• Proceedings of the Korea Water Resources Association Conference
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• 1999.05a
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• pp.775-780
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• 1999

• Proceedings of the Korea Water Resources Association Conference
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• 2000.05a
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• pp.873-878
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• 2000

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.320-324
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• 2013

A crack identification method using an equivalent bending stiffness for cracked beam and committee of neural networks is presented. The equivalent bending stiffness is constructed based on an energy method for a straight thin-walled pipe, which has a through-the-thickness crack, subjected to bending. Several numerical analysis for a steel cantilever pipe using the equivalent bending stiffness are carried out to extract the natural frequencies and mode shapes of the cracked beam. The extracted modal properties are used in constructing a training patterns of a neural network. The input to the neural network consists of the modal properties and the output is composed of the crack location and size. Multiple neural networks are constructed and each individual network is trained independently with different initial synaptic weights. Then, the estimated crack locations and sizes from different neural networks are averaged. Experimental crack detection is carried out for 3 damage cases using the proposed method, and the identified crack locations and sizes agree reasonably well with the exact values.

• Journal of the Korean Institute of Gas
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• v.11 no.2 s.35
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• pp.1-4
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• 2007

Natural gas has different gas composition according to imported gas region, and the difference of gas composition affects pressure loss value occurred in pipe networks, Therefore, using real gas composition instead of averaged gas composition can obtain more reliable results for pipe network analysis. In this study, the effect of real gas composition at gas supply points on the demand pressure has been analyzed. To compare the results, the calculated pressure values for averaged gas composition at all the supply points have been used. From the results, we found that the effect of real gas composition consideration on demand pressure was considerable, and the real gas composition has to be considered for reliable pipe network analysis in gas industry.

• Membrane and Water Treatment
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• v.10 no.1
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• pp.75-82
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• 2019

In a highly urbanized area, land availability is limited for the installation of space consuming stormwater systems for best management practices (BMPs), leading to the consideration of underground stormwater treatment devices connected to the stormwater pipe system. The configuration of a stormwater pipe network determines the hydrological and pollutant transport characteristics of the stormwater discharged through the pipe network, and thus should be an important design consideration for effective management of stormwater quantity and quality. This article presents a multi-objective optimization approach for designing a stormwater pipe network with on-line stormwater treatment devices to achieve an optimal trade-off between the total installation cost and the annual removal efficiency of total suspended solids (TSS). The Non-dominated Sorted Genetic Algorithm-II (NSGA-II) was adapted to solve the multi-objective optimization problem. The study site used to demonstrate the developed approach was a commercial area that has an existing pipe network with eight outfalls into an adjacent stream in Yongin City, South Korea. The stormwater management model (SWMM) was calibrated based on the data obtained from a subcatchment within the study area and was further used to simulate the flow rates and TSS discharge rates through a given pipe network for the entire study area. In the simulation, an underground stormwater treatment device was assumed to be installed at each outfall and sized proportional to the average flow rate at the outfall. The total installation cost for the pipes and underground devices was estimated based on empirical formulas using the flow rates and TSS discharge rates simulated by the SWMM. In the demonstration example, the installation cost could be reduced by up to 9% while the annual TSS removal efficiency could be increased by 4% compared to the original pipe network configuration. The annual TSS removal efficiency was relatively insensitive to the total installation cost in the Pareto-optimal solutions of the pipe network design. The results suggested that the installation cost of the pipes and stormwater treatment devices can be substantially reduced without significantly compromising the pollutant removal efficiency when the pipe network is optimally designed.

• Journal of Korea Water Resources Association
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• v.55 no.spc1
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• pp.1187-1195
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• 2022

To run the algorithm for identifying the segments of a pipe network, the relative positional relation between nodes, pipes, and valves should be prepared as input information of a segment search algorithm. In order to more accurately identify the segments of real pipe network, pipe network GIS/CAD database that contains all isolation valves is more suitable than modeled pipe network information used for a hydraulic analysis program. In this study, we developed an algorithm that can establish the relative positional relations among node-pipe-valve suitable for pipe network segment search algorithms using GIS/CAD data of a real water supply network, and developed a MATLAB program that can implement it. The effectiveness of the developed MATLAB program was confirmed by applying it to a portion of a real municipal pipe network.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.2
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• pp.249-256
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• 2012

The paper describes a design methodology that can select a proper reliability factor and apply the selected reliability factor into the real water distribution system. Reliability factors which are used for the assesment of water supply networks, can be categorized by a connectivity, a reachability, an expected shortage and an availability. Among these factors, an expected shortage is the most proper reliability factor in the aspect of economic evaluation. Therefore, the expected shortage is applied to draw a water supply reliability into Changwon water supply systems. And the economic pipe diameter can be determined as 600mm for a connection pipe in the pipe network from the estimation of the expected shortage. Also, a quantitative effect of the connection pipe can be expressed in terms of the reduction, which is estimated by the expected shortage of 30,269$m^{3}$ from 68,705$m^{3}$ at initial condition to 38,436$m^{3}$ under the connected condition with the diameter 600mm pipe.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.11
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• pp.764-770
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• 2015

A crack identification method using an equivalent bending stiffness and natural frequency for cracked beam is presented. Modal properties of cantilever beam with a tip mass is identified by applying the boundary conditions to a general solution. An equivalent bending stiffness for cracked beam based on an energy method is used to identify natural frequencies of cantilever thin-walled pipe with a tip mass, which has a through-the-thickness crack, subjected to bending. The identified natural frequencies of the cracked beam are used in constructing training patterns of neural networks. Then crack location and size are identified using a committee of the neural networks. Crack detection was carried out for an example beam using the proposed method, and the identified crack locations and sizes agree reasonably well with the exact values.

• Journal of Korea Water Resources Association
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• v.33 no.S1
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• pp.873-878
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• 2000

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.169-169
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• 2023

Most distributed water is not used effectively due to water loss occurring in pipe networks. These water losses are caused by leakage, typically due to high water pressure to ensure adequate water supply. High water pressure can cause the pipe to burst or develop leaks over time, particularly in an aging network. In order to reduce the amount of leakage and ensure proper water distribution, it is important to apply pressure management. Pressure management aims to maintain a steady and uniform pressure level throughout the network, which can be achieved through various operational schemes. The schemes include: (1) installing a variable speed pump (VSP), (2) introducing district metered area (DMA), and (3) operating pressure-reducing valves (PRV). Applying these approaches requires consideration of various hydraulic, economic, and environmental aspects. Due to the different functions of these approaches and related components, an all-together optimization of these schemes is a complicated task. In order to reduce the optimization complexity, this study recommends a sequential optimization method. With three network operation schemes considered (i.e., VSP, DMA, and PRV), the method explores all the possible combinations of pressure management paths. Through sequential optimization, the best pressure management path can be determined using a multiple-criteria decision analysis (MCDA) to weigh in factors of cost savings, investment, pressure uniformity, and CO₂ emissions. Additionally, the contribution of each scheme to pressure management was also described in the application results.