experimental study on the two sensitivities of sloshing
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Experimental Study on the Two Sensitivities of Sloshing Impact Pressures
MHLMarine Hydrodynamics Lab.
Yangjun Ahn*, Sang-Yeob Kim, Yongwhan Kim
Seoul National University
International Research Exchange Meeting on Ship and Ocean Engineering
December 21 – 22, 2012Osaka, Japan
State of the Arts: Gas-liquid Density Ratio• Identifying dimensionless numbers
Abramson et al. (1974), Bass et al. (1980) Viscosity and surface tension do not need to be included.
• Suggestion of Froude number and its Limits Bass et al. (1980), Faltinsen and Timokha (2009) Ullage pressure should be Froude scaled, but Froude number cannot cover local phenomenon.
• Suggestion of various scaling properties Cavitation # : Faltinsen and Timokha (2009), Braeunig et al. (2010) Euler # : Lugni et al. (2010), Mach # : Bass et al. (1080), Dias et al. (2007) Local phenomenon, compressibility, and phase changes require proper scaling method, rather
than Froude scaling.• Phase change and gas-liquid density ratio (ρgas / ρliquid )
Bass et al. (1980), Maillard and Brosset (2009), Yung (2009, 2010), Braeunig et al. (2009, 2010)
Ambient air cannot be representative to the natural gas.
• Problems Limited test conditions, and results. Gas-liquid density ratio (ρgas / ρliquid) needs to be checked.
Research Backgrounds
• Bernoulli Equation (Yung et al., 2009)
• How Many oscillations for each case?• How much affect the asymmetric phenomenon?
0.0040gas NG
liquid LNG
Actual LNG cargo
ambient airρgas = 1.2 kg/m3
waterρliquid = 1000.0 kg/m3
0.0012gas air
liquid water
Most sloshing experiments
0.0012 0.0040gas heavy
liquid water
mixed gasρgas = 4.0 kg/m3
waterρliquid = 1000.0 kg/m3
Present study
22
2 21 2
' ' 1 ' 1 1 1 1' ' ' ,' 2 ' 2 ' '
gl l GG Fr W
uu z zt Fr t k ke
where 1 G
L
Test 1: Gas-liquid Density Ratio
Test 2: Time Window
Condition Test 2 : Time window & Asymmetric motion
Excitation Motion Harmonic, regular with 2D model
Filling level 95%H, 70%H, 50%H, 25%H, and 15%H
Excitation frequency 0.7ω0 - 1.3ω0
Simulation time 1,000 periods
Test Condition
Condition Test 1: Impact pressure measurement
Excitation Motion Harmonic, regular with 2D model
Filling level 95%H, 70%H, 25%H, and 15%H
Excitation frequency 0.7ω0 - 1.4ω0
Density ratio (ρgas / ρliquid) 0.0012 - 0.0039
Simulation time 200 periods
Test 1: Gas-liquid Density Ratio
Test 2: Time Window
%H = % filling of the model tank height
SNU Sloshing Experimental Facility
Storage
Coupler
DAQ board
High-speed camera
Pressure sensor
Motion platform& controller
Model tank
Motion platformMotion controller
Coupler
Data acquisition system
Monitoring system
Pressure sensors
Video recorder
Data storage server
• Components of the mixture
• Problems of Application Density level test method for the Non-flammable gas High green house potency Dissolved mixed gas in water
• Solutions The inverse estimate by using oxygen level tester Confirmation of dissolved gas density
Products Density (kg/m3) Ratio (%)
Sulphur hexafluoride (SF6) 6.162 56.9
Nitrogen (N2) 1.146 43.1
Mixture 3.999 100.0
Application of Mixed Gas (1)
• Airtight model tank Liquid type silicon Rubber ring Bubble test
• Mixed gas injection Valves open Mixed gas injection Check the pressure
• Mixture concentration check Oxygen tester Check the portion of gas Injection up to the target density
• Dissolution Forced excitation motion under the violent condition Check the portion of gas Iteration
Application of Mixed Gas (2)
Model Tank
Geometry of model tank10
946
5
5
10118
Panel 1
Unit = mmTank roof
Panel 2
Configuration of sensors
118.0
67.0 (hʹ = 0.10)
201.0 (hʹ = 0.30)
10
Both sides on the tank roof One side on the side wall
Side wall670
Pressure sensor
KISTLER 211B5 (Φ = 5.54 mm)
Data Analysis• Peak Sampling
Sample peak pressure signals from the experimental data Sampled peaks are used to produce statistical results
• Peak Over Threshold Method Widely-used sampling method Threshold pressure Sampling time window
Test 1 Results (1) : ρgas / ρliquid• Filling : 95%H• Locations : Tank roof• Results
• The average of 1/10 largest peak pressure decreases as the density ratio increases. • Decrease level depends on the excitation frequency.
Excitation amplitude = 0.042 l Excitation amplitude = 0.016 l
l = Tank length in x-direction
Test 1 Results (2) : ρgas / ρliquid• Filling : 70%H• Locations : Tank roof• Results
• The average of 1/10 largest peak pressure decreases as the density ratio increase. • Variation of the density ratio does not affect under the particular frequency.
Excitation amplitude = 0.042 l Excitation amplitude = 0.016 l
• Jump phenomenon The density ratio does not critically affect magnitudes
of pressures around the particular excitation frequencies.
Sloshing flows shows irregular movements.
• Movies Filling : 70%H ω/ω0 : 1.20
Test 1 Results (3) : ρgas / ρliquid
ρgas/ ρliquid = 0.00199 ρgas/ ρliquid = 0.00392 ρgas/ ρliquid = 0.00396
A B C
AB
C
• Filling : 25%H & 15%H• Locations : Side wall• Results
• The average of 1/10 largest peak pressure decreases as the density ratio increases. • Decrease level depends on the excitation frequency.
Test 1 Results (4) : ρgas / ρliquid
Filling level = 15%HExcitation amplitude= 0.1l
Filling level = 25%HExcitation amplitude= 0.1l
Filling Level(% of tank height)
Excitation Amplitude(% of tank length)
Excitation Frequency(ω/ω0)
95 1.5, 4.2, 10.0 0.7 – 1.3
70 1.5, 4.2, 10.0 0.7 – 1.3
50 1.5, 4.2, 10.0 0.7 – 1.3
25 10.0 0.7 – 1.3
15 10.0 0.7 – 1.3
• Test matrix
• Time history
Filling Level(% of tank height)
Excitation Amplitude(% of tank length)
Excitation Frequency(ω/ω0)
95 1.5, 4.2, 10.0 0.7 – 1.3
70 1.5, 4.2, 10.0 0.7 – 1.3
50 1.5, 4.2, 10.0 0.7 – 1.3
25 10.0 0.7 – 1.3
15 10.0 0.7 – 1.3
Test 2 Condition : Sensitivity of Duration
ω 0 : excitation frequencyω0 : Frequency of the fundamental mode of sloshing
200 oscillations200-1
500 oscillations500-1
500 oscillations500-2
200 oscillations200-2
200 oscillations200-3
200 oscillations200-4
200 oscillations200-5
1000 oscillations1000
Test 2 Movies : Sensitivity of Duration• 70%H filling & 0.015L amplitude
ω/ω0 = 0.95 ω/ω0 = 1.00
ω/ω0 = 1.35 ω/ω0 = 1.50
Test 2 Results (1) : Sensitivity of Duration• 70%H filling & 0.015L amplitude
1000 oscillations ( ) 500 oscillations ( )200 oscillations ( )
Average of 1/10 largest peaks
Impact occurs once every 3 times
No impact once or twiceevery 10 times
Impact occurs once every 3 times
Average of 10 largest peaks
Test 2 Results (2) : Probability of Exceedance• 70%H filling & 0.015L amplitude• ω/ω0 = 1.03
1000 oscillations ( ) 500 oscillations ( )200 oscillations ( )
Weibull fitting GEVD fitting
X
Test 2 Results (3) : Probability of Exceedance• 70%H filling & 0.015L amplitude• ω/ω0 = 0.95
1000 oscillations ( ) 500 oscillations ( )200 oscillations ( )
Weibull fitting GEVD fitting
X
Concluding Remarks
• Test 1: Gas-liquid density ratio Sloshing pressure generally decreases as the density ratio (ρgas/ρliquid) increases, but
not always, not linearly. The density ratio locally affects the sloshing pressure. The resonance frequency of each condition does not change. The jump phenomena were observed in certain rages of frequency, and the density
ratio does not affect under the jump phenomena condition.
• Test 2: Time window Duration of 200 oscillation is not enough for 2D regular sloshing experiment, and at
least duration of 500 oscillation is recommended. The average of 1/10 largest peak pressure is rather assembled than the average of 10
largest. It is not clear that which method of statistics of extremes is the most reliable:
Weibull, Pareto, or GEVD. The result depends on the test condition.
THANK YOU
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