Steel Catenary Riser Design Based on Coupled Analysis Methodology

2008 ◽  
Author(s):  
Marcos V. Rodrigues ◽  
Rodrigo A. Bahiense ◽  
Oddrun Steinkjer ◽  
Celso V. Raposo
Keyword(s):  
Computational Effort ◽  
Computational Time ◽  
Coupled Analysis ◽  
Coupling Effects ◽  
Usual Practice ◽  
Environmental Loads ◽  
Steel Catenary Riser ◽  
Deep Waters ◽  
Riser Design ◽  
Platform Motions

In a riser design, the traditionally assessment adopted by industry for attainment of platform motions applied to the top of riser consists in the use of de-coupled methodologies. These formulations consider the static environmental loads over the platform (current and wind) through a static offset and the dynamic environmental loads due to wave through imposition of top riser displacement calculated from cross spectral response of sea spectrum and vessel’s RAOs (Response Amplitude Operators). Nowadays due to shift of oil and gas exploitation to deeper waters more accurate methodologies, based on coupled analysis, have been introduced. The coupled analysis considers the interaction between the hydrodynamic behavior of the hull and the structural behavior of mooring lines and risers submitted to environmental loads. For deep waters the coupling effects of lines over platform motions are especially significant and a reduction of the amplification of platform motions if compared to the platform motions obtained from de-coupled analysis is observed. This paper presents a typical Steel Catenary Riser design, connected to a semi-submersible platform, where the motions applied to the top of riser are obtained from the “traditional” way (de-coupled) and from the coupled analysis. Numerical application is presented in order to assess the comparison of the two presented methods in terms of SCR analysis results and to confirm the reduction of platform motions due to coupling effects. The coupled model here studied is composed of approximately 80 lines connected to the platform which requires an excessive computational effort. In order to reduce the computational time some additional studies are performed considering the variation of line mesh discretization and time step size. The objective of this study is the adoption of an optimized model where the required accuracy is achieved and the computational time consuming is the minimum possible. The computational time consuming and platform motions are also presented. The conclusion of this work is that coupled analysis should be adopted by industry as usual practice of SCR design in deep waters, where more realistic and optimum results are presented, without an excessive computational effort.

Steel Catenary Riser Design Based on Prescribed Motions From Coupled Analysis Methodology

2008 ◽  
Author(s):  
Marcos Vinicius Rodrigues ◽  
Vigleik L. Hansen ◽  
Rodrigo Almeida Bahiense ◽  
Celso Velasco Raposo
Keyword(s):  
Coupled Analysis ◽  
Steel Catenary Riser ◽  
Analysis Methodology ◽  
Riser Design

Understanding the Dynamic Coupling Effects in Deep Water Floating Structures Using a Simplified Model

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Ying Min Low ◽  
Robin S. Langley
Keyword(s):  
Frequency Domain ◽  
Deep Water ◽  
Time Domain ◽  
Low Frequency ◽  
Wave Frequency ◽  
Computational Time ◽  
Coupled Analysis ◽  
Floating Platform ◽  
Coupling Effects ◽  
Mooring Lines

The global dynamic response of a deep water floating production system needs to be predicted with coupled analysis methods to ensure accuracy and reliability. Two types of coupling can be identified: one is between the floating platform and the mooring lines/risers, while the other is between the mean offset, the wave frequency, and the low frequency motions of the system. At present, it is unfeasible to employ fully coupled time domain analysis on a routine basis due to the prohibitive computational time. This has spurred the development of more efficient methods, including frequency domain approaches. A good understanding of the intricate coupling mechanisms is paramount for making appropriate approximations in an efficient method. To this end, a simplified two degree-of-freedom system representing the surge motion of a vessel and the fundamental vibration mode of the lines is studied for physical insight. Within this framework, the frequency domain equations are rigorously formulated, and the nonlinearities in the restoring forces and drag are statistically linearized. The model allows key coupling effects to be understood; among other things, the equations demonstrate how the wave frequency dynamics of the mooring lines are coupled to the low frequency motions of the vessel. Subsequently, the effects of making certain simplifications are investigated through a series of frequency domain analyses, and comparisons are made to simulations in the time domain. The work highlights the effect of some common approximations, and recommendations are made regarding the development of efficient modeling techniques.

A Simplified Model for the Study of Dynamic Coupling Effects in Deepwater Floating Structures

2005 ◽  
Author(s):  
Ying Min Low ◽  
Robin S. Langley
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Low Frequency ◽  
Wave Frequency ◽  
Computational Time ◽  
Coupled Analysis ◽  
Floating Platform ◽  
Coupling Effects ◽  
Fundamental Vibration ◽  
Mooring Lines

As the exploitation of hydrocarbon moves towards deeper waters, the global dynamic response of a floating production system needs to be predicted with coupled analysis methods to ensure accuracy and reliability. Two types of coupling can be identified: one is between the floating platform and the mooring lines/risers, while the other is between the mean offset, the wave frequency and the low frequency motions of the system. At present, it is unfeasible to employ fully coupled time domain analysis on a routine basis due to prohibitive computational time. This has spurred the development of more efficient methods that account for the various couplings, including frequency domain approaches. It is paramount for the complex coupling mechanisms to be well understood before appropriate simplifications and assumptions can be made. In this paper, a simplified two degree-of-freedom system representing the surge motion of a vessel and the fundamental vibration mode of the lines is examined which captures the important underlying physics. Within this framework, the frequency domain equations are rigorously formulated, and the nonlinearities in the restoring forces and drag are stochastically linearized. The model allows key coupling effects to be identified: among other things, the equations demonstrate how the wave frequency dynamics of the mooring lines are coupled to the low frequency motions of the vessel. Subsequently, the effects of making certain simplifications are investigated through a series of frequency domain spectral analyses, and comparisons are made to simulations in the time domain. The work highlights the effect of certain common approximations, and recommendations are made regarding the development of efficient modeling techniques.

Integrated Redesign of Large-Scale Structures by Large Admissible Perturbations

2003 ◽  
Vol 125 (4) ◽  
pp. 234-241 ◽  
Author(s):  
Vincent Y. Blouin ◽  
Michael M. Bernitsas ◽  
Denby Morrison
Keyword(s):  
Degrees Of Freedom ◽  
Large Scale ◽  
Direct Method ◽  
Computational Effort ◽  
Forced Response ◽  
Response Amplitude ◽  
Computational Time ◽  
Performance Constraints ◽  
Large Admissible Perturbations ◽  
Design Selection

In structural redesign (inverse design), selection of the number and type of performance constraints is a major challenge. This issue is directly related to the computational effort and, most importantly, to the success of the optimization solver in finding a solution. These issues are the focus of this paper, which provides and discusses techniques that can help designers formulate a well-posed integrated complex redesign problem. LargE Admissible Perturbations (LEAP) is a general methodology, which solves redesign problems of complex structures with, among others, free vibration, static deformation, and forced response amplitude constraints. The existing algorithm, referred to as the Incremental Method is improved in this paper for problems with static and forced response amplitude constraints. This new algorithm, referred to as the Direct Method, offers comparable level of accuracy for less computational time and provides robustness in solving large-scale redesign problems in the presence of damping, nonstructural mass, and fluid-structure interaction effects. Common redesign problems include several natural frequency constraints and forced response amplitude constraints at various frequencies of excitation. Several locations on the structure and degrees of freedom can be constrained simultaneously. The designer must exercise judgment and physical intuition to limit the number of constraints and consequently the computational time. Strategies and guidelines are discussed. Such techniques are presented and applied to a 2,694 degree of freedom offshore tower.

Strength Performance of Steel Catenary Riser Using Short Term and Long Term Analysis Methodologies

2016 ◽  
Author(s):  
Feng Wang ◽  
Roger Burke ◽  
Anil Sablok ◽  
Kristoffer H. Aronsen ◽  
Oddgeir Dalane
Keyword(s):  
Bending Moment ◽  
Current Profile ◽  
Short Term ◽  
Sea State ◽  
Strength Performance ◽  
Steel Catenary Riser ◽  
Analysis Methodology ◽  
Riser Design ◽  
Term Analysis

Strength performance of a steel catenary riser tied back to a Spar is presented based on long term and short term analysis methodologies. The focus of the study is on response in the riser touch down zone, which is found to be the critical region based on short term analysis results. Short term riser response in design storms is computed based on multiple realizations of computed vessel motions with various return periods. Long term riser response is based on vessel motions for a set of 45,000 sea states, each lasting three hours. The metocean criteria for each sea state is computed based on fifty six years of hindcast wind and wave data. A randomly selected current profile is used in the long term riser analysis for each sea state. Weibull fitting is used to compute the extreme riser response from the response of the 45,000 sea states. Long term analysis results in the touch down zone, including maximum bending moment, minimum effective tension, and maximum utilization using DNV-OS-F201, are compared against those from the short term analysis. The comparison indicates that the short term analysis methodology normally followed in riser design is conservative compared to the more accurate, but computationally more expensive, long term analysis methods. The study also investigates the important role that current plays in the strength performance of the riser in the touch down zone.

scholarly journals Tripod-Supported Offshore Wind Turbines: Modal and Coupled Analysis and a Parametric Study Using X-SEA and FAST

2019 ◽  
Vol 7 (6) ◽  
pp. 181 ◽  
Author(s):  
Pasin Plodpradit ◽  
Van Nguyen Dinh ◽  
Ki-Du Kim
Keyword(s):  
Wind Turbines ◽  
Natural Frequencies ◽  
Offshore Wind ◽  
Computational Time ◽  
Coupled Analysis ◽  
Physical Interaction ◽  
Support Structures ◽  
Coupled Models ◽  
Support Structure ◽  
Offshore Wind Turbines

This paper presents theoretical aspects and an extensive numerical study of the coupled analysis of tripod support structures for offshore wind turbines (OWTs) by using X-SEA and FAST v8 programs. In a number of site conditions such as extreme and longer period waves, fast installation, and lighter foundations, tripod structures are more advantageous than monopile and jacket structures. In the implemented dynamic coupled analysis, the sub-structural module in FAST was replaced by the X-SEA offshore substructure analysis component. The time-histories of the reaction forces and the turbine loads were then calculated. The results obtained from X-SEA and from FAST were in good agreement. The pile-soil-structure interaction (PSSI) was included for reliable evaluation of OWT structural systems. The superelement concept was introduced to reduce the computational time. Modal, coupled and uncoupled analyses of the NREL 5MW OWT-tripod support structure including PSSI were carried out and the discussions on the natural frequencies, mode shapes and resulted displacements are presented. Compared to the uncoupled models, the physical interaction between the tower and the support structure in the coupled models resulted in smaller responses. Compared to the fixed support structures, i.e., when PSSI is not included, the piled-support structure has lower natural frequencies and larger responses attributed to its actual flexibility. The models using pile superelements are computationally efficient and give results that are identical to the common finite element models.

Accurate and efficient representation of intramolecular energy in ab initio generation of crystal structures. II. Smoothed intramolecular potentials

2019 ◽  
Vol 75 (3) ◽  
pp. 423-433 ◽  
Author(s):  
Isaac J. Sugden ◽  
Claire S. Adjiman ◽  
Constantinos C. Pantelides
Keyword(s):  
Structure Prediction ◽  
Weighted Average ◽  
Lattice Energy ◽  
Comparative Investigation ◽  
Computational Effort ◽  
Flufenamic Acid ◽  
Computational Time ◽  
Crystal Structure Prediction ◽  
Efficient Representation ◽  
First Time

The application of crystal structure prediction (CSP) to industrially relevant molecules requires the handling of increasingly large and flexible compounds. A revised model for the effect of molecular flexibility on the lattice energy that removes the discontinuities and non-differentiabilities present in earlier models (Sugden et al., 2016), with a view to improving the performance of CSP is presented. The approach is based on the concept of computing a weighted average of local models, and has been implemented within the CrystalPredictor code. Through the comparative investigation of several compounds studied in earlier literature, it is shown that this new model results in large reductions in computational effort (of up to 65%) and in significant increases in reliability. The approach is further applied to investigate, for the first time, the computational polymorphic landscape of flufenamic acid for Z′ = 1 structures, resulting in the successful identification of all three experimentally resolved polymorphs within reasonable computational time.

A comparison of numerical methods for optimizing even aged stand management

1990 ◽  
Vol 20 (7) ◽  
pp. 961-969 ◽  
Author(s):  
Lauri T. Valsta
Keyword(s):  
Dynamic Programming ◽  
Species Composition ◽  
Random Search ◽  
Optimization Methods ◽  
Global Optimum ◽  
Computational Effort ◽  
Direct Search ◽  
Computational Time ◽  
Discrete State ◽  
Stand Management

A two-species, whole-stand, deterministic growth model was combined with three optimization methods to derive management regimes for species composition, thinnings, and rotation age, with the objective of maximizing soil expectation value. The methods compared were discrete time – discrete state dynamic programming, direct search using the Hooke and Jeeves algorithm, and random search. Optimum solutions for each of the methods varied considerably, required unequal amounts of computational time, and were not equally stable. Dynamic programming located global optimal solutions but did not determine them accurately, owing to discretized state space. Direct search yielded the largest objective function values with comparable computational effort, although the likelihood of finding a global optimum solution was high only for smaller problems with up to two or three thinnings during the rotation. Random search solutions varied considerably with regard to growing stock level and species composition and did not define a consistent management guideline. In general, direct search and dynamic programming appeared to be superior to random search.

Load Effects on the Dynamics of Spur Gear Transmissions

2010 ◽  
Author(s):  
Alfonso Fernandez del Rincon ◽  
Fernando Viadero Rueda ◽  
Miguel Iglesias Santamaria ◽  
Pablo Garcia Fernandez ◽  
Ana de-Juan de Luna ◽  
...  
Keyword(s):  
Gear Tooth ◽  
Hybrid Approach ◽  
Angular Position ◽  
Spur Gear ◽  
Computational Effort ◽  
Contact Forces ◽  
Mode Shapes ◽  
Computational Time ◽  
Applied Torque ◽  
Rolling Elements

Gear transmissions in general and spur gears in particular exhibit a different dynamic behavior depending on the level of the transmitted load. This fact justifies the interest in the study of the role of the load in gear dynamics not only in the context of design, vibration and noise control but also for condition monitoring. This task requires the development of advanced models achieving a compromise between accuracy and computation time. In this work, gear and bearing non-linearities associated with the contact among teeth and roller elements have been included, taking into account the flexibility of gears, shafts and bearings. Besides, parametric excitations coming both from gear and bearing supports, as well as clearance, were also considered. Gear contact force calculations are carried out following a hybrid approach which combines both analytical and numerical tools. This lets to achieve accurate results with an acceptable computational effort and thus dynamic analysis becomes feasible. This approach was improved and the calculation speeded up from the point of view of computational time. This was performed by using a pre-calculated value for gear tooth stiffness as a function of load and the angular position when it operates under stationary conditions. On the other hand, bearings were formulated just as deflections of Hertzian type. This means that bending and shearing of races and rolling elements are neglected. However, the variation in the number of loaded rolling elements as a function of the load and the angular position was taken into account. Shaft flexibilities were added to gear and bearing models to define a simple transmission that was used to study the vibratory behavior under different levels of applied torque. In a preliminary study, this model was linearized for several loads, obtaining the corresponding frequencies and mode-shapes in order to assess their variation with this parameter. Finally, dynamic simulations were carried out, showing the modifications undergone by the orbits, meshing contact forces and transmitted bearing forces.

VERIFICATION OF A MARINE POLLUTANT SURFACE PLUME MODEL FOR USE IN THE DEVELOPMENT OF AUTONOMOUS VEHICLE TRACKING SYSTEMS

2017 ◽  
Vol 2017 (1) ◽  
pp. 1612-1628
Author(s):  
Laura M. Fitzpatrick ◽  
A Zachary Trimble ◽  
Brian S. Bingham
Keyword(s):  
Control Systems ◽  
Surface Concentration ◽  
Computational Effort ◽  
Computational Time ◽  
Type Model ◽  
Fine Scale ◽  
Multiple Model ◽  
Robotic Control ◽  
Statistical Parameters ◽  
Tuning Parameters

ABSTRACT A marine pollutant spill environmental model that can accurately predict fine scale pollutant concentration variations on a free surface is needed in early stages of testing robotic control systems for tracking pollutant spills. The model must reproduce, for use in a robotic control system simulation environment, the fine-scale surface concentration variations observed by a robot. Furthermore, to facilitate development of robotic control systems, the model must reproduce sample spill distributions in minimal computational time. A combination Eulerian-Lagrangian type model, with two tuning parameters, was developed to produce, with minimal computational effort, the fine scale concentrations that would be observed by a robot. Multiple model scenarios were run with different tuning parameters to determine the effects of those parameters on the model’s ability to reproduce an experimental measured pollutant plume’s structure. A qualitative method for analyzing the concentration variations was established using amplitude and temporal statistical parameters. The differences in the statistical parameters between the model and experiment vary from 69%–316%. After tuning, the model produces a sample spill, which includes a high frequency concentration component not observed in the experimental data, but that generally represents the real-time, fine scale pollutant plume structure and can be used for testing control algorithms.

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