Records with Subject: Modelling and Simulations
Showing records 1 to 25 of 79. [First] Page: 1 2 3 4 Last
Distributing Characteristics within Fuel Cell Stacks with features that Fuel/Air Manifolds Penetrated through Plane Zone and Open Outlet Manifold
Dai Fen Chen
September 19, 2018 (v1)
Keywords: 3D large scale simulating, Flow and temperature distribution characteristics, Solid oxide fuel cell stack, Structure features
Although many numerical models based on different fuel cell stack designs have been developed in past decades, most of the achieved optimized results are greatly dependent on the specific designs, cell numbers and geometric values. Achieving the general relationship between the structure features and distribution trends of key physics items, that is independent on the specific design would be high instructive. To achieve high volumetric/gravimetric power density and simple manufacturing process, both fuel and air manifolds of a solid oxide fuel cell (SOFC) stack are always designed to place within cell plane zone and penetrated through it; and open outlet manifold is also adopted. In this study, the three dimension large scale multi-physics numerical model for a typical SOFC stack with the above two design features is well completed by carefully coupling momentum, mass, energy and quasi electrochemical reaction equations. Then, the general relations between these structure features and... [more]
Maintenance Factor Identification in Outdoor Lighting Installations Using Simulation and Optimization Techniques
Ana Ogando-Martínez, Javier López-Gómez, Lara Febrero-Garrido
September 21, 2018 (v1)
Keywords: artificial lighting, calibration, GenOpt, radiance, Simulation, street light points
This document addresses the development of a novel methodology to identify the actual maintenance factor of the luminaires of an outdoor lighting installation in order to assess their lighting performance. The method is based on the combined use of Radiance, a free and open-source tool, for the modeling and simulation of lighting scenes, and GenOpt, a generic optimization program, for the calibration of the model. The application of this methodology allows the quantification of the deterioration of the road lighting system and the identification of luminaires that show irregularities in their operation. Values lower than 9% for the error confirm that this research can contribute to the management of street lighting by assessing real road conditions.
On the Accuracy of Three-Dimensional Actuator Disc Approach in Modelling a Large-Scale Tidal Turbine in a Simple Channel
Anas Rahman, Vengatesan Venugopal, Jerome Thiebot
September 21, 2018 (v1)
Keywords: actuator disc, Telemac3D, tidal energy, turbulence, wake analysis
To date, only a few studies have examined the execution of the actuator disc approximation for a full-size turbine. Small-scale models have fewer constraints than large-scale models because the range of time-scale and length-scale is narrower. Hence, this article presents the methodology in implementing the actuator disc approach via the Reynolds-Averaged Navier-Stokes (RANS) momentum source term for a 20-m diameter turbine in an idealised channel. A structured grid, which varied from 0.5 m to 4 m across rotor diameter and width was used at the turbine location to allow for better representation of the disc. The model was tuned to match known coefficient of thrust and operational profiles for a set of validation cases based on published experimental data. Predictions of velocity deficit and turbulent intensity became almost independent of the grid density beyond 11 diameters downstream of the disc. However, in several instances the finer meshes showed larger errors than coarser meshes... [more]
Flow Simulation of Artificially Induced Microfractures Using Digital Rock and Lattice Boltzmann Methods
Yongfei Yang, Zhihui Liu, Jun Yao, Lei Zhang, Jingsheng Ma, S. Hossein Hejazi, Linda Luquot, Toussaint Dono Ngarta
September 21, 2018 (v1)
Keywords: CT, digital rock, Lattice Boltzmann method, microfractures, pore-scale simulations
Microfractures have great significance in the study of reservoir development because they are an effective reserving space and main contributor to permeability in a large amount of reservoirs. Usually, microfractures are divided into natural microfractures and induced microfractures. Artificially induced rough microfractures are our research objects, the existence of which will affect the fluid-flow system (expand the production radius of production wells), and act as a flow path for the leakage of fluids injected to the wells, and even facilitate depletion in tight reservoirs. Therefore, the characteristic of the flow in artificially induced fractures is of great significance. The Lattice Boltzmann Method (LBM) was used to calculate the equivalent permeability of artificially induced three-dimensional (3D) fractures. The 3D box fractal dimensions and porosity of artificially induced fractures in Berea sandstone were calculated based on the fractal theory and image-segmentation method,... [more]
PC Implementation of a Real-Time Simulator Using ATP Foreign Models and a Sound Card
Renzo G. Fabián Espinoza, Yuri Molina, Maria Tavares
September 21, 2018 (v1)
Keywords: ATP, digital real-time simulation, foreign models, hardware-in-the-loop, intelligent electronic device, MODELS
This work reports the personal computer implementation of a real-time simulator based on the widely used Electromagnetic Transients Program, version Alternative Transients Program (EMTP-ATP) software for testing protection and control devices. The proposed simulator was implemented on a conventional PC with a GNU/Linux operative system including a real-time kernel. Using foreign models programmed in C, ATP was recompiled with the PortAudio (sound card I/O library) with tools for writing and reading the parallel port. In this way, the sound card was used as a digital-to-analog converter to generate voltage waveform outputs at each simulation time step of the ATP, and the parallel port was used for digital inputs and outputs, resulting in a real-time simulator that can interact with protection and control devices by means of hardware-in-the-loop tests. This work uses the minimum possible hardware requirements to try to implement a real-time simulator. Due to the limitation of two channel... [more]
Variable Parameters for a Single Exponential Model of Photovoltaic Modules in Crystalline-Silicon
Ali F. Murtaza, Umer Munir, Marcello Chiaberge, Paolo Di Leo, Filippo Spertino
September 21, 2018 (v1)
Keywords: I-V curve tracer, maximum power point (MPP), modeling of photovoltaic (PV) module, PV simulator, Rp and Rs estimations
The correct approximation of parallel resistance (Rp) and series resistance (Rs) poses a major challenge for the single diode model of the photovoltaic module (PV). The bottleneck behind the limited accuracy of the model is the static estimation of resistive parameters. This means that Rp and Rs, once estimated, usually remain constant for the entire operating range of the same weather condition, as well as for other conditions. Another contributing factor is the availability of only standard test condition (STC) data in the manufacturer’s datasheet. This paper proposes a single-diode model with dynamic relations of Rp and Rs. The relations not only vary the resistive parameters for constant/distinct weather conditions but also provide a non-iterative solution. Initially, appropriate software is used to extract the data of current-voltage (I-V) curves from the manufacturer’s datasheet. By using these raw data and simple statistical concepts, the relations for Rp and Rs are designed. Fi... [more]
Thermal Characteristics Investigation of the Internal Combustion Engine Cooling-Combustion System Using Thermal Boundary Dynamic Coupling Method and Experimental Verification
Junhong Zhang, Zhexuan Xu, Jiewei Lin, Zefeng Lin, Jingchao Wang, Tianshu Xu
September 21, 2018 (v1)
Keywords: combustion, cooling system, dynamic coupling, engine performance, multiphase flow
The engine cooling system must be able to match up with the stable operating conditions so as to guarantee the engine performance. On the working cycle level, however, the dynamic thermo-state of engines has not been considered in the cooling strategy. Besides, the frequent over-cooling boiling inside the gallery changes the cooling capacity constantly. It is necessary to study the coupling effect caused by the interaction of cooling flow and in-cylinder combustion so as to provide details of the dynamic control of cooling systems. To this end, this study develops a coupled modeling scheme of the cooling process considering the interaction of combustion and coolant flow. The global reaction mechanism is used for the combustion process and the multiphase flow method is employed to simulate the coolant flow considering the wall boiling and the interphase forces. The two sub-models exchange information of in-cylinder temperature, heat transfer coefficient, and wall temperature to achieve... [more]
Analysis of Propagation Delay for Multi-Terminal High Voltage Direct Current Networks Interconnecting the Large-Scale Off-Shore Renewable Energy
Muhammad Haroon Nadeem, Xiaodong Zheng, Nengling Tai, Mehr Gul, Sohaib Tahir
September 21, 2018 (v1)
Keywords: high voltage direct current (HVDC) protection, multi-terminal HVDC, propagation delay
Voltage-source-converter-based multi-terminal high voltage direct current (MTDC) networks are extensively recognized as a viable solution for meeting the increasing demand of electrical energy and escalating penetration of renewable energy sources. DC faults are major limitations to the development of MTDC networks. The analysis of variable constraints has become mandatory in order to develop a reliable protection scheme. This paper contributes in assessing the propagation delay with the analytical approximation in MTDC networks. The propagation delay is analyzed in the time domain by taking only the forward traveling wave into account and considering the initial voltage step of magnitude at the fault position. Numerous simulations were carried out for different parameters and arrangements in Power System Computer Aided Design (PSCAD) to explore the proposed expressions. The results accurately depicted the time development of fault current. The results obtained from the real-time digit... [more]
Electromechanical Transient Modeling of Line Commutated Converter-Modular Multilevel Converter-Based Hybrid Multi-Terminal High Voltage Direct Current Transmission Systems
Liang Xiao, Yan Li, Huangqing Xiao, Zheren Zhang, Zheng Xu
September 21, 2018 (v1)
Keywords: electromechanical modeling, hybrid multi-terminal HVDC system, line commutated converter (LCC), modular multilevel converter (MMC), sequential power flow algorithm
A method for electromechanical modeling of line commutated converter (LCC)-modular multilevel converter (MMC)-based hybrid multi-terminal High Voltage Direct Current Transmission (HVDC) systems for large-scale power system transient stability study is proposed. Firstly, the general idea of modeling the LCC-MMC hybrid multi-terminal HVDC system is presented, then the AC-side and DC-side models of the LCC/MMC are established. Different from the conventional first-order DC-side model of the MMC, an improved second-order DC-side model of the MMC is established. Besides considering the firing angle limit of the LCC, a sequential power flow algorithm is proposed for the initialization of LCC-MMC hybrid multi-terminal HVDC system. Lastly, simulations of small scale and large scale power systems embedded with a three-terminal LCC-MMC hybrid HVDC system are performed on the electromechanical simulation platform PSS/E. It is demonstrated that if the firing angle limit is not considered, the accu... [more]
Thermal and Electrical Parameter Identification of a Proton Exchange Membrane Fuel Cell Using Genetic Algorithm
H. Eduardo Ariza, Antonio Correcher, Carlos Sánchez, Ángel Pérez-Navarro, Emilio García
September 21, 2018 (v1)
Keywords: Genetic Algorithm, identification, LabVIEW, model, PEM fuel cell
Proton Exchange Membrane Fuel Cell (PEMFC) fuel cells is a technology successfully used in the production of energy from hydrogen, allowing the use of hydrogen as an energy vector. It is scalable for stationary and mobile applications. However, the technology demands more research. An important research topic is fault diagnosis and condition monitoring to improve the life and the efficiency and to reduce the operation costs of PEMFC devices. Consequently, there is a need of physical models that allow deep analysis. These models must be accurate enough to represent the PEMFC behavior and to allow the identification of different internal signals of a PEM fuel cell. This work presents a PEM fuel cell model that uses the output temperature in a closed loop, so it can represent the thermal and the electrical behavior. The model is used to represent a Nexa Ballard 1.2 kW fuel cell; therefore, it is necessary to fit the coefficients to represent the real behavior. Five optimization algorithms... [more]
Computational Modeling of Gurney Flaps and Microtabs by POD Method
Unai Fernandez-Gamiz, Macarena Gomez-Mármol, Tomas Chacón-Rebollo
September 21, 2018 (v1)
Keywords: flow control, Gurney flaps, microtabs, proper orthogonal decomposition, reduced order method, wind energy
Gurney flaps (GFs) and microtabs (MTs) are two of the most frequently used passive flow control devices on wind turbines. They are small tabs situated close to the airfoil trailing edge and normal to the surface. A study to find the most favorable dimension and position to improve the aerodynamic performance of an airfoil is presented herein. Firstly, a parametric study of a GF on a S810 airfoil and an MT on a DU91(2)250 airfoil was carried out. To that end, 2D computational fluid dynamic simulations were performed at Re = 10⁶ based on the airfoil chord length and using RANS equations. The GF and MT design parameters resulting from the computational fluid dynamics (CFD) simulations allowed the sizing of these passive flow control devices based on the airfoil’s aerodynamic performance. In both types of flow control devices, the results showed an increase in the lift-to-drag ratio for all angles of attack studied in the current work. Secondly, from the data obtained by means of CFD simul... [more]
A Numerical Investigation of Frost Growth on Cold Surfaces Based on the Lattice Boltzmann Method
Jianying Gong, Jianqiang Hou, Jinjuan Sun, Guojun Li, Tieyu Gao
September 21, 2018 (v1)
Keywords: cold surface temperature, frost growth, Lattice Boltzmann (LB)
A numerical investigation of frost growth on a cold flat surface was presented based on two-dimensional Lattice Boltzmann model. This model has been validated to have less prediction error by past experiments. According to the results, it is shown that average frost density appears different at an increasing rate at different frosting stages. In addition, cold surface temperature has great influence on frost growth parameters such as frost crystal deposition mass, frost deposition rate, and frost crystal volume fraction. It was found that the frost crystal deposition mass, frost crystal volume, and the deposition rate first increase rapidly, then gradually slow down, finally remaining unchanged while the cold surface temperature decreases. The further away from the cold surface, the more sparser the frost layer structure becomes due to the smaller frost crystal volume fraction.
An Analytical Model for the Regeneration of Wind after Exiting a Wind Farm
Brian H. Fiedler
September 21, 2018 (v1)
Keywords: atmospheric boundary layer, wind energy, wind turbine wake
The simplest model for an atmospheric boundary layer assumes a uniform steady wind over a certain depth, of order 1 km, with the forces of friction, pressure gradient and Coriolis in balance. A linear model is here employed for the adjustment of wind to this equilibrium, as the wake of a very wide wind farm. A length scale is predicted for the exponential adjustment to equilibrium. Calculation of this length scale is aided by knowledge of the angle for which the wind would normally cross the isobars in environmental conditions in the wake.
Heat Transfer Coefficient Identification in Mini-Channel Flow Boiling with the Hybrid Picard⁻Trefftz Method
Mirosław Grabowski, Sylwia Hożejowska, Anna Pawińska, Mieczysław E. Poniewski, Jacek Wernik
September 21, 2018 (v1)
Keywords: heat transfer coefficient, hybrid Picard–Trefftz method, inverse heat conduction problem, mini-channel flow boiling
This paper summarizes the results of the flow boiling heat transfer study with ethanol in a 1.8 mm deep and 2.0 mm wide horizontal, asymmetrically heated, rectangular mini-channel. The test section with the mini-channel was the main part of the experimental stand. One side of the mini-channel was closed with a transparent sight window allowing for the observation of two-phase flow structures with the use of a fast film camera. The other side of the channel was the foil insulated heater. The infrared camera recorded the 2D temperature distribution of the foil. The 2D temperature distributions in the elements of the test section with two-phase flow boiling were determined using (1) the Trefftz method and (2) the hybrid Picard⁻Trefftz method. These methods solved the triple inverse heat conduction problem in three consecutive elements of the test section, each with different physical properties. The values of the local heat transfer coefficients calculated on the basis of the Robin bounda... [more]
DC/DC Boost Converter⁻Inverter as Driver for a DC Motor: Modeling and Experimental Verification
Víctor Hugo García-Rodríguez, Ramón Silva-Ortigoza, Eduardo Hernández-Márquez, José Rafael García-Sánchez, Hind Taud
September 21, 2018 (v1)
Keywords: bidirectional angular velocity, DC motor, DC/DC boost converter, differential flatness, experimental verification, inverter, Modelling
In this paper, the modeling and the experimental verification of the “bidirectional DC/DC boost converter⁻DC motor„ system are presented. By using circuit theory along with the model of a DC motor, the mathematical model of the system is derived. This model was experimentally tested under time-varying duty cycles obtained via the system differential flatness property. The experimental verification was carried out using Matlab-Simulink and a DS1104 board in a built prototype of the system.
Time-Resolved Temperature Map Prediction of Concentration Photovoltaics Systems by Means of Coupled Ray Tracing Flux Analysis and Thermal Quadrupoles Modelling
Alejandro Mateos-Canseco, Manuel I. Peña-Cruz, Arturo Díaz-Ponce, Jean-Luc Battaglia, Christophe Pradère, Luis David Patino-Lopez
September 21, 2018 (v1)
Keywords: 2D transient thermal analysis, CPV systems, Fresnel lens, ray tracing, solar concentration, temperature field, thermal quadrupoles
A transient 3D thermal model based on the thermal quadrupole method, coupled to ray tracing analysis, is presented. This methodology can predict transient temperature maps under any time-fluctuating irradiance flux—either synthetic or experimental—providing a useful tool for the design and parametric optimization of concentration photovoltaics systems. Analytic simulations of a concentration photovoltaics system thermal response and assessment of in-plane thermal gradients induced by fast tracking point perturbations, like those induced by wind, are provided and discussed for the first time. Computation times for time-resolved temperature maps can be as short as 9 s for a full month of system operation, with stimuli inspired by real data. Such information could pave the way for more accurate studies of cell reliability under any set of worldwide irradiance conditions.
Temperature and Velocity Effects on Mass and Momentum Transport in Spacer-Filled Channels for Reverse Electrodialysis: A Numerical Study
Zohreh Jalili, Jon G. Pharoah, Odne Stokke Burheim, Kristian Etienne Einarsrud
September 21, 2018 (v1)
Keywords: computational fluid dynamics modelling, mass transfer, reverse electrodialysis, spacer-filled channel, temperature effect
Concentration polarization is one of the main challenges of membrane-based processes such as power generation by reverse electrodialysis. Spacers in the compartments can enhance mass transfer by reducing concentration polarization. Active spacers increase the available membrane surface area, thus avoiding the shadow effect introduced by inactive spacers. Optimizing the spacer-filled channels is crucial for improving mass transfer while maintaining reasonable pressure losses. The main objective of this work was to develop a numerical model based upon the Navier⁻Stokes and Nernst⁻Planck equations in OpenFOAM, for detailed investigation of mass transfer efficiency and pressure drop. The model is utilized in different spacer-filled geometries for varying Reynolds numbers, spacer conductivity and fluid temperature. Triangular corrugations are found to be the optimum geometry, particularly at low flow velocities. Cylindrical corrugations are better at high flow velocities due to lower pressu... [more]
Coupled Fluid-Thermal Analysis for Induction Motors with Broken Bars Operating under the Rated Load
Ying Xie, Jinpeng Guo, Peng Chen, Zhiwei Li
September 21, 2018 (v1)
Keywords: broken bars fault, computational fluid dynamic (CFD) method, finite element method, fluid field, induction motors, thermal field
Thermal stress of the rotor in a squirrel cage induction motor is generated due to the temperature rise, it is also one of the factors causing the broken bar fault because the structure of the rotor would be destroyed if the stress of the rotor bars exceed the strength limit. The coupled fluid-thermal analysis for the induction motor with healthy and broken bar rotors is performed in this paper. Much concern has been committed to establishment of the fluid model on the basis of computational fluid dynamic (CFD) theory. The heat field of the prototypes is analysed so that the effect of the asymmetrical rotor on the motor heat performance can be investigated in depth. Eventually, the efficiency of the presented model and method, for the totally enclosed fan cooled (TEFC) induction motor, can be verified through experimental results. In addition, this paper reports a quantitative analysis of the heat flux distribution of the fault rotor, and the heat flux density of the bars is investigat... [more]
Temperature Distribution of HBC Fuses with Asymmetric Electric Current Ratios Through Fuselinks
Adrian Plesca
September 21, 2018 (v1)
Keywords: asymmetry, electric current, fuselinks, HBC fuse, modelling and simulation, temperature analysis
In many industrial applications high breaking capacity (HBC) fuses are used to protect electrical installations against overcurrents, especially in the power distribution network. At high rated current, HBC fuses have more parallel fuselinks mounted inside. The technological and mounting processes of the fuselinks inside the fuse results in an asymmetrical current distribution through the parallel fuselinks. In this article a model of a high breaking capacity fuse using two parallel fuselinks is proposed. The influence of electric current, cross-section of the notches, distance between notches and current imbalance through fuselinks on the maximum temperature rise of both fuselinks, has been investigated. Also, a 3D thermal model for the same HBC fuse has been developed. The temperature spread into the fuse and its elements has been obtained. In order to prove the validity of the mathematical and 3D model different tests have been considered. The experimental, simulation and computed r... [more]
A New Lumped Parameter Model for Natural Gas Pipelines in State Space
Kai Wen, Zijie Xia, Weichao Yu, Jing Gong
September 21, 2018 (v1)
Keywords: lumped parameter, mechanism model, natural gas pipeline, state space model
Many algorithms and numerical methods, such as implicit and explicit finite differences and the method of characteristics, have been applied for transient flow in gas pipelines. From a computational point of view, the state space model is an effective method for solving complex transient problems in pipelines. However, the impulse output of the existing models is not the actual behavior of the pipeline. In this paper, a new lumped parameter model is proposed to describe the inertial nature of pipelines with inlet/outlet pressure and flow rate as outer variables in the state space. Starting from the basic mechanistic partial differential equations of the general one-dimensional compressible gas flow dynamics under isothermal conditions, the transfer functions are first acquired as the fundamental work. With Taylor-expansion and a transformation procedure, the inertia state space models are derived with proper simplification. Finally, three examples are used to illustrate the effectivene... [more]
Dry Fuel Jet Half-Angle Measurements and Correlation for an Entrained Flow Gasifier
Francis Kus, Robin Hughes, Arturo Macchi, Poupak Mehrani, Marc Duchesne
September 21, 2018 (v1)
Keywords: gasification, imaging, jet half-angle, Modelling
Reduced order models (ROMs) are increasingly applied to entrained flow gasification development due to reduced computational requirements relative to computational fluid dynamics (CFD) models. However, they require greater a posteriori knowledge of the reactor physics. A significant parameter influencing ROM outputs is the jet half-angle of the solid fuel and oxidant mixture in the gasifier. Thus, it is important to understand the geometry of the jet in the gasifier, and how it is dependent on operating parameters, such as solid and carrier gas flow rates. In this work, an existing model for jet half-angles, which considers the ratio of surrounding gas density to jet core density, is extended to a dry solids jet with impinging gas. The model is fitted to experimental jet half-angles. The jet half-angle of a non-reactive flow was measured using laser-sheet imaging for solid fluxes in the range of 460⁻880 kg/m²·s and carrier gas fluxes in the range of 43⁻90 kg/m²·s at the transport line... [more]
Numerical Analysis to Determine Reliable One-Diode Model Parameters for Perovskite Solar Cells
Esteban Velilla, Juan Bernardo Cano, Keony Jimenez, Jaime Valencia, Daniel Ramirez, Franklin Jaramillo
September 21, 2018 (v1)
Keywords: I-V curve, numerical sensitivity analysis, one-diode model, perovskite solar cells
With the aim to determine the photo-generated current, diode saturation current, ideality factor, shunt, and series resistances related to the one-diode model for p-i-n planar perovskite solar cells, reference cells with active area of approximately 1 cm² and efficiencies ranging between 4.6 and 12.2% were fabricated and characterized at standard test conditions. To estimated feasible parameters, the mean square error between the I-V curve data of these cells and the circuital model results were minimized using a Genetic Algorithm combined with the Nelder-Mead method. When considering the optimization process solutions, a numerical sensitivity analysis of the error as a function of the estimated parameters was carried out. Based on the errors behavior that is showed graphically through maps, it was demonstrated that the set of parameters estimated for each cell were reliable, meaningful, and realistic, and being related to errors lower than 9.1 × 10−9. Therefore, these results can be c... [more]
Compound Heat Transfer Enhancement of Wavy Fin-and-Tube Heat Exchangers through Boundary Layer Restarting and Swirled Flow
Ali Sadeghianjahromi, Saeid Kheradmand, Hossain Nemati, Jane-Sunn Liaw, Chi-Chuan Wang
September 21, 2018 (v1)
Keywords: heat transfer enhancement, louver fin, numerical simulation, vortex generators, wavy fin-and-tube heat exchanger
This study performs a 3D turbulent flow numerical simulation to improve heat transfer characteristics of wavy fin-and-tube heat exchangers. A compound design encompassing louver, flat, and vortex generator onto wavy fins can significantly enhance the heat transfer performance of wavy fin-and-tube heat exchangers. Replacement of wavy fins around tubes with flat fins is not effective as far as the reduction of thermal resistance is concerned, although an appreciable pressure drop reduction can be achieved. Adding two louvers with a width of 8 mm to the flat portion can reduce thermal resistance up to 6% in comparison with the reference wavy fin. Increasing the louver number and width can further decrease the thermal resistance. Also, it is found that the optimum louver angle is equal to the wavy angle for offering the lowest thermal resistance. Therefore, compound geometry with three louvers, a width of 12 mm, and the louver angle being equal to wavy angle with waffle height to be the sa... [more]
The Optimization of Hybrid Power Systems with Renewable Energy and Hydrogen Generation
Fu-Cheng Wang, Yi-Shao Hsiao, Yi-Zhe Yang
September 20, 2018 (v1)
Keywords: cost, fuel cell, hybrid power system, Hydrogen, Optimization, reliability, solar, Wind
This paper discusses the optimization of hybrid power systems, which consist of solar cells, wind turbines, fuel cells, hydrogen electrolysis, chemical hydrogen generation, and batteries. Because hybrid power systems have multiple energy sources and utilize different types of storage, we first developed a general hybrid power model using the Matlab/SimPowerSystemTM, and then tuned model parameters based on the experimental results. This model was subsequently applied to predict the responses of four different hybrid power systems for three typical loads, without conducting individual experiments. Furthermore, cost and reliability indexes were defined to evaluate system performance and to derive optimal system layouts. Finally, the impacts of hydrogen costs on system optimization was discussed. In the future, the developed method could be applied to design customized hybrid power systems.
Prediction of Mud Pressures for the Stability of Wellbores Drilled in Transversely Isotropic Rocks
Chiara Deangeli, Omoruyi Omoman Omwanghe
September 20, 2018 (v1)
Keywords: fracturing, mud pressure, slip failure, transverse isotropy, ubiquitous joints, weakness planes, wellbore stability
Serious borehole instability problems are often related to the presence of weakness planes in rock formations. In this study, we investigated the stability of wellbores drilled along a principal direction and parallel to the weakness planes. We used three different strength criteria (weakness plane model, Hoek and Brown and Nova and Zaninetti) to calculate the mud pressures to avoid slip and tensile failure along the weakness planes. We identified the orientation of the weakness planes that generate the most critical slip condition as a function of the friction angle of the planes. We also identified the range of orientations of the weakness planes that corresponds with the lower mud pressure window. We confirmed the validity of the proposed relationships with comparative stability analyses by using analytical solutions and numerical simulations (Ubiquitous Joint Model, FLAC). We found that the mud pressures calculated with the Hoek and Brown criterion show a particular trend, which ca... [more]
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