prolonged wet conditions, illegal land mining, and ecological vulnerability. The findings underscore the necessity of continuous monitoring to mitigate landslide risks in mountainous regions, highlighting the efficacy of PS-InSAR technology in assessing such hazards.

Calculation of radiation characteristics of shock heated air by Direct Simulation Monte Carlo method

The results of modeling the radiation characteristics of air behind the front of a strong shock wave, performed using the Direct Simulation Monte Carlo method, are presented. The model used takes into account various physical and chemical processes occurring in shock-heated air, including translational-rotational and translational-vibrational energy exchange, kinetics of chemical reactions, excitation of electronic levels of atoms and molecules, as well as emission and absorption processes for a discrete spectrum. As a result of the calculations, timeintegrated spectrograms of the volumetric radiation power of shock-heated air were obtained in absolute units in the range of shock wave velocities from 7.4 to 10.7 km/s at a gas pressure in front of the shock wave front of 0.25 Torr. The calculation data are compared with experimental data obtained on the double-diaphragm shock tube DDST-M of the Institute of Mechanics of Moscow State University.

Utilizing Quantum Cascade Lasers for Ultranarrow Velocity Resolution and Quantum-State Selectivity in Molecular Beam Scattering and Spectroscopy.

We demonstrate the capability of a narrow linewidth quantum cascade laser (QCL) to selectively excite a very narrow velocity range of nitric oxide (σ ≤ 7(3) m/s) with a pure ro-vibrational quantum state. By implementing a counter-propagating geometry, the molecules are selectively excited according to the Doppler shift of the ro-vibrational transition frequency such that the velocity width associated with the excited molecules depends only on the QCL linewidth. We demonstrate a velocity distribution limited by the effective linewidth of our free-running QCL (Γ = 3.2 MHz). Our development provides a cost-effective, flexible approach to resolve quantum-state selective chemical dynamics with excellent velocity resolution in a wide variety of molecules with infrared-active transitions. This technique has been formulated to provide ultrahigh collisional energy resolution in molecular beams to delineate final quantum-state product pairs in studies of molecular collisions.

Assessment of the Tall Buildings Dynamic Response Considering the Geometric Nonlinearity and the Aerodynamic Damping

This research work aims to evaluate the dynamic structural behaviour of tall buildings when subjected to wind loads considering the effect of the geometric nonlinearity and also the aerodynamic damping, due to the relative movement between the structure and the wind action. This way, the project associated to a steel-concrete composite building with 48 floors and 172.8 m height is investigated, when subjected to wind nondeterministic dynamic actions. The composite building finite element model was developed based on the use of the Finite Element Method (FEM), utilising the ANSYS computational program, and considering the soil-structure interaction effect, aiming to obtain a realistic representation of the dynamic behaviour. The building dynamic response was obtained based on the displacements and accelerations values, determined having in mind a wind velocity range between 5 m/s [18 km/h] and 45 m/s [162 km/h]. The conclusions of this investigation pointed out to the fact that when the geometric nonlinearity effect was considered in the analysis the investigated building dynamic response presented relevant differences, with maximum differences up to 30% to horizontal translational displacements and up to 45% to accelerations. On the other hand, when the aerodynamic damping was considered the contribution was not significant to the structure dynamic response, with maximum differences up to 5% for the displacements and up to 10% for the accelerations.

Assessment of Building Nondeterministic Dynamic Structural Behavior considering the Effect of Geometric Nonlinearity and Aerodynamic Damping

The objective of this research is to evaluate the dynamic structural response of tall buildings subjected to wind loads, taking into account the influence of geometric nonlinearity and aerodynamic damping. The project focuses on a steel-concrete composite structure with 48 floors and a height of 172.8 m, examining its response to wind non-deterministic dynamic actions. The building finite element model was developed based on the Finite Element Method (FEM), using the ANSYS computational program, and considering the soil-structure interaction effect, with the objective of obtaining a realistic representation of the dynamic behavior. The building dynamic response was obtained based on the displacement and acceleration values, determined with the consideration of a wind velocity range between 5 m/s (18 km/h) and 45 m/s (162 km/h). The findings of this study indicate that when the effect of geometric nonlinearity was incorporated into the analysis, the dynamic response of the investigated building exhibited notable discrepancies. The maximum differences observed in the horizontal translational displacements and accelerations were 30% and 45%, respectively. In contrast, the inclusion of aerodynamic damping had a negligible impact on the structural dynamic response, with maximum differences of 5% for displacements and 10% for accelerations.

Unsteady Swirl Distortion in a Short Intake Under Crosswind Conditions

Under crosswind operating conditions, the flow field of an aero-engine intake can be characterized by notable unsteady flow distortion. These distortions are typically associated with flow separation within the intake as well as with the ingestion of the ground vortex. This unsteady flow distortion can have a detrimental effect on the intake performance and potentially on the operability of the downstream compression system. Measurements of the unsteady velocity field within a model-scale intake under crosswind conditions were acquired using stereo particle image velocimetry (S-PIV). This work analyzes the S-PIV data to quantify the unsteady flow distortion, as well as the characteristics of the ingested ground vortex, in a short intake under crosswind conditions. The swirl distortion metrics were calculated for a range of crosswind velocities and intake mass flow capture ratios (MFCRs). The conditions at which the intake flow separates depend on crosswind velocity, ground clearance, the design of the intake, and the MFCR. Flow characteristics of both low MFCR diffusion-driven and high MFCR shock-induced separation were identified. The circumferential extent and intensity of the swirl distortion are strongly dependent on the crosswind velocity and mass flow rate. The swirl distortion caused by the diffusion-driven separation is greater than that due to the shock-induced separation. The diffusion-driven separation affects a larger portion of the intake aerodynamic interface plane with greater time-averaged and peak distortion levels compared to shock-induced separation. The ground vortex characterization at the aerodynamic interface plane showed a decreasing level of unsteadiness in vortex meandering with increasing MFCR.

Research on dynamic penetration of shaped charge jet under the condition of projectile and target rendezvous

Abstract To explore the penetration behavior of jets under dynamic impact conditions and to predict and assess the dynamic penetration power of shaped charge jets, finite element methods were employed to numerically simulate shaped charge warheads under various impact conditions. Combined with theoretical analysis, the simulations analyzed the variations in perforation and dynamic penetration depth of the jet into target plates. Using a random forest algorithm, the influence weights of different factors on the dynamic penetration depth of the jet were obtained. Furthermore, an engineering model for predicting the dynamic penetration depth of shaped charge jets was established through a linear regression model. The research results indicate that the impact velocity is the most critical factor affecting the dynamic penetration depth of shaped charge jets. The dynamic penetration depth of the jet into targets within a certain range of impact velocities is approximately linear. The established engineering model can effectively predict the penetration power of jets under dynamic impact conditions.

Comparison of mechanical response of head structure with different brain material models under impact

Abstract Brian material models and mechanical properties are very important for pressure evolution experiments and numerical simulations in head structure under impact. A simplified head structure with core-shell finite element model was established, and the motion, skull stress, skull deformation, and brain stress were numerically simulated with different soft tissue material models. The equivalence of the material model in stress propagation simulation was discussed. In the present work, it showed that when the head with impact velocity of 1m/s, the head structure rebound with a velocity of 0.6 m/s ∼ 0.8m/s, and occurred between 600μs and 1000μs due to different material models, at this time, the stress wave oscillation propagated in the skull underwent 3-5 repeated loads. The positive pressure on the impact side of brain tissue could reach 400kPa ∼ 800kPa, the negative pressure on the opposite side was between −150 kPa to −385kPa, the skull strain was between −1.8 ‰ to −3.7 ‰, and the skull stress was between 25.3MPa ∼ 41.2MPa. In a larger range of impact velocities, material models with strain rate effect have more advantages in stress wave transmission and pressure changing within the core-shell structure. The strain rate effect characterized only by creep and relaxation has limited effects on impact simulation, and directly introducing different strain rate mechanical property interpolation for hyperelastic model simulation is more effective.

Machine Learning Based Prediction of Ditching Loads

Approaches are presented to predict dynamic ditching loads on aircraft fuselages using machine learning. The employed learning procedure is structured into two parts, the reconstruction of the spatial loads using a convolutional autoencoder (CAE) and the transient evolution of these loads in a subsequent part. Different CAE strategies are assessed and combined with either long short-term memory (LSTM) networks or Koopman operator based methods to predict the transient behavior. The training data are compiled by an extension of the momentum method of von Karman and Wagner, and the rationale of the training approach is briefly summarized. The application included refers to a full-scale fuselage of a DLR-D150 aircraft for a range of horizontal and vertical approach velocities at 6 deg incidence. Results indicate a satisfactory level of predictive agreement for all four investigated surrogate models examined, with the combination of an LSTM and a deep decoder CAE showing the best performance.

Gone with the flow: Whitefish egg drift in relation to substrate coarseness under a range of flow velocities.

Most major rivers in Europe have been dammed for hydropower or other purposes. Such river alterations have decimated natural reproduction of many migratory fish species, including that of the anadromous European whitefish, Coregonus lavaretus, which is now maintained by extensive stocking programmes. In addition to stocking, limited natural reproduction may occur downstream of dams, where peak flow bouts from the dams threaten to flush the eggs into unsuitable habitats. Here, we assessed the effects of water flow velocity and substrate coarseness on downstream drift of whitefish eggs under laboratory conditions. The experiment's two different gravel substrates retained eggs better than cobble or sand substrates; the water velocity needed for notable egg drift was higher for the gravel substrates. The results indicate that egg drift is one of the factors that should be considered when evaluating the effects of hydropower plant operations. Moreover, measures mitigating the effects of the artificial flow regimes should incorporate the type and coarseness of the riverbed's substrate.

Research and simulation study on the penetration behavior of Φ 30 mm armor-piercing bullets penetrating armored steel

Abstract To study the penetration behavior and ballistic characteristics of a Φ30mm tungsten alloy armor-piercing projectile penetrating homogeneous armor steel, penetration tests were conducted, and the penetration process was numerically simulated using LS-DYNA. The experimental results show that the presence of the conical section of the Φ30mm armor-piercing projectile forms a “saddle” shaped crater feature. The simulation results indicate that the penetration efficiency of the projectile and the incident velocity exhibit a quadratic function relationship. In the velocity range of 800-1200m/s, the kinetic energy consumed by the projectile for the same penetration depth is essentially the same, i.e., the lateral crater diameter is consistent at different speeds. Additionally, during the penetration process, the penetration depth as a function of time under different speeds also shows a quadratic relationship.

Effects of ultrafast outflows on X-ray time lags in active galactic nuclei

Context. The time lag between soft (e.g., 0.3–1 keV) and hard (e.g., 1–4 keV) X-ray photons has been observed in many active galactic nuclei (AGNs) and can reveal the accretion process and geometry around supermassive black holes. High-frequency Fe K and soft lags are considered to originate from the light-travel distances between the corona and the accretion disk, while the propagation of the inward mass accretion fluctuation usually explains the low-frequency hard lags. Ultrafast outflows (UFOs) with a velocity range of ∼0.03 to 0.3c have also been discovered in numerous AGNs and are believed to be launched from the inner accretion disk. However, it remains unclear whether UFOs can affect the X-ray time lags. Aims. As a pilot work, we aim to investigate the potential influence of UFOs on X-ray time lags of AGNs in a small sample. Methods. By performing the UFO-resolved Fourier spectral timing analysis of archival XMM-Newton observations of three AGNs with transient UFOs – PG 1448+273, IRAS 13224-3809, and PG 1211+143 – we compare the X-ray timing products, such as lag-frequency and lag-energy spectra, of observations with and without UFO obscuration. Results. Our results find that in each AGN, low-frequency hard lags become weak or even disappear when they are accompanied by UFOs. This change is confirmed by Monte Carlo simulations at a confidence level of at least 2.7σ. In the high-frequency domain, soft lags remain unchanged, while the Fe K reverberation lags tentatively disappear. The comparison between timing products of low- and high-flux observations on another three AGNs without UFOs (Ark 564, NGC 7469, and Mrk 335) suggests that the disappearance of low-frequency hard lags is likely related to the emergence of UFOs, not necessarily related to the source flux. Conclusions. The presence of UFOs can affect X-ray time lags of AGNs by suppressing the low-frequency hard lags, which can be explained by an additional time delay introduced by UFOs or disk accretion energy, which should transferred to heat the corona, carried away by UFOs.

A Multi‐Decade Tracer Study of the Circulation and Spreading Rates of Atlantic Water in the Arctic Ocean

AbstractIn this contribution, we present tritium‐3He (3H‐3He) apparent ages and hydrographic data from 21 expeditions spanning 27 years of Arctic Ocean section work (1987–2013) to estimate flow paths and spreading velocities of the Atlantic Waters (AW) circulation on a pan‐Arctic scale. Tracer data not only corroborate the well‐organized cyclonic flow along the continental slope but also introduce a temporal dimension to these observations. Additionally, they provide insights into other circulation branches of the Atlantic layer, which are hypothesized to be influenced by deep submarine ridges. Tracer measurements indicate that mean spreading rates vary across different branches of the circulation pattern. Along the boundary current, spreading velocities range from approximately 0.7 to 1.5 cm s−1, with no significant difference observed between the waters of the two vertically stacked Atlantic branches. Within the limits of our method, tracer data support the hypothesis originally proposed by Rudels et al. (1994), https://doi.org/10.1029/gm085p0033—of stable pathways in the Atlantic Layer, influenced by topographic constraints.

A phase-field model bridging near-equilibrium and far-from-equilibrium alloy solidification

Mapping to the appropriate Gibbs–Thomson (G–T) condition is essential for phase-field modeling to produce reliable and realistic solidification microstructures. However, existing phase-field models face challenges in simultaneously satisfying both near-equilibrium and far-from-equilibrium G–T conditions. This limitation restricts the applicability of phase-field methods in scenarios with a wide range of interface velocities, such as those observed in additive manufacturing. In this work, we propose a phase-field model that bridges both regimes by redefining each interfacial concentration field into two components: a conservative term representing long-range diffusion and a non-conservative term accounting for short-range redistribution within the diffuse interface. This formulation makes the model fully variational and analytically traceable through thin-interface analysis, allowing for accurate mapping to the G–T condition and determining model parameters. A key advancement of this model is the inclusion of free energy dissipation for short-range redistribution fluxes in the thin-interface limit, providing the necessary degree of freedom to reconcile both near-equilibrium and far-from-equilibrium G–T conditions. This capability is demonstrated by applying the model to simulate banded structures, effectively capturing the transition between near-equilibrium and far-from-equilibrium states.

Haptic-Based Real-Time Platform for Microswarm Steering in a Multi-Bifurcation Vascular Network.

The use of electromagnetic fields to control a collection of magnetic nanoparticles, known as a microswarm, has many promising applications. Current research often makes use of accurate but time-consuming simulations lacking real-time human input. On the contrary, human interaction is possible with a real-time simulator, allowing the collection of valuable user interaction data. This paper presents the development and validation of a real-time two-dimensional microswarm simulator to accommodate the human interaction aspect. A haptic device is used to steer the microswarm through a multi-bifurcation vascular network towards a selected outlet. The percentage of particles reaching the selected outlet is used as the success metric. The simulator is verified against collected real-world experimental data and shows an 8% deviation. Parametric studies demonstrate the most influential parameters. We found that reducing the magnetic gradient from 1000 mT/m to 100 mT/m resulted in a decrease in recorded performance from 100% to 30.8%. Variation in fluid flow also had a considerable effect on the recorded performance, presenting a drop from 100% to 35.3% when fluid flow velocities increased from 0.005 m/s to 0.06 m/s. Changing the starting arrangement of particles resulted in a drop to 59% over the same range of fluid flow velocities.

Experimental investigation of the characteristics of direct injection nozzle sprays in an afterburner environment

This study examined the atomization characteristics of direct injection nozzles under high-temperature, large-Mach inflow conditions using a high-speed camera. The effect of inflow conditions on fuel breakup length, fuel concentration field, and particle size spatial distribution was quantitatively analyzed by using image processing techniques. Experimental results indicate the following: 1) When the liquid-to-gas momentum ratio and inflow Mach number (Ma) are equal, the breakup length, fuel field boundary, and droplet distribution in the jet core region remain consistent for the same nozzle under room-temperature air and high-temperature gas conditions. 2) A breakup length model based on the breakup time of the liquid column is proposed. 3) The logarithmic fuel trajectory formula can effectively predict the physical phenomenon of the movement of fuel particles with the gaseous flow downstream of the injection point after their kinetic energy is depleted, with a prediction error of no >10 %. 4) The spatial distribution of particle sizes reveals that within the selected range of liquid-phase jet velocity, the distribution range of the Sauter mean diameter (SMD) of the jet core area in gas-flow environments with large Ma is similar. At the same axial position, a positive correlation exists between SMD and nozzle diameter. The results of this study have guiding importance for the design of integrated afterburner nozzles.