On the Potential for Low-Frequency Control Valve Vibrations Being Caused by Upstream Oscillating Dean Vortices

2021 ◽  
Author(s):  
Richard Lozowy ◽  
Mario Forcinito
Keyword(s):  
Frequency Control ◽  
Low Frequency ◽  
Control Valve ◽  
Dean Vortices

On the Potential for Low-Frequency Control Valve Vibrations Being Caused by Upstream Oscillating Dean Vortexes

2020 ◽  
Author(s):  
Richard Lozowy ◽  
Mario Forcinito
Keyword(s):  
Frequency Control ◽  
Low Frequency ◽  
Control Valve ◽  
Bend Radius ◽  
Straight Pipe ◽  
Pipe Bend ◽  
Large Eddy ◽  
Flow Oscillations ◽  
Pipe Geometry ◽  
Upstream Flow

Abstract At several natural gas compressor stations control valves have experienced low-frequency vibrations when placed directly downstream of pipe bends. It is know that at pipe bends a pair of counter-rotating vortexes form and extend several diameters downstream. These vortexes are not symmetric and instead oscillate back and forth at a low-frequency phenomenon referred to as swirl-switching. It is suspected that these upstream flow oscillations enter the valve and are the cause of the valve vibrations. Large-eddy simulations have been performed on pipe bends with two different bend radius at a Reynolds number of 80,000. The simulations showed that the frequency of the vortexes decreased as the bend radius increased. When non-dimensionalized the frequency obtained from the simulation is comparable to the field measurement from the compressor station. This consistency provides support to the argument that upstream flow-induced oscillations are the cause of the low-frequency valve vibrations. The velocity fluctuations due to swirl-switching dissipate downstream of the bend and by placing several diameter lengths of straight pipe between a control valve and a pipe bend, the issue of low-frequency vibrations induced at the valve could be avoided. The objective of this study is to provide evidence that low-frequency valve vibrations can be linked to upstream pipe geometry and put forward a plausible explanation of why.

Settling Control of the Triple-Stage Hard Disk Drives Using Robust Output Feedback Model Predictive Control

2016 ◽  
Author(s):  
Huy Nguyen ◽  
Omid Bagherieh ◽  
Roberto Horowitz
Keyword(s):  
Model Predictive Control ◽  
Predictive Control ◽  
Output Feedback ◽  
Frequency Control ◽  
Hard Disk Drives ◽  
Low Frequency ◽  
Hard Disk ◽  
Control Input ◽  
Feedback Model ◽  
Actuator Constraints

Track settling control for a hard disk drive with three actuators has been considered. The objective is to settle the read/write head on a specific track by following the minimum jerk trajectory. Robust output feedback model predictive control methodology has been utilized for the control design which can satisfy actuator constraints in the presence of noises and disturbances in the system. The controller is designed based on a low order model of the system and has been applied to a higher order plant in order to consider the model mismatch at high frequencies. Since the settling control generally requires a relatively low frequency control input, simulation result shows that the head can be settled on the desired track with 10 percent of track pitch accuracy while satisfying actuator constraints.

scholarly journals A Novel Piecewise Frequency Control Strategy Based on Fractional-Order Filter for Coordinating Vibration Isolation and Positioning of Supporting System

Sensors ◽  
2020 ◽  
Vol 20 (18) ◽  
pp. 5307
Author(s):  
Yeying Tao ◽  
Wei Jiang ◽  
Bin Han ◽  
Xiaoqing Li ◽  
Ying Luo ◽  
...  
Keyword(s):  
Fractional Order ◽  
Control Strategy ◽  
Vibration Isolation ◽  
Frequency Control ◽  
Low Frequency ◽  
Stability Margin ◽  
System Stability ◽  
Supporting System ◽  
Frequency Position ◽  
The Stability

A piecewise frequency control (PFC) strategy is proposed in this paper for coordinating vibration isolation and positioning of supporting systems under complex disturbance conditions, such as direct and external disturbances. This control strategy is applied in an active-passive parallel supporting system, where relative positioning feedback for positioning and absolute velocity feedback for active vibration isolation. The analysis of vibration and deformation transmissibility shows that vibration control increases low-frequency position error while positioning control amplifies high-frequency vibration amplitude. To overcome this contradiction across the whole control bandwidth, a pair of Fractional-Order Filters (FOFs) is adopted in the PFC system, which increases the flexibility in the PFC design by introducing fraction orders. The system stability analysis indicates that the FOFs can provide a better stability margin than the Integral-Order Filters (IOFs), so the control gains are increased to get a better performance on the AVI and positioning. The PFC based on FOFs can suppress the peak amplitude at the natural frequency which cannot be avoided when using the IOFs. The constrained nonlinear multivariable function is formed by the required performance and the stability of the system, then the controller parameters are optimized effectively. Lastly, the effectiveness of the proposed method is verified by experiments.

Reducing Electricity Theft by Low Frequency Control Scheme in Bangladesh

2020 ◽  
Author(s):  
Md. Saiam ◽  
Shah Md. Salimullah ◽  
Md. Shoab Akther ◽  
Md. Zahidul Islam ◽  
Tanjir Hossain Bhuiyan
Keyword(s):  
Frequency Control ◽  
Low Frequency ◽  
Electricity Theft ◽  
Control Scheme

Innovative Hydraulic Power Take-Off Construction and Performance Tests for Wave Energy Conversion

2013 ◽  
Vol 432 ◽  
pp. 316-323 ◽  
Author(s):  
J.C. Antolín-Urbaneja ◽  
J. Lasa ◽  
P. Estensoro ◽  
I. Cabanes ◽  
M. Marcos
Keyword(s):  
Energy Conversion ◽  
Wave Energy ◽  
Initial Conditions ◽  
Low Frequency ◽  
Control Valve ◽  
Hydraulic Cylinder ◽  
Geometrical Parameters ◽  
Wave Energy Conversion ◽  
Hydraulic Motor ◽  
Hydraulic Power

This document describes and demonstrates the features of a new innovative hydraulic Power take-Off (PTO) to be used for Wave Energy Conversion. This device is able to transform low frequency oscillating movement into a continuous high frequency angular speed, absorbing high fluctuated torque at the input shaft, which can reach up to 8000Nm. Moreover, the major breakthrough of this device is that it can control the braking torque through the modification of some geometrical parameters, L and R, and through the activation of more than one hydraulic cylinder together with the pressure. The output shaft of the PTO is able to rotate at different continuous rated speed through the actuation on a specific control valve at the inlet of the hydraulic motor. Tests to check the behavior of the PTO related to the smoothening of the power output and concerning the time needed to increase the high pressure and the time available after the accumulation of some quantity of energy in different initial conditions are presented.

scholarly journals The three-dimensional structure of swirl-switching in bent pipe flow

2017 ◽  
Vol 835 ◽  
pp. 86-101 ◽  
Author(s):  
Lorenz Hufnagel ◽  
Jacopo Canton ◽  
Ramis Örlü ◽  
Oana Marin ◽  
Elia Merzari ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Three Dimensional ◽  
Low Frequency ◽  
Dimensional Structure ◽  
Pipe Bend ◽  
Dean Vortices ◽  
Dean Vortex ◽  
Piping Systems ◽  
Bent Pipe ◽  
Pipe Radius

Swirl-switching is a low-frequency oscillatory phenomenon which affects the Dean vortices in bent pipes and may cause fatigue in piping systems. Despite thirty years worth of research, the mechanism that causes these oscillations and the frequencies that characterise them remain unclear. Here we show that a three-dimensional wave-like structure is responsible for the low-frequency switching of the dominant Dean vortex. The present study, performed via direct numerical simulation, focuses on the turbulent flow through a $90^{\circ }$ pipe bend preceded and followed by straight pipe segments. A pipe with curvature 0.3 (defined as ratio between pipe radius and bend radius) is studied for a bulk Reynolds number $Re=11\,700$, corresponding to a friction Reynolds number $Re_{\unicode[STIX]{x1D70F}}\approx 360$. Synthetic turbulence is generated at the inflow section and used instead of the classical recycling method in order to avoid the interference between recycling and swirl-switching frequencies. The flow field is analysed by three-dimensional proper orthogonal decomposition (POD) which for the first time allows the identification of the source of swirl-switching: a wave-like structure that originates in the pipe bend. Contrary to some previous studies, the flow in the upstream pipe does not show any direct influence on the swirl-switching modes. Our analysis further shows that a three-dimensional characterisation of the modes is crucial to understand the mechanism, and that reconstructions based on two-dimensional POD modes are incomplete.

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