Flexible Joint Stiffness Modelling Improving Ultra Deep Water Rigid Risers Fatigue Damage

2019 ◽  
Author(s):  
Germain Venero ◽  
Victor Gomes ◽  
Hugues Corrignan ◽  
Daniel Carneiro
Keyword(s):  
Fatigue Damage ◽  
Deep Water ◽  
Joint Stiffness ◽  
Flexible Joint

Effect of Flexible Joint Modelling Method on Deep Water Catenary Riser Hang-Off Fatigue Response

2019 ◽  
Author(s):  
Guanyu Hu ◽  
Chaojun Huang ◽  
Fengjie Yin ◽  
Mark Cerkovnik ◽  
Guangqiang Yang
Keyword(s):  
Deep Water ◽  
Joint Stiffness ◽  
Fatigue Performance ◽  
Fatigue Load ◽  
Flexible Joint ◽  
Cyclic Bending ◽  
Modelling Method ◽  
The Impact ◽  
Nonlinear Curve ◽  
Modelling Methods

Abstract The Flexible joint is one of the most widely used hang-off systems for deep water catenary riser for its large rotation and load bearing capacity. The fatigue performance of riser hang-off region and fatigue load on the flexible joint highly depend on the rotational stiffness of the flexible joint. Thus, modelling the flexible joint stiffness to accurately simulate the behavior under cyclic bending cycles is critical in global riser fatigue analysis. The load-displacement relationship of a flexible joint typically follows a nonlinear curve, and it shows hysteresis behavior when subject to cyclic bending cycles. However, in current industry practice, the flexible joint stiffness is modelled either as a nonlinear curve or simplified as a fixed value. These simplified methods sometimes can lead to unconservative or over conservative results in riser design. Modelling the flexible joint stiffness in an accurate approach becomes more important especially when the riser fatigue is critical at the hang-off region. In addition, the design of flexible joint will also be impacted by the fatigue load extracted from global fatigue analysis, which is also largely affected by the flexible joint stiffness modelling method. Thus, modelling a flexible joint by accounting for the nonlinear hysteretic stiffness is recommended. This paper compares the different modelling methodologies of the flexible joint for catenary riser hang-off and presents the impact on fatigue performance considering hysteretic behavior. This study considers the effects of wave amplitude and hosting vessel offset. A case study is also presented on the application of all the modelling methods on fatigue performance of an SCR in the Gulf of Mexico. The fatigue behavior is compared for the different modelling methods considering long term wave motion and platform offsets. The impact on the results from different types of hosting platform is also discussed.

scholarly journals Cascaded Control of Flexible-Joint Robots Based on Sliding-Mode Estimator Approach

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Genliang Xiong ◽  
Jingxin Shi ◽  
Haichu Chen
Keyword(s):  
Controller Design ◽  
Sliding Mode ◽  
Joint Stiffness ◽  
Perturbation Approach ◽  
Regular Form ◽  
Flexible Joint ◽  
Flexible Joint Robots ◽  
Highly Nonlinear ◽  
Position Controller ◽  
High Bandwidth

The inherent highly nonlinear coupling and system uncertainties make the controller design for a flexible-joint robot extremely difficult. The goal of the control of any robotic system is to achieve high bandwidth, high accuracy of trajectory tracking, and high robustness, whereby the high bandwidth for flexible-joint robot is the most challenging issue. This paper is dedicated to design such a link position controller with high bandwidth based on sliding-mode technique. Then, two control approaches ((1) extended-regular-form approach and (2) the cascaded control structure based on the sliding-mode estimator approach) are presented for the link position tracking control of flexible-joint robot, considering the dynamics of AC-motors in robot joints, and compared with the singular perturbation approach. These two-link position controllers are tested and verified by the simulation studies with different reference trajectories and under different joint stiffness.

A study of the free vibration of flexible-link flexible-joint manipulators

2011 ◽  
Vol 225 (6) ◽  
pp. 1361-1371 ◽  
Author(s):  
M Vakil ◽  
R Fotouhi ◽  
P N Nikiforuk ◽  
F Heidari
Keyword(s):  
Joint Stiffness ◽  
Sensitivity Study ◽  
Frequency Equation ◽  
Mode Shapes ◽  
Flexible Link ◽  
Flexible Joint ◽  
Mass Moment ◽  
Mass Moment Of Inertia ◽  
Payload Mass ◽  
Analytical Expressions

In this article, explicit expressions for the frequency equation, mode shapes, and orthogonality of the mode shapes of a Single Flexible-link Flexible-joint manipulator (SFF) are presented. These explicit expressions are derived in terms of non-dimensional parameters which make them suitable for a sensitivity study; sensitivity study addresses the degree of dependence of the system’s characteristics to each of the parameters. The SFF carries a payload which has both mass and mass moment of inertia. Hence, the closed-form expressions incorporate the effect of payload mass and its mass moment of inertia, that is, the payload mass and its size. To check the accuracy of the derived analytical expressions, the results from these analytical expressions were compared with those obtained from the finite element method. These comparisons showed excellent agreement. By using the closed-form frequency equation presented in this article, a study on the changes in the natural frequencies due to the changes in the joint stiffness is performed. An upper limit for the joint stiffness of a SFF is established such that for the joint stiffness above this limit, the natural frequencies of a SFF are very close to those of its flexible-link rigid-joint counterpart. Therefore, the value of this limit can be used to distinguish a SFF from its flexible-link rigid-joint manipulator counterpart. The findings presented in this article enhance the accuracy and time-efficiency of the dynamic modeling of flexible-link flexible-joint manipulators. These findings also improve the performance of model-based controllers, as the more accurate the dynamic model, the better the performance of the model-based controllers.

Fatigue Assessment on Reverse–Balanced Flange Connections In Offshore Floating Wind Turbine Towers

2021 ◽  
Author(s):  
Tao Zou ◽  
Wenjie Liu ◽  
Mingxin Li ◽  
Longbin Tao
Keyword(s):  
Wind Turbine ◽  
Fatigue Damage ◽  
Deep Water ◽  
Wind Loading ◽  
Wave Forces ◽  
Local Geometry ◽  
Elastic Analysis ◽  
Wind Turbine Towers ◽  
Welding Joints ◽  
Offshore Floating Wind Turbine

Abstract Offshore floating wind turbines (FWTs) in deep water experience cyclic loadings from both environment and mechanical operations. For FWTs, the upper turbine and tower are mainly subjected to wind loading; and the floater is subjected to wave forces. It has been widely accepted that there is a strong coupling between the floater motions and the turbine forces. As the tower is placed between the upper wind turbine and the floater, both wind and wave loadings affect the cyclic forces on the tower. The construction of towers makes use of prefabricated segments. These prefabricated segments are bolted together with flanges at either end. The paper aims to investigate the axial hotspot stress on FWT’s tower base and analyze its induced fatigue damage at the welding joints around the flanges. A coupled aero-hydro-servo-elastic analysis is conducted to simulate the motion of FWTs. Then, the local welding joint along the reverse-balanced flange connection is modeled to consider the influence of local geometry. At last, the hourly fatigue damages at four locations over the tower base section are compared.

A new control method of flexible-joint manipulator with harmonic drive

2020 ◽  
Vol 234 (9) ◽  
pp. 1868-1883
Author(s):  
Guocai Yang ◽  
Yechao Liu ◽  
Minghe Jin
Keyword(s):  
Control Method ◽  
Controller Design ◽  
Joint Stiffness ◽  
Adaptive Controller ◽  
Harmonic Drive ◽  
Flexible Joint ◽  
Assignment Method ◽  
Uncertain Dynamics ◽  
Tracking Controller ◽  
Flexible Joint Manipulator

Considerable elasticity and nonlinear friction caused by harmonic transmission challenge the performance of flexible-joint manipulators. The uncertain dynamics of manipulator and the inadequate measurable states also limit the controller design. A new control method is proposed to address these problems, achieving the precise motion control of the flexible-joint manipulator. The method consists of three cascaded controllers: an adaptive controller, a torque-tracking controller, and a motor controller. The adaptive controller was adopted to generate the desired torque ensuring the robustness for uncertain dynamics. The torque-tracking controller derived the position compensation for motor control according to the torque error. As the elastic torque is under control, the vibration caused by harmonic drive can be eliminated. The motor was controlled based on poles-assignment method and friction compensation. The Kalman observer based on the Brownian motion model observed both velocity and the high-order derivatives of torque sensing. The stability of the control method was strictly proved. Calibration was performed on each joint to obtain the required joint stiffness and motor friction parameters. The control method was verified on a single joint and the frequency response of the system was obtained. The results show that the controller has good performance. The controller was realized on the self-developed seven-degree-of-freedom manipulator. The results reveal that the controller has high-precision tracking performance.

A Parametric Study on Effects of Environmental Loadings on Fatigue Life of Steel Catenary Risers (Using a Nonlinear Cyclic Riser-Soil Interaction Model)

2010 ◽  
Author(s):  
Mehrdad Kimiaei ◽  
Mark Randolph ◽  
Ivan Ting
Keyword(s):  
Fatigue Damage ◽  
Deep Water ◽  
Interaction Model ◽  
Fatigue Assessment ◽  
Wide Range ◽  
Non Linear ◽  
Wave Heights ◽  
Steel Catenary Risers ◽  
Vessel Motion ◽  
Floating Platforms

Steel catenary risers (SCRs) are often the preferred option for subsea tie-back to floating platforms in deep water due to their conceptual simplicity, ease of construction and installation and simple interface with the flowlines. Fatigue design of SCRs, particularly in the touch down area (TDA), has always been one of the major engineering challenges. Traditionally, fatigue assessment of SCRs has usually been highly conservative, because of lack of precise understanding of the non-linear soil-riser-interaction in the TDA. Most fatigue studies are based on assumed linear stiffness for the seabed, partly because of the lack of robust non-linear riser-seabed interaction models and partly because the linear response simplifies the fatigue study. The recent availability of non-linear seabed response models provides an opportunity to improve fatigue assessment, but it is first necessary to evaluate how best to conduct fatigue studies for such nonlinear systems which can be sensitive to wide range of input parameters. This paper outlines a new advanced numerical model, considering nonlinear cyclic riser-soil interaction behavior, used to determine the contribution of different loading parameters on fatigue damage of SCRs in the TDA in deep water soft sediments. The main loading parameters considered are: different motions of floating vessels, wave heights, wave periods and wave packs ordering. Numerical modeling has shown that over 95% of the fatigue damage corresponds to floating vessel motion parallel to the riser axis at the connection point to the vessel. It is also shown that riser response at TDA is highly influenced with amplitude and period of the environmental loadings.

Designing of Mechanical Structure and Translocating Clamp in Flexible Joint Stiffness Measuring System

2008 ◽  
Vol 392-394 ◽  
pp. 1001-1005
Author(s):  
Hui Feng Wang ◽  
Guang Lin Wang ◽  
C.D. Tao ◽  
Ze Sheng Lu
Keyword(s):  
Rotation Angle ◽  
Joint Stiffness ◽  
Measuring System ◽  
Flexible Joint ◽  
Mechanical Structure ◽  
Repeatability Error ◽  
Better Than

This paper analyzes the measure principle of flexible joint stiffness and constructs the measuring system of flexible joint stiffness. It achieves the measurement of flexible joint’s torque-rotation angle stiffness through designing the measuring appliance and translocating clamp. The result shows that it is efficient to develop the measuring system and repeatability error is better than 1%.

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