Input Velocity Research Articles

УТОЧНЕННЯ ШВИДКОСТІ МЕТЕОРА ЯК ВИПАДКОВОЇ ВЕЛИЧИНИ ЗА ДОПОМОГОЮ ТЕОРЕТИЧНОГО РОЗРАХУНКУ ЇЇ ФУНКЦІЇ ЩІЛЬНОСТІ РОЗПОДІЛУ

When processing the results of simultaneous double-station video observations of meteors and subsequent cataloging of their kinematic parameters, the accuracy of the obtained results, that is, the error of each parameter, is important. The most important characteristic of a meteor is its velocity, because it affects the accuracy of determining the semi-major axis and the eccentricity of the heliocentric orbit of the meteoroid – on the one hand, and on the physics of the meteor motion in the atmosphere – on the other. Since after calculating the velocity vector direction, the velocity vector sizes can be searched “independently” (the results will be partially correlated) for each of the points, it is suggested to use these two values ​​to precize the velocity of the meteor, for example, finding its weighted average value. Earlier, we proposed to search all meteor kinematic parameters as random variables by Monte Carlo method, obtaining probability density distributions for each parameter. Since when calculating the meteor velocity in this way, we get two distributions for each of the observation points, it is suggested to find their section as a product of two input distributions with further normalization of its area by one. At first, a scheme for multiplying histograms was implemented, which was not very convenient because it gave a large scatter of the points of the resulting distribution. In this work, it is proposed to use the fact that both input velocity distributions are of normal type with high probability (probability 0.998 within three standard deviations) and to use the multiplication of analytical functions of the normal distribution, the result of which will also be a Gaussian function. Appropriate theoretical calculations were made, and this approach was tested on an individual meteor. It is shown that the scheme is mathematically and physically justified and gives effective results.

ROBUST OPTIMAL DESIGN BASED ON STORY DUCTILITY RATIO OF ELASTIC-PLASTIC BUILDING STRUCTURES WITH UNCERTAIN OIL DAMPERS SUBJECTED TO CRITICAL DOUBLE IMPULSE

A new robustness evaluation method based on the specified story ductility ratio is proposed for a building model with uncertain oil dampers. Since the influence of input motion uncertainty on the response variation can be simply taken into account, the critical double impulse input is used instead of input ground motions. In the proposed method, the robustness function is derived as a function of the input velocity amplitude for a specified ductility ratio. This procedure is suitable for the performance-based design. A robust optimal design method on damper placement is also presented based on the proposed new robustness function. Numerical examples of robust optimal design of dampers are presented for a 12-story elasto-plastic building model with linear oil dampers.

Distributed Control for Human-Swarm Interaction In Non-Convex Environments using Gaussian Mixture Models

This paper presents a novel implementation of a human-swarm interface that allows humans to define an area with desired shape to be reached by a multi-robot system. Human-swarm interaction can be useful in order to exploit human intelligence and knowledge for the operation of swarm robots. The proposed work deals with limitations usually met when dealing with real-world implementation, e.g. limited sensing capabilities of the agents and hard conditions where communication is difficult or even completely denied. Gaussian Mixture Models are exploited in order to define an appropriate probability density function of the environment based on the area selected by a human operator. Then, velocity input for each robot is calculated in a distributed manner using Voronoi tessellation and Lloyd's algorithm. Finally, results of both virtual and real-world tests are presented, showing the final configuration reached by the multi-robot system in comparison with the desired region defined on the graphical interface.

Comparison Analysis of Liquid and Air-cooling Systems for GPU

Abstract: In order to increase reliability and prevent early failure, heat produced by electronic components and circuits must be drained. Heat sinks, fans, and other air-cooling devices, as well as alternative computer cooling methods like liquid cooling, can all be used as heat dissipation techniques. Here the paper's main focus is on a numerical analysis of temperature distribution in a GPU scenario with various input velocity circumstances, including v = 1 m/s, 3 m/s, and 5 m/s. Air and water are the two distinct fluids employed in this investigation to cool the graphics card. An analysis of the fluid flow and heat transfer simulation of a desktop graphics card heat sink is conducted using the CFD software ANSYS Fluent. According to the findings, cooling with water was 10% more effective than cooling with air. The outcome also shows an inverse correlation between the graphic card chip's intake velocity and temperature. The rate of heat transfer to the heat sink increases as the inflow velocity rises which is helped by the convection.

Experimental studies and 3D simulations for the investigation of thermal performances of a solar air heater with different spiral-shaped baffles heights

A new design of Solar Air Heater (SAH) with spiral flow path is studied experimentally and numerically. The spiral-shaped SAH performance is studied at various mass flow rates, inlet temperatures, radiation intensity and baffle heights. Similarly, a CFD model is developed using “ANSYS Fluent” software to study the fluid flow and heat transfer in the SAH. Mesh independence is performed in order to choose the appropriate mesh. The discrete ordinate (DO) radiation model and the k-ω Shear Stress Transport (SST) turbulence model are used to study the radiative heat transfer and the turbulent flow, respectively in the SAH. Effects of different baffle heights (42 mm,50 mm,70 mm,90 mm, 110 mm and 130 mm) for different mass flow rates (input velocities:5 m/s,10 m/s,15 m/s, 20 m/s and 25 m/s) are numerically investigated. Local flow characteristics are presented and discussed. The results show a good agreement between the numerical model and the experimental data with an average error of 3.6%. The maximum outlet air temperature of the SAH during the test days reached 77.7 °C with input velocity of 5 m/s. The maximum thermal efficiency is founded for geometries having 110 mm and 130 mm baffle-heights ranges between 40% and 59% for an airflow of 0.0075 kg/s and 0.038 kg/s, respectively. The geometry having a 110 mm baffle-heights shows the optimum thermal performance of 13% higher than standard geometry (50 mm baffle height).

Numerical analysis of two-phase nanofluid flow on the thermal efficiency of a circular heat sink for cooling of LEDs

The present paper performed a numerical study on two-phase nanofluid (NFs) flow in a circular heatsink for cooling several LEDs. The heatsink is symmetrically designed and has two inlets and four outlets. Six heat sources or LEDs are placed on the circumference of a circle and a heat source is also mounted in the center of the heatsink. By varying the diameter of the circle, the side length of the heat sources, and the input velocity of the NFs, one may estimate the values of thermal resistance (THR), temperature uniformity (TUY) on the heatsink, heat transfer coefficient (HTC), and pressure drop in the heatsink. The finite element and two-phase mixture method are utilized for NFs simulations. It demonstrate that the heat source placed in the middle has a lower temperature than other heat sources. The results are most significantly affected by changing the NFs' velocity. The value of dimensionless temperature increases and subsequently decreases as the sides of the heat sources get longer. The dimensionless temperature first decreases and then increases as the distance between the heat sources and the heatsink's center increases. The amount of THR is high when the heat sources' side length or velocity values are large.

Improved Response Spectrum Method Based on Real-Complex Hybrid Modal Superposition for Base-Isolated Structures

A novel real-complex hybrid modal response spectrum method (RCHM-RSM) based on the modal superposition of the superstructure is proposed for base-isolated (BI) structures in this paper. In contrast to the traditional analysis method, the method can increase the accuracy of the structural response and avoid complex calculations. Additionally, the direct use of the damping matrix of superstructures for BI structures was found to cause an overestimation of the damping effect and consequently underestimate the deformation of the superstructure. Thus, a new scheme is proposed for determining the damping matrix for BI structures, and general expressions of the damping matrix of the superstructure and the damping constant of the isolation layer are presented. Using the proposed method to construct the damping matrix of BI structures, the equivalent load associated with the coupling damping between the structure and support can be determined when the displacement–velocity input model (D–VIM) is adopted. Analytical expressions of structural matrices are presented for a shear-type model of a BI structure, and a numerical investigation is conducted to demonstrate the feasibility and effectiveness of the proposed methods. The results show that the proposed method (RCHM-RSM) has the advantages of simple calculations and high accuracy. The numerical results obtained also confirm that the direct use of the damping matrix of superstructures for the BI structure will underestimate the superstructure response, while the displacement input model (DIM) overestimates the deformation of the isolation layer and underestimates superstructure responses, the analysis results by using D–VIM are consistent with the acceleration input model (AIM), so the D–VIM should be used instead of the DIM.

Velocity-tuning of somatosensory EEG predicts the pleasantness of gentle caress

Numerous studies have established an inverted u-shaped effect between the velocity of a caress and its pleasantness and linked this effect to the C-tactile (CT) system considered central for physical and mental health. This study probed whether cortical somatosensory representations predict and explain the inverted u-shaped effect and addressed associated individual differences. Study participants (N = 90) rated the pleasantness of stroking at varying velocities while their electroencephalogram was being recorded. An analysis across all participants replicated a preference for intermediate velocities, while a cluster analysis discriminated individuals who preferred slow (N = 43) from those who preferred fast stroking (N = 47). In both groups, intermediate velocities maximized amplitudes of a somatosensory event-related potential referred to as sN400, in line with the average rating effect. By contrast, group differences emerged in how velocity modulated a late positive potential (LPP) and Rolandic power. Notably, both the sN400 and the velocity-tuning of LPP and Rolandic power predicted the participants’ pleasantness ratings. Participants were more likely to prefer slow over fast stroking the better their LPP and Rolandic power differentiated between different velocities. Together, these results shed light on the complexity of tactile affect. They corroborate an average preference for intermediate velocities that relates to largely shared effects of CT-targeted touch on the activity of somatosensory cortex. Additionally, they identify individual differences as a function of how accurately somatosensory cortex represents the velocity of peripheral input and suggest these differences are relevant for the extent to which individuals pursue beneficial, CT-targeted touch.

Thermal performance analysis of a double pipe heat exchanger using biosynthesised silicon carbide and carbon nanotubes

ABSTRACT A nanofluid is a solution of nanoparticles with diameters fewer than 100 nanometers suspended in a base fluid such as water, ethylene glycol, or oil. In the nanofluid, these nanoparticles are suspended. The goal of this research is to look at the functioning of a twin-pipe heat exchanger that uses counter flow arrangements and two different nanofluids as cooling fluids. Alkaline water is a basic fluid made up of silicon carbide (SiC) and carbon nanotubes (CNT). The goal of this research was to see how different compositions of SiC and CNT nanoparticles dispersed in water affected the heat transfer capacities of a twin pipe heat exchanger developed with a counterflow arrangement. The flow rate of the nanofluid and the particle volume concentration of alkaline water were (0.02) and (0.04), respectively. Fluids with constant intake temperatures of 60°C for water and 30°C for nanofluid flow at the same input velocity via a heat exchanger. Both fluids are traveling at the same rate. According to the findings, nanofluid absorbs more heat than water at a range of flow speeds. Because of the improved thermal properties of nanoscale fluids, this results in increased thermal efficiency in heat exchangers.

Tri-Projection Neural Network for Redundant Manipulators

Resolving redundancy for manipulators subject to various limits is significant in robotics. The problem is often handled by an optimization formulation with joint velocity being the decision variable, for which how to address the joint acceleration constraint is challenging. Motivated by this problem, a dynamic neural network with triple projections, called tri-projection neural network (TPNN), is developed for quadratic programs with a constraint on the state evolution of the neuron states. The proposed TPNN is applied to resolving redundancy of an ABB IRB 140 industrial manipulator with velocity inputs subject to joint acceleration constraints. Simulation comparisons with an existing method demonstrate the superiority of the developed TPNN in fully employing the acceleration capability of the manipulator.

3D hybrid formation control of an underwater robot swarm: Switching topologies, unmeasurable velocities, and system constraints

This paper addresses formation control of underactuated autonomous underwater vehicles in three-dimensional space, using a hybrid protocol that combines aspects of centralized and decentralized control with constraints that are particular to underwater vehicles, including switching topologies, unmeasurable velocities, and system constraints. Using a distributed leader–follower model, the hybrid formation protocol does not require velocity sensing, access to global information, or static and connected topologies. To handle switching jointly connected networks—that is, to tolerate temporary disconnections—a distributed observer is designed for followers to cooperatively estimate leader states using local measurements and local interactions. On this basis, a compound formation control strategy is proposed to achieve geometric convergence. Firstly, cascaded extended state observers are developed to recover the unmeasurable velocities and unknown dynamic uncertainties induced by internal model uncertainty and external disturbances. Secondly, an improved three-dimensional line-of-sight guidance law at the kinematic level is used to address the underactuated configuration and the nonzero attack and sideslip angles. Thirdly, to overcome potential instability as a result of system constraints, including velocity constraints and input saturations, two adaptive compensators in the dynamic controller are used to address the negative effects of truncation. Using the proposed approach, the estimation errors and formation tracking errors are proved to be uniformly and ultimately bounded. Additionally, the numerical simulation results verify the performance of the approach and demonstrate improvement over both distributed and centralized state-of-the-art approaches.

Performance Improvement of a Vehicle Equipped with Active Aerodynamic Surfaces Using Anti-Jerk Preview Control Strategy.

This paper presents a formulation of a preview optimal control strategy for a half-car model equipped with active aerodynamic surfaces. The designed control strategy consists of two parts: a feed-forward controller to deal with the future road disturbances and a feedback controller to deal with tracking error. An anti-jerk functionality is employed in the design of preview control strategy that can reliably reduce the jerk of control inputs to improve the performance of active aerodynamic surfaces and reduce vehicle body jerk to enhance the ride comfort without degrading road holding capability. The proposed control scheme determines proactive control action against oncoming potential road disturbances to mitigate the effect of deterministically known road disturbances. The performance of proposed anti-jerk optimal control strategy is compared with that of optimal control without considering jerk. Simulation results considering frequency and time domain characteristics are carried out using MATLAB to demonstrate the effectiveness of the proposed scheme. The frequency domain characteristics are discussed only for the roll inputs, while time domain characteristics are discussed for the corresponding ground velocity inputs of bump and asphalt road, respectively. The results show that using anti-jerk optimal preview control strategy improves the performance of vehicle dynamics by reducing jerk of aerodynamic surfaces and vehicle body jerk simultaneously.

Finite strain-based theory for the superharmonic and subharmonic resonance of beams resting on a nonlinear viscoelastic foundation in thermal conditions, and subjected to a moving mass loading

We address the nonlinear free vibration, superharmonic and subharmonic resonance response of homogeneous Euler–Bernoulli beams resting on nonlinear viscoelastic foundations, under a moving mass and an abrupt uniform temperature rise. The nonlinear differential equation of motion stemming from the Hamiltonian principle and Finite Strain Theory is discretized according to a Galerkin decomposition method, and is solved by means of a multiple time scale method. A comparison between the Finite Strain theory and the Von-Karman approach is discussed, accounting for the effect of temperature rise, linear and nonlinear coefficients of the elastic foundation on the nonlinear vibration history and phase trajectory. At the same time, we check for the sensitivity of the frequency response of the system in superharmonic and subharmonic resonance for different input parameters, namely, location, velocity, and magnitude of the moving load, temperature rise and elastic foundation.

Study on vapour dispersion and explosion from compressed hydrogen spill: Risk assessment on a hydrogen plant

Hydrogen produced from renewable resources is one of the cleanest fuels and could be used to store intermittent solar, wind and other energies. The main concern about using hydrogen is its hazards, such as high storage pressure, wide-range flammability, low mass density, and high diffusion. This study investigated the hazards of compressed hydrogen storage by developing a CFD model to understand the gas dispersion behaviour. The model was validated using the past experimental data and showed a good agreement, which could demonstrate the diffusion characteristics and gas stratification of a buoyant gas. A case study of an accidental release of compressed hydrogen from a storage tank was investigated to evaluate the risk of a hydrogen plant. A mathematical model of the jet spill was used to account for the choking effect from a high-pressure release to ensure the input velocity in CFD simulation is suitable for modelling gas dispersion using verified spatial and temporal scales, then the simulation results were used as inputs of vapour cloud explosions (VCEs) to investigate the potential overpressure effect. It was found the CFD model could predict a more reasonable flammable gas amount in cloud than using the bulk hydrogen release rate. The safety distance based on the overpressure prediction was reduced by 35%. The method proposed in this study can provide more validity for the consequence analysis as part of risk assessment.

Multiple bumps can enhance robustness to noise in continuous attractor networks.

A central function of continuous attractor networks is encoding coordinates and accurately updating their values through path integration. To do so, these networks produce localized bumps of activity that move coherently in response to velocity inputs. In the brain, continuous attractors are believed to underlie grid cells and head direction cells, which maintain periodic representations of position and orientation, respectively. These representations can be achieved with any number of activity bumps, and the consequences of having more or fewer bumps are unclear. We address this knowledge gap by constructing 1D ring attractor networks with different bump numbers and characterizing their responses to three types of noise: fluctuating inputs, spiking noise, and deviations in connectivity away from ideal attractor configurations. Across all three types, networks with more bumps experience less noise-driven deviations in bump motion. This translates to more robust encodings of linear coordinates, like position, assuming that each neuron represents a fixed length no matter the bump number. Alternatively, we consider encoding a circular coordinate, like orientation, such that the network distance between adjacent bumps always maps onto 360 degrees. Under this mapping, bump number does not significantly affect the amount of error in the coordinate readout. Our simulation results are intuitively explained and quantitatively matched by a unified theory for path integration and noise in multi-bump networks. Thus, to suppress the effects of biologically relevant noise, continuous attractor networks can employ more bumps when encoding linear coordinates; this advantage disappears when encoding circular coordinates. Our findings provide motivation for multiple bumps in the mammalian grid network.

Prescribed Performance Attitude Stabilization of a Rigid Body Under Physical Limitations

This article investigates the prescribed performance control problem associated with attitude stabilization of a rigid body, considering angular velocity constraint, actuator faults, and input saturation. The desired performance specifications in transient and steady-state phases including convergence speed, overshoot, and steady-state value for attitude variable are also provided. To this end, the prescribed performance control methodology is combined with backstepping-based barrier Lyapunov function so as to develop a controller with simple structure compared to the existing constrained controls. The main idea behind the control design is to remove partial differential and complex function terms to considerably decrease complexity of the proposed controller. Moreover, a hyperbolic tangent function and an auxiliary system are employed to develop the constrained virtual rotation velocity control and to consider input saturation. The simulation results carried out on a rigid spacecraft confirm efficiency and success of the proposed constrained attitude control method.

Influence of inlet turbulent condition on the formation mechanism of local scalar concentrations

AbstractIn the existing ventilation design, the ventilation rate is defined by the time‐averaged flow rate, and the fluctuating (turbulence) component is not typically considered. However, inlet turbulent conditions are also assumed to have some influence on the formation of contaminant distributions. Therefore, the influence of turbulent kinetic energy at the inlet boundary on scalar transportation in an indoor environment needs to be elucidated when discussing the ventilation rate setpoint via the supply inlet in terms of local contaminant concentration control. This study discusses the impact of turbulent kinetic energy in the ventilation design on scalar transfer and its distribution within an enclosed space. To understand the influence of various inlet turbulent boundary conditions on scalar transfer, a computational fluid dynamics analysis was conducted using two different room models: a simple room and a room with a ventilation system that creates a large velocity gradient. The results indicate that scalar transfer within the room is not solely dominated by the averaged velocity input at the inlet boundary but is also strongly affected by the turbulence conditions at the inlet boundary. The numerical results indicate the possibility of a new ventilation design strategy that simultaneously considers the transfer of turbulent components and contaminants.

Estimating the Average River Cross‐Section Velocity by Observing Only One Surface Velocity Value and Calibrating the Entropic Parameter

AbstractThe current research aims to predict the velocity distribution and discharge rates in rivers based on the entropy concept using only one surface velocity measurement. In this direction, first, the uncrewed aerial vehicle (UAV)‐based image acquisition technique was applied to collect the surface velocity distribution along two European rivers, the Sajó, and the Freiberger Mulde Rivers. Seven cross sections were chosen for the analysis. At each cross section, first, the entropic parameter Φ(M) was calibrated based on the maximum and mean velocity magnitudes, derived from Acoustic Doppler Current Profilers, respectively, showing a trend for all cross sections with a range of 0.6 < Φ(M) < 0.75. Next, the maximum surface velocity provided by the UAV was implemented as a single velocity input. Finally, the bathymetry data, herein collected by UAV, were considered as the input for the entropy approach. In this way, the entropy iterative method allowed estimating the mean flow velocity by identifying the location (dip) of maximum velocities across the river site and inferring the 2D velocity distribution. The results highlighted that the entropy approach can accurately predict the velocity distribution and discharge rates with a percentage error lower than 13%.

Observational constraints on the sensitivity of two calving glaciers to external forcings

AbstractFuture mass loss projections of the Greenland ice sheet require understanding of the processes at a glacier terminus, especially of iceberg calving. We present detailed and high-rate terrestrial radar interferometer observations of Eqip Sermia and Bowdoin Glacier, two outlet glaciers in Greenland with comparable dimensions and investigate iceberg calving, surface elevation, velocity, strain rates and their links to air temperature, tides and topography. The results reveal that the two glaciers exhibit very different flow and calving behaviour on different timescales. Ice flow driven by a steep surface slope with several topographic steps leads to high velocities, areas of extension and intense crevassing, which triggers frequent but small calving events independent of local velocity gradients. In contrast, ice flow under smooth surface slopes leaves the ice relatively intact, such that sporadic large-scale calving events dominate, which initiate in areas with high shearing. Flow acceleration caused by enhanced meltwater input and tidal velocity variations were observed for terminus sections close to floatation. Firmly grounded terminus sections showed no tidal signal and a weak short-term reaction to air temperature. These results demonstrate reaction timescales to external forcings from hours to months, which are, however, strongly dependent on local terminus geometry.

Estimation of the Induced Incidence of a High Reaction Axial Turbine Bucket

This paper describes the effect of the incidence angle of the bucket on the performance of the axial turbine stage. The off-design operating conditions of the turbine stage result in a change in the velocity diagrams. This results in a positive or negative incidence. One of the basic objectives in turbine stage design is to estimate the flow behaviour of the turbine stage during off-design operation as accurately as possible and to quantify the corresponding decrease in efficiency. The available loss prediction models allow the estimation of the loss distribution when the incidence angle changes in the preliminary design phase. However, the incidence angle is actually affected by the velocity of circulation, which changes the input velocity vector (induced incidence). Thus, the blade row angle of attack is different from the angle based on the velocity diagram calculations. The result of our paper is a relation for estimating the angular difference of the input flow angle to the bucket defined as a function of the turbine operation mode.