Deceleration Process Research Articles

Acceleration of hollow carbon nanospheres by gas leakage: An efficient nanomotor

Nanomotors serve as nanoscale engines by converting various energies into mechanical energy. In addition to the huge number of existing nanomotors, we propose a simple nanomotor based on the hollow carbon nanosphere (i.e., fullerene) that is full of gas. We investigate the acceleration of the nanosphere by leakage of gas through a nanopore by molecular dynamics simulations. The nanosphere can be driven to a high speed of 100 m/s under proper simulation conditions, which can be further tuned by temperature, gas density, and pore diameter. We observe rotation of the pore direction during the acceleration process for a nanosphere of different pore diameters. The acceleration process can be well described by the Meshchersky theory. We also simulate the deceleration process of the nanosphere due to the damping force of the gas, which can be analyzed in terms of the kinetic motion of gas molecules. The nanomotor proposed in this work shall be realizable in experiments and may be useful in driving the mechanic motion of fullerenes.

A Car-Following Model considering the Effect of Following Vehicles under the Framework of Physics-Informed Deep Learning

Car-following models have been studied for a long time, and many traffic engineers and researchers have devoted attention to them. With the increase in machine learning, this paper proposes a fusion model based on the physics-informed deep learning framework. The purpose of this paper is to inherit the predecessors’ ideas, transform them to fit a new framework, and improve the framework’s accuracy. The IDM-D (intelligent driver model development) involves reenabling the effect of the following vehicle to form a complementary model (not car-following model) with the IDM (intelligent driver model). The pretreated NGSIM data are used for calibration and validation. The IDM and the IDM-D are combined with the LSTM under the framework of physics-informed deep learning, and the results are mixed in a ratio to form the final result. Using test data for simulation, the results reveal that the IDM-informed LSTM shows better performance than the LSTM and that the fusion model further improves the MSE (mean square error) of the IDM-informed LSTM. The fusion increases the accuracy during the deceleration process, which is better than just a single IDM-informed LSTM. The fusion model further explains drivers’ deceleration behaviors.

Analysis of the horizontal vibration response under gas–solid coupling throughout the entire high-speed elevator operating process

High-speed elevator cars affected by external excitations exhibit complex horizontal vibration responses during their entire operating processes. To accurately explore the horizontal vibration response of a car and the response differences between the operating processes, a gas–solid coupling model for the entire high-speed elevator operating process was developed based on the finite volume method, Lagrange’s theorem, and the external excitations obtained from dynamic mesh technology and the time-variant guideway excitation simulation method. The differences in the car’s horizontal vibration acceleration and the effect of the fluid load disturbance during different high-speed elevator operating processes were analyzed by considering the different operating characteristics of the car during its acceleration–uniform speed–deceleration process. The feasibility of the model and modeling method were verified by testing an actual 7 m/s high-speed elevator. The results showed that the horizontal vibration acceleration of the car reached its maximum value during the uniform speed process, and the shaft fluid pressure load had the most significant effect on the horizontal vibration response of the car during the deceleration process.

Thermal oscillation behavior profiling of supercritical methane in cooling rocket engines

Regenerative cooling is widely used in rocket engines as an efficient cooling method, and nowadays spacecraft shows faster flight speed and greater acceleration. Therefore, the fuel is subjected to large inertial force during flight acceleration or deceleration process. Hence, since it is novel, it is necessary to analyze the thermal performance with large acceleration. To reveal the effect of acceleration on the heat transfer of supercritical methane fuel in the cooling channel, the three-dimensional numerical simulation has been performed with structured mesh. Specifically, the effects of acceleration, mass flux, pressure and ratio of heat flux to mass flux on the flow and heat transfer in the cooling channel have been studied, and the buoyancy parameter (Bo*) and thermal acceleration factor (Kv) have been also employed to analyze the buoyancy effect and thermal acceleration. The results show that at the conditions of low supercritical pressure, low mass flux and large ratio of heat flux to mass flux, the buoyancy effect increases significantly when the acceleration increases from 0 g to 6 g. As a result, the heat transfer is deteriorated gradually, and the average heat transfer coefficient decreases from 3800 to 3000. On the other hand, when the acceleration and heat flux exceed a range, the unstable phenomenon of thermal oscillation will occur with the period of oscillation about 90 s. The thermophysical properties of the fluid near-wall will change rapidly when approaching the pseudo-critical region, which leads to the continuous change of the thickness of the viscous boundary layer.

Multibody dynamics characteristics analysis and safety design research of the Mars parachute descent process

<p indent="0mm">This paper focuses on solving the technical challenges brought by the multibody movement during the Mars parachute deceleration stage. First, the parachute system’s design scheme is introduced. The mechanism and main effects of the dynamic characteristics of the parachute deceleration process are analyzed using simulations and typical experiments. Then, the safety design schemes for parachutes, separation of heatshield, autonomous navigation, and attitude control are proposed. Finally, the in-flight results of Tianwen-1’s parachute descent process are introduced. This research can provide a meaningful reference for subsequent Mars landing missions.

Slowing Down Society? Theoretical Reflections on Social Deceleration in Pandemic Times (and Beyond)

Abstract The COVID-19 pandemic has caused a major change in everyday life and also reinvigorated the theoretical and political discussion on the temporal rhythms of social existence. Taking the situation of the coronavirus crisis as a starting point, the present paper attempts to provide the outlines of a theoretical account of social deceleration, a topic that has been hitherto barely explored in the field of social studies of time. In view of the complexity of the phenomenon, a distinction is made between two ways of theoretically approaching it, namely, a descriptive and a normative perspective. The paper proceeds in three steps: First, upon adopting a descriptive perspective, it advances a definition of social deceleration and proposes a typology of its different manifestations. The second step analyzes the coronavirus crisis as a process of partial deceleration of social life. The final step gives an overview of the current normative, i.e., ethical-political, disputes over social speed.

Aerogravity-assist capture into the three-body system: A preliminary design

Aero-gravity assist (AGA) is a low-cost maneuver for an interplanetary vehicle since it can potentially replace thrust with aerodynamic force to save fuel consumption. In this study, an AGA-maneuver capture scheme to deliver a vehicle into a three-body system is presented, and a successive approximation-based method is proposed to optimize atmospheric trajectories. Based on the analysis of the aerodynamic deceleration process, the AGA capture maneuver is first formulated as a coplanar atmospheric flight process with fixed time and strict endpoint-state constraints. Then, the lossless convexification and successive approximation techniques are applied to construct the solving process of iteratively optimizing the AGA trajectories. Finally, the relaxation strategy to the strict terminal state constraints and the heavily penalized-function method are developed to avoid the artificial infeasibility of the problem and improve the convergence. Numerical simulations, demonstrated by the AGA-capture into Sun-Mars L2 Halo orbits and Sun-Mars backward stable orbits, show the effectiveness and reliability of the proposed method. It is the first time that the AGA-maneuver is combined with the dynamic property of the three-body system, and the proposed method can potentially enrich the possibility of the low-energy interplanetary transfer.

A new type of aerodynamic measurement technology for vehicle model running on bridge under crosswind in wind tunnel test

The existing moving vehicle models generally require a long test-track to realize the acceleration and deceleration processes and the negative effect of data cables is inevitably for the wind pressure measurement using the traditional pressure scanning system. To address the technical obstacle for moving vehicle models in wind tunnel tests, a new type of aerodynamic measurement technology is presented in this study. Firstly, a piece of new kinetic equipment, a U-Shaped launching ramp, is proposed. The U-Shaped launching ramp can realize the acceleration and deceleration of the vehicle model by gravity and makes full use of the test section of the wind tunnel. Then, a wireless pressure acquisition system is developed to virtually eliminate the negative effects of the inertia and friction forces. By comparing with the conventional wind pressure test data, the proposed wireless pressure acquisition system presents a higher accuracy and fully satisfies the test requirement for the moving vehicle-bridge system. From the scaled test, it is confirmed that the aerodynamic forces of the moving vehicle model are larger than that of the static one, implying that the moving test is necessary for studying the aerodynamic characteristics of the vehicle-bridge coupling system.

Numerical Simulation of Internal Flow Characteristics and Pressure Fluctuation in Deceleration Process of Bulb Tubular Pump

In order to explore the change in internal and external characteristics and the pressure fluctuation of the large bulb tubular pump unit during deceleration, a transient and steady three-dimensional (3D) numerical simulation is executed, based on the standard k-ε turbulence model and the change in boundary conditions such as flow rate. Finally, the pressure fluctuation data are analyzed by the wavelet method. There is a good agreement between the experimental data and numerical simulation results. During the deceleration process of the unit, the head decreases linearly while the efficiency remains stable. Meanwhile, the shock phenomenon and hysteresis effect appear before and after the unit head deceleration. Although there are vortex and backflow in the outlet conduit during deceleration, the pressure distribution on the suction surface of the impeller blades changes uniformly and significantly. The pressure fluctuation changes on the inlet surface of the impeller are more obvious during the deceleration: the closer to the hub, the greater the pressure, and this change decreases with decreasing radius. The fluctuation energy is mainly concentrated in the high-frequency region of 100–120 Hz and decreases uniformly with the deceleration of the rotational speed. This paper provides a reference for the energy utilization and safe operation of the water pump unit in adjusting speeds with variable frequency.

Real-Time NURBS Interpolation under Multiple Constraints.

NURBS interpolation is superior to traditional linear or circular interpolation in terms of code size, surface quality, and machining efficiency. However, with the increasing demands for high-accuracy and efficient machining, NURBS interpolation has faced a growing number of challenges. Many researchers are actively involved in this field with great interest. Due to the special form of NURBS curve, there is a nonlinear relationship between its curve and arc length; feed fluctuations and mechanical shocks which are caused during the interpolation process will seriously affect the surface accuracy and quality of machined parts. To solve these problems, a real-time NURBS interpolation is proposed under multiple constraints (RNIC) in this paper. First, the formulas of the constrained feedrate under geometric errors, kinematic constraints, drive constraints, and contour errors are given. Then, the two stages for the proposed interpolation are established. The former stage is offline preprocessing stage, which aims to quickly find feedrate sensitive areas (FSAs), while the latter online stage is the real-time interpolation, which is responsible for smoothing the velocity. In the preprocessing stage, we utilized FSA scan module and feedrate adjustment module to detect the FSAs and adjust the feedrate at the start/end of each subsegment by a bidirectional scanning algorithm. Each segment contains acceleration and deceleration (some contains uniform speed) stages, which can be well matched with the processing process of acceleration and deceleration. Finally, according to the proposed method and the adaptive speed adjustment method, the simulation of a “butterfly-shaped” NURBS curve using the S-shaped ACC/DEC algorithm is carried out, which verifies the reliability and effectiveness of the proposed algorithm.

Dynamic deorbit of small-sized space debris in near-Earth orbit in view of space-based pulse laser

The objective of this work is to address active deorbit of small-sized space debris in the near-Earth orbit by a space-based pulse laser. A dynamic deorbit model based on perigee altitude was established during space-based laser pulse irradiating the debris. The effects of orbital eccentricity, perigee altitude, true anomaly, and action distance of the debris with the number of pulse lasers and laser powers were obtained. Furthermore, the whole deceleration process of the debris removal irradiated by a pulse laser was intuitively described, and the evolution rules of the debris movement in the whole stage of active deorbit were also demonstrated. As a result, the three-dimensional visualization scene of the debris movement and the complete period evolution images of the debris deorbit were displayed. Finally, the results of numerical computations were consistent with the outcomes of visual simulations based on the given conditions. That is, when the laser power was 500 kW and the number of pulses was 965, the purpose of debris deorbit was completed by four laser irradiations, and the semimajor axis and eccentricity of the debris reached were 9915.4 km and 0.338 at the moment. These results can provide an important reference for the integrated research on space-based pulse laser active removal and clearance evaluation of small-sized space debris.

Experimental investigations on coherent flow structures in acoustically excited swirling flames using temporally-separated dual-plane Stereo-PIV

A temporally-separated dual-plane stereoscopic particle image velocimetry (PIV) technique is utilized to investigate the dynamics of periodically-excited vortices in a swirling flame under four experimental conditions. The time-averaged results under the unexcited condition are analyzed to verify the accuracy of the method. For the excited conditions, Q criteria is used to extract and classify the vortex structures within the swirling flame. It is found that under different excitation frequencies of the same amplitude, the outer vortex rings (OVRs) and the inner vortex rings (IVRs) show opposite rotational characteristics. While the excitation frequency has little influence on the central vortices induced by the swirler, the amplitude does have a great influence on the development trajectory of the central vortices. Furthermore, the amplitude and phase of oscillation velocities in three directions are successfully decomposed by using sine curve fittings at each point. A periodic acceleration and deceleration process is observed only in the axial direction. Besides the acoustic wave, it is found that the vortex rings (both OVRs and IVRs) also contribute to the axial velocity oscillations.

Transient Controller Design Based on Reinforcement Learning for a Turbofan Engine with Actuator Dynamics

To solve the problem of transient control design with uncertainties and degradation in the life cycle, a design method for a turbofan engine’s transient controller based on reinforcement learning is proposed. The method adopts an actor–critic framework and deep deterministic policy gradient (DDPG) algorithm with the ability to train an agent with continuous action policy for the continuous and violent turbofan engine state change. Combined with a symmetrical acceleration and deceleration transient control plan, a reward function with the aim of servo tracking is proposed. Simulations under different conditions were carried out with a controller designed via the proposed method. The simulation results show that during the acceleration process of the engine from idle to an intermediate state, the controlled variables have no overshoot, and the settling time does not exceed 3.8 s. During the deceleration process of the engine from an intermediate state to idle, the corrected speed of high-pressure rotor has no overshoot, the corrected-speed overshoot of the low-pressure rotor does not exceed 1.5%, and the settling time does not exceed 3.3 s. A system with the designed transient controller can maintain the performance when uncertainties and degradation are considered.

The role of demographics and migration for the future of economic growth in China

China’s real GDP has been growing by almost 10 percent a year for the last three decades. For how long should we expect this spectacularly high growth to continue? We propose a quantitative two sector model with segmented labor markets and financial frictions to evaluate the prospects for China’s future growth under different policy scenarios. In our model the high growth rate observed in China since the early 1990s is fueled by the large increase in urban labor supply, because of rural–urban migration, and the emergence of private enterprises that absorb those migrant workers. Our simulations suggest that the rapid aging of its population and the decrease of rural migration should significantly decelerate urban labor force and economic growth starting around 2020. Through a counterfactual with a fixed age distribution, we find that population aging is responsible for the deceleration of economic growth between 2020 and 2040. We show that substantial relaxation of labor market segmentation and financial constraints faced by private enterprises could improve efficiency substantially and delay this process of growth deceleration by one decade.

PLL- and FLL-Based Speed Estimation Schemes for Speed-Sensorless Control of Induction Motor Drives: Review and New Attempts

Phase-locked loops (PLLs) and frequency-locked loops (FLLs) are of importance in power and energy applications. Both technologies have been introduced to speed-sensorless- controlled motor drives, and increasing applications of PLLs and FLLs for speed estimation are foreseen. To enable a proper and good design, a thorough review of the PLL- and FLL-based speed estimation schemes is then provided in this article. It is revealed through the review that many PLL- and FLL-based estimation schemes fail to accurately track a frequency ramp (i.e., obvious estimation errors appear), which may lead to a compromised estimation accuracy when these schemes that are applied in induction motor drives operating during acceleration and deceleration processes. To address this, the proven speed estimation schemes together with new attempts are also presented in this article. Moreover, various challenges to the PLL- and FLL-based speed estimation schemes, including harmonics, dc offsets, and parameter variations, are considered when evaluating these schemes. Solutions to tackle these disturbances are accordingly presented. In addition, two representative estimation schemes are exemplified through experimental tests. Finally, further challenges in using the PLL- and FLL-based schemes for speed estimation are discussed.

Research on the influence of length-width ratio on cruciform parachute airdropping performance

Different from the other design parameters in general drogues, there are few studies about the parameter of Length-Width Ratio (LWR). Therefore, the fluid structure coupling model based on the Finite Element Method was used to study the deceleration characteristics and terminal trajectory stability of parachute system in this work. And the graphic transformation technology commonly used in Computer Graphics was used to realize the following of flow field with the trajectory movement. In this work, the cruciform parachutes with different LWR were taken as the research objects, and the above method was used to obtain the trajectory curves, deceleration characteristic curves, and stability curves of the cruciform parachutes under different external conditions. It was found that the deceleration performance was negatively correlated with the LWR when the other design parameters and working conditions remained unchanged, and the trajectory stability and the stability of the parachute were positively correlated with the LWR. Subsequently, the cruciform parachute with the LWR of 4.5 was used for airdropping test, and the accuracy of numerical method used in this work was verified. Then the deceleration processes of cruciform parachute (LWR: 4.5) under different dropping conditions were calculated. It could be found that the external launching conditions had a limited impact on the deceleration performance. The LWR was another design parameter that had a greater impact on the deceleration performance after the parameter of canopy area. Finally, the drag coefficient correction equation representing the deceleration performance was proposed for the first time.

A probability model for predicting the slip velocity of large particles in vertical pipes

The existence of the slip velocity has strong influence on the conveying efficiency in the hydraulic transportation process of mineral nodules. In the present work, a probability model is proposed to predict the slip velocity of large particles in vertical pipes. First, the uniform linear motion of one single particle in a turbulent upward flow is described by energy transfer from vortexes to particles. Second, the interaction is analyzed between a group of particles and turbulent flow. Third, the probabilities of particle-particle collision and particle-vortex collision are calculated to obtain the corresponding deceleration and acceleration rates. When the motion of particles remains stable, the deceleration and acceleration processes reach a dynamic equilibrium. Finally, a balance equation is established to solve the slip velocity of large particles. The validation of the present model is then carried out by comparing the predicted slip velocity with experimental data and empirical models available in the literature, confirming the superior accuracy of the present model. To acquire further knowledge of the transportation, effects of six parameters of the model are investigated in detail, including the fluid flow rate, the particle diameter, the volume concentration, the pipe diameter, the particle density, and the fluid density

Friction dynamics of moisturized human skin under non-linear motion.

Evaluating friction in human skin is important to assess its condition and the effects of skincare cosmetics. In this study, we evaluated the friction dynamics of moisturized skin to show the effects of moisturization on its mechanical properties. Friction force was evaluated using a sinusoidal motion friction evaluation system. The skin of the upper arm of 20subjects was rubbed using a contact probe. The water content of the stratum corneum and the softness of the skin were measured using a Corneometer and a Cutometer, respectively. When human skin was treated with water or 10wt% glycerol aqueous solution, the friction coefficients increased by 0.23±0.01 and 0.17±0.14, respectively, and the delay times (normalized by calculating the time interval from contact with the probe to the friction response divided by the friction time for one round trip) increased by 0.048±0.034 and 0.055±0.024, respectively. Three different friction profiles were observed: (a) a stable pattern, in which a smooth profile was observed during the sliding process; (b) an oscillation pattern, in which significant oscillation was obtained; and (c) a stick pattern, in which the friction coefficient increased even during the deceleration process. In the case of untreated skin, the oscillation pattern was observed for the majority of subjects. The appearance rate of the stick pattern increased by 80.3%±29.4% after treatment with 10wt% glycerol aqueous solution. These characteristic friction profiles can be explained by a two-step friction model consisting of two modes: (a) friction at the skin surface and (b) the delayed response due to skin deformation. Moisturizing the skin with water or 10wt% glycerol aqueous solution increased the friction coefficient and delay time, dramatically changing the friction profile. These changes were considered to be due to the swelling and softening of the stratum corneum and the increased true contact area between the contact probe and the skin surface.

The Resuspension and Deposition of Biomediated Sediments in Upper South Cove, Nova Scotia, Canada

Sutherland, T.F.; Amos, C.L., and Grant, J., 2022. The resuspension and deposition of biomediated sediments in Upper South Cove, Nova Scotia, Canada. Journal of Coastal Research, 38(1), 19–34. Coconut Creek (Florida), ISSN 0749-0208. Coastal seabed sediment stability is mediated by microalgal and bacterial biofilms. The resuspension of organic suspended particulate matter (SPM) in biomediated sediments increases nutrient fluxes to the water column and supplements particulate food supplies for suspension feeders. Thus, quantifying benthic-pelagic exchange pathways of biogeochemical parameters is essential to provide an accurate assessment of carrying capacities of coastal embayments supporting both natural and cultured bivalve populations. Benthic-pelagic transport coefficients such as erosion threshold (U*CRIT-SPM-EROSION), net erosion rate (NERSPM), peak erosion rate (PERSPM), depositional threshold (U*CRIT-SPM-DEPOSITION), and deposition rate (DRSPM) were determined using an in situ benthic flume (Sea Carousel) in the protected inner termination of Upper South Cove (USC). The layered gel-like muddy seabed consisted of a thin biofilm or flocculated material overlying highly reduced black sediments. Eroded material was analyzed for concentrations of SPM, chlorophyll-a (CHL), phaeopigment (PHA), and organic/inorganic content. All stations exhibited a consistent pattern of staggered erosion thresholds of seabed constituents, where U*CRIT-SPM > U*CRIT-PHA > U*CRIT-CHL. Erosion thresholds of these sediment constituents were inversely related to NERSPM, NERCHL, and NERPHA fluxes as part of a principal component analysis. U*CRIT-SPM-EROSION was generally higher than U*CRIT-SPM-DEPOSITION across the individual USC stations, suggesting that SPM deposition largely occurs before erosion. A tight coupling was observed between both the mean NERSPM (1.37×10–3 kg m–2 s–1) and DRSPM (1.23×10–3 kg m–2 s–1) and the occurrence frequency between erosion (44.2%) and deposition (52.5%) phases derived from a 4-day U* time-series profile. Although these results highlight a tight benthic-pelagic coupling system in USC, some overlap appears to occur between the deposition and erosion phases, which can be attributed to the presence of diverse SPM size classes that alter during erosion (shearing) and velocity deceleration (floc-forming) processes. Benthic-pelagic coupling supports the sustained near-bottom turbidity conditions observed in USC.

Numerical investigations into the ventilation elimination mechanism of a surface-piercing hydrofoil

This paper investigates the ventilation elimination mechanisms during the deceleration process of a surface-piercing hydrofoil using the unsteady Reynolds-averaged Navier-Stokes (RANS) method together with a Volume of Fluid (VOF) model. The numerical results are in good agreement with the experimental data. The ventilation elimination mechanism of the surface-piercing hydrofoil is analyzed from the perspectives of the hydrofoil hydrodynamic performance, the ventilated cavity evolution, vortex structures, and re-entrant jets. The results indicate that the ventilation elimination includes three stages, i.e. a decrease in the ventilated cavity, washout, and reattachment. The decrease in the ventilated cavity is due to the hydrofoil speed decrease in the FV flow. Washout is the transition from fully ventilated to partially ventilated flow, and reattachment is the transition from partially ventilated to fully wetted flow. The underwater vortex structures around the surface-piercing hydrofoil are composed of a tip vortex, an unstable vortex induced by the shear layer, and a Karman vortex caused by the vortex shedding from the trailing edge of the hydrofoil. Ventilation stability strongly depends on the re-entrant jet. When Φ (the angle between the flow direction and the closure line of the ventilated cavity) is greater than 45°, the re-entrant jet impinges on the ventilated cavity's leading edge and destabilizes the ventilated cavity.