ICOLD BM Workshop Information Theme A

8/11/2019 ICOLD BM Workshop Information Theme A

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12th

INTERNATIONAL BENCHMARK

WORKSHOP ON NUMERICAL ANALYSIS OF

DAMS

2.-4.OCTOBER,2013,GRAZ AUSTRIA

Organized by

ICOLD

Ad Hoc Committee on Computational Aspects of

Analysis and Design of Dams

THEME A

Fluid Structure Interaction

Arch Dam Reservoir at Seismic loading

Formulator:

Graz University of Technology

Institute of Hydraulic Engineering and Water Resources Management


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Introduction

1.Introduction

Advanced numerical tools with user friendly interfaces are available for structural

analyses. Such numerical analyses require a solid theoretical background of the

applicability of methods to be used. On the other hand, the results gained need a careful

interpretation with respect to the underlying assumptions and their practical relevance.

ICOLD Benchmark examples of generalized engineering problems are devoted to

bridge the gap between numerical analyses, the interpretation of results and their

theoretical as well as practical relevance. Challenges of the analyses of concrete dams

are always the definition of material parameters, the spatial discretization and the

appropriate simulation of loading sequences. Additionally, specific attention is paid on

the structural integrity and entire safety under seismic loading conditions. To account

for this problem, the interaction of the dam and the reservoir is topic of this theme A.

By means of the Finite Element Method linear and nonlinear analyses under dynamic

excitation are carried out. However, for the required and appropriate simulation of the

dam reservoir interaction different approaches are used. With respect to future nonlinear

dynamic analyses, these simulations herein shall be in the time domain only.

A common approach to take the dynamic water interaction into account is to use an

added mass approach. A more sophisticated possibility is the use of Acoustic or Fluid

Elements. The simulations of earthquake excitation of arch dams have shown that the

analyzed stresses in the structure could vary significantly based on the interaction

modeling. The added mass approach is still a widely used technique but tends to

overestimate the stresses and therefore it is conservative in contrary to other techniques.

This benchmark now intends to compare different modeling techniques and will show

the amount of deviations. All investigations are carried out for an artificially generated

symmetric arch dam and simplified loading and boundary conditions.

Universities, engineering companies and regulatory bodies are invited to contribute to

the benchmark and take part in the discussion of results gained.


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Introduction

1.1 Focus of this benchmark example

The focus of this benchmark is to carry out the Dynamic Fluid Structure Interaction for

a large arch dam. Every participant may choose his own order of details in modeling.

The main goal of this example is the application of different approaches like:

Added mass technique (Westergaard, Zangar,)

Acoustic Elements (compressible, incompressible)

Fluid Elements (compressible, incompressible)

Further on, the usage of different Boundary Conditions is possible for:

Reservoir - Foundation

- Reflecting (on the bottom and the sides)

- Non-reflecting (at the end of the reservoir)

The modeling of the block joint opening due to tensile stresses and nonlinear effects -

is not focus of this benchmark example. However, to carry out this analysis in the time

domain will provide the opportunity for further non-linear analyses.

1.2 General basic assumptions

The following general basic assumptions and boundary conditions for the investigations

should be used: Same spatial discretization (Model/Mesh) of the Structure, Foundation and

Reservoir

Same Material Parameters

Acceleration-Time-History in X-,Y-,Z-Direction

Reservoir is infinite in length (non-reflecting)

Rayleigh Damping

Results to be compared - VisualizationBased on these basic assumptions and results gained the contributors are encouraged to

intensify and focus their effort to achieve results with higher profound physical

justification and explain the differences. (E.g.: different spatial discretization, more

appropriate modeling of the interaction; different length of the reservoir; need for

nonlinear effects).

An interpretation of the evaluated results from an engineering point of view should be

given.


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Modell and Geometry

2.Modell and Geometry

An Arch Dam, Foundation and Reservoir Model layout for the benchmark has been

generated and is available for downloading.

2.1 Arch Dam Model

Symmetric Geometry

Total Height: 220 Meters

Valley width (crest): ~ 430 Meters

Valley width (bottom): ~ 80 Meters

2.1.1

Arch Dam Geometry

The Arch Dam Geometry has been generated with the Program Arch Dam Design,

which was developed as part of the Master-Thesis by DI Manuel Pagitsch.

Arch Dam Model Plan View

View from the upstream Main Section


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Modell and Geometry

2.2 Foundation Model

Symmetry is used for the foundation too.

Height: 500 Meters

Length: 1000 Meters

Width 1000 Meters

2.3 Reservoir Model

Length: assumed minimum of 460 Meters (> 2x Height of the Dam)

Modeling the interaction with Acoustic- or Fluid Elements

500m

1000m

1000m


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Material Parameters

2.4 Acceleration Time History

Transient Acceleration (amax0.1g)

X-,Y-,Z- Direction

Artificially generated time history

3.Material Parameters

The Material properties are defined for isotropic and homogenous conditions.

Rock mass

Density: 0 kg/m3

Poisson - ratio: 0,2

Youngs - modulus: 25000 MPa

Water

Density: 1000 kg/m3

Bulk - modulus: 2200 MPa

Dam

Density: 2400 kg/m3

Poisson - ratio: 0,167

Youngs - modulus: 27000 MPa


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Mesh Properties

4.Mesh Properties

Two different Meshes of the entire system are provided for investigations, as these are a

coarse and a fine mesh. If desired, the parts can also be provided as ABAQUS/CAE

Model File, ACIS- or IGES-Files, if a specific mesh is intended to be discretized.

4.1 Coarse Mesh

Arch Dam

Total number of nodes: 2083

Total number of elements: 356

312 quadratic hexahedral elements of type C3D20R (ABAQUS CAE)

44 quadratic wedge elements of type C3D15 (ABAQUS CAE)

Foundation



quadratic hexahedral elements of type C3D20R (ABAQUS CAE)

Reservoir





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Mesh Properties

4.2 Fine Mesh

Arch Dam




Foundation




Reservoir





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Loading

5.Loading

The following loading sequence is intended to be used.

Gravity

Hydrostatic Water Pressure (full supply water level = Crest Height)

Seismic Loading

Modal Superposition or

Direct time integration (Implicit/Explicit)

6.Results

6.1 Eigenfrequencies (1 10)

The evaluation of the first 10 Eigenfrequencies of the structure, including the interaction

with the reservoir, should be provided.

6.2 Mode Shapes (1 10)

The evaluation and plotting of the first 10 Mode-Shapes of the structure, including the

interaction with the reservoir.


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Results

6.3 Hoop Stresses, Vertical Stresses and Min./Max. Principal Stresses

Evaluation of the different stresses should be done for

Static Loads

Seismic Loads (Min., Max.)

3 different sections (Main Section and ~45 degrees on the left and right hand

side)

6.3.1 Evaluation Examples for the Stresses

Left Section

Main SectionRi ht Section


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6.4 Radial Deformation

Evaluation of the Radial Deformation should be done for

Static Loads

Seismic Loads (Min., Max.)

Main sections

6.4.1 Evaluation Example for the Radial Deformation

Left Section

Main SectionRi ht Section

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