Stable finite element methods for the Stokes problem

The mixed finite element scheme of the Stokes problem with pressure stabilization is analyzed for the cross-grid Pk−Pk−1elements, k≥1, using discontinuous pressures. The Pk+−Pk−1 elements are also analyzed. We prove the stability of the scheme using the macroelement technique. The order of convergence follows from the standard theory of mixed methods. The macroelement technique can also be applicable to the stability analysis for some higher order methods using continuous pressures such as Taylor-Hood methods, cross-grid methods, or iso-grid methods

Superconvergence of finite element method for parabolic problem

We study superconvergence of a semi-discrete finite element scheme for parabolic problem. Our new scheme is based on introducing different approximation of initial condition. First, we give a superconvergence of uh−Rhu, then use a postprocessing to improve the accuracy to higher order

Desalination Technology in South Korea: A Comprehensive Review of Technology Trends and Future Outlook

Due to advances in desalination technology, desalination has been considered as a practical method to meet the increasing global fresh water demand. This paper explores the status of the desalination industry and research work in South Korea. Desalination plant designs, statistics, and the roadmap for desalination research were analyzed. To reduce energy consumption in desalination, seawater reverse osmosis (SWRO) has been intensively investigated. Recently, alternative desalination technologies, including forward osmosis, pressure-retarded osmosis, membrane distillation, capacitive deionization, renewable-energy-powered desalination, and desalination batteries have also been actively studied. Related major consortium-based desalination research projects and their pilot plants suggest insights into lowering the energy consumption of desalination and mitigation of the environmental impact of SWRO brine as well. Finally, considerations concerning further development are suggested based on the current status of desalination technology in South Korea

Design of Quad-Edge-Triggered Sequential Logic Circuits for Ternary Logic

1

Control Strategy for Line Overload and Short Circuit Current of Networked Distribution Systems

The expected increase in renewable energy sources (RESs) and electric vehicles (EVs) connected to distribution systems will result in many technical constraints. A meshed network is a promising solution; however, some remarkable challenges must be overcome. Among these, this paper mainly focuses on the line overload and short circuit current of a networked distribution system (NDS) in Korea, an advanced form of meshed network. An NDS refers to a system in which there exists permanent linkages between four feeders and N × N communication-based protection. We propose a method, which employs the tap changing control algorithm of the series reactor to control line overload and short circuit current. MATLAB/Simulink was used to evaluate the proposed method. Three different types of distribution system were employed. First, the utilization rate and feeder imbalance were analyzed in steady-state condition. Subsequently, the short circuit current was analyzed in short circuit condition. The results revealed that the proposed method can effectively prevent line overload in up to 82.7% of cases, enhance the utilization rate by up to 79.9%, and relieve the short circuit current; that is, it can contribute to system stability and the economic operation of an NDS

Mitigating Subsynchronous Torsional Interaction Using Geometric Feature Extraction Method

This paper proposes a method to mitigate subsynchronous torsional interaction detected during power system operation. This innovative method employs the delay reconstruction of the damping controller of a thyristor-controlled series compensator. This addresses the need to detect and manage stability and electromagnetic transients in power systems caused by the increasing use of fast-response power electronics. Previously, severe oscillation conditions could be avoided via analysis of the subsynchronous torsional interaction scenarios during the planning stage, enabling the suppression of oscillations. However, planning, modeling, and analysis for various scenarios becomes more difficult as the complexity of the power system increases, owing to the use of renewable energy and the incorporation of topology changes. Therefore, interest in measurement data-based real-time oscillation analysis has increased. The first step of the mitigation strategy proposed herein reconstructs nonlinear time-series data to detect subsynchronous torsional interaction in real time and generate alert signals. The second step of the strategy is that the controller mitigates oscillations by controlling the firing angle using the geometric feature extraction method. In this paper, the relaxation of the frequency oscillation in the subsynchronous region of about 22 Hz and about 18 Hz was verified through two simulation cases