6 Sep 2022

Method to Evaluate Vessel Wake Forces on Wetland Scarps

Purpose: This Coastal and Hydraulics engineering technical note (CHETN) presents a methodology to compute normal forces on wetland perimeters with vertically scarped edges. The approach uses an empirical algorithm that predicts the normal force given the offshore vessel wake height, period, and water depth at a given point. Wave impact forces are measured using load cells, which have not been applied previously to marsh settings. Load cell and vessel wake measurements from two field sites are combined to generate an empirical transfer function relating forces to incoming vessel wake characteristics.

18 May 2021

Suppressing the pressure-source instability in modeling deep-draft vessels with low under-keel clearance in FUNWAVE-TVD

Abstract: This Coastal and Hydraulics Engineering Technical Note (CHETN) documents the development through verification and validation of three instability-suppressing mechanisms in FUNWAVE-TVD, a Boussinesq-type numerical wave model, when modeling deep-draft vessels with a low under-keel clearance (UKC). Many large commercial ports and channels (e.g., Houston Ship Channel, Galveston, US Army Corps of Engineers [USACE]) are traveled and affected by tens of thousands of commercial vessel passages per year. In a series of recent projects undertaken for the Galveston District (USACE), it was discovered that when deep-draft vessels are modeled using pressure-source mechanisms, they can suffer from model instabilities when low UKC is employed (e.g., vessel draft of 12 m¹ in a channel of 15 m or less of depth), rendering a simulation unstable and obsolete. As an increasingly large number of deep-draft vessels are put into service, this problem is becoming more severe. This presents an operational challenge when modeling large container-type vessels in busy shipping channels, as these often will come as close as 1 m to the bottom of the channel, or even touch the bottom. This behavior would subsequently exhibit a numerical discontinuity in a given model and could severely limit the sample size of modeled vessels. This CHETN outlines a robust approach to suppressing such instability without compromising the integrity of the far-field vessel wave/wake solution. The three methods developed in this study aim to suppress high-frequency spikes generated nearfield of a vessel. They are a shock-capturing method, a friction method, and a viscosity method, respectively. The tests show that the combined shock-capturing and friction method is the most effective method to suppress the local high-frequency noises, while not affecting the far-field solution. A strong test, in which the target draft is larger than the channel depth, shows that there are no high-frequency noises generated in the case of ship squat as long as the shock-capturing method is used.

25 Jun 2020

PUBLICATION NOTICE: Quantification of the Flow Field around a Draghead Using a Physical Model

Abstract: This study quantifies the hydraulic flow field around a draghead using a 1:7 scaled California and general type draghead. The flow field velocity measurements were taken with each draghead stationary and moving with a prototype speed of 2 knots. The measured velocities increased proportionally with the pumping flow rate. Measured velocities were found to be inversely proportional to the distance from the draghead. As a result, the greatest entrainment velocities for the California draghead were measured between the two visors and below the visors. The entrainment velocities laterally of the dragheads were found to increase by a factor of 2 with the addition of either a concrete or sand bed below the draghead. The measured velocities changed dramatically when the draghead was moving with a prototype speed of 2 knots. The measurement locations to the side of the dragheads did not show the presence of fluid entrainment; instead, the velocities were dominated by the forward motion and subsequent generation of a shear layer around the draghead. The velocities behind the draghead indicated the presence of a wake behind the draghead, with the fluid moving forward at velocity equivalent to or greater than the forward translation speed.

22 Jan 2020

PUBLICATION NOTICE: Vessel Wake Prediction Tool

 Link: http://dx.doi.org/10.21079/11681/35153 Report Number: ERDC/CHL CHETN-IV-121Title: Vessel Wake Prediction Tool By Michael A. Hartman and Richard Styles Approved for Public Release; Distribution is Unlimited January 2020 Purpose: The purpose of this Coastal and Hydraulics Engineering Technical Note (CHETN) is to introduce a desktop application