Flow Law Research Articles

A Non-neutral alternate arc suppression method for single phase grounding fault in active distribution network

To fully compensate reactive and active components of the single line-to-ground (SLG) fault current, additional DC power supply devices are usually used for arc suppression devices. Therefore, the alternate arc suppression method is proposed for the non-neutral multi-function arc suppression device (MF-ASD) in this paper, which can achieve energy self-balance in the MF-ASD during the SLG fault without additional DC power supply devices. Firstly, the DC-link charge–discharge characteristic of the MF-ASD is analyzed under different SLG fault conditions. Then, the alternate arc suppression principle and energy flow law between two non-faulty phases of the MF-ASD are described in detail. Further, the relationship between the alternate period, switching time, and the DC-link voltage are deduced as well. Then, the control parameters are reasonably designed for the DC-link voltage stability of two non-faulty phases of the MF-ASD. Finally, the correctness and feasibility of the proposed method are verified by simulation and experiment results.

Compositional noise in nozzles with dissipation

We propose a physical model to predict indirect noise generated by the acceleration of compositional inhomogeneities in nozzles with viscous dissipation (non-isentropic nozzles). First, we derive the quasi-one-dimensional equations from the conservation laws of multicomponent flows. Second, we validate the proposed model with the experimental data available in the literature for binary mixtures of four gases. Third, we calculate the nozzle transfer functions for different Helmholtz numbers and friction factors, in both subsonic and supersonic flows with/without shock waves. We show that friction and dissipation have a significant effect on the generation of indirect noise, for which the physical mechanism is identified and explained. Fourth, we find a semi-analytical solution with path integrals, which provides an asymptotic expansion with respect to the Helmholtz number. Fifth, we introduce the compositional-noise scaling factor, which is applied to quickly estimate compositional noise from the knowledge of only one single-component gas transfer function. The approximation error is less than $1\,\%$ . The proposed low-order model provides accurate estimates of the transfer functions and physical insight into indirect noise for multicomponent gases. This opens up new possibilities to accurately predict, and understand, sound generation in gas turbines.

The distribution law and coupling factors of debris flows in the G318 Linzhi–Lhasa section of the Sichuan–Tibet traffic corridor

In recent years, debris flow disasters have occurred frequently along the highway, causing river blockages and road interruptions, which seriously threaten the safety of people's lives and property. Highway G318 is an important throat project linking Sichuan and Tibet; at the same time, it is an important channel for the economic development of Sichuan and Tibet and the transportation of national defense materials. Taking the Linzhi–Lhasa Section of Highway G318 as an example, this study analyses the distribution law and characteristics of coupling factors of debris flows in the study area (under its topographical, hydrometeorological, geological, and structural conditions) using remote sensing interpretation, field surveys, and mathematical statistics. The research shows that: (1) The types and quantity of debris flows in the region show statistical laws under the factors of the slope, slope aspect, drainage area, and gradient of the gully. The vegetation coverage in the upper reaches of the Nyang River valley gradually decreases, and the average debris flow disaster density is 0.529/km, which is the most densely distributed area of debris flow. (2) The distribution density of regional debris flows in narrow valleys is greater than that in wide valleys, and those in the Nyang River basin are greater than those in the Lhasa River basin. (3) By comparing the tectonic geological map and the debris flow distribution map, it was found that the debris flow distribution is controlled by faults, and 71% of the debris flow basins have faults. (4) There is a significant positive correlation between the gradient of the material source area and the gradient of the debris flow gully, as well as a close positive correlation between the rainfall and the fault density, and a close negative correlation between the average gradient and the drainage area. Due to the unique topography and geomorphology of different regions, a difference in meteorology and hydrology occurred. This further affected the topography, geomorphology, and distribution of debris flow disasters. Based on the study of the distribution law of regional debris flow and geological environmental factors, this study provides strong support for regional debris flow prevention and related research.

Numerical Simulation of Superheated Steam Flow and Heat Transfer in a Balanced Steam Injection Flow Control Device

Dual-string steam injection pipe is widely used in the production of superheated steam injection in heavy oil horizontal wells. Due to the nonuniform steam injection volume at the heel end and the existence of an interlayer and other factors in the reservoir, the distribution of steam cavity is not uniform, so it is necessary to control the flow of the steam injection well. Based on the basic principles of fluid mechanics and heat transfer, a three-phase nozzle outflow control device model is established in this paper. The steam flow and heat transfer law in the flow control device is numerically simulated, and the outflow dynamic law of horizontal well OCD completion in heavy oil reservoir is obtained. On this basis, the influence of OCD aperture parameters, steam injection pressure, and steam injection velocity on OCD throttling effect is studied. The results show that OCD has a good control effect on balancing pressure drop and improving steam injection uniformity. When the throttle aperture occupies 1/3 of the pipe diameter, the throttle effect is the best and the heat loss is low. Increasing the steam injection pressure can rapidly enhance the pressure reduction rate of the throttle hole. The throttling effect of increasing steam injection volume is not obvious, and the energy loss becomes higher. The study of this paper provides a reference for parameter optimization and prediction of steam distribution in the flow control device of horizontal wells.

A mechanism for transient creep in crustal shear zones

The brittle-to-ductile transition in faults and shear zones marks the change from frictional stick-slip behavior in the seismogenic zone to creep accommodated by plastic mechanisms at higher temperatures. Geodetic observations of slow slip events (SSEs) on plate-boundary shear zones indicate that transient periods of elevated aseismic slip rate occur beneath the seismogenic zone where dislocation creep is likely to be active. SSE duration on the San Andreas fault (California, USA) and major subduction zones decreases systematically with increasing depth and temperature. However, current flow laws for dislocation creep are unable to explain the occurrence of transients similar to SSEs. We develop a microphysical model of dislocation creep that shows how small perturbations in stress (of the order kPa) can lead to strain-rate transients orders of magnitude faster than the background during nominally steady-state flow. The model explains the first-order characteristics of SSEs, reconciling the geophysical observations of deep slow slip events with expectations from experimental rock mechanics. Given that these microphysical mechanisms are general to rock-forming silicate minerals, our results suggest that non-steady-state deformation is inherent to natural shear zones that deform by dislocation creep and that the transition from brittle to steady-state creep occurs over a broad depth range within which transients are predominant.

Ten-kilohertz two-photon microscopy imaging of single-cell dendritic activity and hemodynamics in vivo.

The studying of rapid neuronal signaling across large spatial scales in intact, living brains requires both high temporal resolution and versatility of the measurement device. We introduce a high-speed two-photon microscope based on a custom-built acousto-optic deflector (AOD). This microscope has a maximum line scan frequency of 400kHz and a maximum frame rate of 10,000 frames per second (fps) at . For stepwise magnification from population view to subcellular view with high spatial and temporal resolution, we combined the AOD with resonance-galvo (RS) scanning. With this combinatorial device that supports both large-view navigation and small-view high-speed imaging, we measured dendritic calcium propagation velocity and the velocity of single red blood cells (RBCs). We measured dendritic calcium propagation velocity ( ) in OGB-1-labeled single cortical neurons in mice in vivo. To benchmark the spatial precision and detection sensitivity of measurement in vivo, we also visualized the trajectories of single RBCs and found that their movement speed follows Poiseuille's law of laminar flow. This proof-of-concept methodological development shows that the combination of AOD and RS scanning two-photon microscopy provides both versatility and precision for quantitative analysis of single neuronal activities and hemodynamics in vivo.

Identification of Gas-Water Two-Phase Flow Patterns in Horizontal Wells of Shale Gas Reservoirs Based on Production Logging Data

In order to clarify the gas-water two-phase flow law in horizontal wells and study the gas-water two-phase flow characteristics in horizontal wells, firstly, the gas-water two-phase in a horizontal well is numerically simulated and analyzed, and the flow pattern distribution under different well inclination angles and different phase separation flow rates is obtained. Secondly, a series of production logging instruments including CAT instrument was used to conduct experimental research on gas-water two-phase flow under different flow conditions, and the measured values of each CAT probe were extracted to reflect the local holdup under different flow patterns. Finally, SSA-BP neural network algorithm is used to identify a gas-water two-phase flow pattern in a wellbore by using experimental parameters such as center holdup, well inclination angle, spinner revolution, and CAT probe measurements. The recognition accuracy of the neural network was improved from 83.75% to 91.66%, and the operation speed was accelerated. It provides a research idea to explore the flow characteristics of gas-water two-phase flow in horizontal wells.

Stress analysis and microstructure evolution of Cu/Al composite plate during corrugated rolling

A 3D finite element model was developed. The accuracy of the model was verified through a rolling experiment in which the reduction rate of the plate was 50%. The metal flow law in the rolling process was analyzed from the perspective of time during the whole corrugated rolling process. The deformation experienced by all metal particles is divided into two periods: the filling period and the extension period. The stress change is complex during the filling period, but the stress change trend is approximate during the extension period. The stress state of characteristic positions is two tensile stresses and one compressive stress when the plate starts to deform, which was analyzed by the Lode angle parameter and triaxiality parameter. The microstructure evolution of the Cu plate was analyzed using electron backscatter diffraction (EBSD) technology. Compared with the initial plate, grain refinement occurs at each characteristic position of the Cu plate. There is a phenomenon of grain growth at the trough of the Cu plate after refinement due to the adiabatic temperature increase caused by severe plastic deformation.

Research on energy recovery and gas–liquid separation characteristics in diffuser of Helico-Axial Multiphase Pump

An Euler two-fluid model and a Shear Strain Transports (SST) turbulence model were used to study the gas–liquid flow law in a diffuser of a Helico-Axial Multiphase Pump by building a bedstand in this paper and studied energy recovery and gas–liquid separation characteristics of the diffuser in the Helico-Axial Multiphase Pump at different stages. The results show that the pressurization capacity of an impeller decreases gradually when the increase in IGVF (inlet gas volume fraction), and static pressure drops slightly in a dynamtic–static interface. Energy recovery characteristics are more complex at medium and high IGVF in the diffuser. The pressure gradient change perpendicular to the flow direction is the main factor causing two-phase separation on the back surface of the diffuser. The gas–liquid separation is mainly caused by the pressure gradient difference perpendicular to the flow direction on the working surface of the diffuser under the low IGVF, while the pressure gradient difference in the two directions is jointly influenced by the pressure gradient difference at medium and high IGVF.

Numerical Simulation of Oil-Water Two-phase Conductivity in Hydraulic Fracturing Considering Proppant Crushing

Hydraulic fracturing can effectively increase reservoir productivity, and the effect depends on proppant behavior. Crushing of proppant during fracturing induces a series of changes in fracture width and the pore space formed between proppant particles, affecting reservoir fluid flow. For exploring the flow law of oil and water in proppant fractures, the discrete element method (DEM) and Tavares crushing model were combined to simulate the proppant crush process. At the same time, based on the formed pore space, the flow law of two phase fluid under the influence of such factors as the number of proppant placement, combination of particle size, closing pressure, and particle wettability was studied by fluid volume method(VOF). A series of data obtained through simulation show that with the increase of the average particle radius of single-layer and multilayer proppant is, the fracture conductivity and fracture width increase at the same closure pressure,. In the pore space formed by surface water-wet proppant, the ability of pore to transport oil phase increases; the higher of the number of closure pressure is, the larger the ability of pore to transport oil phase is.

Variability in the Wind Spectrum between 10−2 Hz and 1 Hz

Wind is an abundant, yet intermittent, source of renewable energy, with speeds changing both spatially and temporally over a wide range of time scales. While wind variability is well documented on large meteorological time scales and the behavior of turbulent flow at high frequencies is well understood, there remain questions in the literature regarding the intermediate region of these domains. Understanding wind variability at the microscale, here considering a frequency range of 10−2 Hz < f < 1 Hz, is key for wind turbine control and modeling. In this paper, we quantify the variability of wind conditions for the meteorological tower at the Eolos wind research station in Minnesota using power spectral density analysis. Spectral analysis of wind samples with similar mean wind speeds was conducted to test the hypothesis that the wind spectrum’s shape is independent of the mean wind speed. Historical wind speed data were compared and evaluated to identify diurnal, seasonal, and interannual trends in the spectrum of wind at frequencies above 10−3 Hz. We conclude that the shape of the wind spectrum is independent of the mean wind speed following the Kolmogorov −5/3 law for turbulent flows for incoming wind, with some variations in slope and spectrum magnitude. While no conclusive diurnal, seasonal, or interannual trends were observed, it is shown that some variations in both slope and spectrum magnitude can occur on these time scales.

Low-temperature plastic rheology of granitic feldspar and quartz

Deformation of the Earth's continental crust depends largely on the mechanical properties of quartz and feldspar, including deformation by brittle, semi-brittle, and elastoplastic mechanisms. However, elastoplastic deformation of these mineral phases is difficult to achieve in laboratory experiments at temperatures relevant to the upper crust without high confining pressures to suppress microcracking and macroscopic brittle failure. In this study we use instrumented nanoindentation to determine the plastic yield strength of quartz, and orthoclase and plagioclase feldspars at temperatures of 23–500 °C and at strain rates of ∼10−2 s−1. The specimen investigated here is a medium-grained granite from southwestern Rhode Island, grains of which were characterized and oriented using scanning electron microscopy and electron backscatter diffraction (EBSD). Indentation hardness and modulus of oriented grains was measured directly using a diamond Berkovich nanoindenter; these quantities were then used to calculate yield stresses through several existing theoretical and numerical models. The calculated yield stresses are fit to constitutive flow laws for low-temperature plasticity. We find that, in contrast to most observations from nature, quartz is systematically stronger than both feldspars. The conditions of these experiments are comparable to those near the tips of cracks in the mid to upper crust and the results presented here are particularly relevant to geologic settings where brittle and semi-brittle processes dominate, including aseismic creep of faults.

Co-deposition characteristics of hydrates and sands in gas-salty water-sands flow system

The study of hydrate flow assurance is critical for the efficient and safe development of natural gas hydrates. The natural gas produced by the dissociation of hydrate may re-hydrate in the gathering pipeline, and even lead to the blockage of the gathering pipeline. However, the co-deposition mechanism of the Micron-sized Sand Particles(MSPs) produced in the exploitation, and natural gas hydrate particles during pipeline transportation is still unclear. Therefore, the hydrates and MSPs slurry flow law and co-deposition mechanism are studied by horizontal high-pressure flow loop experiments. A new method to calculate the thickness of the deposition layer for water-dominant systems is proposed. Then, based on the variation of deposition layer thickness, the solid deposition process and flow behaviors are discussed in the pure water system, the salt-containing system, the sand-containing system, and the salt-sand coexistence system, respectively. The results show that the hydrate-MSPs co-deposition process is divided into five stages in the salt-sand coexistence system: the initial deposition stage, hydrate formation and adhesion on the pipe wall stage, rapid deposition stage, deposition layer sloughing stage, and stable deposition stage. And the hydrate-MSPs co-deposits in various stages are characterized by the Hydrate Aggregates Deposition Rate, the Hydrate Aggregates Deposition Layer Thickness, and the particle Chord Length Distribution. The influence of sand particle concentration and initial flow velocity on the hydrate-MSPs co-deposition process in the salt-sand coexistence system is also explored. In addition, the interaction between particles in the deposition process is revealed by Particle Vision and Measurement. The findings of this work provide insights into the solid deposition process in the salt-sand coexistence system, which is beneficial for flow assurance in natural gas hydrate production.

Determination of Hazardous Zone of Coal Spontaneous Combustion in Ultra-Long Working Face Based on the Gob Porosity Evolution and Flow Field Distribution

Coal fire remains one of the main hazards of underground work. Spontaneous coal fires cause serious casualties and property losses. At present, most of the studies on coal spontaneous combustion have been conducted on working faces shorter than 200 m. However, the ultra-long working face gob of shallow buried coal seam is much larger, the distribution of its flow field is more complex, and, thus, risk of spontaneous combustion in the gob is higher. Exploring the evolution law of the gob flow field of ultra-long working face to quickly determine the range of the coal spontaneous combustion hazardous zone is of great significance to the safe production of similar mines. In this study, the gas flow field distribution in the gob of an ultra-long working face was measured by buried pipeline method and oxygen concentration was used as the index. It is found that the oxygen concentration decreases with the advance of the working face. Based on the flow field distribution, the oxidation zone of the gob was determined. Meanwhile, a three-dimensional (3D) numerical model of the working face was established, and the overlying stratum collapse and porosity evolution in the gob were simulated using the particle flow software, PFC3D discrete element software, for the porosity distribution law of the gob. The obtained porosity data were then imported into FLUENT using the custom function UDF to construct a 3D grid model. The flow field distribution in the gob was then numerically simulated for the seepage and migration law of the wind flow in the gob. The results reveal an arch-shaped wind flow field distribution with a swirl shape on the intake airway side. In the strike direction, the wind flow gradually becomes weaker with the advance of the working face. In the dip direction, the wind flow seepage range on the return airway side is obviously higher than that on the intake airway side. In the vertical direction, the wind flow range in the upper gob is larger than that in the middle and lower gob. The spontaneous combustion and oxidation zone of the gob is determined to be at 140.4–313.3 m on the intake airway side, 201.2–351.6 m in the middle of the gob, and 153.2–328.1 m on the return airway side. Finally, the residual coal distribution was superimposed onto the oxygen concentration distribution to obtain the spontaneous residual coal combustion hazardous zone in the gob.

A physically based elasto-viscoplastic constitutive model for modeling the hot deformation and microstructure evolution of a near α Ti alloy

In this work, a general elasto-viscoplastic constitutive model incorporating a finite strain viscoplastic flow law, the Kocks-Mecking dislocation density evolution, work hardening, stress softening due to dynamic recovery and dynamic recrystallization (DRX), and the Johnson-Mehl-Avarmi-Kolmogorov (JMAK) DRX kinetics was established for modeling the deformation and microstructure evolution of a near-α Ti alloy. A full-implicit stress integration scheme was proposed to implement the constitutive model into the commercial FEM solver ABAQUS/Standard. Isothermal hot compression experiments under various deformation conditions and detailed microstructure characterizations were conducted to study the deformation and DRX behaviors of the alloy, as well as to validate the developed material model. The alloy exhibits a typical discontinuous DRX behavior, macroscopically sensitive to various deformation conditions and microscopically strongly affected by the orientation of prior grains. The simulation results regarding the macroscopic flow stress curves and the local volume fractions of DRX in various regions in the specimen agree well with the experimental results. The proposed material model and the robust numerical implemental scheme can be extended to consider more physical deformation mechanisms and microstructure evolution of advanced structural metals and alloys.

Forming Analysis and Heat Treatment of TC31 Titanium Alloy Component with High Ribs and Thin Webs

TC31 is a new type of high-temperature titanium alloy, but few researchers have studied the combination of forming and heat treatment of a component using this material. The component with high ribs and thin webs was studied by numerical simulation and trail production. Based on the establishment of the finite element model, the forming process was analyzed by simulation software, and the maximum forming load of the component was 1920 kN. Ultimately, there were no folding defects of the component during the forming process. The material flow law was revealed by selecting the typical section of the component, and then the forming process was verified and the fully filled component was obtained. After that, the component was subjected to post-processing, and three heat treatment methods were designed to conduct heat treatment experiments on it (heat treatment: solution treatment and aging treatment). By analyzing the influence of three heat treatment methods on mechanical properties, the optimal heat treatment method was obtained, namely a solution treatment at 960 °C for 2.5 h and aging treatment at 610 °C for 7 h. The ultimate tensile strength, yield strength, elongation, and section shrinkage of the component through forging forming and heat treatment are higher than those of original material; meanwhile, it also indicates that the designed heat treatment has a better effect on the high-temperature mechanical properties of this titanium alloy at 650 °C than that at 450 °C. The research on the combination of the forming and heat treatment of this component provides a reference for the engineering application of high-temperature titanium alloys.

Analysis and research on the characteristics of pollutants discharged from the separate storm pump station

The separate storm pump station can reduce the overflow pollution in rainy days and reduce the impact on the water environment. However, before or after rainfall, the impact of the discharge of diversion rainwater pump station on the water environment is still prominent, which has become one of the important reasons restricting the improvement of water environment pollution. This paper investigates the diversion rainwater pump stations in Shanghai, analyzes the discharge flow and pollution law of the diversion rainwater pump stations according to the operation data, and studies the characteristics, causes and effects of discharge pollution. Therefore, to provide support for the pollutant discharge control of the diversion rainwater pump station.

Numerical and experimental investigation of flow characteristics in natural gas pipe

To measure the natural gas flow in the natural gas pipeline, a flow measurement method based on a laser Doppler velocimeter (LDV) is proposed, and the flow field in the natural gas pipeline is accurately measured. The flow laws of the flow field in the pipeline are obtained. In this paper, the influence of the jet flow on the flow field in the main pipe during the injection of tracer particles is analyzed by numerical calculations, and the reliability of the calculation is verified by the LDV test. The results show that the influence of the jet on the flow field in the main pipe weakens rapidly within a short distance, which provides good conditions for measuring the flow in the LDV test pipeline. The error between the flow measured by LDV and the turbine standard device is within 0.47%. Meanwhile, the uncertainty of the LDV measurement test system of a natural gas pipeline is evaluated. The system uncertainty is less than 2%, which satisfies the uncertainty requirements of the metering system, verifying the feasibility of the LDV metering flow and providing a reliable basis for the accurate metering of natural gas.

Simulations of the Rotor-Stator-Cavity Flow in Liquid-Floating Rotor Micro Gyroscope

When rotating at a high speed in a microscale flow field in confined spaces, rotors are subject to a complex flow due to the joint effect of the centrifugal force, hindering of the stationary cavity and the scale effect. In this paper, a rotor-stator-cavity (RSC) microscale flow field simulation model of liquid-floating rotor micro gyroscopes is built, which can be used to study the flow characteristics of fluids in confined spaces with different Reynolds numbers (Re) and gap-to-diameter ratios. The Reynolds stress model (RSM) is applied to solve the Reynolds averaged Navier–Stokes equation for the distribution laws of the mean flow, turbulence statistics and frictional resistance under different working conditions. The results show that as the Re increases, the rotational boundary layer gradually separates from the stationary boundary layer, and the local Re mainly affects the distribution of velocity at the stationary boundary, while the gap-to-diameter ratio mainly affects the distribution of velocity at the rotational boundary. The Reynolds stress is mainly distributed in boundary layers, and the Reynolds normal stress is slightly greater than the Reynolds shear stress. The turbulence is in the state of plane-strain limit. As the Re increases, the frictional resistance coefficient increases. When Re is within 104, the frictional resistance coefficient increases as the gap-to-diameter ratio decreases, while the frictional resistance coefficient drops to the minimum when the Re exceeds 105 and the gap-to-diameter ratio is 0.027. This study can enable a better understanding of the flow characteristics of microscale RSCs under different working conditions.

Energy research of three-adjacent structures connected by Kelvin-type dampers based on power flow

The control effect of a three-adjacent structural system connected by Kelvin-type dampers and its energy transfer and distribution under uncertain and deterministic excitations are investigated in this study. A simplified model of multi-degree-of-freedom mechanics is used for establishing structural equations; the power flow equations of this structural system are derived based on the power flow theory. The influence law of a structural parameter changes on the input power flow when the damper that is not connected is investigated; the damper parameters are optimized using the NSGA-II (Non-dominated Sorting Genetic Algorithm-Ⅱ) algorithm after connecting the dampers, and the damping control effect is evaluated. Next, the variation law of the input power flow of the structure and damper is analyzed with the structure and damper parameters as study variables. These results indicate that an increase in structural stiffness has a positive excitation effect on the seismic performance improvement of the structure; the influence of the structural damping ratio on the input power flow is sufficiently small. The influence of change in damper parameters on the input power flow is closely related to the structural parameter setting. The three-adjacent damping structure system connected to optimal parameter dampers exhibits a good damping performance when the structural parameters are determined.