Applications of the Static Condensation Technique to Nonlinear Structural Analysis of Floating Offshore Structures

2017 ◽  
Author(s):  
Min-Han Oh ◽  
Seung-Hwan Boo ◽  
Phill-Seung Lee ◽  
Jong-Min Kim ◽  
Joong-Soo Moon ◽  
...  
Keyword(s):  
Reduction Method ◽  
Cost Effective ◽  
Offshore Structures ◽  
Fe Model ◽  
Contact Interface ◽  
Friction Forces ◽  
Static Condensation ◽  
Load Carrying ◽  
Nonlinear Contact ◽  
Actual Design

A cost effective finite element (FE) procedure is proposed for analysis of load-carrying structures with nonlinear contact and frictional behaviors between large floating offshore structures. The key of the procedure is to use the static condensation technique developed from the Guyan model reduction method. The time for computing contact and friction forces on contact interface areas can be dramatically reduced compared to nonlinear analysis with a full FE model. Two representative applications to offshore projects are presented. One is a problem with nonlinear contact of independent tank support in FLNG hull structures and the second is a sea-fastening system used during offshore dry transportation. The reliability and computing efficiency of the proposed analysis procedure are investigated. It is conclusively confirmed that the proposed procedure is practical for application to actual design of offshore projects.

scholarly journals Bayesian maintenance decision optimisation based on computing the information value from condition inspections

2021 ◽  
pp. 1748006X2097812
Author(s):  
Guang Zou ◽  
Kian Banisoleiman ◽  
Arturo González
Keyword(s):  
Decision Making ◽  
Structural Integrity ◽  
Fatigue Cracking ◽  
Cost Effective ◽  
Offshore Structures ◽  
Information Value ◽  
Bayesian Decision ◽  
Maintenance Strategies ◽  
Optimal Maintenance ◽  
Maintenance Decision

A challenge in marine and offshore engineering is structural integrity management (SIM) of assets such as ships, offshore structures, mooring systems, etc. Due to harsh marine environments, fatigue cracking and corrosion present persistent threats to structural integrity. SIM for such assets is complicated because of a very large number of rewelded plates and joints, for which condition inspections and maintenance are difficult and expensive tasks. Marine SIM needs to take into account uncertainty in material properties, loading characteristics, fatigue models, detection capacities of inspection methods, etc. Optimising inspection and maintenance strategies under uncertainty is therefore vital for effective SIM and cost reductions. This paper proposes a value of information (VoI) computation and Bayesian decision optimisation (BDO) approach to optimal maintenance planning of typical fatigue-prone structural systems under uncertainty. It is shown that the approach can yield optimal maintenance strategies reliably in various maintenance decision making problems or contexts, which are characterized by different cost ratios. It is also shown that there are decision making contexts where inspection information doesn’t add value, and condition based maintenance (CBM) is not cost-effective. The CBM strategy is optimal only in the decision making contexts where VoI > 0. The proposed approach overcomes the limitation of CBM strategy and highlights the importance of VoI computation (to confirm VoI > 0) before adopting inspections and CBM.

On the Plastic Bending Responses of Dented Lined Pipe

2021 ◽  
Author(s):  
Lin Yuan ◽  
Jiasheng Zhou ◽  
Haowei Liu ◽  
Nian-Zhong Chen
Keyword(s):  
Composite Structure ◽  
Cost Effective ◽  
Geometric Feature ◽  
Load Carrying Capacity ◽  
Bending Process ◽  
Load Carrying ◽  
Bending Capacity ◽  
Critical Curvature ◽  
Ultimate Load Carrying Capacity ◽  
Local Dent

Abstract Mechanically lined pipe, which was proven to be cost-effective in transporting corrosive hydrocarbons, has been used in many offshore applications. However, one weakness of this product is that the liner is extremely sensitive to geometric imperfections and can wrinkle and collapse under severe loading. As typical damage of the pipeline, the local dent of the lined pipe involves the deformation of both the carrier pipe and the liner, which poses a severe threat to the integrity of the composite structure. In this paper, we developed a numerical framework to study the responses of the lined pipe during indentation and, more importantly, the influence of local dents on the bending capacity of lined pipes. A slight separation between the liner and the carrier pipe was observed during the indentation, depending on the indenter’s geometric feature. Under bending, the liner typically collapsed earlier than the carrier pipe, causing a considerable reduction of the critical curvature and ultimate load-carrying capacity. The evolution of the deformation of the composite structure during the bending process is presented in this paper. Parametric investigations of some vital variables of the problem were also performed to study their influence on the behavior under indentation and the bending capacity of the composite structure.

Full scale test of a PC bridge to calibrate assessment methods

2021 ◽  
Author(s):  
Niklas Bagge ◽  
Jonny Nilimaa ◽  
Silvia Sarmiento ◽  
Arto Puurula ◽  
Jaime Gonzalez-Libreros ◽  
...  
Keyword(s):  
Prestressed Concrete ◽  
Structural Response ◽  
Sensitivity Study ◽  
Assessment Method ◽  
Full Scale ◽  
Concrete Bridges ◽  
Fractional Factorial ◽  
Fe Model ◽  
Load Carrying ◽  
Existing Bridges

<p>In this paper, experiences on the development of an assessment method for existing bridges are presented. The method is calibrated using the results of full-scale testing to failure of a prestressed bridge in Sweden. To evaluate the key parameters for the structural response, measured by deflections, strains in tendons and stirrups and crack openings, a sensitivity study based on the concept of fractional factorial design is incorporated to the assessment. Results showed that the most significant parameters are related to the tensile properties of the concrete (tensile strength and fracture energy) and the boundary conditions. A finite element (FE) model in which the results of the sensitivity analysis were applied, was able to predict accurately the load-carrying capacity of the bridge and its failure mode. Two additional existing prestressed concrete bridges, that will be used to improve further the method, are also described, and discussed.</p>

scholarly journals Hybrid Finite Element Method Development for Offshore Structures’ Calculation with the Implementation of Industry Standards

2019 ◽  
Vol 26 (4) ◽  
pp. 90-100
Author(s):  
Jacek Łubiński ◽  
Henryk Olszewski
Keyword(s):  
Finite Element ◽  
Method Development ◽  
Structural Model ◽  
Model Development ◽  
Steel Structures ◽  
Cost Effective ◽  
Offshore Structures ◽  
Wind Loading ◽  
Hybrid Finite Element Method ◽  
Industry Standards

Abstract In the design process of offshore steel structures, it is typical to employ commercial calculation codes in which simulation and evaluation of results are performed on the basis of the available standards (e.g. API, DNV, Lloyds). The modeling and solution rely on finite element methods and cover the simulation of the structure’s properties along with the influence of the marine environment – sea currents, wave and wind loading, as well as the influence of vibrations, buoyancy and accompanying mass of water. Both commercial and open source mathematical modeling software which is available nowadays allows for cost effective and flexible implementation of advanced models for offshore industrial structures with high level of credibility and safety. The models can be built to suit task-specific requirements and evaluated on the basis of the selected criterial system best suited to the needs of the customer. Examples of methodology for environmental and structural model development are presented, along with simulation results covering a wide scope of data, ranging from stress and deformation to resonant characteristics and issues of technological feasibility.

Design Under Arctic Conditions: A Summary of the Arctic Materials Project Guideline

2018 ◽  
Author(s):  
Agnes Marie Horn ◽  
Erling Østby ◽  
Odd Akselsen ◽  
Mons Hauge
Keyword(s):  
Cost Effective ◽  
Offshore Structures ◽  
International Standards ◽  
Hydrocarbon Exploration ◽  
Thickness Effect ◽  
The Arctic ◽  
Structural Elements ◽  
Practical Applications ◽  
Arctic Materials ◽  
Offshore Industry

The main goal of the 10 years Arctic Materials KMB project run by SINTEF (2008–2017) and supported by the industry is to establish criteria and solutions for safe and cost-effective application of materials for hydrocarbon exploration and production in arctic regions. The objective of the arctic materials project guideline (PG) is to assist designers to ensure safe and robust, yet cost-effective, design of offshore structures and structural elements in arctic areas through adequate material testing and requirements to material toughness. It is well known that when the temperature decreases, steel becomes more brittle. To prevent brittle fracture in the Arctic, the structure needs adequate toughness for the loading seen at low temperatures. None of the common offshore design codes today consistently address low temperature applications. In this respect, arctic areas are defined as minimum design temperatures below what current international standards have considered per today, i.e. −10 °C to −14°C. For practical applications, the PG defines arctic areas as minimum design temperature lower than −10 °C. It is acknowledging that design standards to a certain degree are based on operational and qualitative experiences gained by the offshore industry since the 1970’s. However, for arctic offshore facilities, limited operational experiences are gained by the industry. The basis of the guideline is that safe and robust design of structures and structural elements are ensured by combining standard industry practice today with learnings and findings from the 10 years Arctic Materials project. This paper is concerned with the rationale behind the material and test requirements provided in the arctic material guideline. The material requirements will be discussed in detail with emphasis on toughness requirement, constraint effect, thickness effect, acceptance criteria and material qualification criteria.

Friction Force Measurements Using the Instantaneous IMEP Method and Comparison With RINGPAK Simulations

2005 ◽  
Author(s):  
Myoungjin Kim ◽  
Thomas M. Kiehne ◽  
Ronald D. Matthews
Keyword(s):  
Friction Force ◽  
Piston Ring ◽  
Cost Effective ◽  
Firing Condition ◽  
Force Measurements ◽  
Connecting Rod ◽  
Friction Forces ◽  
Bench Tests ◽  
Ring Assembly ◽  
Analysis System

Even though many researchers have measured the piston/ring assembly friction force over the last several decades, accurate measurement of the piston/ring assembly friction force is a still challenging problem. The floating liner method is not widely used, in spite of its accuracy, due to the substantial modifications required to the engine. On the other extreme, bench tests of the piston/ring assembly cannot completely simulate the real firing condition although bench tests are rapid, consistent, and cost effective. In this study, friction forces of the piston/ring assembly were measured using the instantaneous IMEP method and compared with modeling results using Ricardo’s RINGPAK software. In this research, a flexible flat cable was used to connect the connecting rod strain gage signal to the analysis system instead of using a grasshopper linkage. Therefore, the piston/ring assembly friction force was measured with the minimum change to the engine hardware.

Developing a Cost-Effective and Functional Prosthetic Foot for Below Knee Amputees Using Topology Optimization and 3D Printing

2019 ◽  
Author(s):  
Hisham Kamel ◽  
Omar Harraz ◽  
Tamer Attia
Keyword(s):  
Topology Optimization ◽  
3D Printing ◽  
Experimental Tests ◽  
Cost Effective ◽  
Metabolic Energy ◽  
Release Mechanism ◽  
Normal Person ◽  
Fe Model ◽  
Prosthetic Foot ◽  
Human Foot

Abstract This paper presents the results of an investigative study on the development of an affordable and functional prosthetic foot for below knee amputees. A prototype was successfully manufactured using 3D printing technology. This continuously evolving technology enables the rapid production of prosthetics that are individually customized for each patient. Our prototype was developed after conducting a topology optimization study that interestingly converged to the shape of the biological human foot. Afterwards, a design was envisioned where a simple energy storage and release mechanism was implemented to replace the Achilles tendon, which minimizes the metabolic energy cost of walking. Our mechanism can successfully manage 70% of the energy compared to a normal person during each walking step. A finite element (FE) model of the prosthetic was developed and validated using experimental tests. Then, this FE model was used to confirm the safe operation of the prosthetic through simulating different loading scenarios according to the ISO standard. Our study clearly showed that customizable prosthetics could be produced at a fraction 1/60 of the cost of the commercially sold ones.

Rapid Preliminary Design of Floating Offshore Structures Using a Modified Genetic Algorithm

2007 ◽  
Author(s):  
Michael J. Perry ◽  
John E. Halkyard ◽  
C. G. Koh
Keyword(s):  
Genetic Algorithm ◽  
Cost Effective ◽  
Offshore Structures ◽  
Preliminary Design ◽  
Optimization Strategy ◽  
Empirical Estimates ◽  
Wind Speed Maximum ◽  
Design Wind Speed ◽  
Truss Spar ◽  
Weight Design

Preliminary design of floating offshore structures involves determining structural dimensions able to provide sufficient buoyancy to carry the required topside, at the lowest possible cost, while satisfying various stability, strength, installation, and response requirements. A novel optimization strategy, capable of carrying out the preliminary design of floating offshore structures, is presented in this paper. The genetic algorithm based strategy searches within prescribed parameter limits for the most cost effective design, while ensuring the design conforms to the constraints given. The design of a truss spar is used to illustrate how the strategy can be applied. The topside weight, design wind speed, maximum wave height, etc are input along with constraints such as, maximum draft at floatoff, maximum heel angle, allowable stress in the truss and limits on pitch and heave period and response. Using empirical estimates for hull weights and simplified response calculations, the strategy is then able to rapidly determine parameters such as hull diameter, hard tank depth, length of keel tank, total length and truss leg diameter such that the total cost of the structure is minimized. The strategy allows for the preliminary design phase to be completed in only a few seconds, while providing initial weight and cost estimates.

Analytical Formulation of Friction Interface Elements for Analysis of Nonlinear Multi-Harmonic Vibrations of Bladed Disks

2003 ◽  
Vol 125 (2) ◽  
pp. 364-371 ◽  
Author(s):  
E. P. Petrov ◽  
D. J. Ewins
Keyword(s):  
Stiffness Matrix ◽  
Normal Force ◽  
Contact Forces ◽  
Contact Interface ◽  
Bladed Disks ◽  
Interface Elements ◽  
Friction Forces ◽  
Analytical Formulation ◽  
Harmonic Vibrations ◽  
Speed Accuracy

An analytical formulation for the vectors of contact forces and the stiffness matrix of the nonlinear friction contact interface is developed for the analysis of multi-harmonic vibrations in the frequency domain. The contact interface elements provided here an exact description of friction and unilateral contact forces at the interacting surfaces, taking into account the influence of the variable normal load on the friction forces, including the extreme cases of separation of the two surfaces. Initial gaps and interferences at the contact nodes, which affect the normal force, as well as the unilateral action of the normal force at the contact surface, are all included in the model. The accurate calculation of the force vector and the tangent stiffness matrix provides a very reliable and fast convergence of the iteration process used in the search for the amplitudes of nonlinear vibrations of bladed disks. Numerical investigations demonstrate excellent performance with respect to speed, accuracy and stability of computation.

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