Deceleration Process Research Articles

On the internal collapse phenomenon at the closure of cavitation bubbles in a deceleration process of underwater vertical launching

In a typical experiment of underwater vertical launching, cavitation bubbles are generated in the low-pressure regions of the vehicle in the water and collapse when the projectile runs through the free surface. A new internal collapse phenomenon that advances from the tail to the head of the axisymmetric projectile has been observed in an underwater launching experiment: it differs from usual collapse phenomena and is rarely observed in water tunnel tests. During this process, cavities shrink upstream quickly, producing high impact pressure, and fast re-entry jets form, inducing strong instabilities. Analysis indicates that this phenomenon is relative to rapid changes in vehicle speed and cavitation number. Thin cavitation bubbles are generated when the vehicle accelerates rapidly, and then vapor condenses rapidly and forms an additional body force at the closure of the cavity in the deceleration process. As a result, large velocity directed to the wall to the wall is generated, and the liquid water layer continues to move toward the wall and impact as an internal collapse. Numerical simulations are also performed on the decelerating effect on the cavity evolution. Results indicate that the pressure increase is a critical factor, which results in a nonlinear change in the cavity length. In proportion to the enlargement of the deceleration, the cavities shorten more quickly.

Modeling the Speed, Acceleration, and Deceleration of Bicyclists for Microscopic Traffic Simulation

Models were developed, calibrated, and evaluated to describe the acceleration and deceleration processes of bicyclists in three states: while they accelerate from a stop, decelerate to a stop, and fluctuate around the desired traveling speed. Such models are necessary to simulate the speed profiles of bicyclists reliably in microscopic traffic simulations. To accomplish this aim, a sample of 1,030 processed trajectories from bicyclists at four intersections in Munich, Germany, was used to analyze the dynamic characteristics of bicyclists. The average crossing speed, the fluctuation in crossing speed, and the minimum and the maximum speeds of uninfluenced bicyclists who crossed at a green light were analyzed, and correlations between these variables were investigated. The acceleration and deceleration profiles of bicyclists who stopped at a red light but were uninfluenced by other bicyclists, were used to evaluate four acceleration–deceleration models: the constant model, the linear decreasing model, the two-term sinusoidal models, and a polynomial model. Two adaptations of the models were developed and evaluated: one to derive acceleration and deceleration as a function of speed rather than time, and the other to account for the observed fluctuation in bicyclist traveling speed. The polynomial model was found to be the most flexible and to produce the overall best estimates of the acceleration profiles. The constant model was found to estimate best the deceleration, acceleration, and deceleration while fluctuation occurred around the desired speed.

On the design and corresponding performance of steam jet ejectors

A thermodynamic model for the design of ejectors is described, validated and applied for conditions prevailing in a multiple effect desalination system with thermal vapour compression. The model, which calculates all the dimensions of the ejector, incorporates several innovations. Firstly, it uses polytropic efficiencies to account for irreversibilities during the acceleration and deceleration processes thus taking into consideration the effect of the pressure ratio on the corresponding losses. Secondly, the proposed parametric relations between the pressure at the fictive throat and at the primary nozzle outlet constitute a generalization of particular geometries and operating conditions treated in previous studies. Thirdly, it considers mixing processes which take place with simultaneous pressure and area changes. The model has initially been used to determine the ejector dimensions and fluid properties for a base case. Parametric studies have then been conducted to demonstrate the existence of design choices which minimize the size of the primary nozzle and the length of the constant diameter duct.

Long queue estimation for signalized intersections using mobile data

Queue length is one of the key measures in assessing arterial performances. Under heavy congestion, queues are difficult to estimate from either fixed-location sensors (such as loop detectors) or mobile sensors since they may exceed the region of detection, which is defined as long queue in the literature. While the long queue problem has been successfully addressed in the past using fixed-location sensors, whether this can be done using mobile traffic sensors remains unclear. In this paper, a queue length estimation method is proposed to solve this long queue problem using short vehicle trajectories obtained from mobile sensors. The method contains vehicle trajectory reconstruction models to estimate the missing deceleration or acceleration process of a vehicle. Long queue estimation models are then developed using the reconstructed vehicle trajectories. The proposed method can provide estimates of the queue profile and the maximum queue length of a cycle. The method is tested in a field experiment with reasonable results.

Linear energy transfer effects on time profiles of scintillation of Ce-doped LiCaAlF6 crystals

We measured temporal profiles of the scintillation of Ce-doped LiCaAlF6 scintillator crystals at different linear energy transfers (LETs). Based on the comparison of high-LET temporal profiles with those at low LET, a fast component was observed only at low LET. The disappearance of the fast component at high LET is tentatively ascribed to the quenching of excited states at crystal defects owing to the interaction between excited states via the Auger process. In addition, the rise and the initial decay behavior were dependent on the LET. This LET-dependent behavior is explained by an acceleration process and a deceleration process in energy transfer at high LET. The LET-dependent temporal profiles provide the basis for a discrimination technique of gamma-ray and neutron detection events using these scintillators based on the nuclear reaction, 6Li(n,α)t.

Thermal equilibrium and prehydration processes of electrons injected into liquid water calculated by dynamic Monte Carlo method

Abstract The thermalization length and spatial distribution of electrons in liquid water were simulated for initial electron energies ranging from 0.1 eV to 100 keV using a dynamic Monte Carlo code. The results showed that electrons were decelerated for thermalization over a longer time period than was previously predicted. This long thermalization time significantly contributed to the series of processes from initial ionization to hydration. We further studied the particular deceleration process of electrons at an incident energy of 1 eV, focusing on the temporal evolution of total track length, mean traveling distance, and energy distributions of decelerating electrons. The initial prehydration time and thermalization periods were estimated to be approximately 50 and 220 fs, respectively, indicating that the initial prehydration began before or contemporaneously with the thermal equilibrium. Based on these results, the prehydrated electrons were suggested to play an important role during multiple DNA damage induction.

Velocity and shear stress profiles for tidal effected channels

Tidal current is a periodic movement of unsteady and non-uniform, which owns obvious acceleration and deceleration process. The vertical distributions of velocity and shear stress in tidal flow possess the extraordinary features from the unidirectional flow. From the fundamental tidal movement equation, a simple-structure velocity profile formula is deduced which is capable of describing the velocity states from bypass to fully-developed, and it can express the velocity distribution of which the maximum velocity is not near the water surface. Based on the velocity profile, the tidal shear stress profile expression is derived and it can depict the characteristics commendably that the shear stress obeys the concave distribution within accelerating flow and a convex distribution within decelerating flow. Meanwhile, the computed values of the surface shear stress, on the conditions of acceleration or deceleration, conform to the fact the surface shear stress is not always equal to zero. Following the results of field observations, indoor experiments and numerical models, the bed shear stress is rather a variable dominated by tidal phase than a constant during the tide. The bed shear stress formula in the tide is derived with the definition raised by Soulsby, which is verified with the measured materials. The results are good agreeing with the field data.

Braking Deceleration Measurement Using the Video Analysis of Motions by Sw Tracker

Abstract This contribution deals with the issue of car braking, particularly with the one of M1 category. Braking deceleration measurement of the vehicle Mazda 3 MPS was carried out by the declerograph XL MeterTM Pro. The main aim of the contribution is to perform comparison of the process of braking deceleration between the decelograph and the new alternative method of video analysis and to subsequently examine these processes. The test took place at the Rosina airfield, the airstrip in a small village nearby the town of Žilina. The last part of this paper presents the results, evlauation and comparison of the measurements carried out.

Computational Method of the Propagation Velocity of Methane Explosion Flame Based on Correlation Coefficient of Images

A computational method for propagation velocity of methane explosion flame was developed based on correlation coefficients of images. Images of propagating flame were captured by a high-speed camera at a very high frequency. In order to calculate the displacement between two adjacent images of flame, the correlation coefficients were utilized. By trimming the two adjacent images and computing the correlation coefficients, the actual displacement of flame was obtained, and the average velocity of flame between two images was subsequently obtained. The flame velocities at different concentrations of methane were calculated during the whole process of explosion. The results showed that explosion flame undergoes a process of acceleration, deceleration, reverse acceleration, and reverse deceleration. By comparing with the measured velocity, the relative error is found to be very tiny. The method can be used to calculate not only the velocity of flame front but also the velocity of the flame wherever it is in the pipe.

Gravity-induced rock mass damage related to large en masse rockslides: Evidence from Vajont

The Vajont landslide is a well-known, reservoir-induced slope failure that occurred on 9 October 1963 and was characterized by an ‘en masse’ sliding motion that triggered various large waves, determining catastrophic consequences for the nearby territory and adjacent villages. During the Vajont dam construction, and especially after the disaster, some researchers identified widespread field evidence of heavy rock mass damage involving the presumed prehistoric rockslide and/or the 1963 failed mass. This paper describes evidence of heavy gravitational damage, including (i) folding, (ii) fracturing, (iii) faulting, and (iv) intact rock disintegration. The gravity-induced rock mass damage (GRMD) characterizes the remnants of the basal shear zone, still resting on the large detachment surface, and the 1963 failed rock mass. The comprehensive geological study of the 1963 Vajont landslide, based on the recently performed geomechanical survey (2006–present) and on the critical analysis of the past photographic documentation (1959–1964), allows us to recognize that most GRMD evidence is related to the prehistoric multistage Mt. Toc rockslide. The 1963 catastrophic en masse remobilization induced an increase to the prehistoric damage, reworking preexisting structures and creating additional gravity-driven features (folds, fractures, faults, and rock fragmentation). The gravity-induced damage was formed during the slope instability phases that preceded the collapse (static or quasi-static GRMD) and also as a consequence of the sliding motion and of the devastating impact between the failed blocks (dynamic GRMD). Gravitational damage originated various types of small drag folds such as flexures, concentric folds, chevron, and kink-box folds, all having a radius of 1–5m. Large buckle folds (radius of 10–50m) are related to the dynamic damage and were formed during the en masse motion as a consequence of deceleration and impact processes that involved the sliding mass. Prior to failure, unstable rock slopes can be affected by diffuse newly formed gravity-driven joints that are absent in the surrounding area and within the underlying bedrock, as the Vajont case history demonstrates (joint sets J9 and J10). These fractures, caused by critical tensile and shear stresses, represent an important mechanical clue to recognizing, on a geological basis, the instability condition of a rock slope under investigation. Owing to its complex geological evolution, the Vajont landslide is an outstanding example to help learn about cumulative GRMD effects that can accumulate over time when an ancient rockslide is further remobilized by a sudden en masse sliding motion.

Evaluation of acceleration and deceleration cardiac processes using phase-rectified signal averaging in healthy and idiopathic dilated cardiomyopathy subjects

The aim of the present study was to investigate the suitability of the Phase-Rectified Signal Averaging (PRSA) method for improved risk prediction in cardiac patients. Moreover, this technique, which separately evaluates acceleration and deceleration processes of cardiac rhythm, allows the effect of sympathetic and vagal modulations of beat-to-beat intervals to be characterized. Holter recordings of idiopathic dilated cardiomyopathy (IDC) patients were analyzed: high-risk (HR), who suffered sudden cardiac death (SCD) during the follow-up; and low-risk (LR), without any kind of cardiac-related death. Moreover, a control group of healthy subjects was analyzed. PRSA indexes were analyzed, for different time scales T and wavelet scales s, from RR series of 24 h-ECG recordings, awake periods and sleep periods. Also, the behavior of these indexes from simulated data was analyzed and compared with real data results. Outcomes demonstrated the PRSA capacity to significantly discriminate healthy subjects from IDC patients and HR from LR patients on a higher level than traditional temporal and spectral measures. The behavior of PRSA indexes agrees with experimental evidences related to cardiac autonomic modulations. Also, these parameters reflect more regularity of the autonomic nervous system (ANS) in HR patients.

Measurement and analysis of friction and dynamic characteristics of PIG’s sealing disc passing through girth weld in oil and gas pipeline

Pipeline inspection gauges (PIGs) are needed for operations such as dewatering, cleaning and internal inspection of the oil and gas pipelines to facilitate improvement in efficiency and safety. The friction and dynamic characteristics, as the sealing disc of a PIG passes through the girth weld in a pipe, has been directly studied using a custom-built experimental setup. The contact behavior between sealing disc and girth weld was analyzed using finite element methods. A two-dimensional section analytical link model of the sealing disc is introduced here and was simulated using the mechanic dynamic analysis software Adams. Our results show that the process of the sealing disc of the PIG passing through the girth weld in the pipe can be separated into three distinct stages: (1) start-up stage, (2) climbing stage, and (3) slope stage. At first, the PIG decelerates due to the friction force and then accelerates after passing through the girth weld. The acceleration and deceleration processes produce axial vibration in PIG.

Investigation of step electric drive as a control system for double-split hydrostatic mechanical transmissions

The research deals with developing the control unit for variable displacement axial-piston pump with a hydromechanical control in the test bed of double-split hydrostatic mechanical transmission. Step electric drive was used as an actuator for controlling the hydraulic pump. During the study, static modes, as well as acceleration and deceleration processes of the tractor were simulated. As a result, high positioning accuracy of the hydraulic pump swash plate, regardless of speed and load on the shaft was observed, and developed software has allowed to reproduce linear and nonlinear control laws. The relationship between the braking torque, applied to the shaft, and a step change in its speed was revealed. Step electric drive in combination with the hydromechanical control of positive-displacement hydraulic machine can serve low-cost alternative to the electric proportional control. The designed stand is reconfigurable, which allows to perform a number of studies for the hydrostatic transmissions with a differential at the output and at the input and has the potential for further improvements.

Dynamic characteristics of the herringbone planetary gear set during the variable speed process

In this study, a dynamic model for herringbone planetary gears is proposed which can be applied in the dynamic analysis of variable speed processes (including acceleration, deceleration, and large speed fluctuation process, etc.). The dynamic responses of the acceleration process of an example of a herringbone planetary gear set are simulated in cases where the profile error excitations are ignored and included. The phenomenon of tooth separations can be observed as the rotating speed increases in the simulation, and the effect of the profile error excitations on the phenomenon is also investigated. Furthermore, the effects of the profile error excitations on the vibrations and dynamic meshing forces are investigated before and after the appearance of tooth separations. Moreover, the dynamic characteristics of the herringbone planetary gear set are also compared with that of the spur/helical herringbone planetary gear set briefly. Finally, some advice for the design of planetary gear sets is given to avoid the phenomena of tooth separation and tooth back contacts and suppress the vibrations and dynamic meshing forces.

Determination of wafer center position during the transfer process by using the beam-breaking method

A wafer on a robot blade may slip due to inertia sliding during the acceleration or deceleration process. This study presents the implementation and experimental verification of a novel real-time wafer positioning system to be used during the transfer process. A system-integration computer program involving a human–machine interface (HMI) was also developed, exhibiting the following functions: (a) moving direction judgment; (b) notch-passing judgment; (c) indicating the sensor by which the notch passes; and (d) computing the wafer center in real time. The position of the wafer center is calculated based on the time-sequence of the beam-breaking signals from two optical sensors, and the geometric relations among the sensing points of the robot blade and wafer. When using eight-inch wafers, the experimental results indicated the capabilities of the proposed positioning system under various conditions, including distinct parameters regarding the moving direction, wafer displacement and notch-passing sensors. The accuracy and precision (repeatability) of the measurement in various conditions were calculated and discussed. Furthermore, the experimental results demonstrate that, after combining the novel wafer positioning system and HMI program, the proposed method can be used to compute the position of the wafer center in real time in various conditions.

Nucleosynthesis of elements in gamma-ray burst engines

We consider the gamma ray burst (GRB) central engine that is powered by the collapse of a massive rotating star or compact binary merger. The engine is a hot and dense accretion disk, which is composed of free nucleons, electron-positron pairs, and helium, and cooled by neutrino emission. A significant number density of neutrons in the inner disk body provide conditions for neutron rich plasma in the GRB outflows or jets. Helium is synthesized in the inner disk if the accretion rate is large, and heavy nuclei are also formed in the outer disk at distances above 150-250 $r_{g}$ from the black hole. We study the process of nucleosynthesis in the GRB engine, depending on its physical properties. The GRB central engine is hydrodynamically modeled in the frame of a dense and hot disk which accretes with a high rate (up to 1 Solar mass per second) onto a maximally spinning, stellar mass black hole. The synthesis of heavy nuclei up to germanium and gallium is then followed by the nuclear reaction network. The accretion at high rate onto a Kerr black hole feeds the engine activity and establishes conditions for efficient synthesis of heavy nuclei in the disk. These processes may have important observational implications for the jet deceleration process and heavy elements observed in the spectra of GRB afterglows.

Mars Science Laboratory Heatshield Development, Implementation, and Lessons Learned

The Mars Science Laboratory is a scientific mission that placed a 900 kg rover with 10 science instruments on the surface of Mars. A key component for landing on the surface of Mars is the aeroshell, which decelerates the entry vehicle to just 1% of its initial kinetic energy at atmospheric entry. The forward portion of the aeroshell is the heatshield, which must be designed to withstand the pressure, heating, and shear stresses it experiences during the atmospheric deceleration process. The original thermal protection system chosen for the heatshield, SLA-561V, was the material used on all previous Mars aeroshells but required new qualification testing. Unfortunately, the material failed testing in the more extreme environment three months after the aeroshell and project critical design reviews. A rapid decision was required to switch to another material under test by the Orion program called phenolic impregnated carbon ablator. With 18 months left to design, fabricate, test, and deliver this new heatshield for the 2009 launch opportunity, the heatshield team had to rapidly respond to the challenge and work in a manner that ensured success. Lessons learned can be had from both the failure of the original SLA-561V design and the success of the phenolic impregnated carbon ablator implementation.

Optimisation of the thickness of the moderator for positron annihilation process study in Ar gas

To investigate the deceleration and annihilation processes of positron in noble gas, we attempted to optimise the thickness of the positron moderator. The results of the decreasing trend of free positron intensity and ortho-positronium intensity with the thickness, and the annihilation rate suggest that the energy of almost all the positrons passed through the metal foils was much above the positronium formation threshold of 9 eV. Total thickness of 0.1 g cm-2 of the moderator and the Ar gas was required to stop almost all the positron in Ar gas.

A deceleration system for near-diameter spheres in pipeline transportation in a pebble bed reactor based on the resistance of a pneumatic cushion

The fuel elements cycle occurring inside and outside the core of a pebble bed reactor is carried out by pneumatic conveying. In some processes of conveyance, it is necessary to reduce the velocity of the moving fuel element in a short time to avoid damage to the fuel elements and the equipment. In this research, a deceleration system for near-diameter spheres in pipeline transportation based on the resistance of a pneumatic cushion is designed to achieve an effective and reliable deceleration process. Dynamic analysis and motion analysis of the deceleration process are conducted. The results show that when the fuel element is moving in the deceleration pipeline, the gas in the pipeline is compressed to create a pneumatic cushion which resists the movement of the fuel element. In this way, the velocity of the fuel element is decreased to below the target value. During this process, the deceleration is steady and reliable. On this basis some key design parameters are studied, such as the deceleration pipeline length, the ratio of the diameter of the fuel element to the internal diameter of the pipeline, etc. The experimental results are generally consistent with the analysis and demonstrate the considerable effectiveness of the deceleration process as well. This research provides a guide for the design of the fuel elements cycling system in a pebble bed reactor along with the optimization of its control.

Study on AFR Control for a PFI Air-Cooled Motorcycle Engine

For PFI (Port Fuel Injection) SI engine, accurate AFR (Air-fuel Ratio) control would keep TWC (Three-Way Catalyst) work in high efficiency range to achieve low pollutants emission. For ZS157FMI-3 motorcycle engine equipped with ZH600 ECS (Electronic Control System), a control strategy with close-loop feedback mode and feed-forward mode was designed for transient, quasi-steady and steady work states. One switching oxygen sensor was installed to form the close loop for quasi-steady and steady work states, and feed-forward control strategy based on a simplified fuel-film model was implemented to cope with transient AFR control. TP (Throttle Position) change rates were selected to be the determinant of which AFR control mode should be activated. For the validation of the control methods, bench tests were carried out in three typical work procedures. The results showed that AFR values of close-loop were close to stoichiometric one with relative error below 3%. AFR in acceleration or deceleration process may exhibit slight fluctuations, but the crest would be eliminated immediately. It concluded that the strategy designed in the study is able to cope with AFR control on variety of operation conditions for the experimental engine.