Velocity Direction Change Research Articles

Analysis of dynamic characteristics of vapor plume of oscillating laser welding of SUS301L-HT stainless steel

Investigations had made much efforts on the vapor plume dynamic characteristics of laser beam welding (LBW) but only showed a little knowledge about the oscillating laser beam welding (OLBW). The velocity magnitude and direction of OLBW varied abidingly, resulting in complicated evolution process of vapor plume. Present research attempted to elucidate the effect of oscillation frequency on the dynamic behavior of vapor plume. The vapor plume morphology was uniform at 50 Hz and 100 Hz. The abrupt change in velocity direction easily led to the occurrence of attenuation and even annihilation of the vapor plume at the frequency less than 20 Hz or greater than 150 Hz. The vapor plume area less than 31.44 mm2 or the vapor plume orientation greater than −40° could be used as the judgment criterion of keyhole instability. The coefficient of variation of vapor plume area or orientation and the proportion of keyhole instability time showed similar trends of first decreasing and then increasing with the increase of oscillation frequency. The stability of vapor plume or keyhole was the best at 50 Hz.

Ductile behavior and heat transfer efficiency in polymer extrusion by self-controlled “flipping melt-pancakes” with multi-fields synergy

A new design approach of “Flipping Melt-Pancakes” structure was proposed to improve the ductile behavior and heat transfer capacity for polymer melt extrusion. Three-dimensional numerical analysis of novel proposed structures was implemented compared with Maddock element and conventional screw that are commonly used in industry. Results indicated that flow patterns of polymer fluid affected by the screw configurations, inducing different ductile deformation, i.e., shear deformation occurred in Maddock channel and torsional deformation yielded in the “Flipping Melt-Pancakes” structure. Deformation flow patterns can contribute to radial mass transfer, achieving effective exchange of local heat and making temperature distribution more uniform. Besides, the change of velocity direction brought by the circumferential movement facilitated the synergy between velocity and temperature gradient and, improved heat transfer. The novel proposed structure based on the polymeric multi-fields synergy principle- “Flipping Melt-Pancakes” structure- has good heat transfer properties, low pressure loss and good synergy effect, reflecting that the field synergy principle can be applied to optimize the screw structures in polymer processing. It provides a new theoretical perspective to solve the increasingly severe challenges due to the insufficient control of mass transfer and heat management in plasticization process of extrusion or injection.

Study on the mechanism of surface topography evolution in melting and transition regimes of laser polishing

Previous studies on the mechanism of laser polishing were limited to the melting regime, this paper proposed a numerical model for the melting and transition regimes of laser polishing, which coupled heat transfer, fluid flow, and material vaporization. Based on the model, the evolution of the temperature and velocity fields of the molten pool in laser polishing was presented. And the mechanism of surface topography evolution was revealed from the perspective of surface forces (capillary force, thermocapillary force, and recoil pressure), fluid velocity, and material removal. Furthermore, the corresponding relationships between surface forces, fluid velocity, and surface topography were determined. The contributions of surface forces and vaporization front velocity in laser polishing were investigated, and the reason for the formation of the bulge structure and the influence of laser power on it were analyzed. And the velocity direction change points which have a great influence on the surface evolution were found, and the method to determine the positions of these points was proposed. Besides, the surface roughness prediction after laser polishing was tried through the numerical model, and the maximum error between the predicted results and the experimental results is 14.9%. Therefore, this model can be used to optimize process parameters.

Flow visualization on SFR wire-wrapped 19-pin bundle geometry using MIR-PIV-PLIF and comparisons with RANS-based CFD analysis

In this study, measurement of turbulence intensity, pressure drop and local velocity field in the sodium fast reactor (SFR) wire-wrapped 19-pin bundle have been conducted to compare with the Reynolds averaged Navier–Stokes equations (RANS)-based computational fluid dynamics (CFD) simulations. The refractive indices between test section and working fluid, anise oil, were matched for the flow visualization. The turbulence intensity measurement showed that the transition of flow regime occurs at around Re = 13,800 at the test section. Pressure drop results revealed that the low-Re model showed the superior agreement with the experimental results. The particle image velocimetry (PIV) measurement was performed at the Reynolds numbers from 15,000 to 17,000. The velocity fields measured in the edge and interior subchannels. From the comparisons, it was found that the CFD simulation showed good agreement with the PIV measurement on specific flow characteristics such as vortex structure, swirl flow, and velocity direction change.

Hydrodynamic effect of biofouling in fish cage aquaculture netting

This paper presents a numerical study to assess the hydrodynamic effects of different levels of biofouling in fish cage aquaculture netting. The methodology adopted includes high resolution Large Eddy Simulation (LES) coupled to a regional model implemented within the framework of the Coastal and Regional Ocean Community Model (CROCO). The physical coherence of this approach has been previously verified and published by the authors. Three levels of biofouling were considered to describe a clean fish cage netting with no biofouling, medium biofouling and high biofouling growth levels. Clean and biofouled fish cage netting were described using a porous media model and the porous media coefficients were taken from the literature. A salmon farm located in the Estero Elefantes Channel in Patagonia (45°39′16.50 S 73°35′59.40 W) was used as study case. A change in the biofouling level in aquaculture fish cages netting can lead to drastic changes in the local velocity field. The high biofouling level produces the largest change in velocity direction and magnitude not only locally in near-cage areas, but also changing features in the overall fjord circulation. Velocity reduction in the shadow zone of fish cages reached values between 30% and 10% of the incident current for null and high biofouling levels, respectively. Simulations also showed dramatic effects of biofouling on flushing time. The predicted water availability of the salmon farm shows decreases of 27% and 36% considering medium and high levels of biofouling. This decrease in the available water is also related to a reduction in the amount of available oxygen and accumulation of waste products, affecting not only the health of farmed fish but also the environment. These and other environmental and productive implications are discussed.

Анализ особых положений плоского многозвенного рычажного механизма четвертого класса

The planar multi-linkage mechanism of the fourth order, the output rocker of which implements an approximate stopping in one critical position is described in the article. The mechanism consists of three dyads passing through their limit positions in a single duty cycle. That is why the singularity problem is relevant for such mechanisms and should be studied to avoid jamming of links or the appearance of uncontrolled movements. The mathematical model is based on the theory of screws and contains the closed-loop equilibrium equations obtained for the investigated mechanism. Based on the obtained results of the geometry and singularity analyses, it is shown that there are eight different positions in which some joints stop momentarily and then their angular velocity direction changes

Displacement Reliability Analysis of Submerged Multi-body Structure’s Floating Body for Connection Gaps

Abstract Aiming at the problem of systems’ dynamic characteristics’ randomness caused by connection gaps of submerged multi-body structures, a stochastic and uncertainty dynamical model were formulated for connection gaps and dynamic elongation of mooring cables. This model considered sag effect caused by light, soft and low damping characteristics of mooring cables and their dynamic elongation under the impact of flow field and connection gaps. The equivalent elastic modulus method was used to modify the sag effect. The Newmark-β method was used to solve the problem. Calculation results showed that the average value and peak value of floating body displacement caused by uncertainty of gap contact states are larger than those of ideal articulated states. The reliability of floating body’s displacement with gap contact will be reduced to different extents and the reliability of displacement in velocity direction changes greatly, especially perpendicular to flow field. When studying multi-body structures, randomness of contact state should be considered to reduce the dispersion of clearance and improve dynamic performance.

VELOCITY CHANGES ANALYSIS DISPLACEMENT DATA USING GNSS (GLOBAL NAVIGATION SATELLITE SYSTEM) IN JATI GEDE DAM

Jati Gede Dam is located around the border of Sumedang-Majalengka region in West Java province. Jati Gede Dam provides several benefits such as for irrigation, hydropower, tourism and fish farming. Dam can also trigger the potential a disaster, especially in the water impounding process. The process of water impounding in the dam has the potential to cause earthquake disaster. The effect of water impounding potentially adds stress accumulation in the dam area so that it can cause earthquakes. Therefore, a research on strain change due to the water impounding in Jati Gede dam is needed. The method used in the research is by GPR survey. Result from GPS observation processed to generate displacement value of GPS observation point, and strain changes from the point that formed grid strain. Based on deformation analysis the effect of water impounding to the strain around Jati Gede Dam can be obtained. Development in this thesis is by using and additional method namely Kinematic PPP to see the different pattern of earth tide phenomenon around the dam which were represented by several GPS station. These results indicate a change of velocity direction in the area around Jati Gede dam. This change can be analyzed for the station near the dam as JTG1 station, jtg2, CSUM, 0355, BDK2, CJR6, and MJLK. BDK2 campaign point leads toward the Southwestern, CJR6 displacements from the Southwest to the North, MJLK displacements from Southeast to the Northwest, and 0355 displacements from Southeast to the North. JTG1 GPS station point tends to lead toward the Southwestern and JTG2 GPS station leads toward the North with 0355 GPS station. CSUM in Sumedang displacements from Northwest to the East. This change can be analyzed for the station near the dam such as JTG1, JTG2, CSUM, 0355, BDK2, CJR6, and MJLK as result of the process of water filling in Jati Gede dam.

Mathematical modelling and numerical simulation of CO2/CH4 separation in a polymeric membrane

CO2 capture from natural gas was experimentally and theoretically studied using a dead-end polymeric permeation cell. A numerical model was proposed for the separation of CO2/CH4 using Polytetrafluoroethylene (PTFE) in a flat sheet membrane module and developed based upon the continuity, momentum and mass transfer equations. The slip velocity condition was considered to show the reflection of gas flow in contact with the membrane surface. The solution method was based on the well-known SIMPLE algorithm and implemented using MATLAB to determine the velocity and concentration profiles. Due to change in velocity direction in the membrane module, the hybrid differencing scheme was used to solve the diffusion–convection equation. The results of the model were compared with the experimental data obtained as part of this work and good agreement was observed. The distribution of CO2 concentration inside the feed and permeate chambers was shown and the velocity profile at the membrane surface was also determined using reflection factor for polymeric membrane. The modelling result revealed that increasing the amount of CO2 in gas feed resulted in an increase in the CO2 in the permeate stream while the gas feed pressure increased. By changing the permeability, the model developed by use of the solution–diffusion concept could be used for all polymeric membranes with flat sheet modules.

Investigation of Transient Flow in a Centrifugal Charging Pump during Charging Operating Process

Centrifugal charging pumps are important components of nuclear power plants and must be operated under multioperating conditions for the requirements of the system. In order to investigate the internal flow mechanism of the centrifugal charging pump during the transient transition process of charging operating from Q = 34 m3/h to Q = 110 m3/h, numerical simulation and experiment are implemented in this study. The relationship between flow rate and time is obtained from the experiment and worked as the boundary condition to accurately accomplish the numerical simulation during the transient process. External and internal characteristics under the variable operating conditions are analyzed through the transient simulation. The results show that the liquid viscosity, large scale vortexes exist in the flow passages in the beginning of the variable operating conditions, which indicates flow separation and the sudden changes in direction of velocity. As the flow rate increases gradually, the flow angles of the fluid in inlet accelerate correspondingly and the flow along the blade is more uniform, which leads to a decrease and movements of the vortexes. The contents of the current work can provide references for the design optimization and fluid control of the pump used in the transient process of variable operating conditions.

Agile Turn Control for Air-to-Air Missile Based on Reaction Jet Control System

This paper focuses on agile turn control for air-to-air missile flying in the horizontal plane. The attitude dynamics is discussed and variable structure control (VSC) method for attitude control is analyzed. After analysis of the dynamic function about velocity angle, a staged control method using VSC based on reaction jet control system (RCS) is proposed to achieve fast change of velocity direction and attitude in a short time. The simplex method is used for trajectory optimization. The simulation results show the feasibility of the staged control method which makes the missile turn faster than the situation of attitude control method. The new method demonstrates that RCS is able to control the missile to realize 180°change both for the velocity angle and attitude angle.

Critical flashing flow in convergent–divergent nozzles with initially subcooled liquid

Investigation on critical flashing flow of initially subcooled water in convergent–divergent nozzles is carried out in this paper. A two-dimensional axial symmetric model is developed. In this model, the explosive flashing process immediately downstream the throat is modeled as an oblique evaporation wave, and the velocity direction change of the supersonic flow downstream the oblique evaporation wave is regarded to be resulted by an oblique shock wave. The further fluid expansion in the divergent section is assumed to be in Isentropic Homogeneous Equilibrium (IHE) except near the throat. The results show that the pressure immediately downstream the throat predicted by Abuaf's model is very close to the experimental result, about 4% deviation from Akagawa's tested value. Non-homogeneous equilibrium region exists downstream the oblique evaporation wave near the throat in the divergent section. The length of the non-homogeneous equilibrium region is increased as the inlet subcooled degree is increased. The pressure profile predicted by the model agrees very well with the tested profile of Akagawa except in the non-homogeneous equilibrium region near the throat.

A Flow Characteristic at the Reattachment Region of a Two-Dimensional Backward-Facing Step Flow.

Many experiments have been performed to study the flow structure around the reattachment region of a two-dimensional backward facing step. This flow field has a large-scale vortex structure with low-frequency fluctuation involving one of instantaneous reattachment point. To clarify these structures, in this experiment, time series velocity profile is measured using an advanced multi-point LDV system and behavior of separated shear layer and reattachment phenomena is visualized clearly. A velocity at the vicinity of the step wall increases rapidly when the separated shear layer reached to the step wall passes the measuring region. A frequency of this event is in good agreement with the one of the flapping of the separated shear layer. There are two patterns of when the velocity direction changes from positive to negative on the step wall around a reattachment region.

Velocity Relaxation of Fast Hydrogen Atoms by Collisions with Rare Gases, N2, O2, and N2O

Quenching energetic atoms by elastic and inelastic collisions with surrounding bath gases is one of the fundamental processes taking place in the upper atmosphere and in chemical reactors as well. The energetic atoms are often generated by photodissociation, photoelectron impact dissociation, dissociative recombination, and so forth. Velocity relaxation of fast hydrogen atoms colliding with rare gas atoms, N{sub 2}, O{sub 2}, and N{sub 2}O molecules has been investigated by measuring Doppler broadened H atom spectra. The fast hydrogen atoms were generated by photodissociation of H{sub 2}S at 243.2 nm, and the H atom spectra were measured by two photon absorption laser induced Lyman-{alpha} fluorescence. The H atom spectra show an anisotropic velocity distribution with the anisotropy parameter, {beta} = {minus}1.0 {+-} 0.05, without any colliding gases. Degradation of the anisotropy of the angular distribution was measured as a function of pressure of the colliding gases, He, Ar, Kr, N{sub 2}, O{sub 2}, and N{sub 2}O and the collision cross sections for velocity direction change were measured.

Computational analysis of open loop handwriting movements in Parkinson's disease: A rapid method to detect dopamimetic effects

We used a computational analysis of open loop handwriting movements and a clinical rating scale for monitoring the effect of apomorphine in 16 patients with early untreated parkinsonism [subsequently L-DOPA responsive, probable Parkinson's disease (PD)], six patients with long-standing PD with L-DOPA associated motor fluctuations, and seven patients with known L-DOPA unresponsive parkinsonism. Subjects were instructed to write fluently concentric circles of approximately 12 mm in diameter. Movements were recorded for two periods of 3 s each, using a digitizing tablet. Mean peak velocity (Vmax) and mean peak acceleration (Amax) were determined. In addition, two sensitive indices describing the degree of automation of handwriting were derived: (a) NCV, calculated as the mean Number of Changes in direction of Velocity per half circle, and (b) NCA, the mean Number of Changes in the direction of Acceleration. Clinical rating was performed according to the Unified Parkinson's Disease Rating Scale part III (UPDRS III). After apomorphine injection, the patients with early untreated probable PD showed significant improvement of Vmax, Amax, NCV, NCA, and UPDRS III scores. Likewise, the patients with long-standing PD improved significantly in all kinematic parameters and UPDRS III scores. Patients with L-DOPA unresponsive parkinsonism failed to change significantly in any of the parameters tested. These observations suggest that the computer-assisted analysis of automated handwriting movements can be used as an objective quick method for quantifying dopamimetic effects on the kinematics of handwriting movements in parkinsonian patients.