Investigation and Prediction of Wave Impact Loads on Ship Appendage Shapes

2007 ◽  
Author(s):  
Anne M. Fullerton ◽  
Thomas C. Fu ◽  
David E. Hess
Keyword(s):  
Wave Height ◽  
Impact Force ◽  
Design Guidelines ◽  
Impact Loads ◽  
Wave Steepness ◽  
Wave Impact ◽  
Ship Structures ◽  
Impact Forces ◽  
Hull Structure ◽  
Horizontal Wave

Navy fleet problems with damage to hatches and other appendages after operation in high sea states suggest that wave impact loads may be greater than the current design guidelines of 1000 pounds per square foot (48 kilopascal) (Ship Specification Section 100, General Requirements for Hull Structure and Guidance Manual for Temporary Alterations, NAVSEA S9070-AA-MME-010/SSN, SSBN). These large impact forces not only cause damage to ships and ship structures, they can also endanger the ship’s crew. To design robust marine structures, accurate estimates of all encountered loads are necessary, including the wave impact forces, which are complex and involve wave breaking, making them difficult to estimate numerically. An experiment to investigate wave impact loads was performed at the Naval Surface Warfare Center, Carderock Division in 2005. During this experiment, the horizontal and vertical loads of regular, non-breaking waves on a 12 inch (0.305 m) square plate and a 19.75 inch (0.5 m) diameter horizontal cylinder were measured while varying incident wave height, wavelength, wave steepness, plate angle and immersion level of the plate and cylinder. Wave heights of up to 1.5 feet (0.46 m) were tested, with wavelenghs of up to 30 feet (9.1 m). In all cases, the horizontal wave impact force increased with wave steepness. For some angles, the horizontal wave impact force increased with greater submergence. A feed-forward neural network (FFNN) developed by Applied Simulation Technologies was used to predict the horizontal forces measured during the experiment based on the values of wave height, wavelength, wave steepness, plate angle and immersion level of the plate and cyclinder. A FFNN is a computational method used to develop nonlinear equation systems that use input variables to predict output variables. Predictions of forces from the FFNN compare well with the experimental data, and may be useful in future design of ships and ship structures.

Distribution of Wave Impact Forces From Breaking and Non-Breaking Waves

2009 ◽  
Author(s):  
Anne M. Fullerton ◽  
Thomas C. Fu ◽  
Edward S. Ammeen
Keyword(s):  
Free Surface ◽  
Wave Height ◽  
Breaking Waves ◽  
Qualitative Assessment ◽  
Total Force ◽  
Impact Loads ◽  
Wave Impact ◽  
Data Set ◽  
Wave Characteristics ◽  
Wide Range

Impact loads from waves on vessels and coastal structures are highly complex and may involve wave breaking, making these changes difficult to estimate numerically or empirically. Results from previous experiments have shown a wide range of forces and pressures measured from breaking and non-breaking waves, with no clear trend between wave characteristics and the localized forces and pressures that they generate. In 2008, a canonical breaking wave impact data set was obtained at the Naval Surface Warfare Center, Carderock Division, by measuring the distribution of impact pressures of incident non-breaking and breaking waves on one face of a cube. The effects of wave height, wavelength, face orientation, face angle, and submergence depth were investigated. A limited number of runs were made at low forward speeds, ranging from about 0.5 to 2 knots (0.26 to 1.03 m/s). The measurement cube was outfitted with a removable instrumented plate measuring 1 ft2 (0.09 m2), and the wave heights tested ranged from 8–14 inches (20.3 to 35.6 cm). The instrumented plate had 9 slam panels of varying sizes made from polyvinyl chloride (PVC) and 11 pressure gages; this data was collected at 5 kHz to capture the dynamic response of the gages and panels and fully resolve the shapes of the impacts. A Kistler gage was used to measure the total force averaged over the cube face. A bottom mounted acoustic Doppler current profiler (ADCP) was used to obtain measurements of velocity through the water column to provide incoming velocity boundary conditions. A Light Detecting and Ranging (LiDAR) system was also used above the basin to obtain a surface mapping of the free surface over a distance of approximately 15 feet (4.6 m). Additional point measurements of the free surface were made using acoustic distance sensors. Standard and high-speed video cameras were used to capture a qualitative assessment of the impacts. Impact loads on the plate tend to increase with wave height, as well as with plate inclination toward incoming waves. Further trends of the pressures and forces with wave characteristics, cube orientation, draft and face angle are investigated and presented in this paper, and are also compared with previous test results.

scholarly journals Wave Impact Loads on Vertical Seawalls: Effects of the Geometrical Properties of Recurve Retrofitting

Water ◽  
2021 ◽  
Vol 13 (20) ◽  
pp. 2849
Author(s):  
Shudi Dong ◽  
Md Salauddin ◽  
Soroush Abolfathi ◽  
Jonathan Pearson
Keyword(s):  
Impact Force ◽  
Vertical Wall ◽  
Impact Loads ◽  
Geometrical Shape ◽  
Wave Loading ◽  
Wave Impact ◽  
Static Loads ◽  
Geometrical Properties ◽  
Overhang Length ◽  
Overturning Moment

This study investigates the variation of wave impact loads with the geometrical configurations of recurve retrofits mounted on the crest of a vertical seawall. Physical model tests were undertaken in a wave flume at the University of Warwick to investigate the effects of the geometrical properties of recurve on the pressure distribution, overall force, and overturning moment at the seawall, subject to both impulsive and non-impulsive waves. Additionally, the wave impact and quasi-static loads on the recurve portion of the retrofitted seawalls are investigated to understand the role of retrofitting on the structural integrity of the vertical seawall. Detailed analysis of laboratory measurements is conducted to understand the effects of overhang length and height of the recurve wall on the wave loading. It is found that the increase in both recurve height and overhang length lead to the increase of horizontal impact force at an average ratio of 1.15 and 1.1 times larger the reference case of a plain vertical wall for the tested configurations. The results also show that the geometrical shape changes in recurve retrofits, increasing the overturning moment enacted by the wave impact force. A relatively significant increase in wave loading (both impact and quasi-static loads) are observed for the higher recurve retrofits, while changes in the overturning moment are limited for the retrofits with longer overhang length. The data generated from the physical modelling measurements presented in this study will be particularly helpful for a range of relevant stakeholders, including coastal engineers, infrastructure designers, and the local authorities in coastal regions. The results of this study can also enable scientists to design and develop robust decision support tools to evaluate the performance of vertical seawalls with recurve retrofitting.

Prediction of Wave-in-Deck Forces on Fixed Jacket-Type Structures Based on CFD Calculations

2008 ◽  
Author(s):  
Benedicte Brodtkorb
Keyword(s):  
Initial Phase ◽  
Central Element ◽  
Load Level ◽  
Impact Loads ◽  
Extreme Waves ◽  
Original Design ◽  
Wave Impact ◽  
Cfd Simulations ◽  
Simplified Method ◽  
Horizontal Wave

The original design requirement for positive air gap is no longer fulfilled for a number of jacket-type structures still in production. When extreme waves impact the deck, the total loads on the structure are increased significantly, so accurate prediction of wave-in-deck forces is a central element in structural reassessment. Simplified methods for evaluating maximum horizontal and vertical loads are useful in an initial phase. In this study, we compare numerical prediction using CFD with the simplified API method for horizontal wave-in-deck load. The global wave impact loads for 0° head-on and 45° oblique waves are calculated for various deck configurations, all heavily equipped (solid). The effect of current is also addressed. In the case of no current, we found that the CFD simulations generally display a reasonable load level compared with the API load method. However, the CFD calculations indicate that the simplified method should be used with care for situations with large upwelling of water and decks with multiple deck girders. A simplified method for predicting vertical wave-in-deck loads on solid decks is developed. The method, first published in DNV-RP-C205, aims to be useful in an initial phase of reassessment.

An Evaluation of Wave Impact Indicators

2009 ◽  
Author(s):  
Zhigang Tian
Keyword(s):  
Wave Breaking ◽  
Offshore Structures ◽  
Phase Method ◽  
Impact Loads ◽  
Wave Steepness ◽  
Wave Load ◽  
Wave Impact ◽  
Large Wave ◽  
Impact Indicators ◽  
Local Wave

Wave impact on offshore structures has been the focus of several studies, due to its significant effect on offshore operations. We evaluate several parameters (wave impact indicators) which can be adopted to indicate the possibility of wave impact on offshore structures due to extreme waves. The indicators can be estimated quickly with given sea states, and thus may provide useful information to offshore structure designers at early design phases. Definitions of three wave impact indicators are presented and discussed. The first indicator, Ψ, is proposed by Stansberg (2008). The second one considered is a wave breaking parameter, μ, originally presented by Song and Banner (2002) in their construction of a wave breaking criterion. Finally, we propose a more generalized impact indicator, βn. The subscript n indicates its dependence on local wave steepness. Our study demonstrates that the three indicators are analytically related. To evaluate these indicators numerically, 2nd order random surface waves are generated with random phase method and Two-Dimensional Fast Fourier Transform (2D FFT). Hilbert analysis of the wave signal reveals that all indicators are able to identify steep and energetic waves that may potentially cause large wave impact loads. Further numerical study demonstrates that the quantitative correlation of wave impact loads to μ is less promising than that to Ψ and βn; while βn provides the best relationship to both local wave impact load and global wave load with its dependence on local wave steepness adjusted (i.e. adjusting n). The correlation is independent of sea states. Estimations and recommendations for thresholds of the two impact indicators (i.e. Ψ and βn with n = 1) are made based on model test results. With proper estimation of the thresholds, both indicators can be applied to predict wave impact and wave impact probability in given sea states.

Transducer Qualification for Wave Impact Load Measurements Using Wedge Drop Tests

2015 ◽  
Author(s):  
Zhenjia (Jerry) Huang ◽  
Robert Oberlies ◽  
Don Spencer ◽  
Jang Kim
Keyword(s):  
Impact Load ◽  
Research Work ◽  
Offshore Structures ◽  
Model Tests ◽  
Impact Loads ◽  
Dynamic Impact ◽  
Wave Impact ◽  
Impact Forces ◽  
Industry Practice ◽  
Drop Tests

For the design of offshore structures in harsh wave environments, it is essential to accurately determine the wave impact loads on the structure. To date, robust numerical prediction methods / algorithms for determining wave impact forces on offshore structures do not exist. Model testing continues to be the industry practice for determining wave impact forces on offshore structures. Accurate measurements of wave impact loads in model tests have been challenging for several decades. Transducers require the ability to capture the short duration, dynamic nature and high magnitude of impact loads. In order to qualify transducers for these types of measurements, we need to develop a way to physically impose dynamic impact loads on the transducers and to establish benchmark values that can be used to check the effectiveness of their measurements. In this paper, we present our recent research work on transducer qualification for wave impact load measurements, including their development, numerical analysis and wedge drop model tests. Our findings show that wedge drop tests can be used to impose dynamic impact loads for transducer qualification, and that the Wagner solution and / or validated computational fluid dynamics (CFD) simulations that include the effects of viscosity, compressibility and hydroelasticity can provide the appropriate benchmarking values. Numerical simulation results, model test measurements and findings on transducer qualification are presented and discussed in the paper.

scholarly journals Hydroelasticity effects on water-structure impacts

2020 ◽  
Vol 61 (9) ◽  
Author(s):  
T. Mai ◽  
C. Mai ◽  
A. Raby ◽  
D. M. Greaves
Keyword(s):  
Vertical Wall ◽  
Water Structure ◽  
Rigid Wall ◽  
Total Force ◽  
Impact Loads ◽  
Wave Impact ◽  
Impact Forces ◽  
Elastic Wall ◽  
Vertical Walls ◽  
The Impact

Abstract Local and global loadings, which may cause the local damage and/or global failure and collapse of offshore structures and ships, are experimentally investigated in this study. The research question is how the elasticity of the structural section affects loading during severe environmental conditions. Two different experiments were undertaken in this study to try to answer this question: (i) vertical slamming impacts of a square flat plate, which represents a plate section of the bottom or bow of a ship structure, onto water surface with zero degree deadrise angle; (ii) wave impacts on a truncated vertical wall in water, where the wall represents a plate section of a hull. The plate and wall are constructed such that they can be either rigid or elastic by virtue of a specially designed spring system. The experiments were carried out in the University of Plymouth’s COAST Laboratory. For the cases considered here, elasticity of the impact plate and/or wall has an effect on the slamming and wave impact loads. Here the slamming impact loads (both pressure and force) were considerably reduced for the elastic plate compared to the rigid one, though only at high impact velocities. The total impact force on the elastic wall was found to reduce for the high aeration, flip-through and slightly breaking wave impacts. However, the impact pressure decreased on the elastic wall only under flip-through wave impact. Due to the elasticity of the plates, the impulse of the first positive phase of pressure and force decreases significantly for the vertical slamming impact tests. This significant effect of hydroelasticity is also found for the total force impulse on the vertical wall under wave impacts. Graphic abstract Hydroelasticity effects on water-structure impacts: a impact pressures on dropped plates; b impact forces on dropped plates; c, d, e, f wave impact pressures on the vertical walls; g wave impact forces on the vertical walls; h wave force impulses on the vertical walls: elastic wall 1 vs. rigid wall (filled markers); elastic wall 2 vs. rigid wall (empty markers)

Processing method and governing parameters for horizontal wave impact loads on a semi-submersible

2020 ◽  
Vol 69 ◽  
pp. 102673 ◽  
Author(s):  
Yinghao Guo ◽  
Longfei Xiao ◽  
Xiaoqing Teng ◽  
Yufeng Kou ◽  
Jiancheng Liu
Keyword(s):  
Processing Method ◽  
Impact Loads ◽  
Wave Impact ◽  
Horizontal Wave

Experimental Evaluation of Wave Impact Loads on Semi-Submersible Structure According to Trim Angle

2019 ◽  
Author(s):  
Min-Guk Seo ◽  
Yoon-Jin Ha ◽  
Nam-Woo Kim ◽  
Bo Woo Nam ◽  
Kang-Su Lee
Keyword(s):  
Experimental Test ◽  
Experimental Evaluation ◽  
Impact Force ◽  
Impact Load ◽  
Impact Loads ◽  
Test Model ◽  
Wave Impact ◽  
Wave Flume ◽  
Wave Elevation ◽  
Series Of Experiments

Abstract This study considers the wave impact loads on the semi-submersible structure. To evaluate wave impact loads on the semi-submersible structure, a series of experiments are conducted in a 2D wave flume. In the experimental test, the semi-submersible half model is used, and 11 uniaxial force sensors are installed in deck side, column side, and deck bottom. Wave probes are, also, attached in the test model to measure the relative wave elevation. To generate horizontal and bottom wave impact on the test model, focusing wave is applied. The test model is fixed without any motion during each test, while the trim angle of the test model is changed to examine the effect of trim angle on wave impact load. Through this, the characteristics of the wave impact force at each position were investigated.

Experimental and Numerical Study of Horizontal Wave Impact Loads for a Semi-Submersible Drilling Unit

2019 ◽  
Author(s):  
Joo-Sung Kim ◽  
Seon Oh Yoo ◽  
Hyun Joe Kim ◽  
Jong Hun Lee ◽  
So Lyoung Han ◽  
...  
Keyword(s):  
Cfd Simulation ◽  
Numerical Study ◽  
Vertical Direction ◽  
Maximum Pressure ◽  
Impact Loads ◽  
Wave Impact ◽  
Vertical Side ◽  
Horizontal Wave ◽  
Drilling Unit ◽  
Run Up

Abstract A semi-submersible drilling unit model was tested to estimate horizontal wave impact loads on vertical side of deckbox following the procedure recommended by DNVGL OTG-14. The present model test data show that there is clear difference in the relationships between upwell and horizontal wave impact pressure between near column/pontoon and around centerline. Near column and pontoon, not only is the maximum pressure much lower but the pressure increases more smoothly to its maximum value, compared to those of centerline. CFD simulations with focusing breaking waves have been made to examine the effect of wave-body interaction on horizontal wave impact on deck-box. The present CFD simulation results clearly show that the flows in front of column are strongly accelerated in vertical direction by blocking effect of column and pontoon, eventually producing strong run-up jets. The run-up jets in the present study are so strong that the direct impact of the incoming breaker on the wall does not occur, which leads to much smaller peak pressures, compared to those of centerline.

scholarly journals Wave Impact Pressures on Stepped Revetments

2018 ◽  
Vol 6 (4) ◽  
pp. 156 ◽  
Author(s):  
Nils Kerpen ◽  
Talia Schoonees ◽  
Torsten Schlurmann
Keyword(s):  
Probability Distribution ◽  
Vertical Axis ◽  
Step Height ◽  
Impact Loads ◽  
Wave Impact ◽  
Wave Flume ◽  
Horizontal Wave ◽  
Normal Probability Distribution ◽  
Log Normal ◽  
The Impact

The wave impacts on horizontal and vertical step fronts of stepped revetments is investigated by means of hydraulic model tests conducted with wave spectra in a wave flume. Wave impacts on revetments with relative step heights of 0.3 < Hm0/Sh < 3.5 and a constant slope of 1:2 are analyzed with respect to (1) the probability distribution of the impacts, (2) the time evolution of impacts including a classification of load cases, and (3) a special distribution of the position of the maximum impact. The validity of the approved log-normal probability distribution for the largest wave impacts is experimentally verified for stepped revetments. The wave impact properties for stepped revetments are compared with those of vertical seawalls, showing that their impact rising times are within the same range. The impact duration for stepped revetments is shorter and decreases with increasing step height. Maximum horizontal wave impact loads are about two times larger than the corresponding maximum vertical wave impact loads. Horizontal and vertical impact loads increase with a decreasing step height. Data are compared with findings from literature for stepped revetments and vertical walls. A prediction formula is provided to calculate the maximum horizontal wave impact at stepped revetments along its vertical axis.

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