Noniterative Implementation of Pressure-Dependent Demands Using the Hydraulic Analysis Engine of EPANET 2

To analyze water distribution networks under pressure-deficient conditions, most of the available hydraulic simulators, including EPANET 2, must be either modified by embedding pressure-dependent demands in the governing network equations or run repeatedly with successive adjustments made to specific parameters until a sufficient hydraulic consistency is obtained. This paper presents and discusses a simple technique that implements the square root relationship between the nodal demand and the nodal pressure using EPANET 2 tools and allows a water distribution network with pressure-dependent demands to be solved in a single run of the unmodified snapshot hydraulic analysis engine of EPANET 2. In this technique, artificial strings made up of a flow control valve, a pipe with a check valve, and a reservoir are connected to the demand nodes before running the engine, and the pressure-dependent demands are determined as the flows in the strings. The resistance of the artificial pipes is chosen such that the demands are satisfied in full at a desired nodal pressure. The proposed technique shows reasonable convergence as evidenced by its testing on example networks.     

The Raduga universal software for calculating parameters for the fault-free operation, working life, reliability, and repairability of gas cleaning and dust trapping equipment

The Raduga software has been written on the basis of mixed derived structures for series-parallel connection of components designed in accordance with an ecological factor. The Raduga software enables one to determine the ecological, economic, technological, and working parameters of equipment and plant and to develop working rules and provide a guarantee of operation with given parameters for a time specified by the customer. Calculations are reported on the working degree of gas cleaning in an electrical filter, and it is pointed out that the error in the calculations does not exceed acceptable limits.     

Convergence of a Hydraulic Solver with Pressure-Dependent Demands

This paper analyzes the convergence of a pressure-driven analysis (PDA) model of a water distribution network solver based on Todini’s global gradient algorithm. The PDA model is constructed by embedding a pressure?demand relationship in the EPANET simulator code. To avoid spurious convergence, a residual-based convergence error was used. The introduction of pressure-dependent demands is shown to result in a far poorer convergence. The study of solver convergence as a function of the smoothness of the pressure?demand curve has demonstrated that, statistically, a smooth pressure?demand relationship gives a somewhat better convergence. To improve convergence, use was made of a quadratic approximation of the Hazen–Williams head loss?flow relationship in the vicinity of zero and the correct implementation of the Darcy?Weisbach formula in the solver. To further improve convergence, an iteration step control technique called the line search was used. The analysis of solver convergence for different line search variants has shown that the line search in its usual form is not efficient enough and may result in poorer convergence. A necessary error decrease algorithm, whose use in the line search improves solver convergence, is proposed. It is shown that due to the convergence improvement methods the convergence of the PDA solver is somewhat better than that of the demand-driven analysis solver and sufficient for direct problems such as design, for example.     

Effect of Sc substitution and pressure on phase transition in Rb2KGaF6 elpasolite

Solid solutions Rb₂KGa_xSc_1-xF₆ (x = 1.0; 0.95; 0.9; 0.8; 0.6) were studied by X-ray, neutron, calorimetric and DTA under hydrostatic pressure methods. Both heat capacity and entropy are strongly influenced by x concentration. According to (T vs. x) phase diagram suggested the phase transition temperatures of compounds with x from 1.0 to 0.8 belong to the same phase boundary.