МЕТОДЫ ОЦЕНКИ И ПОВЫШЕНИЯ НАДЕЖНОСТИ САМОНАПОРНЫХ ЗАКРЫТЫХ ОРОСИТЕЛЬНЫХ СЕТЕЙ

УДК 628.842:631.6

Abstract

The article investigates the issues of assessing and increasing the reliability of energy- and resource-saving self-flow closed pressure irrigation networks (CIN) in the conditions of the foothill regions of Central Asia. The study analyzed the causes of system element failure at the design, construction, and operation stages, specifically contamination, abrasive wear, and structural defects of the water outlet pipes. Based on the principles of reliability theory and the Weibull-Gnedenko distribution, a new block of mathematical models has been developed, taking into account the dynamics of abrasive wear and clogging of water outlet pipes. Methods for predicting parametric pipe failure limits of  and the safe service life of the system (T_res) have been established. A deviation of the water flow rate from the norm by ±10% is justified as a parametric failure of the system, and a set of measures is recommended to ensure the integrity, repair ability, and long-term durability of the network.

Аннотация

В статье исследованы вопросы оценки и повышения надежности энерго- и ресурсосберегающих самонапорных закрытых оросительных сетей в условиях предгорных районов Центральной Азии. Проанализированы основные причины отказов элементов системы на стадиях проектирования, строительства и эксплуатации, включая засорение, абразивный износ и конструктивные дефекты водовыпускных трубопроводов. На основе положений теории надежности и распределения Вейбулла–Гнеденко разработан новый комплекс математических моделей, учитывающих динамику абразивного износа и засорения водовыпускных трубопроводов. Предложены методы прогнозирования параметрических пределов отказа трубопроводов  и определения безопасного срока эксплуатации системы (T_res). Обосновано, что отклонение расхода воды от нормативного значения на ±10 % следует рассматривать как параметрический отказ системы. Рекомендован комплекс мероприятий, направленных на обеспечение целостности, ремонтопригодности и долговечности оросительной сети.

Keywords: closed irrigation network (CIN), self-flow pressure system, reliability assessment, parametric failure, abrasive wear, clogging intensity, service life forecasting.

Ключевые слова: закрытая оросительная сеть (ЗОС), самонапорная напорная система, оценка надежности, параметрический отказ, абразивный износ, интенсивность засорения, прогнозирование срока службы.

Introduction

The growing shortage of water and energy resources in the country's Central Asian region, as well as environmental problems, require the development of energy- and resource-saving irrigation technologies [5]. The self-flow closed pressure irrigation networks (CIN) being implemented in foothill areas allow for a significant increase in water utilization efficiency and elevate the technical condition of irrigation systems to a new level.

However, insufficient experience in the field of design, low quality of construction and installation work, and violations of operational rules reduce the advantages of such systems [2]. A decrease in agricultural crop yields is being observed due to malfunctions in network elements and the uneven distribution of moisture along the length of the furrows. Therefore, ensuring the reliability of these systems is of great economic importance.

The practice of operating irrigation systems shows that the development of measures to increase reliability is a complex task that must be carried out comprehensively at the stages of design, construction, and operation [6]. The objective of this study is to develop mathematical methods for assessing the reliability of a self-flow pressure SFP at the design and operation stages, as well as to increase its technical resource.

Materials and methods

Due to the topological similarity to drip irrigation systems, the study utilized probability methods that account for the random nature of water flow in space and time [9]. When assessing irrigation quality by furrow length, the range of changes in discharge in the discharge pipes, pressure fluctuations in the pipeline, and the probability of continuous irrigation furrow operation  were taken into account comprehensively [4]. The uniform wetting coefficient  along the furrow length was determined based on the following mathematical dependence.

 ,

here (, ) is the water layer (volume) absorbed at the end and beginning of the furrow at the initial stage of operation (t = 0), m;

 — a coefficient representing the uniform distribution of water flow through the outlet pipes;

 is a coefficient characterizing the reliable operation of the irrigation furrow.

The probability of continuous furrow operation for 1 year was taken as , taking into account the number of reserves (n=6) [6].

Model of pipe diameter expansion due to abrasive wear

As a result of the friction of solid particles (sand, sediment) in the water against the pipe walls, the hole radius increases over time [8]. The change in the pipe radius over time (t) is expressed by the following differential equation:

 ,

here  is the radius of the pipe opening at time t, m;

 is the abrasive wear resistance coefficient of the pipe material;

 is water density, kg/m³;

 is the turbidity level of the irrigation water (solid sediment concentration), kg/m³;

 is the water outlet velocity from the pipe, m/s.

According to hydraulic laws, the time-increasing function of water flow due to abrasive wear takes the following form:

,

here  is the initial radius of the pipe,   is the maximum allowable expansion, and  is the ultimate wear time.

Model of turbidity and clogging intensity of pipes

The clogging of water outlet pipes over time due to algae and fine sediments was modeled based on the Poisson distribution [1]. The model for reducing water consumption due to the decrease in the useful cross-sectional area of the pipe over time is expressed as follows.

here λ is the turbidity and clogging intensity of the pipe, determined as follows:            (α is the design coefficient,  is the amount of organic waste in the water, and  is the pipe diameter);

Results and discussion

Analysis of the long-term operation of the self-flow GOST showed that the failure of the water outlet pipes is characterized by the deviation of the water flow from the permissible limits over a certain period of time, i.e., parametric failure.

Based on the conditions of hydraulic studies and the prevention of soil erosion, the following permissible criterion limits for the flow rate of the pipe () relative to the design value () were determined [12,13]:

If the water discharge exceeds these limits (), the element is considered to have failed [3]. Based on these criteria, the safe service life (T_res) of the pipe was predicted using the following expression:

.

Based on the Weibull-Gnedenko distribution law, the probability of the water outlet pipe functioning correctly  was determined:

Based on the 90% confidence interval of the pipe flow rate, a parametric failure of the irrigation pipeline was considered if the number of elements in the pipeline with a flow rate exceeding the permissible deviations exceeded 10% (F) [9]. In this case, the systemic service life of the general irrigation pipeline () corresponds to the following condition:

.

In the studies of G.Yu. Sheynkin (1970), V.A. Surin, and N.K. Nurmatov (1972), the water distribution was high at the initial stage of system operation, with a standard deviation of δ=0.04–0.09. However, under real operational conditions, system reliability decreases under the influence of two factors.:

1. Reduced water consumption (): This occurs as a result of floating debris and algae clogging the pipes due to malfunctions in the waste-trapping grilles of the water intake, as well as siltation of the pipes [1]. This leads to incomplete irrigation of crops.

2. Increased water flow rate (): Under the influence of solid debris (sand, pebbles) in the water composition, wear and expansion of pipe holes occur [8]. This leads to excessive deep penetration, surface discharges, and soil erosion [13].

The proposed new mathematical model, unlike previous studies, made it possible to dynamically correlate the state of the system with the time factor and water quality () [17]. To ensure system reliability, it is necessary to implement the following set of preventive measures:

-At the design stage: Provision of multi-stage settling tanks and mobile cleaning nets in water intake structures, use of pipes made of wear-resistant polymer materials.

-At the construction stage: Strict control over the accuracy of geodetic slopes and the density of welded joints during pipe laying and pipe installation [2].

-At the operational stage: mandatory flushing of pipes (cleaning of silt) before and after each irrigation season, as well as scheduled preventive repair of the system when the number of faulty pipes reaches an estimated 10%.

Conclusion

1. The main criterion for evaluating the quality of furrow irrigation from a self-flowing is the  coefficient, which accounts for the range of technological variations in the discharge of discharge pipes and the reliability of the furrow.

2. Parametric pipe failure limit . When the number of such defective elements exceeds 10% of the total number, the irrigation pipeline enters a state of complete failure and requires maintenance.

3. The developed mathematical models of abrasive wear and clogging allow for the high-precision prediction of the safe service life of the system (, ) depending on water quality and structural parameters   .

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