Optimal Velocity Research Articles

Numerical investigation of bed-to-tube heat transfer in a shallow fluidized bed containing mixed-size particles

Mixed-size particles with low processing cost have great potential to act as the absorbing media in the next-generation concentrated solar power plants. However, the research on the heat transfer from the particles to heated surfaces in gas–solid fluidized beds is limited. In this paper, the bed-to-tube heat transfer coefficient (HTC) in a shallow fluidized bed with immersed tubes is determined numerically. The Eulerian–Eulerian approach that incorporated the kinetic theory of granular flow has been implemented in a two-dimensional model. The distribution of the local HTC around the tube is investigated for various particle systems. The results show that the HTC reaches a maximum at the upper right (45°) and upper left (135°) of the tube, respectively, indicating a strong relation between the local HTC and solid volume fraction (SVF). The average HTC increases as the mean particle size gets smaller. For monosized particles, the HTC increases from 925 W/(m2·K) to 3033 W/(m2·K) as the particle size decreases from 300 to 100 µm. For binary particles, the growth in the HTC is nonlinear, with an increase in growth rate being observed as the small-size component becomes dominant. For mixed-size particles with the same mean size, a higher HTC can be achieved by enlarging the size difference between the components. A modified correlation for predicting the bed-to-tube HTC is established. Besides, the impacts of gas velocity and temperature, and heat radiation on the bed-to-tube HTC are discussed. It is found that an optimal gas velocity exists to maximize the average HTC and SVF simultaneously, while the gas temperature has a minor contribution. Due to the small heat transfer temperature difference, the effect of thermal radiation on the HTC can be neglected even though the bed temperature reaches 800 °C.

Experimentation and Mathematical Modelling of Process Parameters for Prevention of Infectious Disease Caused by Staphylococcus aureus Bacteria in Indoor Environment.

Performance optimization using process parameters of an indoor air filtration system is a requirement that has to be established through experimental and analytical means for increasing machine efficacy. A closed casing containing a motor-driven blower is placed in a glass-encapsulated control volume. Air flows axially through an inlet filter and is thrown radially by the blower. In the radial path, air is treated with free radicals from the UVC-irradiated nano-TiO2 coated in the inner wall of casing. A known quantity of Staphylococcus aureus bacteria is populated (Courtesy: EFRAC Laboratories) in the glass-encapsulated control volume. The bacterial colony count is measured at different time intervals after the machine is switched on. Machine learning approaches are applied to develop a hypothesis space and the hypothesis based on best R2 score is used as a fitness function in genetic algorithm to find the optimal values of input parameters. The present research aims to determine the optimum time for which the setup is operated, the optimum air flow velocity in the chamber, the optimum setup-chamber-turning-radius affecting the air flow chaos, and the optimum UVC tube wattage, which when maintained yields the maximum reduction in bacterial colony count. The optimal values of the process parameters were obtained from genetic algorithm using the hypothesis obtained from multivariate polynomial regression. A reduction of 91.41% in bacterial colony count was observed in the confirmation run upon running the air filter in the optimal condition.

FREE-RDW: A Multi-user Redirected Walking Method for Supporting Non-forward Steps.

Multi-user redirected walking (RDW) is widely used in large-scale virtual scenes because it allows more users to move synchronously in both virtual and physical environments. To ensure the freedom of virtual roaming, which can be used in various situations, some redirected algorithms have been dedicated to non-forward movements, such as vertical movement and jumping. However, the existing RDW methods still mainly focus on forward steps, ignoring sideward and backward steps, which are also common and necessary in virtual reality. RDW algorithms for non-forward steps can enrich the movement direction of users' virtual roaming and improve the realism of VR roaming. In addition, the non-forward motions have a larger curvature gain, which can be used to better reduce resets in RDW. Therefore, this paper presents a new method of multi-user redirected walking for supporting non-forward steps (FREE-RDW), which adds the options of sideward and backward steps to extend the VR locomotion. Our method adopts a user collision avoidance strategy based on optimal reciprocal collision avoidance (ORCA) and optimizes it into a linear programming problem to obtain the optimal velocity for users. Furthermore, our method uses APF to expose the user to repulsive forces from other users and walls, thus further reducing potential collisions and improving the utilization of physical space. The experiments show that our method performs well in virtual scenes with forward and non-forward steps. In addition, our method can significantly reduce the number of resets compared with reactive RDW algorithms such as DDB-RDW and APF-RDW in multi-user forward-step virtual scenes.

Air-traffic controller and autopilot joint control of aircraft as mixed integer quadratic problem

One of the traditional problems in air-traffic management is optimal safe scheduling aircraft at a point of air-routes join. However, this problem implies another one, namely, the problem of guiding the aircraft to the prescribed point of its route at the necessary instant. The latter problem is studied much less attentively. Change of the arrival instant can be provided by alternating the aircraft motion trajectory on the basis of near-airport air-routes scheme or by alternating its velocity. Such a control can be worked out as automatically by the aircraft autopilot as manually by an air-traffic controller. But it can be difficult to an air-traffic controller to construct such a control especially during rush hours in loaded airports. In this paper, the authors suggest an optimizational formalization of the problem of automatic directions generation for such a guiding. The criterion to be minimized in this formalization is the number of controller-pilot interactions, because each such an interaction is a long, difficult process liable to linguistic, technical, psychological, and other errors. Since the criterion and other processes are of discrete kind, the formalization is done in the framework of mixed integer quadratic programming. The obtained problems are solved numerically by means of MIQP-solver provided by the Gurobi library. Each subproblem is solved quite fast within 0.1-0.5 seconds. So, solution of the entire problem (which includes enumeration of trajectories and choice of the optimal velocity regime for each of them) takes one-two seconds. Thus, the problem for the entire group of aircraft can be solved during a time acceptable for a real time application.

Study on early seal failure of CO2-injected packer based on orthogonal experimental method

Early seal failure occurs frequently in the of CO2 injection well packer, which is mainly manifested as failure of packer rubber, which seriously affects the normal production of gas well. Aiming at the packer rubber of CO2 injection well, three factors affecting the seal failure of packer rubber were selected, namely temperature, pressure and decompression velocity and the sensitivity of each factor was analyzed by orthogonal experimental design. The results show that the mechanical properties of rubber decrease gradually with the increase of temperature, pressure, and decompression velocity. With the increase of the decompression velocity, the surface of the rubber gradually formed small bubbles, large bubbles and even bubble cracking phenomenon, rubber sealing performance parameters are significantly worse; the main cause of early packer seal failure is the gas injection well was suddenly released, and the gas that could not exude in the rubber in a short time expanded and formed bubbles or even burst under the action of the pressure difference between inside and outside. The optimal decompression velocity is obtained to keep the packer rubber seal well in the downhole corrosion environment, which provides a basis for the determination of the construction parameters of CO2 injection well.

Modelling of two-lane car-following behaviour considering driver’s visual effect

In this paper, a novel two-lane car-following model considering driver’s visual effect is proposed. Changes in driver behaviour are directly stimulated from visual information and an improved time-to-collision (TTC) calculation is presented. Using TTC, stimuli are formulated for describing the influence of leading vehicles. Besides, the model is established based on the optimal velocity model framework. The stability of the proposed model is discussed by theoretical analysis and numerical simulation. Moreover, the influences of parameters and the comparison between models are investigated by simulations, which show that the proposed model can effectively describe the influences. Finally, the model is calibrated and verified by NGSIM trajectory data, which shows that the proposed model fitting effect can be improved by 7.78%, 44.96%, and 32.07% respectively compared with other three models. This study may provide a basis for the design of control strategies for future intelligent connected vehicles in multi-lane environments.

Analysis of the Sludge Settling Behavior of the Kibendera Waste Stabilization Ponds in Ruiru, Kenya

Waste Stabilization Ponds (WSP) provide both cost-effective and high-performance wastewater treatment benefits in the tropical regions. The 3-month sludge settling behavior in the Kibendera WSP in Ruiru, Kenya, was studied between July and September 2022. The study aimed at determining the sludge volume index (SVI) and hindered settling velocity during the dry weather flow regime. Based on these experimental data, Vesilind Model was used to characterize the settling behavior in the anaerobic and primary facultative ponds. Whereas Standard Methods for the examination of water and wastewater were used to determine the total suspended solids (TSS) concentrations in the ponds, batch column settling tests were used to generate the batch settling curves for each pond. Generally, good settling behavior characterized by SVI values of less than 150 mL/g was observed during the study period. Highest settling velocities of 1.16 m/hr and 1.22 m/hr were recorded in the anaerobic and primary facultative ponds respectively for TSS concentrations of 0.6 g/L and 0.416 g/L. Optimal maximum velocity (<i>V_max</i>) values of 3.42 m/hr and 1.78 m/hr were observed in the anaerobic and primary facultative ponds respectively. The corresponding optimal model parameters (n) describing the measured data accurately were 0.47 L/g and 0.51 L/g respectively. The model parameters so obtained may be useful in characterizing the sedimentation behavior in the WSP during the dry weather flow regimes.

Approaching and pointing tracking control for tumbling target under motion constraints

On-orbit servicing for the failed spacecraft involves two necessary stages: on-orbit observing and approaching. For these two stages, a novel approaching and pointing tracking control scheme under motion constraints and input saturation is proposed in this paper. For the security of approaching, a relative position guidance law for specific surface hovering is proposed. Then, a model predictive controller based on quadratic programming algorithm is designed. For the continuous observation task, the optimal maneuver angular velocity under the motion constraint is planned through model predictive control. In order to reduce the dimensionality of the optimization problem to reduce the computational effort, only the attitude kinematics equation is used as the process model. Thereafter, the adaptive anti-saturation attitude controller is designed to track the optimal maneuver angular velocity. The anti-saturation auxiliary system and the adaptive update law are used to cope with the control torque saturation and the integrated uncertainties, respectively. Finally, the stability of the closed-loop system is demonstrated by Lyapunov method. Simulation results demonstrate that the proposed control scheme accomplishes the approaching and pointing tracking task, and finally service spacecraft maintains hovering above the tumbling target and observing its specific surface.

Improving the energy efficiency of wind turbines for charging batteries

The article describes the method for determining the optimal angular velocity and the number of turns of the generator winding on permanent magnets powered by a wind turbine operating in specific operating conditions according to the wind speed regime. The optimization criterion is the maximum potential of energy that can be used to charge the battery. The permissible power of the generator and wind turbine, current and battery charging voltage are accepted as limiting factors. The restriction is provided by connecting a ballast resistor to the generator output. The power developed by the turbine is determined taking into account the wind energy utilization factor, which depends on the angular velocity of its shaft and wind speed. Two variants of power limitation are compared: by limiting the angular velocity by aerodynamic means and by stopping the wind turbine. The return of energy to charging in both cases is determined taking into account the distribution of wind speeds, obeying the Weibull probability distribution law. As an example, the calculation of the possible annual power generation for charging a battery with a capacity of 200 A∙h with a voltage of 24 volts from a synchron generator with a number of poles of 48 driven by a wind turbine with a radius of 2 meters, operating in an area with an average wind speed of 5 m/s. The calculation shows that for the parameters and operating conditions of the electrical installation used in the example, the maximum annual energy output (3.3 × 103 kWh) is observed at optimal 11 turns of the winding at each of the poles of the generator. The deviation of the number of turns from the optimal one in both directions by 2 times leads, with the same dimensions of the wind turbine, to a decrease in annual energy output by 3...5 times, which is a clear proof of the need to carry out such a calculation for each specific wind turbine.

Industrial wastewater treatment: Case study on copper removal from colloidal liquid using coagulation

In this study, two coagulants based on aluminum and ferric, as well as three poly-acrylamide flocculants with different charges were used to compare the intensity and how each parameter affects. Using the Plackett-Burman method, aluminum sulfate coagulant and anionic flocculant showed the greatest effect. Among the operational influencing factors, the speed of the mixer in the fast mode had the greatest effect. In the optimal conditions, the amount of coagulant (17.5 ppm), flocculant (1 ppm), and the speed of the mixer in fast mode (75 rpm) were reported, and the optimal sedimentation velocity was equal to 0.95 cm/min. The percentage of turbidity, total suspended solids, Total Dissolved Solid, Chemical Oxygen Demand, and Biological Oxygen Demand are respectively equal to 100 (with an approximation of 0.01), 100 (with an approximation of 0.01), 53, 92 and 86 % was obtained. All these results were obtained at a confidence level of 0.95 % with a confidence factor of 0.99 %, which means that the experimental data are in very good agreement with the modeling. In general, the combination of the screening method (Plackett-Burman) and response surface method (Box-Benkhen) is applicable to optimize the chemical coagulation process for the management and treatment of wastewater for reuse.

Association between coronary flow and aortic stenosis during transcatheter aortic valve implantation.

In patients with aortic stenosis (AS), the coronary flow reserve decreases even in the absence of epicardial coronary artery stenosis. Systolic coronary flow reversal (SFR) reflecting reduced coronary microcirculation, often seen in patients with severe AS, has a potential negative impact on the pathogenesis of cardiac dysfunction. However, there are limited data on the relationship between the severity of AS and SFR, as well as on the benefits of transcatheter aortic valve implantation (TAVI). The aim of this study was to evaluate the relationship between the severity of AS and efficacy of TAVI in improving SFR. Consecutive patients with AS who had undergone TAVI using transoesophageal echocardiography (TEE) from November 2020 to February 2022 were prospectively enrolled. Coronary flow in the left anterior descending artery as well as the aortic valve peak velocities, and the mean aortic valve pressure gradients (AVPGs), indicating the severity of AS, were measured using intraprocedural TEE before and after TAVI. The following parameters were measured as coronary flow: systolic and diastolic peak velocity (cm/s) and systolic and diastolic velocity-time integral (VTI) (cm). SFR was defined as the presence of a reversal coronary flow component in systole. The enrolled patients were classified into two groups according to the presence or absence of SFR before TAVI. A total of 25 patients were included: 13 had SFR and 12 who had no SFR, before TAVI. Patients with SFR had significantly higher aortic valve peak velocities (451.1±45.9 vs. 372.1±52.1cm/s; P<0.001) and mean AVPGs (49.2±14.5 vs. 30.3±11.6mmHg; P=0.002) than those without. The optimal binary cut-off aortic valve peak velocity values and the mean AVPG associated with the presence of SFR before TAVI were >410.0cm/s (specificity, 75.0%; sensitivity, 92.3%) and >37.4mmHg (specificity, 83.3%; sensitivity, 92.3%), respectively. After TAVI, SFR immediately disappeared in 11 of 13 patients with SFR (84.6%). Overall, the systolic coronary VTI significantly increased after TAVI (2.0±4.7 vs. 6.4±3.2cm, P<0.001), and this increase was greater in patients with SFR than in those without SFR before TAVI (interaction P=0.035). SFR was found to be associated with the severity of AS and with a greater increase in systolic coronary flow immediately after TAVI.

Dissociative photoionisation of O2 with tunable 10, 20 and 30 eV photons

Atomic oxygen ions, O+, created by photoexcitation of a cold supersonic beam of O2 by the output of a free-electron laser operating in the 128–122 nm region are detected by sliced velocity map imaging. Analysis of the richly structured high resolution kinetic energy and angular distributions obtained show that O+ production is due to the second and third harmonics present in the laser output. Excellent slicing and optimal velocity mapping allows separation of overlapping signal from dissociative photoionisation processes driven by 20 eV versus 30 eV photons. A two-colour experiment combining the free electron laser and a nanosecond dye laser output at 225.6 nm allowed detection of direct photodissociation of the metastable O2 + b 4Σg - (v = 0–4) state is observed and assigned to a parallel b 4Σg - – (c 4Σu -)4s Rydberg transition followed by dissociation to O+ (4S) + O(3P2).

Smith–Purcell Radiation from Highly Mobile Carriers in 2D Quantum Materials

AbstractTerahertz (THz) radiation has broad applications ranging from medical imaging to spectroscopy. One viable source of high‐intensity THz radiation is the Smith–Purcell (SP) effect, which involves charge carriers moving over a periodic surface. Conventional SP emitters use electron beams to generate charge carriers, necessitating bulky electron acceleration stages. Here, a compact design for generating THz SP radiation using mobile charge carriers within 2D materials is proposed. This circumvents the beam alignment and beam divergence challenge, allowing for a reduction in the electron‐grating separation from tens of nm to 5 nm or less, leading to more efficient near‐field excitation and a potentially chip‐level THz source. In such a configuration, it is shown that the optimal electron velocity and the corresponding maximum radiation intensity can be predicted from the electron‐grating separation. The numerical demonstration shows that hot electrons can excite SP radiation in graphene on a silicon grating, and the radiation intensity can be increased by graphene surface plasmons. This study can be extended to a broad variety of charge carriers in 2D materials, thus allowing for compact, tunable, and low‐cost THz sources.

Numerical study of microjet and heat flux effects on flow separation and heat transfer over a ramp

The control of flow and heat transfer has recently been of great interest to engineering researchers in light of computational technology advances. Microjets are used as control solutions to avoid flow separation and increase heat transfer. The present study evaluates a microjet over a ramp at microjet velocity ratios (jet to inflow velocity) of V jet / U 0 = 1, 2, and 4 and heat flux ratios (heat flux to based heat flux) of q s / q 0 = 1, 2, and 3 to examine the flow separation area and heat transfer improvement numerically. The numerical velocity and temperature gradients were compared to earlier numerical and experimental works. Then, the flow over the ramp was analyzed at the aforementioned microjet velocity and heat flux ratios. Moreover, streamlines, bed pressure, fluid temperature, and bed Nusselt number were evaluated. It was found that a microjet with the optimal velocity could not only diminish the separation bubble but also improve heat transfer. A rise in the velocity ratio from 2 to 4 led to a nearly 33% decrease in the separation bubble and an approximately 20% rise in the Nusselt number. In addition, the microjets enhanced heat transfer by up to 50%.

A Punishment Mechanism-Combined Recurrent Neural Network to Solve Motion-Planning Problem of Redundant Robot Manipulators.

In order to make redundant robot manipulators (RRMs) track the complex time-varying trajectory, the motion-planning problem of RRMs can be converted into a constrained time-varying quadratic programming (TVQP) problem. By using a new punishment mechanism-combined recurrent neural network (PMRNN) proposed in this article with reference to the varying-gain neural-dynamic design (VG-NDD) formula, the TVQP problem-based motion-planning scheme can be solved and the optimal angles and velocities of joints of RRMs can also be obtained in the working space. Then, the convergence performance of the PMRNN model in solving the TVQP problem is analyzed theoretically in detail. This novel method has been substantiated to have a faster calculation speed and better accuracy than the traditional method. In addition, the PMRNN model has also been successfully applied to an actual RRM to complete an end-effector trajectory tracking task.

Defrosting Characteristics of the Cockpit Windshield of Manned Airships

Frost covering of the cockpit windshield will seriously obstruct the driver’s vision and even affect flight safety of the low-altitude manned airship. To solve the problem, this paper proposes a rapid defrosting strategy using hot gas injection method. The influences of the air inlet type, air temperature, air velocity and air angle on the defrosting characteristics of the transparent windshield are investigated and the defrost characteristics of the manned airship are obtained by fluid dynamics simulation. The result shows: (1) Defrosting effect of single inlet is not as good as double inlets. The defrosting area of the double inlet is relatively large, mainly concentrated at both ends of the windshield. (2) The effect of air supply temperature on defrosting effect of windshield surface is more significant when double air supply inlets are used. But when the air supply temperature reaches a certain value and continues to rise, the defrosting time does not change much, so there is an optimal air supply temperature range. (3) The higher the air supply velocity is, the shorter the phase transformation time of frost layer is and the faster the melting velocity is. Considering energy consumption and defrosting characteristics, the optimal air supply velocity is about 6 m/s. (4) When the angle between the air supply direction and the horizontal plane of the bridge near the windshield is 100°, the frost layer has the shortest melting time.

Mixed Combustion Characteristics of Various Biomass Particles

As a promising pollutant emission reduction technology, biomass mixed combustion has attracted widespread attention worldwide. This paper aimed to study the characteristics of biomass mixed combustion and temperature distribution. A combination of simulation and experimental methods was adopted. The results showed when four kinds of biomass were burned separately, their highest temperatures in the center section of combustion chamber were corn stalk>cotton stalk>sawdust>rice straw in descending order. Compared with other three biomass, the highest temperature of corn stalk was more than 100 K higher, which mainly occurred during the full combustion stage, mainly because corn stalk had high volatile content and caught fire easily. In addition, with the optimal mixed combustion parameters, biomass mixed combustion improved the combustion characteristics of single biomass combustion. The optimal blending ratio of corn stalk to rice straw was 7:3, and the optimal primary air velocity and temperature were 48 m/s and 1300 K, respectively. With the optimal blending ratio, the maximum temperature in the center section was higher than that of single biomass combustion, with advanced ignition point, relatively uniform temperature distribution in the combustion chamber and good combustion performance, because the precipitation and combustion of high volatile components during mixed combustion caused the surface temperature of fixed carbon to rise rapidly to reach the ignition temperature. Finally, this paper studied the combustion characteristics of corn stalk and rice straw with the optimal mixed combustion parameters in mixed combustion experiment, and verified the good consistency between the simulation and experimental values. Therefore, biomass mixed combustion technology provides an important reference for solving the problem of low calorific value of single biomass combustion.

Bifurcation analysis and control strategy for a car-following model considering jerk behavior

To further improve the adaptability of the optimal velocity model (OVM) in the actual traffic flow, this paper proposes a car-following model that considers both the jerk effect and time-delayed feedback control. To study the dynamic behavior of this model, the following analysis is carried out: A stability conditions and equilibrium points controlling OVM are obtained by stability analysis and Hopf bifurcation analysis; Using the intuitive and accurate definite integral stabilization method (DIS), by calculating the number of all unstable eigenvalues of the characteristic equation, we obtain a stable time-delayed interval, and a time-delayed feedback controller is designed to stabilize the traffic system. The results show that the time-delayed feedback controller expands stable time-delayed interval, suppresses the influence of unstable factors on the traffic system, and improves stability of vehicle traffic; Numerical simulations agree with the theoretical results, indicating that the time-delayed feedback controller can effectively suppress traffic congestion and control the managed traffic.

Active Debris Removal Mission Planning Method Based on Machine Learning

To prevent the proliferation of space debris and stabilize the space environment, active debris removal (ADR) has increasingly gained public concern. Considering the complexity of space operations and the viability of ADR missions, it would be necessary to schedule the ADR process in order to remove as much debris as possible. This paper presents an active debris removal mission planning problem, devoted to generate an optimal debris removal plan to guide the mission process. According to the problem characteristics, a two-layer time-dependent traveling salesman problem(TSP) mathematical model is established, involving the debris removal sequence planning and the transfer trajectory planning. Subsequently, two main novel methods based on machine learning are proposed for the ADR mission planning problem, including a deep neural networks(DNN)-based estimation method for approximating the optimal velocity increments of perturbed multiple-impulse rendezvous and an reinforcement learning(RL)-based method for optimizing the sequence of debris removal and rendezvous time. Experimental results of different simulation scenarios have verified the effectiveness and superiority of the proposed method, indicating the good performance for solving the active debris removal mission planning problem.

Outflow geometry for electrochemical desalination cells

Electrochemical desalination approaches continue to gain in application. Here, we introduce an electrochemical desalination system utilizing a novel flow geometry with symmetric, porous Ag/AgCl electrodes. The system takes advantage of advection to continuously deliver input solution to the surface of the electrodes and reduce depletion that limits throughput and energy efficiency of many desalination systems. We explore the system behavior using steady-state analytical and transient numerical models along with experimental characterization of a small (1 cm2 active area) cell. Desalination performance is explored in terms of degree of separation, throughput, charge efficiency, and energy usage. Optimal flowrate corresponding to minimum energy per mole of salt removed is found based on steady state models when advective separation and system resistive loss is balanced. As an example, for idealized flow, with 65% removal and 50% recovery from a 50 mM NaCl solution, system energy usage at optimum velocity is predicted to be 16.5x the thermodynamic minimum. A gradual tradeoff between energy efficiency and cell throughput exists, potentially allowing vastly higher superficial velocities (e.g., > 0.1 mm/s) and more compact systems than comparable techniques such as reverse osmosis. At example experimental operating conditions, the test cell provides 83% removal of NaCl from a 50 mM input solution at 0.32 V cell voltage with 50% recovery.