نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه مهندسی عمران، واحد بین‌الملل کیش، دانشگاه آزاد اسلامی، جزیره کیش، ایران.
2 گروه سازه های آبی، دانشکده مهندسی آب و محیط زیست، دانشگاه شهید چمران اهواز، اهواز، ایران
3 گروه مهندسی عمران، واحد رودهن، دانشگاه آزاد رودهن، ایران
چکیده
معضل هدر رفت آب و انرژی و در نتیجه کاهش کارآمدی سیستم های آبرسانی، وجود انشعاب غیرمجاز است. این پدیده هم در سیستم های آبرسانی شرب و هم کشاورزی اتفاق می افتد. در این تحقیق بهصورت آزمایشگاهی به بررسی اثر انشعاب غیر مجاز بر موج فشار جریان گذرا در خطوط لوله ویسکوالاستیک پرداخته شده است. مدل آزمایشگاهی این تحقیق متشکل از یک لوله پلی اتیلنی 2 اینچ به طول 158 متر، و ضخامت 6 میلیمتر است. انشعاب های مورد استفاده نیز از جنس پلی اتیلن با طول ها، قطرها، و مکان های مختلف اند. مقایسۀ اثر انشعاب ها با طول مختلف نشان داد که با افزایش طول انشعاب، بازتاب آن شدیدتر می شود و اثر آن بر پایین افتادگی سیگنال فشار مشهودتر است. وجود انشعاب باعث تغییر فاز سیگنال می شود و این تغییر فاز با گذشت زمان از شروع جریان گذرا بیشتر است. مقدار تغییر فاز در مکان نزدیک به شیر بین 8 تا 15 درصد و در مکان نزدیک به مخزن بین 5 تا 12 درصد تغییر می کند. مقایسۀ نوسان های فشار در حوزۀ زمان نشان داد که فعال بودن انشعاب، استهلاک بیشتری بر موج جریان گذرا اعمال می کند. با این همه، تغییر فاز محسوسی در سیگنال فشار ایجاد نمی شود. در پایان، اثر انشعاب غیر مجاز با سیستم لولۀ سالم و لوله با وجود نشت نیز مقایسه و رویکرد مدلسازی عددی انشعاب غیرمجاز ارائه شد.
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
Experimental investigation of the illegal connection effect on transient pressure wave characteristics in viscoelastic transmission pipelines
نویسندگان [English]
- Ehsan Ebrahimi 1
- Mahmoud Shafai Bajestan 2
- Babak Aminnejad 3
1 Department of Civil Engineering, Kish International Branch, Islamic Azad University, Kish Island, Iran
2 Professor, Department of Water Engineering and Environment, Shahid Chamran, University of Ahvaz,, Ahvaz, Iran.
3 Assistant Professor, Faculty of Engineering, Islamic Azad University of Rudehen, Iran.
چکیده [English]
Extended Abstract
Introduction
In recent years, due to the increase in population, demands, and water consumption, the limitation of freshwater resources on the one hand, and the lack of comprehensive and targeted management programs in the water resources sector, on the other hand, there are many problems facing water resources management. It has created countries. One of the sources of water wastage in water supply systems is the presence of illegal connections.
This research investigates the effect of illegal connections on the transient pressure signal in viscoelastic pipelines. This research can be the basis for detection methods of illegal connections based on transient flow analysis in the future. Most past research has been done numerically to detect illegal connections based on transient flow. More work has been done on the elastic pipe system than the laboratory research.
Methodology
In this research, building a laboratory model of a suitable viscoelastic polyethylene pipe system has been tried to investigate the effect of illegal connections on the pressure signal at Shahid Chamran University of Ahvaz, Ahvaz. The experimental program consisted of hydraulic transient tests with simulated illegal connections. The pipeline is made of HDPE with PE100 and NP16 bar. The pipeline's total length is about 158 meters, with built-in sloping rings upwards. The pipes are fixed to a metal structure to restrain them from axial movement.
The analysis includes removing noise from experimental signals, calculating overpressure in the time domain, and generating the system's frequency response using a Fast Fourier transform (FFT). There are different methods to remove the noises in the laboratory pressures. However, to avoid removing the valuable information of the pressure signal, by comparing different noise removal methods, including moving average, a frequency filter, etc., the best method for the transient was using the Butterworth low-pass frequency filter. In this method, by transferring the pressure signal from the time domain to the frequency domain, the high frequencies of the wave, which are mainly caused by environmental conditions, are removed, and the low frequencies of the signal are preserved.
Results and Discussion
Comparing the behavior of an intact pipe system and a pipe with a leak showed that compared to these systems, the pipe with an illegal connection has a more complex behavior and cannot be solved with a multi-step approach. In fault-finding methods based on transient with this behavior that causes a phase change in the signal, it is inevitable to optimize all the decision variables together or look for another mathematical approach to solve such problems. Knowing the behavior of a viscoelastic pipe with an illegal viscoelastic connection can be a way to decide to provide new solutions in the frequency domain.
Conclusions
Comparing the effect of the illegal connection with different lengths shows that with the increase in the length of the branch, its reflection is more intense and its impact on lowering the pressure signal is more evident. In general, the illegal connection's presence causes the signal's phase change, which increases over time. The comparison of the effect of transient intensity on the pressure response of the pipe system with the presence of the illegal connection shows that with the increase in the transient intensity, only the signal difference increases, which is caused by the more substantial reflection of the illegal connection. Also, approaching the transient valve, the amount of phase difference becomes more intense with time and the contrast of signals increases. The comparison of pressure fluctuations in the time domain shows that the activation of the bifurcation exerts more attenuation on the transient flow wave. However, there is no noticeable phase change in the pressure signal.
کلیدواژه‌ها [English]
- Transient wave
- waterhammer
- polymer pipes
- illegal connection
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