Reliability Analysis of Jack-Up Platforms Based on Fatigue Degradation

2002 ◽  
Author(s):  
Naser Shabakhty ◽  
Pieter van Gelder ◽  
Hotze Boonstra
Keyword(s):  
Service Time ◽  
Great Part ◽  
Fatigue Reliability ◽  
Original Design ◽  
Operational Conditions ◽  
Stress Fluctuation ◽  
The Difference ◽  
Offshore Industry ◽  
Jack Up ◽  
Load Conditions

Generally, jack-up structures are used for production drilling and exploration of hydrocarbons. The combination of mobility and the behavior as a fixed structure in operational conditions has made it an important structure in the offshore industry over the last 40 years. When a jack-up structure has been in operation for a great part of its original design-life and intention is there to extend the usage of this structure at a specific location, an investigation on fatigue degradation of the structure is an essential factor that has to be carried out before taking any decision. Fatigue is the process of damage accumulation in material due to stress fluctuation caused by variation of loads in service time. The fatigue failure occurs when accumulated damage has exceeded a critical level. In this paper, the remaining fatigue capacity of the jack-up structure is considered as an indicator for adequate use of the structure. It can be specified based on the difference between design-fatigue and fatigue experienced by the structure. The design-fatigue can be determined based on fluctuation of loads during the lifetime of the structure and experienced fatigue is specified by the load conditions, which the structure has experienced during its service time. When the information on the load conditions which the structure has experienced in its service time is available or known precisely, determination of the remaining fatigue capacity could be carried out by using the Palmgren–Miner’s rule. In practice, uncertainties are present in loads and characteristics of material. Hence it will be reasonable to determine the remaining fatigue reliability of the structure by the reliability methods. In this paper, based on a crack propagation approach and achieved information from inspection, it is shown that the remaining fatigue reliability of jack-up structures could be determined and updated by using a Bayesian procedure in the duration of the service time.

Comparing Fatigue Reliability of Jack-Up Platforms Based on Selected Nonlinear Stress Models

2008 ◽  
Author(s):  
Naser Shabakhty
Keyword(s):  
Nonlinear Models ◽  
Nonlinear Behaviour ◽  
Fatigue Reliability ◽  
Offshore Structure ◽  
Advanced Technique ◽  
Stress Fluctuation ◽  
Nonlinear Stress ◽  
Exploration And Production ◽  
Offshore Industry ◽  
Jack Up

Jack-up is typically an exploration and production platform in shallow water operation. The possibility of moving this type of offshore structure from one location to other place and lifting up the deck above sea level made it attractive for offshore industry to use in deeper water and harsher environments. The jack-up structure consists of various components and behaves in a nonlinear and dynamic manner. Degradation phenomena such as fatigue may influence the structural performance and reduce strength of platform during its lifetime. Appropriate estimation of fatigue degradation strongly related to the suitable assessment of stress fluctuation, however, there are some uncertainties both in fatigue characteristics and environmental loads. These uncertainties can be taken into account in fatigue reliability framework. In this paper, several nonlinear models proposed by Wirsching and Light (W&L), Zhao and Baker (Z&L), Winterstein (Hermite model), in addition to the typical narrow banded model are utilized to specify nonlinearity in the stress fluctuation. The fatigue reliability is calculated based on these models and are compared with more advanced technique of rain flow counting method. The result shows a dependency between nonlinear behaviour of stress response and the selected model.

Correlation between membrane fouling and soluble/colloidal organic substances in membrane bioreactors for municipal wastewater treatment

2005 ◽  
Vol 51 (6-7) ◽  
pp. 1-8 ◽  
Author(s):  
B. Lesjean ◽  
S. Rosenberger ◽  
C. Laabs ◽  
M. Jekel ◽  
R. Gnirss ◽  
...  
Keyword(s):  
Membrane Fouling ◽  
Extracellular Polymeric Substances ◽  
Municipal Wastewater ◽  
Membrane Bioreactors ◽  
Size Exclusion ◽  
Water Phase ◽  
Parallel Operation ◽  
Municipal Wastewater Treatment ◽  
Operational Conditions ◽  
The Difference

Two similar membrane bioreactors of 2 m3 each were operated in parallel over two years under the same operational conditions, fed with the same municipal wastewater. The only process and operational difference between both pilot plants was the position of the denitrification zone (pre-denitrification in pilot 1 and post-denitrification in pilot 2). Despite parallel operation, the two MBRs exhibited different fouling rates and decreases in permeability. These differences could not be accounted for by MLSS concentrations, loading rates, or filtration flux. In a one-year investigation, soluble and colloidal organic material in the activated sludge of both MBR was regularly analysed by spectrophotometric and Size Exclusion Chromatography (SEC) methods. The larger organic molecules present in the sludge water phase (i.e. polysaccharides, proteins and organic colloids) originating from microbial activity (extracellular polymeric substances) were found to impact on the fouling and to explain the difference in membrane performance between the two MBR units. In both pilot plants, a linear relationship could be clearly demonstrated between the fouling rate of the membrane and the concentration of polysaccharides in the sludge water phase during a 5 month operational period at an SRT of 8 days.

scholarly journals Imperialismo en el siglo XXI

2016 ◽  
Vol 6 (10) ◽  
pp. 49-74
Author(s):  
John Smith ◽  
Keyword(s):  
North America ◽  
Low Income ◽  
Great Part ◽  
Low Income Countries ◽  
Capitalist Development ◽  
Neoliberal Globalization ◽  
The North ◽  
Foreign Labor ◽  
Economic Foundation ◽  
The Difference

The globalization of production and its spread to low-income countries is the most notable transformation of the neoliberal era. Its driving force is the efforts by companies in Europe, North America and Japan to cut costs and raise profits, replacing relatively well-paid domestic labor for cheaper foreign labor. The gap in global wages, in great part the result of the suppression of the free movement of labor, provides a distorted view of the global differences in the rate of exploitation (simply, the difference between the value generated by the workers and what they are paid) upon which profits, prosperity and social peace in Europe, North America and Japan are ever-more reliant. Thus, neoliberal globalization should be seen as a new imperialist stage in capitalist development, where «imperialism» is defined by its economic foundation: the exploitation of labor in the South by capitalists from the North.

RECOMPRESSION PHENOMENA IN STEAM NOZZLES: PART I

1941 ◽  
Vol 19a (5) ◽  
pp. 67-85 ◽  
Author(s):  
Charles Alexander Robb
Keyword(s):  
Cross Section ◽  
Inlet Pressure ◽  
Flowing Fluid ◽  
Vena Contracta ◽  
Venturi Effect ◽  
Change Of State ◽  
Expansion Curve ◽  
Nozzle Shape ◽  
The Difference ◽  
Load Conditions

The purpose of the investigation was to find when and how recompression occurs in the flow of steam through a nozzle, its causes and effects, how the results can be predicted, and what losses are caused by these phenomena. Four types of recompression were observed: equilibrium, latent, vena contracta, and shock recompression.It is shown that steam in flowing through a nozzle of varying cross-section responds to the changes of area within certain limits and recompression phenomena may be expected. The Venturi effect has been observed in single nozzles, and in both parts of a composite nozzle.The behaviour of steam in equilibrium recompression in convergent-divergent nozzles can be predicted by means of an equation from which a valuers obtained for the pressure pr at which overexpansion ends and an increase in pressure begins; the pressure pr depends on the inlet pressure to the nozzle and on the difference in pressure at inlet and outlet.The recompression due to the contraction of the section can be controlled and avoided by suitable provision in the design. The compression following a change of state of a flowing fluid can be controlled by adjusting the rate of expansion of the fluid in specified pressure ranges. Novel evidence of latent recompression is found in a break or notch in the pressure expansion curve plotted from search tube observations.The experiments were carried out at inlet pressures within the range at which turbine-condition curves may cross the saturation line between the superheat and wet regions on the Mollier diagram, and the effects of recompression to be expected under varying load conditions can be interpreted for particular nozzle designs.Comparative studies of the effect of the nozzle shape on recompression phenomena and the losses resulting therefrom have indicated that the conditions for favourable efficiency require a larger inlet radius at the throat and a length shorter than the lengths commonly found in practice.

Het Aanpassen Van Informatieve Schoolboekteksten In Groep Vijf Van Het Basisonderwijs

1991 ◽  
Vol 39 ◽  
pp. 31-45
Author(s):  
Mark Wouters
Keyword(s):  
Text Comprehension ◽  
Great Part ◽  
Number Of Factors ◽  
Level Of Difficulty ◽  
The Difference

This article describes research which has focused on the level of difficulty of texts and questions as an explanation for the difference in text comprehension between non-native and native pupils. The degree to which text comprehension in native and non-native pupils could be facilitated by means of controlling texts and questions was investigated. From the results the following conclusions were drawn: 1) Non-native pupils scored significantly lower than native Dutch pupils in all tests that dealt with text comprehension; 2) When the test questions were controlled by changing a number of factors which supposedly made understanding more difficult, the scores of both non-native and native pupils improved significantly; 3) When the texts of the tests were rewitten, the non-native pupils improved in their scores and the native pupils did not; 4) When both the texts and questions were controlled, the results seemed to show that the non-native pupils had caught up for a great part where they were found to have "lagged behind".

Sensitivity of Fatigue Assessment to the Use of Different Reference S-N Curves

2003 ◽  
Author(s):  
Xiaozhi Wang ◽  
Zhan Cheng
Keyword(s):  
Loading Condition ◽  
Offshore Structures ◽  
Constant Amplitude ◽  
Fatigue Assessment ◽  
Tubular Joints ◽  
Environment Effects ◽  
Assessment Approach ◽  
The Difference ◽  
Offshore Industry ◽  
Number Of Cycles

The S-N curve based fatigue assessment approach is the most widely used one in both ship and offshore industry, in contrast with a fracture mechanics approach. The S-N approach, implemented by either simplified or spectral method, has to apply S-N curves to calculate fatigue strength. The S-N curve, which represents the number of cycles (N) of a constant amplitude stress range (S) that will cause a fatigue failure, is normally developed based on experimental data. Which S-N curve should be applied to a particular detail depends very much on the geometry of the detail, welding information as well as loading condition. There are various S-N curves published by different institutions, e.g., S-N curves published by UK HSE, IIW, AWS etc. The newly developed ABS “Guidance on Fatigue Assessment of Offshore Structures”, [1], proposes the ABS S-N curves, in which two categories of joints, tubular and non-tubular, are included, and both size and environment effects are taken into account. However, the application in Gulf of Mexico is also influenced by API recommendations. In API RP 2A, AWS S-N curves are referred, which in US practice is accepted for fixed (buoyant and non-buoyant) platform deck structures. The objective of this paper is to address the difference between different S-N curves and to present the detailed results of fatigue assessment by using different S-N curves for non-tubular joints. Conclusions made based on the study provide more background on the S-N curve application in fatigue assessment.

Characterisation of biodegradable organic matter in reclaimed water using a bacterial growth fingerprint assay

2016 ◽  
Vol 16 (5) ◽  
pp. 1255-1265 ◽  
Author(s):  
Parinda Thayanukul ◽  
Futoshi Kurisu ◽  
Ikuro Kasuga ◽  
Kizuku Kanaya ◽  
Hiroaki Furumai
Keyword(s):  
Organic Matter ◽  
Bacterial Growth ◽  
Reclaimed Water ◽  
Maximum Growth ◽  
Bacterial Strains ◽  
Operational Conditions ◽  
Assimilable Organic Carbon ◽  
The Difference ◽  
Microbial Regrowth ◽  
Biodegradable Organic Matter

Microbial regrowth, microbial growth after disinfection, is an important problem that deteriorates water quality during the storage and distribution of reclaimed water. Biodegradable organic matter (BOM) that remains after water reclamation processes directly promotes microbial regrowth. In this study we propose a novel assay called the ‘bacterial growth fingerprint (BGF)’ to characterise BOM based on the maximum growth of bacterial strains, which is the extension of the conventional assimilable organic carbon assay for drinking water. Nine bacterial strains were selected from nearly 200 isolates from various reclaimed water systems. These selected bacterial strains exhibited unique substrate utilisation patterns. The BGF assay clearly reflected the difference in the quantity and quality of BOM between six different reclamation plants and the changes in BOM during a full-scale reclamation process. The information on BOM revealed by the BGF assay is useful to optimise the treatment processes or operational conditions for biologically stable reclaimed water.

A Procedure for Non-Linear Structural Collapse Analysis

2014 ◽  
Author(s):  
Shengming Zhang ◽  
Lei Jiang
Keyword(s):  
Structural Engineering ◽  
Standard Procedure ◽  
Analysis Procedure ◽  
Structural Collapse ◽  
Element Analysis ◽  
Collapse Analysis ◽  
Non Linear ◽  
Mesh Density ◽  
The Difference ◽  
Offshore Industry

It is a normal practice nowadays in structural engineering, including ships and offshore industry, to perform non-linear finite element analysis to assess the structure’s capacity for design or evaluation purposes. However, experience has shown that the quality and accuracy of the non-linear FE analysis results are highly dependent on the skill of the person performing the analysis and the analysis procedure used. The difference between results obtained by different people can be significant. In some cases, the results can be misleading. It is considered that a unified procedure is necessary. This paper is moving a step further and trying to develop a standard procedure which can provide a guideline for structural collapse analysis of stiffened panels under any load combinations. The paper provides the technical background on the analysis procedure and the key steps such as model extent, mesh density, initial imperfections, and boundary conditions. Analysis examples are provided in the paper for reference and discussions.

scholarly journals Dropped Object Impact Analysis Considering Frequency and Consequence for LNG-FPSO Topside Module

2021 ◽  
Vol 11 (16) ◽  
pp. 7753
Author(s):  
Kwangkook Lee ◽  
Hyunsu Ryu
Keyword(s):  
Impact Energy ◽  
Impact Analysis ◽  
Quantitative Risk Assessment ◽  
Production Area ◽  
The Difference ◽  
Offshore Industry ◽  
Impact Energies ◽  
The Impact ◽  
External Loads ◽  
Specific Orientation

Recently, quantitative risk assessment (QRA) has been widely used as a decision-making tool in the offshore industry. This study focused on analyzing dropped objects in the design of a modern offshore platform. A modified QRA procedure was developed for assessing production module protection against accidental external loads. Frequency and consequence analyses were performed using the developed QRA procedure. An exceedance curve was plotted, and a high-risk management item was derived through this process. In particular, simulations and experiments were used to verify the difference between the potential and impact energies according to drop orientation. When the object dropped in a specific orientation, the impact energy was confirmed to be up to 4.7 times greater than the potential energy. To reflect the QRA results in structural design, the proposed procedure should be used to calculate the maximum impact energy. The proposed procedure provides a step-by-step guide to assess the damage capacity of a production area as well as the damage frequency and consequences.

scholarly journals Comparison the Strength of Midship Structures With Margin Plate and Without Margin Plate

2021 ◽  
Vol 4 (1) ◽  
pp. 63-70
Author(s):  
Andi Ardianti ◽  
Rosmani Munandar ◽  
Haryono Haryono ◽  
Ganding Sitepu ◽  
Hamzah Hamzah
Keyword(s):  
Maximum Load ◽  
Bottom Plate ◽  
Ship Model ◽  
Maximum Moment ◽  
Longitudinal Strength ◽  
The Difference ◽  
Moment Load ◽  
The Right ◽  
Frame Construction ◽  
Load Conditions

Margin plate is a part of bottom construction that joint the floor and frame construction of the ship, so the inner bottom plate will be installed cut off on the margin plate. Lately the bottom construction of the ship tends not to use the margin plate. The ship is currently built with an inner bottom plate continuously from the left side to the right side of the ship.This study aims to determine the transversal and longitudinal strength ratio of ships with and without margin plate. The  analysis was carried out by using Finite Element Method so-called ANSYSTM. The result shows if the loadvariatied 0.2 x maximum load on the calculation of the transverse strength of the ship, the stress value on the ship model with a margin plate was 9.6242 (N/mm2) and on the ship model without margin plate was 8.4739 (N/mm2) under conditions 100%. The results of the comparison due to bottom load averaged 15.82%. The difference in stress due to the effect of deck loads was an average of 13.49% while the effect of side loads was on average 8.74%. The longitudinal strength of the ship was also a varied of every increase of 0.2 x maximum moment with a review point of meeting between bottom plate and bilga plate for the ship model without margin plates using the Multi Point Constraint (MPC) method looking for results in sagging conditions of 12,443 (N / mm2) and the hogging condition was -11.045 (N / mm2) at 100% x maximum moment load conditions. So that  the ship model with a margin plate sagging condition was 23,189 (N / mm2) and hagging condition was  -20,585 (N / mm2). The results showed the stress that occurred in the ship model without using margin plate was better to withstand the transverse and longitudinal strength of the ship compared to the ship model with the margin plate.

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