Andrew L. Silver

VALIDATION OF A RISK-BASED NUMERICAL MODEL FOR PREDICTING DEEP-DRAFT UNDERKEEL CLEARANCE

AbstractThe channel analysis and design evaluation tool (CADET) is a numerical program to determine the optimum dredge depth for the offshore portions of entrance channels. A brief description of the theoretical basis and risk assessment in CADET is presented. Validation comparisons between CADET predictions and field measurements of wave-induced vertical motions at Ambrose Channel, New York, are presented. Prototype ship motions were measured with a differential global positioning system in April 1998 along three 488-m-long reaches. Comparisons were made with six ships, three tankers and three containerships, during inbound and outbound transits. In general, the CADET predictions matched the field measurements reasonably well, especially considering the wave heights were relatively small during the measurement period.

Comparison of Measured Ship Squat with Numerical and Empirical Methods

The Beck, Newman and Tuck (BNT) numerical predictions are used in the Coastal and Hydraulics Laboratory (CHL) Channel Analysis and Design Evaluation Tool (CADET) model for predicting underkeel clearance (UKC) resulting from ship motions and squat. The Ankudinov empirical squat prediction formula has been used in the CHL ship simulator and was recently updated. The World Association for Waterborne Transport Infrastructure (formerly The Permanent International Association of Navigation Congresses, PIANC) has recommended several empirical and physics-based formulas for the prediction of ship squat. Some of the most widely used formulas include those of Barrass, Eryuzlu, Huuska, International Commission for the Reception of Large Ships (ICORELS), Romisch, Tuck, and Yoshimura. The purpose of this article is to compare BNT, Ankudinov, and PIANC predictions with measured differential global positioning system (DGPS) squat data from the Panama Canal for four ships. These comparisons demonstrate that the BNT, Ankudinov, and PIANC predictions fall within the range of squat measurements and can be used with confidence in deep draft channel design.

RISK-BASED PREDICTIONS FOR SHIP UNDERKEEL CLEARANCE

This paper describes two new risk-based models for predicting ship underkeel clearance (UKC) in deep-draft entrance channels. In the first model, recurrence intervals are estimated for the number of years between accidents or groundings using Poison and Bernouilli probability distributions for ship arrivals and groundings. The second model predicts channel accessibility based on an acceptable level of risk for different wave, ship, and channel combinations by modeling the uncertainty in these parameters using Gaussian and Rayleigh distributions. Comparisons between both methods are presented

PROBABILISTIC MODEL FOR PREDICTING SHIP UNDERKEEL CLEARANCE: FIELD AND LABORATORY VALIDATION

This paper presents validation comparisons between field and laboratory measurements and a new probabilistic model for predicting ship underkeel clearance (UKC). Prototype ship motions and environmental data were obtained in May 1999 in the deep-draft entrance channel at Barbers Point, HI. These field measurements were reproduced in controlled laboratory studies in 2000 and 2002 with a model of the World Utility (WU) bulk carrier. These measurements constitute some of the data being used to validate the Corpss Channel Analysis and Design Evaluation Tool (CADET), a suite of programs to determine the optimum dredge depth for entrance channels. In general, the CADET predictions matched the field and laboratory measurements within cm-accuracy for wave heights that ranged from 45 cm to 75 cm.

6 Degree of Freedom Motion Analysis of Surface Ship Models

A 6 degree of freedom (DOF) optical motion analysis system has been adapted for the measurement of surface ship model motion. The motions measured by the optical system are surge, sway, heave, roll, pitch, and yaw. Apparently, the calibration of the system is not traceable to a National Metrology Institute (NMI). Measurement results are compared to on-board instruments for the measurement of roll, pitch, and heave, which were calibrated prior to the test. Test results are presented for a Large Medium Speed Roll-on Roll-off (LMSR) ship model with a Transformable Craft (T-Craft) Surface Effect Ship (SES) in tandem connected by a ramp. The LMSR model was attached to a carriage in a rectangular wave-making basin. The results presented in this paper were conducted at a simulated Sea-State 4 and model speed of 0.372 m/s. The results were in reasonable agreement in pitch and roll where the instrument calibration uncertainties were between ±0.19° and ±0.67°, while the manufacturer’s specification is ±1.0°. Heave was measured near the stern by the optical system. The uncertainty in the correction to the center of gravity is estimated to be ±17 mm for the LMSR in comparison to the direct measurement of heave by a string pot at the cg, where the calibration uncertainty was ±1.3 mm.© 2011 ASME