Journal articles on the topic 'Method of characteristics (MOC)'
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1
Moghanloo, R. Ghanbarnezhad, and F. Javadpour. "Applying Method of Characteristics to Determine Pressure Distribution in 1D Shale-Gas Samples." SPE Journal 19, no. 03 (December 31, 2013): 361–72. http://dx.doi.org/10.2118/168218-pa.
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Summary This paper examines application of the method of characteristics (MOC) to determine pressure distribution in a 1D matrix of shale gas. Because of gas expansion and local desorption in shale gas, pressure distribution changes during production. We developed a semianalytic MOC solution of gas flow in shale by use of the analogous-continuum approximation (apparent permeability). The MOC solution is derived with the inclusion of compressibility, gas-slippage effect, and desorption. Through quantitative comparison of pressure profiles and history plots, we used a simulation approach to verify the accuracy of the analytic solution. Results suggest that the simulation results are consistent with our MOC solution, which can also be used to evaluate impacts of different parameters on pressure distribution. Prediction of pressure distribution over time will greatly enhance approximation of reservoir performance.
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Nie, Yafei, Kai Fu, and Xianqing Lv. "CIP Method of Characteristics for the Solution of Tide Wave Equations." Advances in Mathematical Physics 2018 (July 2, 2018): 1–10. http://dx.doi.org/10.1155/2018/3469534.
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The CIP-MOC (Constrained Interpolation Profile/Method of Characteristics) is proposed to solve the tide wave equations with large time step size. The bottom topography and bottom friction, which are very important factor for the tidal wave model, are included to the equation of Riemann invariants as the source term. Numerical experiments demonstrate the good performance of the scheme. Compared to traditional semi-implicit (SI) finite difference scheme which is widely used in tidal wave simulation, CIP-MOC has better stability in simulating large gradient water surface change and has the ability to use much longer time step size under the premise of maintaining accuracy. Besides, numerical tests with reflective boundary conditions are carried out by CIP-MOC with large time step size and good results are obtained.
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Jayamani, Ananthkumar, and Frank K. Lu. "Method-of-characteristics model for a low-enthalpy, detonation-driven shock tube." Physics of Fluids 34, no. 6 (June 2022): 066109. http://dx.doi.org/10.1063/5.0093888.
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A reduced-order model for a detonation-driven shock tube was developed using the method of characteristics (MoC). The scope of this work was limited to calorically perfect slugs of gases. Effects of momentum and heat losses were included. The governing equations for inviscid, one-dimensional flow of a calorically perfect gas were simplified using MoC. These simplified equations represented and resolved various gasdynamic phenomena such as weak compressions, rarefactions, shocks, and contact surfaces. The momentum losses in the governing equations were estimated using established friction factors. Various empirical methods were explored to determine an appropriate heat-transfer model. Based on the expected ideal wave processes in a detonation-driven shock tube, MoC subroutines were assembled into a global algorithm representing detonation tube operation. To validate the results from the reduced-order model, experiments were carried out in a small-scale detonation tube. The experiments used nitrogen as the high-pressure driver gas, stoichiometric oxyhydrogen as the detonation driver gas, and nitrogen or helium as the driven gas. Comparison with experiments showed that the detonation tube model reasonably replicated detonation tube operation for all the experimental cases. Specifically, the decaying incident shock trajectory in the driven section was replicated well, and so was the peak pressure at the driven end wall. The quasisteady plateau pressure in the detonation driver was replicated reasonably, with experimental pressure traces showing earlier decay than MoC pressure traces. The wave system produced by the reflected shock wave–contact surface interaction in the driven section was also predicted accurately by the MoC model.
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Wu, Wenbin, Yingrui Yu, Qi Luo, Dong Yao, Qing Li, and Xiaoming Chai. "Matrix MOC: The method of characteristics in matrix form." Progress in Nuclear Energy 125 (July 2020): 103378. http://dx.doi.org/10.1016/j.pnucene.2020.103378.
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Ahmadi, Kaveh, Russell T. Johns, Kristian Mogensen, and Rashed Noman. "Limitations of Current Method-of-Characteristics (MOC) Methods Using Shock-Jump Approximations To Predict MMPs for Complex Gas/Oil Displacements." SPE Journal 16, no. 04 (October 25, 2011): 743–50. http://dx.doi.org/10.2118/129709-pa.
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Summary An accurate minimum miscibility pressure (MMP) is one of the key factors in miscible-gasflood design. There is a variety of experimental and analytical methods to determine the MMP, but the most-reliable methods are slimtube experiments, 1D slimtube simulations, mixing-cell models, and the fast key-tie-line approach using the method of characteristics (MOC). Direct comparisons of all these methods generally agree well, but there are cases in which they do not. No explanation has yet been given for these anomalies, although the MMP is critically important to recovery. The focus of this paper is to explain when current MOC results assuming that shocks exist from one key tie line to the next may not be reliable, and how to identify when this is the case. We demonstrate, using fluid characterizations from Middle East oils, that the MMPs using this MOC method can be more than 6,500 psia greater than those calculated using a recently developed mixing-cell method. The observed differences in the MMP increase substantially as the API gravity of the oil decreases, likely the result of the onset of L1-L2-V behavior. We show that the key tie lines determined using this MOC method do not control miscibility for such cases. We explain the reasons for these differences using simplified pseudoternary models and show how to determine when an error exists. We also offer a way to correct the MMP predictions using the MOC for these complex gas/oil displacements without solving for the complete compositional path.
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Namdar Zanganeh, M., S. I. I. Kam, T. C. C. LaForce, and W. R. R. Rossen. "The Method of Characteristics Applied to Oil Displacement by Foam." SPE Journal 16, no. 01 (August 19, 2010): 8–23. http://dx.doi.org/10.2118/121580-pa.
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Summary Solutions obtained by the method of characteristics (MOC) provide key insights into complex foam enhanced-oil-recovery (EOR) displacements and the simulators that represent them. Most applications of the MOC to foam have excluded oil. We extend the MOC to foam flow with oil, where foam is weakened or destroyed by oil saturations above a critical oil saturation and/or weakened or destroyed at low water saturations, as seen in experiments and represented in foam simulators. Simulators account for the effects of oil and capillary pressure on foam using algorithms that bring foam strength to zero as a function of oil or water saturation, respectively. Different simulators use different algorithms to accomplish this. We examine SAG (surfactant-alternating-gas) and continuous foam-flood (coinjection of gas and surfactant solution) processes in one dimension, using both the MOC and numerical simulation. We find that the way simulators express the negative effect of oil or water saturation on foam can have a large effect on the calculated nature of the displacement. For instance, for gas injection in a SAG process, if foam collapses at the injection point because of infinite capillary pressure, foam has almost no effect on the displacement in the cases examined here. On the other hand, if foam maintains finite strength at the injection point in the gas-injection cycle of a SAG process, displacement leads to implied success in several cases. However, successful mobility control is always possible with continuous foam flood if the initial oil saturation in the reservoir is below the critical oil saturation above which foam collapses. The resulting displacements can be complex. One may observe, for instance, foam propagation predicted at residual water saturation, with zero flow of water. In other cases, the displacement jumps in a shock past the entire range of conditions in which foam forms. We examine the sensitivity of the displacement to initial oil and water saturations in the reservoir, the foam quality, the functional forms used to express foam sensitivity to oil and water saturations, and linear and nonlinear relative permeability models.
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Li, Jin, Yunlin Xu, Dean Wang, Qicang Shen, Brendan Kochunas, and Thomas Downar. "DEMONSTRATION OF A LINEAR PROLONGATION CMFD METHOD ON MOC." EPJ Web of Conferences 247 (2021): 03006. http://dx.doi.org/10.1051/epjconf/202124703006.
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Coarse Mesh Finite Difference (CMFD) method is a very effective method to accelerate the iterations for neutron transport calculation. But it can degrade and even fail when the optical thickness of the mesh becomes large. Therefore several methods, including partial current-based CMFD (pCMFD) and optimally diffusive CMFD (odCMFD), have been proposed to stabilize the conventional CMFD method. Recently, a category of “higherorder” prolongation CMFD (hpCMFD) methods was proposed to use both the local and neighboring coarse mesh fluxes to update the fine cell flux, which can solve the fine cell scalar flux discontinuity problem between the fine cells at the bounary of the coarse mesh. One of the hpCMFD methods, refered as lpCMFD, was proposed to use a linear prolongation to update the fine cell scalar fluxes. Method of Characteristics (MOC) is a very popular method to solve neutron transport equations. In this paper, lpCMFD is applied on the MOC code MPACT for a variety of fine meshes. A track-based centroids calculation method is introduced to find the centroids coordinates for random shapes of fine cells. And the numerical results of a 2D C5G7 problem are provided to demonstrate the stability and efficiency of lpCMFD method on MOC. It shows that lpCMFD can stabilize the CMFD iterations in MOC method effectively and lpCMFD method performs better than odCMFD on reducing the outer MOC iterations.
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Asli, Kaveh Hariri, Faig Bakhman Ogli Naghiyev, Soltan Ali Ogli Aliyev, and Hoosein Hariri Asli. "Modeling of Fluid Interaction Produced by Water Hammer." International Journal of Chemoinformatics and Chemical Engineering 1, no. 1 (January 2011): 29–41. http://dx.doi.org/10.4018/ijcce.2011010103.
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This paper compares the computational performance of two numerical methods for two models of Transient Flow. One model was defined by method of the Eulerian based expressed in a method of characteristics “MOC”, finite difference form. The other model was defined by method of Regression. Each method was encoded into an existing hydraulic simulation model. Results indicated that the accuracy of the methods was comparable but that the “MOC” was more computationally efficient for analysis of large water transmission line. Practical investigations in this article have shown mainly this tendency.
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Su, Lijuan, and Pei Cheng. "A High-Accuracy MOC/FD Method for Solving Fractional Advection-Diffusion Equations." Journal of Applied Mathematics 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/648595.
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Fractional-order diffusion equations are viewed as generalizations of classical diffusion equations, treating super-diffusive flow processes. In this paper, in order to solve the fractional advection-diffusion equation, the fractional characteristic finite difference method is presented, which is based on the method of characteristics (MOC) and fractional finite difference (FD) procedures. The stability, consistency, convergence, and error estimate of the method are obtained. An example is also given to illustrate the applicability of theoretical results.
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Wu, Juan, Hui Xian Zhang, Zi Ming Kou, and Chun Yue Lu. "Numerical Simulation on Dynamic Analysis for Pipe Vibration Control Based on an Actively Generated Hydraulic Excitation Force." Advanced Materials Research 490-495 (March 2012): 2328–32. http://dx.doi.org/10.4028/www.scientific.net/amr.490-495.2328.
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In order to study dynamic characteristics of fluid filled pipe under hydraulic excitation force generated actively by a new developed vibration exciter, at first mathematical model of pulsating fluid was established and a computer code based on the method of characteristics (MOC) was developed. Then the excitation force calculated by MOC was forced upon the corresponding nodes of finite element of pipe, meanwhile, the nodes of fluid by MOC were assured to coincide with that of the pipe by the method of finite element (FEM). Finally, using Newmark’s method, the dynamic response at every cross section of pipe was solved. The numerical simulations show that a simple harmonic motion arises at every cross section of the pipe. The lateral vibration amplitude of every node along the pipe increases as the rising system pressure. So, this work is expected to provide some theoretical and exploratory basis for studying two dimensional vibration characteristics of fluid filled pipe.
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Meng, Wanwan, Yongguang Cheng, Jiayang Wu, Zhiyan Yang, Yunxian Zhu, and Shuai Shang. "GPU Acceleration of Hydraulic Transient Simulations of Large-Scale Water Supply Systems." Applied Sciences 9, no. 1 (December 27, 2018): 91. http://dx.doi.org/10.3390/app9010091.
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Simulating hydraulic transients in ultra-long water (oil, gas) transmission or large-scale distribution systems are time-consuming, and exploring ways to improve the simulation efficiency is an essential research direction. The parallel implementation of the method of characteristics (MOC) on graphics processing unit (GPU) chips is a promising approach for accelerating the simulations, because GPU has a great parallelization ability for massive but simple computations, and the explicit and local features of MOC meet the features of GPU quite well. In this paper, we propose and verify a GPU implementation of MOC on a single chip for more efficient simulations of hydraulic transients. Details of GPU-MOC parallel strategies are introduced, and the accuracy and efficiency of the proposed method are verified by simulating the benchmark single pipe water hammer problem. The transient processes of a large scale water distribution system and a long-distance water transmission system are simulated to investigate the computing capability of the proposed method. The results show that GPU-MOC method can achieve significant performance gains, and the speedup ratios are up to hundreds compared to the traditional method. This preliminary work demonstrates that GPU-MOC parallel computing has great prospects in practical applications with large computing load.
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Hwang, Yao-Hsin, Ho-Shuenn Huang, Nien-Mien Chung, and Pai-Yi Wang. "Particle method of characteristics (PMOC) for unsteady pipe flow." Journal of Hydroinformatics 15, no. 3 (December 18, 2012): 780–97. http://dx.doi.org/10.2166/hydro.2012.116.
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A novel particle method of characteristics (PMOC) to simulate unsteady pipe flows is introduced and validated in the present study. Contrary to the conventional method of characteristics (MOC), the present formulation is built by reallocating the computational nodes along the characteristic lines. Both the right- and left-running characteristics are accurately traced and imitated with their associated computational particles. The annoying numerical inconveniences in the fixed-grid arrangement due to incompatible Courant–Friedrichs–Lewy (CFL) condition by repeating solution interpolations is effectively eliminated. Special particles with dual states satisfying the Rankine–Hugoniot relations are deliberately imposed to emulate the shock structure. Efficacy of this formulation is verified by solving some benchmark problems with significant transient effects in pipe flows. Computational results of piezometric head and flow velocity are meticulously compared with available analytical solutions. It is concluded that the proposed PMOC will be a useful tool to replicate transient phenomena in pipe flows.
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Gao, Peixin, Hongquan Qu, Yuanlin Zhang, Tao Yu, and Jingyu Zhai. "Experimental and Numerical Vibration Analysis of Hydraulic Pipeline System under Multiexcitations." Shock and Vibration 2020 (March 10, 2020): 1–13. http://dx.doi.org/10.1155/2020/3598374.
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Pipeline systems in aircraft are subjected to both hydraulic pump pressure fluctuations and base excitation from the engine. This can cause fatigue failures due to excessive vibrations. Therefore, it is essential to investigate the vibration behavior of the pipeline system under multiexcitations. In this paper, experiments have been conducted to describe the hydraulic pipeline systems, in which fluid pressure excitation in pipeline is driven by the throttle valve, and the base excitation is produced by the shaker driven by a vibration controller. An improved model which includes fluid motion and base excitation is proposed. A numerical MOC-FEM approach which combined the coupling method of characteristics (MOC) and finite element method (FEM) is proposed to solve the equations. The results show that the current MOC-FEM method could predict the vibration characteristics of the pipeline with sufficient accuracy. Moreover, the pipeline under multiexcitations could produce an interesting beat phenomenon, and this dangerous phenomenon is investigated for its consequences from engineering point of view.
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Zeng, Wei, Chao Wang, and Jiandong Yang. "Hydraulic Transient Simulation of Pipeline-Open Channel Coupling Systems and Its Applications in Hydropower Stations." Water 14, no. 18 (September 16, 2022): 2897. http://dx.doi.org/10.3390/w14182897.
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Hydraulic systems may involve both pipelines and open channels, which challenges the hydraulic transient analysis. In this paper, a method of characteristics (MOC)-finite volume method (FVM) coupling method has been developed with the pipeline modelled using the MOC and the open channel modelled using the FVM. The coupling boundaries between these two simulation regions are developed based on Riemann invariants. The simulated parameters can be transmitted from the MOC region to the FVM region and in the reverse direction through the coupling boundaries. Validation of the method is conducted on a simple tank-pipe system by comparing the simulated result using 3D computational fluid dynamics (CFD) analysis. The new method is then applied to a prototype hydropower station with a sand basin located between the upstream reservoir and the turbines. The sand basin is modelled as an open channel coupled with the pipes in the system. The transient processes are also simulated by modelling the sand basin as a surge tank. The comparison with the results by the MOC-FVM coupling method shows the new coupling method can provide more reliable and accurate results. This is because the flow velocity in the horizontal direction in the sand basin is considered in the coupling method but neglected when the sand basin is modelled as a surge tank in the MOC.
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Wiens, Travis, and Elnaz Etminan. "An Analytical Solution for Unsteady Laminar Flow in Tubes with a Tapered Wall Thickness." Fluids 6, no. 5 (April 23, 2021): 170. http://dx.doi.org/10.3390/fluids6050170.
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Transient fluid flows through tubes are critical in such topics as water hammer, ram pumps and pipeline dynamics. While analytical solutions exist in the literature for simple geometries such as tapered and non-tapered tube diameters, one area that is lacking is the case where the wave speed changes along the length. An example of this is a flexible pipe with a tapered wall thickness. In order to calculate the transient pressure response of such a system, this previously required a computationally expensive gridded method of characteristics (MOC) solution. This paper describes an analytical solution to the dynamic laminar flow of liquid in a tube where the wave speed varies along its length. This frequency-domain solution includes frequency-dependent friction effects. A comparison to a method of characteristics (MOC) solution is used to verify the solution. The paper also discusses some numerical issues and provides an approximate method that can be used for high-frequency calculations where limited numerical precision can cause errors. Finally, a preliminary comparison of the computational performance is presented, in which the new method is an order of magnitude faster to calculate than an MOC solution.
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Zhang, Hui Xian, and Ling Xia Miao. "Modeling and Experiment on Active Vibration Control of Hydraulic Excitation System." Applied Mechanics and Materials 187 (June 2012): 130–33. http://dx.doi.org/10.4028/www.scientific.net/amm.187.130.
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For studying dynamic characteristics of fluid filled pipe under hydraulic excitation force generated actively by a new developed vibration exciter, at first a computer code based on the method of characteristics (MOC) was developed. Then the excitation force calculated by MOC was applied to the corresponding nodes of finite element of pipe, by using Newmark’s method, the dynamic response at every cross section of pipe was obtained. The numerical simulations show that a simple harmonic motion arises at every cross section of the pipe, and the lateral vibration amplitude of every node along the pipe increases as the rising excitation force. In addition, measured data were compared with numerical simulation, which were basically consistent with each other.
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Hébert, Alain, Julien Taforeau, and Jean-Jacques Ingremeau. "APPLICATION OF THE SPH EQUIVALENCE TECHNIQUE TO THE CABRI FULL CORE IN NON-FUNDAMENTAL MODE." EPJ Web of Conferences 247 (2021): 03019. http://dx.doi.org/10.1051/epjconf/202124703019.
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We developed a SPH equivalence technique in non-fundamental mode condition between a CABRI full-core model solved with the method of characteristics (MOC) in 2D and a simplified full-core model solved with the simplified P3 (SP3) method, linear anisotropic sources and discretized with Raviart-Thomas finite elements over a pure Cartesian mesh. The MOC and SP3 calculations are performed with DRAGON5 and DONJON5 codes, respectively. A three-parameter database is generated by DRAGON5 and is interpolated in DONJON5 as a function of the core condition. An objective function is set as the root mean square (RMS) error (MOC-SP3 discrepancy) on absorption distribution and leakage rates defined over the macro-geometry in DONJON5. Our algorithm is a quasi-Newtonian gradient search based on the Limited memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS) method. Numerical results are presented with Hafnium bars withdrawn or inserted.
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Niu, Xiaorui, Kang Zhang, Chao Wan, Xiangmin Chen, Lida Liao, and Zeyu Tian. "The Rational Spline Interpolation Based-LOD Method and Its Application to Rotating Machinery Fault Diagnosis." Applied Sciences 10, no. 4 (February 13, 2020): 1259. http://dx.doi.org/10.3390/app10041259.
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Local oscillatory-characteristic decomposition (LOD) is a relatively new self-adaptive time-frequency analysis methodology. The method, based on local oscillatory characteristics of the signal itself uses three mathematical operations such as differential, coordinate domain transform, and piecewise linear transform to decompose the multi-component signal into a series of mono-oscillation components (MOCs), which is very suitable for processing multi-component signals. However, in the LOD method, the computational efficiency and real-time processing performance of the algorithm can be significantly improved by the use of piecewise linear transformation, but the MOC component lacks smoothness, resulting in distortion. In order to overcome the disadvantages mentioned above, the rational spline function that spline shape can be adjusted and controlled is introduced into the LOD method instead of the piecewise linear transformation, and the rational spline-local oscillatory-characteristic decomposition (RS-LOD) method is proposed in this paper. Based on the detailed illustration of the principle of RS-LOD method, the RS-LOD, LOD, and empirical mode decomposition (EMD) are compared and analyzed by simulation signals. The results show that the RS-LOD method can significantly improve the problem of poor smoothness of the MOC component in the original LOD method. Moreover, the RS-LOD method is applied to the fault feature extraction of rotating machinery for the multi-component modulation characteristics of rotating machinery fault vibration signals. The analysis results of the rolling bearing and fan gearbox fault vibration signals show that the RS-LOD method can effectively extract the fault feature of the rotating mechanical vibration signals.
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Twyman, John. "Transient flow analysis using the method of characteristics MOC with five-point interpolation scheme." Obras y proyectos, no. 24 (December 2018): 62–70. http://dx.doi.org/10.4067/s0718-28132018000200062.
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Štrba, Dominik, Peter Mlynár, Michal Masaryk, and Georgios Manganos. "Design of the Minimal Length Nozzle for Ejector Cooling System by Using Method of Characteristics." Advances in Thermal Processes and Energy Transformation 3, no. 3 (2020): 75–80. http://dx.doi.org/10.54570/atpet2020/03/03/0075.
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In this paper will be presented design of the minimal length nozzle (MLN) used for ejector cooling system (ECS). Working fluid in this circuit is water (steam). Correct and precious design of the nozzle is crucial for the right operation of the ECS system. For design of MLN was used method of characteristics (MOC), which was explained in the article. In the end there was shown program made for calculation of the MLN in Graphical User Interface (GUI) of open source program Scilab.
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Peng, Chuan Long, and Xiao Dong Wang. "Influence of Temperature Factor on Fluid–Structure Coupling Characteristics of Hydraulic Piping System." Applied Mechanics and Materials 241-244 (December 2012): 1338–43. http://dx.doi.org/10.4028/www.scientific.net/amm.241-244.1338.
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The fluid-structure coupling vibration due to the output flow ripple of pump or water hammer phenomenon does harm to piping system. Multi-physics field factor, especially the thermal field, should be considered while the vibration characteristics are analysed. A novel mathematical model based on Wiggert and Hatfield’s method of characteristic (MOC) is constructed, which is used to describe the vibration characteristics of the pipeline system at different temperatures. A simulation using one classic problem of pressure jump from the upstream is performed to verify the relationship between the temperature and pipeline coupling vibration.
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Zhou, Xijun, Yongjin Ye, Xianyu Zhang, Xiuwei Yang, and Haijun Wang. "Refined 1D–3D Coupling for High-Frequency Forced Vibration Analysis in Hydraulic Systems." Energies 15, no. 16 (August 20, 2022): 6051. http://dx.doi.org/10.3390/en15166051.
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High-Frequency Pressure Fluctuation (HFPF) is an extensively observed hydraulic phenomenon in pumped-storage power stations and water conveyance projects. The investigation of the propagation characteristics of the pressure perturbation is of great significance for the safe operation of hydraulic facilities. In this study, a one-dimensional (1D)–three-dimensional (3D) coupling model is established based on the combination of the Method of Characteristics (MOC) and Computational Fluid Dynamics (CFD) and implanted in the open source software OpenFOAM. The established model in this study implants the dynamic mesh module into the original OpenFOAM solver sonicLiquidFoam and presents the complete solution procedure of the CFD model with the dynamic mesh considered. The vibration of the pipe walls modeled by the mesh motion is employed to numerically generate the HFPF in the hydraulic system, which could not be implemented in the traditional MOC model. The independence of the pressure perturbation in the pipeline system is validated by the time-domain pressure variation. The graphical method is applied to describe the multiple reflection and superposition characteristics of the traveling wave in a simplified hydraulic system. Based on this, the mechanism of the superimposed characteristic of the traveling and standing pressure waves in the hydraulic system are analyzed, and the theoretical superimposed time-domain processes and the variations of the pressure oscillation magnitude are analyzed and presented. The 1D–3D coupling method and the theoretical analysis method could be referenced by other complex hydraulic systems.
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Prathapar, SA, and DL Reddell. "Weighted method of characteristics solutions for solute transport models." Soil Research 26, no. 4 (1988): 595. http://dx.doi.org/10.1071/sr9880595.
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Method of characteristics (MOC) solutions are widely employed in solute transport models to estimate tracer concentration. The conventional approach to obtain average tracer concentration for a particular cell is to arithmetrically average the concentration of moving points within the cell during a particular time step. This results in the prediction of a stepwise or a 'jerky' dispersion front unless a large number of moving points are introduced and/or smaller grid size are used. Criteria proposed in the past to avoid this 'jerky' behaviour are unsuitable if the flow is non-uniform and/or unsteady or if the grid size is large. To overcome this problem, a distance weighted criterion was incorporated in a solute transport model which utilizes the method of characteristics. Results were compared with those from analytical solutions and the conventional arithmetical averaging algorithm. The distance weighting algorithm performed as well as the arithmetic averaging algorithm for small grid sizes. When the grid size was large and/or the seepage velocity was low, the conventional approach resulted in a stepwise dispersion front, whereas the distance weighting approach resulted in a smoother dispersion front, consistent with analytical solution. Application of the proposed method should facilitate the selection of larger grid size for simulating solute transport in porous media.
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Khorsandi, Saeid, Kaveh Ahmadi, and Russell T. Johns. "Analytical Solutions for Gas Displacements With Bifurcating Phase Behavior." SPE Journal 19, no. 05 (March 10, 2014): 943–55. http://dx.doi.org/10.2118/166487-pa.
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Summary Minimum miscibility pressure (MMP) is one of the most important parameters in the design of a successful gasflooding process. The most-reliable methods to calculate the MMP are based on slimtube experiments, 1D slimtube simulations, mixing-cell calculations, and the analytical methods known as the method of characteristics (MOC). The calculation of MMP by use of MOC is the fastest method because it relies solely on finding the key tie lines in the displacement path. The MOC method for MMP estimation in its current form assumes that the composition path is a series of shocks from one key tie line to the next. For some oils, however, these key tie lines do not control miscibility, and the MMP calculated by use of the key-tie line approach can be significantly in error. The error can be as high as 5,000 psia for heavier oils or CO2 displacements at low temperature in which three-phase hydrocarbon regions can exist (L1–L2–V). At higher pressures, the two- or three-phase region can split (or bifurcate) into two separate two-phase regions (L1–L2 and L1–V regions). Thus, for the MMP calculation from MOC to be correct, we must calculate the entire composition path for this complex phase behavior, instead of relying on the shock assumption from one key tie line to the next. In this paper, the MOC-composition route is developed completely for the bifurcating phase-behavior displacement for pure CO2 injection by use of a simplified pseudoternary system that is analogous to the complex phase behavior observed for several real displacements with CO2. We develop the MOC analytical solutions by honoring all constraints required for a unique solution—velocity, mass balance, entropy, and solution continuity. The results show that a combination of shocks and rarefaction waves exists along the nontie-line path, unlike previous MOC solutions reported to date. We show that by considering the entire composition path, not just the key tie lines, the calculated MMP agrees with the mixing-cell method. We also show that, in this complex ternary displacement, the displacement mechanism has features of a both condensing and vaporizing (C/V) drive, which was thought to be possible only for gasfloods with four or more components. For pure CO2 injection, the solution also becomes discontinuous for oils that lie on the tie line envelope curve. Finally, we show that shock paths within the two-phase region are generally curved in composition space and that there is no MMP for some oil compositions considered in the displacements by CO2. Recovery can be large even though the MMP is not reached.
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Aldo, A. C., and B. M. Argrow. "Dense Gas Flow in Minimum Length Nozzles." Journal of Fluids Engineering 117, no. 2 (June 1, 1995): 270–76. http://dx.doi.org/10.1115/1.2817140.
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Recently, dense gases have been investigated for many engineering applications such as for turbomachinery and wind tunnels. Supersonic nozzle design can be complicated by nonclassical dense-gas behavior in the transonic flow regime. In this paper, a method of characteristics (MOC) is developed for two-dimensional (planar) and axisymmetric flow of a van der Waals gas. A minimum length nozzle design code is developed that employs the MOC procedure to generate an inviscid wall contour. The van der Waals results are compared to perfect gas results to show the real-gas effects on the flow properties and inviscid wall contours.
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Ahmadi, Kaveh, and Russell T. Johns. "Multiple-Mixing-Cell Method for MMP Calculations." SPE Journal 16, no. 04 (October 25, 2011): 733–42. http://dx.doi.org/10.2118/116823-pa.
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Summary The minimum miscibility pressure (MMP) is a key parameter governing the displacement efficiency of gasfloods. There are several methods to determine the MMP, but the most accurate methods are slim-tube experiments, analytical methods, and numerical-simulation/cell-to-cell methods. Slim-tube experiments are important to perform because they use actual crude oil, but they are costly and time consuming. Analytical methods that use the method of characteristics (MOC) are very fast and help to understand the structure of gasfloods. MOC, however, relies on finding the unique and correct set of key tie lines in the displacements, which can be difficult. Slim-tube simulation methods and their simplified cell-to-cell derivatives require tedious fluid and rock inputs, and their MMP estimates can be clouded by dispersion. This paper presents a simple and accurate multiple-mixing-cell method for MMP calculations that corrects for dispersion, and is faster and less cumbersome than 1D simulation methods. Unlike previous mixing-cell methods, our cell-to-cell mixing model uses a variable number of cells, and is independent of gas/oil ratio, volume of the cells, excess oil volumes, and the amount of gas injected. The new method only relies on robust P/T flash calculations using any cubic equation-of-state (EOS). The calculations begin with only two cells and perform additional cell-to-cell contacts between resulting equilibrium-phase compositions based on equilibrium gas moving ahead of the equilibrium liquid phase. We show for a variety of oil and gas compositions that all key tie lines can be found to the desired accuracy, and that they are nearly identical to those found using analytical MOC methods. Our approach, however, is more accurate and robust than those from MOC because we do not make approximations regarding shocks along nontie-line paths, and the unique set of key tie lines converges automatically. The MMP using our mixing-cell method can be calculated in minutes using an Excel spreadsheet and is estimated from a novel bisection method of the minimum tie-line lengths observed in the cells at four or five pressures. Our multiple-mixing-cell method can calculate either the MMP or the minimum miscibility for enrichment (MME) independent of the number of components in the gas or oil. Our approach further supports the notion that the MMP is independent of fractional flow because we obtain the same key tie lines independent of how much fluid is moved from one cell to another.
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Ayas, Hillal, Mohamed Chabaat, and Lyes Amara. "Dynamic analysis of a cracked bar by the method of characteristics." International Journal of Structural Integrity 10, no. 4 (August 12, 2019): 438–53. http://dx.doi.org/10.1108/ijsi-01-2018-0001.
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Purpose The purpose of this paper is to introduce a new numerical approach for studying a cantilever bar having a transverse crack. The crack is modeled by an elastic longitudinal spring with a stiffness K according to Castiglione’s theorem. Design/methodology/approach The bar is excited by different longitudinal impulse forces. The considered problem based on the differential equation of motion is solved by the method of characteristics (MOC) after splitting the second-order motion equation into two first-order equivalent equations. Findings In this study, effects of the crack size and crack’s position on the reflected waves from the crack are investigated. The results indicate that the presence of the crack in the cantilever bar generates additional waves caused by the reflection of the incident wave by the crack. Originality/value A numerical approach developed in this paper is used for detecting the extent of the damage in cracked bars by the measurement of the difference between the dynamic response of an uncracked bar and a cracked bar.
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Li, Xiaoqin, Xuelin Tang, Min Zhu, and Xiaoyan Shi. "1D-3D coupling investigation of hydraulic transient for power-supply failure of centrifugal pump-pipe system." Journal of Hydroinformatics 21, no. 5 (July 22, 2019): 708–26. http://dx.doi.org/10.2166/hydro.2019.122.
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Abstract In the pumping station, the main feedwater system and the reactor system of nuclear power plant, power-supply failure causes strong hydraulic transients. One-dimensional method of characteristics (1D-MOC) is used to calculate the transient process in the pipeline system while three-dimensional (3D) computational fluid dynamics is employed to analyze the turbulent flows inside the pump and to obtain the performance parameters of the pump, and the data exchanges on the boundary conditions of the shared interface between 1D and 3D domains are updated based on the MpCCI platform. Based on the equation of motion of the pump motion parts, the relationship between the external characteristics and the internal flow field in the pump is further investigated because the dynamic behavior of the pump and the detailed fluid field evolutions inside the pump are captured during the transition process, and the transient flow rate, rotating speed, and pressure inside the impeller are comprehensively investigated. Meanwhile, compared with the data gained by experiment and traditional 1D-MOC, the relative errors of rotating speed and the flow rate obtained by 1D-3D coupling method are smaller than those by 1D-MOC. Furthermore, the influences of the main coupling parameters and coupling modes on the calculation results are analyzed, and the cause of the deviation is further explained.
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Wang, Rong He, Zhi Xun Wang, Feng Zhang, Ji Long Sun, Xiao Xue Wang, Jing Luo, and Hai Bo Yang. "Hydraulic Transient Prevention with Dipping Tube Hydropneumatic Tank." Applied Mechanics and Materials 316-317 (April 2013): 762–65. http://dx.doi.org/10.4028/www.scientific.net/amm.316-317.762.
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The dipping tube hydropneumatic tank is one of the most efficient equipments to prevent water hammer in water distribution and long distance transmission pipe systems. Due to its low costs and easy to maintain features, dipping tube hydropneumatic tank has many irreplaceable advantages, however it is difficult to determine the correct size and gas volume for real world engineering applications. This paper presents a robust method to solve the problems from theory and application. Based on the Method of Characteristics (MOC) equations, this paper derives the equations for modeling dipping tube hydropneumatic tanks in water distribution systems to prevent water hammer. The equations include MOC, differential orifice head loss equation, gas law, air mass, air velocity and etc. The IBMs scientific subroutine package (SSP) is applied to solve the equations by deriving to the form of X=f (X). The method has been integrated into HAMMER. This paper also presents an example to illustrate the methods of determining the tank size, and the comparison results with sealed hydropneumatic tank and surge tank equipment.
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Chiou, J.-S., M.-S. Chiang, and C.-K. Chen. "Numerical Simulation Method Applied to the Multi-Expansion Exhaust System of a Two-Stroke Engine." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 208, no. 4 (October 1994): 281–88. http://dx.doi.org/10.1243/pime_proc_1994_208_195_02.
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A numerical method is presented to simulate the pressure wave in the multi-expansion exhaust system of a two-stroke engine. In the simulated processes, the inlet pipe, scavenge pipe and exhaust pipe of the two-stroke engine are simplifed by the pipe model, while the engine cylinder, crankcase and the expansion chamber are treated as the vessel model. The cubic-interpolated pseudo-particle (CIP) method combined with the method of characteristics (MOC) is used to solve the hyperbolic equations. The results from simulation compare reasonably well with the experimental data.
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Negharchi, Saeid Mohammadzade, and Rouzbeh Shafaghat. "Evaluation of service pressure regulation strategy on the performance of a rural water network based on pulse demand; using the method of characteristics." Water Supply 22, no. 3 (November 29, 2021): 3204–23. http://dx.doi.org/10.2166/ws.2021.407.
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Abstract Reducing the occurrence of pipe bursts, reducing leakage, and reducing energy consumption are the three main goals in implementing pressure control programs in water distribution networks. Service pressure regulation strategy is an evolved approach that encompasses all goals of pressure management. This paper has investigated this approach in a rural network with hydraulic complexities as a case study so that some parts of the network have excess pressure and other low pressure. A computer code based on the method of characteristics (MOC) has been developed for network hydraulic analysis. The generated code analyzes unsteady flow, pressure-driven demand analysis, and dynamic adjustment of pressure control valves based on the target node. Also, the experimental results of a laboratory network have been applied to validate and calibrate the numerical simulation. In addition, by measuring the flow rate and pressure of the network and the results of the minimum night flow method, three consumption patterns were used to generate pulsed nodal demands. Studies show that creating pressure-management areas by hydraulic analysis by MOC will determine the best control strategies. The mean pressure decreased 54% by applying this strategy. Furthermore, the average fluctuations of pressure reduced from 9.7 meters to 3.5 meters.
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Pal, Susovan, Prashanth Reddy Hanmaiahgari, and Bryan W. Karney. "An Overview of the Numerical Approaches to Water Hammer Modelling: The Ongoing Quest for Practical and Accurate Numerical Approaches." Water 13, no. 11 (June 5, 2021): 1597. http://dx.doi.org/10.3390/w13111597.
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Here, recent developments in the key numerical approaches to water hammer modelling are summarized and critiqued. This paper summarizes one-dimensional modelling using the finite difference method (FDM), the method of characteristics (MOC), and especially the more recent finite volume method (FVM). The discussion is briefly extended to two-dimensional modelling, as well as to computational fluid dynamics (CFD) approaches. Finite volume methods are of particular note, since they approximate the governing partial differential equations (PDEs) in a volume integral form, thus intrinsically conserving mass and momentum fluxes. Accuracy in transient modelling is particularly important in certain (typically more nuanced) applications, including fault (leakage and blockage) detection. The FVM, first advanced using Godunov’s scheme, is preferred in cases where wave celerity evolves over time (e.g., due to the release of air) or due to spatial changes (e.g., due to changes in wall thickness). Both numerical and experimental studies demonstrate that the first-order Godunov’s scheme compares favourably with the MOC in terms of accuracy and computational speed; with further advances in the FVM schemes, it progressively achieves faster and more accurate codes. The current range of numerical methods is discussed and illustrated, including highlighting both their limitations and their advantages.
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Shafii, Mohamad Ali. "Solution methods of neutron transport equation in nuclear reactors." Jurnal ILMU DASAR 14, no. 2 (December 4, 2013): 59. http://dx.doi.org/10.19184/jid.v14i2.320.
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A few numerical methods that usually used to solve neutron transport equation in nuclear reactor are SN dan PN method, Monte Carlo, Collision Probability and Methods of Characteristics . First two methods have been developed using diffusion approach, and last three methods suitable are applicated for transport approximation. Those of three methods have important role in the desain of nuclear reactors. In addition to follow the development of advanced reactor designs, the three methods were chosen because they do not use diffusion approach these are more accurate methods, as well as less need considerable computer memory. Of all the existing methods, the CP method has several advantages among the others. Keywords : Neutron transport, SN, PN, CP, MOC, MC
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Ho, Ming Tsu. "Two-Dimensional Simulation of EM Scattering from a Rotating Circular Dielectric Cylinder." Applied Mechanics and Materials 284-287 (January 2013): 1007–11. http://dx.doi.org/10.4028/www.scientific.net/amm.284-287.1007.
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The computational results of the scattered electromagnetic (EM) fields from a rotating circular dielectric cylinder were presented in this paper. The method of characteristics (MOC) was applied in a two dimensional modified O-type grid system to the solutions of the time-dependent Maxwell equations. To accurately model the rotating cylinder under the illumination of EM pulse, the passing center swing back grids (PCSBG) technique is employed in cooperation with MOC to overcome the difficulty of grid distortion due to the rotational movement of the cylinder. A number of electric and magnetic field distributions over the whole computational space were demonstrated in a side-by-side fashion for the comparison of the scattered EM fields from rotating circular dielectric cylinder with those from the stationary one. The numerical results exhibit feasible trends.
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Pal, Susovan, Prashanth Reddy Hanmaiahgari, and Martin F. Lambert. "Efficient approach toward the application of the Godunov method to hydraulic transients." Journal of Hydroinformatics 22, no. 5 (July 9, 2020): 1370–90. http://dx.doi.org/10.2166/hydro.2020.037.
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Abstract The proposed study investigated the applicability of the finite volume method (FVM) based on the Godunov scheme to transient water hammer with shock front simulation, in which intermediate fluxes were computed using either first-order or second-order Riemann solvers. Finite volume (FV) schemes are known to conserve mass and momentum and produce the efficient and accurate realization of shock waves. The second-order solution of the Godunov scheme requires an efficient slope or a flux limiter for error minimization and time optimization. The study examined a range of limiters and found that the MINMOD limiter is the best for modeling water hammer in terms of computational time and accuracy. The first- and second-order FVMs were compared with the method of characteristics (MOCs) and experimental water hammer measurements available in the literature. Both the FV methods accurately predicted the numerical and experimental results. Parallelization of the second-order FVM reduced the computational time similar to that of first-order. Thus, the study presented a faster and more accurate FVM which is comparable to that of MOC in terms of computational time and precision, therefore it is a good substitute for the MOC. The proposed study also investigated the implementation of a more complex convolution-based unsteady friction model in the FVM to capture real pressure dissipation. The comparison with experimental data proved that the first-order FV scheme with the convolution integral method is highly accurate for computing unsteady friction for sudden valve closures.
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Wen, Jing, Hong Fa Yu, Xue Ying Xiao, and Jin Mei Dong. "Influence of Materials Ratio on the Hydration Process of Magnesium Oxychloride Cement." Materials Science Forum 817 (April 2015): 180–84. http://dx.doi.org/10.4028/www.scientific.net/msf.817.180.
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Magnesium oxychloride cement (MOC) has the characteristics of big heat and heat concentration in the hydration process. During the hydration process there is an adverse effect on the formation of hydration products and strength as well as volume stability. The hydration heat method was used to study the hydration process of MOC and analyze the influence of materials ratio on the hydration process in the present investigation. The results show that the hydration process could be divided into five stages, inclding initial stage, induction stage, acceleration stage, retardation stage and stable stage. It has been found that with the increasing of the molar ratio of MgO/MgCl2, the induction stage and acceleration stage extended, and heat release ratio and total heat of 3 days were reduced. With the increasing of the molar ratio of H2O/MgCl2, the induction stage is cut down, acceleration stage is in advance and heat release ratio first rising and then down, and the total heat of 3 days are reduced. It may be concluded that the influence of ratio on the hydration process of MOC is mastered, providing the bases to further improve the properties of magnesium oxychloride cement products.
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Zhang, Qingqing, Jinghua Huang, Feinan Hu, Na Huo, Yingni Shang, Wenqian Chang, and Shiwei Zhao. "The distribution of organic carbon fractions in a typical loess-paleosol profile and its paleoenvironmental significance." PeerJ 6 (April 13, 2018): e4611. http://dx.doi.org/10.7717/peerj.4611.
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Background The loess-paleosol sequence on the Loess Plateau has been considered an important paleoclimatic archive to study global climatic and environmental changes in the Quaternary. So far, little attention has been paid to the characteristics of soil organic carbon fractions in loess-paleosol sequences, which may provide valuable information for exploring the evolution of climate and environment in the Quaternary on the Loess Plateau. Methods In order to explore the significance of mineral-associated organic carbon to total organic carbon (MOC/TOC) ratios in the loess-paleosol sequence for reconstructing paleoenvironmental and paleoclimatic evolution in the Quaternary on the Loess Plateau, we selected a typical loess-paleosol profile in Chunhua county, Xianyang city, Shaanxi province, as the research object. The content of total organic carbon (TOC) and MOC/TOC ratio in each loess and paleosol layers of the Chunhua loess-paleosol profile were analyzed, together with the paleoclimatic proxies, such as soil grain size, CaCO3 content and their correlations with organic carbon parameters. Results The main results were as follows: (1) the total content of soil organic carbon and MOC/TOC ratios were generally higher in paleosol layers than in the underlying loess layers of the Chunhua loess-paleosol profile. Compared to total organic carbon content, MOC/TOC ratios changed more obviously in soil layers below a paleosol layer S8; (2) soil clay content and median grain size (Md (ϕ)) were higher in paleosol than in the underlying loess, while CaCO3 content showed an opposite tendency. In the Chunhua profile, the distribution characteristics of the three paleoclimatic proxies showed good indications of paleoclimate changes in the Quaternary; (3) in the Chunhua loess-paleosol profile, MOC/TOC ratios were positively correlated with clay content and median grain size (ϕ), while negatively correlated with CaCO3 content, and the correlations were more significant in soil layers below S8. Discussion Our results indicated that MOC/TOC ratios in the Chunhua loess-paleosol profile correlated with the cold dry-warm wet paleoclimatic cycle in the Quaternary. The high MOC/TOC ratios in the loess-paleosol profile might reflect warm and humid climate, while lower ratios indicated relatively cold and dry climate. That is because when the climate changed from warm-humid to cold-dry, the vegetation coverage and pedogenesis intensity decreased, which increased soil CaCO3 content and decreased soil clay content and Md (ϕ), leading to decreased MOC/TOC ratios. Compared to TOC, MOC/TOC ratios had greater significance in indicating paleoenvironmental evolution in the Quaternary on the Loess Plateau. Therefore, investigating MOC/TOC ratios in loess-paleosol profile can offer new evidence to reconstructing paleoenvironmental changes, and also provide a basis for predicting responses of soil organic carbon pools to vegetation and climate changes in the future.
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Zhang, Kaiyi, Bahareh Nojabaei, Kaveh Ahmadi, and Russell T. Johns. "Effect of Gas/Oil Capillary Pressure on Minimum Miscibility Pressure for Tight Reservoirs." SPE Journal 25, no. 02 (December 31, 2019): 820–31. http://dx.doi.org/10.2118/199354-pa.
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Summary Shale and tight reservoir rocks have pore throats on the order of nanometers, and, subsequently, a large capillary pressure. When the permeability is ultralow (k < 200 nd), as in many shale reservoirs, diffusion might dominate over advection, so that the gas injection might no longer be controlled by the multicontact minimum miscibility pressure (MMP). For gasfloods in tight reservoirs, where k > 200 nd and capillary pressure is still large, however, advection likely dominates over diffusive transport, so that the MMP once again becomes important. This paper focuses on the latter case to demonstrate that the capillary pressure, which has an impact on the fluid pressure/volume/temperature (PVT) behavior, can also alter the MMP. The results show that the calculation of the MMP for reservoirs with nanopores is affected by the gas/oil capillary pressure, owing to alteration of the key tie lines in the displacement; however, the change in the MMP is not significant. The MMP is calculated using three methods: the method of characteristics (MOC); multiple mixing cells; and slimtube simulations. The MOC method relies on solving hyperbolic equations, so the gas/oil capillary pressure is assumed to be constant along all tie lines (saturation variations are not accounted for). Thus, the MOC method is not accurate away from the MMP but becomes accurate as the MMP is approached when one of the key tie lines first intersects a critical point (where the capillary pressure then becomes zero, making saturation variations immaterial there). Even though the capillary pressure is zero for this key tie line, its phase compositions (and, hence, the MMP) are impacted by the alteration of all other key tie lines in the composition space by the gas/oil capillary pressure. The reason for the change in the MMP is illustrated graphically for quaternary systems, in which the MMP values from the three methods agree well. The 1D simulations (typically slimtube simulations) show an agreement with these calculations as well. We also demonstrate the impact of capillary pressure on CO2-MMP for real reservoir fluids. The effect of large gas/oil capillary pressure on the characteristics of immiscible displacements, which occur at pressures well below the MMP, is discussed.
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Bell, Anthony, Ghasem-Sam Toloo, Julia Crilly, John Burke, Ged Williams, Bridie McCann, and Gerry FitzGerald. "Emergency department models of care in Queensland: a multisite cross-sectional study." Australian Health Review 43, no. 4 (2019): 363. http://dx.doi.org/10.1071/ah17233.
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Objective The acuity and number of presentations being made to emergency departments (EDs) is increasing. In an effort to safely and efficiently manage this increase and optimise patient outcomes, innovative models of care (MOC) have been implemented. What is not clear is how these MOC reflect the needs of patients or relate to each other or to ED performance. The aim of this study was to describe ED MOC in Queensland, Australia. Methods Situated within a larger mixed-methods study, the present study was a cross-sectional study. In early 2015, leaders (medical directors and nurse managers) from public hospital EDs in Queensland were invited to complete a survey detailing ED activity, staffing profiles, treatment space, MOC and National Emergency Access Target (NEAT) performance. Routinely collected ED information system data was also used. Results Twenty of the 27 EDs invited participated in the study (response rate 74%). An extensive array of MOC were identified that were categorised into those that facilitate input, throughput and output from the ED. There was no consistent evidence as to the relative effectiveness of these MOC in achieving ED performance benchmarks, such as NEAT performance. Conclusion There is considerable variability in the MOC used throughout EDs in Queensland. A more complete analysis of the relative effectiveness of different MOC either in isolation or as part of a comprehensive approach would help inform more consistent MOC in Queensland EDs. What is known about the topic? MOC in any given ED are implemented in response to factors such as the geographical location of the hospital, hospital-specific characteristics and service profile, staffing profile and patient demographic profile. In the era of time-based targets, they may also serve to address a particular aspect of flow in the face of rising ED demand. Although many of the MOC attempt to deal with flow in a linear fashion, target specific phases of the ED journey or address particular patient cohorts, what is clear is that not all EDs are shaped and formed the same. What does this paper add? The study provides a comprehensive description of the varied models of care operating within Queensland public hospital EDs and how they relate to ED performance. A basic taxonomy of contemporary ED MOC is necessary to allow comparison between departments and inform decisions regarding safety, efficiency and cost-effectiveness. What are the implications to practitioners? A contemporary understanding of the presence and profile of ED MOC that currently exist within a network of hospitals and health services is important for managers, clinicians and patients to inform decision-making regarding the safety, clinical effectiveness and cost-effectiveness of these models. This understanding can also inform where and how further improvements in care delivery can progress.
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Usman, Jakaria, and Shafii Ali Mohammad. "Perhitungan Matriks Pij dan Distribusi Fluks Neutron pada Sel Bahan Bakar Nuklir U-235 dan U-238 Berbentuk Slab Menggunakan MOC." Jurnal Fisika Unand 6, no. 1 (January 5, 2017): 74–80. http://dx.doi.org/10.25077/jfu.6.1.74-80.2017.
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Telah dilakukan perhitungan matriks Pij serta distribusi fluks neutron di dalam geometri slab pada sel bahan bakar nuklir U-235 dan U-238 dalam kondisi homogen dan tidak homogen. Penelitian ini bertujuan untuk memperoleh nilai fluks skalar dan nilai Pij yang menggunakan Method of Characteristic (MOC). Besarnya fluks neutron dan nilai Pij bergantung pada penampang lintang bahan bakar nuklir, lebar region, jumlah region dan parameter input lainnya. Hasil penelitian ini secara umum telah sesuai dengan teori yaitu nilai Pij total pada beberapa region bernilai ≈ 1. Nilai Pij dan distribusi fluks neutron pada keadaan homogen lebih baik dan seragam dibandingkan pada keadaan tidak homogen, hal ini terlihat dari bentuk distribusi fluks pada slab sesuai dengan penelitian yang dilakukan oleh Karriem (2012) Kata kunci: Matriks Pij, fluks neutron, Method of Characteristic(MOC), homogen, tidak homogen
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Tomazello F, M., P. C. Botosso, C. S. Lisi, and P. Spathelf. "Cedrela angustifolia Ses. et Moc. ex Dc., Meliaceae: Potential species for tropical dendrochronology." Journal of Palaeosciences 50, no. (1-3) (December 31, 2001): 47–53. http://dx.doi.org/10.54991/jop.2001.1804.
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The characteristics of Cedrela angustifolia, i.e., its dendrology, ecology, silviculture and wood anatomy were described. This Meliaceae species naturally occurring in Latin America produces annual growth rings with sensibility to climatic variables, such as rainfall and temperature, showing potentiality to climatic reconstruction. The X-ray densitometry of the wood constitutes, besides the usual wood anatomy analysis, a suitable method to delimit the annual growth rings, as well as, to determine the wood density variation from pith to bark and within the growth rings.
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Mo, Tiexiang, and Guodong Li. "Parallel Accelerated Fifth-Order WENO Scheme-Based Pipeline Transient Flow Solution Model." Applied Sciences 12, no. 14 (July 21, 2022): 7350. http://dx.doi.org/10.3390/app12147350.
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The water hammer phenomenon is the main problem in long-distance pipeline networks. The MOC (Method of characteristics) and finite difference methods lead to severe constraints on the mesh and Courant number, while the finite volume method of the second-order Godunov scheme has limited intermittent capture capability. These methods will produce severe numerical dissipation, affecting the computational efficiency at low Courant numbers. Based on the lax-Friedrichs flux splitting method, combined with the upstream and downstream virtual grid boundary conditions, this paper uses the high-precision fifth-order WENO scheme to reconstruct the interface flux and establishes a finite volume numerical model for solving the transient flow in the pipeline. The model adopts the GPU parallel acceleration technology to improve the program’s computational efficiency. The results show that the model maintains the excellent performance of intermittent excitation capture without spurious oscillations even at a low Courant number. Simultaneously, the model has a high degree of flexibility in meshing due to the high insensitivity to the Courant number. The number of grids in the model can be significantly reduced and higher computational efficiency can be obtained compared with MOC and the second-order Godunov scheme. Furthermore, this paper analyzes the acceleration effect in different grids. Accordingly, the acceleration effect of the GPU technique increases significantly with the increase in the number of computational grids. This model can support efficient and accurate fast simulation and prediction of non-constant transient processes in long-distance water pipeline systems.
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Matsumura, Yuta, Kan Okubo, Norio Tagawa, Takao Tsuchiya, and Takashi Ishizuka. "Evaluation of numerical simulation of acoustic wave propagation using method of characteristics-based constrained interpolation profile (CIP-MOC) method with non-uniform grids." Acoustical Science and Technology 38, no. 1 (2017): 31–34. http://dx.doi.org/10.1250/ast.38.31.
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Liu, Jinhao, Jianhua Wu, Yusheng Zhang, and Xinhao Wu. "Sensitivity Analysis of Hydraulic Transient Simulations Based on the MOC in the Gravity Flow." Water 13, no. 23 (December 6, 2021): 3464. http://dx.doi.org/10.3390/w13233464.
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The purpose of this study was to evaluate the sensitivity of input parameters to output results when using the method of characteristics (MOC) for hydraulic transient simulations. Based on a gravity flow water delivery project, we selected six main parameters that affect the hydraulic transient simulation and selected maximum pressure as the output parameter in order to perform a parameter sensitivity analysis. The Morris sensitivity analysis (Morris) and the partial rank correlation coefficient method based on Latin hypercube sampling (LHS-PRCC) were both adopted. The results show that the sensitivity of each parameter is the same except for the friction factor. The flow rate and Young’s modulus are positively correlated with the maximum pressure, whereas the pipe diameter, valve closing time, and wall thickness are negatively correlated. It is discussed that the variability of the friction factor comes from the function of the flow and pressure regulating valve. When other conditions of the gravity flow project remain unchanged, the maximum pressure increases with the increase in the friction factor. The flow rate, pipe diameter, and valve closing time are the key parameters that affect the model. Meanwhile, Morris and LHS-PRCC proved to be effective methods for evaluating parameter sensitivity in hydraulic transient simulations.
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Park, Ho Jin, and Jin Young Cho. "Critical Buckling Generation of TCA Benchmark by the B1 Theory-Augmented Monte Carlo Calculation and Estimation of Uncertainties." Energies 14, no. 9 (April 30, 2021): 2578. http://dx.doi.org/10.3390/en14092578.
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The Korea Atomic Energy Research Institute (KAERI) has developed the DeCART2D 2-dimensional (2D) method of characteristics (MOC) transport code and the MASTER nodal diffusion code and has established its own two-step procedure. For design code licensing, KAERI prepared a critical experiment on the verification and validation (V&V) of the DeCART2D code. DeCART2D is able to perform the MOC calculation only for 2D nuclear fuel systems, such as the fuel assembly. Therefore, critical buckling in the vertical direction is essential for comparison between the results of experiments and DeCART2D. In this study, the B1 theory-augmented Monte Carlo (MC) method was adopted for the generation of critical buckling. To examine critical buckling using the B1 theory-augmented MC method, TCA critical experiment benchmark problems were considered. Based on the TCA benchmark results, it was confirmed that the DeCART2D code with the newly-generated critical buckling predicts the criticality very well. In addition, the critical buckling generated by the B1 theory-augmented MC method was bound to uncertainties. Therefore, utilizing basic equations (e.g., SNU S/U formulation) linking input uncertainties to output uncertainties, a new formulation to estimate the uncertainties of the newly generated critical buckling was derived. This was then used to compute the uncertainties of the critical buckling for a TCA critical experiment, under the assumption that nuclear cross-section data have uncertainties.
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Yu, Xiao Dong, Jian Zhang, and Cheng Yu Fan. "Influence of Successive Load Rejections on Water Hammer Pressure of Spiral Case in Long Diversion-Type Hydropower Station." Applied Mechanics and Materials 607 (July 2014): 551–55. http://dx.doi.org/10.4028/www.scientific.net/amm.607.551.
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Based on the theory of hydraulic transients and method of characteristics (MOC), the numerical model of hydraulic transients in water way system was established using the data of a practical hydropower station, and the probable transients were simulated. The influence of successive load rejection conditions on water hammer pressure of spiral case was analyzed. Compared with simultaneous load rejection, successive load rejection can make maximum pressure in spiral case and maximum rotating speed of runner more serious if the bifurcated pipe converging under surge tank in diversion-type hydropower station.
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Ge, Dangke, Haiying Cheng, Mingjun Cai, Yang Zhang, and Peng Dong. "A New Predictive Method for CO2-Oil Minimum Miscibility Pressure." Geofluids 2021 (January 4, 2021): 1–8. http://dx.doi.org/10.1155/2021/8868592.
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Gas injection processes are among the effective methods for enhanced oil recovery. Miscible and/or near miscible gas injection processes are among the most widely used enhanced oil recovery techniques. The successful design and implementation of a miscible gas injection project are dependent upon the accurate determination of minimum miscibility pressure (MMP), the pressure above which the displacement process becomes multiple-contact miscible. This paper presents a method to get the characteristic curve of multiple-contact. The curve can illustrate the character in the miscible and/or near miscible gas injection processes. Based on the curve, we suggest a new model to make an accurate prediction for CO2-oil MMP. Unlike the method of characteristic (MOC) theory and the mixing-cell method, which have to find the key tie lines, our method removes the need to locate the key tie lines that in many cases is hard to find a unique set. Moreover, unlike the traditional correlation, our method considers the influence of multiple-contact. The new model combines the multiple-contact process with the main factors (reservoir temperature, oil composition) affecting CO2-oil MMP. This makes it is more practical than the MOC and mixing-cell method, and more accurate than traditional correlation. The method proposed in this paper is used to predict CO2-oil MMP of 5 samples of crude oil in China. The samples come from different oil fields, and the injected gas is pure CO2. The prediction results show that, compared with the slim-tube experiment method, the prediction error of this method for CO2-oil MMP is within 2%.
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Chen, Qichang, Hongchun Wu, and Liangzhi Cao. "Auto MOC—A 2D neutron transport code for arbitrary geometry based on the method of characteristics and customization of AutoCAD." Nuclear Engineering and Design 238, no. 10 (October 2008): 2828–33. http://dx.doi.org/10.1016/j.nucengdes.2008.04.014.
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Tramm, John R., Geoffrey Gunow, Tim He, Kord S. Smith, Benoit Forget, and Andrew R. Siegel. "A task-based parallelism and vectorized approach to 3D Method of Characteristics (MOC) reactor simulation for high performance computing architectures." Computer Physics Communications 202 (May 2016): 141–50. http://dx.doi.org/10.1016/j.cpc.2016.01.007.
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S. Chaharborj, Sarkhosh, Zuhaila Ismail, and Norsarahaida Amin. "Detecting Optimal Leak Locations Using Homotopy Analysis Method for Isothermal Hydrogen-Natural Gas Mixture in an Inclined Pipeline." Symmetry 12, no. 11 (October 26, 2020): 1769. http://dx.doi.org/10.3390/sym12111769.
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The aim of this article is to use the Homotopy Analysis Method (HAM) to pinpoint the optimal location of leakage in an inclined pipeline containing hydrogen-natural gas mixture by obtaining quick and accurate analytical solutions for nonlinear transportation equations. The homotopy analysis method utilizes a simple and powerful technique to adjust and control the convergence region of the infinite series solution using auxiliary parameters. The auxiliary parameters provide a convenient way of controlling the convergent region of series solutions. Numerical solutions obtained by HAM indicate that the approach is highly accurate, computationally very attractive and easy to implement. The solutions obtained with HAM have been shown to be in good agreement with those obtained using the method of characteristics (MOC) and the reduced order modelling (ROM) technique.