Optimality and Acceptance Criteria in Offshore Design

2002 ◽  
Author(s):  
Oliver Ku¨bler ◽  
Michael Havbro Faber
Keyword(s):  
Optimal Design ◽  
Service Life ◽  
Net Present Value ◽  
Steel Structures ◽  
Offshore Structures ◽  
Theoretical Problem ◽  
Offshore Structure ◽  
Construction Costs ◽  
Suggested Approach ◽  
Wide Range

The optimal design of offshore structures is formulated as a decision theoretical problem. The objective is to maximize the net present value of the service life benefit. The general optimization problem is simplified by taking into account the cost impacts of only one possible reconstruction of the structure. The analytical solution to this problem has been derived for the case, where failure events follow a stationary Poisson process. The service life benefit is formulated in terms of the production profile, the design and construction costs, the costs of failure and the costs of reconstruction. In order to assess the effect of potential loss of lives, the costs of fatalities are included applying the concept of the Imp lied Costs of Averting a Fatality (ICAF). The suggested approach to optimal design, which can be applied for any type of offshore structure, is exemplified considering the special case of steel structures. Here it is standard to represent the ultimate structural capacity in terms of the Reserve Strength Ratio (RSR). For the purpose of illustration, the relation between material usage and RSR valid for monopod structures is applied. Optimal RSR’s and annual failure rates are assessed for both manned and un-manned structures covering a wide range of different realistic ratios between the potential income and costs of construction, failure and re construction costs.

Optimality and Acceptance Criteria in Offshore Design

2004 ◽  
Vol 126 (3) ◽  
pp. 258-264 ◽  
Author(s):  
Oliver Ku¨bler ◽  
Michael Havbro Faber
Keyword(s):  
Life Cycle ◽  
Optimal Design ◽  
Net Present Value ◽  
Steel Structures ◽  
Offshore Structures ◽  
Theoretical Problem ◽  
Offshore Structure ◽  
Suggested Approach ◽  
Structural Capacity ◽  
Wide Range

The optimal design of offshore structures is formulated as a decision theoretical problem. The objective is to maximize the expected net present value of the life cycle benefit. The general optimization problem is simplified by taking into account the cost impacts of a possible reconstruction of the structure. The analytical solution to this problem has been derived for the case, where failure events follow a stationary Poisson process. The life cycle benefit is formulated in terms of the production profile, the design and construction costs, failure costs and reconstruction costs. In order to assess the effect of potential loss of lives, the costs of fatalities are included applying the concept of the Implied Costs of Averting a Fatality ICAF. The suggested approach to optimal design, which can be applied for any type of offshore structure, is exemplified considering the special case of steel structures. Here, it is standard to represent the ultimate structural capacity in terms of the Reserve Strength Ratio RSR. For the purpose of illustration, the relation between material usage and RSR, which is valid for monopod structures, is applied. Optimal RSR’s and corresponding annual failure rates are assessed for both manned and unmanned structures covering a wide range of different realistic ratios between the potential revenues and costs for construction, failure and reconstruction.

scholarly journals Stress Concentration Factor of A Two-Planar Double KT Tubular Joint due to In-Plane Bending Loading in Steel Offshore Structures

2018 ◽  
Vol 177 ◽  
pp. 01006
Author(s):  
Prastianto Rudi Walujo ◽  
Hadiwidodo Yoyok Setyo ◽  
Fuadi Ibnu Fasyin
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Element Model ◽  
Offshore Structures ◽  
Geometrical Parameters ◽  
Offshore Structure ◽  
Wide Range ◽  
Tubular Joint

The purpose of this study is to investigate the proper Stress Concentration Factor (SCF) of a 60° two-planar DKT tubular joint of a tripod wellhead offshore structure. So far, calculation of SCF for a multi-plane tubular joint was based on the formulation for the simple/uniplanar tubular joints that yield in over/under prediction of the SCF of the joint. This situation in turn decreasing the accuracy of fatigue life prediction of the structures. The SCF is one of the most important parameters in the tubular joint fatigue analysis. The tubular joint is modelled as finite element models with bending loads acting on the braces that cover a wide range of dimensionless geometrical parameters (β, τ, γ). The effect of such parameters on the SCF distribution along the weld toe of braces and chord on the joint are investigated. Validation of the finite element model has shown good agreement to the global structural analysis results. The results of parametric studies show that the peak SCF mostly occurs at around crown 2 point of the outer central brace. The increase of the β leads to decrease the SCF. While the increase of the τ and γ leads to increase the SCF. The effect of parameter β and γ on the SCF are greater than the effect of parameter τ.

Fatigue Analysis of Load-Carrying Fillet Welds

2005 ◽  
Vol 128 (1) ◽  
pp. 65-74 ◽  
Author(s):  
John Dalsgaard Sørensen ◽  
Jesper Tychsen ◽  
Jens Ulfkjær Andersen ◽  
Ronnie D. Brandstrup
Keyword(s):  
Steel Structures ◽  
Offshore Structures ◽  
Fatigue Tests ◽  
Fillet Welds ◽  
Fatigue Lifetime ◽  
Fatigue Stress ◽  
Wide Range ◽  
Load Carrying ◽  
Plate Connection ◽  
Throat Section

The fatigue strength of load-carrying fillet welds is, in most codes of practice, performed neglecting the influence of bending in the weld throat section. However, some commonly applied structural details give rise to significant bending in the weld throat section. An example of such a detail is a doubler plate connection, which is often applied in connection with modifications of offshore structures. As a part of the present work, fatigue tests have been performed with test specimens fabricated by the current industry standard for welded offshore steel structures. The fatigue tests show that the degree of bending (DOB) has an influence on the fatigue lifetime. The fatigue lifetime decreases significantly when increasing the bending stress. In order to take into account the effect of the bending, a new fatigue stress definition applicable for fillet welds failing through the weld is presented. Using the test results, it is shown that the new definition of fatigue stress can be used for a wide range of DOB with a low standard deviation of the resulting SN curve.

Reliability-Based Design and Assessment for Lifetime Extension of Ageing Offshore Structures

2016 ◽  
Author(s):  
E. Mat Soom ◽  
M. K. Abu Husain ◽  
N. I. Mohd Zaki ◽  
N. U. Azman ◽  
G. Najafian
Keyword(s):  
Service Life ◽  
Offshore Structures ◽  
Risk Level ◽  
Type I ◽  
Offshore Structure ◽  
Design Assessment ◽  
Reliability Based Design ◽  
Remaining Service Life ◽  
The North ◽  
Cost Efficient

The methodology for Reliability-Based Design and Assessment (RBDA) of an ageing fixed steel offshore structure was established to support detailed re-assessment applied to the management of the structure’s safety, integrity analysis and reliability by evaluating the loading acting on the structure. It is a tool for the high-end analysis of the structure for risk-based design assessment and has been succesfully implemented in the North Sea under Shell operating company. The main purposes of RBDA are to manage a structure’s risk level over its remaining service life and to initiate the cost-efficient inspection or mitigation actions (if required). This method consists of Type I and II uncertainties used to determine the probability of failure for the structure over its remaining service life. However, limited work has been done so far on its application at many different regions, particularly in the South East Asia. Therefore, this paper investigates the robustness of the RBDA methodology applied to fixed offshore structures at shallow waters of Malaysia by considering the native environmental criteria, local authorities’ obligation and company requirements. It is shown that this procedure can efficiently assist in understanding the structure’s failure mechanism and correctly define the relevant type of mitigations required.

scholarly journals An Overview of classifications and incidents/accidents in offshore structures: Oil and gas

2020 ◽  
Vol 1 (4) ◽  
pp. 13-18
Author(s):  
Jean Pierre Lukongo Ngenge ◽  
Abdallah M.S. Wafi
Keyword(s):  
Oil And Gas ◽  
Offshore Structures ◽  
Research Topic ◽  
Offshore Platforms ◽  
Offshore Structure ◽  
The Past ◽  
Wide Range ◽  
Advanced Knowledge ◽  
Construction Accidents ◽  
The Impact

Offshore platforms are considered among the most significant structures in the world that humans have ever built, having to function in a wide range of extremely challenging environments and have a major impact on the economy and industrial progress of countries. It is extremely important to properly plan, design, construct, transport and install such offshore structures. In the absence of commitment to this, the consequences could be severe in both economic and environmental terms. An overview of offshore structures is presented in this paper, and its purpose is to offer a consistent vision for the various types of offshore structures to be used for the extraction of oil and gas. In addition, the paper focuses on the expected accidents that may occur during and after construction. Accidents do not only cover the difficult environment where these structures are to be built, but they also cover the impact of climate change on these structures. The approach considered in this paper involves a systematic literature review that deals with reviewing different studies done on the similar research topic. The results found in this study determined that the type of offshore structure to be built or fixed at a particular location in water, depends mainly on the water depth and also on the past and present environmental records. Nonetheless, the outcomes of this study are still general; thus, further studies have to be completed in order to acquire more advanced knowledge in this particular field.

IMPROVEMENT OF INNOVATIVE ACTIVITY OF THE ENTERPRISE

2017 ◽  
Author(s):  
Nataliya Stoyanets ◽  
◽  
Mathias Onuh Aboyi ◽  
Keyword(s):  
Value Chain ◽  
Net Present Value ◽  
Successful Implementation ◽  
Innovative Development ◽  
Technological Equipment ◽  
Alliance Partner ◽  
Innovation Potential ◽  
Wide Range ◽  
Technological Platform ◽  
The Cost

The article defines that for the successful implementation of an innovative project and the introduction of a new product into production it is necessary to use advanced technologies and modern software, which is an integral part of successful innovation by taking into account the life cycle of innovations. It is proposed to consider the general potential of the enterprise through its main components, namely: production and technological, scientific and technical, financial and economic, personnel and actual innovation potential. Base for the introduction of technological innovations LLC "ALLIANCE- PARTNER", which provides a wide range of support and consulting services, services in the employment market, tourism, insurance, translation and more. To form a model of innovative development of the enterprise, it is advisable to establish the following key aspects: the system of value creation through the model of cooperation with partners and suppliers; creating a value chain; technological platform; infrastructure, determine the cost of supply, the cost of activities for customers and for the enterprise as a whole. The system of factors of influence on formation of model of strategic innovative development of the enterprise is offered. The expediency of the cost of the complex of technological equipment, which is 6800.0 thousand UAH, is economically calculated. Given the fact that the company plans to receive funds under the program of socio-economic development of Sumy region, the evaluation of the effectiveness of the innovation project, the purchase of technological equipment, it is determined that the payback period of the project is 3 years 10 months. In terms of net present value (NPV), the project under study is profitable. The project profitability index (PI) meets the requirements for a positive decision on project implementation> 1.0. The internal rate of return of the project (IRR) also has a positive value of 22% because it exceeds the discount rate.

DOMEX 550MC

Alloy Digest ◽  
2009 ◽  
Vol 58 (3) ◽  
Keyword(s):  
Physical Properties ◽  
Hsla Steel ◽  
Steel Structures ◽  
High Strength ◽  
Heat Treating ◽  
Bend Strength ◽  
Cold Forming ◽  
Wide Range ◽  
Hot Rolled ◽  
Earthmoving Machines

Abstract Domex 550MC is a hot-rolled, high-strength low-alloy (HSLA) steel for cold forming operations. It is available in thicknesses of 2.00-12.80 mm. The alloy meets or exceeds the requirements of S550MC in EN 10149-2. Applications include a wide range of fabricated components and steel structures, including truck chassis, crane booms, and earthmoving machines. This datasheet provides information on composition, physical properties, tensile properties, and bend strength as well as fatigue. It also includes information on forming, heat treating, and joining. Filing Code: SA-594. Producer or source: SSAB Swedish Steel Inc.

A CFD Study of Focused Extreme Wave Impact on Decks of Offshore Structures

2014 ◽  
Author(s):  
Xin Lu ◽  
Pankaj Kumar ◽  
Anand Bahuguni ◽  
Yanling Wu
Keyword(s):  
Real World ◽  
Offshore Structures ◽  
Air Gap ◽  
Irregular Waves ◽  
Linear Wave ◽  
Extreme Wave ◽  
Wave Impact ◽  
Loading Test ◽  
Wide Range ◽  
Wave Maker

The design of offshore structures for extreme/abnormal waves assumes that there is sufficient air gap such that waves will not hit the platform deck. Due to inaccuracies in the predictions of extreme wave crests in addition to settlement or sea-level increases, the required air gap between the crest of the extreme wave and the deck is often inadequate in existing platforms and therefore wave-in-deck loads need to be considered when assessing the integrity of such platforms. The problem of wave-in-deck loading involves very complex physics and demands intensive study. In the Computational Fluid Mechanics (CFD) approach, two critical issues must be addressed, namely the efficient, realistic numerical wave maker and the accurate free surface capturing methodology. Most reported CFD research on wave-in-deck loads consider regular waves only, for instance the Stokes fifth-order waves. They are, however, recognized by designers as approximate approaches since “real world” sea states consist of random irregular waves. In our work, we report a recently developed focused extreme wave maker based on the NewWave theory. This model can better approximate the “real world” conditions, and is more efficient than conventional random wave makers. It is able to efficiently generate targeted waves at a prescribed time and location. The work is implemented and integrated with OpenFOAM, an open source platform that receives more and more attention in a wide range of industrial applications. We will describe the developed numerical method of predicting highly non-linear wave-in-deck loads in the time domain. The model’s capability is firstly demonstrated against 3D model testing experiments on a fixed block with various deck orientations under random waves. A detailed loading analysis is conducted and compared with available numerical and measurement data. It is then applied to an extreme wave loading test on a selected bridge with multiple under-deck girders. The waves are focused extreme irregular waves derived from NewWave theory and JONSWAP spectra.

Downtime Analysis Techniques for Complex Offshore and Dredging Operations

2004 ◽  
Author(s):  
Remmelt J. van der Wal ◽  
Gerrit de Boer
Keyword(s):  
Wind Waves ◽  
Weather Forecast ◽  
Offshore Structures ◽  
Operational Mode ◽  
Offshore Structure ◽  
Hydrodynamic Models ◽  
Time Step ◽  
Made In

Offshore operations in open seas may be seriously affected by the weather. This can lead to a downtime during these operations. The question whether an offshore structure or dredger is able to operate in wind, waves and current is defined as “workability”. In recent decades improvements have been made in the hydrodynamic modelling of offshore structures and dredgers. However, the coupling of these hydrodynamic models with methods to analyse the actual workability for a given offshore operation is less developed. The present paper focuses on techniques to determine the workability (or downtime) in an accurate manner. Two different methods of determining the downtime are described in the paper. The first method is widely used in the industry: prediction of downtime on basis of wave scatter diagrams. The second method is less common but results in a much more reliable downtime estimate: determination of the ‘job duration’ on basis of scenario simulations. The analysis using wave scatter diagrams is simple: the downtime is expressed as a percentage of the time (occurrences) that a certain operation can not be carried out. This method can also be used for a combination of operations however using this approach does not take into account critical events. This can lead to a significant underprediction of the downtime. For the determination of the downtime on basis of scenario simulations long term seastate time records are used. By checking for each subsequent time step which operational mode is applicable and if this mode can be carried out the workability is determined. Past events and weather forecast are taken into account. The two different methods are compared and discussed for a simplified offloading operation from a Catenary Anchor Leg Mooring (CALM) buoy. The differences between the methods will be presented and recommendations for further applications are given.

Optimal Design of Power System Stabilizer Using a Novel Evolutionary Algorithm

2018 ◽  
Vol 7 (3) ◽  
pp. 24-46
Author(s):  
Sourav Paul ◽  
Provas Roy
Keyword(s):  
Optimal Design ◽  
Power System ◽  
Search Algorithm ◽  
Low Frequency ◽  
Optimal Solution ◽  
Power System Stabilizer ◽  
Low Frequency Oscillation ◽  
Large Power ◽  
Wide Range ◽  
System Stabilizer

In this article, an Oppositional Differential search algorithm (ODSA) is comprehensively developed and successfully applied for the optimal design of power system stabilizer (PSS) parameters which are added to the excitation system to dampen low frequency oscillation as it pertains to large power system. The effectiveness of the proposed method is examined and validated on a single machine infinite bus (SMIB) using the Heffron-Phillips model. The most important advantage of the proposed method is as it reaches toward the optimal solution without the optimal tuning of input parameters of the ODSA algorithm. In order to verify the effectiveness, the simulation was made for a wide range of loading conditions. The simulation results of the proposed ODSA are compared with those obtained by other techniques available in the recent literature to demonstrate the feasibility of the proposed algorithm.

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