SCR and TTR modeling using shell and beam elements to deal with local interests, such as touch-down compression or buckling. Two examples are presented. The FEA tool employed is ABAQUS. Videos can only be seen when downloaded.
Characterization of residual stress in addtively manufactured ti 6 al-4v afte...Dr. Suraiya Zabeen
Selective laser melting (SLM) is a relatively new additive manufacturing technology for aerospace components. Due to high thermal gradient associated with the excessively high melting and cooling rate, significant amount of residual stresses are generated in the material in combination with a strong texture along the build direction. SLM process parameters including scanning strategy play an important role to control mechanical properties, texture and associated residual stress Ti-6Al-4V finished product. This study investigates the effect of scanning strategy on the residual stress generation. Four scanning strategies were investigated; they are: continuous unidirectional, continuous bidirectional, Island scan bidirectional, and chess scan bidirectional (surface profile is shown in Figure 1. The results infer that residual stresses as high as the yield stress of the material were introduced in as-fabricated specimens. Although 90% of the residual stresses were relaxed by a subsequent hot isostatic pressing (HIP) method, a thin layer tensile residual stresses were still present in all specimens after HIPing. These tensile residual stresses in combination with surface imperfections may accelerate fatigue crack initiation and growth when the component is in service that ultimately may result in catastrophic failure of the component.
Laser shock peening is a surface treatment technology that provides enhanced fatigue properties of metallic materials by introducing deep compressive residual stress that delays fatigue crack initiation and reduces fatigue crack growth rate. The specimens were laser shock peened after HIPing, and the resultant residual stresses are also characterized to investigate whether laser peening can successfully eliminate the surface tensile residual stresses by introducing a deep compressive residual stress.
Characterization of residual stress in addtively manufactured ti 6 al-4v afte...Dr. Suraiya Zabeen
Selective laser melting (SLM) is a relatively new additive manufacturing technology for aerospace components. Due to high thermal gradient associated with the excessively high melting and cooling rate, significant amount of residual stresses are generated in the material in combination with a strong texture along the build direction. SLM process parameters including scanning strategy play an important role to control mechanical properties, texture and associated residual stress Ti-6Al-4V finished product. This study investigates the effect of scanning strategy on the residual stress generation. Four scanning strategies were investigated; they are: continuous unidirectional, continuous bidirectional, Island scan bidirectional, and chess scan bidirectional (surface profile is shown in Figure 1. The results infer that residual stresses as high as the yield stress of the material were introduced in as-fabricated specimens. Although 90% of the residual stresses were relaxed by a subsequent hot isostatic pressing (HIP) method, a thin layer tensile residual stresses were still present in all specimens after HIPing. These tensile residual stresses in combination with surface imperfections may accelerate fatigue crack initiation and growth when the component is in service that ultimately may result in catastrophic failure of the component.
Laser shock peening is a surface treatment technology that provides enhanced fatigue properties of metallic materials by introducing deep compressive residual stress that delays fatigue crack initiation and reduces fatigue crack growth rate. The specimens were laser shock peened after HIPing, and the resultant residual stresses are also characterized to investigate whether laser peening can successfully eliminate the surface tensile residual stresses by introducing a deep compressive residual stress.
Final project for my vibrations class was to preform modal analysis of an object of our choosing as well as compare our results using FEA software simulations.
Компанія Seoul Semiconductor анонсувала початок масового виробництва світлодіода SZDR5A0D для тепличних застосувань з довжиною хвилі 660нм у керамічному корпусі 3535.
"Parametric analysis of modelling governing the seismic response of free-stan...TRUSS ITN
Abstract: Spent fuel racks are steel structures designed to store the spent fuel assemblies removed from the nuclear power reactor. They rest in free-standing conditions submerged in the depths of the spent fuel pool. During a strong-motion earthquake, racks undergo large displacements subjected to inertial forces. An accurate estimation of their response is essential to achieve a safe pool layout and a reliable structural design. A transient analysis with direct integration of the equation of motion throughout the whole earthquake duration becomes therefore unavoidable. The computational cost associated to this analysis leads to the use of simplified finite element models giving rise to a certain dose of uncertainty. This paper carries out a parametric analysis of the key modelling properties for a two-rack system. This technique examines the behavior of the main transient outputs as a modelling parameter is systematically varied. Numerical results provide a source of insight into the general behavior of the rack system and an effective tool to propose an efficient and reliable modeling and meshing. The trade-off between outputs and computational cost and is also discussed.
Presentation of my first year result during my PhD thesis. The congress held at Athenes the last May 2009. These slides deal with the study of the forced wetting during the fall and spreading of a single zinc drop onto a steel surface after annealing according to the galvanizing process.
Final project for my vibrations class was to preform modal analysis of an object of our choosing as well as compare our results using FEA software simulations.
Компанія Seoul Semiconductor анонсувала початок масового виробництва світлодіода SZDR5A0D для тепличних застосувань з довжиною хвилі 660нм у керамічному корпусі 3535.
"Parametric analysis of modelling governing the seismic response of free-stan...TRUSS ITN
Abstract: Spent fuel racks are steel structures designed to store the spent fuel assemblies removed from the nuclear power reactor. They rest in free-standing conditions submerged in the depths of the spent fuel pool. During a strong-motion earthquake, racks undergo large displacements subjected to inertial forces. An accurate estimation of their response is essential to achieve a safe pool layout and a reliable structural design. A transient analysis with direct integration of the equation of motion throughout the whole earthquake duration becomes therefore unavoidable. The computational cost associated to this analysis leads to the use of simplified finite element models giving rise to a certain dose of uncertainty. This paper carries out a parametric analysis of the key modelling properties for a two-rack system. This technique examines the behavior of the main transient outputs as a modelling parameter is systematically varied. Numerical results provide a source of insight into the general behavior of the rack system and an effective tool to propose an efficient and reliable modeling and meshing. The trade-off between outputs and computational cost and is also discussed.
Presentation of my first year result during my PhD thesis. The congress held at Athenes the last May 2009. These slides deal with the study of the forced wetting during the fall and spreading of a single zinc drop onto a steel surface after annealing according to the galvanizing process.
Temperature Cycling and Fatigue in ElectronicsCheryl Tulkoff
The majority of electronic failures occur due to thermally induced stresses and strains caused by excessive differences in coefficients of thermal expansion (CTE) across materials.
CTE mismatches occur in both 1st and 2nd level interconnects in electronics assemblies.
-1st level interconnects connect the die to a substrate.
-This substrate can be underfilled so there are both global and local CTE mismatches to consider.
-2nd level interconnects connect the substrate, or package, to the printed circuit board (PCB). This would be considered a “board level” CTE mismatch.
-Several stress and strain mitigation techniques exist including the use of conformal coating.
The purpose of this presentation is to show that accelerated testing can be successfully used to predict solder joint and plated through hole (PTH) fatigue behavior.
In the material testing laboratory, Tensile test was done on a mild steel specimen as figure 4 to identify the young’s modulus, ultimate tensile strength, yield strength and percentage elongation. The results were as table 1
Parametric Study of Multi-Spot Welded Lap Shear Specimen for Shear StrengthIJERA Editor
The effect of number of spots, spot spacing, squeezing force, welding current, weld time , overlapping length
and sheet thicknesson the shear strength of two similar galvanized steel sheets are investigated through
experiments using RSM method. Similar sheets of galvanized steel sheets are made by resistance spot welding
at different processing conditions and these joint populations were tested under lap-shear loading conditions.
Specially fabricated fixture is used to load the lap shear specimen in the universal testing machine Regression
analysis is done to obtain relationship between shear strength and selected parameters. The experimental results
indicate that the failure loads of spot welds in lap-shear specimens increase when number of spot, squeezing
force, welding current and sheet thickness increase for the given ranges.
Optimizing Fusion Zone Grain Size and Ultimate Tensile Strength of Pulsed Cur...drboon
Pulsed Current Micro Plasma Arc welding (PCMPAW) process is an important joining process widely used in sheet metal fabrication industries. The paper focuses on developing mathematical models to predict grain size and ultimate tensile strength of pulsed current micro plasma arc welded Inconel 625 nickel alloy using Response Surface Method (RSM). The experiments were carried out based on Central Composite Design (CCD) with 31 combinations of experiments. The adequacy of the models is checked by Analysis of Variance (ANOVA) technique. Hooke and Jeeves method is used to minimize grain size and maximize the ultimate tensile strength.
ASTM developed a collection of documents called material specifications for
standardizing materials of large use in the industry.
• Specifications starting with “A” are for steel.
• Specifications starting with “B” are for non-ferrous alloys (bronze, brass,
copper nickel alloys, aluminum alloys and so on).
• Specifications starting with “D” are for plastic material, as PVC.
An ASTM specification specifies the basic chemical composition of material and the
process through which the material is shaped into the final product. Some of the
common material standards are
Similar to Modeling of risers using hybrid fea (20)
Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
For more technical information, visit our website https://intellaparts.com
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Event Management System Vb Net Project Report.pdfKamal Acharya
In present era, the scopes of information technology growing with a very fast .We do not see any are untouched from this industry. The scope of information technology has become wider includes: Business and industry. Household Business, Communication, Education, Entertainment, Science, Medicine, Engineering, Distance Learning, Weather Forecasting. Carrier Searching and so on.
My project named “Event Management System” is software that store and maintained all events coordinated in college. It also helpful to print related reports. My project will help to record the events coordinated by faculties with their Name, Event subject, date & details in an efficient & effective ways.
In my system we have to make a system by which a user can record all events coordinated by a particular faculty. In our proposed system some more featured are added which differs it from the existing system such as security.
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
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Automobile Management System Project Report.pdfKamal Acharya
The proposed project is developed to manage the automobile in the automobile dealer company. The main module in this project is login, automobile management, customer management, sales, complaints and reports. The first module is the login. The automobile showroom owner should login to the project for usage. The username and password are verified and if it is correct, next form opens. If the username and password are not correct, it shows the error message.
When a customer search for a automobile, if the automobile is available, they will be taken to a page that shows the details of the automobile including automobile name, automobile ID, quantity, price etc. “Automobile Management System” is useful for maintaining automobiles, customers effectively and hence helps for establishing good relation between customer and automobile organization. It contains various customized modules for effectively maintaining automobiles and stock information accurately and safely.
When the automobile is sold to the customer, stock will be reduced automatically. When a new purchase is made, stock will be increased automatically. While selecting automobiles for sale, the proposed software will automatically check for total number of available stock of that particular item, if the total stock of that particular item is less than 5, software will notify the user to purchase the particular item.
Also when the user tries to sale items which are not in stock, the system will prompt the user that the stock is not enough. Customers of this system can search for a automobile; can purchase a automobile easily by selecting fast. On the other hand the stock of automobiles can be maintained perfectly by the automobile shop manager overcoming the drawbacks of existing system.
Courier management system project report.pdfKamal Acharya
It is now-a-days very important for the people to send or receive articles like imported furniture, electronic items, gifts, business goods and the like. People depend vastly on different transport systems which mostly use the manual way of receiving and delivering the articles. There is no way to track the articles till they are received and there is no way to let the customer know what happened in transit, once he booked some articles. In such a situation, we need a system which completely computerizes the cargo activities including time to time tracking of the articles sent. This need is fulfilled by Courier Management System software which is online software for the cargo management people that enables them to receive the goods from a source and send them to a required destination and track their status from time to time.
Democratizing Fuzzing at Scale by Abhishek Aryaabh.arya
Presented at NUS: Fuzzing and Software Security Summer School 2024
This keynote talks about the democratization of fuzzing at scale, highlighting the collaboration between open source communities, academia, and industry to advance the field of fuzzing. It delves into the history of fuzzing, the development of scalable fuzzing platforms, and the empowerment of community-driven research. The talk will further discuss recent advancements leveraging AI/ML and offer insights into the future evolution of the fuzzing landscape.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
2. Overview
1. Background
2. Codes and Buckling Criteria
3. Hybrid FEA Modeling Details
4. SCR Touchdown Area Simulation
5. TTR Dynamic Buckling Check
6. Q & A
3. 1. Background
• Automobile vs Offshore Oil Industry
• Compression, Buckling & FEA
• Beam & Shell Elements
4. 3. Codes and Buckling Criteria
• API 2RD: compression likely
unacceptable for single string riser
systems
• DNV OS-F101: εp ≤ 0.3%, otherwise ECA
needed
• ISO WD 13628-12 (Petro. & Nat. Gas Ind.-Des. & Opr.
of Subsea Prod. Sys. –Pt12: Dyn. Risers for Float. Prod. Instl.):
bending buckling strain limit εp = t/2D
• JFE ‘08 test (30”x0.61” pipe), εp ≈
(0.5~1) t/D
• Local ε < material elongation
Definition of Plastic strain εp:
εp ≈ ε - 0.2%
: True stress/strain curve
: Engineering stress/strain curve
Ultimate strength
Yield strength
Rupture
Hardening Necking
elongation
5. 4. Hybrid FEA Modeling Details
• Shell elements used to model pipe portion of interest and
capture features such as ovality, defects, local buckling etc
• External/internal pressure effects can be modeled by
applying pressures on shell elements
• Beam elements used to model other portions of riser to
reduce model size
• Shell- and beam-element portions connected by rigid
elements
• Non-linear material stress-strain curve used
• Hydrodynamics and riser-seabed interaction (SCR)
considered for both shell and beam portions
• Correlations made validated the methodology
6. 5. Touchdown Area Simulation for a SCR
Export SCR Information
Description Value
OD (in) 20
WT (in) 1.21
Water Depth (ft) 7900
Departure Angle (°) 15
Strake Coverage 80%
Internal Pressure (psi) 3250
Material API X-65
Independence Hub with SCRs
Nonlinear Stress/Strain Curve
“Compression Assessment of Deepwater Steel Catenary Risers at Touch Down Zone”, Paper no. OMAE2007-29332 pp. 345-353
7. 5. Touchdown Area Simulation for a SCR
ABAQUS Model with Shell
Elements at Touchdown
Area of a 300 ft Portion
8. 5. Touchdown Area Simulation for a SCR
Shell Element Mesh-size Sensitivity Study
for the 300 ft SCR TDA Section
Mesh 1: 12x200 = 2400
aspect ratio = 2.9 ~ 4.6
Mesh 2: 16x600 = 9600
aspect ratio = 1.2 ~ 2.1
9. 5. Touchdown Area Simulation for a SCR
Sensitivity Study Results
Description
Case 1 Case 2
Max
Displacement
Max Stress
Max
Displacement
Max Stress
Theory 100% 100% 100% 100%
FEA by Mesh 1 104.8% 115.4% 105.9% 113.3%
FEA by Mesh 2 102.5% 97.0% 103.5% 98.2%
P
L
L/2
Test Cases with Theoretical Results
P
L
Case 1 Case 2
13. 5. Touchdown Area Simulation for a SCR
Animation Example 2
Plastic Strain
14. Stress Joint
Transition Joint
Standard
Joints
Standard Joints
Connectors
FEA Model with 7200 Total Elements (6550 Shell)
6. Dynamic Buckling Check of a Prod TTR
“Production TTR Modeling and Dynamic Buckling Analysis”, Engineering Sciences, Chinese Academy of Engineering, Vol. 11 No.4,Aug. 2013
15. w/o current w/ current
Von Mises Stress on Riser Outer
6. Dynamic Buckling Check of a Prod TTR
Analysis Results
16. w/o current w/ current
Plastic strain on Inner Tubing
6. Dynamic Buckling Check of a Prod TTR
Analysis Results
17. w/o current w/ current
Tension Variation on Tensioner Cylinders
(One Tensioner Cylinder Damaged)
6. Dynamic Buckling Check of a Prod TTR
Analysis Results
18. w/o current w/ current
Tension and Moment Variations at SJ Top
(One Tensioner Cylinder Damaged)
6. Dynamic Buckling Check of a Prod TTR
Analysis Results
19. w/o current w/ current
Centralizer Force Variations
(One Tensioner Cylinder Damaged, Centralizer Position: 1,2-top, 3,4-btm)
6. Dynamic Buckling Check of a Prod TTR
Analysis Results
I’d like to share with you some of my former experiences on marine riser FEA.
First this is an overview of the presentation.
I’d like to mention several things as background information of this presentation.
As a former automobile engineer and a naval architecture and ocean engineering major in college, and having been working in the oil industry for the past 9 years, I have the privilege to involve in FEA activities of these two gigantic yet distinctive industries, and know something about both worlds. The differences in practices and design philosophy are large, for example, the auto design has been using very detailed FE modeling for local as well as global simulations, and for the oil industry, since uncertainties of environmental conditions and the severe nature of the consequences of any failure in an open and deep sea, a safety factor of 10 is usually used in design, which is unheard of for its auto counterpart. I think a sharing of these experiences would help, and one such example is for the offshore engineering, detailed FEA in a global setting, i.e. using hybrid modeling, or shell elements locally and beam globally for riser simulation.
Buckling is a failure mode due to elastic instability, characterized by a sudden failure of a structural member subjected to high compressive stresses, where the actual compressive stress at the point of failure is less than the ultimate compressive stresses that the material is capable of withstanding. It is proved that linear FEA buckling load calculation in combination with material yielding property consideration will give a more accurate, convenient and consistent way of buckling check.
Beam elements are used in global FEA, and shell elements in detailed FEA. They can be used jointly in a hybrid FEA, where shell elements are used to model an area of concern with local features, such as ovality, local defects and buckling, and beam elements to simulate riser global behaviors in various boundary and environmental conditions.
For an accurate simulation of a structure, a precise material stress-strain curve should be used. Plastic strain is a useful concept in structure failure mode simulation. Here is a definition of plastic strain, and an illustration of the engineering stress-strain curve, which is obtained from material sample test, and the true stress-strain curve. Usually an engineering stress-strain curve without modification is used in FEA, and this gives a conservative simulation.
For compressive buckling of a cylindrical pipe, here are what the usual design codes say. An ‘08 paper published by researchers from JFE, one of the largest Japanese steel producing companies, showed test results of 30” pipes, that criteria of plastic strain for pure compression is t/2D, and for pure bending t/D.
As for risers, especially in TDA of SCR, its loading can be characterized as compression + bending. Detailed FEA will show buckling mode and associated plastic strain. For a specific event, a fracture would not occur unless local strain passes the material elongation, which means the plastic strain could reach 10~15% or even more.
Some details of FEA using hybrid modeling.
The first example presents the export SCR (Steel Catenary Riser) on Independence Hub in GoM. Characteristics of the SCR and material stress-strain curve used are displayed here. This has been published in an OMAE ’07 paper.
About 500 beam elements and 2400 shell elements were used. The shell elements were for a 300ft portion of SCR.
Two meshes, with 2400 and 9600 shell elements and different aspect ratio ranges, were used to see sensitivity of mesh size. This was not a complete investigation.
Two simple test cases with theoretical solutions were used.
It can be seen with finer mesh, the results are converging.
The coarse mesh, Mesh 1, over-predicted both displacement and stress, while the fine mesh, Mesh 2, over-predicted displacement and under-predicted stress.
Mesh 1’s results are more conservative, and will be used.
An example of compression, where tension at TDA and 100-yr Hurricane heave motion time-traces are displayed. It can be seen the compression is about 200 Kips.
Simulation results for 100-yr Hurricane at near condition, of both Mesh 1 and Mesh 2, are displayed in tabulated form with those of beam model.
Pictures of stress and plastic strain distributions for Mesh 1 are also shown. More details can be found in the published paper.
An example of animation of stress distribution of about 50s duration. It should be noted this is not for the original problem as the original video clip has been lost.
An example of animation of plastic distribution. This is for the the same problem as in the previous slide.
The second example is for a production TTR(Top Tensioned Riser) on a TLP (Tension Leg Platform), during an extreme metocean event where compression is present at top of the stress joint.
Water depth is 3800ft. TTR is 14” in OD and 0.65” in wall thickness for outer casing, and 7” in OD and 0.362” in wall thickness for inner tubing .
Details of the hybrid model is shown. 6550 shell elements are used to model the stress joint, transition joint, and several standard joints of 780ft length.
Details can be found in the paper published in an engineering magazine.
Von Mises stress distributions at a moment on TTR outer casing with and without current.
Plastic strain on TTR inner tubing.
Tension variation on different tensioner cylinders (5) with one cylinder damaged, in comparison of heave motion.
Tension and moment variations at stress joint top with one tensioner cylinder damaged. It can be seen for the case w/o current there is a compression of about 40 kips on TTR outer casing, and tension of about 175 kips on inner tubing.
Time-trace variations of forces on top 2 and bottom 2 centralizers.
Animation of stress distribution on outer casing w/o current of 200s duration.
Animation of plastic strain distribution on outer casing w/o current of 200s duration.
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