Tim Gourlay

Instantaneous Global Navigation Satellite System (GNSS)-Based Attitude Determination for Maritime Applications

Global Navigation Satellite System (GNSS) is a valuable technology for a large number of maritime applications. Other than providing the absolute positioning service, it aids many demanding applications, such as precise docking, formation of surface craft, autonomous vehicles, sinkage monitoring, etc. GNSS carrier-phase-based algorithms provide high-precision positioning solutions, but an integer number of cycles inherent to the observed signal have to be resolved. A newly developed GNSS carrier-phase ambiguity resolution method is tested. The new method solves for the unknown number of integer cycles by exploiting the known placement of the GNSS antennas aboard the vessel. The a priori information on the antennas baseline separation is employed as a hard constraint. A simplified (linearized) version of the method, suitable for large vessels, is also analyzed. The new method was tested against the most challenging scenario when processing GNSS data: single-frequency, single-epoch, unaided ambiguity resolution. Through different tests, the high performance of the new method is demonstrated: high fixing rate, large robustness, and short time-to-fix after initialization, cycle slips, and/or loss of locks. Considerations about the wide spectra of maritime applications are given, and a specific experiment is carried out to demonstrate the capabilities of the method for navigation in shallow waters.

Shallowflow: A program to model ship hydrodynamics in shallow water

In this article we present details of “ShallowFlow”, a computer program to model the hydrodynamic flow around ships in calm shallow water. The program is based on slender-body shallow-water theory. Outputs from the program include far-field hydrodynamic pressure and flow velocities; free surface drawdown; sinkage and trim. Varying transverse bathymetry including open water, dredged channels, and canals of arbitrary cross-section may be modelled. The method is best suited to displacement ships, including cargo ships, ferries, cruise ships, warships and superyachts.Copyright

Validation Studies on Numerical Prediction of Ship Squat and Resistance in Shallow Water

vッイァ・ウ」ィャ。ァ・ョ・@zゥエゥ・イキ・ゥウ・Osオァァ・ウエ・、@」ゥエ。エゥッョZ mオ」ィ。L@pィゥャゥーー[@d・ョァL@g。ョ「ッ[@gッオイャ。ケL@tゥュ[@eャ@mッ」エ。イL@b・エエ。イ@oオャ、@HRPQVIZ@v。ャゥ、。エゥッョ sエオ、ゥ・ウ@ッョ@nオュ・イゥ」。ャ@pイ・、ゥ」エゥッョ@ッヲ@sィゥー@sアオ。エ@。ョ、@r・ウゥウエ。ョ」・@ゥョ@sィ。ャャッキ@w。エ・イN@iョZ@uャゥ」コォ。L kャ・ュ・ョウ[@b￶エエョ・イL@c。イャMuキ・[@k。ウエ・ョウL@m。イォッ[@eャッッエL@k。エイゥ・ョ[@d・ャ・ヲッイエイゥ・L@gオゥャャ。オュ・[ v。ョエッイイ・L@m。イ」[@c。ョ、イゥ・ウL@m。クゥュ[@l。エ。ゥイ・L@eカ・イエ@HhァNIZ@Tエィ@mashcon@M@iョエ・イョ。エゥッョ。ャ cッョヲ・イ・ョ」・@ッョ@sィゥー@m。ョッ・オカイゥョァ@ゥョ@sィ。ャャッキ@。ョ、@cッョヲゥョ・、@w。エ・イ@キゥエィ@sー・」ゥ。ャ@fッ」オウ@ッョ@sィゥー bッエエッュ@iョエ・イ。」エゥッョN@k。イャウイオィ・Z@bオョ、・ウ。ョウエ。ャエ@ヲイ@w。ウウ・イ「。オN@sN@QRRMQSSN ィエエーウZOO、クN、ッゥNッイァOQPNQXTUQOYWXMSMYSYRSPMSXMP⦅QVN

Comparison of AQWA, GL Rankine, MOSES, OCTOPUS, PDStrip and WAMIT with model test results for cargo ship wave-induced motions in shallow water

A benchmarking study is carried out concerning wave induced ship motions in shallow water, predicted with commercially available codes AQWA, GL Rankine, MOSES, OCTOPUS, PDStrip and WAMIT. Comparison is made with experiments for three cargo ship models tested at Flanders Hydraulics Research. The same IGES models of the ship hulls were used in all codes to ensure consistent representation of the model geometry. The comparisons may be used to assess the suitability of each code for zero-speed applications such as berthed ship motions and under-keel clearance, as well as forward-speed applications such as under-keel clearance in navigation channels. Another, quickly developing, application area that requires analysis of seaway-induced ship motions in shallow water, is analysis of motions, accelerations and loads on cargo transport, installation and service vessels for offshore wind parks.

Numerical Modeling of Radiated Sound for Impact Pile Driving in Offshore Environments

In this paper, a coupled near-to-far-field numerical model for predicting the acoustic emissions from impact pile driving in offshore environments is presented. The near-field region of the pile is modeled via an axisymmetric finite element method (FEM) model which is solved in the frequency domain. The calculated radiated field at a chosen radial distance in the FEM model is then expanded into a series of local normal modes (NMs) which are propagated into the far field, to predict the piling sound characteristics, such as the peak pressure and sound exposure levels, at large ranges. Numerical examples are presented for the same pile configuration adopted for the COMPILE 2014 benchmark workshop on predicting offshore pile-driving noise, and these results are compared in both the near and far fields to those of several other research groups who presented results at the workshop. Results from the present FEM-NM near-to-far-field model are shown to be generally in good agreement with those results from the other research groups. In the near field, similar signal waveforms are predicted by the various models which employ the same pile wall boundary conditions. In the far field, the selected models showed a variation of ±1 dB at 1.5 km, and ±4 dB at 50 km for the predicted peak pressure levels, and a variation of ±1.5 dB over the 50-km range for the predicted sound exposure levels.

Application of Potential Flow Methods to Ship Squat in Different Canal Widths

This paper presents a comparison of numerical methods with model test results for squat (sinkage and trim) of a 1:75 KVLCC2 model in the Flanders Hydraulics Research towing tank, at a range of rectangular canal widths and depths. The numerical methods are the Linear-2D and Nonlinear-1D methods in ShallowFlow, the Double-Body method in HullWave and the Rankine-Source method in GL Rankine. Analysis of the model tests showed that in the narrowest canals, mass flux past the ship was not conserved, nevertheless it appears that the Nonlinear-1D method may give good results for the narrowest canals. The Linear-2D method was found to give good results in the widest canal, particularly at the shallowest water depth. The Rankine-Source method was found to give good results for the widest canal, particularly at high speed. The Double-Body method was found to give quite consistently good results across all conditions.