The Physics of Structure-Structure Impact in Free Surface Flow

The Physics of Structure-Structure Impact in Free Surface Flow Solomon Yim Gang Cao Dept. of Civil Engineering Oregon State University 1

Tsunami Effects on Bridges Dec. 26, 2004 Banda Aceh, Indonesia 2

Storm Surge Effects on Bridges Aug. 29, 2005 Biloxi, MS, Gulf of Mexico 3

Tsunami/Storm Surge Effects on Bridges Dec. 26, 2004 Banda Aceh, Indonesia Aug. 29, 2005 Biloxi, MS, Gulf of Mexico 4

Tsunami/Storm Surge Effects on Bridges Dec. 26, 2004 Banda Aceh, Indonesia Aug. 29, 2005 Mobile River, AL, Gulf of Mexico 5

Tsunami Effects on Bridges Dec. 26, 2004 Southeast India 6

Storm Surge Effects on Bridges Aug. 29, 2005 Mobile, AL 7

Tsunami transported bridge at Jantang, Aceh (Sumatra) Higman 8

Navier-Stokes Equations u i u σ i 1 ij + uj = + j ρ j t x x f i u x i i = 0 9

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3D Model of an Oregon Coastal Bridge 1 1

3D Model of an Oregon Coastal Bridge 1 2

PFEM 2D Fluid-Structure Interaction Examples (CIMNE) 1 3

PFEM 2D Fluid-Structure Interaction Examples (CIMNE) 1 4

PFEM 2D Fluid-Structure Interaction Examples (CIMNE) 1 5

RANS with k-epsilon closure model U x i i = 0 U U P ρ U τ t x x x i i ij + j = + j j i f i k k μ t k Ui ρ + ρu j = μ+ ρuu i j ρε t xj xj σ k xj xj 2 ε ε μ t ε ε Ui ε ρ + ρu j = μ + fε1cε1ρ uu i j fε2cε2ρ t xj xj σ ε xj k xj k U U i j 2 Uk whereτ ij = ( μ+ μt )( + ) ( μ + ρk) δij x x 3 x j i k ρ U U i j 2 uu μ i j = t( + ) k ij x x 3 ρ δ j i 1 6

Structure-Structure Impact Structure - structure impact in a fluid medium At low relative speed At high relative speed Free surface effects Computational Aspects 1 7

Wall damping function (LRN) Explicitly boundary layer dependent coefficients μ = t ρ fc μ μ 2 k ε f ε1 0.05 = 1+ f μ 3 where f μ 0.0165R 2 20.5 k = 1 e 1+ Rt and R k = 1/2 k y ν Implicitly boundary layer dependent coefficient f = e Rt ε 2 1 2 where R t 2 k = νε 1 8

Structure-Structure Impact at Low Relative Speed (Low Re) V1 V2 Laminar boundary layer on each structural surface Fluid jets in both orthogonal directions during approach Singular point may appear Overlapping of boundary layers Reversed flow directions and opposite singular effect during separation 1 9

Boundary Layer Laminar and turbulent shear in the near wall region 2 0

Boundary Layer Typical velocity profile for a turbulent boundary layer 2 1

Structure-Structure Impact at Low Relative Speed (Low Re) V1 U Singular point V2 Laminar boundary layer on each structural surface Fluid jets in both orthogonal directions during approach Singular point may appear Overlapping /interacting boundary layers Reversed flow directions and opposite singular effect during separation 2 2

Structure-Structure Impact at Low Relative Speed (Low Re) V1 y1 P y2 V2 Laminar boundary layer on each structural surface Fluid jets in both orthogonal directions during approach Singular point may appear Overlapping /interacting boundary layers Reversed flow directions and opposite singular effect during separation 2 3

Structure-Structure Impact at Low Relative Speed (Low Re) Laminar boundary layer on each structural surface Fluid jets in both orthogonal directions during approach Singular point may appear Overlapping /interacting boundary layers Reversed flow directions and opposite singular effect during separation 2 4

Structure-Structure Impact at Low Relative Speed (Low Re) V1 U Singular point V2 Laminar boundary layer on each structural surface Fluid jets in both orthogonal directions during approach Singular point may appear Overlapping of boundary layers Reversed flow directions and opposite singular effect during separation 2 5

Structure-Structure Impact at High Relative Speed (High Re) Turbulent boundary layer on each structural surface Fluid jets in both orthogonal directions during approach Singular point may appear Overlapping/interacting boundary layers Reversed flow directions and opposite singular effect during separation Cavitation may occur 2 6

Structure-Structure Impact at High Relative Speed (High Re) V1 P V2 Turbulent boundary layer on each structural surface Fluid jets in both orthogonal directions during approach Singular point may appear Overlapping /interacting boundary layers Reversed flow directions and opposite singular effect during separation Cavitation may occur 2 9

Structure-Structure Impact at High Relative Speed (High Re) V1 V2 Turbulent boundary layer on each structural surface Fluid jets in both orthogonal directions during approach Singular point may appear Overlapping of boundary layers Reversed flow directions and opposite singular effect during separation Cavitation may occur 3 0

Cavitation Cavitation in propeller blades The same phenomenon happens in the tip and root of a propeller blade. The corrosion caused by the implosion of bubbles will crack the blade when sustained cavitation occurs Well studied in propeller analysis literature 3 1

Effects of Free Surface V1 P=constant V2 Constant pressure at free surface Preferred fluid jet direction during approach Singular point may appear Interaction of free surface with boundary layers Cavitation may occur and interact with free surface 3 2

Effects of Free Surface Constant pressure at free surface Preferred fluid jet direction during approach Singular point may appear Interaction of free surface with boundary layers Cavitation may occur and interact with free surface 3 3

Computational Aspects V1 y1 P y2 V2 Which normal distance is valid when using damping functions? y1 or y2? When the solid is very close to the wall, say, when y1 and y2 are overlapped, how to calculate y1? Directly use the law for linear layer? After the contact elements are generated in numerical code, can we just neglect this boundary layer? 3 7

Summary The physics of structure-structure impact in free surface flow have been examined. The following are important issues that need to be addressed: Interaction between boundary layers around the structures needs to be taken into account for both low and high Re flows Cavitation in high Re flow (propeller literature) Free surface interaction with structural boundary layers Free surface interaction with cavitation 3 8