Complex Pipeline Systems Research Articles

Precision and uncertainty in natural gas calorific value estimation: advanced combinatorial predictive models for complex pipeline systems

Abstract In recent years, natural gas pipelines have been characterized by multiple intake points, the mixing of different gas sources, and significant variations in gas quality. The existing volumetric measurement system is no longer suitable for the development and operation of natural gas pipelines in China. To ensure accurate and equitable implementation of natural gas measurement, there is a gradual shift towards energy measurement. However, due to numerous measurement interfaces, installing chromatographs at all measurement stations would lead to substantial investment costs. Therefore, predicting the calorific value of natural gas is a key technology for energy measurement. In view of the issues existing in the current methods of obtaining natural gas calorific value, different prediction models of natural gas calorific value are constructed. According to the influencing factors of natural gas calorific value, the uncertainty evaluation is carried out, and the accuracy of different calorific value prediction models is analyzed by case data. The maximum error of regression equation (RE), response surface analysis (RSA), BP neural network and genetic algorithm (GA) prediction model is 2.29%, 0.43%, 0.59% and 0.45% respectively. However, the combined calorific value (CCV)prediction model is 0.41%. The results indicate that the predicted value calculated by the CCV prediction model is closer to the actual value and has higher prediction performance, which provides a new method for the calorific value prediction and measurement management of natural gas.

Investigations of the Formation Mechanism and Pressure Pulsation Characteristics of Pipeline Gas-Liquid Slug Flows

The pipeline system is widely used in marine engineering, and the formation mechanism and flow patterns of two-phase slug flows are of great significance for the optimal design of and vibration prevention in a complex pipeline system. Aiming at the above problems, this paper proposes a modeling and solving method for gas-liquid slug flows. First, a VOF-PLIC-based coupling gas-liquid slug flow transport model is conducted. Second, to reduce the fuzzy boundary between the gas-liquid coupling interfaces, an artificial compression term is added to the transport equations, and the formation and evolution mechanism of severe slugging flow in piping systems is investigated. The pressure pulsation and gas content characteristics of the gas-liquid coupling process are explored. Research results found that the slugging phenomenon occurs at the gas-liquid interface, where liquid slugging frequency reaches its peak. The pipeline system has prominent periodic characteristics of the slugging phenomenon, and the period decreases when the gas-phase converted speed rises; pressure fluctuation amplitude increases, and the gas-phase velocity change is the inducing factor for the drastic change of pressure fluctuation. The research results can offer theoretical references for optimal designs of and vibration prevention in marine pipeline systems.

Vibration Control of Reinjection Pump Room Pipeline System Based on Dynamic Characteristic Analysis

The reinjection pump room plays a crucial role in industries such as petroleum and chemical engineering. Its main responsibility is to safely and effectively inject treated wastewater, exhaust gas, or other fluid substances into the formation, aiming to achieve resource recycling and environmental protection. However, the pipeline system of the reinjection pump room usually has complex spatial distribution, long span, and multi-point elastic support characteristics, which may cause structural vibration during operation, and have adverse effects on the stable operation, safety, and surrounding environment of the equipment. Therefore, in the pipeline design stage, it is crucial to conduct in-depth vibration analysis of complex pipeline systems to ensure that harmful resonance phenomena do not occur in the pipeline under working conditions. Given the potential impact of pipeline system vibration on equipment performance and surrounding environment, effective suppression of pipeline system structural vibration is of great practical significance. This article focuses on the vibration control strategy of the reinjection pump room pipeline system based on dynamic characteristic analysis. By conducting in-depth research on the dynamic characteristics of pipeline systems, including vibration frequency, modal analysis, and vibration transmission paths, the aim is to propose a set of targeted vibration control measures.

Three-dimensional mapping of pipelines using laser ranging and a gyroscope

Conventional underground gas pipeline equipment can only map straight pipelines at close distances. As such, a dual-robot mapping technique is proposed in this study, based on laser ranging and a gyroscope, for application to straight, bent, or sloped underground pipelines. This process is facilitated by two robots (a detecting vehicle and a mapping vehicle) alternately moving from the entrance to the exit of a pipe system. The two vehicles acquire data using individual distance sensors and a gyroscope, producing 3D maps of each section. Mapping results can then be produced for the entire pipeline by splicing images from multiple sections. Simulated validation experiments were conducted using horizontal straight, bent horizontal fixed turning radius, sloped uphill or downhill, and composite sections. Results showed this approach could effectively map different types of pipelines with inner diameters of 300–500 mm. Distance errors over 2000 m of travel were within 1 m, while the angular error was within 1.5°, demonstrating our approach to be highly accurate for complex pipeline system mapping.

IMPLEMENTATION OF A MATHEMATICAL MODEL OF NONSTATIONARY GAS MOVEMENT IN A COMPLEX PIPELINE UNDER MIXED BOUNDARY CONDITIONS

The study of the movement of real fluid is necessary in the design of not only gas and oil pipelines, but also other hydraulic machines. Mathematical models of the unsteady movement of a liquid or gas are also necessary when solving a number of prob-lems in the operation of pipeline systems. Such tasks can be: pipeline condition monitoring, operating modes optimizing, emergency situations analyzing and others. Attempts to model the dynamics of pressure in pipelines with selection or pumping at given points led to systems of partial differential equations with boundary conditions between the zones of the pipeline section in question. If there are n sampling points (swapping), then we have to solve a system of n + 1 equations. This is due to cumbersome calculations, and sometimes with insurmountable difficulties. Use of the impulse function by Dirac M.A. Huseynzade and his students in oilfield mechanics and in pipe hydraulics made it possible to describe non-stationary processes in complex pipeline systems using a single equation. A section of a pipeline system is usually called «complex» if there are sampling-pumping points, pumping station or different sections of the pipeline have different coefficients of hydraulic resistance or diameters. This article discusses the horizontal section of the pipeline with sampling and pumping points. The problem is solved under mixed boundary conditions using a finite Fourier sine transform. Graphs of pressure dynamics for cases of selection, pumping and without them have been constructed. Special cases are considered. Calculation formulas convenient for practical application are obtained.

Design of a Robot for Inspecting the Multishape Pipeline Systems

Aiming at the question that most of the existing pipeline robots can only move in parts of common pipeline environments, in this study, we introduce a novel pipeline robot configuration with excellent environmental adaptability and obstacle avoidance capability for inspecting a more complex pipeline system. To ensure adaptability and mobility, the pipeline robot's general configuration was divided into three parts: the head, waist, and tail, with axisymmetric and planar symmetric structural distributions. Two active articulated joints connect the three sections of the pipeline robot, driving the head and tail to complete yaw and roll motions and allowing the pipeline robot to avoid raised obstacles and broken gaps. Furthermore, the pipeline robot can travel through annular gaps, straight pipelines with different diameters, and funnel-type pipelines due to the combination of scissor mechanism legs and a caterpillar track. Finally, a pipeline robot with the configuration and test bed with six common pipeline environments was built, and the obstacle avoidance ability and environmental adaptation experiments were conducted to evaluate the movement effectiveness. According to the experimental results, the pipeline robot can navigate smoothly within a complex pipeline environment. The pipeline robot in this setup has considerable potential in the real world.

Экспериментальное исследование динамических характеристик трубопровода гидромеханической системы

The article considers vibration resistance of hydromechanical system pipelines characterizing the reliability of their operation. As a rule, vibrations and noise in pipelines are caused by pressure pulsations in the flow of the working medium and structural vibrations from superchargers propagating along the pipeline structure. An experimental analysis of vibroacoustic parameters of a real complex pipeline system with a supercharger was performed to study its dynamic behavior. At this stage of the study, the stationary process of pump operation forming a turbulent flow in the pipeline, was researched. In the course of the physical experiment, a spectral analysis was performed and vibroacoustic spectra were built at the selected control points of a separate straight section of the pipeline in the frequency range of 0.5 ... 400.0 Hz. An analysis of the change in dynamic parameters along the length of a straight section was made at various flow rates of the working fluid. The influence of the operating parameters of the supercharger (supply and pressure) on the vibroacoustic characteristics of the pipeline was studied. It was found that transverse oscillations are of greater importance in the formation of the dynamic behavior of the studied area. It is determined that with increasing the flow rate, the relative vibrational displacement of the pipeline along the X axis (longitudinal vibrations) also increases.

Quantitative Analysis Regarding the Incidents to the Pipelines of Petroleum Products for an Efficient Use of the Specific Transportation Infrastructure

The transportation infrastructure for petroleum products contains complex pipeline systems, developed on a global scale and totaling investments of hundreds of millions of dollars. The operation and maintenance of these systems have to be performed in relation to the analysis of incidents of various types, which take place in various areas of the world. The present paper aims to analyze in as much detail as possible, from a statistical point of view, the case of the pipeline system for petroleum products in Romania in order to streamline the operation of this critical infrastructure for Romania. Through the statistical tools, we established the hierarchies of the causes of the analyzed incidents, weights of the effects generated by these sources of accidents, and correlations between various parameters, in order to create a useful plan of measures and actions in the efficient operation of the pipeline system. The importance and topicality of the subject is also demonstrated by the major negative impact of the accidents in this sector, through product leaks from pipes in the soil and in watercourses, which generate significant pollution values, thus influencing the balance of the environment.

Dynamic optimization analysis of hydraulic pipeline system based on a developed response surface method

When designing a complex pipeline with long distance and multi-supports for offshore platform, it is necessary to analyze the vibration characteristics of the complex pipeline system to ensure that there is no harmful resonance in the working conditions. Therefore, the optimal layout of support is an effective method to reduce the vibration response of hydraulic pipeline system. In this paper, a developed dynamic optimization method for the complex pipeline is proposed to investigate the vibration characteristics of complex pipeline with multi-elastic supports. In this method, the Kriging response surface model between the support position and pipeline is established. The position of the clamp in the model is parameterized and the optimal solution of performance index is obtained by genetic algorithm. The number of clamps and the interval between clamps are considered as the constraints of layout optimization, and the optimization objective is the natural frequencies of pipeline. Taking a typical offshore pipeline as example to demonstrate the effectiveness of the proposed method, the results show that the vibration performance of the hydraulic pipeline system is distinctly improved by the optimization procedure, which can provide reasonable guidance for the design of complex hydraulic pipeline system.

Leak detection in virtually isolated pipe sections within a complex pipe system using a two-source-four-sensor transient testing configuration

Abstract Leak detection in complex pipeline systems is challenging due to complex wave reflections. This research proposes a new technique for leak detection in targeted pipe sections within complex water supply pipe systems using controlled hydraulic transient pressure waves. To ‘virtually isolate’ a targeted pipe section for independent analysis, a two-source-four-sensor transient testing configuration is used to extract the transfer matrix of the targeted pipe section, and it is independent of the system boundary conditions. The imaginary part of the difference between two elements in the transfer matrix is sensitive to leaks. The result should be zero if no leak is present, while a leak will introduce a sinusoidal pattern. An algorithm is developed to extract the leak information, which is applicable to multiple leaks. Two numerical case studies are conducted to validate the new leak detection technique. Case 1 is on a single pipe system with two leaks and deteriorated pipe sections, and pulse pressure waves are used as the excitation. Case 2 is on a simple pipe network with one leak, and pseudo-random binary signals are used as the excitation. The successful determination of the leak location and impedance validates the concept.

Adaptive condition predictive-fuzzy PID optimal control of start-up process for pumped storage unit at low head area

In order to overcome the rotational speed oscillation under no-load start-up condition caused by the ‘S’ characteristic area of the pump-turbine and the difficulty in improving the dynamic process under low head area of pumped storage unit (PSU), this paper uses the model predictive control and fuzzy logic control theory to study the optimal control of PSU under no-load start-up condition at low head area. Firstly, the instantaneous linearized controlled autoregressive integrated moving average model (CARIMA) of PSU is proposed. This model contains the dynamic equations of the complex pipeline system and pump-turbine generator-motor that accurately describe the hydraulic and mechanical dynamic characteristics. Based on the CARIMA, a novel adaptive condition predictive-fuzzy PID (ACP-FPID) controller is designed. The controller contains the operating point prediction and the avoidance of critical curves of the ‘S’ characteristic area. Then, multi-objective optimization control method combined with bacterial foraging algorithm is utilized for the optimal parameters selection of controller, guide opening time and frequency switching point when the closed-loop controller is put into operation. Furthermore, numerical simulation tests under start-up condition in typically low head are conducted to demonstrate the feasibility and robustness of the ACP-FPID optimal control method. The results indicate that the proposed method can effectively avoid the deep running of the unit into the ‘S’ characteristic area compared with traditional ones. The approximate periodic oscillations times and overshoot index of rotational speed obtained by ACP-FPID are less than 1 and 2% respectively, which are much smaller than that values obtained by the traditional ones. Moreover, strong robustness of ACP-FPID is testified when PSU disturbed by mechanical factors.

Computer models of hydraulic systems of district heating

A mathematical and computer model of a district heating network fed by two heat sources located at significantly different elevation marks has been developed. The model is based on the electrohydraulic analogy of electric current spread in conductors and liquid pressure spread in pipelines, which are described by the same equations. In particular, the first and second Kirchhoff’s laws used in the calculation of electrical networks are applied to calculate the velocities and pressures in a complex multi-ring pipeline system. In order to maximize the approximation of the computer model to the real hydraulic network (in resistance to the process of heating agent flow), the method of automatic identification of the model is applied. This method is an iterative process of changing the hydraulic resistances in pipelines of the model in such a way that the results obtained from the calculations would have the least differences from the experimental data. The accuracy of identification depending on the number of points with known experimental data is 3 – 5%.

Transient Wave Scattering and Its Influence on Transient Analysis and Leak Detection in Urban Water Supply Systems: Theoretical Analysis and Numerical Validation

This paper investigates the impacts of non-uniformities of pipe diameter (i.e., an inhomogeneous cross-sectional area along pipelines) on transient wave behavior and propagation in water supply pipelines. The multi-scale wave perturbation method is firstly used to derive analytical solutions for the amplitude evolution of transient pressure wave propagation in pipelines, considering regular and random variations of cross-sectional area, respectively. The analytical analysis is based on the one-dimensional (1D) transient wave equation for pipe flow. Both derived results show that transient waves can be attenuated and scattered significantly along the longitudinal direction of the pipeline due to the regular and random non-uniformities of pipe diameter. The obtained analytical results are then validated by extensive 1D numerical simulations under different incident wave and non-uniform pipe conditions. The comparative results indicate that the derived analytical solutions are applicable and useful to describe the wave scattering effect in complex pipeline systems. Finally, the practical implications and influence of wave scattering effects on transient flow analysis and transient-based leak detection in urban water supply systems are discussed in the paper.

Application of the LBM with adaptive grid on water hammer simulation

A lattice Boltzmann method (LBM) is utilized to solve single-phase transient flow in pipes. In order to eliminate grid limitation related to the method of characteristics, governing equations are modified using appropriate coordinate transformation. The introduced modification removes connection between Courant number and spatial disposition of the computational nodes, forming a more flexible and robust mathematical base for numerical simulations. The computational grid is configured independently of the wave speed, significantly decreasing the demand for computational resources and maintaining the required accuracy of the method. Thereafter, the appropriate equilibrium distribution function for the D1Q3 lattice has been defined. In order to give a comprehensive base for modeling transient flow in complex pipeline systems, detailed elaboration of the corresponding boundary conditions has been given. Two benchmark problems with the corresponding error analysis are used to validate the proposed procedure.

Uncertainty Analysis of Transient Flow Modeling and Transient-Based Leak Detection in Elastic Water Pipeline Systems

In the transient flow modeling and analysis of practical water pipeline systems, discrepancies commonly exist between numerical simulation results and experimental measurement data. Such discrepancies are usually accounted for the inaccuracy and inadequacy of the used mathematical models and/or the lack of understanding of the hydrodynamic physics for transient pipe flows in the literature. However, the variability or uncertainty of the parameters for such numerical model inputs may also attribute to these discrepancies, especially in complex pipeline systems. This paper investigates the effects of different system uncertainties on the transient flow modeling and analysis such as pipe system design and leak detection. Different factors of pipe and fluid properties as well as system operations and complexities are considered for the uncertainty analysis. The one-dimensional (1D) water hammer model and the Monte-Carlo simulation (MCS) method are used in this investigation. The analysis results in this study demonstrate that the variability of the transient flow modeling can be easily affected by the uncertainty factors of wave speed and system complexities, while the transient-based leak detection is more sensitive to the uncertainty factors of wave speed and data measurement than the factors of valve operation and initial hydraulic condition.

Methods for Analysis of Transition Regimes in Water-Carrying Runs at Hydroelectric Power Plants Based on Self-Organizing Mathematical Models

Results are presented for development of self-adapting sets of numerical models permitting analyses of complex pipeline systems with a variable flow regime in individual sections (empty, movement over dry bottom, transition from a gravity-flow regime of water in tunnels to a pressure regime, and conversely, and so forth. This system controls movement of the boundaries of the modeling domain (during filling and emptying of sections of conduits), and selects appropriate boundary conditions for variation in the flow regime on the boundary of the modeling domain of the flow (non-overflow spillway — overflow spillway, etc.).

Computer models of complex multiloop branched pipeline systems

This paper describes the principal theoretical concepts of the method used for constructing computer models of complex multiloop branched pipeline networks, and this method is based on the theory of graphs and two Kirchhoff’s laws applied to electrical circuits. The models make it possible to calculate velocities, flow rates, and pressures of a fluid medium in any section of pipeline networks, when the latter are considered as single hydraulic systems. On the basis of multivariant calculations the reasons for existing problems can be identified, the least costly methods of their elimination can be proposed, and recommendations for planning the modernization of pipeline systems and construction of their new sections can be made. The results obtained can be applied to complex pipeline systems intended for various purposes (water pipelines, petroleum pipelines, etc.). The operability of the model has been verified on an example of designing a unified computer model of the heat network for centralized heat supply of the city of Samara.

On Optimizing Autonomous Pipeline Inspection

This paper studies the optimal inspection of autonomous robots in a complex pipeline system. We solve a 3-D region-guarding problem to suggest the necessary inspection spots. The proposed hierarchical integer linear programming optimization algorithm seeks the fewest spots necessary to cover the entire given 3-D region. Unlike most existing pipeline inspection systems that focus on designing mobility and control of the explore robots, this paper focuses on global planning of the thorough and automatic inspection of a complex environment. We demonstrate the efficacy of the computation framework using a simulated environment, where scanned pipelines and existing leaks, clogs, and deformation can be thoroughly detected by an autonomous prototype robot.

Application of rectangular integral to numerical simulation of hydraulic transients in complex pipeline systems

The hydraulic oscillation of surge tank was analyzed through numerical simulation. A rectangular integral scheme was established in order to improve the numerical model. According to the boundary control equation of surge tank, the rectangular integral scheme omits the second-order infinitesimal and simplifies the solving process. An example was provided to illustrate the rectangular integral scheme, which is compared with the traditional trapezoid integral scheme. Appropriate numerical solutions were gained through the new scheme. Results show that the rectangular integral scheme is more convenient than the trapezoid integral one, and it can be applied to the numerical simulation of various surge tanks in complex pipeline systems.

Four-terminal parameter formulation of solving induced voltages and currents on a pipeline system

An analytical method of calculating steady-state induced voltages and currents on a complex pipeline system based on a four-terminal parameter has been developed. The developed method makes it very easy to deal with and at the same time to understand the effect of the system parameters, inducing currents and boundary conditions that are different in each section of the pipeline system. Analytical results show that there exists a position where the pipeline voltage to ground becomes zero. When both ends of the pipeline are grounded through a resistance, the position of the zero potential is nearly the centre of the pipeline. If one end is open-circuited, the other end shows zero potential. This fact has not been well recognised by engineers in this field. Also, the effect of the inducing currents, which are different in each section along the pipeline, is explained from the physical viewpoint based on the analytical results. The accuracy of the proposed method is confirmed to be satisfactory in comparison with Electromagnetic Transients Programme (EMTP) simulation and field test results.