PSI - Issue 45

Mark Mogeke et al. / Procedia Structural Integrity 45 (2023) 36–43 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Keywords: naval ship performance; structural fatigue; virtual hull monitoring; instrumented hull monitoring, wave hindcast

1. Introduction Efficient management of the hull structure, under exposure to long-term and sometimes harsh operational loads, is vital to ensuring the availability of a ship. Ship structures are prone to fatigue because of cyclic loading caused primarily by waves. Fatigue damage leads to degradation of the hull structure. Methods to determine the operability of naval ships – to limit excessive motions, overloads, slamming, and fatigue damage – are often based on speed and significant wave height (H s ) thresholds. The probability distributions of the latter are provided for selected regions within industry guidelines. However, this approach has shortcomings; H s alone generally provides an inadequate representation of the complex sea states in which naval ships are required to operate, and the response of the ship may be sensitive to the wave energy at particular frequencies (Guachamin-Acero and Portilla-Yandún, 2021, Magoga et al., 2019, Milne and Zed, 2018). Instrumented hull monitoring (IHM) systems have been used to monitor the stresses experienced by ships during voyages and to aid in the prediction of when the ship requires maintenance. Although IHM is accurate, the cost of deployment and subsequent maintenance of such systems can be significant. Also, the management of the resulting large data sets is challenging, especially in defence vessels where data security is vital (Thompson, 2020). These factors limit the deployment of IHM.

Nomenclature CMEMS

Copernicus Marine Environment Monitoring Service

FE

Finite element

FPSO GPS HMAS HSLC

Floating Production Storage and Offloading

Global Positioning System Her Majesty's Australian Ship

High speed light craft

IHM

Instrumented hull monitoring

MAXWB MFWAM

Micro Air-Launched Expendable Wave Buoy

Meteo France Wave Model

NOAA SFA VHM WWIII

National Oceanic and Atmospheric Administration

Spectral fatigue analysis Virtual hull monitoring WAVEWATCH III Normalising constant Significant wave height Wave spreading exponent Number of runs/observations Root mean squared error Mean bias

b

D

H s

[m]

n

N

RMSE

SI S  S ζ T p T z

Scatter Index

Stress spectral response Wave spectral energy Peak wave period

[MPa

2 /(rad/s)]

[m [s] [s]

2 /(rad/s)]

Mean zero-crossing wave period Ship speed (over the ground) Rank correlation coefficient

v  θ  

[kn]

Wave spreading angle

[°] [°]

Ship heading relative to principal wave direction

Stress

[MPa]