A Simple Numerical Method for Evaluation of Water Impact Loads on Decks of Large-Volume Offshore Platforms

2005 ◽  
Author(s):  
Rolf Baarholm
Keyword(s):  
Diffraction Analysis ◽  
Large Volume ◽  
Transfer Functions ◽  
Added Mass ◽  
Second Order ◽  
Suggested Method ◽  
Impact Loads ◽  
Water Impact ◽  
Simple Method ◽  
The Impact

A simple method for solving water impact loads underneath decks of offshore structures is developed. In the present paper the emphasis is on the vertical loads, but in principle the suggested method can also be applied to horizontal loading. The suggested method is three-dimensional and valid for general deck geometries and arbitrary incoming wave direction. First and second order wave amplification due to the large-volume structure is included in the analysis. An important feature of the present approach is that added mass of the instantaneous wetted deck area is approximated by the added mass of thin rectangular or elliptical plates. A numerical tool for solving the impact loads is implemented. This tool uses the results from an a priori second order diffraction analysis of the platform hull. In particular the wave-in-deck simulation program applies linear and quadratic transfer functions from the diffraction analysis as input. Since pre-computed hydrodynamic quantities are used in the simulations, very fast computations can be performed. The method is validated against experiments. Results from scaled model tests of the Statfjord A gravity-based structure (GBS) have been compared to numerical results. The comparisons are limited to regular waves. Satisfactory results are obtained from the numerical simulations. The theoretical results compare well with the experiments for the most severe cases. The vertical loads on the deck are well reproduced both during the water entry phase and the water exit phase. Moreover, the duration of the wave-in-deck event is satisfactorily predicted.

A Simplified Method of Water Impact on Elastic Plate in Early Stage

2016 ◽  
Author(s):  
Hua Sun ◽  
Deyu Wang
Keyword(s):  
Elastic Plate ◽  
Early Stage ◽  
Impact Loads ◽  
Arbitrary Lagrangian Eulerian ◽  
Water Impact ◽  
Flat Bottom ◽  
Initial Stage ◽  
Simplified Method ◽  
Bottom Structures ◽  
The Impact

For most flat-bottom marine structures, the impact loads are generated by complex transient coupling effects of solid, air and water. However, there are rare simplified forecasting methods to obtain the impact loads and dynamic response of the flat-bottom structures by considering both hydro elastic and air cushion effects. In the paper, a new simplified analysis method of water impact on the elastic plate is proposed referred to Verhagen’s model of the rigid plate. The analysis is focused on the initial stage during which the highest hydrodynamic loads are generated. The method simulates the interaction between the plate, the air and the water. Also, fluid-structure coupling results from the simplified method are compared to numerical results from Arbitrary Lagrangian–Eulerian method and experimental results to validate the feasibility and accuracy of this simplified method.

scholarly journals Evaluation of Water Impact For Symmetric Wedge by Experimental and Numerical Methods

2019 ◽  
Vol 24 (1) ◽  
pp. 221-230
Author(s):  
M. Nikfarjam ◽  
J. Koto ◽  
O.B. Yaakob ◽  
M.S. Seif ◽  
A. Aref
Keyword(s):  
Experimental Tests ◽  
Water Entry ◽  
Impact Loads ◽  
Water Impact ◽  
Wave Surface ◽  
Effective Parameters ◽  
Hydrodynamic Impact ◽  
Impact Speed ◽  
Marine Vehicles ◽  
The Impact

Abstract Evaluation of impact loads when a ship hull contacts the wave surface is one of the main issues for researchers who are going to design the structure of marine vehicles. In this paper, the results of experimental tests and numerical modeling of the distribution of pressure on different wedge-shaped models are reported and the effect of related parameters such as the deadrise angles, the weight and drop heights, is assessed. The output of analyses and the results can give appropriate approximations of the maximum impact pressures for the geometries that are similar to marine vehicle’s hull sections to estimate the hydrodynamic impact loads in different sea-states. In addition, other effective parameters such as the impact speed, acceleration and water entry process can be used for evaluating the performance of such crafts.

Second-Order Low-Frequency Wave Forces on a SPM Offloading Tanker in Shallow Water

2008 ◽  
Author(s):  
S. Ma ◽  
S. Shi ◽  
M. H. Kim
Keyword(s):  
Shallow Water ◽  
Transfer Functions ◽  
Low Frequency ◽  
Wave Force ◽  
Second Order ◽  
Dynamic Responses ◽  
Mooring Line ◽  
Wave Forces ◽  
Frequency Wave ◽  
The Impact

This paper studies the influence of three different calculation methods of the second-order low-frequency (LF) wave forces on the tanker responses and hawser/mooring tensions in relatively shallow water region. The vessel-mooring-riser coupled dynamic analysis computer program HARP is used to simulate the coupled dynamic responses of offloading tanker moored to a SPM (Single Point Mooring). Because the SPM is supposed to be deployed in shallow water and the slowly varying drift motions of the tanker are to dominate the motion responses in typical operational conditions, the accurate calculation of LF wave-force quadratic transfer functions (QTFs) becomes important especially for mooring and hawser tensions. Like common practice, the so-called Newman’s approximation and another approximation method without including complicated free-surface integrals are first used to calculate the LF QTFs on the offloading tanker and they are compared with the complete QTF results. Further comparison is performed by calculating the resulting LF wave-force spectra and response time series by using the three different methods. The impact of the three different approaches on vessel surge motions and hawser/mooring line tensions is also addressed.

A simple way for producing holographic filters suitable for image improvement

1978 ◽  
Vol 36 (1) ◽  
pp. 226-227
Author(s):  
K.-H. Herrmann ◽  
E. Reuber ◽  
P. Schiske
Keyword(s):  
Transfer Functions ◽  
Diffraction Order ◽  
Lateral Position ◽  
Simple Method ◽  
Spatial Frequencies ◽  
Resolution Electron ◽  
Wiener Filters ◽  
Image Improvement ◽  
Optical Reconstruction ◽  
Set Up

Aposteriori deblurring of high resolution electron micrographs of weak phase objects can be performed by holographic filters [1,2] which are arranged in the Fourier domain of a light-optical reconstruction set-up. According to the diffraction efficiency and the lateral position of the grating structure, the filters permit adjustment of the amplitudes and phases of the spatial frequencies in the image which is obtained in the first diffraction order.In the case of bright field imaging with axial illumination, the Contrast Transfer Functions (CTF) are oscillating, but real. For different imageforming conditions and several signal-to-noise ratios an extensive set of Wiener-filters should be available. A simple method of producing such filters by only photographic and mechanical means will be described here.A transparent master grating with 6.25 lines/mm and 160 mm diameter was produced by a high precision computer plotter. It is photographed through a rotating mask, plotted by a standard plotter.

Eating Behavior of Brazilian College Students: Influences of Lifestyle, Negative Affectivity, and Personal Characteristics

2020 ◽  
pp. 003151252098308
Author(s):  
Bianca G. Martins ◽  
Wanderson R. da Silva ◽  
João Marôco ◽  
Juliana A. D. B. Campos
Keyword(s):  
College Students ◽  
Eating Behavior ◽  
Emotional Eating ◽  
Eating Behaviors ◽  
Structural Model ◽  
Negative Affectivity ◽  
Personal Characteristics ◽  
Second Order ◽  
The Impact ◽  
The Relationship

In this study we proposed to estimate the impact of lifestyle, negative affectivity, and college students’ personal characteristics on eating behavior. We aimed to verify that negative affectivity moderates the relationship between lifestyle and eating behavior. We assessed eating behaviors of cognitive restraint (CR), uncontrolled eating (UE), and emotional eating (EE)) with the Three-Factor Eating Questionnaire-18. We assessed lifestyle with the Individual Lifestyle Profile, and we assessed negative affectivity with the Depression, Anxiety and Stress Scale-21. We constructed and tested (at p < .05) a hypothetical causal structural model that considered global (second-order) and specific (first-order) lifestyle components, negative affectivity and sample characteristics for each eating behavior dimension. Participants were 1,109 college students ( M age = 20.9, SD = 2.7 years; 65.7% females). We found significant impacts of lifestyle second-order components on negative affectivity (β = −0.57–0.19; p < 0.001–0.01) in all models. Physical and psychological lifestyle components impacted directly only on CR (β=−0.32–0.81; p < 0.001). Negative affectivity impacted UE and EE (β = 0.23–0.30; p < 0.001). For global models, we found no mediation pathways between lifestyle and CR or UE. For specific models, negative affectivity was a mediator between stress management and UE (β=−0.07; p < 0.001). Negative affectivity also mediated the relationship between thoughts of dropping an undergraduate course and UE and EE (β = 0.06–0.08; p < 0.001). Participant sex and weight impacted all eating behavior dimensions (β = 0.08–0.34; p < 0.001–0.01). Age was significant for UE and EE (β=−0,14– −0.09; p < 0.001–0.01). Economic stratum influenced only CR (β = 0.08; p = 0.01). In sum, participants’ lifestyle, negative emotions and personal characteristics were all relevant for eating behavior assessment.

scholarly journals Assessing an Atmospheric Correction Algorithm for Time Series of Satellite-Based Water-Leaving Reflectance Using Match-Up Sites in Australian Coastal Waters

2021 ◽  
Vol 13 (10) ◽  
pp. 1927
Author(s):  
Fuqin Li ◽  
David Jupp ◽  
Thomas Schroeder ◽  
Stephen Sagar ◽  
Joshua Sixsmith ◽  
...  
Keyword(s):  
Coastal Waters ◽  
Atmospheric Correction ◽  
Correction Method ◽  
In Situ Measurements ◽  
Landsat 8 ◽  
Correction Algorithm ◽  
Simple Method ◽  
North East ◽  
The Impact

An atmospheric correction algorithm for medium-resolution satellite data over general water surfaces (open/coastal, estuarine and inland waters) has been assessed in Australian coastal waters. In situ measurements at four match-up sites were used with 21 Landsat 8 images acquired between 2014 and 2017. Three aerosol sources (AERONET, MODIS ocean aerosol and climatology) were used to test the impact of the selection of aerosol optical depth (AOD) and Ångström coefficient on the retrieved accuracy. The initial results showed that the satellite-derived water-leaving reflectance can have good agreement with the in situ measurements, provided that the sun glint is handled effectively. Although the AERONET aerosol data performed best, the contemporary satellite-derived aerosol information from MODIS or an aerosol climatology could also be as effective, and should be assessed with further in situ measurements. Two sun glint correction strategies were assessed for their ability to remove the glint bias. The most successful one used the average of two shortwave infrared (SWIR) bands to represent sun glint and subtracted it from each band. Using this sun glint correction method, the mean all-band error of the retrieved water-leaving reflectance at the Lucinda Jetty Coastal Observatory (LJCO) in north east Australia was close to 4% and unbiased over 14 acquisitions. A persistent bias in the other strategy was likely due to the sky radiance being non-uniform for the selected images. In regard to future options for an operational sun glint correction, the simple method may be sufficient for clear skies until a physically based method has been established.

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