Model For Transient Analysis Research Articles

A Three-Dimensional Transient Thermal Model for Machining

This article presents an enhanced mathematical model for transient thermal analysis in machining processes. The proposed mathematical model is able to simulate transient tool, workpiece, and chip temperature fields as a function of time for interrupted processes with time varying chip loads such as milling and continuous machining processes such as turning and drilling. A finite difference technique with implicit time discretization is used for the solution of partial differential equations to simulate the temperature fields on the tool, workpiece, and chip. The model validations are performed with the experimental temperature measurement data available in the literature for the interrupted turning of Ti6Al6V–2Sn, Al2024, gray cast iron and for the milling of Ti6Al4V. The simulation results and experimental measurements agree well. With the newly introduced modeling approach, it is demonstrated that time-dependent dynamic variations of the temperature fields are predicted with maximum 12% difference in the validated cases by the proposed transient thermal model.

A quasi-transient model of a transcritical carbon dioxide direct-expansion ground source heat pump for space and water heating

In this study, a theoretical quasi-transient model is developed for detailed simulations of a carbon dioxide (CO2) direct-expansion ground source heat pump (DX-GSHP). This model combines a transient analytical model for the ground, steady-state numerical models for the borehole and the gas cooler, as well as several thermodynamic models for the remaining components of a conventional heat pump, organized in interacting subroutines to form a powerful simulation tool. Extensive validation combining experimental data and CFD-generated results was performed for the borehole before the tool was used to simulate a practical application case.Performance is investigated for a system satisfying both space heating and domestic hot water requirements of a typical single family detached home in a cold climate region. The variation of different system parameters is also evaluated in this study. It is shown that CO2 DX-GSHPs can offer relatively efficient and stable performance for integrated water and space heating applications. Furthermore, the importance of an accurate geothermal borehole sizing is highlighted for the DX-CO2 heat pump systems. It is shown that, due to changes in the system working conditions, the total borehole length is not linearly correlated with the heat pump energy consumption and other parameters such as heat pump coefficient of performance and pressure drop in ground heat exchangers. Results showed that increasing the total borehole length of an optimum design (reference case study) by 25% decreases the total annual energy consumption by only 6%. However, reducing total borehole length of the reference case by 25% increases the total annual energy consumption by 10%.

Impact of Static VAR Compensator in Stability and Harmonics Mitigation for Real Time System with Cogeneration

Main objective of the paper is to study the impact of SVC on stability and enhancing the power quality for a real time industrial system. Modified RK method is used for transient stability analysis and detailed frequency modeling is used for harmonic analysis. Real time system of 3.5 MTPA Steel plant at Raichur in Karnaraka, India with Electric Arc Furnace and Laddle Refining Furnace are considered for study. ETAP 12.6 software is used to simulate both transients and harmonic analysis. Harmonic study is performed with sinusoidal source non linear loads and Non sinusioidal source non linear loads. SVC performance when the non sinusoidal source is also verified to have the practical meaning. For Transient stability enhancement the controller tuning fault at 11V and 33KV bus is verified.

Estimating reliable gas rate with transient-temperature modeling for interpreting early-time cleanup data during transient testing

Abstract In drillstem testing (DST), analyses of transient data are generally restricted to the post-cleanup period because rates often go unmonitored at early times during the cleanup phase, unless aided by multiphase flow metering. The value of early-time production data monitoring may be overlooked for two reasons: first, transients may be difficult to interpret because of two-phase flow in the formation; second, two-phase flow metering becomes a requirement. The objective of this study is two-fold: to estimate rate from multipoint-temperature sensor (MTS) data available for downhole telemetry with a rigorous transient analytical model, and to show the possible use of the computed rates to perform transient analysis for both the pre- and post-cleanup periods. Comparing and contrasting permeability estimates from the two periods provides guidance on the suitability of this approach. To that end, this study compares and contrasts rate computation with analytical methods. The new methods entail transient-temperature modeling with and without superposition effects. Two field examples strengthened the new rate-computation methods introduced here, and simulated examples probed the possibility of extracting meaningful information from the cleanup data.

Lumped models for transient thermal analysis of multilayered composite pipeline with active heating

In this study, improved lumped parameter models were proposed for transient thermal analysis of multilayered composite pipeline with active heating, which is essential for flow assurance design and operating strategies of deepwater subsea pipelines. Improved lumped models for transient heat conduction in multilayered composite pipelines were based on two-points Hermite approximations for integrals. The transient energy equation for the bulk temperature of the produced fluid was transformed into a set of ordinary differential equations in time by using a finite difference method. The coupled system of ordinary differential equations for average temperatures in the solids and bulk temperature of the fluid at each longitudinal discretization point along the pipeline was solved by using an ODE solver. With the proposed method, we analyzed the transient heat transfer in stainless steel-polypropylene-stainless steel sandwich pipes (SP) with active electrical heating. Convergence behaviors of the average temperature of each layer and the bulk temperature of the produced fluid calculated by using the improved lumped models (H0,0/H1,1 and H1,1/H1,1 approximations) against the number of grid points along the pipelines were presented. Case studies were performed to investigate the effect of the linear rate of power input and the average velocity on the bulk temperature distribution of the produced fluid.

Development of a New Superconducting Generator Model for Power System Transient Analysis with XTAP

Superconducting generators (SCGs) are considered to bring many advantages to electric power grids such as high generation efficiency, improvement of power quality, capability to enhance power system stability, and so on. In order to investigate these benefits in the conditions similar to those of a real power system, electromagnetic transient (EMT) analysis in three-phase instantaneous values is very useful. In this study, a new SCG model for power system transient analysis has been developed with an EMT software named Expandable Transient Analysis Program. Novelty of the newly developed model is in the calculation procedure using a two-stage diagonally implicit Runge-Kutta method and a second-order Runge-Kutta method (RK2). The proposed method enabled us to interface the SCG model with the outer power system without prediction or delay. The method is considered to enhance the numerical stability of transient analyses including SCGs by explicitly limiting the integral calculation errors through the use of RK2. It was confirmed that the developed model is useful to EMT analysis including SCGs.

동시 이중주파수를 이용한 기어 열처리의 열·전자기 연성 해석

In this paper, Finite Element Analysis (FEA) for gear heat treatment using simultaneous dual frequency (SDF) induction heating is conducted. To do this, thermal-electromagnetic coupled FE model is built. A two dimensional FE model of gear and heater is introduced to reduce computation time. For more time-efficient analysis, harmonic analysis for electromagnetic model is adopted and transient analysis model, for heat transfer model. Through the coupled analysis, it can be found that the proposed FE model can solve for SDF induction heating of gear and heat treatment parameters can also be determined.

SPICE model implementation of quantum phase‐slip junctions

Quantum phase-slips, which are the exact duals of Josephson junctions (JJs), are promising for several applications in classical and quantum superconducting electronic circuits. The experimental testing of the phase-slip phenomena and identifying these applications has been challenging. In this reported work, the use of a dual to a JJ model to implement a SPICE model of a quantum phase-slip junction (QPSJ) in JSPICE3, in order to explore possible circuit applications, is demonstrated. A transient analysis model of the device is presented and an example of an I–V curve simulation of the device, along with a simulation of a possible circuit application of the device, are also shown.

A quadruple-porosity model for transient production analysis of multiple-fractured horizontal wells in shale gas reservoirs

Multiple types of pores are present in shale gas reservoirs, including organic pores of nano scale, non-organic pores, natural and hydraulic fractures. Gas flow in different types of pores is controlled by different mechanisms, and Darcy’s law is not able to describe all these processes adequately. This paper presents a “quadruple-porosity” model and corresponding analytical solutions to describe the different permeable media and simulate transient production behavior of multiple-fractured horizontal wells in shale gas reservoirs. Dimensionless transient production decline curves are plotted, and characteristic bilinear flow and linear flow periods are identified based on the analysis of type curves. Sensitivity analysis of transient production dynamics suggests that desorption of absorbed gas, Knudsen diffusive flow, gas slippage and parameters related to hydraulic fractures have significant influence on the production dynamics of a multiple-fractured horizontal well in shale gas reservoirs. The model provides insights into multiple shale gas flow mechanisms and production prediction of shale gas reservoirs.

Unified fluid flow model for pressure transient analysis in naturally fractured media

Naturally fractured reservoirs present special challenges for flow modeling with regards to their internal geometrical structure. The shape and distribution of matrix porous blocks and the geometry of fractures play key roles in the formulation of transient interporosity flow models. Although these models have been formulated for several typical geometries of the fracture networks, they appeared to be very dissimilar for different shapes of matrix blocks, and their analysis presents many technical challenges. The aim of this paper is to derive and analyze a unified approach to transient interporosity flow models for slightly compressible fluids that can be used for any matrix geometry and fracture network. A unified fractional differential transient interporosity flow model is derived using asymptotic analysis for singularly perturbed problems with small parameters arising from the assumption of a much smaller permeability of the matrix blocks compared to that of the fractures. This methodology allowed us to unify existing transient interporosity flow models formulated for different shapes of matrix blocks including bounded matrix blocks, unbounded matrix cylinders with any orthogonal crossection, and matrix slabs. The model is formulated using a fractional order diffusion equation for fluid pressure that involves Caputo derivative of order 1/2 with respect to time. Analysis of the unified fractional derivative model revealed that the surface area-to-volume ratio is the key parameter in the description of the flow through naturally fractured media. Expressions of this parameter are presented for matrix blocks of the same geometrical shape as well as combinations of different shapes with constant and random sizes. Numerical comparisons between the predictions of the unified model and those obtained from existing transient interporosity ones for matrix blocks in the form of slabs, spheres and cylinders are presented for linear, radial and spherical flow types for both fixed boundary pressure and rate.

Effect of flow mechanism with multi-nonlinearity on production of shale gas

Different from oil reservoirs, variations of gas properties (such as viscosity, Z-factor and gas compressibility) under different pressures is strongly nonlinear and non-Darcy effect is significant in fractures due to high rate. Shale gas reservoirs are extremely tight with nanopores, where Darcy's law breaks down and the flow behavior is significantly influenced by pore scale and pressure. 20%–80% of the shale gas in place (in-situ) is adsorbed to organic matters and the desorption is a nonlinear process varying with pressure. Furthermore, hydraulic fractures and natural fractures close gradually, as the production proceeds, resulting in a non-linear relationship between permeability and pressure. However, the multi-nonlinear flow mechanism, as well as its effect on gas production, in the process of shale gas development is always overlooked by both laboratories and industrial analyses.Based on the five-region model, finite difference method is applied to get numerical solution in this paper. Afterwards, the effect of nonlinear mechanism on production is analyzed, according to which, the enhanced ultimate recovery (EUR) schemes are proposed. The results show that the effects of compressibility, multi-scale flow, stress sensitivity and non-Darcy flow in fractures on production are significant during early stage and should be considered in well testing model. For middle and late production stages, the effects of compressibility, multi-scale flow, stress sensitivity in natural fractures should be considered in the Rate Transient Analysis (RTA) model and long-term production prediction model. The negative effect of stress sensitivity and non-Darcy flow can be reduced or mitigated by optimizing schedule and controlling early pressure drawdown. Furthermore, some nonlinear factors can be used positively by refracturing, which reduces formation pressure and consequently leading to the increase of gas compressibility, desorption compressibility and apparent permeability.

Detailed PVT-water model for transient analysis using RC networks

A new detailed transient model for PVT-water collectors is presented. The model uses a nodal approach based on the electrical–thermal analogy using RC networks to model the thermal response of the PVT collector. Unlike models found in the literature, the RC network is directly used to simulate the PVT collector in an electronic circuit simulator. Heat flow is modelled in one dimension only and average temperatures are used for the fluid and absorber plate in order to calculate the transient thermal output of the collector. A discussion on the correct calculation of the average temperatures for the collector and possible approximations is presented. The model was used to simulate a PVT collector coupled to a domestic hot water load, in order to study the daily performance of a PVT-water system and its transient behaviour. Results show that the proposed solution can achieve extremely good agreement with experimental data, and that the model could be used for performance analysis and product design.

Numerical simulation of side heating for controlling angular distortion in multipass MMAW butt welded plates

Distortion is a severe problem in weld products. It depends on various process parameters like plate thickness, current, voltage, type of weld joint and restraints put on. If distortion is not properly dealt during welding then the product may become useless from geometric accuracy point of view. In the present study, a 3-D coupled transient thermal analysis model with auxiliary side heating (parallel heating) is developed to control angular distortion. During analysis, parallel heating flames are placed at several locations from weld line in cross direction. A user defined subroutine is used to apply transient heat source and side heating flames. Element birth and death technique is used to simulate the filler material deposition. One side multipass ‘V’ butt weld configuration is used for this study. A series of observational tests are done with a special experimental fixture using Manual Metal Arc Welding (MMAW) to validate the proposed FEA model. It is found that the angular distortion has decreased from 2 mm to 0.4 mm with change in side heating distance from 50 to 90 mm from the weld line.

Performance analysis of an earth-to-air heat exchanger assisted by a wind tower for passive cooling of buildings in arid and hot climate

In this paper, a new design of passive cooling system which consists in an Earth-to-Air Heat Exchanger (EAHE) assisted by a wind tower is presented. This system is intended for the summer cooling in hot and arid regions of Algeria. A transient analytical model was developed in order to investigate the influence of design parameters on the performance of the EAHE. The model of the EAHE is validated against both theoretical and experimental data carried out by other authors. Since it is well-known that the performance of the EAHE systems is more influenced by the air flow velocity, another model was presented to predict the air velocity inside the buried pipe. Moreover, a burying depth of 2m was adopted and the period under consideration is July where the ambient temperature exceeds 45°C. This study was also extended to examine the behaviour of system during the whole year.In addition, a sensitivity survey was curried out to investigate the influence of tower and pipe dimensions on the air flow velocity and the performances of the EAHE. Results showed that the wind tower dimensions (height, cross section) have not an important impact compared to the pipe dimensions (length, diameter). It is found that a tower with a total height of 5.1m and a cross section area of 0.57m2 can generate an air flow rate of 592.61m3/h. Furthermore, it has been also observed that the daily cooling potential reached a maximum of 30.7kWh corresponding to a pipe length of 70m.The cooling effectiveness of the system is compared to that of traditional passive cooling system consisting in a wind tower with wet surfaces. The results indicated that the ambient air after passing through the wind tower coupled to the EAHE is colder than of that of the leaving the conventional cooling tower.

Transient pressure analysis and interpretation for analytical composite model of CO2 flooding

Abstract This work deals with the inverse problems of parameters estimation for mass transfer during CO 2 injection in oil reservoir. Such method is based on well testing theory which monitors reservoir dynamic performance through transient pressure. In this paper, considering the skin and storage effect of well, three-region composite transient pressure analysis model for CO 2 flooding is established by introducing pseudo pressure for real gas, and then non-dimensional transport equations for each region are derived and solved analytically by the method of Laplace transformation. According to the type curves of the model pressure, fluid flowing in reservoir can be divided into seven stages, and the flowing factors׳ effect on curve shape is discussed too. Then relevant parameters during mass transferring can be achieved by type curve matching field testing data. We also provide a new method for parameter matching during testing data interpretation through feature points׳ analysis, which facilitates the matching process and reduces ambiguity of parameters estimation.

Two-phase pressure transient analysis for multi-stage fractured horizontal well in shale gas reservoirs

Most researches on shale gas production and pressure transient analysis placed more emphasis on single-phase flow, the two-phase flow caused by flowback after hydrofracture in shale gas reservoirs does not attract much attention. This paper presents a two-phase pressure transient analysis model of multi-stage fractured horizontal well with the consideration of wellbore storage, skin effect, two-phase saturation, hydraulic fractures parameters and desorption characteristics of shale gas reservoirs. Accurate solution to this flow model is obtained by the use of source function theory, Laplace transform, three-dimensional eigenvalue method and orthogonal transformation. Pseudo-pressure and pseudo-pressure derivative type curve is plotted by using the Stehfest algorithm. Seven different flow regimes have been identified and the effects of influence factors such as initial saturation, skin factor, absorption index, fracture stages, horizontal well lateral length and wellbore storage coefficient have also been discussed. The presents research could be used to interpret the pressure behavior more accurately and effectively of shale gas reservoirs.

Transient Analytical Model of a Solar-Assisted Indoor Swimming Pool Heating System

AbstractThis study deals with the thermal performance of a solar-assisted heating system for the Jordan University of Science and Technology indoor Olympic swimming pool. Solar heating is accomplished by using hot water generated by heat exchange with the solar evacuated tube collector working fluid. A transient analytical approach has been adopted for developing an explicit expression for the pool temperature, including all thermal losses. Detailed computations have been made from the beginning of September until the end of May. The effect of relevant parameters such as collector area, heat removal factors, collector heat loss coefficient, and evaporation losses on the performance of the proposed systems is investigated. The effect of covering the pool has been manifested in the analysis to reduce heat losses. The percentage of primary energy savings is used to measure the performance of the system. It is found that using a collector area equal to 53% of the pool surface results in 100% savings in primar...

Power-Line Communication Channel Characteristics Under Transient Model

This paper discusses the channel gain characteristics of a two-conductor power-line communication system under a given transient analytical model. The channel frequency responses are derived with different transmission-line lengths and terminal loads. Compared with previous works on power-line communication, the transient model can more accurately describe the variation of the channel frequency responses, especially when transients occur on the transmission line. Simulation results show higher accuracy is achieved compared with the results under the traditional lumped-circuit π model.

Implementation of time domain transformer winding models for fast transient analysis using Simulink

To date, programs available for the simulation of electromagnetic transients in power components and networks do not include transformer winding models able to simulate an impulse test response. This is an important omission, since the standard impulse test defines for most cases the highest dielectric stress that a power transformer will suffer once installed. In this work, two transformer winding models for fast transient analysis are implemented in Simulink: a lumped parameter model based on state-space equations and a distributed parameter model based on multiconductor transmission line theory and Bergeron’s method. A test case consisting of a 286 turns winding is provided to demonstrate the performance of the models implemented. Both models are applied to the computation of the transient voltage along the turns of the transformer winding considering lossless case and including series losses.

English

Pipelines are principal devices for natural gas transportation which are amenable to operational challenges such as leakages. Several methods for predicting leakages in natural gas pipeline have been developed. Some of these techniques detect leakages after several hours while some are prone to false alarms or inaccurate predictions. This study developed a pressure transient analysis model for predicting gas pipeline leakages in real time. The method of characteristics was employed to solve the resultant non-linear gas flow equations without neglecting the inertia term as in previous studies. The system behaviour was simulated after discretizing the pipe length and the differences between observed and calculated variables were used to predict single and multiple leakages. Results were validated using field data.   Key words: Pipeline leakages, natural gas, pressure transient, analytical method, method of characteristics.