Hybrid Grid System Research Articles

Aerodynamic noise from a high-speed train bogie with complex geometry under a leading car

Among the various aerodynamic noise sources associated with high-speed trains, the bogie regions, and particularly the leading bogie, contribute most to the overall noise. To control this noise, insight into the noise generation mechanisms is imperative but relevant studies are limited due to the difficulties of simulating the flow in regions with complex geometry. An investigation is presented of the aerodynamic noise from a bogie under the leading car of a high-speed train using Delayed Detached Eddy Simulation method. A hybrid grid system is utilized to simulate the flow field, which provides input for the far-field noise calculations based on the Ffowcs Williams and Hawkings equation. Analysis shows that the outer bogie components experience large pressure fluctuations as they are immersed in the shear layer detached from upstream, which is therefore identified as playing a critical role in the noise generation. The resulting noise spectra are broadband and dominated by low frequencies. Compared with the bogie, the bogie cavity and train nose emit 5 dB greater sound power for the current geometry. This study improves understanding of the mechanisms behind the generation of aerodynamic noise in train bogies and lays the foundations for future studies of train bogie noise reduction.

Pressure transient characteristics of non-uniform conductivity fractured wells in viscoelasticity polymer flooding based on oil–water two-phase flow

Polymer flooding in fractured wells has been extensively applied in oilfields to enhance oil recovery. In contrast to water, polymer solution exhibits non-Newtonian and nonlinear behavior such as effects of shear thinning and shear thickening, polymer convection, diffusion, adsorption retention, inaccessible pore volume and reduced effective permeability. Meanwhile, the flux density and fracture conductivity along the hydraulic fracture are generally non-uniform due to the effects of pressure distribution, formation damage, and proppant breakage. In this paper, we present an oil–water two-phase flow model that captures these complex non-Newtonian and nonlinear behavior, and non-uniform fracture characteristics in fractured polymer flooding. The hydraulic fracture is firstly divided into two parts: high-conductivity fracture near the wellbore and low-conductivity fracture in the far-wellbore section. A hybrid grid system, including perpendicular bisection (PEBI) and Cartesian grid, is applied to discrete the partial differential flow equations, and the local grid refinement method is applied in the near-wellbore region to accurately calculate the pressure distribution and shear rate of polymer solution. The combination of polymer behavior characterizations and numerical flow simulations are applied, resulting in the calculation for the distribution of water saturation, polymer concentration and reservoir pressure. Compared with the polymer flooding well with uniform fracture conductivity, this non-uniform fracture conductivity model exhibits the larger pressure difference, and the shorter bilinear flow period due to the decrease of fracture flow ability in the far-wellbore section. The field case of the fall-off test demonstrates that the proposed method characterizes fracture characteristics more accurately, and yields fracture half-lengths that better match engineering reality, enabling a quantitative segmented characterization of the near-wellbore section with high fracture conductivity and the far-wellbore section with low fracture conductivity. The novelty of this paper is the analysis of pressure performances caused by the fracture dynamics and polymer rheology, as well as an analysis method that derives formation and fracture parameters based on the pressure and its derivative curves.

Comparison of the Grid and Off-Grid Hybrid Power Systems for Application in University Buildings in Nigeria

The Nigerian Universities rely on weak and unreliable fossil-based electric grids with diesel engine generators (DEG) as a backup. However, there is a potential to light up the campuses using power systems derived from primary renewable power systems (RPS) like wind turbine (WT) and solar photovoltaic (PV), that can be on or off-grid to improve the energy mix and duration reliably. This study presents the comparative analysis of the optimal hybrid grid and off-grid systems (OGS & OOGS) for serving the demand load of university buildings in four climatic regions of Nigeria. HOMER Pro is used to design and select the systems based on minimal net present cost (NPC) and cost of electricity (COE). The impact of a minimal renewable fraction of 95% on the optimal system architecture (OSA) and COE is studied for both grid and off-grid modes. Also, sensitivity analysis of the impact of key variables on performance for the sites is carried out. It is found that the OGS in the four regions is PV/Converter (Conv), while for the OOGS, it is PV/WT/DEG/battery (BB)/Conv except in Port Harcourt (PH), where it is PV/DEG/BB/Conv. The COE for the OGS in the Savana and monsoon climes of Enugu and PH are 10 and 19% more than that in the warm-semi arid climate zones of Maiduguri and Kano, which is approximately 0.09 $/kWh. The COE ($/kWh) for the OOGS is 0.21 in Maiduguri, 0.245 in Kano, 0.275 in Enugu and 0.338 in PH. An obligatory 95% RF changes the architecture and increases COE in all the locations except Maiduguri, with a slightly improved COE but higher NPC like other locations. It is established that the suggested hybrid system is beneficial and feasible for supplying more reliable and clean energy to educational buildings in different Nigerian locations.

Design of Automatic Transfer Switch on A Renewable Energy Hybrid Grid System at PT Lentera Bumi Nusantara


 Currently, the transition between renewable energy sources and PLN sources at PT LBN is done manually by conducting scheduled monitoring. However, this method is less efficient and depends on the readiness of the operator. Therefore, in this Final Project, the design and construction of an Automatic Transfer Switch (ATS) on a renewable energy hybrid grid system at PT LBN is carried out where the source switching is based on the battery voltage value so as to shorten the source switching time while protecting the battery from undervoltage conditions. The main components used in the construction of this ATS system are contactors, relays, relay control circuits, ESP32, LCD 1604, and voltage divider circuits. The result of this final project is an ATS system that has a voltage sensor error of 0 - 1.187%. The monitoring of the ATS system was also successfully accessed from near and remotely in real time. The ATS that was built has a faster source switching time than the manual method, which is 21.6 ms - 40.1 ms.

Photovoltaic power forecasting: A hybrid deep learning model incorporating transfer learning strategy

Accurate forecasting of photovoltaic power is essential in the integration, operation, and scheduling of hybrid grid systems. In particular, modeling for newly built photovoltaic sites is restricted by insufficient data and training burden. In this study, a novel hybrid photovoltaic power forecasting model assisted with a transfer learning strategy is proposed. The hybrid model, named the attention-dilate convolution neural network-bidirectional long short-term memory network, consists of three steps. Step 1 - Input reconstruction: the historical power and meteorological factors are reconstructed as new inputs based on their relevance to the forecast by introducing a long short-term memory-based attention mechanism; Step 2 - Feature extraction: a hybrid structure is applied to extract spatial and temporal features from new inputs in parallel; Step 3 - Feature mapping: the extracted features are mapped into the forecasted photovoltaic output. Furthermore, to address the modeling for new sites, a transfer learning strategy that fine-tunes the pre-trained model is proposed in this work. The structure by step-wise division allows fine-tuning to be applied to the necessary parts rather than the entire model. Subsequently, the data from the actual photovoltaic system was acquired to validate the proposed model and transfer learning strategy. The proposed model showed significantly superior performance than the other models in the tests, and the parameter transferring not only makes up for the data shortage but also effectively accelerates the model training. With the transfer learning strategy, the maximum improvement in accuracy and training efficiency reached 69.51% and 71.42%, respectively.

Development of the microbubble pump having ‘S-shape’ impeller using experimental and numerical analysis

Abstract Microbubble pumps for water treatment can be used in a variety of fields, including wastewater treatment of semiconductor factories, sewage treatment, and aquaculture. In this study, a microbubble pump, with the ‘S-shape’ impeller, for sewage treatment has been developed in two steps. In the first step, a numerical design optimization was performed to develop a small-scaled microbubble pump. In the second step, a microbubble pump with a capacity that can be used in an actual water treatment facility has been developed through the scale-up process of a small-scaled optimum design of microbubble pump. The experimental test rig of the microbubble pump has been developed to investigate the performances of the microbubble pump, such as air and water flow rate, pressure differences and torque. To analyse three-dimensional flow field in the micro-bubble pump, general analysis code, CFX, has been employed. SST turbulence model has been employed to estimate the eddy viscosity and compared the pump performance to k-ε model. Unstructured grids have been used to represent a hybrid grid system including blade, casing and inlet casing. The results in the first step, a small-scaled optimum design shows the efficiency about 30.4%, which corresponds to a 0.4 percentage points increase compared to the conventional one. The results in the second step, the final design of microbubble pump shows an efficiency of 32.5% at the flow rate of 200 lpm.

A high-resolution numerical well-test model for pressure transient analysis of multistage fractured horizontal wells in naturally fractured reservoirs

In this study, a high-resolution numerical well-test model based on hybrid discrete fracture methods for pressure transient analysis of multistage fractured horizontal wells in naturally fractured reservoirs is proposed. Given the complexity of gridding for a numerical transient model, a new type of hybrid grid system honoring complex geometries of high-velocity transient flow near wellbore and hydraulic fractures is developed. Meanwhile, the methods of identifying fracture intersections in 3D unstructured space, transmissibility corrections and stochastic fracture network generation algorithm are proposed to greatly improve the accuracy and efficiency of capturing the pressure transients in complex fracture networks. After comparison with the well-test software KAPPA, it shows that the model can not only accurately reproduce the complex 3D convergence of flow regimes but also has a much better computational performance. Then, the type curves of a multistage fractured horizontal well with complex fracture networks and the sensitivity analysis of nonuniform properties of fracture networks are developed and analyzed in detail. The results show that the early-time horizontal radial flow and dip are positively related to the properties of natural fractures, and the fluid contribution and pressure distribution mainly depend on fracture connectivity rather than fracture number. The orthogonal fracture connections can result in stronger fluid supply and less fracture interference. Besides, the fracture linear flow and first/second bilinear flow are mainly affected by hydraulic and natural fractures, respectively. Finally, it proves that the proposed model can be much more efficient than KAPPA in history match for well-test data by an actual fractured field case.

Power Management of Hybrid Grid System With Battery Deprivation Cost Using Artificial Neural Network

Continuous power supply in an integrated electric system supplied by solar energy and battery storage can be optimally maintained with the use of diesel generators. This article discusses the optimum setting-point for isolated wind, photo-voltaic, diesel, and battery storage electric grid systems. Optimal energy supply for hybrid grid systems means that the load is sufficient for 24 h. This study aims to integrate the battery deprivation costs and the fuel price feature in the optimization model for the hybrid grid. In order to count charge–discharge cycles and measure battery deprivation, the genetic algorithm concept is utilized. To solve the target function, an ANN-based algorithm with genetic coefficients can also be used to optimize the power management system. In the objective function, a weight factor is proposed. Specific weight factor values are considered for simulation studies. On the algorithm actions, charging status, and its implications for the optimized expense of the hybrid grid, the weight factor effect is measured.

The Effect of Rheology of Viscoelastic Polymer on Pressure Transient Response in Near-Wellbore Regions

Viscoelastic polymer solution shows shear thinning behavior at low shear rates and shear thickening behavior at high shear rates in reservoirs. However, models that ignored shear thickening behavior were commonly employed to interpret transient pressure data derived from tested wells in viscoelastic polymer flooding systems; although, viscoelastic polymer solutions show shear thickening behavior in the near-wellbore region due to high shear rate. To better characterize the oilfield with pressure transient analysis in viscoelastic polymer flooding systems, we developed a numerical model that takes into account both shear thinning behavior and shear thickening behavior. A finite volume method was employed to discretize partially differential flow equations in a hybrid grid system including PEBI mesh and Cartesian grid, and the Newton-Raphson method was used to solve the fully implicit nonlinear system. To illustrate the significance of our model, we compared our model with a model that ignores the shear thickening behavior by graphing their solutions on log-log plots. In the flow regime of near-wellbore damage, the pressure derivative computed by our model is distinctly larger than that computed by the model ignoring shear thickening behavior. Furthermore, the effect of shear thickening behavior on pressure derivative differs from that of near-wellbore damage. We then investigated the influence of shear thickening behavior on pressure derivative with different polymer injection rates, injection rates, and permeabilities. The results can provide a benchmark to better estimate near-wellbore damage in viscoelastic polymer flooding systems. Besides, we demonstrated the applicability and accuracy of our model by interpreting transient pressure data from a field case in an oilfield with viscoelastic polymer flooding treatments.

A Two-Phase Numerical Model of Well Test Analysis to Characterize Formation Damage in Near-Well Regions of Injection Wells

Formation damage usually occurs in near-well regions for injection wells completed in offshore oilfields under the development of line drive patterns. However, current works on characterizing the damage by well test analysis were basically focused on using single-phase analogy to solve two-phase flow issues, resulting in errors on the diagnosis and interpretation of transient pressure data. In this paper, we developed a two-phase model to simulate the pressure transient behavior of a water injection well in a multiwell system. To solve the model more efficiently, we used the finite volume method to discretize partially differential flow equations in a hybrid grid system, including both Cartesian and radial meshes. The fully implicit Newton-Raphson method was also employed to solve the equations in our model. With this methodology, we compared the resulting solutions with a commercial simulator. Our results keep a good agreement with the solutions from the simulator. We then graphed the solutions on a log-log plot and concluded that the effects of transitional zone and interwell interference can be individually identified by analyzing specific flow regimes on the plot. Further, seven scenarios were raised to understand the parameters which dominate the pressure transient behavior of these flow regimes. Finally, we showed a workflow and verified the applicability of our model by demonstrating a case study in a Chinese offshore oilfield. Our model provides a useful tool to reduce errors in the interpretation of pressure transient data derived from injection wells located in a line drive pattern.

Optimization to Limit the Effects of Underloaded Generator Sets in Stand-Alone Hybrid Ship Grids

For the safety of the supply, diesel generator (DG) sets are used in various stand-alone power systems using variable-speed generators. The stand-alone hybrid grid system presented in this article, with a wind generator and a diesel generator, but also the system of a ship’s network, serves as an example. To ensure the safety of the ship’s exploitation, the parallel operation of two stand-alone power supplies is required. In parallel operation with the required symmetrical active power load (regardless of the load size), the internal combustion engine of the DG set is often underloaded. This leads to deterioration of its technical properties and, consequently, to a negative impact on the environment. This article presents an analysis of the stand-alone hybrid power system of a ship’s grid consisting of a DG with a speed and voltage regulator and a shaft generator of variable speed—a permanent magnet synchronous generator (PMSG). The possibility of controlling the active and reactive power distribution between the DG and shaft generator (SG) was also studied. Control over the mechatronic SG–DG system limits the harmful influence of the DG on the environment and, most of all, improves the technical qualities of the engine of the DG system, which is often underloaded. Analytic studies of the system were performed, and simulation results of the mechatronic model are presented.

An Evaluation of Flux-Coupling Type SFCL Placement in Hybrid Grid System Based on Power Quality Risk Index

Due to the expansion of restructured electricity markets and consequently power network operation approaching dynamic and static margins, the probability of transient instability has remarkably been increased. To reduce the transient instability risk or probabilistic cost of power quality, the present study focuses on determining the optimum location of a flux-coupling type SFCL. To this end, the candidate locations with lower related transient instability risk are selected as the best locations for installing flux-coupling type SFCLs. Nowadays, the type of SFCL employed in this study, which enjoys the benefits of both resistive and inductive type SFCLs, is a suitable means for enhancing the transient stability of electrical grids. Despite being another useful approach in transient stability evaluation, the equal-area criterion is merely restricted to the analysis of the stability of a single-machine power system connected to an infinite bus and also a two-machine power system. The online approach employed in this study is based on the corrected transient energy margin (CTEM), some probabilistic factors, and the cost of transient instability. Furthermore, CTEM index is a useful tool for calculating the critical clearing time (CCT). Therefore, in recent years, this index has become more and more useful. The studies carried out on the IEEE New England 39-bus test system ascertain the high applicability of the proposed method.

Derivation of knockdown factors for grid-stiffened cylinders considering various shell thickness ratios

PurposeThe purpose of this paper is to derive knockdown factor functions in terms of a shell thickness ratio (i.e. the ratio of radius to thickness) for conventional orthogrid and hybrid-grid stiffened cylinders for the lightweight design of space launch vehicles. Design/methodology/approachThe shell knockdown factors of grid-stiffened cylinders under axial compressive loads are derived numerically considering various shell thickness ratios. Two grid systems using stiffeners – conventional orthogrid and hybrid-grid systems – are used for the grid-stiffened cylinders. The hybrid-grid stiffened cylinder uses major and minor stiffeners having two different cross-sectional areas. For modeling grid-stiffened cylinders with various thickness ratios, the effective thickness (teff) of the cylinders is kept constant, and the radius of the cylinder is varied. Thickness ratios of 100, 192 and 300 are considered for the orthogrid stiffened cylinder, and 100, 160, 200 and 300 for the hybrid-grid stiffened cylinder. Postbuckling analyses of grid-stiffened cylinders are conducted using a commercial nonlinear finite element analysis code, ABAQUS, to derive the shell knockdown factor. The single perturbation load approach is applied to represent the geometrical initial imperfection of a cylinder. Knockdown factors are derived for both the conventional orthogrid and hybrid-grid stiffened cylinders for different shell thickness ratios. Knockdown factor functions in terms of shell thickness ratio are obtained by curve fitting with the derived shell knockdown factors for the two grid-stiffened cylinders. FindingsFor the two grid-stiffened cylinders, the derived shell knockdown factors are all higher than the previous NASA’s shell knockdown factors for various shell thickness ratios, ranging from 100 to 400. Therefore, the shell knockdown factors derived in this study may facilitate in the development of lightweight structures of space launch vehicles from the aspect of buckling design. For different shell thickness ratios of up to 500, the knockdown factor of the hybrid-grid stiffened cylinder is higher than that of the conventional orthogrid stiffened cylinder. Therefore, it is concluded that the hybrid-grid stiffened cylinder is more efficient than the conventional orthogrid-stiffened cylinder from the perspective of buckling design. Practical implicationsThe obtained knockdown factor functions may provide the design criteria for lightweight cylindrical structures of space launch vehicles. Originality/valueDerivation of shell knockdown factors of hybrid-grid stiffened cylinders considering various shell thickness ratios is attempted for the first time in this study.

Adaptive Grid Controller - Cost Reduction and Dispatch with Emphasis on Renewable Energy Sources

The combination of energy storage systems (ESS) and renewable energy source (RES) in hybrid grid provide benefits towards the system operation and as well as for end users. The main problem with RES is irregularity and ESS should be cost effective in order to provide economically operation of hybrid grid system. In this paper, we proposed the adaptive grid controller based upon the Super capacitor (SC) and battery at ESS in order to optimize the operation of grid system. An adaptive controller module includes hybrid ESS and consist of two modules, the Corse grain controller module is used to schedule the power dispatch in order to decrease the operational cost, while fine grain controller module is used to overcome the power fluctuation by RESs and to predict the uncertainties during real time power demand. The major aim is to minimize the energy loss through minimizing the average long period cost of hybrid ESS. The two-controller module optimizes the energy resources and power sources in a fixed interval of time, so the grid performs economically with several operational limits.

Technical and economical evaluation of grid-connected renewable power generation system for a residential urban area

This research investigates the techno-economic assessment of a hybrid grid system of solar and wind power for a residual urban area in Khvaf town located in the eastern part of Iran. The temperature profiles of a 10-year period are gathered based on the existing solar and wind condition data. Simulation, economical and technical evaluations of this hybrid system are studied with the aid of HOMER software. To reach a proper independent structure from the total net present cost and energy cost viewpoints, thousands of cases were studied. Change of the factor investing on PV panels together with the amount of the sun radiance as well as change of the investment factor of wind turbines with the consideration of wind velocity and sun radiance on the system layout are studied and discussed. The initial investment is 440 thousand dollars and the contribution portion of the renewable energies is 84% for the case containing four wind turbines and a power grid system (optimal system). This optimal system returns the investment over a 4-year period which is very economically attractive. The optimal system for the case with a low mean wind speed of 3 m/s is preferred to involve 13-kW photovoltaic (PV) panels, one-wind turbine and a 10-kW converter with a power grid network. Results shown that when the cost of the PV panel is 0.6 times higher than the current cost, a system consisting 4-wind turbines connected to the grid network is still the optimal system. In addition, a sensitivity analysis is made on the load demand of the hybrid system and the renewable energy resource. As a result, the most influential variables on the performance of the system are identified in this research. Based on the economic and technical evaluation, establishing a hybrid grid system for a residential urban area is perfectly reasonable with the investment return during the fourth year of a 25-year project lifetime. Also, among the systems studied, a system with four wind turbines and a power grid system is chosen as an optimal system due to the fact that the region has favorable potential for wind energy.

Postbuckling analyses and derivations of Knockdown factors for hybrid-grid stiffened cylinders

In this work, postbuckling behaviors of grid-stiffened cylinders under compressive loads are examined in an attempt to establish an analytical method to derive the shell Knockdown factor for space launch vehicle structures. Two grid systems using stiffeners – traditional orthogrid and hybrid-grid systems – are considered for the stiffened cylinders. The hybrid-grid system consists of major and minor stiffeners, which have two different cross-sectional sizes. Additionally, the baseline and minimum weight models are considered for each grid-stiffened cylinder model. The single perturbation load approach is used to represent the geometrical imperfection of cylinders. A commercial finite element analysis code, ABAQUS, is used for the postbuckling analyses. The present numerical simulations investigate the global and local instabilities for both stiffened cylinders using orthogrid and hybrid-grid systems. The global buckling load for the hybrid-grid stiffened cylinder is higher than that for the traditional orthogrid stiffened cylinder for both the baseline and minimum weight models. However, the postbuckling behaviors for the hybrid-grid stiffened cylinders are more complex, as compared to those for the orthogrid stiffened cylinders. Additionally, the shell Knockdown factors are derived using obtained numerical analysis results for the grid-stiffened cylinders. Since the shell Knockdown factor of the hybrid-grid stiffened cylinder is higher than that of the traditional orthogrid stiffened cylinders for both the baseline and minimum weight models, the hybrid-grid stiffened cylinder is more efficient in terms of the buckling design when compared to a traditional orthogrid stiffened cylinder. Furthermore, the derived Knockdown factors in the present work are higher than the values by NASA's buckling design criteria.

Information-Based Allocation Strategy for GRID-Based Transshipment Automated Container Terminal

In this paper, we introduce a storage allocation strategy for a transshipment container hub using a new automated container terminal called the hybrid GRID system. This study provides a novel approach of developing an efficient storage allocation strategy for new terminal concepts so that the complex formulations can be approximated by simple functions that can be quickly computed. Specifically, the storage allocation strategy is derived from an optimal allocation decision learned from a Mixed Integer Programming (MIP) model. Some input parameters of the MIP model are collected from a simulation model. An index measuring the storage location convenience is proposed and we regress this index with important variables to build an empirical model that provides recommendations on where to allocate containers to storage locations. The advantage of using the empirical approach is that it allows for fast computation which is expected in the dynamic and uncertain port environment. Numerical results show that four variables can significantly affect the performance of the allocation decision. This strategy is shown to be robust for different scenarios in terms of terminal configuration and container workload. In addition, the new strategy performs better than the commonly used strategies found in warehousing literatures, and the solution is close to the optimal allocation decision. The online appendix is available at https://doi.org/10.1287/trsc.2017.0736 .

Hybrid lattice Boltzmann method on overlapping grids.

In this work, a hybrid lattice Boltzmann method (HLBM) is proposed, where the standard lattice Boltzmann implementation based on the Bhatnagar-Gross-Krook (LBGK) approximation is combined together with an unstructured finite-volume lattice Boltzmann model. The method is constructed on an overlapping grid system, which allows the coexistence of a uniform lattice nodes spacing and a coordinate-free lattice structure. The natural adaptivity of the hybrid grid system makes the method particularly suitable to handle problems involving complex geometries. Moreover, the provided scheme ensures a high-accuracy solution near walls, given the capability of the unstructured submodel of achieving the desired level of refinement in a very flexible way. For these reasons, the HLBM represents a prospective tool for solving multiscale problems. The proposed method is here applied to the benchmark problem of a two-dimensional flow past a circular cylinder for a wide range of Reynolds numbers and its numerical performances are measured and compared with the standard LBGK ones.

A hybrid-grid 3D model for regular waves interacting with cylinders

ABSTRACTA hybrid-grid 3D non-hydrostatic model is developed and applied to predict nonlinear regular waves interacting with vertical circular cylinders. The model solves unsteady momentum and mass conservation equations by means of an explicit projection method. The 3D grid system is built from a 2D horizontal grid by adding several horizontal layers. The Perot’s scheme is used to treat horizontal advection terms in momentum equations. The 2D horizontal domain is discretized using a hybrid-grid system comprising rectangular and triangular cells to improve the model boundary-flexibility. The numerical model is validated against the experimental data of Stokes wave and cnoidal wave interacting with a vertical circular cylinder, respectively. Good agreement between model results and the experimental data are achieved, demonstrating the capability of the model on resolving interactions between nonlinear regular waves and vertical circular cylinders.

A Seismic Multi-Level Hybrid Grid System for Post-Earthquake Loss Assessment

A Seismic Multi-Level Hybrid Grid System for Post-Earthquake Loss Assessment