Critical comparison of the different versions of the OpenFOAM on the simulation of spillway

2021 ◽  
pp. 44-57
Author(s):  
Абдикерим Ырысбаевич Курбаналиев ◽  
Бурулгул Рахманбердиевна Ойчуева ◽  
Анипа Ташбаевна Калмурзаева ◽  
Аманбек Жайнакович Жайнаков ◽  
Топчубай Чокоевич Култаев
Keyword(s):  
Mass Flow ◽  
Transient Flow ◽  
Time Derivative ◽  
Numerical Calculations ◽  
Local Dynamic ◽  
Time Step ◽  
Two Phase ◽  
Current Time ◽  
Previous Time ◽  
Previous Time Step

Приведены предварительные результаты численного моделирования двухфазного течения двух несжимаемых и несмешивающихся жидкостей через водослив трапециевидной формы. Целью работы была демонстрация возможностей решателя interFoam различных версий открытого пакета OpenFoam при моделировании рассматриваемого класса течений. Численные расчеты проведены с использованием входящего в состав OpenFoam руководства weirOverFlow. В пакете OpenFOAM6 коэффициент fvcDdtPhiCoeff для вычисления потоков массы на гранях ячеек изменен в целях улучшения устойчивости/точности и исключения осцилляций давления при высоких числах Куранта. Он вычисляется с использованием значений плотности и потока массы с предыдущего временн´ого шага. Результаты численных расчетов показывают, что такие изменения вызывают чрезмерно быстрый переход от нестационарного течения к стационарному. The results of numerical simulation for a two-phase flow of two incompressible and immiscible liquids through a trapezoidal spillway are presented. To simulate the free boundary, we used the method of fluid volume. The aim of the work was to demonstrate the capabilities of the various versions of interFoam solver of the OpenFOAM package for modelling the considered class of flows. Numerical calculations were performed using the OpenFOAM weirOverFlow tutorial. In order to improve the consistency, usability, flexibility and ease of modifying the interFoam solver, the existing interDyMFoam solver with the local dynamic mesh adaptation function was combined with the interFoam solver with a static computational mesh. In addition, in the OpenFOAM6 package, the fvcDdtPhiCoeff coefficient used for calculating the time derivative and taking into account the Rhie- Chow correction on the collocated grid for calculating mass fluxes on the cell faces was changed in order to improve stability/accuracy and eliminate pressure oscillations at high Courant numbers. The calculation of fvcDdtPhiCoeff coefficient in OpenFOAM5 requires the density value from the current time step along with the mass flow value from the previous time step, while in OpenFOAM6, both density and mass flow values are taken from the previous time step for calculation of the fvcDdtPhiCoeff coefficient. The results of numerical calculations of the OpenFOAM6 package show that such changes lead to an excessively fast transition of the transient flow to the stationary one in comparison with other versions of the OpenFOAM package.

Performance Evaluation of Gear Pump by 2D Unsteady CFD Analysis

2013 ◽  
Author(s):  
K. Anil Kumar ◽  
N. Balamuralikrishnan
Keyword(s):  
Mass Flow ◽  
Transient Flow ◽  
Flow Analysis ◽  
Adverse Pressure Gradient ◽  
Implant Design ◽  
Gear Pump ◽  
Time Step ◽  
Design Synthesis ◽  
Angular Velocities ◽  
Rotation Motion

Gas Turbine development activities have been associated with development of different pumps and its allied subsystems used for fuel supply and lubrication oil supply at different engine operating condition. 2D transient flow analysis of a Dual pump has been carried out in an environment with an adverse pressure gradient to map important parameters like pressure, velocity, mass flow and effect of slip. Three achievable close tolerances were selected and carried out the analysis. Finally identified tolerance to be maintained during manufacturing based on the analysis. A moving dynamic mesh concept was adopted because of its capability to facilitate solving transient flow problem and motion of the domain boundaries. A simulated motion control was decided based on the time step, angular velocities of gears rotation motion and coded through a User defined function (UDF) to give angular momentum. Each analysis was carried out for 180 degree of rotation. The main parameter mass flow rate was monitored for different speed and outlet pressures. A validation experimental test was carried out at one rpm thus build up a confidence in implant design synthesis to meet challenges in future.

Parallel Time-Integration of Flexible Multibody Dynamics Based on Newton-Waveform Method

2017 ◽  
Author(s):  
Shilei Han ◽  
Olivier A. Bauchau
Keyword(s):  
Multibody Dynamics ◽  
Time Integration ◽  
Flexible Multibody Dynamics ◽  
Small Scale ◽  
Time Step ◽  
Current Time ◽  
Parallel Time ◽  
Previous Time ◽  
Flexible Multibody ◽  
Multi Body

Traditionally, the time integration algorithms for multibody dynamics are in sequential. The predictions of previous time steps are necessary to get the solutions at current time step. This time-marching character impedes the application of parallel processor implementation. In this paper, the idea of computing a number of time steps concurrently is applied to flexible multi-body dynamics, which makes parallel time-integration possible. In the present method, the solution at the current time step is computed before accurate values at previous time step are available. This method is suitable for small-scale parallel analysis of flexible multibody systems.

A Numerical Study of BWR Steam Separator

2002 ◽  
Author(s):  
Haruo Terasaka ◽  
Sensuke Shimizu
Keyword(s):  
Transient Flow ◽  
Numerical Study ◽  
Fluid Model ◽  
Flow Analysis ◽  
Phase Flow ◽  
Step Size ◽  
Time Step ◽  
Two Phase ◽  
Time Step Size ◽  
Steam Separator

An advanced numerical method based on two-fluid model of two-phase flow has been developed to simulate the swirling gas-liquid flow and the phase separation process in a Boiling Water Reactor separator. The goal is to correctly predict the performance of operating steam separator as well as new designs. The solution method present here is an extension of SIMPLEST scheme, a fully implicit scheme for single-phase flow analysis. It is robust and unconditionally stable, therefore enable us to use very large time step size. This feature is suitable for steady and/or slow transient flow analyses. Furthermore, it enhances numerical stability during rapid transient calculations. By employing this method, separator hydrodynamics around swirler were calculated.

scholarly journals Temporal rainfall disaggregation using a micro-canonical cascade model: possibilities to improve the autocorrelation

2020 ◽  
Vol 24 (1) ◽  
pp. 169-188 ◽  
Author(s):  
Hannes Müller-Thomy
Keyword(s):  
Time Series ◽  
Extreme Event ◽  
Cascade Model ◽  
Special Focus ◽  
Rainfall Time Series ◽  
Lower Saxony ◽  
Step Method ◽  
Time Step ◽  
Previous Time ◽  
Previous Time Step

Abstract. In urban hydrology rainfall time series of high resolution in time are crucial. Such time series with sufficient length can be generated through the disaggregation of daily data with a micro-canonical cascade model. A well-known problem of time series generated in this way is the inadequate representation of the autocorrelation. In this paper two cascade model modifications are analysed regarding their ability to improve the autocorrelation in disaggregated time series with 5 min resolution. Both modifications are based on a state-of-the-art reference cascade model (method A). In the first modification, a position dependency is introduced in the first disaggregation step (method B). In the second modification the position of a wet time step is redefined in addition by taking into account the disaggregated finer time steps of the previous time step instead of the previous time step itself (method C). Both modifications led to an improvement of the autocorrelation, especially the position redefinition (e.g. for lag-1 autocorrelation, relative errors of −3 % (method B) and 1 % (method C) instead of −4 % for method A). To ensure the conservation of a minimum rainfall amount in the wet time steps, the mimicry of a measurement device is simulated after the disaggregation process. Simulated annealing as a post-processing strategy was tested as an alternative as well as an addition to the modifications in methods B and C. For the resampling, a special focus was given to the conservation of the extreme rainfall values. Therefore, a universal extreme event definition was introduced to define extreme events a priori without knowing their occurrence in time or magnitude. The resampling algorithm is capable of improving the autocorrelation, independent of the previously applied cascade model variant (e.g. for lag-1 autocorrelation the relative error of −4 % for method A is reduced to 0.9 %). Also, the improvement of the autocorrelation by the resampling was higher than by the choice of the cascade model modification. The best overall representation of the autocorrelation was achieved by method C in combination with the resampling algorithm. The study was carried out for 24 rain gauges in Lower Saxony, Germany.

A Numerical Simulation of Swirling Two-Phase Flow in BWR Steam-Water Separator and Its Optimization

2003 ◽  
Author(s):  
Haruo Terasaka ◽  
Sensuke Shimizu ◽  
Minoru Kawahara
Keyword(s):  
Transient Flow ◽  
Fluid Model ◽  
Flow Analysis ◽  
Phase Flow ◽  
Step Size ◽  
Time Step ◽  
Two Phase ◽  
Time Step Size ◽  
Fully Implicit ◽  
Water Separator

An advanced numerical method based on the two-fluid model has been developed. The solution method presented here is an extension of the SIMPLEST scheme, a fully implicit scheme for single-phase flow analysis. It is robust and unconditionally stable, and therefore it enables us to use a very large time step size. This feature is suitable for steady and/or slow transient flow analyses. Furthermore, it enhances numerical stability during rapid transient calculations. By using this method, swirling gas-liquid flow in a steam-water separator of Boiling Water Reactors (BWRs) was calculated and the hydrodynamics characteristics were investigated for optimization.

scholarly journals 2P-AGRCFN: Two Phase Attention Gated Recurrent Context Filtering Network for Sequential Recommender Systems

2019 ◽  
Vol 9 (1) ◽  
pp. 3693-3700
Keyword(s):  
Recommender Systems ◽  
Second Phase ◽  
Short Term ◽  
Time Step ◽  
Two Phase ◽  
Current Time ◽  
Sequence Modeling ◽  
Term Dependency ◽  
Hidden States

The recent trends in recommender systems have focused on modeling long-term tastes as well as short-term preferences. The various recurrent architectures have used for sequence modeling in recommender systems, since each state is a combination of current and previous layer output recurrently. Although the Recurrent Neural Networks (RNNs) have the ability for modeling both long-term and short-term dependency to some extent, the monotonic nature of temporal dependency of RNN reduces the effect of short-term interests of the user. Thus final interests of the users can’t be predicted from the hidden states. We propose a Two Phase- Attention Gated Recurrent Context Filtering Network (2P-AGRCF) for dealing with user’s long-term dependency as well as short-term preferences. The first phase of 2P-AGRCFN is performed in the input level by constructing a contextual input using certain number of recent input contexts for handling user’s short-term interests. This can handle the correlation among recent inputs and leads to strong hidden states. In the second phase, the contextual-hidden state is computed by fusing the attention mechanism and the hidden state at current time step, which leads to the effective modeling of overall interest of the user on recommendation. We experiment our model with YooChoose DataSet and it shows efficacy in generating personalized as well as ranked recommendations.

scholarly journals Numerical Fractional-Calculus Model for Two-Phase Flow in Fractured Media

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Wenwen Zhong ◽  
Changpin Li ◽  
Jisheng Kou
Keyword(s):  
Porous Media ◽  
Large Time ◽  
Two Phase Flow ◽  
Time Derivative ◽  
Fractured Porous Media ◽  
Phase Flow ◽  
Petroleum Reservoir ◽  
Time Step ◽  
Two Phase ◽  
Large Time Step

Numerical simulation of two-phase flow in fractured porous media is an important topic in the subsurface flow, environmental problems, and petroleum reservoir engineering. The conventional model does not work well in many cases since it lacks the memory property of fracture media. In this paper, we develop a new numerical formulation with fractional time derivative for two-phase flow in fractured porous media. In the proposed formulation, the different fractional time derivatives are applied to fracture and matrix regions since they have different memory properties. We further develop a two-level time discrete method, which uses a large time step for the pressure and a small time step size for the saturation. The pressure equation is solved implicitly in each large time step, while the saturation is updated by an explicit fractional time scheme in each time substep. Finally, the numerical tests are carried out to demonstrate the effectiveness of the proposed numerical model.

Fast Conjugate Heat Transfer Simulation of Long Transient Flexible Operations Using Adaptive Time Stepping

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
R. Maffulli ◽  
L. He ◽  
P. Stein ◽  
G. Marinescu
Keyword(s):  
Heat Transfer ◽  
Conjugate Heat Transfer ◽  
Time Derivative ◽  
Computational Cost ◽  
Strong Impact ◽  
Time Step ◽  
Time Stepping ◽  
Adaptive Time ◽  
Fully Coupled ◽  
Adaptive Time Stepping

The emerging renewable energy market calls for more advanced prediction tools for turbine transient operations in fast startup/shutdown cycles. Reliable numerical analysis of such transient cycles is complicated by the disparity in time scales of the thermal responses in fluid and solid domains. Obtaining fully coupled time-accurate unsteady conjugate heat transfer (CHT) results under these conditions would require to march in both domains using the time-step dictated by the fluid domain: typically, several orders of magnitude smaller than the one required by the solid. This requirement has strong impact on the computational cost of the simulation as well as being potentially detrimental to the accuracy of the solution due to accumulation of round-off errors in the solid. A novel loosely coupled CHT methodology has been recently proposed, and successfully applied to both natural and forced convection cases that remove these requirements through a source-term based modeling (STM) approach of the physical time derivative terms in the relevant equations. The method has been shown to be numerically stable for very large time steps with adequate accuracy. The present effort is aimed at further exploiting the potential of the methodology through a new adaptive time stepping approach. The proposed method allows for automatic time-step adjustment based on estimating the magnitude of the truncation error of the time discretization. The developed automatic time stepping strategy is applied to natural convection cases under long (2000 s) transients: relevant to the prediction of turbine thermal loads during fast startups/shutdowns. The results of the method are compared with fully coupled unsteady simulations showing comparable accuracy with a significant reduction of the computational costs.

Thermal Characterization of Interlayer Microfluidic Cooling of Three-Dimensional Integrated Circuits With Nonuniform Heat Flux

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Yoon Jo Kim ◽  
Yogendra K. Joshi ◽  
Andrei G. Fedorov ◽  
Young-Joon Lee ◽  
Sung-Kyu Lim
Keyword(s):  
Integrated Circuits ◽  
Mass Flow Rate ◽  
Thermal Management ◽  
Mass Flow ◽  
Flow Rate ◽  
Single Phase ◽  
Hot Spot ◽  
Three Dimensional ◽  
Two Phase ◽  
Two Phase Cooling

It is now widely recognized that the three-dimensional (3D) system integration is a key enabling technology to achieve the performance needs of future microprocessor integrated circuits (ICs). To provide modular thermal management in 3D-stacked ICs, the interlayer microfluidic cooling scheme is adopted and analyzed in this study focusing on a single cooling layer performance. The effects of cooling mode (single-phase versus phase-change) and stack/layer geometry on thermal management performance are quantitatively analyzed, and implications on the through-silicon-via scaling and electrical interconnect congestion are discussed. Also, the thermal and hydraulic performance of several two-phase refrigerants is discussed in comparison with single-phase cooling. The results show that the large internal pressure and the pumping pressure drop are significant limiting factors, along with significant mass flow rate maldistribution due to the presence of hot-spots. Nevertheless, two-phase cooling using R123 and R245ca refrigerants yields superior performance to single-phase cooling for the hot-spot fluxes approaching ∼300 W/cm2. In general, a hybrid cooling scheme with a dedicated approach to the hot-spot thermal management should greatly improve the two-phase cooling system performance and reliability by enabling a cooling-load-matched thermal design and by suppressing the mass flow rate maldistribution within the cooling layer.

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