Global Strength Analysis in Head Waves, for an Offshore Support Vessel

Offshore structure global strength analysis based on finite element plate model is a requirement for today’s classification societies and designers. Wave, wind, current loads have to be applied to the global strength model as a pre processing step to allow the analysis to take place. After the analysis, code checking must be performed to verify if the structure meets class or other requirements. Due to its complex nature, a large amount of engineering hours have to be spent for the pre and post processing. This is not only lengthy if performed manually or semi-automatically, but also mistake prone. General guidelines from classification societies exist, but general purpose commercial software is scarce and often still requires significant amount of engineering time to perform these tasks. This paper shows a rational approach to automate the pre and post processing of offshore structure global strength finite element analysis. Utilizing the FEMAP Application Program Interface (API), a complete automatic pre and post processing is implemented in one integrated program, Exmar Design Suite (EDS). The program will load the model from WAMIT generated wave pressure, apply internal pressure induced from motions to internal tanks, and also apply other environmental loads. After the finite element analysis, the program can execute strength code checking including yielding and buckling for the model. Both beam and stiffened plate panels can be identified using an automatic search algorithm, which is not a function available for general finite element software. The panels and beams are then checked against various common codes such as API/AISC/ABS/DNV. In addition, fatigue analysis can also be performed in either spectral or simplified approach. The benefits of automation are timesaving, accuracy and reliability. It also makes the check of whole model possible. Instead of relying more on “screening” or experience based structure check, engineers will have more confidence in the results by going through the whole model.

Download Full-text

Computation of Wave Induced Loads for Global Strength Analysis of Container Ships

10.3940/rina.icsotin.2013.07 ◽

2013 ◽

Author(s):

Jai Ram Saripilli ◽

◽

Sharad Dhavalikar ◽

Apurva Ranjan Kar ◽

◽

...

Keyword(s):

Strength Analysis ◽

Global Strength ◽

Wave Induced

Download Full-text

Gulf of Mexico's First Ship Shape FPU: Overview of the Global Strength Analysis

10.4043/21434-ms ◽

2011 ◽

Author(s):

Majid M. Al-Sharif ◽

Partha Chakrabarti ◽

Kaushik Bose

Keyword(s):

Gulf Of Mexico ◽

Strength Analysis ◽

Global Strength

Download Full-text

Free Standing Hybrid Riser Global Parametric Sensitivity Analysis and Optimum Design

Volume 4: Pipeline and Riser Technology ◽

10.1115/omae2011-49606 ◽

2011 ◽

Cited By ~ 1

Author(s):

Wei Qin ◽

Zhuang Kang ◽

Youwei Kang

Keyword(s):

Sensitivity Analysis ◽

Optimum Design ◽

Mathematic Model ◽

Strength Analysis ◽

General Description ◽

Free Standing ◽

Near Surface ◽

Parametric Sensitivity ◽

Parametric Sensitivity Analysis ◽

Global Strength

With a rigid pipe for the vertical free standing portion and a flexible pipe for the near surface dynamic motion region, Free Standing Hybrid Riser (FSHR) has been widely accepted within the offshore oil and gas industry, especially in the field of West of Africa, Gulf of Mexico and field of Brazil. So the optimum design of FSHR system is becoming increasingly meaningful and necessary. This paper mainly presents the parametric sensitivity analysis and optimization of deepwater Free Standing Hybrid Riser (FSHR). First of all, a general description about FSHR system is given in the introduction. The components of FSHR and their function are presented in detail. Secondly, the procedure for parameters optimum design is discussed, and in order to make it looks more clearly and directly, a flowchart is illustrated to show the process. Considering the design requirements for a deepwater FSHR, the optimum design mathematic model is presented with the optimal objective - minimum of FSHR total weight which is directly proportional to project cost. Thirdly, a design instance is given to make clear the flow of FSHR optimum design with the best performance. The global strength analysis is carried out with the use of generic FEA tools. Then the parametric sensitivity analysis is performed through Single-Variable Control Method. Based on FSHR global strength analysis, four sensitivity parameters are carried out, and the minimum bending radius (MBR) of Flexible Jumper and the max von Misses stress are checked according to API RP 2RD. The relationship between sensitivity parameters and the response of the riser system is briefly discussed and the regress analysis can be used to quantify the relativity. Finally, the parameters optimum design is analyzed and the optimum results are checked to ensure its validity.

Download Full-text

Time Trace Window Based Approach for SCR Strength Analysis in Ultra Deepwater of Gulf of Mexico

Volume 3: Pipeline and Riser Technology ◽

10.1115/omae2009-79529 ◽

2009 ◽

Author(s):

Jack Chen ◽

Peimin Cao ◽

Huadong Zhu ◽

Paul Jukes

Keyword(s):

Stress Response ◽

Gulf Of Mexico ◽

Ocean Waves ◽

Strength Analysis ◽

Storm Event ◽

Peak Time ◽

Sea State ◽

Stress Strain ◽

Time Trace ◽

Global Strength

For a steel catenary riser (SCR) in the ultra deep water of the Gulf of Mexico (GOM), the areas of major concern from a dynamic stress response point of view are the sagbend region near the touchdown and the region below the hang-off at the SCR top where local bending must be accommodated. Usually global strength (stress/strain/buckling) analysis focuses primarily on the sagbend region, while more detailed analysis associated with design of the riser hang-off assembly concentrates on the SCR top region. The global strength design of the SCR is controlled by dynamic response in the sagbend region, which is primarily driven by the host vessel motions. Vessel motions are in turn induced by metocean conditions such as hurricanes and winter storms. Given the random nature of the ocean waves, to obtain statistically sound results, random wave simulations involving multiple (usually ten (10)) three (3) hour realizations have been a well accepted practice by the offshore industry. Just as waves in an extreme or survival storm event are randomly distributed, stress (and strain) response events are randomly distributed as well. For a comprehensive design, there will be far more than one sea state to be analyzed with each sea state undergoing multiple three (3) hour simulations. In addition, the design often progresses iteratively, i.e., there will be several cycles of analyses to be performed before the final design can be concluded. Therefore, the overall computational resources in terms of time and data storage are quite significant. This paper presents the methodology that significantly reduces the computer simulation time without compromising the analysis accuracy for the strength analysis of the SCR. The paper uses the example of a SCR in the ultra deepwater of the GOM attached to a DeepDraft Semi™ designed by SBM Atlantia Inc. The methodology builds on time traces of the host vessel motions, and the correlation between the vessel/porch motion and the SCR sagbend response. Generally the maximum riser sagbend stress occurs when the wave pushes the vessel, then the riser porch toward its touchdown point (slack position). One vessel/porch motion characteristic — the downward speed at the riser porch dominates the SCR sagbend response. By screening the downward speeds at the riser porch under slack condition, the time at which the sagbend response (stress/strain/buckling) peaks is identified. A time trace window containing the peak time and with band width of about 200 seconds is located and the SCR global dynamic analysis is performed based on this time trace window. In some scenarios, up to five (5) windows associated with the top five (5) downward speeds at the riser porch for one realization are needed to capture the peak stress response in the SCR sagbend.

Download Full-text

Global Strength Assessment of Trimaran Structure

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.538-541.2860 ◽

2012 ◽

Vol 538-541 ◽

pp. 2860-2863 ◽

Cited By ~ 1

Author(s):

Khurram Shehzad ◽

Hui Long Ren ◽

Chun Bo Zhen ◽

Asifa Khurram

Keyword(s):

Structural Strength ◽

Direct Calculation ◽

Fe Analysis ◽

Strength Analysis ◽

Stress Concentrations ◽

Strength Assessment ◽

Analysis Technique ◽

Current Design ◽

Design Loads ◽

Global Strength

This paper presents structural strength assessment of trimaran by global FE-analysis. Global strength analysis using the finite-element method is a powerful tool extensively used to design well-balanced and reliable sea going vessels. This analysis technique is particularly recommended in unconventional and new ship designs. Lloyd’s Register rules (LR Rules) for classification of trimaran are used to compute design loads and load cases. Global FE analysis is performed as per direct calculation procedure of LR Rules. Maximum stress concentration locations or hot spots corresponding to each load case are identified. The stresses induced in trimaran structure for all load cases are less than the maximum allowable stress. Furthermore, some modifications in current design are suggested to reduce the stress concentrations and hence to improve the structural strength.

Download Full-text