DBB Method

A Parametric Ship Design Application

The DBB (Design Building Blocks) approach aims to assist the designer in separating the ship’s functions and sub-functions into discrete elements and position them appropriately, putting architectural factors in the center of the process, in contrast to the traditional sequential design process (Andrews and Dicks, 1997).

This web application makes use of the DBB method to provide an initial assessment of hydrostatics, hydrodynamics, and seakeeping properties. The hull is parametric and can be designed through its basic dimensions and auxiliary factors, from which various properties are obtained. Bulkheads can be added throughout the length. Additionally, blocks representing the main ship's functions can be added, removed, and resized.

The analysis is structured in four sequential steps, in which the inputs of one section directly impact the next, as follows:

1. Parametric Hull Modelling
2. Hydrostatic and Stability
3. Hydrodynamics Analysis
4. Seakeeping

More details of the implementation and coding framework can be found in the Code Flowcharts.

1. Parametric Hull Modelling

In order to efficiently control the building blocks, it is necessary to download the standard DBB data, change it accordingly, and upload it again. To retrieve data from each building block, the top view of of the hull (left) sections is entirely clickable and will provide a short summary of the main properties (right).

Two default vessels are available to an initial assessment. The first is a frigate based in the KNM Narvik F304 model. The second, a Platform Supply Vessel, based on the PX121 model by Ulstein.

2. Hydrostatic and Stability

The previously designed vessel presents different properties depending on the loadin condition. Below, the main hydrostatic properties can be found. Have in mind that you should match next section's dimensions with the output presented below. Besides that, an estimatived for the GZ curve is given.

A. Properties according to the loading condition

B. GZ Curve

Validity of method is limited to: 0.40 < C_b < 0.56, 2.85 < B/T < 4.00, -5deg < K_f < 15 deg, 0.38 < T/D < 0.56, 0deg < heel angle < 90deg.

Based on Ali, H. (2003).

3. Hydrodynamic Analysis

Holtrop is a method based on statistical regression of model tests and results from ship trials. The method is used to estimate the resistance of displacement ships. The database covers a wide range of ships. For extreme shapes, the accuracy of the estimates is not good. The method may be used to assess qualitatively the resistance of a ship design. More info. Initially developed by Jefferson Flor, Thiago Gabriel Monteiro, and Henrique M. Gaspar as a ShipLab web app.

*Attention, the dimensions at 3.A should be update according to the Table 2.A, this arrangement allows you to easily foresee how any change in the dimensions affect the overall resistance.

F. Resistance Components

G. Power Required

4. Seakeeping

Graphical representation of estimated motion responses for ships. Heave, pitch, roll, vertical motion and vertical acceleration responses are calculated as function of length, breadth, draft, block coefficient, waterline breadth and operational profile. Bending moment is also estimated. Values can be changed by clicking and dragging the sliders. Based on the article Estimation of ship motions using closed-form expressions by Jensen and Mansour (2004).

Initially developed by Sthefano L. Andrade and Henrique M. Gaspar as a ShipLab web app.

C. Plots

References

Ali, H. (2003). GZ Curves of Warships from Form Parameters, MSc Dissertation, UCL, London.

Andrews, D.J. and Dicks, C.A. (1997). The Building Block Design Methodology Applied to Advanced Naval Ship Design. In: Proceedings of IMDC 97, Newcastle, UK.

Jensen, J. J., Mansour, A. E., & Olsen, A. S. (2004). Estimation of ship motions using closed-form expressions. Ocean Engineering, 31(1), 61-85.

van Griethuysen, J. and Fellows, D. (2003). Simple Holtrop - Monohull, [Computer Software], UCL, London.