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-driven drag forces on near-bed vegetation in shallow water based on deepwater wind conditions

2019 ◽  
Vol 233 (4) ◽  
pp. 1287-1290
Author(s):  
Dag Myrhaug
Keyword(s):  
Shallow Water ◽  
Drag Force ◽  
Wind Waves ◽  
Wave Spectrum ◽  
Random Wave ◽  
Random Waves ◽  
Coastal Zones ◽  
Drag Forces ◽  
Mean Wind Speed ◽  
Wave Induced

This article provides a simple analytical method for giving estimates of random wave-driven drag forces on near-bed vegetation in shallow water from deepwater wind conditions. Results are exemplified using a Pierson–Moskowitz model wave spectrum for wind waves with the mean wind speed at the 10 m elevation above the sea surface as the parameter. The significant value of the drag force within a sea state of random waves is given, and an example typical for field conditions is presented. This method should serve as a useful tool for assessing random wave-induced drag force on vegetation in coastal zones and estuaries based on input from deepwater wind conditions.

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.

Parameterization for Nonlinearity of Random Waves Over Slopes

2013 ◽  
Author(s):  
Hongzhou Chen ◽  
Guohai Dong ◽  
Yuxiang Ma
Keyword(s):  
Coastal Region ◽  
Least Square Method ◽  
Peak Frequency ◽  
Least Square ◽  
Wave Transformation ◽  
Random Wave ◽  
Random Waves ◽  
Nonlinear Characteristics ◽  
Wave Flume ◽  
Physical Experiments

Nonlinearity of gravity waves in coastal region plays crucial role in the wave evolution and the sediment transport. Parameterization of the nonlinear characteristics of random waves is an efficient and important way to descript the wave process. It is well known that coastal topography has a key effect on the wave transformation. However, the related previous studies have ignored the slope effects. It is the primary motivation of the research. To implement this aim, physical experiments of random waves propagating over three slopes (1/15, 1/30, 1/45) were carried out in a wave flume with 50m long, 3m wide and used with a water depth of 0.52m. About 20 random wave simulations based on JONSWAP spectra with varying wave height and peak frequency were considered. The wavelet based bispectrum is adopted to obtain the nonlinear parameters, bicoherence, biphase, skewness and asymmetry. On each slope bottoms, several empirical relationships between these parameters and the local Ursell number are derived using the least square method. The results indicate that the bicoherence and the asymmetry of waves relate to the slope. However, the slopes have negligible effect on the formulae of the skewness. Then, the empirical formulae on the bicoherence and asymmetry combining with the bottom slope are constructed.

scholarly journals DIFFRACTION DIAGRAMS FOR DIRECTIONAL RANDOM WAVES

1978 ◽  
Vol 1 (16) ◽  
pp. 35 ◽  
Author(s):  
Yoshimi Goda ◽  
Tomotsuka Takayama ◽  
Tasumasa Suzuki
Keyword(s):  
Wave Diffraction ◽  
Spectral Characteristics ◽  
Wave Spectrum ◽  
Standard Form ◽  
Random Wave ◽  
Random Waves ◽  
Directional Spectrum ◽  
Spreading Function ◽  
Wave Heights ◽  
Directional Wave

Conventional wave diffraction diagrams often yield erroneous estimation of wave heights behind breakwaters in the sea, because they are prepared for monochromatic waves while actual waves in the sea are random with directional spectral characteristics. A proposal is made for the standard form of directional wave spectrum on the basis of Mitsuyasu's formula for directional spreading function. A new set of diffraction diagrams have been constructed for random waves with the proposed directional spectrum. Problems of multi-diffraction and multi-reflection within a harbour can also be solved with serial applications of random wave diffraction.

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.

Estimates of Surface Waves Using Subsurface EM-APEX Floats under Typhoon Fanapi 2010

2018 ◽  
Vol 35 (5) ◽  
pp. 1053-1075 ◽  
Author(s):  
Je-Yuan Hsu ◽  
Ren-Chieh Lien ◽  
Eric A. D’Asaro ◽  
Thomas B. Sanford
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Wave Spectrum ◽  
Nonlinear Least Squares ◽  
Peak Frequency ◽  
Wave Propagation Direction ◽  
Model Studies ◽  
Surface Wave Propagation ◽  
Left Quadrant ◽  
Field Inclination

AbstractSeven subsurface Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats measured the voltage induced by the motional induction of seawater under Typhoon Fanapi in 2010. Measurements were processed to estimate high-frequency oceanic velocity variance associated with surface waves. Surface wave peak frequency fp and significant wave height Hs are estimated by a nonlinear least squares fitting to , assuming a broadband JONSWAP surface wave spectrum. The Hs is further corrected for the effects of float rotation, Earth’s geomagnetic field inclination, and surface wave propagation direction. The fp is 0.08–0.10 Hz, with the maximum fp of 0.10 Hz in the rear-left quadrant of Fanapi, which is ~0.02 Hz higher than in the rear-right quadrant. The Hs is 6–12 m, with the maximum in the rear sector of Fanapi. Comparing the estimated fp and Hs with those assuming a single dominant surface wave yields differences of more than 0.02 Hz and 4 m, respectively. The surface waves under Fanapi simulated in the WAVEWATCH III (ww3) model are used to assess and compare to float estimates. Differences in the surface wave spectra of JONSWAP and ww3 yield uncertainties of <5% outside Fanapi’s eyewall and >10% within the eyewall. The estimated fp is 10% less than the simulated before the passage of Fanapi’s eye and 20% less after eye passage. Most differences between Hs and simulated are <2 m except those in the rear-left quadrant of Fanapi, which are ~5 m. Surface wave estimates are important for guiding future model studies of tropical cyclone wave–ocean interactions.

Extreme wave analysis methods in the gulf of Cagliari (South Sardinia, Italy)

2017 ◽  
Vol 140 ◽  
pp. 79-87 ◽  
Author(s):  
Andrea Sulis ◽  
Riccardo Cozza ◽  
Antonio Annis
Keyword(s):  
Wave Analysis ◽  
Extreme Wave ◽  
Analysis Methods

Evaluation Method for Seismic Fatigue Damage of Plant Pipeline

2019 ◽  
Vol 141 (2) ◽  
Author(s):  
Fumio Inada ◽  
Michiya Sakai ◽  
Ryo Morita ◽  
Ichiro Tamura ◽  
Shin-ichi Matsuura ◽  
...  
Keyword(s):  
Fatigue Damage ◽  
Nuclear Power ◽  
Power Plants ◽  
Evaluation Method ◽  
Response Spectrum ◽  
Damage Mechanism ◽  
Peak Frequency ◽  
Cumulative Damage ◽  
Cumulative Absolute Velocity ◽  
Seismic Index

Although acceleration and cumulative absolute velocity (CAV) are used as seismic indexes, their relationship with the damage mechanism is not yet understood. In this paper, a simplified evaluation method for seismic fatigue damage, which can be used as a seismic index for screening, is derived from the stress amplitude obtained from CAV for one cycle in accordance with the velocity criterion in ASME Operation and Maintenance of Nuclear Power Plants 2012, and the linear cumulative damage due to fatigue can be obtained from the linear cumulative damage rule. To verify the performance of the method, the vibration response of a cantilever pipe is calculated for four earthquake waves, and the cumulative fatigue damage is evaluated using the rain flow method. The result is in good agreement with the value obtained by the method based on the relative response. When the response spectrum obtained by the evaluation method is considered, the value obtained by the evaluation method has a peak at the peak frequency of the ground motion, and the value decreases with increasing natural frequency above the peak frequency. A higher peak frequency of the base leads to a higher value obtained by the evaluation method.

scholarly journals Performance of Linear Generator Designs for Direct Drive Wave Energy Converter under Unidirectional Long-Crested Random Waves

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 5098
Author(s):  
Budi Azhari ◽  
Fransisco Danang Wijaya ◽  
Edwar Yazid
Keyword(s):  
Output Power ◽  
Wave Height ◽  
Wave Energy ◽  
Significant Wave Height ◽  
Analytical Calculation ◽  
Weight Ratio ◽  
Peak Frequency ◽  
Random Waves ◽  
Direct Drive ◽  
Significant Wave

For generating electricity, direct-drive wave energy converters (WECs) with linear permanent magnet generators (LPMGs) have advantages in terms of efficiency, simplicity, and force-to-weight ratio over WEC with rotary generators. However, the converter’s work under approaching-real wave conditions should be investigated. This paper studies the performance of a pico-scale WEC with two different LPMGs under unidirectional long-crested random waves. Different significant wave heights (using data in the Southern Ocean of Yogyakarta, Indonesia) and peak frequencies are tested. The JONSWAP energy spectrum is used to extract the wave elevations, while the MSS toolbox in MATLAB Simulink is employed to solve the floater’s dynamic responses. Next, the translator movements are extracted and combined with the flux distribution from FEMM simulation and analytical calculation, and the output powers are obtained. An experiment is conducted to test the output under constant speed. The results show for both designs, different tested significant wave height values produce higher output powers than peak frequency variation, but there is no specific trend on them. Meanwhile, the peak frequency is inversely proportional to the output power. Elimination of the non-facing events results in increasing output power under both parameters’ variation, with higher significant wave height resulting in a bigger increase. The semi iron-cored LPMG produces lower power loss and higher efficiency.

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