Hydrodynamic Aspects on Vulnerability Criteria for Surf-Riding of Ships

2014 ◽  
Vol 66 (2) ◽  
Author(s):  
Yuto Ito ◽  
Naoya Umeda ◽  
Hisako Kubo
Keyword(s):  
Empirical Formula ◽  
Global Bifurcation ◽  
Quantitative Agreement ◽  
Hydrodynamic Theory ◽  
Safety Level ◽  
Slender Body Theory ◽  
Model Experiments ◽  
Intact Stability ◽  
Surf Riding ◽  
Wave Induced

For developing the International Maritime Organization (IMO) second-generation intact stability criteria regarding broaching, draft vulnerability criteria for surf-riding were agreed at the IMO in 2012. This paper describes their hydrodynamic backgrounds with captive model experiments for seven ships, a hydrodynamic theory and a random process theory. In the first level vulnerability criteria, a ship is required to reduce her Froude number of less than 0.3 in case of severe following waves. For predicting the surf-riding threshold in a global bifurcation theory, it is necessary to precisely estimate wave-induced surge force. Thus, the authors execute captive model experiments for three ships in model basins. As a result, we confirmed that the Froude-Krylov calculation overestimates the amplitude of wave-induced surge force so that an empirical formula for regulatory application is presented. For investigating the reason of this discrepancy, a slender body theory assuming low encounter frequency is applied to the situation where a ship runs with a wave. This theory suggests that change of wave-making resistance due to incident wave could reduce the amplitude of the wave-induced surge force and quantitative agreement with model experiment requires the use of CFD or an empirical formula. Thus, the authors can recommend the use of experimental correction formula for the vulnerability criteria. Based on sample calculation results of surf-riding probability of six ships in the North Atlantic, the safety level to be required in the criteria is proposed.

THE INFLUENCE OF CENTRE BOW LENGTH ON SLAMMING LOADS AND MOTIONS OF LARGE WAVE-PIERCING CATAMARANS

2021 ◽  
Vol 160 (A1) ◽  
Author(s):  
J R Shahraki ◽  
G A Thomas ◽  
M R Davis
Keyword(s):  
Wave Height ◽  
Full Scale ◽  
Bending Moments ◽  
Regular Waves ◽  
Large Wave ◽  
Towing Tank ◽  
Segmented Model ◽  
Model Experiments ◽  
Slamming Load ◽  
Wave Induced

The effect of various centre bow lengths on the motions and wave-induced slamming loads on wave-piercing catamarans is investigated. A 2.5 m hydroelastic segmented model was tested with three different centre bow lengths and towed in regular waves in a towing tank. Measurements were made of the model motions, slam loads and vertical bending moments in the model demi-hulls. The model experiments were carried out for a test condition equivalent to a wave height of 2.68 m and a speed of 20 knots at full scale. Bow accelerations and vertical bending moments due to slamming showed significant changes with the change in centre bow, the longest centre bow having the highest wave-induced loads and accelerations. The increased volume of displaced water which is constrained beneath the bow archways is identified as the reason for this increase in the slamming load. In contrast it was found that the length of centre bow has a relatively small effect on the heave and pitch motions in slamming conditions.

Experimental Research on the Surf-Riding Region for High Speed Vessels

2015 ◽  
Author(s):  
Atsuo Maki ◽  
Yoshiki Miyauchi
Keyword(s):  
Experimental Research ◽  
High Speed ◽  
Safety Assessment ◽  
Estimation Methods ◽  
Model Experiments ◽  
Size Limitation ◽  
Analytical Estimation ◽  
Free Running ◽  
Surface Combatant ◽  
Surf Riding

It is well known that surf-riding phenomenon is the prerequisite of the broaching-to in following and quartering conditions. For the safety assessment of the fast vessel such as surface combatant sand patrol crafts, the estimation of the surf-riding condition is important. Therefore, so far several experimental efforts have been made. However, in these previous researches, the free running model experiments in high speed region, i.e.up to Froude number of 0.6 or 0.7, have not been conducted because of tank size limitation. As shown in this paper, there are occurrence and disappearance boundaries of surf-riding in lower and faster region, respectively. In our study, free running model experiments are carried out in high speed region, and then both boundaries are experimentally obtained. By using obtained results, the analytical estimation methods proposed by the authors can be well validated. Furthermore, the free running model experiments in irregular seas are also conducted. Then, surf-riding phenomenon in irregular seas is also discussed.

Numerical Simulation and Experimental Validation on the Surf-Riding and Broaching of a Fishing Vessel

2016 ◽  
Author(s):  
Liwei Yu ◽  
Ning Ma ◽  
Sheming Fan ◽  
Peiyuan Feng ◽  
Xiechong Gu
Keyword(s):  
Numerical Simulation ◽  
Numerical Simulations ◽  
Model Test ◽  
Periodic Motion ◽  
Following Seas ◽  
Weakly Nonlinear ◽  
Model Experiments ◽  
Time Histories ◽  
Wave Heights ◽  
Surf Riding

Model experiments and numerical simulations on the surf-riding and broaching in following seas of a 42.5m long purse seiner are conducted. Firstly, the free running model experiments with various ship speeds and wave heights are performed in the towing tank to reproduce the phenomena of surf-riding and broaching. Then, the 6-DOF weakly nonlinear unified model is applied to simulate the motions of the purse seiner with the same cases as the model experiments. Through the comparison between results of model test and numerical simulation, the occurrence conditions of periodic motion, surf-riding and broaching are roughly determined. Finally, it is found that although it is difficult for the numerical simulations to get the same time histories as model tests, the modes of motion (periodic motion, surf-riding or broaching) obtained from the numerical simulations agree well qualitatively and quantitatively in part with the model test results.

A boundary-element analysis of flagellar propulsion

1987 ◽  
Vol 184 ◽  
pp. 533-549 ◽  
Author(s):  
N. Phan-Thien ◽  
T. Tran-Cong ◽  
M. Ramia
Keyword(s):  
Boundary Element ◽  
Cell Body ◽  
Quantitative Agreement ◽  
Optimum Number ◽  
Element Analysis ◽  
Slender Body Theory ◽  
Aspect Ratios ◽  
Optimal Value ◽  
Micro Organisms ◽  
Body Theory

The swimming of a flagellar micro-organism by the propagation of helical waves along its flagellum is analysed by a boundary-element method. The method is not restricted to any particular geometry of the organism nor does it assume a specific wave motion for the flagellum. However, only results for an organism with a spherical or ellipsoidal cell body and a helically beating flagellum are presented here.With regard to the flagellum, it is concluded that the optimum helical wave (amplitude α and wavenumber k) has αk ≈ 1 (pitch angle of 45°) and that for the optimum flagellar length L/A = 10 (L being the flagellar length, A being the radius of the assumed spherical cell body) the optimum number of wavelengths Nλ is about 1.5. Furthermore there appears to be no optimal value for the flagellar radius a, with the thinner flagella being favoured. These conclusions show excellent quantitative agreement with those of slender-body theory.For the case of an ellipsoidal cell body, the optimum aspect ratios B/A and C/A of the ellipsoid are about 0.7 and 0.3 respectively; A, B and C are the principal radii of the ellipsoid. These and all of the above conclusions show good qualitative agreement with experimental observations of efficiently swimming micro-organisms.

scholarly journals A Time-Domain Simulation for Predicting the Downwind Performance of Yachts in Waves

2001 ◽  
Author(s):  
Dougal Harris ◽  
Giles Thomas ◽  
Martin Renilson
Keyword(s):  
Aerodynamic Force ◽  
Wave Force ◽  
Longitudinal Force ◽  
Design Tool ◽  
Resistance Force ◽  
Following Seas ◽  
Model Experiments ◽  
Free Running ◽  
America’S Cup ◽  
Wave Induced

Yachts racing in many of today's high profile races, such as the America's Cup and the Volvo Ocean Race, spend much time sailing downwind in following seas. The development of a method for predicting the performance of yachts sailing downwind in waves would therefore provide a valuable design tool for racing yacht designers. This paper describes the development of a time­domain simulation for predicting the performance of yachts sailing in irregular seas for apparent wind angles between 90 and 180 degrees. The simulation output may be used to either directly compare different designs or augment existing polar plots for the effect of a following sea. The simulation is comprised of three main modules: the wave induced longitudinal force, the resistance force and the sail aerodynamic force. The resistance and wave force modules have been validated through semi-captive model experiments. Results from the complete simulation have been compared with those obtained from free running model experiments. Numerical experiments on a number of hull and rig configurations have been conducted using the simulation. Results are presented with conclusions being drawn on the effect of hull form and environmental conditions on downwind performance.

The Influences of Centre Bow Length on Slamming Loads and Motions of Large Wave-Piercing Catamarans

2018 ◽  
Vol Vol 160 (A1) ◽  
Author(s):  
J R Shahraki ◽  
G A Thomas ◽  
M R Davis
Keyword(s):  
Wave Height ◽  
Full Scale ◽  
Bending Moments ◽  
Regular Waves ◽  
Large Wave ◽  
Towing Tank ◽  
Segmented Model ◽  
Model Experiments ◽  
Slamming Load ◽  
Wave Induced

The effect of various centre bow lengths on the motions and wave-induced slamming loads on wave-piercing catamarans is investigated. A 2.5 m hydroelastic segmented model was tested with three different centre bow lengths and towed in regular waves in a towing tank. Measurements were made of the model motions, slam loads and vertical bending moments in the model demi-hulls. The model experiments were carried out for a test condition equivalent to a wave height of 2.68 m and a speed of 20 knots at full scale. Bow accelerations and vertical bending moments due to slamming showed significant changes with the change in centre bow, the longest centre bow having the highest wave-induced loads and accelerations. The increased volume of displaced water which is constrained beneath the bow archways is identified as the reason for this increase in the slamming load. In contrast it was found that the length of centre bow has a relatively small effect on the heave and pitch motions in slamming conditions.

Study on the IMO Second Generation Intact Stability Criteria of Surf-riding/Broaching Failure Mode

2015 ◽  
Author(s):  
Peiyuan Feng ◽  
Xingrong Shen ◽  
Sheming Fan
Keyword(s):  
Failure Mode ◽  
Model Experiment ◽  
Ship Design ◽  
Sensitivity Analyses ◽  
Numerical Code ◽  
Stability Criteria ◽  
Intact Stability ◽  
Free Running ◽  
Surf Riding ◽  
Potential Impact

A series of investigations on the vulnerability criteria for the surf-riding/broaching stability failure mode is conducted. First and foremost, free running model experiment of a purse seiner in severe following waves is performed to demonstrate the fatalness of surf-riding/broaching. The latest IMO proposal to assess broaching stability failure mode is then studied in detail. A numerical code with user interface is developed to facilitate sensitivity analyses and sample ship calculations. The appropriateness of the proposal is analyzed and its potential impact on ship design is discussed.

FULL SCALE OIL CONTAINMENT BOOM TESTING AT SEA

1995 ◽  
Vol 1995 (1) ◽  
pp. 31-38 ◽  
Author(s):  
Atle Nordvik ◽  
Paul Hankins ◽  
Ken Bitting ◽  
Larry Hannon ◽  
Robert Urban
Keyword(s):  
New York ◽  
Atlantic Ocean ◽  
Empirical Formula ◽  
Quantitative Data ◽  
Coast Guard ◽  
Hydrodynamic Theory ◽  
Management Service ◽  
Calculation Methods ◽  
The Mean ◽  
The U.S

ABSTRACT In May 1994 the Marine Spill Response Corporation, U.S. Coast Guard, U.S. Navy, and Minerals Management Service conducted a joint test of oil containment booms in Lower New York Bay and in the Atlantic Ocean east of Sandy Hook New Jersey. These tests allowed the collection of quantitative data on boom performance, including tow forces, skirt draft, and boom freeboard, as a function of tow speed and environmental forces due to currents, wind, and waves. Four booms were chosen for testing based on their different physical characteristics: The 3M Fire Boom, the Barrier Boom, the USCG/Oil Stop inflatable boom, and the U.S. Navy USS-42 boom. Use of these booms allowed data acquisition over a range of buoyancy to weight ratios from 5:1 up to 52:1, nominal skirt drafts from 61 cm up to 150 cm, and freeboards from 37 cm up to 119 cm. The data collected allows a comparison between methods for calculating boom loads and measured loads. Existing calculation methods predict towing loads below the mean loads experienced by a boom when used at sea. Further research will be required to develop an encompassing dimensionless empirical formula, based on hydrodynamic theory and the dynamics of vessel motions, to more closely predict oil containment boom tow loads.

scholarly journals PERMEABLE GROYNES: EXPERIMENTS AND PRACTICE IN THE NETHERLANDS

1984 ◽  
Vol 1 (19) ◽  
pp. 136 ◽  
Author(s):  
W.T. Bakker ◽  
C.H. Hulsbergen ◽  
P. Roelse ◽  
C. De Smit ◽  
J.N. Svasek
Keyword(s):  
The Netherlands ◽  
Protected Areas ◽  
Coastal Erosion ◽  
Statistical Significance ◽  
Coastal Current ◽  
Tidal Channels ◽  
Negative Experience ◽  
Model Experiments ◽  
Induced Currents ◽  
Wave Induced

This paper reports on model experiments and up to 20 years of practice in nature with a permeable groyne system, consisting of single or double permeable rows of wooden piles perpendicular to the beach, without bottom protection. This system costs only 10 to 25% of the impermeable stone groynes which have for centuries been used in the Netherlands. Model experiments confirm that wave-induced currents in the protected areas are reduced to 65%, and tidal currents even to 50%, depending on the pile screen configuration. Prototype measurements could not lead to straightforward conclusions with statistical significance: the effect of the pile screens on beach evolution is partly merged into natural fluctuations and trends. Wooden pile screens do not prevent the shoreward motion of tidal channels, which can cause washing out of piles. Furthermore, constructional failures, which in the future can be avoided, at some places resulted in negative experience. It is concluded that permeable pile screens deserve serious consideration as a first flexible and cheap phase in combating coastal erosion. Its application however should be based on a thorough analysis of the local coastal current climate.

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