Truncation Design and Model Testing of a Deepwater FPSO Mooring System

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Hongwei Wang ◽  
Gang Ma ◽  
Liping Sun ◽  
Zhuang Kang
Keyword(s):  
Hybrid Model ◽  
Dynamic Properties ◽  
Model Testing ◽  
Model Tests ◽  
Mooring System ◽  
Lumped Mass ◽  
Mass Model ◽  
Numerical Reconstruction ◽  
Lumped Mass Model ◽  
System Configurations

Limitation of offshore basin dimensions is a great challenge for model tests of deepwater mooring system. The mooring system cannot be modeled entirely in the basin with a reasonable model scale. A classical solution is based on hybrid model tests for the truncated mooring system. An efficient truncation method is proposed in this paper taking advantage of the mechanical characteristics of catenary mooring system. Truncation procedures are presented both in vertical and horizontal directions. A turret moored floating production storage and offloading (FPSO) is analyzed, and its mooring system is truncated from the original 914 m water depth to 736 m and 460 m, respectively. Numerical simulations are performed based on catenary theory and lumped mass model to these three systems, including the original untruncated system and two truncated systems. The static characteristics and dynamic response are investigated, and the results are compared between the truncated and untruncated system, and good agreements are obtained, verifying the preliminary truncation design. Model tests are conducted to the three mooring system configurations in the deepwater basin of the Harbin Engineering University. The static and dynamic properties are found to be mostly consistent between the untruncated system and two truncated systems, except for some discrepancy in 460 m system. It indicates that the truncation design is successful when the truncation factor is large, while difference still exists when the truncation factor is small. Numerical reconstruction to the model test in 460 m and extrapolation to 914 m are also implemented. The results are found to be consistent with those in 914 m, verifying the robustness and necessity of the hybrid model testing, especially for the mooring system with large truncation.

Nonlinear Dynamics of Multi-Segment Mooring Systems

2017 ◽  
Author(s):  
Sandeep B. Reddy ◽  
Allan Ross Magee ◽  
Wei Bai
Keyword(s):  
First Principles ◽  
Current Problem ◽  
Time Integration ◽  
Single Line ◽  
Mooring System ◽  
Lumped Mass ◽  
Mass Model ◽  
Tangent Stiffness Matrix ◽  
Lumped Mass Model ◽  
Dissipative Model

A general formulation applicable to multi-segment mooring systems is derived from first principles using the concept of lumped mass model and presented in this paper. The problem of seabed contact is addressed using an elastic-dissipative model of seabed. The contribution of seabed force along with the tension force is considered in creating global tangent stiffness matrix of the system. An implicit generalized-α method is used for time integration and it is modified for the current problem by developing an incremental iterative version of the method with corresponding predictor and corrector terms. An in house code named LM3D is developed based on the derived formulation. The code is verified with orcaflex results and also validated with experimental results. The main purpose of this paper is to showcase the reduction in tension observed in a simple branched mooring system when compared to a single line. Three configurations of branched system were considered and compared against a single line arrangement with same material properties. The dynamic analysis of this branched system was carried out with the developed in-house code.

A Comparison of Inverse Models for the Estimation of Ice-Induced Propeller Moments on a Polar Vessel

2021 ◽  
Author(s):  
Brendon M. Nickerson ◽  
Anriëtte Bekker
Keyword(s):  
Rotational Speed ◽  
Continuous Model ◽  
Full Scale ◽  
Lumped Mass ◽  
Mass Model ◽  
Inverse Models ◽  
Lumped Mass Model ◽  
Ill Posed ◽  
Shaft Torque ◽  
Measurement Location

Abstract Full-scale measurements were conducted on the port side propulsion shaft the S.A. Agulhas II during the 2019 SCALE Spring Cruise. The measurements included the shaft torque captured at two separate measurement locations, and the shaft rotational speed at one measurement location. The ice-induced propeller moments are estimated from the full-scale shaft responses using two inverse models. The first is a published discrete lumped mass model that relies on regularization due to the inverse problem being ill-posed. This model is only able to make use of the propulsion shaft torque as inputs. The second model is new and employs modal superposition to represent the propulsion shaft as a combination of continuous modes, resulting in a well-posed problem. This new model requires the additional measurement of the shaft rotational speed for the inverse solution. The continuous model is shown to be more consistent and efficient, which allows its use in real-time monitoring of propeller moments.

Coupled Torsional Vibration and Fatigue Damage of Turbine Generator Due to Grid Disturbance

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Chao Liu ◽  
Dongxiang Jiang ◽  
Jingming Chen
Keyword(s):  
Fatigue Damage ◽  
Torsional Vibration ◽  
Coupled System ◽  
Lumped Mass ◽  
Mass Model ◽  
Turbine Generator ◽  
Failure Prevention ◽  
Lumped Mass Model ◽  
Continuous Mass ◽  
Fatigue Evaluation

Crack failures continually occur in shafts of turbine generator, where grid disturbance is an important cause. To estimate influences of grid disturbance, coupled torsional vibration and fatigue damage of turbine generator shafts are analyzed in this work, with a case study in a 600MW steam unit in China. The analysis is the following: (i) coupled system is established with generator model and finite element method (FEM)-based shafts model, where the grid disturbance is signified by fluctuation of generator outputs and the shafts model is formed with lumped mass model (LMM) and continuous mass model (CMM), respectively; (ii) fatigue damage is evaluated in the weak location of the shafts through local torque response computation, stress calculation, and fatigue accumulation; and (iii) failure-prevention approach is formed by solving the inverse problem in fatigue evaluation. The results indicate that the proposed scheme with continuous mass model can acquire more detailed and accurate local responses throughout the shafts compared with the scheme without coupled effects or the scheme using lumped mass model. Using the coupled torsional vibration scheme, fatigue damage caused by grid disturbance is evaluated and failure prevention rule is formed.

Combining Physics-Based and Data-Driven Models for Estimation of WOB During Ultra-Deep Ocean Drilling

2018 ◽  
Author(s):  
Tatsuya Kaneko ◽  
Ryota Wada ◽  
Masahiko Ozaki ◽  
Tomoya Inoue
Keyword(s):  
Hybrid Model ◽  
Numerical Models ◽  
Drill String ◽  
Operating Conditions ◽  
Data Driven ◽  
High Frequency Oscillation ◽  
Lumped Mass ◽  
Unknown Parameters ◽  
Mass Model ◽  
Time Operation

Offshore drilling with drill string over 10,000m long has many technical challenges. Among them, the challenge to control the weight on bit (WOB) between a certain range is inevitable for the integrity of drill pipes and the efficiency of the drilling operation. Since WOB cannot be monitored directly during drilling, the tension at the top of the drill string is used as an indicator of the WOB. However, WOB and the surface measured tension are known to show different features. The deviation among the two is due to the dynamic longitudinal behavior of the drill string, which becomes stronger as the drill string gets longer and more elastic. One feature of the difference is related to the occurrence of high-frequency oscillation. We have analyzed the longitudinal behavior of drill string with lumped-mass model and captured the descriptive behavior of such phenomena. However, such physics-based models are not sufficient for real-time operation. There are many unknown parameters that need to be tuned to fit the actual operating conditions. In addition, the huge and complex drilling system will have non-linear behavior, especially near the drilling annulus. These features will only be captured in the data obtained during operation. The proposed hybrid model is a combination of physics-based models and data-driven models. The basic idea is to utilize data-driven techniques to integrate the obtained data during operation into the physics-based model. There are many options on how far we integrate the data-driven techniques to the physics-based model. For example, we have been successful in estimating the WOB from the surface measured tension and the displacement of the drill string top with only recurrent neural networks (RNNs), provided we have enough data of WOB. Lack of WOB measurement cannot be avoided, so the amount of data needs to be increased by utilizing results from physics-based numerical models. The aim of the research is to find a good combination of the two models. In this paper, we will discuss several hybrid model configurations and its performance.

Identification of firefly algorithm-based fluctuation coefficient of the exciting torque for vehicle driveline

2018 ◽  
Vol 233 (2) ◽  
pp. 317-326
Author(s):  
Qiaobin Liu ◽  
Wenku Shi ◽  
Zhiyong Chen
Keyword(s):  
Torsional Vibration ◽  
Firefly Algorithm ◽  
Vibration Response ◽  
Theoretical Modelling ◽  
Lumped Mass ◽  
Mass Model ◽  
Engine Torque ◽  
Lumped Mass Model ◽  
Vibration Performance ◽  
Engine Excitation

The unbalanced excitation force and torque generated by an engine that resonate with the natural frequency of drivetrain often causes vibration and noise problems in vehicles. This study aims to comprehensively employ theoretical modelling and experimental identification methods to obtain the fluctuation coefficients of engine excitation torque when a car is in different gear positions. The inherent characteristics of the system are studied on the basis of the four-degree-of-freedom driveline lumped mass model and the longitudinal dynamics model of vehicle. The correctness of the model is verified by torsional vibration test. The second order's engine torque fluctuation coefficients are identified by firefly algorithm according to the curves of flywheel speed in different gears under the acceleration condition of the whole open throttle. The torque obtained by parameter identification is applied to the model, and the torsional vibration response of the system is analysed. The influence of the key parameters on the torsional vibration response of the system is investigated. The study concludes that proper reduction of clutch stiffness can increase clutch damping and half-axle rigidity, which can help improve the torsional vibration performance of the system. This study can provide reference for vehicle drivetrain modelling and torsional vibration control.

Dynamic Gear Loads Due to Coupled Lateral, Torsional and Axial Vibrations in a Helical Geared System

1999 ◽  
Vol 121 (2) ◽  
pp. 141-148 ◽  
Author(s):  
S. H. Choi ◽  
J. Glienicke ◽  
D. C. Han ◽  
K. Urlichs
Keyword(s):  
Load Condition ◽  
Coupled System ◽  
Transmission Error ◽  
Lumped Mass ◽  
Mass Model ◽  
Shaft Line ◽  
Transmission Errors ◽  
Lumped Mass Model ◽  
Vibration Problems ◽  
Axial Vibrations

In this paper we investigate the rotordynamics of a geared system with coupled lateral, torsional and axial vibrations, with a view toward understanding the severe vibration problems that occurred on a 28-MW turboset consisting of steam turbine, double helical gear and generator. The new dynamic model of the shaft line was based on the most accurate simulation of the static shaft lines, which are influenced by variable steam forces and load-dependent gear forces. The gear forces determine the static shaft position in the bearing shell. Each speed and load condition results in a new static bending line which defines the boundary condition for the dynamic vibration calculation of the coupled lateral, torsional and axial systems. Rigid disks and distributed springs were used for shaft line modeling. The tooth contact was modeled by distributed springs acting normally on the flank surfaces of both helices. A finite element method with distributed mass was used for lateral and torsional vibrations. It was coupled to a lumped mass model describing the axial vibrations. The forced vibrations due to unbalances and static transmission errors were calculated. The eigenvalue problem was solved by means of a stability analysis showing the special behavior of the coupled system examined. The calculation was successfully applied, and the source of the vibration problem could be located as being a gear-related transmission error. Several redesign proposals lead to a reliable and satisfactory vibrational behavior of the turboset.

Modal Interactions in Resonant Microscanners

2006 ◽  
Author(s):  
Mohammed F. Daqaq ◽  
Elihab M. Abdel-Rahman ◽  
Ali H. Nayfeh
Keyword(s):  
Multiple Scales ◽  
Fast Response ◽  
Modal Interactions ◽  
Lumped Mass ◽  
Mass Model ◽  
Torsional Mode ◽  
Large Rotation ◽  
Wavelength Sensitivity ◽  
Bending Mode ◽  
Lumped Mass Model

The fast response of micromirrors and their ability to achieve large scanning angles and low wavelength sensitivity, has made them an appealing substitute for traditional scanning and display technologies. To achieve large rotation angles, while minimizing the voltage requirements, the microscanner is excited at its resonance frequency and then used to steer a light beam along a surface. In this work, we develop a comprehensive model of a torsional microscanner. Based on the eigenvalue problem, we reduce the model to a 2-DOF lumped-mass model that captures the significant dynamics of the microscanner. We use the method of multiple scales to derive an approximate analytical solution of the microscanner response to combined DC and resonant AC voltage excitation. We examined the characteristics of the solution and found that, for a range of DC voltage, a two-to-one internal resonance occurs between the first two modes. Therefore, the energy fed to the first (torsional) mode may be channeled to the second (bending) mode causing an undesirable steady-state response. This phenomenon results in significant degradation in the microscanner performance, therefore, the designer needs to identify it, design around it, or control it.

Active Control of Wind-Induced Building Vibration Using a Linear Coupling Strategy

2001 ◽  
Author(s):  
S. Mohammad Hashemi ◽  
M. F. Golnaraghi
Keyword(s):  
Control System ◽  
Active Control ◽  
Lumped Parameter Model ◽  
Test Bed ◽  
Lumped Mass ◽  
Mass Model ◽  
Linear Coupling ◽  
Lumped Parameter ◽  
Coupling Strategy ◽  
Lumped Mass Model

Abstract The active control of building vibration is addressed. The aeroelastic lumped mass model of a building is designed to be used as the test bed for the active control system. The five story lumped parameter model was modeled as a cantilever beam exhibiting planar vibration. A Linear Coupling Control (LCC) strategy was implemented to eliminate the vibrations. An active (moving) mass damper (AMD) was first designed and experimentally implemented to control the first mode vibration of the system. An alternative pendulum control system was then designed and implemented. The proposed pendulum, having three times smaller mass than the AMD, was found to be more effective in reducing the building vibrations.

scholarly journals Simulations of dense-snow avalanches on deflecting dams

1998 ◽  
Vol 26 ◽  
pp. 265-271 ◽  
Author(s):  
Fridtjov Irgens ◽  
Bonsak Schieldrop ◽  
Carl B. Harbitz ◽  
Ulrik Domaas ◽  
Runar Opsahl
Keyword(s):  
Three Dimensional ◽  
Angle Of Incidence ◽  
Snow Avalanches ◽  
Centre Of Mass ◽  
Lumped Mass ◽  
Mass Model ◽  
One Dimensional ◽  
Lumped Mass Model ◽  
Flowing Material ◽  
Run Up

Two models simulating snow avalanches impacting retaining dams at oblique angles of incidence are presented.First, a lumped-mass model applying the Voellmy-Perla equation is used to calculate the path of the centre-of-mass along the side of a retaining dam.Secondly, a one-dimensional continuum model, applying depth-integrated equations of balance of mass and linear momentum, is expanded to take into account that real avalanche flows are three-dimensional. The centre-line of the avalanche path is determined by the flowing material as it progresses down the channelized avalanche path. The nonlinear constitutive equations comprise viscosity, visco-elasticity and plasticity.Both models are calibrated by simulations of a registered avalanche following a strongly curved channel. The path and the run-up height of the avalanche on the natural deflecting dam with oblique angle of incidence as calculated by the two models, are compared with the observations made.

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