Pumping processes often require different operating conditions for the same pipeline. The conditions downstream in the pipeline can change in such a way that the pressure at the discharge of the pump may vary, which automatically introduces changes in the flow supplied by the pump into the pipeline due to the head vs flow characteristic curve of the pump. Even under varying pipeline pressure conditions, it may be necessary to keep the flow discharge of the pump constant. The two most commonly used control strategies for flow control with centrifugal pumps are by means of a fixed-speed pump and a control valve at the outlet of the pump, or by means of a variable frequency drive which avoids the need for the control valve. It has been demonstrated that the approach with the fixed-speed pump and the control valve provides poor power efficiency results, so a variable frequency drive is normally the solution of choice in industry applications. The use of a variable frequency drive allows reaching the flow required by the system without changing the physical characteristic of the pump or pipeline, i.e., it is not necessary to shut the system down to replace the impeller of the pump. However, affinity laws of centrifugal pumps dictate that a change in the rotational speed of the impeller shifts the characteristic curves of the pump, not only the flow vs head curve, but also the efficiency curves, among others. Besides, searching for a different operating point by changing the speed of the pump does not necessarily guarantees optimal operating power efficiency. This paper proposes an optimization approach where a compromise is made between flow control and power efficiency by minimizing the error in the flow rate while at the same time maximizing the power efficiency. To accomplish this goal, this paper presents the modeling of the pump and pipeline, and the design of a linear quadratic regulator control for the fluid flow passing through a given pipeline. The fluid under consideration is water. The mathematical model of the overall system is derived by considering the model of an AC motor, the pump and the hydraulic circuit. Then, with the help of the software MATLAB, the controller was designed and implemented with the linearized mathematical model. The actuator of the control system is the variable frequency drive that changes the speed of the impeller to adjust the flow rate to the required operating point under different loading conditions. The results show the behavior of the compensated system with the optimal controller. In practice, the control system must take into account the constraints of the control effort, which means, the frequency of the pump must be kept within safe values to achieve proper functioning of the pumping system.
Monitoring the integrity of structures in the oil and gas industry is a mandatory task to prevent both natural disasters and economical losses. This paper presents the optimization of the geometry of a magnetic circuit for the detection of defects in pipelines by the magnetic flux leakage method. The main goal is to perform a sensitivity analysis on the geometrical parameters of the circuit to find configurations that improve the performance of the defect searching tool. The sensitivity analysis of the design parameters of the magnetic circuit is based on numerical evaluations of the performance of the tool using the finite element method. The commercial finite elements software utilized for this analysis is COMSOL Multiphysics®. The results obtained in this investigation serve to identify the geometrical configurations that provide better performance, with respect to other configurations, for the detection of the same defect. Also, by using the analytical model of the magnetic flux leakage, the results obtained by means of the analytical model can be compared to the results from the finite elements model. The findings of this investigation can be utilized as guidelines for the design of magnetic circuits for non-destructive testing using the magnetic flux leakage technique.Key words: Magnetic flux leakage; Non-destructive testing; Magnetic circuit; Sensitivity analysis; Finite elements. RESUMENEl monitoreo de integridad estructural en la industria petrolera es una tarea muy importante para prevenir desastres tanto ambientales como económicos. Este artículo presenta la optimización de la geometría del circuito magnético para la detección de fallas en oleoductos por la técnica de fuga de flujo magnético. El objetivo principal es realizar un análisis de los parámetros geométricos del circuito para encontrar la configuración que incremente el desempeño del sistema para la detección de fallas. El análisis de la sensibilidad de los parámetros del circuito se basa en una evaluación numérica del desempeño del sistema usando el análisis por el método de los elementos finitos. El software comercial utilizado para este análisis fue COMSOL Multiphysics®. Los resultados obtenidos en esta investigación sirven para identificar la configuración geométrica adecuada para la mejora del desempeño del sistema, con respecto a otras configuraciones, para la detección de la misma falla. También haciendo uso del modelo matemático del fenómeno, se pretende comparar los resultados obtenidos por el modelo matemático y el modelo por elementos finitos. Los descubrimientos en esta investigación pueden ser usados como guías para el diseño de circuitos magnéticos para ensayos no destructivos por la técnica de fuga de flujo magnético.Palabras claves: Fuga de flujo magnético; Ensayos no destructivos; Circuito magnético; Análisis de sensibilidad; Elementos finitos.Cite this article as: C. Jaimes, S.Roa, "Sensitivity analysis of a magnetic circuit for non-destructive testing by the magnetic flux leakage technique
Monitoring the integrity of structures in the oil and gas industry is a mandatory task to prevent both natural disasters and economical losses. This paper presents the optimization of the geometry of a magnetic circuit for the detection of defects in pipelines by the magnetic flux leakage method. The main goal is to perform a sensitivity analysis on the geometrical parameters of the circuit to find configurations that improve the performance of the defect searching tool. The sensitivity analysis of the design parameters of the magnetic circuit is based on numerical evaluations of the performance of the tool using the finite element method. The commercial finite elements software utilized for this analysis is COMSOL Multiphysics®. The results obtained in this investigation serve to identify the geometrical configurations that provide better performance, with respect to other configurations, for the detection of the same defect. Also, by using the analytical model of the magnetic flux leakage, the results obtained by means of the analytical model can be compared to the results from the finite elements model. The findings of this investigation can be utilized as guidelines for the design of magnetic circuits for non-destructive testing using the magnetic flux leakage technique.
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