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Modeling the Spreading of Large LNG Spills on Water

Nicolas F. Ponchaut, Ph.D.

Solutions to governing equations (Exponent Spill Model, ESM)
Instantaneous release of finite spill
Instantaneously started constant spill rate
Test cases: typical Coast Guard IRA spill
Conclusions
Effect of friction on the pool
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Assumptions


ABS/FERC friction: smooth, 0.063 mm vapor layer
F LE CI
Neutrally buoyant equilibrium at each location
Uniform evaporation rate
K = 1.4: Suchon, 1970 (oil spills)
K = 1.34: Raj and Kalelkar, 1974
K = 2.0: Briscoe and Show, 1980
K = 1.64: Chang and Reid, 1982 (liquid n-pentane)
K = 1.16: Effective value used by GASP, 1990
K > 4: PHAST
LELE hgKU *

Reality: constant height and stagnant initial condition
Similarity distribution: thickness and radial speed
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250 m pool at steady state
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Sudden flow rate increase
24,890 kg/s for t < 400 s (250 m pool radius at equilibrium)
35,840 kg/s for t > 400 s (300 m pool radius at equilibrium)
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Sudden flow rate decrease
24,890 kg/s for t < 400 s (250 m pool radius at equilibrium)
15,930 kg/s for t > 400 s (200 m pool radius at equilibrium)
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GASPExponent Spill Model
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Upstream of the headwave (closer to the spill location):

Downstream of the headwave (closer to the pool edge): Flow is subcritical: U2 < g* h The flow goes slower than the wave propagation speed
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Conclusions 1 MODELS




Upstream of the headwave, the pool thickness profile is largely independent of downstream conditions
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The interface can be rough, and exhibit significant turbulence
For spills of large surface area, friction will impact the character of the pool
Using the “vapor layer” friction model results in a headwave that separates from the pool
With a turbulent friction model, the headwave decays and remains attached to the pool
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Conclusions 3 POOL SIZE
If the friction is assumed to be low, the headwave propagates and separates as a ring that evaporates away

With more realistic turbulent friction, the headwave does not separate
Turbulent friction results in slower pool growth and smaller maximum pool size
Slide Number 1
GASP (Gas Accumulation over Spreading Pools, Webber 1990)
Exponent Spill Model: ESM
Instantaneous release
Instantaneous release
Instantaneous release
Steady spill rate
Steady spill rate
Steady spill rate
Steady spill rate
Steady spill rate