Deceleration Process Research Articles

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.

Heterogeneous traffic flow characteristics on the highway with a climbing lane under different truck percentages: The framework of Kerner’s three-phase traffic theory

Nowadays, in order to improve the traffic conditions in mountainous areas, the demand of climbing lanes is increasing. In this paper, car–truck heterogeneous traffic flow characteristics on the highway with a climbing lane are studied up based on an improved Kerner–Klenov–Schreckenberg–Wolf (KKSW) cellular automation (CA) model. To depict the speed characteristics of vehicle’s climbing and lane-changing behaviors, additional evolution rules for trucks are introduced into the KKSW model. Specifically, the motion of trucks climbing on the slope is described as a deceleration process and an equilibrium process. Furthermore, we define the probability of a truck driver using the climbing lane as a function of the observed real-time occupancy on it. We have found that in accordance with Kerner’s theory, traffic breakdown is an F→S transition that occurs in metastable free flow with respect to the F→S transition. When the traffic demand increases, the bottleneck appears due to the merging of trucks from the climbing lane to the inner lane. Localized synchronized flow patterns (LSP) emerge on both the inner and outer lanes. When traffic demand increases further, wide moving jams emerge in synchronized flow and general pattern (GP) appears on the inner lane, whereas synchronized flow patterns remain on the outer lane only. In addition, the macroscopic traffic flow characteristics under varying truck percentages are analyzed. We have found that the improving effect of climbing lane on traffic efficiency is closely related to the truck percentage.

Incident wind angle and topographic steering through excavated foredune notches

Artificial foredune ‘notching’ aims to increase sand transport between the beach and backdune environments to enhance biodiversity and increase foredune resilience. Recent research has examined the morphodynamics of dunes in the lee of notches, however the conditions that favour sand transport through the notches, and the associated processes of topographic steering, flow acceleration and deceleration, have not been systematically examined. It is important to examine the relationship between these processes because on most temperate coasts regional winds cross shorelines at oblique angles.This study combines field-based experiments and Computational Fluid Dynamics (CFD) modelling to examine the relationship between the relative incident wind approach angle, topographic steering and flow acceleration through an excavated foredune notch located at St Kilda, New Zealand. Secondary wind speed and direction is recorded in the notch by 12 ultrasonic anemometers and compared with incident wind conditions measured at 6.5 m above the foredune crest. Field data is used to validate the CFD simulations, which is used to examine the flow dynamics at a larger spatial scale, across the beach, as well as through the notch.Wind speeds inside the notch are strongly correlated with incident wind angles ranging from −6° to 77° relative to notch orientation. Wind flow realignment to notch orientation, compression and acceleration through the notch occurs when the relative incident wind angle is less than 27° for a notch oriented 77° to the shoreline. Wind flow separation and deceleration occurs when the relative angle is greater than 27°. An empirical model relating incident wind speed, direction and notch activation (i.e. when sand transport occurs) is developed. The threshold of incident wind speed for notch activation increases when the relative wind angle increases, and vice versa.

SCIENCE VERSUS PHILOSOPHY, PROPOUNDED BY ANNMBHATT SPECIAL PERSPECTIVE ON GRAVITY

Annambhatna, the author of the argument, has said "adyapatana samvayikaranam gravitvam"1 while defining the property called gravity in the order of merits in the collection of arguments. That is to say that the unusual cause of the first reaction is called gravity. “Dvitiya dipatnasyavega samvayikaranatvada veges tivyaptivaranayadyeti” i.e. to prevent overlapping in velocity etc There is an unusual reason for that first process. Here it is certainly necessary to appreciate the subtle vision and technical and scientific knowledge of Annabhatt. The symptoms were also reasonable to some extent but they knew that once the deceleration process has started in the object, the velocity generated by that deceleration process is the cause of the forward reaction. Thus the progressively generated velocity is the cause of the progressive deceleration process. The scientific explanation of the process is as follows.

Emergence of representative signals for sudden stratospheric warmings beyond current predictable lead times

Abstract. Major sudden stratospheric warmings (SSWs) are extreme wintertime circulation events of the Arctic stratosphere that are accompanied by a breakdown of the polar vortex and are considered an important source of predictability of tropospheric weather on subseasonal to seasonal timescales over the Northern Hemisphere midlatitudes and high latitudes. However, SSWs themselves are difficult to predict, with a predictability limit of around 1 to 2 weeks. The predictability limit for determining the type of event, i.e., wave-1 or wave-2 events, is even shorter. Here we analyze the dynamics of the vortex breakdown and look for early signs of the vortex deceleration process at lead times beyond the current predictability limit of SSWs. To this end, we employ a mode decomposition analysis to study the potential vorticity (PV) equation on the 850 K isentropic surface by decomposing each term in the PV equation using the empirical orthogonal functions of the PV. The first principal component (PC) is an indicator of the strength of the polar vortex and starts to increase from around 25 d before the onset of SSWs, indicating a deceleration of the polar vortex. A budget analysis based on the mode decomposition is then used to characterize the contribution of the linear and nonlinear PV advection terms to the rate of change (tendency) of the first PC. The linear PV advection term is the main contributor to the PC tendency at 25 to 15 d before the onset of SSW events for both wave-1 and wave-2 events. The nonlinear PV advection term becomes important between 15 and 1 d before the onset of wave-2 events, while the linear PV advection term continues to be the main contributor for wave-1 events. By linking the PV advection to the PV flux, we find that the linear PV flux is important for both types of SSWs from 25 to 15 d prior to the events but with different wave-2 spatial patterns, while the nonlinear PV flux displays a wave-3 wave pattern, which finally leads to a split of the polar vortex. Early signs of SSW events arise before the 1- to 2-week prediction limit currently observed in state-of-the-art prediction systems, while signs for the type of event arise at least 1 week before the event onset.

Simulating the collision of a moving droplet against a moving particle: Impact of Bond number, wettability, size ratio, and eccentricity

This paper presents a direct numerical simulation for the collision of a moving droplet against a moving particle under gravity, based on the pseudopotential lattice Boltzmann model. The effects of Bond number (Bo), particle surface wettability, particle–droplet size ratio (α), and eccentricity ratio (B) on the collision processes are investigated comprehensively. Six findings are reported and analyzed for the first time: (1) an agglomeration process is observed for the collision with a very small Bond number. During the agglomeration process, the vertical velocity of the particle will experience a deceleration, and the deceleration will become weak against the increase in the Bond number. (2) The wettability will influence the variation of the vertical velocity of the moving particle remarkably. The vertical velocity of the neutral particle is nearly linearly accelerated, but the lyophilic particle experiences an obvious deceleration. In addition, the velocity history of the lyophobic particle shows a nonlinear acceleration. (3) The increase in the particle–droplet size ratio will postpone the emergence of the deceleration process. Therefore, the appearance of the peak vertical velocity is delayed against the increase in the particle–droplet size ratio. (4) For different eccentricity ratios, the differences of the velocities (e.g., the horizontal, vertical, and angular velocity) are very small in the beginning of collision, while a big difference appears with time elapses. Besides, the variation of velocities becomes very obvious. (5) There is a critical value for B, where the horizontal velocity, vertical velocity, and angular velocity of the particle investigated in the work all will reach their maximum values. (6) A rebound regime is observed when a moving droplet collides vertically against a moving particle. In the available literature, a rebound regime was observed only when a droplet colliding against a fixed particle, but never for a vertically moving particle. The present research reveals when a rebound process will appear. The finding here may shed some light on the mechanism of the collision of a moving droplet against a moving particle.

A continuous traffic flow model considering predictive headway variation and preceding vehicle’s taillight effect

The car taillights in the deceleration process of preceding vehicle may greatly affect the acceleration and deceleration processes of the following vehicle. Additionally, the driver can predict the headway at the next time period from surrounding traffic information, and adjust the vehicle acceleration based on the difference between the predicted headway and the current headway information. To analyze these combined effects, we propose a new continuous traffic flow model taking into account the predictive headway variation and preceding vehicle’s taillight. The stability condition and KdV–Burgers equation of the continuum model are derived in linear and nonlinear stability analysis. The density wave solution obtained by solving the KdV–Burgers equation can be used to describe the formation and propagation mechanism of traffic jams near stable conditions. The complex traffic phenomena such as shock waves, rarefaction waves and local cluster effects are reproduced by simulation. Results show that the taillight information of preceding vehicle and the driver’s prediction time step both contribute greatly to the stability of the traffic flow and energy consumption.

Noise-induced instability of a class of stochastic higher order continuum traffic models

Traffic flow dynamics are complex and nonlinear, and depend on the interactions of many vehicles moving together. Especially, the stochastic driving behavior is a significant reason for many complex traffic phenomena such as the capacity drop or traffic instabilities without lane changing. To date, there has not been a satisfactory general theory that can be consistently applied to represent such traffic flow conditions. While there have been efforts to introduce stochastic behavior in deterministic traffic flow models, these attempts have mainly focused on the small stochastic fluctuations around the theoretical equilibrium fundamental diagram or model parameters. Little attention has been given to the physical relevance of the stochastic component, and the existing models do not consider large deviations from the equilibrium fundamental diagram that occur in the transient phases of traffic flow (i.e acceleration and/or deceleration). The goal of this paper is thus to improve current continuum traffic models, with the primary focus on the stochastic behavior arising in the acceleration and/or deceleration process. Our analytical results show noise-induced (long-wave length) stop-and-go waves in the low speed regime, which conform to the recent empirical findings. In addition, it is found that the stochasticity can lead to situations in which a bottleneck sometimes is activated and at other times is not activated under identical traffic demand.

High-resolution numerical simulation of the performance of vertical axis wind turbines in urban area: Part II, array of vertical axis wind turbines between buildings

Vertical axis wind turbines can harvest wind energy from every direction, and they are suitable for the complex flow conditions in urban areas. The flow field around buildings consists some high speed regions, and the blockage effect can provide higher wind velocity. Meanwhile, they can be installed at a certain altitude with no interference to pedestrians and vehicles. In this paper, we investigate the characteristics of wind turbines in an array by arranging them between two buildings. For this aim, a high-resolution numerical simulation method is adopted to simulate the accurate flow field and force coefficients. The high-resolution numerical simulation method is composed of adaptive mesh refinement and overset grid techniques. Firstly, there are two array types with wind turbines uniformly arranged in a line, which is perpendicular to the free stream. The result shows that array type A with asymmetric wake achieves a greater mean power coefficient. It reveals that the wake matching phenomenon of array type B causes a loss of wind energy between each couple. Secondly, five column positions between the two buildings are arranged in different positions. The five positions correspond to different flow conditions, and they belong to three typical processes: contraction acceleration process, uniform velocity process, and expansion deceleration process. When mounting array type A in contraction acceleration or expansion deceleration regions, the velocity profile is non-uniform along with the array. The power coefficients of wind turbines in one array are significantly different from each other. The array in the contraction acceleration region reaches the maximum mean power coefficient. Thirdly, in order to evaluate the influence of wind directions in urban area, there are four cases with different wind directions. The simulation results show that the array at α∞=15∘ obtains the maximum mean power coefficient. In summary, the mean output power of the wind turbine array in urban areas is always greater than that of a single wind turbine.

X-ray emission from magnetized neutron star atmospheres at low mass-accretion rates. I. Phase-averaged spectrum

Recent observations of X-ray pulsars at low luminosities allow, for the first time, the comparison of theoretical models of the emission from highly magnetized neutron star atmospheres at low mass-accretion rates (Ṁ ≲ 1015 g s−1) with the broadband X-ray data. The purpose of this paper is to investigate spectral formation in the neutron star atmosphere at low Ṁ and to conduct a parameter study of the physical properties of the emitting region. We obtain the structure of the static atmosphere, assuming that Coulomb collisions are the dominant deceleration process. The upper part of the atmosphere is strongly heated by the braking plasma, reaching temperatures of 30–40 keV, while its denser isothermal interior is much cooler (∼2 keV). We numerically solve the polarized radiative transfer in the atmosphere with magnetic Compton scattering, free–free processes, and nonthermal cyclotron emission due to possible collisional excitations of electrons. The strongly polarized emitted spectrum has a double-hump shape that is observed in low-luminosity X-ray pulsars. A low-energy “thermal” component is dominated by extraordinary photons that can leave the atmosphere from deeper layers because of their long mean free path at soft energies. We find that a high-energy component is formed because of resonant Comptonization in the heated nonisothermal part of the atmosphere even in the absence of collisional excitations. However, these latter, if present, affect the ratio of the two components. A strong cyclotron line originates from the optically thin, uppermost zone. A fit of the model to NuSTAR and Swift/XRT observations of GX 304−1 provides an accurate description of the data with reasonable parameters. The model can thus reproduce the characteristic double-hump spectrum observed in low-luminosity X-ray pulsars and provides insights into spectral formation.

Variable step control to improve scanning speed of gene sequencing stage

High-speed scanning is a huge challenge to the motion control of step-scanning gene sequencing stage. The stage should achieve high-precision position stability with minimal settling time for each step. The existing step-scanning scheme usually bases on fixed-step motion control, which has limited means to reduce the time cost of approaching the desired position and keeping high-precision position stability. In this work, we focus on shortening the settling time of stepping motion and propose a novel variable step control method to increase the scanning speed of gene sequencing stage. Specifically, the variable step control stabilizes the stage at any position in a steady-state interval rather than the desired position on each step, so that reduces the settling time. The resulting step-length error is compensated in the next acceleration and deceleration process of stepping to avoid the accumulation of errors. We explicitly described the working process of the step-scanning gene sequencer and designed the PID control structure used in the variable step control for the gene sequencing stage. The simulation was performed to check the performance and stability of the variable step control. Under the conditions of the variable step control where the IMA6000 gene sequencer prototype was evaluated extensively. The experimental results show that the real gene sequencer can step 1.54 mm in 50 ms period, and maintain a high-precision stable state less than 30 nm standard deviation in the following 10 ms period. The proposed method performs well on the gene sequencing stage.

Investigation of Specific FDM Process Parameters to Optimize the Polymer Discharge of Carbon Fiber Reinforced PEEK

AbstractFused deposition modeling (FDM) is a widely used manufacturing process and the materials market is growing due to the increased requirements on materials. In particular, processing of high‐temperature materials such as PEEK is challenging. The aim of these studies is to investigate and improve the processability of a carbon fiber reinforced polyether ether ketone (PEEK) material in the FDM process. The first step is to define the relevant process parameters, which remain constant over the entire investigation. In particular, the material‐specific temperatures must be defined. Based on previous investigations regarding the weld seam strength and the warpage of the selected PEEK materials, a method to determine and adjust essential process parameters should be developed. One approach is the consideration of the volumetric polymer discharge at a stationary filament feed rate. The optimized adjustment of the feed rate ensures increased component densities and an improved process reliability. In this context, the component areas with non‐stationary extruder movement, such as in corner areas, have got a huge influence on the component quality. The acceleration and deceleration processes do not result in a desired uniform strand geometry due to the pressure changes within the nozzle. The acceleration can result in thinner strands while the deceleration can lead to a thickening of the polymer discharge. The aim is to adjust the pressure inside the nozzle depending on the acceleration profile to enable a homogenous strand geometry. The method should therefore allow the improvement of the processability of PEEK materials.

Modeling and analysis of the compressor for the closed cycle system on anti-surge process

In order to study the interaction mechanism of the pipe network, the compressor and the control system in the process of the anti-surge regulation, the simulation model of the overall Closed Cycle System (CCS) is established in this paper. By comparing the simulation results with the target values at the Design Operation and the Maximum Mach Operation, the calculation deviation is less than 1%, which verifies the accuracy of the model. At the Maximum Mach Operation, the analysis of the CCS during the quasi steady process and the dynamic process is carried out respectively. According to the result of quasi steady state analysis, the effectiveness of the designed anti-surge circuit during the normal operating process of the CCS is verified. By opening the Anti-Surge Valve, additional 38.5% surge margin is provided. And the surge margin at the simulation process would be slightly higher than the design value for the variation of the inlet condition from the different operations. Through the dynamic analysis, the changes of the different performance parameters are studied in the process of sudden blockage in the pipe network, and during this process the compressor surge could be induced easily due to the sharp decline of the inlet pressure. To ensure the safety of the compressor during the acceleration and deceleration process, the moving trajectory of the operation point on the Compressor Characteristic Map should be studied by considering the effect of the resistance characteristics of the CCS pipe network. In addition, the anti-surge system should have a high response frequency to deal with the sudden blockage.

Sound radiation of the exhaust gas turbocharger as a function of the compressor inflow

The use of exhaust gas turbochargers in modern engine concepts is essential to achieve high efficiencies, low fuel consumption, and low emissions. However, the high rotational speed, a wide range of compression ratios, and dynamic acceleration and deceleration processes cause both tonal and broadband sound radiation. Due to packaging constraints, the intake cycle is often characterized by deflections and cross-section jumps. That leads to a strong secondary flow at the inflow of the compressor. Therefore, in this study, we intensively investigated the influence of disturbed inflow conditions on the sound radiation of the exhaust gas turbocharger. As a result, we found that the flow caused by a 105∘-bend in front of the compressor leads to an increase in broadband flow noise up to 5.5dBA. The decisive factor here is the amount of pre-whirl at the outer radius of the pipe. A high velocity gradient additionally shifts the surge line towards lower flow coefficients and mass flows, respectively. That indirectly reduces the sound radiation due to the greater distance of the operating points to the surge line. However, pre-whirl can counteract this effect. The surge line shifts to larger mass flows due to the decrease of the relative flow angle. In contrast, low turbulence levels and homogeneous compressor inflow lead to reduced flow separation and thus lower broadband sound radiation. The reduction of the secondary flow in the intake of the compressor, e.g. due to pre-guidance devices, therefore represents a promising way of reducing the noise emission of the exhaust gas turbocharger in a passenger car.

High-power graphene supercapacitors for the effective storage of regenerative energy during the braking and deceleration process in electric vehicles

The practical applicability of a high-power graphene supercapacitor as an effective primary and auxiliary energy storage system for storing regenerative energy from the braking and deceleration process in electric vehicles (EVs) is studied.

Eco-Driving Operation of Connected Vehicle With V2I Communication Among Multiple Signalized Intersections

Eco-driving through multiple intersections has significant fuel benefit for road transportation. Most existing studies assume that vehicles travel at a constant speed between intersections, which naturally leads to large errors in fuel prediction and trajectory planning. This article focuses on eco-driving operation through multiple signalized intersections considering more realistic powertrain dynamics, which directly contain the engine and the transmission as well as aerodynamic drag, rolling resistance, and so on. This feature enables explicit descriptions of dynamic behaviors and fuel characteristics in acceleration, deceleration, and constant speed driving. An open-loop optimal control problem (OCP) is formulated to minimize fuel consumption between two red-signalized intersections, and the two- or three-stage operation rules are then proposed to approximate its optimal solution. The eco-driving of passing multiple intersections is then numerically solved by combining the two- or three-stage driving rule and the Dijkstra algorithm. This method can consider the acceleration and deceleration processes at each intersection and achieve improved fuel economy.

Features of the Flow of an Adverse Pressure Gradient Boundary Layer

Vertical velocity profiles are obtained experimentally for the boundary layer of a flow with an inverse pressure gradient in different phases of the periodic process of fluid deceleration. At the greatest drop in velocity, the profile has a local minimum with two inflection points at the upper boundary of the viscous layer. Chains of vortices then form at this location, testifying to a loss of stability of the laminar motion.

An Improved Intelligent Driver Model Considering the Information of Multiple Front and Rear Vehicles

This paper proposes an improved intelligent driver model (IDM) by considering the information of multiple front and rear vehicles to describe the car-following behaviour of CAVs (Connected and autonomous vehicles). The model involves the velocity and acceleration of multiple front and rear vehicles as well as the velocity difference and headway between the host vehicle and its surrounding vehicles. By introducing location-related parameters, the model quantitatively expresses the change in influence degree of a surrounding vehicle with its location to the host vehicle. To maximize traffic stability, we obtain the optimal value of the parameters in the model and the effect of specific time delays on the stability of traffic flow with numerical simulation. The results indicate that for a single vehicle control, the proposed model provides a much quicker and smoother acceleration and deceleration process to the desired speed than the IDM and multi-front IDM. And for fleet control, the proposed multi-front and rear IDM is superior to the other two models in decreasing the starting and braking time and increasing the stability of speed and acceleration. With effective car-following behaviour control, it is helpful to improve the operation efficiency of CAVs and enhance the stability of traffic flow. In addition to the car-following behaviour control, the model can be utilized for fleet control in the case of CAVs’ homogeneous flow. This model can also serve as an effective tool to simulate car-following behaviour, which is beneficial for road traffic management and infrastructure layout in connected environments.

Researching acceleration and deceleration processes of supercavitating strikers under the conditions of hydroballistic track

Laboratory researches of the processes accompanying high-velocity motion of super-cavitating strikers under water, conducted under the conditions of a hydroballistic track imply the acceleration of a striker within a ballistic barrel to speeds exceeding 200 m/s and consequent partial or complete deceleration within a water tank. The results of experimental and theoretical researches concerning the acceleration and deceleration processes are considered in the given work as well as the estimation of the force and pressure values impacting the striker.