Leigh McCue

A Numerical Feasibility Study of a Parametric Roll Advance Warning System

This work studies the practicality of using finite-time Lyapunov exponents (FTLEs) to detect the inception of parametric resonance for vessels operating in irregular longitudinal seas. Parametrically excited roll motion is modeled as a single-degree-of-freedom system, with nonlinear damping and restoring terms. FTLEs are numerically calculated at every integration time step. Using this numerical model of parametric roll and through tracking trends in the FTLE time series behavior, warnings of parametric roll are identified. This work serves as a proof of concept of the FTLE technique’s viability in detecting parametric resonance. The ultimate aim of the research contained in this paper, along with future work, is the development of a real-time, onboard aid to warn of impending danger allowing for avoidance of severe, even catastrophic, vessel instabilities.

Use of Lyapunov Exponents to Predict Chaotic Vessel Motions

It is the aim of this paper to further the use of Lyapunov and local Lyapunov exponent methods for analyzing phenomena involving nonlinear vessel dynamics. Lyapunov exponents represent a means to measure the rate of convergence or divergence of nearby trajectories thus denoting chaos and possibly leading to the onset of conditions that produce capsize. The work developed here makes use of Lyapunov exponent methodologies to study capsize and chaotic behavior in vessels both experimentally and numerically using a multi-degree of freedom computational model. Since, the Lyapunov exponent is defined in the limit as time approaches infinity, one encounters fundamental difficulties using Lyapunov exponents on the capsize problem, which is inherently limited to a finite time. This work also incorporates the use of local Lyapunov exponents, which do not require an infinite time series, to demonstrate their usefulness in analyzing finite time chaotic vessel phenomena. The objective is to demonstrate the value of the Lyapunov exponent and local Lyapunov exponent as a predictive tool with which to indicate regions with crucial sensitivity to initial conditions. Through the intelligent use of Lyapunov exponents in vessel analysis to indicate specific regions of questionable stability, one may significantly reduce the volume of costly simulation and experimentation.

Simulator-based flight test engineering as a capstone to the dynamics and control curriculum

This paper details the development and curricular impact of Virginia Tech’s new course on “Flight Test Techniques.” By using the motion based flight simulator at Virginia Tech, students enjoy a semester-long flight testing experience that gives the realism of flight testing, without the costs, risks, and delays of actual aircraft. The first oering of this course, in the Spring of 2006, has shown high potential as a capstone course in the aerospace engineering curriculum assimilating material from dynamics and control courses with hands-on, real-world application. for the first time a course titled ‘Flight Test Techniques, AOE 4984’. The course is designed to expose senior level undergraduates to industry and government accepted methods used in flight testing aircraft by introducing real world problems into the department’s curriculum in a controlled environment. It also serves as a capstone course where concepts previously taught in several classes are integrated to give students an overarching view of aircraft operation. In order to facilitate a learning environment and mitigate safety issues associated with using real aircraft, two modern high performance aircraft models in the Virginia Tech Flight Simulation Laboratory are used instead of test aircraft. This allows for accomplishment of targeted learning objectives. It also gives students the ability and opportunity to serve in all of the various roles required to flight test an aircraft, from test pilot, to test conductor, to discipline engineer. The course is based on the principal that hands-on application of concepts learned in an academic setting is key to deep understanding. Due to safety issues, the cost of owning and operating aircraft and liability concerns, application of aerospace concepts learned in a classroom is often delayed until students arrive in industry. In industry employees are expected to perform their tasks without time to revisit concepts learned in school. This course oers students a means to apply lessons learned in a conventional classroom so that when students arrive in the workplace they already have the requisite experience in applying their academic skills to real-world problems. The goals of the course are threefold, namely to reinforce concepts taught in aircraft performance and stability and control classes, expose students to flight testing by reproducing the flight test environment in a classroom setting, and teach students flight test techniques based on currently used manuals in government evaluation of aircraft to prepare them for careers on flight test teams. The team teaching and supporting this course has unique credentials to enable this eort branching the fields of flight test engineering, test

The Effect of Coupled Heave/Heave Velocity or Sway/Sway Velocity Initial Conditions on Capsize Modeling

Obar et al. (2001) described a series of model tests and a numerical model of a rectangular barge in regular beam seas with three degrees of freedom in roll, heave, and sway used to investigate the onset of capsize. The model had minimal freeboard resulting in significant water-on-deck. This paper employs the numerical model to examine specifically the impact of the coupling in heave with heave velocity initial conditions or in sway with sway velocity initial conditions on ultimate stability. Direct comparison with experimental results was used to validate the numerical model and can be found in Lee et al (Lee, 2001; Lee et al, 2006).

Applications of Finite-Time Lyapunov Exponents to the Study of Capsize in Beam Seas

This paper demonstrates the use of finite-time Lyapunov exponents (FTLE) for the detection of large amplitude roll motions and capsize. The study is conducted for a simple, single degree of freedom model of the Edith Terkol in regular and random beam seas. The effectiveness of the FTLE technique is qualitatively compared to a scalar ship motion metric based upon the ‘energy index (EI)’ concept used for real-time identification of quiescence.

Modal Analysis of the Ice-Structure Interaction Problem

In this paper the authors build upon the single degree of freedom ice-structure interaction model initially proposed by Matlock, et al. (1969, 1971). The model created by Matlock, et al. (1969, 1971), assumed that the primary response of the structure would be in its fundamental mode of vibration. Modal analysis is used in this study, in which the response of each mode is superposed to find the complete modal response of the entire length of a pier subject to incremental ice loading. In Matlock, et al., the physical system is a bottom supported pier modeled as a cantilever beam. Realistic conditions such as ice accumulation on the pier modeled as a point mass and uncertainties in the ice characteristics are introduced in order to provide a stochastic response. The impact of number of modes in modeling is studied as well as dynamics due to fluctuations of ice impact height as a result of typical tidal fluctuations. A Poincare based analysis following on the research of Karr, et al. (1992) is employed to identify any periodic behavior of the system response. The intention of this work is to provide a foundation for future work coupling multiple piers and connecting structure for a comprehensive ice-wind-structural dynamics model.

Concepts and Conclusions from the “2010 Pan- American Advanced Studies Institute on Dynamics and Control of Manned and Unmanned Marine Vehicles”

In the summer of 2010, the first ever NSF’s Pan-American Advanced Studies Institute (PASI) in Colombia was held in Barranquilla and Cartagena. The two-week institute brought together researchers of the Americas to discuss topics related to dynamics and control of manned and unmanned marine vehicles. This paper presents a summary of the program organization and findings, along with lecturer and participant feedback. It is intended to serve as a lead-in to the technical papers by PASI participants contained in this special edition of Ship Science & Technology.

Identification of nonlinear and chaotic behavior in model-scale liquefied natural gas (LNG) carrier experimental data

This paper presents the results of an experimental study simulating the behavior of LNG carriers with partially filled tanks exposed to beam seas. Details of the experimental model and method of data collection are presented. Additionally, surrogate data testing is employed to demonstrate nonlinearity in vessel roll time series. Lastly, Lyapunov exponent calculations are performed to detect chaotic behavior resulting from nonlinear vessel motions coupled with the dynamics of fluid sloshing in on-board tanks. The nonlinear time series analysis programs contained in the TISEAN package [1] are used extensively throughout this work.Copyright