Airgap and Wave in Deck Impact Statistics

2016 ◽  
Author(s):  
Øistein Hagen ◽  
Thomas B. Johannessen ◽  
Jørn Birknes-Berg
Keyword(s):  
Structural Reliability ◽  
Gap Analysis ◽  
Impact Load ◽  
Wave Theory ◽  
Limit States ◽  
Wave Impact ◽  
Weakly Nonlinear ◽  
Horizontal Wave ◽  
Wave Heights ◽  
Simple Limit

As offshore reservoirs are depleted, the seabed may subside. Bottom fixed installations which have previously had sufficient clearance between the deck and the sea surface may be in a situation where wave impact with the deck must be considered at relevant probability levels. Some statistical aspects associated with the calculation of a deck impact load with a prescribed probability of occurrence are the subject of the present paper. The Short Crest JIP addressed the distribution of the crest height in extreme sea states, the properties of the largest crests and the deck impact loading on a closed deck. It was concluded that the largest waves in the sea may be in the process of breaking and thus have properties which deviate significantly from estimates found from weakly nonlinear irregular or regular wave theory. The present paper addresses findings from the Short Crest JIP regarding • long-term analysis of wave heights and crest, including the effect of wave breaking • air gap analysis for jacket, TLP and semisubmersible using 2nd order time domain simulations over the platform area • statistics for horizontal wave-in-deck impacts for short crested sea versus for long crested sea • structural reliability analysis of jackets for some simple limit states that are governed by loads caused by impact of extreme crests

scholarly journals Focusing of long waves with finite crest over constant depth

2013 ◽  
Vol 469 (2153) ◽  
pp. 20130015 ◽  
Author(s):  
Utku Kânoğlu ◽  
Vasily V. Titov ◽  
Baran Aydın ◽  
Christopher Moore ◽  
Themistoklis S. Stefanakis ◽  
...  
Keyword(s):  
Source Region ◽  
Wave Theory ◽  
Long Waves ◽  
Constant Depth ◽  
Large Wave ◽  
Weakly Nonlinear ◽  
Scaling Relationships ◽  
2011 Japan Tsunami ◽  
Wave Heights ◽  
Run Up

Tsunamis are long waves that evolve substantially, through spatial and temporal spreading from their source region. Here, we introduce a new analytical solution to study the propagation of a finite strip source over constant depth using linear shallow-water wave theory. This solution is not only exact, but also general and allows the use of realistic initial waveforms such as N -waves. We show the existence of focusing points for N -wave-type initial displacements, i.e. points where unexpectedly large wave heights may be observed. We explain the effect of focusing from a strip source analytically, and explore it numerically. We observe focusing points using linear non-dispersive and linear dispersive theories, analytically; and nonlinear non-dispersive and weakly nonlinear weakly dispersive theories, numerically. We discuss geophysical implications of our solutions using the 17 July 1998 Papua New Guinea and the 17 July 2006 Java tsunamis as examples. Our results may also help to explain high run-up values observed during the 11 March 2011 Japan tsunami, which are otherwise not consistent with existing scaling relationships. We conclude that N -waves generated by tectonic displacements feature focusing points, which may significantly amplify run-up beyond what is often assumed from widely used scaling relationships.

Methods for Establishing Governing Deck Impact Loads in Irregular Waves

2015 ◽  
Author(s):  
Jørn Birknes-Berg ◽  
Thomas Berge Johannessen
Keyword(s):  
Wave Theory ◽  
Order Theory ◽  
Irregular Waves ◽  
Impact Loads ◽  
Wave Impact ◽  
Sea State ◽  
Simple Method ◽  
Weakly Nonlinear ◽  
Cfd Method ◽  
The Individual

As offshore reservoirs are depleted, the seabed may subside. Bottom fixed installations which previously have had sufficient clearance between the deck and the surface may be in a situation where wave impact with the deck must be considered at relevant probability levels. The accurate calculation of deck impact loads with a prescribed probability of occurrence taking into account the relevant properties of the incident waves, presents a considerable challenge. The ShorTCrest JIP has addressed both the distribution of the crest height in extreme sea states, the properties of the largest crests and the deck impact loading on a closed deck. It has been concluded that the largest waves in the sea may be in the process of breaking and thus have properties which deviate significantly from estimates found from weakly nonlinear irregular or regular wave theory /5/. The present paper investigates a simple method to calculate deck impact loads in irregular waves which take into account the irregularity of the sea state and the possibility of wave breaking. The method is a two-step approach. Firstly, a long duration simulation of surface elevation is carried out using second-order theory in order to identify possible deck impact events. The individual wave events which are capable of impacting the deck is then reproduced using a CFD method and the distribution of the deck impact loads is established. The calculations are compared with model test results for wave impact with a large volume deck box in a single steep sea state and with CFD calculations of deck impact with regular waves.

STRUCTURAL RELIABILITY ANALYSIS BASED ON P-BOXES

2020 ◽  
Vol 92 (6) ◽  
pp. 51-58
Author(s):  
S.A. SOLOVYEV ◽  
Keyword(s):  
Probability Distribution ◽  
Reliability Analysis ◽  
Structural Reliability ◽  
Epistemic Uncertainty ◽  
Random Variable ◽  
Strength Criterion ◽  
Structural Elements ◽  
Structural Element ◽  
Limit States ◽  
Distribution Shape

The article describes a method for reliability (probability of non-failure) analysis of structural elements based on p-boxes. An algorithm for constructing two p-blocks is shown. First p-box is used in the absence of information about the probability distribution shape of a random variable. Second p-box is used for a certain probability distribution function but with inaccurate (interval) function parameters. The algorithm for reliability analysis is presented on a numerical example of the reliability analysis for a flexural wooden beam by wood strength criterion. The result of the reliability analysis is an interval of the non-failure probability boundaries. Recommendations are given for narrowing the reliability boundaries which can reduce epistemic uncertainty. On the basis of the proposed approach, particular methods for reliability analysis for any structural elements can be developed. Design equations are given for a comprehensive assessment of the structural element reliability as a system taking into account all the criteria of limit states.

Influence of Human Error on Structural Reliability

2017 ◽  
Author(s):  
Eric Brehm ◽  
Robert Hertle ◽  
Markus Wetzel
Keyword(s):  
Human Error ◽  
Structural Reliability ◽  
Failure Modes ◽  
Structural Model ◽  
Limit State ◽  
Design Procedure ◽  
Material Strength ◽  
Limit States ◽  
The Impact

In common structural design, random variables, such as material strength or loads, are represented by fixed numbers defined in design codes. This is also referred to as deterministic design. Addressing the random character of these variables directly, the probabilistic design procedure allows the determination of the probability of exceeding a defined limit state. This probability is referred to as failure probability. From there, the structural reliability, representing the survival probability, can be determined. Structural reliability thus is a property of a structure or structural member, depending on the relevant limit states, failure modes and basic variables. This is the basis for the determination of partial safety factors which are, for sake of a simpler design, applied within deterministic design procedures. In addition to the basic variables in terms of material and loads, further basic variables representing the structural model have to be considered. These depend strongly on the experience of the design engineer and the level of detailing of the model. However, in the clear majority of cases [1] failure does not occur due to unexpectedly high or low values of loads or material strength. The most common reasons for failure are human errors in design and execution. This paper will provide practical examples of original designs affected by human error and will assess the impact on structural reliability.

Reliability Based Assessment of Deck Elevations for Offshore Jacket Platforms

2004 ◽  
Vol 126 (4) ◽  
pp. 331-336 ◽  
Author(s):  
Ernesto Heredia-Zavoni ◽  
Dante Campos ◽  
Gallegher Ramı´rez
Keyword(s):  
Reliability Index ◽  
Structural Reliability ◽  
Failure Modes ◽  
Probability Of Failure ◽  
Upper And Lower Bounds ◽  
Series System ◽  
Wave Loading ◽  
System Components ◽  
Storm Wave ◽  
Wave Heights

Structural reliability analyses of fixed marine platforms subjected to storm wave loading are performed to assess deck elevations. Platforms are modeled as a series system consisting of the deck and jacket bays. The structural reliability analyses are carried out assuming dominant failure modes for the system components. Upper and lower bounds of the probability of failure are computed. The variation of the reliability index per bay component as a function of wave height, with a focus on those wave heights that generate forces on the deck, is analyzed. A comparison is given for the deck probability of failure and the lower bound probability of failure of the jacket in order to assess how the deck or the jacket controls the probability of failure of the system. Results are also given for reliability analyses considering different deck elevations. Finally, an analysis of the total probabilities of failure, unconditioned on wave heights, is given.

Limit State of Torsion of Ship Hulls with Large Hatch Openings

2001 ◽  
Vol 45 (02) ◽  
pp. 95-102
Author(s):  
Yuren Hu ◽  
Bozhen Chen
Keyword(s):  
Cross Section ◽  
Structural Reliability ◽  
Limit State ◽  
Safety Margin ◽  
Plastic Shear ◽  
Torsional Moment ◽  
Limit States ◽  
Ship Hulls ◽  
Design Values ◽  
Bound Theorem

The limit state of torsion of ship hulls with large hatch openings is studied. A method to determine the distribution of the plastic shear flow on the hull cross section in the limit state by using the lower-bound theorem is presented together with the corresponding linear programming problem. The limit torsional moment of the hull cross section is obtained based on the distribution of the shear stress in the limit state. Three example limit states for typical containerships of different sizes with large hatch openings are calculated. The calculated limit torsional moments are compared with the design values of wave torque calculated by using the equations given by main classification societies in their rules. A rough estimate of the safety margin is obtained. The results show that for large containerships, it is necessary to pay attention to the safety with respect to torsion. The present method can serve as an effective tool in structural reliability analysis of ships with large hatch openings when the failure mode of torsion is taken into account.

scholarly journals Calibrating Partial Factors – Methodology, Input Data and Case Study of Steel Structures

2019 ◽  
Author(s):  
Vitali Nadolski ◽  
Árpád Rózsás ◽  
Miroslav Sýkora
Keyword(s):  
Input Data ◽  
Structural Reliability ◽  
Construction Materials ◽  
Steel Structures ◽  
Structural Performance ◽  
Limit States ◽  
Different Types ◽  
Load Effects ◽  
Previous Design

Partial factors are commonly based on expert judgements and on calibration to previous design formats. This inevitably results in unbalanced structural reliability for different types of construction materials, loads and limit states. Probabilistic calibration makes it possible to account for plentiful requirements on structural performance, environmental conditions, production and execution quality etc. In the light of ongoing revisions of Eurocodes and the development of National Annexes, the study overviews the methodology of probabilistic calibration, provides input data for models of basic variables and illustrates the application by a case study. It appears that the partial factors recommended in the current standards provide for a lower reliability level than that indicated in EN 1990. Different values should be considered for the partial factors for imposed, wind and snow loads, appreciating the distinct nature of uncertainties in their load effects.

scholarly journals Effect of Girder Spacing and Depth on the Solitary Wave Impact on Coastal Bridge Deck for Different Airgaps

2019 ◽  
Vol 7 (5) ◽  
pp. 140 ◽  
Author(s):  
Rameeza Moideen ◽  
Manasa Ranjan Behera ◽  
Arun Kamath ◽  
Hans Bihs
Keyword(s):  
Solitary Wave ◽  
Bridge Deck ◽  
Impact Force ◽  
Storm Surges ◽  
Wave Impact ◽  
Wave Condition ◽  
Bridge Damage ◽  
Wave Heights ◽  
The Impact ◽  
Vertical Impact

Coastal bridge damage has become a severe issue of concern in the recent past with the destruction of a considerable number of bridges under the impact of waves during tsunami and storm surges. These events have become more frequent, with waves reaching the bridge deck and causing upliftment and destruction. Past studies have demonstrated the establishment of various theoretical equations which works well for the submerged deck and regular wave types but show much scatter and uncertainty in case of a deck that is above still water level (SWL). The present study aims to generate a solitary wave to represent an extreme wave condition like a tsunami in the numerical wave tank modeled using the open source computational fluid dynamics (CFD) model REEF3D and to study the vertical impact force on the coastal bridge deck. A parametric study is carried out for increasing wave heights, girders spacing and depth for varying airgaps to analyze the effect of these parameters on the peak vertical impact force. It is observed that increasing the girder spacing and girder depth is effective in reducing the peak vertical impact force for the cases considered.

Observed Wave Actions on Norwegian Semi-Submersible and TLP Decks

2018 ◽  
Author(s):  
Arne Kvitrud ◽  
Anders H. Løland
Keyword(s):  
Physical Appearance ◽  
Weather Conditions ◽  
Wave Impact ◽  
Drilling Rig ◽  
Common Causes ◽  
Horizontal Wave

Waves have impacted decks on Norwegian semi-submersibles (semis) and TLPs several times. However, it did not get necessary attention before two accidents in 2015. In 2015, a wave impact caused a fatality and four injured on the semi-submersible drilling rig COSLInnovator. The same year, a wave washed away gratings on Scarabeo 8, causing a man to fall 13.5m to the sea. When examining our records, we found 29 reported incidents related to waves in deck on 17 platforms from 2000–2017. 27 of the wave actions were mainly directed upward and the remaining two were mainly horizontal wave hits. We describe each incident and the circumstances. We discuss common causes related to weather conditions and the physical appearance of the platforms. Further, we summarise design and operational precautions taken by the industry.

Wave Impact Load and Corresponding Nonlinear Response of a Semi-Submersible

2019 ◽  
Author(s):  
Yinghao Guo ◽  
Longfei Xiao ◽  
Handi Wei ◽  
Lei Li ◽  
Yanfei Deng
Keyword(s):  
Spatial Distribution ◽  
Structural Integrity ◽  
Impact Load ◽  
Wave Crest ◽  
Impulsive Effect ◽  
Offshore Platforms ◽  
Wave Impact ◽  
Global Response ◽  
Local Wave ◽  
Incident Waves

Abstract Offshore platforms operating in harsh ocean environments often suffer from severe wave impacts which threaten the structural integrity and staffs safety. An experimental study was carried out to investigate the wave impact load and its effect on the global response of a semi-submersible. First, two typical wave impact events occurring successively in the wave test run are analyzed, including the characteristics of incident waves, relative wave elevations and the spatial distribution of the wave impact load. Subsequently, the corresponding global response of the semi-submersible under these two wave impacts are investigated in time domain. It reveals that compared with the incident wave, the relative wave elevation has a more straightforward relationship with the wave impact load. The relative wave crest height is associated with the spatial distribution of the wave impact load, while the local wave steepness matters more in the magnitude of the wave impact load. The impulsive effect of the wave impact load on the motion behaviors is not obvious. But severe wave impacts can introduce excessive horizontal accelerations and nonlinear behaviors like ringing in the acceleration response.

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