Hydraulic Factors Research Articles

Validation of Applying Simulation Models for Different Irrigation Systems: Review Article

In Egypt, agriculture is shaped by two goals. The first goal is maximum national production per unit area and the second goal is maximum production per cubic meter of water. Therefore, this strategy relates the utilization of national resources, soil and water, and to do this in a proper way we need tools and technologies which will allow to develop these resources in a suitable manner. The design and managing of irrigation systems must have its base in criteria that are relevant, which implies to take into account agronomic, soil, hydraulic, economic, energetic, and environmental factors. The optimal design and managing of irrigation systems at farm level is the first important factor for a rational use of water, economic development of agriculture and its environmental sustainability. Computer simulation models have the potential to improve the efficiency of irrigation systems and thus deliver significant water savings. This can be achieved by optimizing the design and management decisions at the field level. Irrigation simulation models are useful tools both at the design and management stages of irrigation systems. When used for irrigation design purposes, simulation models help to optimize irrigation variables such as field slope, length of the field and the design flow rate...etc. These models can aid the designer in making decisions as to the appropriate values of variables that produce the best performance. This is mostly applicable to newly established fields or when converting from one irrigation system to another. In the majority of the irrigation simulation models currently in use, previous field characteristics are used to optimize future irrigations. However, numerous researchers have established that these characteristics change both with time and space, and hence the accuracy of such models may be affected. Therefore, the aim of this article is to analyse knowledge and investigations that enable to identify the principal criteria and processes that allow improving the design and managing of the irrigation systems, based on using irrigation systems simulation models to develop agriculture more efficient and sustainable, as well as using them as a tool for farmers, researchers, and decision makers.

Vibration Characteristics of a Hydroelectric Generating System with Different Hydraulic-Mechanical-Electric Parameters in a Sudden Load Increasing Process

In a sudden load increasing process (SLIP), the hydroelectric generating system (HGS) experiences a severe vibration response due to the sudden change of the hydraulic-mechanical-electric parameters (HMEPs). The instability of HGS limits the ability of sudden load increase, and its flexibility and reliability are reduced. Thus, in this study, a new transient nonlinear coupling model of HGS is proposed, which couples the hydro-turbine governing system (HTGS) and the hydro-turbine generator shafting system (HGSS) with the hydraulic-mechanical-electric coupling force, rotating speed, flow rate, hydro-turbine torque, electromagnetic torque, and guide vane opening. By using numerical simulation, the influences of different HMEPs on the vibration characteristics of HGS in SLIP are analyzed. The result shows that, compared with stable operating conditions, the vibration amplitude of HGS increases sharply in SLIP. The increase of the sudden load increasing amount, blade exit flow angle, mass eccentricity and excitation current, and the decrease in guide bearing stiffness and average air gap between the stator and rotor cause abnormal vibration of different degrees in the HGS. Hydraulic factors have the greatest influence on the nonlinear dynamic behavior of HGS. The maximum vibration amplitude of HGS in SLIP is increased by 70.46%, compared with that under stable operating conditions. This study provides reasonable reference for the analysis of the nonlinear dynamic behavior of HGS in SLIP under the multiple vibration sources.

Risk coupling analysis of subsea blowout accidents based on dynamic Bayesian network and NK model

Risk analysis of subsea blowout accidents is critical to well control strategies and the overall safety of offshore drilling operations. Therefore, the interactive relationships among different types of risk factors should not be neglected. This paper proposes a novel method to quantify risk coupling of subsea blowout accidents based on dynamic Bayesian network (DBN) and NK model. First, causation of subsea blowout accidents is analyzed and risk factors are classified. Second, the types of risk coupling caused by human factors, electrical factors, hydraulic factors and mechanical factors are defined. Third, the DBN model is developed based on risk analysis of subsea blowout accidents and its NK model. Forth, parameters of risk coupling nodes in the developed DBN are determined by the calculation results from NK model. Finally, the developed model is validated by a three-axiom-based method. Dynamic characteristics of risk evolution and risk coupling of the subsea blowout accidents could be described by the developed DBN. In addition, sensitivity analysis of risk coupling types is performed and influences of risk factors are quantified by mutual information. With the developed model, uncertainty analysis is perform to research the effects of failure rates of risk factors on main risk coupling types.

Riverscape-Scale Modeling of Fundamentally Suitable Habitat for Mussel Assemblages in an Ozark River System, Missouri

Identifying the physical habitat characteristics associated with riverine freshwater mussel assemblages is challenging but crucial for understanding the causes of mussel declines. The occurrence of mussels in multispecies beds suggests that common physical factors influence or limit their occurrence. Fine-scale geomorphic and hydraulic factors (e.g., scour, bed stability) are predictive of mussel-bed occurrence, but they are computationally challenging to represent at intermediate or riverscape scales. We used maximum entropy (MaxEnt) modeling to evaluate associations between riverscape-scale hydrogeomorphic variables and mussel-bed presence along 530 river km of the Meramec River basin, USA, to identify river reaches that are fundamentally suitable for mussels as well as those that are not. We obtained the locations of mussel beds from an existing, multiyear dataset, and we derived river variables from high-resolution, open-source datasets of aerial imagery and topography. Mussel beds occurred almost exclusively in reaches identified by our model as suitable; these were characterized by laterally stable channels, absence of adjacent bluffs, proximity to gravel bars, higher stream power, and larger areas of contiguous water (a proxy for drought vulnerability). We validated our model findings based on model sensitivity using a set of mussel-bed locations not used in model development. These findings can inform how resource managers allocate survey, monitoring, and conservation efforts.

Population demographics of golden perch (

An understanding of population demographics and life history processes is integral to the rehabilitation of fish populations. In Australia’s highly modified Murray–Darling Basin, native fish are imperilled and fish deaths in the Darling River in 2018–19 highlighted their vulnerability. Golden perch (Macquaria ambigua) is a long-lived percichthyid that was conspicuous in the fish kills. To guide population rehabilitation in the Darling River, pre-fish kill age structure, provenance and movement of golden perch were explored using otolith microstructure and chemistry (87Sr/86Sr). Across the Lower and Mid-Darling River, recruitment was episodic, with dominant cohorts associated with years characterised by elevated discharge. There was substantial variability in age structure, recruitment source and movement patterns between the Lower and Mid-Darling River. In the Mid-Darling River, tributaries were an important recruitment source, whereas in the Lower Darling fish predominantly originated in the Darling River itself. Downstream movement of juveniles, upstream migration of adults and return movements to natal locations were important drivers of population structure. Restoring resilient golden perch populations in the Darling River will be reliant on mitigating barriers to movement, promoting a connected mosaic of recruitment sources and reinstating the hydrological and hydraulic factors associated with spawning, recruitment and dispersal. Globally, increasing water resource development and climate change will necessitate such integrated approaches to the management of long-lived migratory riverine fishes.

Effects of Long-Term Increases in Water Temperature and Stratification on Large Artificial Water-Source Lakes in South Korea

Long-term changes in air and water temperatures and the resulted stratification phenomena were observed for Soyang Lake (SY), Paldang Lake (PD), Chungju Lake (CJ), and Daecheong Lake (DC) in South Korea. Non-parametric seasonal Kendall and Mann-Kendall tests, Sen slope estimator, and potential energy anomaly (PEA) were applied. The lake surface water temperatures (LSWTs) of SY and DC increased at the same rate (0.125 °C/y), followed by those of CJ (0.071 °C/y) and PD (0.06 °C/y). Seasonally, the LSWT increase rates for all lakes, except PD, were 2–3 times higher than the air temperature increase rates. The lake stratification intensity order was similar to those of the LSWT increases and correlations. SY and DC displayed significant correlations between LSWT (0.99) and PEA (0.91). Thus, the LSWT significantly affected stratification when the water temperature increased. PD demonstrated the lowest correlation between LSWT and PEA. Inflow, outflow, rainfall, wind speed, and retention time were significantly correlated, which varied within and between lakes depending on lake topographical, hydraulic, and hydrological factors. Thus, hydraulic problems and nutrients should be managed to minimize their effects on lake water quality and aquatic ecosystems because lake cyanobacteria can increase as localized water temperatures increase.

Probabilistic Prediction of Multi-Wells Production Based on Production Characteristics Analysis Using Key Factors in Shale Formations

In this study, we propose a novel workflow to predict the production of existing and new multi-wells. To perform reliable production forecasting on heterogeneous shale formations, the features of these formations must be analyzed by classifying the formations into various groups; the groups have different production characteristics depending on the key factors that affect the shale formation. In addition, the limited data obtained from nearby existing multi-wells should be used to estimate the production of new wells. The key factors that affect shale formation were derived from the correlation and principal component analysis of available production-related attributes. The production of existing wells was estimated by classifying them into groups based on their production characteristics. These classified groups also identified the relationship between hydraulic fracturing design factors and productivity. To estimate the production of new wells (blind wells), we generated groups with different production characteristics and leveraged their features to estimate the production. Probabilistic values of the group features were entered into the input layer of the artificial neural network model to consider the variation in the production of shale formations. All the estimated productions exhibited less error than the previous analytical results, suggesting the utilization potential of the proposed workflow.

Assessing the hydraulic reduction performance of HYDRUS-1D for application of alkaline irrigation in variably-saturated soils: Validation of pH driven hydraulic reduction scaling factors

Land application of alkaline irrigation water is an increasing practice in most agricultural lands around the world due to the shortage of freshwater resources. Accurate evaluation of the effects of alkalinity on soil properties is essential to avoid environmental risks. In this study, we used long leaching columns to evaluate alkalinisation and sodification hazards in soils in the laboratory at different water qualities (0, 100, 310 and 650 HCO3-, mg L−1) with electrical conductivity (EC) ≈ 2.1 dS m−1 and sodium adsorption ratio (SAR) ≈ 12 (mmolc L−1)0.5. The ability of the HYDRUS-1D model to simulate solute and water movement under unsaturated conditions in columns of 40 cm height filled with acidic, neutral or alkaline soils was also assessed. Changes in soil EC, SAR, pH and alkalinity were monitored at 5, 15, 25 and 35 cm depths for 290 days. Increased solution alkalinity resulted in increased pH, alkalinity and sodicity within the soil profile, in particular for the soil surface and acidic soils. In general, the HYDRUS model, using the standard hydraulic reduction scaling factor, was able to simulate the effects of alkalinity in the soil profile and the associated hydraulic conductivity reduction. Amending the pH driven hydraulic reduction scaling factor in the model to a non-linear, soil-specific, pedotransfer function significantly improved the correlation between predicted and observed hydraulic conductivity. The findings of this study provide validation for a non-linear approach towards determining the pH hydraulic reduction scaling factor in the HYDRUS-1D model for unsaturated conditions. However, it is noted that further improvement of this non-linear approach is required to incorporate other factors governing soil structural stability.

Research on variation law of geophysical drill-bit downhole flow field under the interaction of multiple hydraulic factors.

Mountain geophysical prospecting operations play an important role in the entire petroleum exploration field. Geophysical drill-bit is the main tool for mountain geophysical prospecting operations. Its hydraulic structure directly affects the downhole flow field and then affects the chip removal efficiency and drilling efficiency of the bit. At present, most of the scholars' research is focused on Poly Diamond Crystalline bit, roller bit, etc., and the research on geophysical drill-bit is less, and most of them study the downhole flow field based on the change of single hydraulic structure. The primary objective of this research is to study the variation law of the downhole flow field under the interaction of multiple hydraulic structure factors. The drilling time and cuttings size of two geophysical drill-bits with different hydraulic structures are compared, and the key hydraulic structure factors are selected for analysis. Using numerical simulation software, take different levels of key hydraulic structure parameters and carry out orthogonal experiments. Under the interaction of various factors, study the flow field distribution in the flow channel, the downhole, and the annulus area of the shaft lining. The hydraulic structure of the geophysical drill-bit is closely related to the drilling speed and chip removal efficiency. When multiple hydraulic factors are changed, the diameter of the flow channel is the best when it is 10-12.5 mm, the inclination of the flow channel should be set as close as possible to the center of the downhole, and the length of the chip groove increases, the movement of cuttings is more stable. Variation law of downhole flow field under the interaction of multiple hydraulic factors is studied. This study provides a basis for the hydraulic structure design and optimization of the geophysical drill-bit.

Water Level Fluctuation Patterns in Restricted Intermediate Navigable Channels with Different Lock Emptying Processes

The fluctuation of water level caused by the unsteady flow of lock discharge, where the key problem is the relationships between the hydraulic factors in the restricted middle navigable channel and the transformation of unsteady flow and the corresponding scales are investigated. Based on the restricted middle navigable channel of the Baise navigation project, the relationship between the unsteady flow discharge process of lock and the water surface fluctuation process in the restricted middle channel is studied through systematic experiments, and the conclusion is drawn as follows. The main reason caused the flow fluctuation is attributed to the insufficient energy dissipation and rapid increase of discharge during the lock discharge process. And the sectional discharge method which reduces the peak value of the discharge process can reduce the fluctuation of upstream and downstream water level effectively. By reducing the peak value of the time-discharge curve, the energy dissipation along with restricted middle navigable channel increases, with the fluctuation amplitude of upstream and downstream flow reduces, and the attenuation rate of the energy dissipation increases. Furthermore, a fixed phase lag is formed between the reflection wave formed by the downstream ship lift gate and the discharge wave formed by the upstream ship lock discharge, which has little relationship with the discharge curve.

Mixed‐coefficient panel model for evaluating the overall deformation behavior of high arch dams using the spatial clustering

The mathematical monitoring models that are currently used for the displacement of arch dams are mostly established for a single monitoring point, without considering the spatial association of the displacements at multiple monitoring points. The main purpose of this paper is to develop and verify a mixed-coefficient panel model for dam displacements of multiple monitoring points. To maintain the largest similarities of the deformation mechanism of different monitoring points represented by one panel model, the displacement monitoring points on dam body are first divided into several groups according to the similarity index of the incremental distance between their measured displacement time series. The mixed-coefficient panel models are then established for each clustered zone in which the adjustment coefficient of the FEM-calculated hydraulic component is determined to be identical for all the monitoring points in the same zone, whereas the regression coefficients of the temperature and time effect component are considered to be variable, in order to reflect the similarities and differences of deformation mechanism in different dam regions. Based on the hydraulic, hysteretic, seasonal, and time (HHST) causal factors, the proposed panel model is verified by the measured radial displacement field of the Jinping-I arch dam. The modeling results demonstrate that the proposed mixed-coefficient panel model can effectively represent the overall deformation behavior and structural integrity of a high arch dam, and it has good performance in the interpretation and prediction of the dam displacement and the inversion analysis of viscoelastic parameters of the dam body concrete.

Numerical study on Unstable Hydraulic Factors of Kaplan turbine with semi-spiral case at large flow rate conditions

The operation of semi-spiral case Kaplan turbines at large flow rate conditions is restricted by factors such as severe cavitation and severe vibration, which limit the maximum output of the unit. In order to explore the main hydraulic factors that cause the poor operating stability of the unit at large flow rate conditions, and provide a reference for the operation and design of the turbine, the numerical simulation method is adopted to conduct the performance study of an semi-spiral case Kaplan turbine at different operating conditions, by comparing and analysing the results at the optimal conditions and large flow rate conditions, the unstable hydraulic factors at large flow rate conditions is obtained. The research results show that: at large flow rate conditions, the uneven flow distribution in the semi-spiral case cause vortices between the guide vanes, lead to the large fluctuations of blade torque, and generate unstable back-flow and vortices in the draft tube. These phenomena combined with the various gap flows in the runner, make the internal flow of the Kaplan turbine at large flow rate conditions deteriorate, cavitation increase, efficiency decrease, and cause severe vibration, thereby limiting the stable operation of Kaplan turbine at large flow rate conditions.

Unsteady state contaminants transport in sandy mediums using CFD model

This study was conducted to provide a CFD simulation model to simulate the transfer of pollutants through sandy soils. A physical model and simulation model were designed and implemented with the help of CFD programs using COMSOL 5.4 software to study the process of transporting pollutants within the porous medium. To study the pollutant transmission in the porous media, a sand size of less than 0.36 mm diameters was used as porous media. For an analysis of the problem, several groups of factors were considered and assumed. The first group concerned with the physical properties of the media likes coefficient of adoption Kd. The second group represented the hydraulic factor of flow likes velocity. The results of the physical and CFD models showed there is a clear effect of soil physical properties due to the coefficient of adsorption Kd action. The velocity has a significant effect on the concentrations of pollutants and the time of transmission where the lower velocities produce lower concentrations and delayed transport of pollutants in the soil. The CFD simulated model showed that the change in the Kd-value has a significant impact on the results. The study also showed a good agreement between the results of the laboratory work provided by the physical model and that of the CFD model depending on several statistical indexes. This indicates that the CFD models could be considered as an efficient tool to simulate the complex problems of contaminates transport through a porous medium.

Characterizing shear-thinning fluids transitioning from rheology- to inertia-dominated flow regimes in porous media

Understanding and predicting non-Newtonian fluid flows in porous media is crucial for many geophysical and environmental problems. Although extensive studies have investigated nonlinear flow for shear thinning fluids, the critical Reynolds number (Rec) for identifying nonlinearity in transition from rheology-dominated to inertia-dominated flows remains unclear. To determine Rec, we conducted hundreds of direct numerical simulations of power law fluids with diverse fluid rheology (quantified by a power law exponent n) through a variety of pore geometries which are characterized by a non-dimensional hydraulic shape factor (β). The numerically-derived pressure gradient and fluid flux were used to compute the bulk viscosity ~ Reynolds number curves, which were further employed to determine Rec. With knowing Rec, we established a predictive function between Rec and (β, n). This function allows for the estimation of Rec based on the measurable properties (β, n) via imaging technique. Our mechanistic modelling work sheds light on predicting nonlinear flow for non-Newtonian fluids at the continuum scale by knowing under what conditions the inertial effects are significant.

Stability analysis of hydro-turbine governing system based on machine learning

Hydro-turbine governing system is a time-varying complex system with strong non-linearity, and its dynamic characteristics are jointly affected by hydraulic, mechanical, electrical, and other factors. Aiming at the stability of the hydro-turbine governing system, this paper first builds a dynamic model of the hydro-turbine governing system through mechanism modeling, and introduces the transfer coefficient characteristics under different load conditions to obtain the stability category of the system. BP neural network is used to perform the machine study and the predictive analysis of the stability of the system under different working conditions is carried out by using the additional momentum method to optimize the algorithm. The test set results show that the method can accurately distinguish the stability category of the hydro-turbine governing system (HTGS), and the research results can provide a theoretical reference for the operation and management of smart hydropower stations in the future.

طراحی و ساخت دستگاه آزمایشگاهی مطالعه فرسایش داخلی خاک در جریان دوبُعدی

غالب مطالعات و معیارهایی که درخصوص ارزیابی وقوع فرسایش داخلی در خاک‌های مستعد ارائه شده است، در شرایط جریان‌های یک‌بُعدی (رو به بالا یا رو به پایین) که در جهت عمود بر لایه‌های خاک اعمال شده، بوده است. در حالی که در طبیعت و حتی خاکریزهای مهندسی لزوماً جهت جریان عمود بر جهت لایه‌ها نیست. از این رو در پژوهش حاضر، یک مدل فیزیکی ویژه با قابلیت مطالعه‌ی نمونه‌های تا اندازه‌ی شن و جهت‌های مختلف لایه‌ها و جریان، طراحی و ساخته شد. نتایج آزمایش‌هایی که بر روی خاک‌های با دانه‌بندی گسسته انجام شده است، نشان می‌دهد که مقادیر گرادیان‌های بحرانی در خاک‌های با لایه‌های عمود بیشتر از خاک‌های با لایه‌های موازی است. همچنین با افزایش زاویه‌ی جریان نسبت به جهت ثقل، به‌طور کلی مقدار گرادیان‌های بحرانی نیز افزایش می‌یابد. علاوه بر این، جهت جریان و جهت لایه‌ها در گسترش زمانی و مکانی فرسایش داخلی، کاملاً مؤثر است.

Intra-pore tortuosity and diverging-converging pore geometry controls on flow enhancement due to liquid boundary slip

The liquid boundary slip, in contrast to the conventional no-slip boundary condition, exists due to a less wetting or the non-wetting nature of sediment grains, which can significantly control fluid hydraulics of porous media, specifically which consists of smaller pore-throats, e.g., siltstones and mudstones. Most studies to date presume a no-slip boundary condition and a few who have investigated the aspects of slip-boundary presume a simplified straight tube or a non-tortuous pore shape. Therefore, how the degree of tortuosity and pore-geometry control flow enhancement in porous media remains underexplored. In this computational study, we design a set of diverging-converging staggered tortuous (DCST) pores, which account for a variable amount of intra-pore tortuosity. To compare, a set of capillary pores are designed that can account for tortuosity by taking the form of sinusoidal and helical shapes. Our results quantify how the diverging-converging nature of pore geometry and its intra-pore tortuosity alone have a significant impact on modifying the microscopic flow behavior -accounting of which is a key in upscaling these effects to a macroscopic continuum or the Darcy-scale. We find, DCST pores contribute to an asymptotic flow enhancement behavior in response to boundary slip.In comparison, capillary pores lead to a linearly ‘unlimited’ flow enhancement. This unlimited nature of flow enhancement can lead to differences over several orders in magnitude. We test theoretical models to predict flow enhancement from all pores. We determine constitutive relations that can predict flow enhancement as a function of intra-pore tortuosity and hydraulic shape factor. We examine the physical mechanisms of energy dissipation and find that the microscopic fluid-structure interactions can contribute to significant variation in how intra-pore geometry and boundary slip manifest as the flow enhancement factor relevant to the continuum-scale. We find that the ‘asymptote’ in the flow enhancement factor of DCST pores manifests as a result of an equilibrium between energy dissipation and enhancing flow due to boundary slip, at least in the laminar flow regime.

Three-Dimensional Membrane Imaging with X-ray Ptychography: Determination of Membrane Transport Properties for Membrane Distillation

Membrane distillation (MD) is a desalination technique that uses a membrane to thermally separate potable water from sea or brackish water. The mass transport processes through the membrane are commonly described by the dusty gas model. These processes are modeled assuming uniform, ideally cylindrical capillaries and are adjusted for the membrane geometry by including porosity and tortuosity. The tortuosity is usually set to 2 or is used as an adjusting parameter to fit theoretical models to experimentally measured data. In this work, ptychographic X-ray computed tomography is employed to map the three-dimensional (3D) structure of three commercial state-of-the-art PTFE membranes in MD. The porosity, tortuosity and permeability (viscous flow coefficient) of the samples are computed using the lattice Boltzmann method. The intrinsic permeability is compared to the dusty gas model and an apparent permeability is proposed which is corrected for Knudsen slip effects at the membrane structure.Article Highlights3D structure of membranes for distillation measured at full height at an unprecedented detail using X-ray ptychography for the first time.Comparison of the dusty gas model to 3D direct numerical simulation: permeability and Knudsen effects.Membrane characterization and calculation of the hydraulic tortuosity factor from 3D flow field simulations.

Analysis of convection heat transfer on multiscale rough superhydrophobic and liquid infused surfaces

Multiscale rough superhydrophobic or slippery liquid infused porous surfaces have gained much interest in recent years for their improved transport phenomena properties. While there have been several studies on drag reduction and condensation on non-wetting surfaces, convection heat transfer that is important in many thermal and thermochemical applications has not been addressed systematically. This article utilizes a fractal description of rough surface topographies to develop analytical models for the Nusselt number and the thermal hydraulic factor for fluid flow and heat transfer inside a cylinder with non-wetting surfaces. For air-infused superhydrophobic surfaces, the model considers the dynamic stability of the air/fluid interface in the asperities. Using the analytical formulations and the stability criteria, systematic studies are presented on the effects of the fractal surface parameters, cylinder radius and Reynolds number on the convective heat transfer characteristics, from which surface texture design maps are developed for maximizing the convection heat transfer. It is shown that multiscale non-wetting surfaces are most effective in the range of lower Reynolds number and small cylinder radius for achieving the best convective heat transfer and thermal hydraulic performance. Applying the models to actual non-wetting surface topographies fabricated using electrodeposition and chemical etching, it is shown that contrary to prevailing notion, superhydrophobicity, characterized by the highest contact angles, does not always lead to the maximum convective heat transfer performance, and that under certain fluid flow conditions, hydrophobic surfaces may offer a greater thermal performance.

Nonlinear modeling and multi-scale damping characteristics of hydro-turbine regulation systems under complex variable hydraulic and electrical network structures

In hydropower dominated power systems, low-frequency oscillations (LFO), that challenge the safe and stable operation of the system, occur from time to time. Although the study of system damping is an important way to reveal the mechanism of LFO, relevant analysis is mainly based on simplified models that consider a single scale, leading to an incomplete understanding of the phenomenon. Against this background, a cluster of hydropower units in a real power station is taken in this paper as the research object. Firstly, a refined non-linear model of the hydro-turbine regulation system with the layout of three units sharing one common tailrace tunnel is established and validated based on mechanism analysis and measured data. Then, an accurate quantitative evaluation method of damping for complex systems is proposed to overcome the application limitations of traditional methods. Finally, the variation laws of the damping of a hydropower unit with the hydraulic-electrical network structures and the operating conditions, studied from the scales of hydraulic coupling and electrical coupling, respectively, reveal the influence mechanism of the hydraulic-mechanical–electrical coupling on unit damping. The results show that the increase in the complexity of the hydraulic or electrical network structure will reduce the damping of the hydropower unit, which changes from 1.3860 to −1.3223 for hydraulic factor and from 1.1869 to −0.8817 for electrical factor. The operating conditions of the adjacent units have different degrees of influence on the damping of the unit itself due to their hydraulic or electrical connections. Some measures to suppress LFO are also given.