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ASNE Day 2016 - Technical Paper Session 6 : Thursday, March 3, 2016 1515-1700

Future Trends in Naval Applications



Authors: Joshua T. Knight, Margaret A. Craig, Marc V. Smith, Justin W. Skenyon, and David C. Kring

Title: Trends in Transverse Global Loads for Multihulls


Multihull vessels, such as catamarans and trimarans, are subjected to seaway loads in the transverse direction that may have a significant effect on structural design of cross structure and wet decks. Of particular interest when calculating loading conditions for design of multihulls are the combined effects of multi-directional loading. An example of combined loading is simultaneous vertical bending about the midship and centerline planes. The literature on ship lifetime extreme loads has focused primarily on midship vertical bending moment. Comparatively little has been written about multihull extreme loads in the transverse direction, or the correlation between maxima in the load time series for multiple directions.

In a previous paper, Knight and Smith (2015) investigated the effect of varying mass properties of a catamaran on its sagging moment and torsion in both the longitudinal and transverse directions. However, this research treated all loads as independent. In this paper, results are given showing trends in transverse and combined loading conditions for a notional high speed catamaran. The Weibull approach for lifetime load extrapolation is used. Discussion of the Weibull assumption and alternative distributions has been reported by Collette et al. (2007), Kim et al. (2011), and others. This paper applies that theory and creates a new focus on the variation of transverse loads with incident wave headings, such as shown in Figure 1 for torsion about the transverse axis, sometimes referred to as the pitch connecting moment.

The correlations between the maxima of different loads are explored. Additionally, distributions of transverse loads conditioned at the time of a maxima in midship vertical bending is investigated. The results demonstrate the significance of combined loads for multihull structural design. Limitations of the Weibull approach for combined loading conditions are discussed, and the case is made for the need to predict extreme values of combined loading conditions, as well as the characteristics of the incident waves that generate them.

Collette, Matthew, Woei-Min Lin, Jun Li, Han Yu, and Allen Engle. 2007. "Automated Long-Term Motions and Loads Analysis for the Design of Novel Vessels." International Symposium on Practical Design of Ships and Other Floating Structures. Houston, Texas.
Kim, Dae-Hyun, Allen H. Engle, and Armin W. Troesch. 2011. "Estimates of Long-Term Combined Wave Bending and Whipping for Two Alternative Hull Forms." Transactions of the Society of Naval Architects and Marine Engineers 137-166.
Knight, Joshua T., and Marc V. Smith. 2015. "Preliminary Comparison of Polynomial Chaos and Splines for the Uncertainty Quantification of Multihull Structural Loads." International Conference on Fast Sea Transportation. Washington D.C.

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