• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.68-72
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• 2001

Two different methods of free span analysis of offshore pipelines by DnV codes were introduced and compared in order to calculate the allowable free span lengths of the offshore pipelines. The allowable span lengths of the offshore pipelines for installation, hydrotest and operation conditions by static and dynamic span analysis were determined. Static analysis was performed by ASME codes and dynamic span analysis was performed by both 1981 DnV code. Comparison of two codes were carried out. A new design procedure to calculate the allowable span lengths was developed with new DnV code.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.1
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• pp.81-86
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• 1996

Subsea pipelines have an important role in the overall tasks of offshore oil and gas production but arc exposed to various hazards with high potential risks of damage resulting in serious economic loss and impact on ocean environment. In this paper, the dynamic free span is analysed, which is one of main risk factors against the safety of subsea pipelines and the allowable length of dynamic free span which is important for the design of subsea pipelines is determined. The allowable free span length is examined by considering the relationship between vortex shedding frequency and natural frequency of pipeline free span, and the variation of the allowable length is analysed for different boundary conditions of pipe ends. The free span is regarded as a beam on elastic foundations and the boundary condition of the beam is generalized by modelling as restrained by linear and rotational spring at each end. A non-dimensionalized curve is obtained to facilitate the determination of exact allowable length of dynamic free span for subsea pipelines and is applied to the pipelines which is to be installed in the gas fields of the south of East Sea of Korea.

• Journal of Ocean Engineering and Technology
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• v.19 no.2 s.63
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• pp.47-52
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• 2005

This paper introduces a procedure for free span and fatigue analysis of offshore pipelines per DNV-RP-F105, 2002. The new method includes the axial force and deflection load in pipelines. The screening criteria were established to calculate the allowable span lengths in the new design codes. The screening criteria allows a certain amount of vortex-induced vibration due to wave and current loading. However, the induced pipe stresses are very small and usually below the limit stresess of typical S-N curves. In contrast, the conventional criteria did not allow any vortex-induced vibration in the free span of pipelines. Thus, the screening criteria yields reduced allowable span lengths. A simplified procedure was established to calculate the fatigue damage due to long-term current distribution. The long-term current statistics was assumed with a 3-parameter Weibull distribution. The fatigue damage was estimated for the span lengths obtained from the screening criteria for various conditions. Sample calculations show the effect of axial force for various boundary conditions. Comparisons with conventional criteria are included.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.4
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• pp.290-295
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• 2001

Subsets pipelines are exposed to several potential risks of damage due to corrosion, soil instability, anchor impact and other hazards. One of the main risk factors for the safety of a subsea pipeline is its free spanning. This paper examines the safety of subsea pipelines with free span under axial compressive load. The variation of allowable lengths of dynamic free span is examined for generalized boundary conditions. The free span is modelled as a beam with an elastic foundations and the boundary condition is replaced by linear and rotational springs at each end. A dynamic free span curve is obtained with a function of non-dimensional parameters and can be used usefully for the design of subsea pipelines with a free span. A case study is carried out to introduce the application method of the curve.

• Journal of the Korean Society for Marine Environment & Energy
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• v.6 no.2
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• pp.54-62
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• 2003

The free span of a subsea pipeline due to seabed scouring can result in structural failure by severe ocean environmental loads and vortex induced vibrations. This Paper examines the safety of subsea pipelines with free spans under axial compressive load. The variation of allowable lengths of static and dynamic free spans is examined for generalized boundary conditions. The free span is modelled as a beam with an elastic foundations and the boundary condition is replaced by linear and rotational springs at each end. The static and dynamic free span curves are obtained with a function of non-dimensional parameters. A case study is carried out to introduce the application method of the curve. The results of this study can be usefully applied for the design of subsea pipelines with a free span.

• Journal of the Korean Society of Marine Environment & Safety
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• v.2 no.1
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• pp.77-82
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• 1996

Subsea pipelines are exposed to several potential risks of damage due to wave, soil instability and other hazards. Structural failure of the steel pipelines will result in serious consequences such as release of transported hydrocarbons, pollution to the ocean environment and heavy costs due to repair. This paper examines the safety of subsea pipelines with free span which is one of high potential damages. The variation of an allowable length of static free span is examined for different boundary conditions and is given in a curve which is useful for the dsign of the subsea pipeline with a free span.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• v.3 no.1
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• pp.49-55
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• 2000

Improvement was made on the free span analysis of the offshore pipelines. The effect of axial force (both tension and compressive force) can be explicitly applied to the current design code. The closed form solutions of beam-column equation were derived for the typical boundary conditions. The solutions can be used to find the natural frequencies of the span using the energy balance concept. The results can be applied to the current design code and will result more realistic calculation of free span lengths of offshore pipelines.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.29-33
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• 2002

A procedure of free span and fatigue analysis of offshore pipelines was made per DNV-RP-F105, 2002. The new method includes the axial force and deflection load in pipelines. The screening criteria were used to calculate the allowable span lengths. The screening criteria allow small amplitudes of vortex-induced vibration due to wave and current loading. However, the induced pipe stress is very small and usually below the limit stress of a typical S-N curve. A simplified method was established to calculate the fatigue damage due to long-term current distribution. The long-term current statistics was assumed with a 3-parameter Weibull distribution. The fatigue damage was estimated for the span lengths obtained from the screening criteria for various conditions. Sample calculations show the effect of axial force for various boundary conditions.

• Wind and Structures
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• v.11 no.5
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• pp.391-411
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• 2008

A design procedure of stabilizing cable is proposed using buffeting analysis to stabilize the seesaw-like motion of the free cantilevered structure of a cable-stayed bridge during its construction. The bridge examined is a composite cable-stayed bridge having a main span length of 500 m. Based on the buffeting analysis, the stress in bare structure exceeded the allowable limit and a set of stabilizing cable was planned to mitigate the responses. The most efficient positions of the hold-down stabilizing cables were numerically investigated by means of an FE-based buffeting analysis and the required dimensions and pretension of the stabilizing cables were also calculated. The proposed stabilizing measure would be expected to secure the aerodynamic safety of a cantilevered structure under construction with considerable mitigation of buffeting responses.