Szerkezet Es Aramlas Egymasra Hatása Hagyomanyos Modon Es Immersed-solid Modszerrel Megvalositva

8/15/2019 Szerkezet Es Aramlas Egymasra Hatása Hagyomanyos Modon Es Immersed-solid Modszerrel Megvalositva

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FLUID STRUCTURE INTERACTIONSOLVED IN TRADITIONAL WAY,

AND BY IMMERSED SOLID METHOD

BUDAÖRS / 2015. 04. 23. Ákos Horváth eCon Engineering


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Fluid Structure Interaction – Modelling Approaches

3http://www.econengineering.com ANSYS felhasználói konferencia 2015 – Horváth Ákos / 2015. 04. 23.

• FSI can be categorised by the degree of physical coupling between the

fluid and solid solution fields• How sensitive is one field to a change in the other field?

• Fields that are strongly coupled

physically require strong

numerical coupling

• Generally more difficult to solve

• Solution fields that are

relatively independent can be

solved with weaker coupling or

even uncoupled (1-way)


4/17

Motion of Rigid Body


• Simpler FSI approaches are possible when simplifying assumptions can be made

• If the solid moves but does not deform (rigid body), then a 6-Degree of Freedom rigid bodysolver can be used

• Rotation about 3 axes, translation along 3 axes = 6-DOF

• A 6-DOF rigid body solver is available in CFX

• This gives a 2-way explicit or implicit solution

• Depending on whether the solid body position is

updated once or multiple times per time step

• More efficient than using a full FEA solver

• No structural solution field

• Limitations

• No contact/collision modelling with walls or other rigid bodies

• Can’t be used in rotating domains

• General constraints can’t be applied

• Can’t make a translatable rigid body rotate about a point, other than its center of mass

•

Examples: Boats in waves, falling objects, valves


5/17

Realizing Motion of Rigid Body

5http://www.econengineering.com

• Boundary motion imposed via the 6-DOF

solver results in mesh deformation

• Large displacements may result in poor

mesh quality or the mesh may collapse

•

Traditional, Mesh Resolving Approach• Mesh deformation with automatic re-meshing

• Immersed Solid Method

• Use when mesh deformation is not practical

• Fluid mesh remains stationary• Solid motion can be specified or calculated by

the 6-DOF solver

• Limited boundary layer resolution

• Single phase, incompressible only

ANSYS felhasználói konferencia 2015 – Horváth Ákos / 2015. 04. 23.


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Plate Check Valve in Oil Control Valve


• Oil Control Valve for intake/exhaust camshaft

adjustment system (phaser)



7/17

Plate Check Valve in Oil Control Valve


• Oil Control Valve for intake/exhaust camshaft

adjustment system (phaser)


Check valve plate

in closed position

Linear spring

with pretension


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Solid mesh

• Structured hexahedral

• 12672 nodes

• 10075 elements

• Can be arbitrarily coarse

inside the domain

Immersed Solid

•

Mom. Source Scaling Factor: 10• Motion by Rigid Body Solution

• Mass: 0.5 g

• Linear spring force

• 84.5 N/m

• 0.334 N pretension

• Rigid Body Solver Coupling:

Every Coefficient Loop

…by Immersed Solid Method


Fluid mesh

• Tetrahedral mesh with prism layers

• Extremely fine in region of

motion

• 1.4 Million nodes

• 7.6 Million elements

Inlet

• 1.5 bar relative

static pressure

Outlet

• 0 Pa Relative

static pressure

Symmetry planes

C.O.G. of plate

Solver Settings

• Advection Scheme: High Resolution

• Transient Scheme: Second Order Backward Euler

• Min / Max. Coeff. Loops: 4 / 12

• Convergence Criteria: RMS


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…by Mesh Resolving A pproach


Simulation Domain• Made in Design Modeler

• Plate is extracted at its

initial position (0.05 mm)

• Multiple bodies in one

part

Finite Volume Mesh

• Fully structured

hexahedral mesh in

region of motion and

downstream of that

• Tetrahedral and swept

mesh upstream

• 324800 nodes

• 352300 elements


10/17

• Plate’s surface is moved by Rigid Body SolutionDispX=rbstate(Position X )@Rigid Body 1–(X2+X3)/2

• Rigid Body Solver with identical settings as in Immersed Solid Method

• Mesh is kept the same next to plate (above and below)

• Mesh is deformed up- and downstream

• A linear function is defined

• Lin1=(Initial X -X1)/(X2-X1)

• Lin2=(Initial X -X4)/(X3-X4)

• Node’s displacement• DispX × Lin1

• DispX × Lin2

• Disadvantages

• Not possible to contact the wall

• Mesh quality

• Aspect ratio

•

Ratio to neighbouring cells

…by Mesh Resolving A pproach


X1X2X3X4

The figure here above is only for demonstration of mesh deformation. Initial plate position differs.

C o m p r e s s e d r e

g i o n

( s u b d o m a i n

)

S t r e t c h e d r e g i o n ( s u b d o m a i n )


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Results


• Velocity contour plot in

symmetry plane

• There is flow through

plate in ISM

• Initial flow rate(steady-state solution)

is larger by ISM

• Flow field is very

similar during, and at

the end of motion

ISM

MRA


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Results


ISM

MRA

• Static pressure

contour plot insymmetry plane

• Initial pressure field is

slightly different

• Pressure field is very

similar during, and at

the end of motion


13/17

Results


-2,5

-2

-1,5

-1

-0,5

0

0 0,00025 0,0005 0,00075 0,001 0,00125 0,0015

D i s p l a c e m e n t [ m m ]

Time [s]

Displacement of plate

ISM

MRA

-3

-2,5

-2

-1,5

-1

-0,5

0

0 0,00025 0,0005 0,00075 0,001 0,00125 0,0015

V e l o c i t y [ m / s ]

Time [s]

Velocity of plate

ISM

MRA

-25

-20

-15

-10

-5

0

5

0 0,00025 0,0005 0,00075 0,001 0,00125 0,0015

A c c e l e r a t i o n [ m / s 2 ]

x 1 0 0 0

Time [s]

Acceleration of plate

ISM

MRA


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Advantages and disadvantages


Immersed Solid Method

• Fast model generation

• ≈ 2 hours

• Easy to change fluid / solid part

• Design

• Initial position• Accuracy of force and torque are problem

dependent

• Viscous force contribution is typicallyunderestimated

• Many Limitations

• Mesh deformation

• Heat transfer

• Initial conditions (rigid body)

• Multiphase flow

• etc. (please see Ansys-CFX help)

Traditional Way – MRA

• Time consuming model/mesh generation

• Blocking for structured meshes requireexperience

• ≈ 1-2 days

• Hard to change model• Requires full remeshing (and new

blocking)

• Mesh deformation (and remeshing) setup

• Might be hard to achieve convergence

• Experience in FSI is necessary• Time step size, under-relaxation,

number of inner iterations, etc.

• No limitations on special features

• Accurate



15/17

Summary


• FSI of plate check valve has been investigated… •

…by Immersed Solid Method• …in traditional way, with Mesh Resolving Approach

• Motion of plate is solved by Rigid Body Solution of Ansys-CFX• No need for external mechanical model

• ISM issued in very similar results as MRA• Slightly faster opening time originated from begining of motion

• Model setup and design change is much faster with ISM• It is possible to investigate more design variants easier

• More complex solid bodies can be modeled

• Do not use ISM as a standalone solution for FSI!• Comparative studies with MRAs are necessary to assess accuracy of specific problem



16/17

Thank you for

your attention…

ww w.e co ne ng in ee ring . co m


Ákos Horváth [email protected]


17/17

Szerkezet Es Aramlas Egymasra Hatása Hagyomanyos Modon Es Immersed-solid Modszerrel Megvalositva

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