Mesh System Research Articles

Computation of free surface waves in coastal waters with SWASH on unstructured grids

This paper aims to present the extension of the non-hydrostatic wave-flow model SWASH with the covolume method to build discretization schemes on unstructured triangular grids. Central to this method that is free of spurious pressure modes, is the use of dual pairs of meshes that are mutually orthogonal, such as the Delaunay-Voronoi mesh systems. The approximants sought are the components of the flow velocity vector normal to the cell faces of the primal mesh. In addition to the covolume approach, a novel upwind difference scheme for the horizontal advection terms in the momentum equation is proposed. This scheme obeys the Rankine-Hugoniot jump relations and prevents the odd-even decoupling of the velocity field accordingly. Moreover, cases with flow discontinuities, such as steady bores and broken waves, are properly treated. In spite of the low-order accuracy of the proposed method, unstructured meshes easily allow for local refinement in a way that retains the desired accuracy. The unstructured-grid version of SWASH is applicable to a wide range of 2DH wave-flow problems to investigate the nonlinear dynamics of free surface waves over varying bathymetries. Its efficiency and robustness is tested on a number of these problems employing unstructured triangular meshes.

Designing a new reaction system by stacking use of Ti mesh supported Ag/N-TiO2 nano-sheets for enhanced photocatalytic degradation of bisphenol A

In this work, Ag nano-particles deposited and N-doped TiO2 nanosheets grown on the Ti mesh (Ag/N-TiO2/Ti mesh) were synthesized through combination of a hydrothermal process and a photo-reduction deposition strategy, and then applied to photocatalytic (PC) degradation of bisphenol A (BPA). The physicochemical performances of Ag/N-TiO2/Ti mesh were investigated by a series of characterizations. Results showed that N doping promoted the formation of rutile, and increased the thickness of TiO2 nanosheets (30 nm–40 nm). Furthermore, N element was existed in the form of substitutional nitrogen state (O-Ti-N) in the lattice of TiO2, generating N2p doping energy level. The Ag nanoparticles were deposited on the surface of N-TiO2 in the form of Ag0. The PC removal efficiency of BPA by Ag/N-TiO2/Ti mesh was 90.5% within 60 min, much higher than that of N-TiO2/Ti mesh (78.0%) and TiO2/Ti mesh (59.5%). The N adulteration and surfaceplasmaresonance of Ag0 significantly enhanced the visible-light absorbance and photo-excited electrons-holes separation, which accounted for the improved PC degradation of BPA. By using the light transmittance performance of Ti mesh to stack three Ag/N-TiO2/Ti mesh (named 3-Ag/N-TiO2/Ti mesh) in a distance interval of 0.5 cm constructed a new reaction system, and it removed over 99.99% of BPA within 30 min, which was significantly higher than that of Ag/N-TiO2/Ti mesh system (59.5%). This was mainly ascribed to the effective optical energy utilization and the enhanced mass transfer. This study not only indicated that Ag/N-TiO2/Ti mesh was a promising photocatalyst, but also offered useful information for designing specific reactor in practical application (such as amplified cylindrical reactor).

Experience with Prolift Mesh System for Correction of Uterovaginal Prolapse: Analysis of 149 Cases

Objective: The objective of this retrospective chart review was to assess the feasibility, potential complications, safety, and efficacy of the Prolift® system to correct uterovaginal prolapse. Mat...

Approaching Module based Vertical Mesh System for Green Living in Densely-Populated Zone: A Study on Lower Middle-Income Group, Bangladesh

Approaching Module based Vertical Mesh System for Green Living in Densely-Populated Zone: A Study on Lower Middle-Income Group, Bangladesh

Optimal current flow technique for distribution systems with renewable energy generation

This article presents an optimal current flow (OCF) technique for analyzing distribution systems with renewable energy generation. The overall aim of this study is to reduce the complexity of the traditional nonlinear models by representing the problem as a quadratic optimization network flow model with linear constraints. The objective of the OCF method is minimization of renewable generation costs with or without consideration of transmission losses. Taking advantage of the topological characteristic of the distribution system, the network constraints are represented by Kirchhoff current and voltage laws. In addition, the model considers the capacity limits of the distribution components (renewable generators, transformers and lines current flow). The robustness and fastness of the OCF method is tested on 34-bus, 69-bus, and 400-bus systems under balanced and unbalanced, conditions and in radial or meshed distribution systems under different load scenarios. The results demonstrate the accuracy, and efficiency of the proposed approach in determining the optimal operation of a distribution system with renewable energy generation.

A Generic Power Flow Algorithm for Unbalanced Islanded Hybrid AC/DC Microgrids

This paper proposes a precise power flow algorithm for islanded hybrid AC/DC microgrids (HMGs). In our analysis, we have considered a multi-grounded unbalanced bipolar DC microgrid and a multi-grounded four-wire AC microgrid connected through one or more interlinking converters (ICs). The proposed method is based on the implicit Z BUS method, presenting fast convergence and robustness regardless of the R / X ratio of the lines. It can be applied in all network configurations including highly meshed distribution systems. Numerical simulations are conducted in a 12-Bus and a 47-Bus islanded unbalanced HMG to verify the validity of the proposed power flow approach considering several distributed generator (DG) operational modes. A case study in a large 1024-Bus islanded HMG further highlights the outstanding accuracy and computational performance of the proposed approach against other existing power flow methods.

Novel stepwise and combined stepwise–piece‐wise linear tripping characteristics for coordinating numerical overcurrent relays

Technological developments in protective devices have established the basis for appearance of numerical overcurrent relays (OCRs), which enable the users to apply their desired time-current characteristics (TCCs). This study propounds novel stepwise and combined stepwise–piece-wise linear TCCs and presents clear procedure to utilise them for coordinating OCRs in large meshed power systems. The TCCs keep constant time interval between the main/backup relay pairs within entire fault current range. They are examined first by coordinating the OCRs in a 4-bus power system and by coordinating the ground fault OCRs in a practical 60 kV looped power system. Then, the OCRs of the IEEE 14-bus test system, which is a rather large meshed power system with 39 OCRs and 102 main/backup pairs, are coordinated by using the novel TCCs. The same relays in the aforesaid power systems are coordinated using some non-standard TCCs recently introduced in the literature. The comparison verifies that the lowest operating times are achieved by using the novel TCCs. The devised TCCs are simply formed as look-up tables to be exactly set on the existing industrial relays. This fact is verified by setting them on an industrial OCR, and then, by testing the relay through the current injection method.

Moving least-squares aided finite element method (MLS-FEM): A powerful means to predict pressure discontinuities of multi-phase flow fields and reduce spurious currents

A technique based on the finite element method (FEM) is developed to precisely predict the pressure jump due to the surface tension forces in two-phase flow problems. In this method, the FEM shape functions of the active elements (the elements containing both phases) are enhanced by the aid of the moving least-squares (MLS) interpolation functions and used in the FEM calculations. Therefore, this technique is named as moving least-squares aided finite element method (MLS-FEM).The enhanced shape function correlates the value of any unknown parameters (e.g., the velocity, pressure, or stress values) at any arbitrary point inside an active element to its surrounding nodes. When the enhancement is performed only for the pressure (P) shape functions, we briefly name the MLS-FEM as the PMLS method (pressure shape function enhanced by the MLS technique). In this case, it would be possible to predict the pressure discontinuities in a two-phase flow domain.To assess the performance of the PMLS method in the calculation of the velocity components and pressure values in two-phase flow fields, the stationary drop problem is investigated. The results show that by employing the PMLS method, not only the magnitude of the spurious current is significantly reduced but also the pressure jump approaches toward its analytical value, without any pressure fluctuation at the interface. It is also explained that the method can be used to evaluate the extent of the drop deformation in a structured or an unstructured meshing system. Finally, the limitation of the introduced method is discussed, which is the basis for further developments.

A New Approach for the Setting of Directional Overcurrent Relays by Incorporating Cascading Outages

Directional overcurrent relays (DOCRs) are the essential protective devices in distribution networks which are usually set without considering any contingencies. However, the current challenge in power systems is the existence of uncertainty and its unfavorable consequences. It sometimes appears that some elements simultaneously fail which makes other parts to be overloaded to the extent that it leads to cascading outages. Therefore, DOCRs may have mal-operation which ends in unwanted trips when there is no fault, or they may not operate in the case the fault is located within their reach point. In such cases, the coordination setting will need complex programming with many related non-linear inequality constraints. In this paper, a novel hybrid method is proposed based on multi-objective optimization including new objective functions by using the genetic algorithm (GA). Also, the cascading outages are considered in the presented method based on network data analysis. This approach is performed on distribution part of the IEEE 14-bus meshed system, and a real industrial radial feeder named TOSEE, located in Iran. The simulations have been implemented in MATLAB and PowerFactory-DIgSILENT software packages in different models, and the results are evaluated.

Integrating layered recurrent ANN with robust control strategy for diverse operating conditions of AGC of the power system

This study presents the structural, operational and control aspects of doubly fed induction generator (DFIG) based wind integrated power systems. The automatic generation control (AGC) of a meshed power system including DFIG-based wind turbines has been framed and investigations under various system perturbation are presented. The two-area system consisting of non-reheat thermal turbines with DFIG and interconnected through parallel AC/DC tie-lines is considered for the study. The system non-idealities such as governor lag and generation rate constraints are taken into consideration. An AGC strategy using a layered recurrent artificial neural network (ANN) is proposed in this work. The gains of the proposed AGC are obtained by effectively training the ANN using a set of reliable data obtained from a widespread range of operating system conditions using robust control strategy. The study also incorporates the design of AGC for the power system using the fuzzy logic concept and other AGC actions such as integral (I), proportional–integral (PI) and proportional–integral–derivative (PID) calculated via the means of particle swarm optimization (PSO). The results obtained with the proposed ANN created AGC are linked and demonstrated their superiority over fuzzy logic PI and traditional PSO-based I/PI/PID AGC strategies under numerous system operating conditions.

1089 - Are there differences in the urodynamic findings after laparoscopic sacrocolpopexy and Trocarless Transvaginal Mesh System for symptomatic pelvic organ prolapse?

1089 - Are there differences in the urodynamic findings after laparoscopic sacrocolpopexy and Trocarless Transvaginal Mesh System for symptomatic pelvic organ prolapse?

A new two-level defect-correction method for the steady Navier–Stokes equations

A new defect-correction method based on subgrid stabilization for the simulation of steady incompressible Navier–Stokes equations with high Reynolds numbers is proposed and studied. This method uses a two-grid finite element discretization strategy and consists of three steps: in the first step, a small nonlinear coarse mesh system is solved, and then, in the following two steps, two Newton-linearized fine mesh problems which have the same stiffness matrices with only different right-hand sides are solved. The nonlinear coarse mesh system incorporates an artificial viscosity term into the Navier–Stokes system as a stabilizing factor, making the nonlinear system easier to resolve. While the linear fine mesh problems are stabilized by a subgrid model defined by an elliptic projection into lower-order finite element spaces for the velocity. Error bounds of the approximate solutions are estimated. Algorithmic parameter scalings are derived from the analysis. Effectiveness of the proposed method is also illustrated by some numerical results.

Numerical Simulation of Phase–change Heat Transfer Problems Using Heat Fluxes on Phase Interface Reconstructed by Contour-Based Reconstruction Algorithm

The numerical analysis of phase–change heat transfer is challenging owing to the multiple inherent limitations of solution procedures for a finite-sized mesh system. For instance, the cell face or node point is not coincident with the phase interface, and thermal-fluidic properties, such as viscosity, specific heat, and thermal conductivity, change sharply through the phase interface. In this study, we introduce a new numerical phase–change model that reflects the thermal-fluidic discontinuities through the phase interface more faithfully. The basic solution procedure is same as the one used in the previous models. However, to obtain the phase–change rate, the new model first reconstructs the phase interface shape and calculates the heat fluxes toward both phases by using the temperature data of the region surrounding the reconstructed phase interface. In this study, we first solved one- and two-dimensional Stefan problems, in addition to the bubble-growth problem. In a comparison with the results of a few existing phase–change models, the superiority of the proposed phase–change model was confirmed in terms of solution continuity and computational costs. Next, we solved flow condensation in micro- and mini-channels and quantitatively compared local variations in the quality and heat transfer coefficient with the corresponding experimental and numerical results obtained by other researchers. Our model exhibited superior consistency with the empirical correlation than the Lee model.

Control Effects of Pretensioned Partially Encapsulated Resin Bolting with Mesh Systems on Extremely Soft Coal Gateways: a Large-Scale Experimental Study

Pretensioned partially encapsulated resin bolting with mesh systems (PPERBMSs) are commonly employed in underground mines, particularly for soft coal gateways requiring immediate support. However, the behavior of bolts and reinforced coals has not been explained, and supporting schemes are determined by engineering analogy and experience. Herein, two large-scale physical models of extremely soft coal gateway sidewalls, reinforced with traditional and improved PPERBMSs, were constructed to probe the performance of pretensioned bolts and the deformation evolution of reinforced coal during roadway driving and panel extraction. Results reveal the bolting effect distribution characteristics of traditional PPERBMS. The mechanism and mode of bolts-mesh-surrounding coal system (BMSCS) instability were analyzed. The control effects of the two supporting schemes were compared, and stability-controlling principles for extremely soft coal roadways were proposed. High bolt pretension force and mesh stiffness are found to be important for improving the bearing capability of BMSCS, especially for reducing the extent of squeezing deformation and severe failure zones in shallow coals. The control method of “high-pretension-force bolts + fine mesh steel–plastic or rhombic screen + high-stiffness welded wire mesh + long bolt/cable for compensating reinforcement at key parts” is proposed to promote the formation of a supporting force interaction zone within surface and shallow coals, reduce the weakly reinforced region causing BMSCS structural instability, and improve the stability and bearing capability of the interaction zone in the bolt anchorage section. These findings are helpful for understanding the bolting effect of PPERBMSs and could provide guidelines for bolting design in soft coal roadways.

Novel numerical method to simulate hydrodynamic characteristic of moving body through free surface and stratified-fluid interface

In order to solve the difficult physical problem of moving structures through free surface and stratified fluid interface, the paper presents and develops a new method based on surface capturing method and Cartesian cut cell mesh to handle transient density interface and moving boundary. Therein, quad-tree data storage structure, adaptive grid techniques, and high-resolution reconstruction limiter are introduced to improve computational efficiency and precision. Hybrid mesh systems of structural and Cartesian cut cell mesh are extended to be applied in the laminar flow problem at low Reynolds number. On this basis, a series of experimental tests of cylindrical models falling through air-water, air-oil and oil-water interfaces are carried out respectively, then several cases are taken to validate the numerical method. Sequentially, the characteristics of interface variation and closure shape versus different density ratios are compared, and the effect of stratified fluid interface on the hydrodynamic force of moving body is mainly discussed. In summary, this paper unifies free surface and stratified fluid interface together as density interface, which can be handled and studied by the same numerical method. Thus, by combining water entry with stratified fluid problem, the influence of various density interfaces on moving body can be better analyzed.

Numerical study on hydrodynamic coefficients and longitudinal motions of trimaran in head seas for various wave slopes

In this study, numerical simulations for the prediction of hydrodynamic coefficients and longitudinal motions of a trimaran vehicle in regular head waves with varying wave slopes are presented for a wide range of wave conditions. Wave excitation and radiation terms in 2DOF equations of longitudinal motions of the ship in regular head seas are obtained, using an unsteady Reynolds averaged Navier–Stokes (URANS) solver based on finite volume method. A trimaran hull form is used for the calculations at a relative high Froude number of 0.628. Numerical simulations are performed for eight different regular wave conditions with varying wave slopes. Firstly, the verification study is performed to determine an optimal mesh system and time step for CFD simulations. Secondly, numerical simulations are carried out to predict hydrodynamic coefficients and longitudinal motion responses and the results are compared with those obtained from the fully URANS approach and experiments. Finally, the relationship between the hydrodynamic coefficients and longitudinal motions are investigated with varying wave slopes. Systematic studies of the numerical simulations demonstrate that the numerical results have a reasonable agreement with the experimental data. The nonlinearities effects of wave slopes on the hydrodynamic coefficients and vertical motion of the trimaran are studied and analyzed taking the viscous effect and free surface nonlinearities into consideration.

Effective Utilization of Transmission Line Capacity in a Meshed Network with Series Capacitor Upto its Thermal Limit

Power system networks are becoming interconnected for the purpose of power delivery to decrease the overall power generation cost. With insufficient control, the power systems become more complicated to function and less secure. The economics of AC power transmission have always forced the planning engineers to transmit as much power as possible through a given transmission line. The smaller and thermally limited lines are crowded in many networks while other higher capacity lines run well below their thermal maximum. When series capacitors are introduced in the higher voltage cables, power may be transferred from the overloaded lines, maximizing the use of the existing line as well as complementing the performance of the power system. In this paper, a three-line meshed power system network with different thermal line limits is considered for the purpose of showing effective utilization of line network for maximum power flow through the intended line with series capacitor compensation. The simulations are performed by using PowerWorld simulator confirms the addition of series capacitor increases the power transfer through the line up to its thermal limit

PERENCANAAN SISTEM PEMBUMIAN GRID-ROD PADA GARDU INDUK 150 KV NEW SANUR

At the substation there are several electrical equipment including power transformers, power breakers, phase change devices, and protective equipment, to keep all equipment in the substation a grounding system is needed. To obtain a good earth system in the planning of the substation must pay attention to the type of soil. In this study there are several methods of earthing system analyzed, including: plate earthing system, mesh earthing system and grid-rod earthing system. This analysis aims to obtain a good earthing system design with a low earth resistance value. From the results of analysis and calculation of the earth grounding system, the earth resistance value is obtained using 34 plates of 0.3555 Ohm. The Earth Mesh system obtained the value of the ground resistance of 0.3447 Ohm with a distance of D is 10 meters then for the planning of the ground-up systems construction of the New Sanur subsite that will be used as a reference is a grid-rod ground system, with The length of the grid is 100 meters, and the width of the grid is 60 meters, then the optimization design obtained from the results of analysis and calculation is 0,3324 useing the distance between the conductor of the grid is 10 meters and the number of rod is 32 Rod.

The Effect of Temperature Variations on Wood’s Metal Plate Melting Simulation by Using MPS

Two-dimensional simulation of Wood’s Metal Plate (WMP) Melting Process has been conducted by varying the molten temperature. This simulation was performed by using Moving Particle Semi-Implicit (MPS) method which can calculate the Navier-Stokes and heat transfer equation without divining mesh system. As a substitute, particles are selected to represent every part of simulation such as fluid, wall and dummy type. The experiment of WMP melting process has been conducted by Sudha (2018). The molten Wood’s Metal was originally set at 573 K. In this simulation, the holes formation in WMP will be investigated as a consequence of molten temperature variation. Furthermore, temperature distribution at top side of WMP and solid-liquid phase change will be analyzed for initial temperature of molten are 523 K, 473 K and 423 K. The results show that the phases change significantly in a short time when the molten temperature is increased. However, until the end of simulation which on 1.5 s just for molten temperature 573 K shows the breaching process to the WMP. This study can be implemented when the reactor nuclear severe accident happened.

Highly reliable overcurrent protection scheme for highly meshed power systems

To improve the transient stability of synchronous generators, overcurrent relays should react to electrical faults as fast as possible. In some cases, the backup relays cannot be coordinated properly with their primary relays using non-communication overcurrent protection schemes. In this study, a highly reliable overcurrent protection scheme is proposed to overcome this problem. Firstly, criteria are proposed to identify the pairs in which the backup relays fail to react to faults in some fault locations and communication links are used for preserving the coordination. Then, a novel optimization method is proposed, which consists of metaheuristic and deterministic parts. Although a well-known equation is used to obtain critical clearing time for overcurrent coordination in the literature, only fault at busbar is taken into account using this equation. Moreover, the postfault network topology has a significant effect on the transient stability of synchronous generators. In this research, the transient stability is analyzed for faults at different distances from overcurrent relays. Moreover, the circuit breaker operation and network reconfiguration are taken into account for finding the critical clearing time. As a result, the transient stability of the synchronous generator is improved. The proposed algorithm is applied to both the 33 kV distribution part of the 30 and 39-bus transmission IEEE standard test systems. It is shown that the relays operating and pairs discrimination times are significantly reduced. For the 30-bus power system, the obtained total relays operating time using the proposed method satisfying a highly reliable coordination is less than 1/10 of those obtained from conventional coordination methods. It is shown that, the total relays operating time obtained for the 39-bus power system considering non-zero fault impedance was dropped, and it came to the range of the obtained results for the 30-bus system using conventional methods and zero fault impedance.