3.3 Step 3: Performing Thermo-Elastic Calculations

Once chosen all the above parameters, 3D FE models (i, j) will be built up and performed with a conventional FEM code for several thermo-elastic calculations.

As soon as obtained results (in stresses and deflections), some available 3D models (i, j) will be selected by passing through two tests:

- the first one is on the effective buckling limit "σ_cr"

- the second one is on the limit tolerance of the Quality Standard "δ₀"

For these two tests, only the maximum value of stress (longitudinal compressive stress on the top surface layer) and of deflection are pointed out from the median line (case 1) and on the free edge (case 2) of the plate.

　

3.4 Step 4: Selecting the Optimum 3D Model (i, j)

The optimum model (i, j) selected from the available 3D models (i, j) issued from step 3, must satisfy the condition of minimum structural weight; that means that the width B_i (span of plate between two consecutive stiffeners) of the optimum model is the largest one so that the number of stiffeners to be welded is minimum and in consequence the minimum of welding assembly operations.

　

4. APPLICATION TO A MODEL TYPE OF THIN STIFFENED PLATE PANEL

　

As for example, an application of the procedure is briefly presented below in reducing some number of parameters to be taken into account in the calculations.

So, let us suppose that we are at fabrication stage and that we have to operate the stiffeners-plate assembly by arc-welding process Fig.7.

The design parameters are previously fixed such as length (A_i = 2800 mm), thickness (T_i = 5.7 mm) and stiffener size (HP 100 x 6), except the width value (B_i) that will be variable and lower than 700 mm.

For executing assembly operations, the Constructor-Engineer has to use some control techniques in order to get higher productivity by choosing some appropriate welding parameters enabling to obtain the optimum welded assemblies.

Two possible linear heat input energies that he wishes to employ in order to ensure the best quality of his weld joints are:

H_low = 520 J/mm and H_high = 720 J/mm.

In this delicate situation, the proposed procedure is quite helpful for choosing the best one of these two energies and the optimum width of two models which are finally selected:

　

3D Model (1, 1): (Table 1)

3D Model (2, 2): (Table 2)

Fig.7: Stiffeners-Plate Assembly and FE 3D Model for Calculations

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