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Strength Assessment of Barge hull

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Strength Assessment of 62m barge hull for further modernization

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Introduction

The set of works was carried out to check the general and local strength and stability of the structure of a non-self-propelled barge in accordance with the requirements of the Register of Shipping of Ukraine.
As the initial design, the body of a non-self-propelled barge-platform was used, which should be modernized into a bunker barge for the transport of bulk cargo or sand pulp. According to the design data, the life of the upgraded hull is 12 years.
For a detailed determination of the stress-strain state of the hull of a non-self-propelled barge, a finite element model (FEM) with a sufficient level of detail should be prepared. In accordance with the requirements of the classification society, calculations of static strength from the action of general and local loads should be performed, as well as buckling calculations. To obtain reliable data on safety margins, a calculated FEM of the barge hull was prepared in Siemens FEMAP with NX Nastran.

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Initial data

Initial package includes existing drawings and preliminary modernization design. General view of existing barge is presented in Figure 1. Project modernization can be seen in Figure 2.

Figure 1. Initial structural design of existing barge hull

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Figure 2. Preliminary design modernization

Loads

Information about load conditions has been supplied by the Customer. According to the Register of Shipping of Ukraine, the following load cases are considered:

  1. Full uniform load and maximum draft.
  2. Partial uniform loading and corresponding draft.
  3. Ballast vessel with minimal draft.
  4. Partial uneven loading in the bow and stern of the cargo tank and intermediate draft.
  5. Partial uneven loading in the mid-section of the cargo tank and intermediate draft.

For each of loading options, the following wave conditions are considered:

  • still water;
  • hogging;
  • sagging.

Total list of 15 load cases (LC's) have been applied to the barge Fhull FEM. Global wave conditions like hoggging and sagging are shown in Figures 8 and 9, hydrostatic levels change depending on draft - Figure 10.

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FEA model

FEM model of the hull is represented mainly by PLATE and BEAM elements. Cargo in the barge is presented within concentrated mass elements which transfer weigh to the hull via RBE3 rigid elements. Hull corrosion was taken into account using plate thickness correction. Hull thickness distribution is shown in Figure 3. FEM realization of barge hull can be seen in Figures 4 - 7.

Figure 3. Plate thickness [mm] distribution in FEM

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Figure 4. FEM of barge hull fore

Figure 5. FEM of barge hull aft

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Figure 6. FEM of longitudinal frame in the fore part

Figure 7. FEM of aft frame

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Figure 8. Hogging wave condition

Figure 9. Sagging wave condition

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Figure 10. Hydrostatic load for middle section

Results overview

The strenghth and buckling results (max. equivalent stress, normal compression/tension stress, shear stress ) were determined for each LC. Obtained stress levels are not exceed the allowable values and safety factors according to the Register of Shipping of Ukraine.

Global stress level distribution in barge hull for hogging and sagging wave condisions can be seen in Figures 11 and 12.

Local stress concentration, localized on longitudinal bulkhead - for hogging LC and on transversal bulkhead - for sagging LC, are shown in Figures 13 and 14.

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Figure 11. Equivalent Von Mises stress distribution in barge hull for one of the hogging LC

Figure 12. Equivalent Von Mises stress distribution in barge hull for one of the sagging LC

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Figure 13. Local Von Mises stress concentration on man hole of longitudinal bulkhead for hogging LC

Figure 14. Local Von Mises stress concentration on transversal bulkhead for sagging LC