CFD Study of Air-Gap and Wave Impact Load on Semisubmersible Under Hurricane Conditions

2014 ◽  
Author(s):  
Sing-Kwan Lee ◽  
Kai Yu ◽  
Stanley Chenpey Huang
Keyword(s):  
Impact Load ◽  
Random Wave ◽  
Random Waves ◽  
Extreme Wave ◽  
Regular Waves ◽  
Wave Impact ◽  
Computational Fluid Dynamics Simulations ◽  
The Common ◽  
Run Up ◽  
Dynamics Simulations

CFD (Computational Fluid Dynamics) simulations of airgap and wave impact load on a semisubmersible under extreme wave conditions are performed in this study. Unlike the common practice, in which environmental waves are modeled as regular waves, a random wave series based on a JONSWAP spectrum for a 100-year return wave in the Gulf of Mexico is used to interact with a moored semisubmersible to simulate a more realistic environment condition. Wave run-up and impact loads on a moored semisubmersible due to both regular and random waves are computed and compared to investigate the influence of these different extreme waves on motion and impact load.

scholarly journals Time Scale for Scour Beneath Pipelines Due to Long-Crested and Short-Crested Nonlinear Random Waves Plus Current

2021 ◽  
Vol 9 (2) ◽  
pp. 114
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Time Scale ◽  
Current Flow ◽  
Irregular Waves ◽  
Wave Crest ◽  
Random Wave ◽  
Random Waves ◽  
Flow Conditions ◽  
Regular Waves ◽  
Nonlinear Random Waves ◽  
2D And 3D

This article derives the time scale of pipeline scour caused by 2D (long-crested) and 3D (short-crested) nonlinear irregular waves and current for wave-dominant flow. The motivation is to provide a simple engineering tool suitable to use when assessing the time scale of equilibrium pipeline scour for these flow conditions. The method assumes the random wave process to be stationary and narrow banded adopting a distribution of the wave crest height representing 2D and 3D nonlinear irregular waves and a time scale formula for regular waves plus current. The presented results cover a range of random waves plus current flow conditions for which the method is valid. Results for typical field conditions are also presented. A possible application of the outcome of this study is that, e.g., consulting engineers can use it as part of assessing the on-bottom stability of seabed pipelines.

Numerical Study of Air Gap Response and Wave Impact Load on a Moored Semi-Submersible Platform in Predetermined Irregular Wave Train

2010 ◽  
Author(s):  
Xiufeng Liang ◽  
Jianmin Yang ◽  
Longfei Xiao ◽  
Xin Li ◽  
Jun Li
Keyword(s):  
Impact Load ◽  
Numerical Study ◽  
Wave Train ◽  
Air Gap ◽  
Navier Stokes ◽  
Design Stage ◽  
Wave Impact ◽  
Irregular Wave ◽  
Run Up ◽  
Steep Waves

The importance of understanding air gap response and potential deck impact is well-known in the design stage of semi-submersible platform. The highly non-linear nature of wave elevation around large structures in steep waves makes it difficult to accurately predict wave field under the deck and wave run up along the columns. Present engineering tools for the prediction of air gap response generally based on simplified models. Even the models accounting for nonlinear wave diffraction is not free of uncertainties. A method adopted here couples a Navier-Stokes solver, VOF technique capturing violent free surface and DNV/Seasam predicting motions of moored semi-submersible platform. Air gap response at different locations of the hull was evaluated in predetermined irregular wave train. Wave run up was also measured by wave probes near the columns. Load cells were mounted under the deck of the platform to trace potential deck impact. The predetermined irregular wave train was simulated in a numerical wave tank and verified against physical tank results. Analysis of the air gap response, wave run up and impact loads on the semi-submersible platform were conducted.

scholarly journals THE DYNAMIC RESPONSE OF SHINGLE BEACHES TO RANDOM WAVES

1988 ◽  
Vol 1 (21) ◽  
pp. 130 ◽  
Author(s):  
K.A. Powell
Keyword(s):  
Field Data ◽  
Wave Reflection ◽  
Relative Magnitude ◽  
Random Wave ◽  
Random Waves ◽  
Wave Flume ◽  
Probabilistic Distribution ◽  
Laboratory Results ◽  
Run Up ◽  
Reflection Characteristics

An extensive laboratory investigation into the behaviour of shingle beaches has been undertaken using a large random wave flume. The study utilised a lightweight material scaled to reproduce the correct permeability of the beach, and the correct threshold and relative magnitude of the onshore/offshore movement. Results are presented describing both the wave reflection characteristics of the beach and the probabilistic distribution of wave run-up crests on the foreshore. Where possible the laboratory results are validated against field data.

Response of a Porous Seabed Under Random Wave Loading

2006 ◽  
Author(s):  
Haijiang Liu ◽  
Dong-S. Jeng
Keyword(s):  
Soil Parameters ◽  
Random Wave ◽  
Wave Loading ◽  
Random Waves ◽  
Regular Waves ◽  
Offshore Pipelines ◽  
Soil Response ◽  
Significant Difference ◽  
Wave Induced ◽  
Soil Responses

The evaluation of the wave-induced soil response is particularly important for many coastal engineering installations such as offshore pipelines, platforms and breakwaters. Most previous investigations have been limited to the linear regular wave loading, even though the real situation is under random waves. In this study, we propose a semi-analytical solution for the random wave-induced pore pressure and effective stresses in marine sediments. Based on the new analytical solutions, different soil responses under the random wave loading are investigated and compared with the corresponding results under the linear regular waves. Numerical examples demonstrate the significant difference on wave-induced seabed response between these two wave loadings due to the irregularity introduced by the random waves. Finally, the influence of several soil parameters on the soil response under random wave loading is also examined.

Random Extreme Wave Analysis of Deepwater Structures

1989 ◽  
Vol 111 (4) ◽  
pp. 331-336 ◽  
Author(s):  
C. Y. Chen ◽  
S. Armbrust ◽  
C. Llorente
Keyword(s):  
Second Harmonic ◽  
Response Spectrum ◽  
Wave Spectrum ◽  
Peak Frequency ◽  
Random Wave ◽  
Random Waves ◽  
Wave Analysis ◽  
Extreme Wave ◽  
Peak Response ◽  
Two Peaks

This paper reviews various wave analysis procedures for designing deepwater structures under an extreme seastate. The random wave analysis procedures suitable for fixed stiff platforms and compliant towers are discussed. The random wave analysis procedures are then applied to a 1350-ft water depth fixed platform. The reduction in design force levels due to random waves is indicated by comparing with the conventional regular wave analysis approach. The second harmonic effects due to waves can be easily identified through the dynamic response spectrum which has two peaks occurring at the peak frequency of the input wave spectrum and the natural frequency of the structure. The study also shows that the expected extreme value estimated based on the upcrossing approach agrees well with the snapshot peak response derived from a wave record containing an extreme wave height.

scholarly journals Random Wave-Induced Momentary Liquefaction around Rubble Mound Breakwaters with Submerged Berms

2020 ◽  
Vol 8 (5) ◽  
pp. 338
Author(s):  
Daniele Celli ◽  
Yuzhu Li ◽  
Muk Chen Ong ◽  
Marcello Di Risio
Keyword(s):  
Irregular Waves ◽  
Random Wave ◽  
Random Waves ◽  
Regular Waves ◽  
Peak Period ◽  
Soil Response ◽  
Minimum Number ◽  
Rubble Mound ◽  
Wave Induced ◽  
Rubble Mound Breakwaters

The effects of submerged berms in attenuating the momentary liquefaction beneath rubble mound breakwaters under regular waves were investigated in a recent study. The present work aims to investigate the momentary liquefaction probabilities around and beneath breakwaters with submerged berms under random waves. The interaction between waves and breakwaters with submerged berms has been simulated through a phase-resolving numerical model. The soil response to the seabed pressure induced by random waves has been investigated using a poro-elastic soil solver. For three different breakwater configurations, the liquefaction depths under random wave conditions have been compared with those cases under representative regular waves. In the present study, the offshore spectral wave height ( H m 0 ) and the peak period ( T p ) of irregular waves are used as representative regular wave parameters. Results reveal the importance of considering random waves for a safe estimation of the momentary liquefaction probability. Indication about the minimum number of random waves, which is required to properly catch the liquefaction occurrences, has been also addressed.

scholarly journals Aerodynamic analysis of uphill drafting in cycling

2021 ◽  
Vol 24 (1) ◽  
Author(s):  
T. van Druenen ◽  
B. Blocken
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Speed ◽  
Scientific Literature ◽  
Sensitivity Analyses ◽  
Air Resistance ◽  
Wind Tunnel Measurements ◽  
Aerodynamic Effect ◽  
Computational Fluid Dynamics Simulations ◽  
Dynamics Simulations

AbstractSome teams aiming for victory in a mountain stage in cycling take control in the uphill sections of the stage. While drafting, the team imposes a high speed at the front of the peloton defending their team leader from opponent’s attacks. Drafting is a well-known strategy on flat or descending sections and has been studied before in this context. However, there are no systematic and extensive studies in the scientific literature on the aerodynamic effect of uphill drafting. Some studies even suggested that for gradients above 7.2% the speeds drop to 17 km/h and the air resistance can be neglected. In this paper, uphill drafting is analyzed and quantified by means of drag reductions and power reductions obtained by computational fluid dynamics simulations validated with wind tunnel measurements. It is shown that even for gradients above 7.2%, drafting can yield substantial benefits. Drafting allows cyclists to save over 7% of power on a slope of 7.5% at a speed of 6 m/s. At a speed of 8 m/s, this reduction can exceed 16%. Sensitivity analyses indicate that significant power savings can be achieved, also with varying bicycle, cyclist, road and environmental characteristics.

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