Multi-commodity flow problems（MCFs） can be found in many areas, such as transportation, communication, and logistics. Therefore, such problems have been studied by a multitude of researchers, and a variety of method...Multi-commodity flow problems（MCFs） can be found in many areas, such as transportation, communication, and logistics. Therefore, such problems have been studied by a multitude of researchers, and a variety of methods have been proposed for solving it. However, most researchers only discuss the properties of different models and algorithms without taking into account the impacts of actual implementation. In fact, the true performance of a method may differ greatly across various implementations. In this paper, several popular optimization solvers for implementations of column generation and Lagrangian relaxation are discussed. In order to test scalability and optimality, three groups of networks with different structures are used as case studies. Results show that column generation outperforms Lagrangian relaxation in most instances, but the latter is better suited to networks with a large number of commodities.展开更多
In order to investigate the data reliability of the core liquid permeability flow experiment evaluation test results, the uncertainty of the test results was evaluated. First of all, the core liquid permeability evalu...In order to investigate the data reliability of the core liquid permeability flow experiment evaluation test results, the uncertainty of the test results was evaluated. First of all, the core liquid permeability evaluation device is used to conduct a complete test according to the industry standard requirements. Then, according to the method in JJF 1059.1-2012 "Evaluation and Expression of Measurement Uncertainty", the known mathematical model is used to accurately identify and calculate each component causing uncertainty in the flow test process. The results show that the uncertainty component caused by mass weighing contributes the most to the combined standard uncertainty, followed by the uncertainty component caused by pressure measurement and the uncertainty component caused by the time flowing through the upper and lower scribing lines of the viscometer, and the accuracy grade of the measuring instrument also has a great influence on the evaluation result of the uncertainty.展开更多
The article addresses the results of effective water losses prevention in public water supply systems, focusing on procedures for monitoring hidden leaks as the main part of losses and as the first step to control and...The article addresses the results of effective water losses prevention in public water supply systems, focusing on procedures for monitoring hidden leaks as the main part of losses and as the first step to control and prevent them. The described methodology has been applied based on a cross-border cooperation between twin capital cities Vienna and Bratislava in the Central Europe Region within the project deWaloP （Developing Water Loss Prevention） and adopted in Bratislava Water Company （BVS） in the Slovak Republic. The paper provides a complex of simple and easily available practices for analyses of water distribution measurements bringing essential information as to the necessity to use advanced procedures to actively reduce leakage. These practices involve minimum night flows analyses, hydrodynamic pressures analyses, pinpointing of water leakages by working with valves in the water network, the methodology of setting alarm limits for measured data, as well as use of advanced practices to obtain missing topologic data. As the water infrastructure in former socialistic countries are in bad technical condition and the lack of pertinent operational data is a significant obstacle to the application of a more sophisticated methodology based on GIS and other information systems, the procedures focus on using the most simple way to evaluate and control water losses. Finally, the introduction of described methodology in Bratislava Water Company after many years of unsuccessful effort even with expensive sophisticated leakage equipment brought positive outputs and the graph line of water losses level is finally going down. The use of expensive multi-correlating equipment together with human resources on the basis of implementing the above described leakage monitoring will subsequently become more effective, as it shall pinpoint major leakages, disclosure and removal of that shall significantly contribute to the effective reduction of water losses.展开更多
基金supported by research funds from the National Natural Science Foundation of China (Nos. 61521091, 61650110516, 61601013)
文摘Multi-commodity flow problems（MCFs） can be found in many areas, such as transportation, communication, and logistics. Therefore, such problems have been studied by a multitude of researchers, and a variety of methods have been proposed for solving it. However, most researchers only discuss the properties of different models and algorithms without taking into account the impacts of actual implementation. In fact, the true performance of a method may differ greatly across various implementations. In this paper, several popular optimization solvers for implementations of column generation and Lagrangian relaxation are discussed. In order to test scalability and optimality, three groups of networks with different structures are used as case studies. Results show that column generation outperforms Lagrangian relaxation in most instances, but the latter is better suited to networks with a large number of commodities.
文摘In order to investigate the data reliability of the core liquid permeability flow experiment evaluation test results, the uncertainty of the test results was evaluated. First of all, the core liquid permeability evaluation device is used to conduct a complete test according to the industry standard requirements. Then, according to the method in JJF 1059.1-2012 "Evaluation and Expression of Measurement Uncertainty", the known mathematical model is used to accurately identify and calculate each component causing uncertainty in the flow test process. The results show that the uncertainty component caused by mass weighing contributes the most to the combined standard uncertainty, followed by the uncertainty component caused by pressure measurement and the uncertainty component caused by the time flowing through the upper and lower scribing lines of the viscometer, and the accuracy grade of the measuring instrument also has a great influence on the evaluation result of the uncertainty.
文摘The article addresses the results of effective water losses prevention in public water supply systems, focusing on procedures for monitoring hidden leaks as the main part of losses and as the first step to control and prevent them. The described methodology has been applied based on a cross-border cooperation between twin capital cities Vienna and Bratislava in the Central Europe Region within the project deWaloP （Developing Water Loss Prevention） and adopted in Bratislava Water Company （BVS） in the Slovak Republic. The paper provides a complex of simple and easily available practices for analyses of water distribution measurements bringing essential information as to the necessity to use advanced procedures to actively reduce leakage. These practices involve minimum night flows analyses, hydrodynamic pressures analyses, pinpointing of water leakages by working with valves in the water network, the methodology of setting alarm limits for measured data, as well as use of advanced practices to obtain missing topologic data. As the water infrastructure in former socialistic countries are in bad technical condition and the lack of pertinent operational data is a significant obstacle to the application of a more sophisticated methodology based on GIS and other information systems, the procedures focus on using the most simple way to evaluate and control water losses. Finally, the introduction of described methodology in Bratislava Water Company after many years of unsuccessful effort even with expensive sophisticated leakage equipment brought positive outputs and the graph line of water losses level is finally going down. The use of expensive multi-correlating equipment together with human resources on the basis of implementing the above described leakage monitoring will subsequently become more effective, as it shall pinpoint major leakages, disclosure and removal of that shall significantly contribute to the effective reduction of water losses.
