scholarly journals A Study on the Effects of Model Structure and Demand Allocation on Water Network Modeling

2020 ◽  
Vol 42 (3) ◽  
pp. 110-120
Author(s):  
Seonghan Kim ◽  
Kwansue Jung ◽  
Sukmin Yoon ◽  
No-Suk Park
Keyword(s):  
Steady State ◽  
Network Modeling ◽  
Extended Period ◽  
Model Structure ◽  
Water Network ◽  
Detailed Model ◽  
Water Head ◽  
Models Comparison ◽  
The Difference ◽  
Steady State Simulation

Objectives:In order to reduce the uncertainty of the pipe network modeling, the model structure was basically included all distribution pipes and several models were proposed according to the location of the water meters.Methods:For models verification, first, a steady state simulation of each model was made by constructing a model including all water supply pipes (All-meters Model), which are the bases of 3 simplified models, and considering the location of all water meters. The network analysis was performed by dividing into the steady state and the extended period simulation.Results and Discussion:From the results of models comparison, ‘All-meters Model’ and ‘All-connections Model’ were found to obtain more accurate results for constructing a water network model for simulation of water quality events in distribution network. When constructing an ‘All-meters Model’ in all networks, the model becomes complicated and data management does difficult. Therefore this study suggests a hybrid model construction.Conclusions:It would be reasonable to construct a detailed model (All-meters or All-connections Model) in looped network in which the water flow path can be changed according to the difference of water head, and a skeletonized model (Street-meters aggregation or Reduced-meters Model) for a branch network that does not have a significant impact on demand allocations.

An Improved Algorithm of Evaporator Steady-State Simulation

2010 ◽  
Author(s):  
Baoshi Jiang ◽  
Wenzhi Cui ◽  
Yong Xiang ◽  
Tien-Chien Jen
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Weighted Average ◽  
Lumped Parameter Model ◽  
Outlet Temperature ◽  
Average Temperature ◽  
Lumped Parameter ◽  
Chilled Water ◽  
The Difference ◽  
Steady State Simulation

The characteristics of heat pump evaporator are simulated using steady-state lumped parameter model. Considering the difference between the heat transfer of vapor and liquid refrigerant, the calculating method of the weighted average temperature in evaporator is revised, and the scope of the calculation is expanded to superheat section. The assumption of the chilled water outlet temperature is generally used in conventional simulation program and iteration of the temperature is necessary, which is a time-consuming process. In this paper, the outlet temperature of chilled water is determined by energy conservation and only the outlet enthalpy of refrigerant needs to be iterated, making the calculating process much fast. The effects of inlet parameters of chilled water on overall heat transfer and outlet chilled water temperature are examined using the new program. The prediction of simulation is compared with experimental results and good agreement obtained.

A Dynamic Model of a Locomotive Diesel Engine and Electrohydraulic Governor

1988 ◽  
Vol 110 (3) ◽  
pp. 405-414 ◽  
Author(s):  
C. I. Rackmil ◽  
P. N. Blumberg ◽  
D. A. Becker ◽  
R. R. Schuller ◽  
D. C. Garvey
Keyword(s):  
Steady State ◽  
Diesel Engine ◽  
Rate Of Change ◽  
Regression Equations ◽  
Detailed Model ◽  
Engine Simulation ◽  
System A ◽  
Load Demand ◽  
The Difference ◽  
Exhaust Energy

As part of a comprehensive simulation of a prototype locomotive propulsion system, a detailed model has been developed that predicts the dynamic response of an experimental two-stroke, turbocharged and intercooled diesel engine. Engine fueling and brake torque are computed from regression equations derived from an extensive data base. Corrections are applied to the calculated steady-state torque to account for dynamic deviations of in-cylinder trapped air-fuel ratio from the steady-state value. The engine simulation accurately represents the operation of the turbocharger, which is gear-driven at low turbocharger speeds, and freewheels through an overrunning clutch when exhaust energy accelerates the turbocharger beyond its geared speed. Engine fueling level, i.e., rack, is determined from a dynamic simulation of an electrohydraulic governor, which responds to the difference between the desired and the actual engine speeds. The governor representation includes: (1) finite rate of change of engine set speed; (2) load regulator feedback for control of applied engine loads; and (3) fuel limiting under conditions of excessively high load demand. The fundamentals of the engine/governor model are given in the paper along with examples that emphasize the dynamic operation of these particular components.

scholarly journals Generalizing WDN simulation models to variable tank levels

2011 ◽  
Vol 14 (3) ◽  
pp. 562-573 ◽  
Author(s):  
Orazio Giustolisi ◽  
Luigi Berardi ◽  
Daniele Laucelli
Keyword(s):  
Steady State ◽  
Mass Balance ◽  
Water Distribution ◽  
Extended Period ◽  
Water Distribution Network ◽  
Simulation Models ◽  
Gradient Algorithm ◽  
Initial State ◽  
Cross Sectional ◽  
Steady State Simulation

In water distribution network (WDN) steady-state modelling, tanks and reservoirs are modelled as nodes with known heads. As a result, the tank levels are upgraded after every steady-state simulation (snapshot) using external mass balance equations in extended period simulation (EPS). This approach can give rise to numerical instabilities, especially when tanks are in close proximity. In order to obtain a stable EPS model, an unsteady formulation of the WDN model has recently introduced. This work presents an extension of the steady-state WDN model, both for demand-driven and pressure-driven analyses, allowing the direct prediction of head variation of tank nodes with respect to an initial state. Head variations at those nodes are introduced as internal unknowns in the model, the variation of tank levels can be analyzed in the single steady-state simulation and EPS can be performed as a sequence of simulations without the need for external mass balances. The extension of mass balance at tank nodes allows the analysis of some technically relevant demand components. Furthermore, inlet and outlet head losses at tank nodes are introduced and large cross-sectional tank areas are allowed by the model and reservoirs become a special case of tanks. The solution algorithm is the generalized-global gradient algorithm (G-GGA), although the proposed WDN model generalization is universal.

Comparisons of Steady and Time-Averaged Unsteady Flow Predictions for Impeller–Diffuser Interactions in a Centrifugal Compressor Stage

2007 ◽  
Author(s):  
N. He ◽  
A. Tourlidakis ◽  
R. L. Elder
Keyword(s):  
Steady State ◽  
Velocity Field ◽  
Pressure Field ◽  
Vaned Diffuser ◽  
Unsteady Simulation ◽  
Simulation Results ◽  
The Difference ◽  
Steady Simulation ◽  
Steady State Simulation ◽  
Isentropic Efficiency

In the present paper a computational analysis of the interactions between a backswept impeller and its downstream vaned diffuser in a high-speed centrifugal compressor is presented. Both steady and unsteady simulations are carried out at the peak efficiency point. Geometry scaling was used in the unsteady simulation in order to deal with the problem of unequal pitch. For the steady simulation, an averaging approach is used at the interface between the impeller and the diffuser. A detailed comparison between the time averaged unsteady results and the steady simulation results is performed and some unsteady phenomena are also discussed in order to advance the understanding of the flow physics involved. One important conclusion is that the unsteady simulation is important since the difference between the time averaged unsteady results and steady simulation results is quite significant especially in the velocity field and the stage efficiency. From the comparisons of the predicted results with available experimental data in terms of velocity vectors and isentropic efficiency, it can be concluded that the geometry scaling method used in the current unsteady simulation is reasonable and successful and the computational model employed for the predictions consists a reliable computational tool. In general, the contours of different flow variables for the averaged unsteady simulation results are more uniform than the steady ones, especially in the vaneless space. In the static pressure field, there are relatively small differences. The main differences occur in the region of the vaneless space and downstream of the throat area, and in general the difference is found to be quite small. In the velocity field, the differences are large compared with the ones occurring in the pressure field. The area with the largest differences extends from the vaneless space into the semi-vaneless and vaned diffuser channel. The unsteadiness also modifies the flow angle and hence the incidence angle at the leading edge of the vaned diffuser, the maximum difference can reach 3 degrees. The difference in the stage isentropic efficiency can reach above 1 per cent, which is considered to be quite high. The results also indicate that the larger differences between the time-averaged unsteady and steady state simulation results usually occurred in the area that flows are highly unsteady or nearly separated. Consequently the steady state simulation is still not very accurate to predict highly unsteady flow and separated flows.

scholarly journals Effects of Genotypes and Treatment on Oxygenscan Parameters in Sickle Cell Disease

Cells ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 811
Author(s):  
Camille Boisson ◽  
Minke A. E. Rab ◽  
Elie Nader ◽  
Céline Renoux ◽  
Celeste Kanne ◽  
...  
Keyword(s):  
Steady State ◽  
Sickle Cell Disease ◽  
Blood Cell ◽  
Sickle Cell ◽  
Red Blood Cell ◽  
Cell Disease ◽  
Oxygen Gradient ◽  
Acute Complication ◽  
Adults And Children ◽  
The Difference

(1) Background: The aim of the present study was to compare oxygen gradient ektacytometry parameters between sickle cell patients of different genotypes (SS, SC, and S/β+) or under different treatments (hydroxyurea or chronic red blood cell exchange). (2) Methods: Oxygen gradient ektacytometry was performed in 167 adults and children at steady state. In addition, five SS patients had oxygenscan measurements at steady state and during an acute complication requiring hospitalization. (3) Results: Red blood cell (RBC) deformability upon deoxygenation (EImin) and in normoxia (EImax) was increased, and the susceptibility of RBC to sickle upon deoxygenation was decreased in SC patients when compared to untreated SS patients older than 5 years old. SS patients under chronic red blood cell exchange had higher EImin and EImax and lower susceptibility of RBC to sickle upon deoxygenation compared to untreated SS patients, SS patients younger than 5 years old, and hydroxyurea-treated SS and SC patients. The susceptibility of RBC to sickle upon deoxygenation was increased in the five SS patients during acute complication compared to steady state, although the difference between steady state and acute complication was variable from one patient to another. (4) Conclusions: The present study demonstrates that oxygen gradient ektacytometry parameters are affected by sickle cell disease (SCD) genotype and treatment.

Cyclic Breathing Simulations in Large Scale Models of the Lung Airway From the Oronasal Opening to the Terminal Bronchioles

2012 ◽  
Author(s):  
D. Keith Walters ◽  
Greg W. Burgreen ◽  
Robert L. Hester ◽  
David S. Thompson ◽  
David M. Lavallee ◽  
...  
Keyword(s):  
Steady State ◽  
Boundary Conditions ◽  
Large Scale ◽  
Whole Body ◽  
Patient Specific ◽  
Cfd Simulations ◽  
Reduced Order ◽  
Scale Models ◽  
Steady State Simulation ◽  
Conducting Zone

Computational fluid dynamics (CFD) simulations were performed for unsteady periodic breathing conditions, using large-scale models of the human lung airway. The computational domain included fully coupled representations of the orotracheal region and large conducting zone up to generation four (G4) obtained from patient-specific CT data, and the small conducting zone (to G16) obtained from a stochastically generated airway tree with statistically realistic geometrical characteristics. A reduced-order geometry was used, in which several airway branches in each generation were truncated, and only select flow paths were retained to G16. The inlet and outlet flow boundaries corresponded to the oronasal opening (superior), the inlet/outlet planes in terminal bronchioles (distal), and the unresolved airway boundaries arising from the truncation procedure (intermediate). The cyclic flow was specified according to the predicted ventilation patterns for a healthy adult male at three different activity levels, supplied by the whole-body modeling software HumMod. The CFD simulations were performed using Ansys FLUENT. The mass flow distribution at the distal boundaries was prescribed using a previously documented methodology, in which the percentage of the total flow for each boundary was first determined from a steady-state simulation with an applied flow rate equal to the average during the inhalation phase of the breathing cycle. The distal pressure boundary conditions for the steady-state simulation were set using a stochastic coupling procedure to ensure physiologically realistic flow conditions. The results show that: 1) physiologically realistic flow is obtained in the model, in terms of cyclic mass conservation and approximately uniform pressure distribution in the distal airways; 2) the predicted alveolar pressure is in good agreement with previously documented values; and 3) the use of reduced-order geometry modeling allows accurate and efficient simulation of large-scale breathing lung flow, provided care is taken to use a physiologically realistic geometry and to properly address the unsteady boundary conditions.

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