Determination of monopile offshore structure response to stochastic wave loads via analog filter approximation and EV-GDEE procedure

2022 ◽  
pp. 103197
Author(s):  
Yi Luo ◽  
Jianbing Chen ◽  
Pol D. Spanos
Keyword(s):  
Wave Loads ◽  
Analog Filter ◽  
Offshore Structure ◽  
Structure Response ◽  
Filter Approximation

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.

Effect of Seabed Slope on Offshore Pile Lateral Behaviour Under Wave Force

2010 ◽  
Author(s):  
Sathyanarayanan Dhandapani ◽  
Muthukkumaran Kasinathan
Keyword(s):  
Finite Element ◽  
Vertical Direction ◽  
Pile Group ◽  
Element Model ◽  
Wave Force ◽  
Wave Forces ◽  
Extreme Conditions ◽  
Offshore Platforms ◽  
Wave Loads ◽  
Offshore Structure

Fixed offshore platforms supported by pile foundations are required to resist dynamic lateral loading due to wave forces. The response of a jacket offshore tower is affected by the flexibility and nonlinear behavior of the supporting piles. In this study, a typical fixed offshore platform is chosen, and dynamic wave analysis is performed on it. Analysis has been performed for normal environmental conditions and extreme conditions. For the foundation, the deflections and reactions at regular intervals along the vertical direction from the seabed have been found out from the dynamic analysis, and the results have been compared for normal and extreme conditions. The aim of this study is to investigate the effects of the combined lateral and vertical loads on pile group foundation of a fixed offshore structure and the effects of seabed slope on the pile responses. To provide a more accurate and effective design for offshore pile foundation systems under axial structural loads and lateral wave loads, a finite element model which is modelled in FLAC3D is employed herein to determine the soil structure interaction under similar loading conditions. Three dimensional modelling and the analyses are done using FLAC3D — a finite element package.

The Effect of Wave Directionality on Low Frequency Motions and Mooring Forces

2009 ◽  
Author(s):  
Olaf J. Waals
Keyword(s):  
Water Depth ◽  
Transfer Functions ◽  
Low Frequency ◽  
Sensitivity Study ◽  
Wave Loads ◽  
Offshore Structure ◽  
Frequency Wave ◽  
Drift Theory ◽  
Mooring Forces ◽  
Drift Forces

Operability of offshore moored ships can be affected by low frequency wave loads. The low frequency motions of a moored ship may limit the uptime of an offshore structure such as an LNG offloading terminal. The wave loads that cause the main excitation of these low frequency motions are usually computed using second order wave drift theory for long crested waves, which assumes that the low frequency components are only related to waves coming from the same direction. In this method short crested seas are dealt with as a summation of long crested seas, but no interaction between the wave components traveling in different directions is usually taken into account. This paper describes the results of a study to the effect of 2nd order low frequency wave loads in directional seas. For this study the drift forces related to the interaction between waves coming from different directions is also included. This is done by computing the quadratic transfer functions (QTF) for all possible combinations of wave components (frequencies and directions). Time traces of drift forces are generated and compared to the results without wave directional interaction after which the motions of an LNG carrier are simulated. A sensitivity study is carried out towards the number of direction steps and the water depth. Finally the motions of an LNG carrier in shallow water (15m water depth) are simulated and mooring forces are compared for various amounts of wave spreading.

FEATURES OF DETERMINATION OF SEA WAVE PARAMETERS FOR CONSTRUCTION OF HYDRAULIC ENGINEERING CONSTRUCTIONS TO FROM REVER TUAPSE TO RIVER PSOU

2018 ◽  
Author(s):  
Е. Дзагания ◽  
E. Dzaganiya
Keyword(s):  
Black Sea ◽  
Wave Mode ◽  
Water Area ◽  
Hydraulic Engineering ◽  
The Black Sea ◽  
Wave Loads ◽  
New Wave ◽  
Engineering Construction ◽  
A Site

East coast is the most storm part of the Black Sea because extent of the water area of the Black Sea more than 800 km. In a year there are about 17 days strong storm. Almost rectilinear outlines of the coast on a site from the river Tuapse to river Psou testify to destructive force of storm at low durability of the rocks composing the coast. The wave mode in the high sea can be determined by standard fields of a wind which build with use of weather maps. For a basis of typification take the direction and gradation of speed of a wind for that part of the water area within which it is required to define elements of waves. The main lack of a method is a short row – 10 years therefore the forecast for 25, 50 and 100 years on this row is estimated. Besides, for the district of Sochi the considerable share of excitements of a ripple (50–75 %) which are formed in different areas of the sea is characteristic. Therefore for this region any settlement method for wind excitement in the high sea won't reflect the actual mode of excitement and parameters of waves at the coast. Therefore in this case it is necessary to use all available actual data on excitement at probably bigger depth of supervision and all data on impact of the maximum storm on the coast in similar to the area of research conditions. The most qualitative for the considered coast are materials of supervision in Pitsunda. For application of these data for other sites of the coast taking into account a refraction recalculation of these supervision from shallow water is made for excitement of the deep sea. These data can be used for calculation of elements of waves on the Sochi coast. For the accounting of features of a wave mode at construction of such responsible and expensive constructions as ports, creation of new wave posts for long-term supervision is necessary. Especially it is actual in the Adler district of the city of Sochi where parameters of extreme storm are estimated generally on the put damage, instead of on series of observations over excitement. Tool supervision over excitement were carried out on northern to a pier of the Sochi port after the completion of its construction and allowed to define instrumentalno wave loads of a hydraulic engineering construction during a storm. Again created constructions of Mzymta seaport on the coast of the Imeretinsky bay and created during reconstruction of the Sochi seaport a new northern pier could form base for the organization of tool supervision over excitement on rather big depths near 15–20 M that it is quite enough for supervision of the maximum waves to their collapse.

Engineering Establishment of Living Quarters for Jack-Up Rig Structures

2016 ◽  
Author(s):  
Yeong Su Ha ◽  
Joo Shin Park ◽  
Jeong Bon Koo ◽  
Byung Jin Cho ◽  
Kuk Yeol Ma ◽  
...  
Keyword(s):  
Structural Engineering ◽  
Three Dimensional ◽  
Technical Specification ◽  
International Standards ◽  
Structural Safety ◽  
Fe Model ◽  
Wave Loads ◽  
Offshore Structure ◽  
Local Loads ◽  
Jack Up

The Living-Quarters (hereafter referred to as ‘LQ’) is one of the major structures for ship and offshore structure. The LQ gives safe living conditions to crews on board. Until now the structural design of LQ structure is based on simplistic beam calculation to determine the initial scantling under design load. These days, safety for people is a raising issue. It is needed to meet the high oil company’s needs as well as technical specification throughout offshore project. But, the engineering procedure for LQ structure is not clearly defined by classification of society rules and international standards. In this paper, the newly engineering procedure for LQ design is established considering LQ global loads with local loads for large equipment such as helideck structure, telecom mast and life saving appliances, and so on. To consider LQ global loads with local loads, the integrated three dimensional FE model and high technology engineering should be needed to require many kind of rules for equipment. Recently, the damage of LQ structure is occasionally reported during towing condition for jack-up rig structure. The LQ of jack-up rig is encountered such as slamming pressure and greenwater produced by harsh wave loads during towing condition because of small height of freeboard comparing to the wave height. To verify the structural safety under towing condition, the detailed non-liner analysis is performed to verify the load-carrying capacity against greenwater pressure. We newly propose a structural engineering procedure to improve the reliability of the LQ design in the jack-up rigs. From basis of this procedure, a more reasonable and optimized results are proposed as a practical manner as well as scientific approach.

A Comparative Research on Computation Methods for Wave Loads of Semi-Submersible Platform

2018 ◽  
Author(s):  
Zhiyong Pei ◽  
Shenyi Wu ◽  
Keqiang Chen ◽  
Xiaoming Hu ◽  
Weiguo Wu
Keyword(s):  
Wave Method ◽  
Wave Loads ◽  
Wave Load ◽  
Fundamental Research ◽  
Wave Methods ◽  
Long Term Prediction ◽  
External Loads ◽  
Selection Of

Wave load is one of the main external loads for semi-submersible platform, which is usually calculated by design wave method. In the present research, three design wave methods are investigated and compared on design wave parameters determination of semi-submersible platforms, i.e., the deterministic design wave method, stochastic design wave method and long-term prediction design wave method. Moreover, the specified calculation methods and the detailed wave load computation procedure are summarized considering the load characteristics of global hydrodynamic response. Finally, a semi-submersible platform is regarded as objective and the design wave results of three design wave methods are compared and analyzed. The fundamental research can provide reference for rational selection of wave loads calculation method.

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