II. How To Use ATILA

6.3 Tonpilz Sonar (1)
GEOMETRY/DRAWING MATERIAL ASSIGNMENT


PROBLEM - Tonpilz Transducer under Water, Axisymmetry, PZT8, Steel and Aluminum


This part describes the harmonic (frequency domain) analysis of a Tonpilz-type transducer. First, the transducer is considered without loading (in-vacuum); then, it is considered to be radiating in water. The transducer is assumed to be axisymmetrical, thus the model is two-dimensional and only a cross-section of the transducer is represented.

GEOMETRY/DRAWING

The dimensions used for the geometry are (in mm) shown in the next table, along with the material type.

Ceramic Rings Inner Radius 6 PZT8
Outer Radius 18
Prestress Rod Length 64 Steel
Small Radius 4
Large Radius 6
Headmass Inner Radius 6 Aluminum
Small Outer Radius 18
Large Outer Radius 20
Tailmass Inner Radius 6 Steel
Small Outer Radius 20
Large Outer Radius 23
Nut Inner Radius 6 Steel
Outer Radius 10
Water Radius 56 Water

Because this is an axisymmetrical problem, many quantities are affected by a 2π factor of symmetry, such as the impedance, for instance. Always make sure to verify that the factor of symmetry is properly taken into account. Generally speaking, all results in the ATILA-GiD interface are provided without correction for the factor of symmetry.

The coordinates of the points you will need to create are shown in the table below, for reference. It is better for acoustic radiation problems to position the origin of the acoustic source (center of the piston face) at the origin of the global coordinate system. Although, we do not consider the acoustic radiation problem in the first part of this tutorial, it will save time later to follow the same rules. For this reason, the solid part of the transducer is located in the negative X region, and the fluid domain is in the positive X region.

Note that because ATILA uses the X axis as the axis of axisymmetry, the points are all in the positive Y region of the plane. The coordinates of the points you need to create are arranged in the following table.

      (-39,23) (-33,23)        
  (-55,20)   (-39,20)       (-8,20) (0,20)
        (-33,18) (-23,18) (-13,18)    
(-64,10) (-55,10)              
(-64,6) (-55,6)     (-33,6) (-23,6) (-13,6) (-8,6) (0,6)
    (-50,4)       (-13,4)    
(-64,0)               (0,0)

Remember that there is more than one way to enter points in GiD in Cartesian and polar coordi-nates. Please refer to the online help in GiD for further details. Use GiD functions to create points, lines, and surfaces until you obtain the same result as that shown in the next figure.

MATERIAL ASSIGMENT
Piezoelectric Materials

Assign material PZT8 to the two ceramic surfaces. Note that the definition of the material PZT8 includes losses. You can verify the loss angles by clicking on the Losses tab. The values Delta_m, Delta_p, and Delta_d correspond to the loss angle for the mechanical, piezoelectric and dielectric tensors, respectively.

Elastic Materials

Assign material STEEL1 to the Tailmass, Prestress Rod, and Nut surfaces, then material ALUMINUM1 to the Headmass surface.

Assign material STEEL1 to the Tailmass, Prestress Rod, and Nut surfaces, then material ALUMINUM1 to the Headmass surface.

When this is done, the material assignment should be similar to the following image (you can obtain this by selecting, on any material window, the option Draw | All materials).

Surrounding Medium

Add the required points, lines, and surfaces, to create the water domain. The water domain has a radius of 56mm. Because the geometry of the transducer was created such that the center of the piston would be at the origin of the global coordinate system, the water domain is also centered at the origin. If needed, look in the GiD documentation about how to create an arc.

Open the Fluid materials window and assign Water to the water domain. Verify the material assignment with Draw | All materials.