Combined Method of Flow-Reduced Dump Load for Frequency Control of an Autonomous Micro-Hydropower in AC Microgrids

Nowadays, microgrids (MGs) play a crucial role in modern power systems due to possibility of integrating renewable energies into grid-connected or islanded power systems. The Load Frequency Control (LFC) is an issue of paramount importance to ensure MGs reliable and safe operation. Specifically, in AC MGs, primary frequency control of each energy source can be guaranteed in order to integrate other energy sources. This paper proposes a micro-hydro frequency control scheme, combining the control of a reduced dump load and the nozzle flow control of Pelton turbines operating in autonomous regime. Some works have reported the integration of dump load and flow control methods, but they did not reduce the dump load value and adjust the nozzle flow linearly to the power value demanded by users, causing the inefficient use of water. Simulation results were obtained in Matlab®/Simulink® using models obtained from previous research and proven by means of experimental studies. The simulation of the proposed scheme shows that the frequency control in this plant is done in correspondence with the Cuban NC62-04 norm of power energy quality. In addition, it is possible to increase energy efficiency by reducing the value of the resistive dump load by up to 7.5% in a case study. The validation result shows a 60% reduction of overshoot and settling time of frequency temporal behavior of the autonomous micro-hydro.

Influences on the Seismic Response of a Gravity Dam with Different Foundation and Reservoir Modeling Assumptions

The seismic design and dynamic analysis of high concrete gravity dams is a challenge due to the dams’ high levels of designed seismic intensity, dam height, and water pressure. In this study, the rigid, massless, and viscoelastic artificial boundary foundation models were established to consider the effect of dam–foundation dynamic interaction on the dynamic responses of the dam. Three reservoir water simulation methods, namely, the Westergaard added mass method, and incompressible and compressible potential fluid methods, were used to account for the effect of hydrodynamic pressure on the dynamic characteristics and seismic responses of the dam. The ranges of the truncation boundary of the foundation and reservoir in numerical analysis were further investigated. The research results showed that the viscoelastic artificial boundary foundation was more efficient than the massless foundation in the simulation of the radiation damping effect of the far-field foundation. It was found that a foundation size of 3 times the dam height was the most reasonable range of the truncation boundary of the foundation. The dynamic interaction of the reservoir foundation had a significant influence on the dam stress.

Liquid water simulation using hydrogen bond corrected SCAN and neural network potentials.

Accurately reproducing the structure of liquid water with ab initio molecular dynamics (AIMD) simulation is a crucial first step on the path towards accurately predicting the properties of liquid solutions without relying on experiment. Density functional theory (DFT) is normally used to approximate the forces in these simulations. However, no DFT functional has been shown to give an entirely satisfactory description of the structure of liquid water. Here, I propose a simple correction to the strongly constrained and appropriately normalised (SCAN) DFT functional, that corrects the strength of the hydrogen bonding interaction with a simple exponential potential fitted to dimer energy calculations. The resulting SCAN-CH functional provides an excellent description of the structure of liquid water. Long time scale NPT simulations are enabled by the use of neural network potentials, which demonstrate that the simulations are well converged and that the density of water is also more accurately reproduced with this method.

Newly Developed Thermal Load Profile for Enhancement in Hot Water System

In recent years with the advancement of technologies, the demand of a reliable and flexible hot water system has increased tremendously. A reliable system includes several critical points which are the degree of safety that a system can offer, the conservation of the energy used and the issue of cost saving. While a flexible system must provide the flexibility in the control of the output from a system desired by the consumers itself. This paper reported on newly developed system for hot water that will greatly benefit consumer. It focuses on building an extension of the cyber physical system in the existing system with purposes of implementing a thermal load profile for consumer who use the hot water system in their daily life. The implementation of the thermal load profile to the system is significant especially in conserving the energy used in the system simultaneously saving any related cost to operate the system. Based on the implemented thermal load profile, the system works in maintaining an output of thermal energy from the hot water supplied to the consumer at a certain value. In addition, it also allows flexibility in controlling the desired temperature by consumers. This new system is simulated in a test bench in the form of laboratory setup. The system uses a control loop feedback mechanism, which means that it will continuously regulate the temperature and mass flow rate of the flowed water in the pipeline for the consumer hot water simulation based on the calculated difference of the actual supplied values and the set values. With the use of standard devices and actuators to drive the system, a robust system can be realized.

Self-preservation Effect of Gas Hydrates

This work was performed to improve the storage and transportation technology of gas hydrates in nonequilibrium conditions. At atmospheric pressure and positive ambient temperature, they gradually dissociate into gas and water. Simulation of the gas hydrate dissociation will determine optimal conditions for their transportation and storage, as well as minimize gas loss. Thermodynamic parameters of adiabatic processes of forced preservation of pre-cooled gas hydrate blocks with ice layer were determined theoretically and experimentally. Physical and mathematical models of these processes were proposed. The scientific novelty is in establishing quantitative characteristics that describe the gas hydrates thermophysical parameters thermophysical characteristics influence on the heat transfer processes intensity on the interphase surface under conditions of gas hydrates dissociation. Based on the results of experimental studies, approximation dependences for determining the temperature in the depths of a dissociating gas hydrate array have been obtained. Gas hydrates dissociation mathematical model is presented.

Improving the rational use of water resources of the Chograi reservoir based on water simulation modeling

Purpose: to develop scenarios for filling and rational exploitation of the Chograi reservoir under the conditions of water resources shortage of (to conduct water balance studies). Materials and methods. The analysis of the use and distribution of water resources of the Chograi reservoir was carried out on the basis of actual data obtained for the period 2016–2020. To conduct water balance studies, a simulation water management model has been developed. It is based on the water allocation regime established in 2020. Results and discussion. Three possible scenarios for water management situation development in the Chograi reservoir have been developed, from which the optimal one has been selected. As the initial conditions for modeling, the regimes of water supply through the Tersko-Kumsky and Kumo-Manychsky canals, as well as water intake into the Chernozemelsky irrigation and watering system (CHOS) through the Chernozemelsky main canal were used. It was found that the actual value of water intake from the Terek river exceeded the plan, but remained below the water intake limit. Thus, it is possible to increase the volume of water supply to the reservoir due to withdrawal up to the values of the permitted limit. The analysis shows that the largest volume of water resources is used for feeding water bodies and for estuary irrigation. The second largest volume taken from the Chograi reservoir is the water supply through the bottom spillway to the downstream of the hydroelectric complex in the Eastern Manych river with expenditures exceeding sanitary releases. It is possible to reduce the consumed water resources by optimizing water management at the CHOS and reducing discharges. Conclusions. An optimal scenario for filling and rational operation of the Chograi reservoir has been developed, the fulfillment of the conditions of which will ensure the filling of the reservoir to the level of 20.35 m BS. At the same time, the volume of filling will be 209.75 million m³. The development of the water management situation according to the scenario under consideration will provide water resources for the CHOS for the period 2021–2022.

An Urban Water Simulation Model for the Design, Testing and Economic Viability Assessment of Distributed Water Management Systems for a Circular Economy

The concept of Circular Economy, although not entirely new, has in recent years gained traction due to growing concern with regards to the Earth’s natural reserves. In this context, Sewer Mining, a wastewater management method based on extracting wastewater from local sewers for reuse applications, presents an interesting option that lies in the interplay between reuse at a household scale and centralized reuse at a wastewater treatment plant. As part of the EU-funded program NextGenWater, a new unit is being prepared for operation in Athens’s Plant Nursery, in Goudi. This paper examines the water flow within the proposed installation, using the Urban Water Optioneering Tool (UWOT). Further research is focused on the economic viability of Sewer Mining and the proposed investment. The results produced are promising regarding Sewer Mining’s capabilities and benefits, as well as its future prospects, in the hopes that this technology can provide an attractive alternative to conventional water sources within the urban water cycle.

Evaluating SWAT Performance to Quantify the Streamflow Sediment Yield in a Highly Urbanized Basin

Hydrological predictive models represent the most recently developed tools in the field of water simulation. In this study, the Soil and Water Assessment Tool (SWAT) model was applied in the Aspio basin in central Italy. After a calibration and validation procedure based on daily streamflow-observed data, the sediment erosion rate from the basin was estimated in the 4 years of simulation. The years of 2016 and 2018 were characterized by a higher amount of transported sediment, which coincided with the run-off peaks events. Regarding the land-use classification, this study shows how the agricultural and artificial areas provide a higher contribution to the transported sediments. This study shows that SWAT can be used for land management in highly urbanized watersheds.