Velocity Direction Research Articles

Effect of shear flow on the transverse thermal conductivity of polymer melts.

The effect of shear flows on the thermal conductivity of polymer melts is investigated using a reversed nonequilibrium molecular-dynamics (RNEMD) method. We extended the original RNEMD method to simultaneously produce spatial gradients of temperature and flow velocity in a single direction. This method enables accurate measurement of the thermal conductivity in the direction transverse to shear flow. The Weissenberg number defined with the shear rate and the relaxation time of the polymer conformation can uniformly differentiate the occurrence of shear rate dependence of the thermal conductivity across different chain lengths. The stress-thermal rule (STR) (i.e., the linear relationship between anisotropic parts of the stress tensor and the thermal conductivity tensor) holds for entangled polymer melts even under shear flows but not for unentangled polymer melts. Furthermore, once entanglements form in polymer chains, the stress-thermal coefficient in the STR remains independent of the polymer chain length. These observations align with the theoretical foundation of the STR, which focuses on energy transmission along the network structure of entangled polymer chains [B. van den Brule, Rheol. Acta 28, 257 (1989)0035-451110.1007/BF01329335]. However, under driven shear flows, the stress-thermal coefficient is notably smaller than that measured in the literature for a quasiquiescent state without external forces. Although the mechanism of the STR in shear flows has yet to be fully elucidated, our study confirmed the validity of the STR in shear flows. This allows us to use the STR as a constitutive equationfor computational thermofluid dynamics of polymer melts, thus having broad engineering applications.

A general framework for the design of efficient passive pitch systems

Mitigating the impact of variable inflow conditions is critical for a wide range of engineering systems such as drones or wind and tidal turbines. Passive control systems are of increasing interest for their inherent reliability, but a mathematical framework to aid the design of such systems is currently lacking. To this end, in this paper a two-dimensional rigid foil that passively pitches in response to changes in the flow velocity is considered. Both an analytical quasi-steady model and a dynamic low-order model are developed to investigate the pivot point position that maximizes unsteady load mitigation. The paper focuses on streamwise gusts, but the proposed methodology would apply equally to any change in the inflow velocity (speed and/or direction). The quasi-steady model shows that the force component in any arbitrary direction can be kept constant if the pivot lies on a particular line, and that the line coordinates depend on the gust and the foil characteristics. The dynamic model reveals that the optimum distance of the pivot location from the foil increases with decreasing inertia. For a foil at small angles of incidence, the optimum pivot point is along the extended chord line. This knowledge provides a methodology to design optimum passively pitching systems for a plethora of applications, including flying and swimming robotic vehicles, and provides new insights into the underlying physics of gust mitigation.

Pitot tube measure-aided air velocity and attitude estimation in GNSS denied environment

This paper addresses the problem of estimating air velocity and gravity direction for small autonomous fixed-wing drones in GNSS11Global Navigation Satellite Systems.-denied environments. The proposed solution uses a minimal sensor suite, relying on Pitot tube measurements and Inertial Measurement Unit (IMU) signals, including only gyrometers and accelerometers. The approach combines the Riccati observer and Equivariant Filter designs, using an over-parametrization technique to design an observer on SO(3)×R3 and subsequently re-project to S2×R3 to estimate the gravity direction. The system’s observability is analyzed, and local exponential stability of the origin of the observer error is demonstrated as long as the aircraft attitude is persistently exciting. The observer was evaluated using simulated and real flight data to showcase the estimator’s performance.

2D model of groundwater flow and total dissolved HCH transport through the Gállego alluvial aquifer downstream the Sardas landfill (Huesca, Spain)

The organic pollutants disposed at the Sardas landfill in Sabiñánigo (Huesca, northeastern Spain) by the INQUINOSA lindane factory have reached the Gállego alluvial aquifer and could affect the Sabiñánigo reservoir. The daily oscillations of the reservoir water level produce a tidal effect on the piezometric heads of the aquifer. These oscillations are transmitted in a damped way with a time lag, thus attesting that the silting sediments of the reservoir and the natural silts of the Gállego alluvial are interposed between the reservoir water and the layer of sands and gravels. A 2D finite element groundwater flow and total dissolved hexachlorocyclohexane (HCH) transport model through the Gállego alluvial aquifer is presented here. The flow model was constructed to: (1) Quantify the tidal effect, produced by the daily fluctuations of the reservoir water level on the aquifer; (2) Estimate the hydrodynamic parameters of the layer of sands and gravels; and 3) Estimate the vertical hydraulic conductivity of the silting sediments and silts; and (4) Quantify aquifer/reservoir interactions. The flow model reproduces the dynamics of the tidal effect and attests that groundwater velocity and flow direction changes daily in response to the oscillations of the reservoir level. Model results reproduce the measured well hydrographs and the Darcy velocity derived from tracer tests and confirm the validity of the conceptual model. The transport model of total dissolved HCH simulates the time evolution of the contaminant plume. The computed concentrations of total dissolved HCH and the contaminant mass outflux are very sensitive to changes in the source terms and the distribution coefficient, Kd of HCH. The best fit to the measured HCH plumes in September 2010 and December 2020 is obtained with a Kd ranging from 1 to 3 L/kg. The computed flux of dissolved HCH leaving the Sardas site in 2020 towards the Sabiñánigo reservoir ranges from 0.6 kg/year for Kd = 3 L/kg to 3.1 kg/year for Kd = 1 L/kg. The findings of this study will be most useful for planning and designing remedial and containment actions at the Sardas site and other similar lindane-affected sites.

Simulating charged particles in electromagnetic fields

Relativistic charged particles in electromagnetic fields follow paths that increase in complexity with an increasingly complex field. When traveling in these fields, the particles are acted upon by an electromagnetic force comprised of an electric component and a magnetic component. While solving for these paths in simple electromagnetic fields can be done analytically, the task becomes significantly more difficult when the fields get more complex. Thus, in these situations, numerical methods are required to find solutions. One of the most well-known such methods is the Boris method, which is explored in this paper. Before this method is applied to any complex situations, its accuracy must be ensured by testing on simple cases which are solvable by hand. These cases include a 1D electric field in the direction of the initial velocity of the particle, and a 1D magnetic field perpendicular to the particle's velocity. With the accuracy proven, the method was applied to the cases of a force-free field, a dipolar field, and a quadrupolar field. In the latter two cases the method produced very interesting results that could provide significant insight that would be very difficult to achieve analytically. In the case of the force-free field, however, the method shows some limitations, as a precise cancellation of the force produced by the electric and magnetic fields is required to produce a straight line and the Boris method has some difficulty achieving this, especially when using a large time step.

Learning solid dynamics with graph neural network

Deep learning has shown great promise in solid physic dynamic simulation. By incorporating physical laws, recent works have further improved performance. However, existing methods rarely conform to macrophysics and incur computational costs. Furthermore, the velocity direction features of the current model have not been decomposed, forcing the model to learn vector operations. To address the aforementioned problems, we propose a Solid-Graph Network (Solid-GN), designed for more accurate and efficient learning of solid dynamics. Firstly, we design a novel and cost-effective symmetric direction encoding system that achieves macroscopic equivariance in 2D space by representing same relative directional relationships among particle pairs and their flipping version. Secondly, we propose a message-passing mechanism incorporated with the contact process, facilitating an accurate description of interactions through the decomposition of normal and tangential effects. Lastly, four novel datasets for solid dynamics with non-uniform radius particles are released, thereby enabling more complex and realistic physical simulations. Experimental evaluations conducted on five datasets demonstrate our model's performance concerning predictive accuracy, macroscopic equivariance, and computational cost over the state-of-the-art ones.

Statistical Analysis of Bubble Parameters from a Model Bubble Column with and without Counter-Current Flow

Bubble columns are widely used in numerous industrial processes because of their advantages in operation, design, and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially in continuous mode with counter-current liquid flow. For the design and optimization of such reactors, precise numerical simulations and modelling are needed. These simulations and models have to be validated with experimental data. For this reason, experiments were carried out in a laboratory-scale bubble column using shadow imaging and particle image velocimetry (PIV) techniques with and without counter-current liquid flow. In the experiments, two types of gases—relatively poorly soluble air and well-soluble CO2—were used and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates, overall, 108 different flow conditions were investigated. In addition to the liquid flow fields captured by PIV, shadow imaging data were also statistically evaluated in the measurement volume and bubble parameters such as bubble diameter, velocity, aspect ratio, bubble motion direction, and inclination. The bubble slip velocity was calculated from the measured liquid and bubble velocities. The analysis of these parameters shows that the counter-current liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO2 bubbles, remarkable bubble shrinkage was observed with counter-current liquid flow due to the enhanced mass transfer. The results obtained for bubble aspect ratio are compared to known correlations from the literature. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the development of correlations needed in the validation of numerical simulations and models. The data are available from the authors on request.

Comparison of the monitoring of surface deformations in open-pit mines with Sentinel-1A and TerraSAR-X satellite radar data.

In case necessary precautions are not taken in surface mines, serious accidents and loss of life may occur, particularly due to large mass displacements. It is extremely important to identify the early warning signs of these displacements and take the necessary precautions. In this study, free medium-resolution satellite radar images from the European Space Agency's (ESA) C-band Sentinel-1A satellite and commercial high-resolution satellite radar images (SAR, Synthetic Aperture Radar) from the Deutsches Zentrum für Luft- und Raumfahrt's (DLR) X-band TerraSAR-X satellite were obtained, and it was attempted to reveal the traceability and adequacy of monitoring of deformations and possible mass displacements in the dump site of an open-pit coal mine. The compatibility of the results obtained from the satellite radar data with two devices of Global Positioning System (GPS) which were installed in the field was evaluated. Furthermore, the velocity results in the Line Of Sight (LOS) direction and vertical deformation velocity results obtained with all three approaches (GPS/Sentinel-1A, GPS/TerraSAR-X, and Sentinel-1A/TerraSAR-X) were compared. It was observed that the results were statistically equal and the directions of movement were similar/compatible. The result of this study showed that deformations at mine sites can be monitored with sufficient accuracy for early warning with free Sentinel-1A satellite data, although the TerraSAR-X satellite offers a higher resolution.

A deflected ray model of the transit time difference in ultrasonic flow meters applied to non-ideal flow profiles

Transit time difference (TTD) ultrasonic meters have widespread applications due to their high dynamic range, lack of moving parts and low maintenance requirements. In earlier work, the TTD is considered to arise due to the fluid flow changing the effective speed of sound along a fixed ray path, but recent publications have introduced a new way of viewing how the TTD arises. The flow velocity in the axial direction does not affect the speed of sound in the direction normal to the pipe wall. Therefore, in a clamp-on meter with the fluid at constant temperature and pressure, the transit time in the liquid must be constant with changing flow rate. The TTD then arises due to the ray path in the water being deflected, and the received wavefront travelling some extra distance along the pipe axis, which results in a different transit through the transducer wedge than for zero flow conditions. In a meter with wetted transducers, the mechanism causing the TTD is slightly different. The deflected ray travels a different distance in the fluid along the direction normal to the pipe walls due to the transducer surface being at an angle to the flow direction, and this is responsible for the TTD that is measured.Previous work has focused on calculating the magnitude of the ray deflection effect in clamp-on meters for ideal flow conditions, where the flow velocity does not depend on the position in the pipe. In this article, the ray deflection is calculated for a series of analytic profiles, and it is shown that the two models result in the same calculated TTD for both clamp-on meters and meters with wetted transducers at low flow speeds. The hydraulic correction factors calculated using the model which considers a change in the effective speed of sound are recovered using the ray deflection models. The resulting equations for beam deflection are the same as those for the conventional fixed ray path model, but the beam deflection model is more physically realistic and presents new opportunities for calibration methods utilising carefully controlled movement of the transducers. The conventional model typically has a correction factor which is allowed to vary in cases where the flows are expected to approach the speed of sound to account for the effect of ray deflection. However, the ray deflection model automatically takes this into account, so is expected to be useful in these circumstances.

Controlled refraction and focusing of spin waves determined by the Aharonov-Casher effect

The influence of an external static electric field on spin wave (SW) dynamics leads to an additional topological phase called the Aharonov-Casher (AC) phase. It is manifested as a shift in dispersion and the group velocity direction of the spin wave under the electric field. Within a linear approximation, the AC effect can be considered by including the Dzyaloshinskii-Moriya-like interaction between neighboring spins, which is proportional to the applied electric field. In this paper, we use these findings to examine the possibility of the electric field control of the refraction of coherently propagating SWs. This is done by studying the propagation SWs across the boundary between two regions of a homogeneous ferromagnetic film under the influence of different external electric fields. We have derived an analytical expression for a magnetic Snell's law and performed micromagnetic simulations to demonstrate how the AC phase shift can control SW refraction. This effect enables us to quantify the topological AC phase action. It presents a promising approach for guiding and manipulating the phase and energy flow of SWs using an external electric field, opening a way to control magnonic devices. Published by the American Physical Society 2024

Effect of Air Parameters on LiCl-H2O Film Flow Behavior in Liquid Desiccant Systems

The wettability and stability of a solution’s film on the filler surface are the key factors determining heat and mass transfer efficiency in liquid desiccant air conditioning systems. Therefore, this study investigates the effects of different air parameters on the flow behavior of a lithium chloride solution’s film. The effects of air velocity, air flow pattern, and pressure on the wettability and critical amount of spray are discussed. The results show that the main mechanism by which the air velocity affects the wettability is that the shear stress generated by the direction of the air velocity disperses the direction of the surface tension and weakens its effect on the liquid film distribution. In addition, in the counter flow pattern, the air flow blocks the liquid film from spreading longitudinally and destroys the stability of the liquid film at the liquid outlet, which increases the critical amount of spray. The pressure distribution is similar under different operating pressures when the flow is stable; thus, pressure has little effect on wettability. The simulation results under 8 atm are compared with the experimental results. It is found that the sudden increase in the amount of moisture removal when the amount of spray changes from 0.05 to 0.1 m3/(m·h) in the experiment is caused by the change in the liquid film flow state. In addition, the results show that within the range of air flow parameters for the liquid desiccant air conditioning system, air flow shear force is not the main factor affecting the stability of the solution’s film, and there is no secondary breakage of the solution’s film during the falling-film flow process.

Simulations of beta-induced Alfvén eigenmode mitigation by off-axis energetic particle distribution

The effect of different off-axis energetic particle (EP) slowing down distribution on beta-induced Alfvén eigenmode (BAE), driven by the on-axis EP distribution, is systematically studied using kinetic-magnetohydrodynamic code M3D-K. The aim is to analyze the optimal parameter region for controlling AEs via varying EP distribution parameters. The simulation results reveal that by modifying the gradients of the EP distribution, the off-axis EP can further destabilize or mitigate the on-axis EP driven BAE, depending on the off-axis EP distribution’s parameters: deposition profile, EP beta, pitch angle, injection velocity and direction. When the off-axis EP is deposited outside the mode center, and its injection velocity is sufficiently large to satisfy the resonance with BAE, the stabilization of BAE is achieved. This stabilizing effect is directly proportional to the off-axis EP beta, while excessive off-axis EP beta can trigger a new EP-driven instability located outside the BAE. Furthermore, to achieve a stronger stabilizing effect, the pitch angle distribution and velocity direction of the off-axis EP should be close to those of the on-axis EP. For instance, compared to the off-axis counter-passing EP, the off-axis co-passing EP can lead to a more effective mitigation of the BAE driven by the on-axis co-passing EP.

Analytical and numerical study of water-based silver nanofluid (Ag) across a Riga plate with nonlinear radiation and viscous dissipation: A three-dimensional study

The primary endeavor of this investigation is to determine the Darcy–Forchheimer flow of water-based silver nanofluid (Ag) across a bidirectional Riga plate with viscous dissipation and nonlinear radiation. By manipulating the pertinent variables, the governing equations undergo a transformation into nonlinear ordinary differential equations. The remodeled flow problems are investigated numerically and analytically using the MATLAB (bvp4c built-in function) algorithm and the homotopy analysis method scheme. The repercussions of the appropriate factors on the x− and y− direction velocity profiles, temperature profile, skin friction coefficient of the x− and y− directions, and local Nusselt number are examined via tables and graphs. It is found that both directional fluid velocities decline in the presence of the suction/injection parameter. Increasing the radiation parameter and the Eckert number exalts the fluid temperature. The surface shear stress decays as the suction/injection parameter and the Forchheimer number grow larger. In addition, a greater heat transfer rate appears on the Riga plate compared to the stationary plate.

Direct Current Motor Velocity Control With Integral Retarded Controller Under Unintentional Delay

Abstract Delay-based controllers have been recently revisited over proportional-integral-derivative (PID) controllers, with promising analytical tuning formulae and capabilities to effectively control plants with noisy measurements even without low-pass filters. One such controller is the integral retarded (IR) controller, which utilizes an intentional delay to reduce actuator chattering against noisy measurements while its integral part achieves zero steady-state error for set-point regulation of Type-0 open-loop systems. However, measurements can be unintentionally delayed in many applications. The integral retarded framework for such cases has not been studied in the literature. Here, we provide new analytical tuning rules of the controller in such cases, as well as validations through simulations and a direct current (DC) motor velocity control hardware experiment.

How the multiplanar trunk resistance affects the dynamic postural control during single-leg vertical jumps in college athletes with poor movement quality

BACKGROUND: Poor movement quality of the trunk and the lower limbs as well as dynamic postural control have a strong relation with non-contact injuries in sport. Aiming to reduce the risk of injuries, training approaches using loaded jumps with trunk resistance have been proposed. AIM: To describe how a multiplanar trunk load affects the dynamic postural control and the peak vertical ground reaction force of college athletes with poor movement quality of the trunk and the lower limbs. METHOD: Center of Pressure (COP) variables and peak vertical ground reaction force of 24 female college athletes during single-leg jumps with and without a trunk resistance were compared. RESULTS: There was a significant decrease of the COP displacement (p=0.006), RMS (p=0.009) and velocity (p=0.007) in the anteroposterior direction, and an increase of the COP displacement (p=0.016), RMS (p=0.043) and velocity (p=0.043) in the mediolateral direction, with a moderate effect size. No significant difference was found in the peak vertical ground reaction force. CONCLUSION: Exercises involving multiplanar trunk resistance may negatively impact dynamic postural control in women with poor movement quality.

Additional visual information on postural control mechanisms in Parkinson's disease: a pilot study

Additional visual information on postural control mechanisms in Parkinson's disease: a pilot study

Backaction-evading receivers with magnetomechanical and electromechanical sensors

Today's mechanical sensors are capable of detecting extremely weak perturbations while operating near the standard quantum limit. However, further improvements can be made in both sensitivity and bandwidth when we reduce the noise originating from the process of measurement itself—the quantum-mechanical backaction of measurement—and go below this ‘standard’ limit, possibly approaching the Heisenberg limit. One of the ways to eliminate this noise is by measuring a quantum nondemolition variable such as the momentum in a free-particle system. Here, we propose and characterize theoretical models for direct velocity measurement that utilize traditional electric and magnetic transducer designs to generate a signal while enabling this backaction evasion. We consider the general readout of this signal via electric or magnetic field sensing by creating toy models analogous to the standard optomechanical position-sensing problem, thereby facilitating the assessment of measurement-added noise. Using simple models that characterize a wide range of transducers, we find that the choice of readout scheme—voltage or current—for each mechanical detector configuration implies access to either the position or velocity of the mechanical subsystem. This in turn suggests a path forward for key fundamental physics experiments such as the direct detection of dark matter particles. Published by the American Physical Society 2024

Coastal Tidal Flat And Tidal Current Observation Based On Satellite Remote Sensing

Satellite remote sensing has been an effective way to acquire surface image sequences of costal field, and the satellite video at a frame rate of multiple frames per second could provide chance for short-time observations at high temporal resolution such as the observation of surface tidal currents. The observation of surface tidal currents has been facilitated by advanced image preprocessing methods and large-scale image velocimetry, while the space-time volume velocimetry (STVV) was used in this study. STVV can simultaneously obtain the direction and magnitude of the flow velocity through the surface texture without any artificial tracers, hence it is considered as a promising method. Since it has only been proposed in recent years, this study evaluated the accuracy of the STVV algorithm and tested the robustness of the STVV to environmental disturbance factors firstly. The simulated image sequences were used so that the exact accuracy of STVV can be known by comparing the measured and ground truth values since the ground truth of the pixel flow velocity is predictable and modifiable. The effects of the two main STVV parameters, the size of the search area and the selected frames of images, on the results were analyzed, and the robustness against image noise and fog was examined. The size of the search area and selected frames of images were found having the similar effects on the calculation results that the larger both are, the higher the calculation accuracy will be. Although the lower Signal-to-noise ratios lead to more inaccurate results, STVV is robust to image noises from the results in the given cases. Additionally, the accuracy of STVV is acceptable for a small amount of mist, but thicker fog results in large errors. Further research to develop image processing methods to improve the accuracy of STVV in the future is highly necessary. Therefore, based on one satellite video with the frame rate of 10fps and the resolution of 0.95m shooting on September 15th, 2017, surface tidal current observation of the New York Harbor during the flood tide using STVV was achieved. The flow velocity magnitude can reach 3m/s, and the flow direction is consistent with the actual situation. The feasibility of surface tidal current observation using STVV from the satellite video was proved

Comparison of foot pressure distribution and foot kinematics in undulatory underwater swimming between performance levels

ABSTRACT This study aimed to elucidate the foot kinematics and foot pressure difference characteristics of faster swimmers in undulatory underwater swimming (UUS). In total, eight faster and eight slower swimmers performed UUS in a water flume at a flow velocity set at 80% of the maximal effort swimming velocity. The toe velocity and foot angle of attack were measured using a motion capture system. A total of eight small pressure sensors were attached to the surface of the left foot to calculate the pressure difference between the plantar and dorsal sides of the foot. Differences in the mean values of each variable between the groups were analysed. Compared to the slower swimmers, the faster swimmers exhibited a significantly higher swimming velocity (1.53 ± 0.06 m/s vs. 1.31 ± 0.08 m/s) and a larger mean pressure difference in the phase from the start of the up-kick until the toe moved forward relative to the body (3.88 ± 0.65 kPa vs. 2.66 ± 1.19 kPa). The faster group showed higher toe vertical velocity and toe direction of movement, switching from lateral to medial at the time of generating the larger foot pressure difference in the up-kick, providing insight into the reasons behind the foot kinematics of high UUS performance swimmers.

Exploration Of Key Approaches to Enhance Evacuated Tube Solar Collector Efficiency

Exploration Of Key Approaches to Enhance Evacuated Tube Solar Collector Efficiency