Dynamic Positioning Systems: Comparison Between Wave Filtering Algorithms and Their Influence on Performance

2003 ◽  
Author(s):  
Eduardo A. Tannuri ◽  
Tiago T. Bravin ◽  
Celso P. Pesce
Keyword(s):  
Analog Circuits ◽  
High Frequency ◽  
Control Strategies ◽  
Low Frequency ◽  
Design Parameters ◽  
Dynamic Positioning ◽  
Frequency Wave ◽  
Filtering Algorithms ◽  
Positioning Systems ◽  
Dynamic Positioning System

Wave filtering is an essential function of a Dynamic Positioning System, being responsible for the separation between high-frequency wave induced motions and low-frequency ones, which must be controlled. Low attenuation of the first components may cause oscillatory control action, high fuel consumption and can damage propeller systems. On the other hand, depending on filtering design, high levels of attenuation may be associated with non-admissible delay-times, which may cause instability in the closed-loop system. Traditionally, low-pass or notch-type filters have been used since the first DP systems, due to the simplicity, acceptable performance and possibility of being implemented using analog circuits. Alternatively, observers based on Kalman Filtering Theory have also been used, based on simplified ship models, separating low and high frequency motions. Two wave filters, representing each of those categories, were implemented in a complete DP simulator. All DP components and algorithms are considered and modeled in the simulator, including propellers, thrust allocation, wind-feedforward and different control strategies. Environmental loads are evaluated using fully validated models, including wind, current and wave actions. A pipe-laying barge under typical Campos Basin environmental conditions has been considered as example. Several aspects of the filtering algorithms were analyzed and compared, involving the influence of each filter in the overall DP performance, relationship of design parameters with physical system, ease of commissioning and tuning. The trade off between low frequency tracking (which is associated with the delay time) and wave response suppression is analyzed and discussed for both categories of filters.

The Investigation of the Optimization Scheme of the Low-cycle Fatigue Cropping Based on the Acoustic Emission Technique

2021 ◽  
Author(s):  
Yujian Ren ◽  
Jingxiang Li ◽  
Yuanzhe Dong ◽  
Dong Jin ◽  
Shengdun Zhao
Keyword(s):  
Acoustic Emission ◽  
High Frequency ◽  
Control Method ◽  
Low Cycle Fatigue ◽  
Control Strategies ◽  
Low Frequency ◽  
Loading Frequency ◽  
Cycle Fatigue ◽  
Al 6061 ◽  
Whole Process

Abstract High efficiency and good section quality are two main objectives of metal bar cropping. A suitable control method can help to achieve both goals. An investigation of the control method of low-cycle fatigue cropping (LCFC) based on the acoustic emission (AE) technique has been proposed in this study. Ring-down counts and kurtosis are used to monitor the whole process of LCFC. The results showed that kurtosis is more suitable for monitoring the LCFC process and as a critical parameter to optimize the control method than ring-down counts in the noisy factory environment.Moreover, three types of materials are studied in this experiment; by combine with the AE results, macroscopic images and microscopic images of sections, characteristics of various LCFC stages are obtained. The results also indicated reduce the area of the transient fracture zone is the key to improve the section quality. Reducing the load frequency before the unstable crack propagation stage will beneficial to realize the goals. Based on the evaluation of kurtosis, an optimized control method is presented, and two control parameters: transient time T and the critical value of the slope of kurtosis C are determined. For 16Mn, 1045 and Al 6061, the T is 5s, 10s, and 1s, respectively. For 16Mn, 1045, and Al 6061, the C is 100, 300, and 0, respectively. Two parameters, h and S, are used to evaluate the section quality and four control strategies are compared. The results indicate the optimal control methods can improve the section quality effectively. The influence trend of reducing loading frequency is investigated by further comparison. It can be seen as the frequency decreases, the efficiency of the section quality improving decreases. In order to realize the optimal results, different control strategies are adopted for different materials. Strategy 1 (high frequency is 20Hz，high frequency thought the whole process), strategy 2 (high frequency is 20Hz，low frequency is 8.33Hz), and strategy 3 (high frequency is 20Hz，low frequency is 6.67Hz) is suitable for Al 6061, 1045, and 16Mn, respectively.

Mitigation of Current-Driven, Vortex-Induced Vibrations of a Spar Platform via “SMART” Thrusters

2004 ◽  
Vol 126 (1) ◽  
pp. 96-104 ◽  
Author(s):  
F. Joseph Fischer ◽  
Stergios I. Liapis ◽  
Yannis Kallinderis
Keyword(s):  
Active Control ◽  
Control Strategies ◽  
Low Frequency ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Frequency Wave ◽  
Fluid Forces ◽  
Vortex Induced Vibrations ◽  
Helical Strakes ◽  
The Cost

The possibility of using active-control technology to mitigate long-period (100–300 s) motions of spar platforms was investigated. In particular, the technical feasibility and cost-effectiveness of using a thruster-based active-control system was examined. Only vortex-induced vibrations (VIV) of a moored spar were considered for this study, although it is believed that similar active-control systems can contend equally well with low-frequency wave-drift and wind-induced motions. VIV has been selected for this demonstration due to the considerable attention it has received for spars, because of the high cost for passive VIV-mitigation means. The investigation employed numerical simulations of the hydrodynamics around the spar in two and three dimensions. In particular, for this study, Navier-Stokes methods were used to compute the strongly nonlinear interactions between the current-flow field and the spar hull. The fluid forces (hull-integrated pressures) were then used to compute the unsteady motions of the moored spar. The effect of the motion-controlling thrusters was included as an additional external force—that also varies with time. Of the several different control strategies that were examined, it was found that the most effective one is “D-Control” wherein thruster forces are proportional to spar velocities. Using such control, spar motions can be kept below 35% of the spar diameter, whereas uncontrolled responses were computed to be as high as 80% of the spar diameter. Similar uncontrolled motions have actually been observed in current-tank model tests of spars. As part of this study, discussions were held with engineers from three different thruster companies to ascertain the number and type of thrusters that would be required to achieve desirable VIV mitigation—given the computed thruster-forces, and to provide prudent reliability. Associated costs were also very much of interest. For the spar system examined here, which is representative of those introduced into or being considered for the Gulf of Mexico, it was found that the cost of the thrusters and their electric motors is around $8 million—a cost that is significantly less than that estimated for passive VIV-control devices such as helical strakes, or discontinuous hull geometries. Furthermore, the proposed thruster system could also be employed to contend with (to mitigate) other undesirable, large-amplitude, near-resonant spar motions, e.g., low-frequency drift, for which there are no alternative remedies at present.

Intelligent Control Circuit Integral with Pattern Recognition Techniques for High-Pressure Sodium Lamps

2017 ◽  
Vol 26 (07) ◽  
pp. 1750108
Author(s):  
Yuzhuo Pan ◽  
Chen Lv ◽  
Shanhe Su ◽  
Jincan Chen
Keyword(s):  
Pattern Recognition ◽  
High Pressure ◽  
Intelligent Control ◽  
High Frequency ◽  
Pulse Width Modulation ◽  
Smart Cities ◽  
Control Strategies ◽  
Low Frequency ◽  
Acoustic Resonance ◽  
Working Device

The paper presents the analysis, simulation, and experimental methods to eliminate acoustic resonance in high-frequency high-pressure sodium (HPS) lamps and integrate intelligent control strategies in the working device. Based on the pulse-width modulation (PWM) output generated by the microcontroller, the acoustic resonance in the high-frequency lamp can be successfully eliminated by modulating the high-frequency driving current via a low-frequency signal. Particularly, by implementing the pattern recognition, the control system enables the lamp to have the abilities of accurate timing, gradient dimming, automatic protection, and intellisense. The proposed model will provide useful information for designing intelligent lighting system towards smart cities.

Study on Absorbing Properties of Honeycomb Absorbing Materials

2013 ◽  
Vol 815 ◽  
pp. 645-649
Author(s):  
Hui Min Sun ◽  
Zhao Zhan Gu ◽  
Ran Ran Yang
Keyword(s):  
Layer Thickness ◽  
High Frequency ◽  
Free Space ◽  
Low Frequency ◽  
Resonance Peak ◽  
Test Method ◽  
Electromagnetic Parameters ◽  
Frequency Wave ◽  
Absorbing Materials

Honeycomb absorbing materials were measured using the method of free space in this paper. The reflectance of honeycomb absorbing materials was calculated and simulated, and it was verified based on the measured results. It was demonstrated that this test method was feasible. Through studying on absorbing properties of honeycomb, the results have showed that the radar absorbing properties of honeycomb are related to electromagnetic parameters, as well as thickness of the dip-coatings. With the increase of thickness of the dipping layer, the radar absorbing capability of high frequency and low frequency wave are significantly increased. It is worth noting that the resonance peak moved to the low frequency with the increase of dipping layer thickness. These results are useful for design of honeycomb absorbing materials.

An Expert Experience Based Model Predictive Control Strategy for Dynamic Positioning

2015 ◽  
Author(s):  
Shi Lei ◽  
Han Bing ◽  
Cao Jianming
Keyword(s):  
Model Predictive Control ◽  
Predictive Control ◽  
Control Strategy ◽  
Low Frequency ◽  
Good Control ◽  
Dynamic Positioning ◽  
Positioning System ◽  
Dynamic Positioning System ◽  
Technical Requirements ◽  
Control Accuracy

In this paper, an expert experience model predictive control strategy is suggested based on the feed forward control of wind and current, and the Kalman filter for the low frequency motion estimation. For the examination of control accuracy and control stability, a pool test of the dynamic positioning system is designed and completed based on the actual situation of the target ship in this paper. The test results with different simulated environments show that the control strategy of dynamic positioning system meets the technical requirements of the target ship with good control accuracy and stability.

Wave Filtering of Ship Dynamic Positioning System Using Particle Filter

2013 ◽  
Vol 397-400 ◽  
pp. 551-555
Author(s):  
Wen Juan Li ◽  
Hai Xiang Xu ◽  
Hui Feng
Keyword(s):  
Particle Filter ◽  
Low Frequency ◽  
Nonlinear Filter ◽  
Dynamic Positioning ◽  
Positioning System ◽  
Dynamic Positioning System ◽  
Frequency Position ◽  
Particle Filter Algorithm

This paper presents a nonlinear filter which is particle filter. The filter produces accurate estimates of low-frequency position and velocity only from measured values of ship position and heading in Dynamic Positioning System. The results of simulation confirm the validity and adaptability of the particle filter algorithm.

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