Analysis Of Transient Flow Research Articles

Analysis of Transient Flow and Inclusion Transport in Vertical-Bending Slab Continuous Caster with Mold Electromagnetic Stirring

Analysis of Transient Flow and Inclusion Transport in Vertical-Bending Slab Continuous Caster with Mold Electromagnetic Stirring

Analysis of Transient Current and Heat Flow during Voltage Holds: For Relaxed and Unrelaxed G/NMC811 Cells

This study investigates the transient heat flow during voltage holds for multi-layer pouch G/NMC811 lithium-ion cells. When applying a voltage hold to estimate the amount of parasitic side reactions, there is first a transient phase followed by a steady state. According to the literature, reversible processes mainly influence the transient phase, while the steady state presents the side reaction current. This work investigates the contributions to the transient behavior, evaluating the thermal and electrical signals and deconvoluting the different parasitic side reactions. In addition, a comparison between relaxed and unrelaxed states is performed, analyzing different temperatures and voltages. The results show that the relaxed graphite cells quickly reached a constant parasitic heat flow value with minimal transient effects. In contrast, the unrelaxed cells presented increased transient effects in the parasitic heat flow signal that can last more than 300 h. The electric transient originates mainly from anode overhang effects and SEI regrowth, while the thermal transient consists predominantly of SEI regrowth. Overall, the thermal signals stabilize faster than the electrical signals, giving calorimetry an advantage for faster estimation of parasitic side reactions.

Stable isotope hydrology of a polymictic lake: Capturing transience of groundwater interactions

Although there have been many studies of groundwater inflow to small lakes, no systematic attention has been paid to the role of the time interval in the reliability of transient flow analysis. We addressed this issue in a two-year study of the isotope hydrology and water budget of a small lake in eastern Washington State (USA) that has been subject to limited management over several decades. The weighted local meteoric water line is δ2H = 7.14 δ18O – 5.22, reflecting the impact of convective recycling in this semi-arid region of inland northwestern North America. Groundwater inflow to the lake was quantified over two years using a short-interval isotopic transient mass balance approach. Calculated inflow was less than a fifth of the lake’s total water budget. Unrealistic temporal fluctuation of the calculated inflow was apparently correlated with fluctuation of the observed isotopic ratio of lake water (δL). We obtained realistic lake fluctuation and groundwater–lake exchange estimates by experimenting with the time interval of the isotope mass balance. It is crucial to acknowledge that each lake possesses unique characteristics that influence hydrologic and isotopic variations. Therefore, the optimal time interval for sampling and calculating mass balance may vary among different small lakes. Our findings have implications for long-term studies with frequent interval sampling.

Determining effective sampling frequencies for transient pressure events in water distribution systems optimal sampling for WDS transients

This study introduces a novel methodology for determining the optimal frequency for pressure data acquisition in water distribution systems (WDSs) in response to transient-flow events such as pipe ruptures. By leveraging actual design and operational data, we simulated potential rupture scenarios and their resultant pressure wave patterns through transient-flow analysis. Harmonic series modeling was used to identify significant periods that closely replicate the observed pressure-wave time series. This allowed the derivation of recommended data acquisition intervals tailored to each monitoring site within the network. The proposed approach facilitates comprehensive analysis of all possible hydraulic shock scenarios, which can provide insights into both the existing monitoring infrastructure and strategic planning in the design phase of the WDS. Although the methodology focuses on rupture events, its application can extend to various water-quality indicators and flow rates, albeit with consideration of their typically static behavior.

Employing the Akbari Ganji Method (AGM) to conduct a semi-analytical analysis of transient Eyring-Powell compressible flow in a tensile Surface under the influence of a magnetic field

This study explores the transfer of mass and heat within unstable two-dimensional flows of non-Newtonian material under conditions involving radiation generation, absorption, and thermal radiation. Additionally, it investigates the impact of magnetic hydromagnetic joule (MHD) heating on these processes. The researchers converted the partial differential equations into ordinary ones through appropriate transformations. Subsequently, a new idea was considered, involving coupling fractional differential equations using the AGM method, with an order of 0.5 < a <0.8 and the initial condition x (0) = x0. A new technique is introduced to find the exact solution of fractional differential equations by solving the correct order differential equations. The primary aim of this paper is to explore the impact of parameter variations on velocity, temperature, local skin friction coefficient, and local Nusselt and Sherwood numbers. This article investigates the effect of multi-parameter changes on local skin friction coefficient and Schmidt number. In most fluid heat transfer problems, especially in non-Newtonian fluids, fractional differential equations are widely used in liquids. The obtained results indicate that the Lorentz force, influenced by the magnetic field parameter (Ha), diminishes the velocity distribution. Additionally, it is observed that the temperature profile decreases as the radiation parameter (R) increases.

Conjugate transient flow and thermal analysis of non-isothermal rubber curing process in autoclave system

Autoclave manufacturing under high pressure and elevated temperature was required to vulcanize the rubber compound applied in the aerospace industry. Nevertheless, few works have comprehensively explored the transient effect of flowing factors on curing efficiency, thermal uniformity, and exergy destruction in autoclave processing. In this study, the three-dimensional model and non-isothermal vulcanization of an autoclave with a built-in combustion chamber were solved by combining the finite volume method and the proposed mixed kinetic model, and exergy destruction was determined to estimate the energy consumption using a direct method. Variations in the Reynolds number (Re), gas pressure (P), temperature, rate of temperature change, and Prandtl number (Pr) were analyzed to improve the unstable thermo-vulcanization and reduce energy consumption in autoclave processing. The results demonstrate that increasing the inlet Re can significantly increase the curing rate while decreasing the temperature difference in the rubber area, and a reduction of 41.89 %−46.62 % for the complete vulcanization time is achieved by changing Re from 105 to 2 × 106; however, adjusting P and temperature has only a minor effect on the heat transfer under constant higher Re. Furthermore, changing the rate of temperature change and Pr is also advantageous for optimizing the curing process and reducing exergy destruction. A minimal non-dimensional exergy destruction rate arises for a given P, rate of temperature change, or Pr when the Re is raised. The knowledge gathered from this research could provide a theoretical foundation for reducing energy consumption and boosting productivity during autoclave curing.

Mathematical Modeling of Transient and Steady-State Groundwater Flow in a Confined Aquifer

Groundwater flow problems can be expressed mathematically with the employ of partial differential equations and which could be solved analytically or numerically. The results obtained showed that the direction of flow of groundwater is from a region of higher hydraulic head to a lower hydraulic head, and that pumping groundwater from the well faster than it is recharged leads to dry wells. The numerical methods used for the analysis of Transient and steady-state groundwater flow produced efficient, effective and accurate solution and can be used for all real-life problems.

Transient flow analysis of pool-type reactor coolant pump under flow coast-down

When power is off, the flow rate of coolant in the RCP decreases rapidly and irregular phenomena appear. However, the inflow coolant tends to be uneven and unsteady due to the design of coolant pool. To simulate the actual situation of pool-type RCP under flow coast-down, Circulation-loop model and Open-border model were established. It provides two prediction methods of the power-off condition of pool-type RCP. The flow rate of Open-border model drops synchronously with rotation speed, and that of Circulation-loop model is dynamically fed back through calculation. Variation trends of external characteristics of the two models are similar. However, it is found that a large-scale and low-speed vortex appears at the horizontal suction part of the pool in Circulation-loop model, blocking the coolant transport channel. Thus, there is obvious fluctuation and hysteretic nature phenomenon in the decline of flow rate compared to the decline of rotation speed in Circulation-loop model.

CFD simulation with analytical verification of discharging of nitrogen and helium from a high-pressure gas vessel

Many applications and industrial processes may necessitate the storage of large amounts of gases at high pressures. These compressed gases could be extremely dangerous if unintentionally released. since they could be poisonous or combustible when mixed with air. This research seeks to create a CFD model and undertake an analytical investigation of the process of de-pressurization of high-pressure gas from a vessel. The vessel to be studied is used in a pneumatic power system used to operate the control surface of a flying vehicle. The study involved two working fluids (nitrogen and helium). The discharging process is considered as a typical mass and heat transfer problem solved analytically by adopting The First Law of Thermodynamics to an unsteady flow control volume and simulated by employing transient flow analysis to the CFD model. The research was carried out on 440 bars (absolute pressure) of pressurized gas vessels. Working gases for the study included nitrogen and helium. Analytical solution results for the two different gases have been compared with the CFD simulation results to assess the CFD model’s accuracy. A good match is achieved when the gas temperature, pressure, density, and outlet mass flow rate variations are compared. The results demonstrated a good match between the CFD and analytical data, proving the validity of the CFD model.

A transient flow analysis method for high-rate mud pulse telemetry in rotary steerable system

With the development of ultra-deep offshore and onshore deep-water wells, there is a growing demand for high-speed data transmission. Mud pulse telemetry (MPT) is the most commercially mature wireless data transmission method. The time-domain parameter analysis of the down-hole mud pulse pressure signal is useful to study the optimization measures of the down-hole signal. Currently, the main approaches are experiment and computational fluid dynamics (CFD) numerical simulations, but both methods are time-consuming and costly, which is not conducive to multi-parameter studies. transient flow modelis widely used to analyze water hammers in pipelines, but its application to mud pulse telemetry (MPT) systems has been less studied. In this paper, based on the classical transient flow equation, the method of characteristics (MOC) is used to solve the governing equation, and the boundary conditions suitable for the MPT are proposed and verified with the experiment and CFD method. Based on the newly established transient flow mathematical model, the generation characteristics of the downhole pressure wave and the influence law of key parameters are studied. The results show that the essence of continuous wave is a three-wave coupling of pressure wave, density wave and flow wave. With the transmission of continuous wave, unsteady friction will be generated in the wave region of the wellbore, increasing the attenuation degree of the signal. The amplitude of continuous wave increases with the increase of density and displacement, independent of frequency and viscosity. However, as the frequency and viscosity increase, the continuous wave will decay faster. This paper provides the new transient flow method with fast computational time and a technical means for MPT studies under subsequent drilling conditions.

A 2D Hydraulic Simulation Model Including Dynamic Piping and Overtopping Dambreach

Numerical simulation of unsteady free surface flows using depth averaged equations that consider the presence of initial discontinuities has been often reported for situations dealing with dam break flow. The usual approach is to assume a sudden removal of the gate at the dam location. Additionally, in order to prevent any kind of dam risk in earthen dams, it is very interesting to include the possibility of a progressive dam breach leading to dam overtopping or dam piping so that predictive hydraulic models benefit the global analysis of the water flow. On the other hand, when considering a realistic large domain with complex topography, a fine spatial discretization is mandatory. Hence, the number of grid cells is usually very large and, therefore, it is necessary to use parallelization techniques for the calculation, with the use of Graphic Processing Units (GPU) being one of the most efficient, due to the leveraging of thousands of processors within a single device. The aim of the present work is to describe an efficient GPU-based 2D shallow water flow solver (RiverFlow2D-GPU) supplied with the formulation of internal boundary conditions to represent dynamic dam failure processes. The results obtained indicate that it is able to develop a transient flow analysis taking into account several scenarios. The efficiency of the model is proven in two complex domains, leading to &gt;76× faster simulations compared with the traditional CPU computation.

Effect of Instantaneous Starting Pump on Fluid Transient Flow in Managed Pressure Cementing

Abstract The fluctuating pressure generated by the instantaneous starting pump of cementing operation might easily cause formation fracture in narrow safety window formations. Accurate transient fluctuating pressure calculation and dynamically managed backpressure are required to achieve precise control of wellbore pressure in managed pressure cementing. Considering the transient flow characteristics of cementing fluids in the wellbore, unsteady transient friction, and the variation of high pressure-high temperature (HTHP) cementing fluid properties, a transient flow mathematical model of instantaneous starting pump during managed pressure cementing is established, and the method of characteristics is used for solution. Based on tht established model analyzes the magnitude and variation of wellbore pressure under different model factors, temperature conditions, pump start duration, and target pump flowrate, which can achieve more accurate analysis of transient flow. The pressure and flow fluctuations generated during the instantaneous starting pump of cementing are significant, and the dynamically managed wellhead backpressure can effectively control the wellbore pressure in the safe pressure window formations. This can reduce the risk of well leakage and provide reliable technical support for safe operations of instantaneous starting pumps during managed pressure cementing.

A Dimension-Reduced Line Element Method for 3D Transient Free Surface Flow in Porous Media

In order to reduce the numerical difficulty of the 3D transient free surface flow problems in porous media, a line element method is proposed by dimension reduction. Different from the classical continuum-based methods, homogeneous permeable pores in the control volume are conceptualized by a 3D orthogonal network of tubes. To obtain the same hydraulic solution with the continuum model, the equivalent formulas of flow velocity, continuity equation and transient free surface boundary are derivable from the principle of flow balance. In the solution space of transient free surface flow, the 3D problem is transformed into 1D condition, and then a finite element algorithm is simply deduced. The greatest advantage of the line element method is line integration instead of volume/surface integration, which has dramatically decreased the integration difficulty across the jump free surface. Through the analysis of transient free surface flow in the unconfined aquifer, trapezoidal dam, sand flume and wells, the transient free surface locations predicted from the proposed line element method generally agree well with the analytical, experimental and other numerical data in the available literatures, the numerical efficiency can also be well guaranteed. Furthermore, the hydraulic anisotropy has significant effect on the evolution of free surface locations and the shape of depression cones in spatial. The line element method can be expanded to model the 3D unsaturated seepage flow, two-phase flow and thermos problems in porous media because of the similarity between the similarity of Darcy’s law, Buckingham Law and Fourier’s law.

Energy analysis of transient flow with cavitation by considering the effect of water temperature in viscoelastic pipes

Abstract Numerous studies on the pressure fluctuations and cavity volume variations of a transient cavitation flow in viscoelastic pipes are available in the literature. However, the effect of water temperature on the cavity volume and energy conversion has been studied less often. This paper employs the discrete vapor cavity model using quasi-steady friction and quasi-two-dimensional friction models to calculate the cavity volume for different water temperatures and investigates the effects of water temperature on the appearance of the first cavitation at the downstream valve, and on the pressure damping in a tank-piping-valve system using an integrated energy analysis approach. The results show that the differences between the pressure and energy variations of the transient cavitation flow simulated using different models were minimal under different water temperature conditions. Moreover, as the water temperature increased, the appearance time of the cavity is postponed, and the volume of the cavity decreases. The energy dissipation increases continuously with an increase in the volume of the cavitation and water temperature in viscoelastic pipes. This study provides valuable insights into the variation pattern of the cavity and the effect of vapor cavities on the rise and decay of the pipeline pressure in different situations.

New design and transient flow analysis of a claw vacuum pump with novel gear-claw rotors

The claw vacuum pump is regarded as the most potential pump type used as the vacuum system due to its remarkable advantages of oil-free, structure compact and high reliability. During operation, serious gas leakage between two conventional claw rotors occurs and then the pump efficiency decreases. With the aim for reducing gas leakage, a novel pair of gear-claw rotors were proposed, in which a new gear-type structure was generated to produce special twisting clearance between two claw rotors for preventing gas leakage, and then a new claw vacuum pump with high comprehensive performance was developed. A geometric model of the gear-claw rotor was established, and the impact of design parameters on the performance of the proposed rotor was analyzed. Furthermore, the transient flow and pressure distribution of the conventional and the proposed claw vacuum pumps were compared by means of numerical simulations. It is found that the volumetric efficiency and gas leakage velocity between two claw rotors in the conventional claw vacuum pump are 69.5% and 347.665 m/s, respectively; while the volumetric efficiency and gas leakage velocity between two gear-claw rotors in the proposed claw vacuum pump are 77.4% and 274.020 m/s, respectively. Compared with conventional claw rotors, the gas leakage velocity between two gear-claw rotors is reduced by 21.18%, and its volumetric efficiency is increased by 7.9%. The efficiency and sealing performance of the proposed gear-claw vacuum pump are significantly superior to those of the conventional claw pump.

Study on water hammer effect and tubing string vibration in high-pressure high-production gas wells

The transient internal flow in high-pressure high-production gas wells generates severe water hammer and tubing string vibration, which accelerates fatigue damage, joint wear, thread loosening, and other wellbore integrity problems. Based on the analysis of transient flow in gas wells, a mathematical model for fluid pressure surge and the induced tubing string vibration is developed and validated by similarity experiments. This method considers fluid-structure interaction, initial loads of tubing string, and compressibility of natural gas, and can fill the gap in quantification of water hammer pressure and tubing sting dynamic load in high-pressure high-production gas wells. On this basis, the effects of valve closure time, production rate, liquid content, and tubing string structure on transient flow and tubing string characteristics are analyzed systematically. The calculations show that wellhead pressure increases rapidly, and pressure wave propagates along tubing string to induce vibrations in the string after an instantaneous shut-in at the wellhead. During this transient process, fluid pressure and axial stress at wellhead reach their maximum valves. Owing to the fixed constraint effect of wellhead and downhole packer, the lack of restrictions on tubing distant from wellhead and packer enhances the severity of axial vibration. As valve closure time increases, the maximum wellhead pressure, tubing vibration displacement, and velocity gradually decrease. Therefore, the most direct way to control water hammer effect and tubing string vibration is to extend the shut-in time or prevent a rapid shut-in of gas well. The methods used in this study and the results obtained therein can serve as both a theoretical framework and practical foundation for the prediction and control of water hammer effect and tubing string vibration in high-pressure high-production gas wells.

Analysis of 3D Transient Flow in a High-Speed Scroll Refrigeration Compressor

In mobile devices such as aircraft and electric vehicles, due to limited space, there are strict requirements on the volume and weight of the compressor mounted on the vehicle. Therefore, high-speed scroll compressors have attracted more and more attention because of their small size and light weight. In this paper, the numerical calculations and analysis of the three-dimensional (3D) transient flows in a high-speed scroll refrigeration compressor were established and validated. Circumferential gas intake was used in the simulation. According to the actual compressor size, the mesh generation accurately considers clearances. The radial and the axial clearances were both set as 0.01 mm. A dynamic and high-quality hexahedral structured mesh was generated for the working chamber, and the problem of insufficient grid density in radial clearance was solved. When the rotational speed was set as 3000 rpm, 6000 rpm, and 9000 rpm alternatively, the difference in the volume efficiency of the simulation and the experiment results was below 6.3%. The results show that the higher rotational speed contributed to the greater pressure fluctuation in the compression chamber and the discharge process, and the over-compression phenomenon was more obvious. The maximum leakage velocity was 160 m/s, and the tangential leakage velocity was higher than the radial leakage velocity. Meanwhile, radial leakage velocity will increase significantly in high-speed operation mode. With the increasing rotational speed, the position of the maximum axial and tangential leakage velocity was closer to the start of the scroll. Therefore, the seal of the scroll starting part is very important in the design of a high-speed scroll compressor.

Nested physics-informed neural network for analysis of transient flows in natural gas pipelines

Natural gas pipeline systems are commonly designed under the assumption of constant supply and demand flow conditions. This is while gas flows are transient because of the compression stations, presence of gas storage facilities and fluctuating supply and consumer demands. Analyzing such transient flows substantially benefits design, control, and monitoring of natural gas pipeline systems. The nonlinear partial differential equations describing the physics of transient flows in pipelines are solved using conventional methods, which are computationally demanding especially for uncertainty quantification purposes where many simulations are required. In this study, we propose an alternative physics-informed neural network (PINN) framework for the transient analysis of pipeline networks that can perform transient flow analysis in natural gas pipelines that the original PINNs cannot solve due to the high complexity of the problem. We propose a nested structure for the PINNs with a loss model that greatly reduces the number of tasks in the emergent complex multi-task learning process. We also integrate an adaptive weights approach that tackles the imbalanced gradients caused by the extremely large coefficients in the equations of the natural gas pipeline problem. The proposed framework, for the first time, can produce accurate results for the complex natural gas pipeline network problem using PINNs. Furthermore, we investigate the parameterization of the nested PINNs as a surrogate model for the natural gas pipeline system. With merely 26% more training costs, the surrogate model can perform the transient flow analysis given thousands of realizations of parameters in a split millisecond, while the costs of performing the same simulations using conventional methods can be prohibitively expensive. This can greatly boost the efficiency of complex many-query analyses such as sensitivity analysis, uncertainty propagation and design optimization.

Effect of blade chord length on startup performance of H-type tidal current turbine rotor

This study aims to reveal the effect of the blade chord length on the startup performance of the lift rotor that converts the kinetic energy of tidal currents. The computational fluid dynamics technique was used to simulate unsteady flows around the rotor. The six degrees of freedom method was adopted to model the correlation between the rotational speed of the rotor and influential torques acting on the rotor. A comparative analysis of transient flows, rotational speed, and output torque was implemented at different initial azimuthal angles. The results show that as the rotor starts up at the minimum torque, the time required to attain the maximum rotational speed is longer than that associated with the maximum torque. As the maximum rotational speed is reached, low-pressure elements are produced in the area enclosed by the rotor blades, which is insensitive to the initial setting angle. A large area of low pressure is responsible for low output torque. During the startup process, the rotational speed experiences stages of sharp increase, fluctuating decrease, and moderate fluctuation, as is common at different blade chord lengths. As the chord length increases from 0.16 to 0.24 m, the startup process is extended by 0.63 s, and the average rotational speed in the stabilization stage decreases.

A comprehensive computer aided approach to design of earthen dams of dry flood-control reservoirs

A generalized, comprehensive approach to geotechnical design of earthen dams of dry flood-control reservoirs is developed. It consists of three steps:•In Step 1 three-dimensional (3D) model of terrain and dam subsoil is created. The arrangement of geotechnical layers is reconstructed based on results of geotechnical investigation using geostatistical interpolation, namely, kriging.•Step 2 involves 3D finite element (FE) analysis of transient groundwater flow through the subsoil. Anti-filtration barrier extent is determined by appropriate parametric analysis and the condition of critical hydraulic gradients is verified.•Step 3 concerns deformation assessment and stability analysis. Computations are carried out for selected cross-sections of the dam. At this stage transient coupled problem of deformation and groundwater flow is considered. Stability is assessed with the use of shear strength reduction technique.The proposed approach enables verification of all relevant conditions of limit states. Furthermore, it has been developed in such a way as to enable computationally efficient analysis of considered phenomena. The method constitutes a general framework of design procedure. It can be easily adapted to conform any standard requirements, e.g., by taking adequate values of partial safety factors. Moreover, design solutions can be optimized through parametric analyzes.