Arthur Reed

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Interpretation of Results of Numerical Simulation

Fluid mechanics and its applications, 2023

Running a numerical simulation of motions in waves is in and of itself of little significance. Th... more Running a numerical simulation of motions in waves is in and of itself of little significance. The results of the simulation-the motion time histories must be processed to produce statistical quantities if they are to be of any practical use. Techniques for dealing with time histories of non-rare and rare events are presented. In the realm of nonrare statistics, the techniques are further divided into statistics for the linear and nonlinear motion regimes. The focus is on non-rare events, but predicting rare event statistics is discussed.

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Characterization of Physical Phenomena for Large Amplitude Ship Roll Motion

Day 1 Wed, August 11, 2010

An experiment was performed to examine and characterize physical phenomena which occur during the... more An experiment was performed to examine and characterize physical phenomena which occur during the process of large amplitude ship roll motions. These phenomena result in distinctly different behavior compared to the small amplitude roll motion regime. Because these processes are highly nonlinear, it is important to consider them when modeling ship motions in heavy seas. An understanding of the relevant physics for large amplitude ship roll motions and the characterization of the phenomena from this investigation are intended to provide additional understanding of the processes which should be modeled, to enable more accurate predictions of ship roll motion. The results from this experiment provide useful insight in the physical phenomena which occur during large amplitude roll motion and will help with the formulation of a new model for large amplitude ship roll motion, including ship roll damping and forces on the bilge keel.

Air Pressure Scale Effects During Damage Model Tests

Fluid mechanics and its applications, 2014

The Stability in Waves committee of the 27 th ITTC has investigated the significance of scale eff... more The Stability in Waves committee of the 27 th ITTC has investigated the significance of scale effects in air pressure on flooding model tests under atmospheric conditions. For this purpose, the committee classified the flooding cases into the trapped air case and vented air cases, and investigated the flooding process for a simple geometry using the state equation of air and the orifice equation. As a result, the committee concluded that the scale effect is large for the case of trapped air and small vent area. For the other cases, the effect is small and can therefore be neglected in the model test of a damaged ship. The committee further proposed some guidelines that can be used to reduce the scale effect of air pressure.

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Model Characteristics and Validation Approach for a Simulation Tool Supporting Direct Stability Assessment

Contemporary Ideas on Ship Stability, 2019

Significant challenges exist in the validation and formal acceptance of dynamic stability simulat... more Significant challenges exist in the validation and formal acceptance of dynamic stability simulation tools, which can have a limiting effect on operations or concept design due to a need for conservatism. These challenges primarily consist of validation metrics and criteria, uncertainty characterization, and defining the scope of conditions (both environmental and operating) that must be examined in order to ensure that the simulation tool is valid for all conditions of interest. In discussing these challenges, this paper proposes approaches to the problem of validation and formal acceptance that can be applied in future efforts.

Applicability of the Difference between Population Statistics as an Acceptance Criteria Metric for Seakeeping Validation

The difference between population statistics is proposed as a primary acceptance criteria metric ... more The difference between population statistics is proposed as a primary acceptance criteria metric for the direct quantitative validation of ship simulation tools in support of accreditation for uses related to ship motions in irregular seas. The discussion is applicable to comparisons of statistical quantities calculated from ship motion time histories generated by simulations and benchmark data such as scale-model test results. The difference between population statistics provides several of the key characteristics desirable in acceptance criteria, including quantifiable measures of accuracy, completeness, and self-consistency. Further, this metric can be applied to a variety of statistical quantities of interest, provides an opportunity to extend parameter-level comparison results to a broader measure of overall accuracy, and allows for straightforward application of engineering margins traceable to simulation tool performance requirements. Use of the difference between values (oft...

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Erratum: SNAME transactions 2001 (vol. 109): "Modern computational methods for ships in a seaway" (Marine Technology 109)

Marine technology, 2002

New models of irregular waves — way forward

In a series of papers, Degtyarev and Reed have presented the theory and provided the results from... more In a series of papers, Degtyarev and Reed have presented the theory and provided the results from an autoregressive model for representing a seaway—at a point in space, over a line and over a plane, all as a function of time (1-D, 2-D & 3-D, respectively). In several other papers, Degtyarev and Gankevich have provided the theory for a technique for efficiently computing the velocity potential beneath a prescribed 1-D or 2-D surface, varying with time. Together this series of papers provides the information needed to compute the fully nonlinear hydrostatic and Froude-Krylov pressures under a seaway in an efficient manner without having to be concerned with the computing-time constraints imposed by the use of a Fourier series representation of a seaway imposed by the use of a Longuet-Higgins model. The next step is to apply these models in a seakeeping code so that the practical aspects of using these appealing theoretical approaches can be assessed. This paper provides a very brief d...

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A Method to Model Large Amplitude Ship Roll Damping

A method is proposed to model large amplitude ship roll damping, with considerations for large am... more A method is proposed to model large amplitude ship roll damping, with considerations for large amplitude roll motion effects, such as bilge keel interaction with the free-surface. The method is based on consideration of distinct ship-specific physical phenomena, such as bilge keel emergence and deck submergence. Abrupt physical changes occur with these events, resulting in significant changes in the damping of the system. Without these considerations, roll motion may be underpredicted. Additional considerations for practical implementation of the proposed method are also discussed.

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Advances in the Predictive Capability for Ship Dynamics in Extreme Waves

An Analysis of the Bilge Keel Roll Damping Component Model

Since the 1970s, component-based frequency-domain models based on Ikeda’s method have been used t... more Since the 1970s, component-based frequency-domain models based on Ikeda’s method have been used to predict roll damping. These are based on data from conventional wall-sided hull forms at small roll angles. The limits of applicability for large roll amplitudes and unconventional hull form geometries are not well understood. Bilge keel roll damping component predictions are computed using Ikeda’s formulas for three vessels. Comparisons were made to highlight differences in bilge keel roll damping components for modern hull forms and to identify limits of application with roll amplitude. The bilge keel-hull interaction damping component is influenced by both bilge keel size and hull proportions, resulting in unreasonable behavior at larger roll amplitudes and roll frequencies. A simple model for the bilge keel wave-making component is proposed and examined to determine when this component should be considered.

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Validating a six-degrees-of-freedom maneuvering in irregular-waves code for extreme conditions—The practical aspects

Probabilistic Engineering Mechanics, 2020

Abstract This paper focuses on issues related to Validation, i.e., determining for a computationa... more Abstract This paper focuses on issues related to Validation, i.e., determining for a computational tool that predicts the motions of a vessel in extreme seas if the theory and the code that implements the theory accurately models the relevant physical problem of interest. The challenge of this validation is the fact that the excitation process— waves—are stochastic and that as a consequence, the responses are in turn stochastic. Therefore, there are three aspects of the problem that must be dealt with: how much data is sufficient; what statistical techniques should be used to analyse the data; and how should the data be compared? Possible answers to these questions are provided.

Numerical Modeling of Nonlinear Interactions Between Ships and Surface Gravity Waves, Part 1: Ship Waves in Calm Water

Journal of Ship Research, 2005

This paper presents a pseudo-spectral model for nonlinear ship-surface wave interactions. The alg... more This paper presents a pseudo-spectral model for nonlinear ship-surface wave interactions. The algorithm used in the model is a combination of spectral and boundary element methods: the boundary element method is used to translate physical quantities between the nonuniform ship surface and the regular grid of the spectral representation; the spectral method is used throughout the remainder of the fluid domain. All possible wave-wave interactions are included in the model (up to N-wave interactions for the truncation order N of the spectral expansions). This paper focuses on the mathematical theory and numerical method of the model and presents some numerical results for steady Kelvin waves in calm water. The nonlinear bow waves at high Froude numbers from the pseudo-spectral model are much closer to the experimental results than those from linear ship wave models. Our results demonstrate that the pseudo-spectral model is significantly faster than previous ship wave models: with the s...

Propeller Design of U.S. Navy's Swath, T-Agos 19

The authors discuss the process by which a propeller for a U.S. Navy research vessel, the SWATH s... more

Probability of Capsizing in Beam Seas with Piecewise Linear Stochastic GZ Curve

Fluid Mechanics and Its Applications, 2011

The probability of capsizing for a dynamical system with time-varying piecewise linear stiffness ... more The probability of capsizing for a dynamical system with time-varying piecewise linear stiffness is presented. The simplest case is considered, in which only the angle of the maximum of the restoring curve is changing. These changes are assumed to be dependent on wave excitation; such a system can be considered as a primitive model of a ship in beam seas, where all changes in stability are caused by heave motions. A split-time approach is used, in which capsizing is considered as a sequence of two random events: upcrossing through a certain threshold (non-rare problem) and capsizing after upcrossing (rare problem). To reflect the time-varying stability, a critical roll rate is introduced as a stochastic process defined at any instant of time. Capsizing is then associated with an upcrossing when the instantaneous roll rate exceeds the critical roll rate defined for the instant of upcrossing. A self-consistency check of the method, in which a statistical frequency of capsizing was obtained by time-domain evaluation of the response of the piecewise linear dynamical system and favorably compared with the theoretical prediction is described.

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End-To-End Simulator Development at DTMB

ABSTRACT

A Vane-Wheel Propulsor for a Naval Auxiliary

ABSTRACT

Modeling of Incident Waves near the Ship's Hull (Application of Autoregressive Approach in Problems of Simulation of Rough Seas)

A holistic approach to the problem of modeling irregular waves for simulation of ship behavior is... more A holistic approach to the problem of modeling irregular waves for simulation of ship behavior is proposed. The mathematical basis considered is a representation of the stochastic processes of interest by a generalized autoregressive model (ARM) and related models of periodically correlated random process. ARM is used to generate space-time realizations of the wave surface of any duration. Application of the aforesaid model takes into account both the true stochastic process (lack of repetition in quasi-steady implementation of the process inherent in other models of wind waves), and synoptic and seasonal variability of wave forecasts for a specific geographic region can be incorporated.

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Synoptic and short-term modeling of ocean waves

International Shipbuilding Progress

The problem of wave climate description and modeling are considered on both a short-term and syno... more The problem of wave climate description and modeling are considered on both a short-term and synoptic basis. The wave climate is considered as an ensemble of conditions of spatio-temporal wave fields characterized by frequency-directional spectra. Using an expanded set of wave and wind characteristics makes it possible to correctly introduce the concept of a wave weather “scenario” and to use it to evaluate vessel safety. The mathematical basis of the short-term wave description is by the representation of the stochastic processes by a generalized autoregressive model (ARM) and related models of periodically correlated random process. An ARM is used to generate space-time realizations of the wave surface of any short-term duration. Application of the aforesaid model takes into account the true stochastic process (lack of repetition in quasi-steady implementation of the process inherent in other models of wind waves). Ways of treating synoptic and seasonal variability of wave forecas...

A Piecewise Model for Prediction of Large Amplitude Total Ship Roll Damping

Volume 6: Ocean Engineering, 2011

A piecewise model is presented to model total ship roll damping, with considerations for large am... more A piecewise model is presented to model total ship roll damping, with considerations for large amplitude roll motion effects, such as bilge keel interaction with the free-surface. The model is based on the consideration of distinct ship-specific physical phenomena, such as bilge keel emergence. Abrupt physical changes occur with these events, resulting in significant changes in the damping characteristics of the system. Without these considerations, roll motion may be under-predicted. Some additional considerations needed for the practical implementation of the proposed piecewise model are also discussed.

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Lagrangian velocity profiles in the wake of a high speed vessel

Ocean Engineering, 1994

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