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the ship condenser supports Strength

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Strength Resistance of the ship condenser supports Under dynamic impact (Dynamic Design Analysis Method)

 

Initial data

  • D = 1430 mm

  • nominal pressure in the condenser -  0.024 MPa

  • inner temperature - 100 deg. С

  • temperature in tube - 30 deg. C

  • Material (GOST) - 10XCНД

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Introduction

Strength analysis of a ship condenser supporting elements were performed for a given shock loads. Condeser 3D CAD model is shown in Figure 1.

Project aim is to determine max. (crash) stresses for condenser supports during inertia shock loads. The dynamic load spectrum was determined using Dynamic Design Analysis Method (DDAM) module used in the Femap and NX Nastran software. DDAM is an engineering methodology for determining the response of a ship's onboard equipment to a shock pulse of an underwater explosion.

Figure 1. 3D CAD model of ship condeser.

Boundary conditions

Mounting flanges of the ship condenser have been fixed though special NX Nastran rigid elements RBE2D.

In its chain that rigid element RBE2 was constrained in one node in all linear and rotational directions: Tx, Ty, Tz, Rx, Ry and Rz.

Used approach is conservative and provides higher stress results.

Finite element model (FEM) general representation and constraints scheme is presented in Figure 2. Detail welds modeling is shown in Figure 3.

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Figure 2. FEM of the ship condenser and constraints scheme.

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Figure 3. Support welds representation in FEM.

Shock loads

Load spectrum was determined via the following formulas:

 

 

 

 

Acceleration coefficients were determined according to [1].

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Brief results overview

FEM results show max. stresses have concentration in welds and areas near support welds.

For longitudinal (X) and vertical (Y) application of shock load spectrum max. stresses almost not exceed allowable stress or have not sagnificant exceeding.

For transverse (Z) direction of shock load spectrum max. stresses extremly exceed allowable level and aprear in whole section cut of weld. In that case design need to be reviewed and update. Based on the results of the analysis, it was found that the values ​​of the calculated stresses of the supporting elements are higher than allowable levels. Structural modifications have been proposed and developed to ensure the strength of the parts under research.

Stress distribution in condenser model can be seen in Figures 4, 5 and 6. Hot spot stress results in weld is shown in Figure 7.

Figure 4. Von Mises stress distribution [MPa] according to longitudinal (X) shock load spectrum.

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Figure 5. Von Mises stress distribution [MPa] according to vertical (Y) shock load spectrum.

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Figure 6. Von Mises stress distribution [MPa] according to transverse (Z) shock load spectrum.

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Figure 7. Hot spot Von Mises stress concentration [MPa] in welds.