A Generalized Mathematical Procedure for Ship Motion Stability Analysis

Author(s):  
Ibiba Emmanuel- Douglas

The challenges of providing safe and high performance marine vehicles present strict and often conflicting constraints that require rational and holistic analysis methodologies to obtain efficient design solutions. This paper presents a mathematical framework for stability analysis, which is one of the key elements in the design and operation of ships and floating bodies that still require considerable improvement. The method is based on the application of the Lyapunov stability analysis concept, which has been highly successful in some other engineering and scientific disciplines. The paper presents the fundamental concepts on the applicability of the Lyapunov method to ship motions stability analysis. Governing mathematical models are derived from first principles and interpreted in the context of geometrical and physical interrelationships. The analytical models are primarily developed for the generalized case of non-linear forced non-conservative systems and simplified by linearization in the case of coupled motion for detailed analysis and characterization of stability conditions and domain. The concept of “motion boundedness” is introduced to satisfy requirements of the Lyapunov method to ship motions subjected to continuous excitations. The analysis leads to some valuable deductions and insight that would be useful in the formulation of stability criteria for ships and marine vehicles in general. The most significant contribution is the possibility of explicit determination of geometric and hydrostatics/hydrodynamics parameters that govern ship stability characteristics.

Author(s):  
Metin Karayaka ◽  
Atle Steen ◽  
Roy Shilling ◽  
Rod Edwards

The Buoyancy Can Riser Tensioner (BCRT) systems are designed to provide tension to Top-Tensioned Risers (TTRs). BCRT systems do not transfer the riser weight to the floater and they minimize the interaction between the floating platform and the riser system. For deepwater field developments, this attractive feature allows efficient design of the floaters as well as the riser systems. Although, the vertical riser load is not transferred to the hull, the BCRT system makes lateral contact with the hull at several locations. During the past 3 years, analytical models have been developed to characterize mechanics of the contact between two large floating bodies (buoyancy can and hull) and compliant guide hardware has been developed. Placement of a compliant guide between the hull and the BCRT has become the current practice for design of Spar floaters. The initial development of the analytical models and the compliant guide hardware coincided with the Horn Mountain project. The project team placed extensive instrumentation on the hull and compliant guides with a vision to confirm robustness of the guides and to calibrate analytical models used during the design phase. This paper presents a summary of the data collected on the performance of the Spar hull, compliant guides, and the riser systems for storms up to 25 ft of significant wave height. Analytical methods and predictions are presented to characterize the dynamic interaction between the BCRT system and Spar hull.


2015 ◽  
Author(s):  
William A. Hockberger

The Quadrimaran was invented in France in the mid-1980s by Daniel Tollet. It was an inspired design and a radical departure from traditional ship design by a man from outside the marine industry unconstrained by industry technical practices and education. Technical experts could see it would entail more structure and subsystems than other high-performance vessels, but its promise was that those penalties would be more than offset by its claimed low power and fuel consumption. A prototype/demonstrator, Alexander, was built in 1990 and operated for five years carrying and impressing many hundreds of riders. Alexander performed beautifully and appeared to bear out what was claimed. Contracts for several Quadrimarans of different sizes came quickly, especially considering how conservative an industry this is. That was significantly due to Tollet's personal charisma and skill in selling riders on the dream of carrying passengers and freight over the water fast and in comfort, yet economically. Great skepticism prevailed in some quarters, especially among naval architects knowledgeable about AMVs (advanced marine vehicles) and early-stage whole-ship design. At technical meetings, one Quadrimaran principal would comment, for example, "Why would you carry freight across the Atlantic at 38 knots on 230,000 horsepower (a reference to the planned Fastship Atlantic TG-770) when you could do it at 60 knots on only 65,000 horsepower?" Listeners would ask how this could be possible, and he would assert again that the Quadrimaran could do it, but would decline to explain. Respected technical people were working with Tollet and his company and becoming convinced of the Quadrimaran's merit. Along with the contracts came engineers with experience in ship detail design and construction (very different from early-stage whole-ship design), or responsibilities for assessing and approving ships for service. Others were with engine and equipment suppliers. Their opinion that there was something unique and special about the Quadrimaran gave it credibility and influenced more people to accept the major claims made for it. Some dismissed the most extreme claims but still accepted the idea that the Quadrimaran was capable of unusually high performance - considerably less than was being claimed, perhaps, but high nevertheless. In hindsight it is clear the skeptics were right. Results never met expectations, nor could they have. In reality, the Quadrimaran has aspects that inherently prevent it from achieving the characteristics and performance its inventor believed attainable. It cannot be built in a commercially useful size and actually perform as intended. Why this is so will be explained. A crucial fact in the Quadrimaran's history is that Daniel Tollet and his close associates believed strongly that naval architects and engineers who had been immersed in working with the existing ship types would be unable to give the Quadrimaran the very different treatment they believed it required. (Their own educations and professional work were nontechnical.) Such people were excluded from the development of Quadrimaran designs, and the belated discovery of many fundamental technical problems can be attributed to this. The company Tollet established had a number of names over the years, and other associated entities were created at times for various purposes. In this paper they are referred to collectively as QIH (Quadrimaran International Holdings) so as not to confuse things unnecessarily. In 2004 QuadTech Marine LLC was established and acquired the Quadrimaran patent (US Patent No. 5,191,849) and related intellectual property from QIH. QuadTech laid out an extensive R&D program to close gaps in the technical background and address identified issues. In the process, additional information on earlier QIH projects and products was obtained and studied, which brought to light problems that significantly compromised the Quadrimaran's prospective performance and utility. The resulting much-reduced set of potential uses and users led the company to effectively stop pursuing Quadrimaran projects after 2009. (Note: The author was Chief Technology Officer for QuadTech Marine during 2006-9, studying the Quadrimaran and planning the R&D.)


2015 ◽  
Author(s):  
Hyun Y. Kim ◽  
Stephanie L. Fitzpatrick ◽  
David C. Kring

This paper describes the development and implementation of a reduced-order model to represent the hydrodynamic forces acting on a ship using Impulse-Response Functions (IRF). The approach will be conducted using Aegir, a timedomain seakeeping program that uses an advanced, Non-Rational Uniform B-Spline (NURBS) based, high-order boundary element method. The Cummins equation is slightly modified such that the memory function is decomposed into two terms: one for the impulsive velocity and the other term for the impulsive displacement. The present approach also further develops a method to simulate interactions between multiple floating bodies. The IRF convolutions for the free surface memory effect significantly reduce the computational effort compared to direct simulation. This will be demonstrated for both single and multi-body forward-speed, seakeeping simulations.


Author(s):  
Suman Lata Tripathi

An efficient design for testability (DFT) has been a major thrust of area for today's VLSI engineers. A poorly designed DFT would result in losses for manufacturers with a considerable rework for the designers. BIST (built-in self-test), one of the promising DFT techniques, is rapidly modifying with the advances in technology as the device shrinks. The increasing complexities of the hardware have shifted the trend to include BISTs in high performance circuitry for offline as well as online testing. Work done here involves testing a circuit under test (CUT) with built in response analyser and vector generator with a monitor to control all the activities.


2019 ◽  
Vol 37 (4) ◽  
pp. 1049-1069 ◽  
Author(s):  
Thanh T Tran

Abstract This paper investigates an equivalence between feedback linearization and backstepping control. Implications from equivalence are that stability and performance properties of one method are the same for another method. Thus, a property known to exist only for one method could be used to prove property also holds for another. Also, a suspected advantage of one method over the other could be proven to be a false conjecture. Control laws in both approaches are achieved by coordinate transformations and non-linear feedbacks. Further, resulting non-linear feedback control law achieved by feedback linearization method matches exactly with non-linear controller achieved by the backstepping control design. This equivalence is a general analytical match within the specific class of non-linear dynamic systems under investigation. Demonstrations are considered and validated via flight control of longitudinal dynamics of a high performance aircraft simulation model. Algorithms are tested and evaluated with analytical models and non-linear closed-loop simulation.


Electronics ◽  
2020 ◽  
Vol 9 (11) ◽  
pp. 1935
Author(s):  
Fares Alharbi ◽  
Muhammad Khurram Hameed ◽  
Anusha Chowdhury ◽  
Ayesha Khalid ◽  
Anupam Chattopadhyay ◽  
...  

The demand for low resource devices has increased rapidly due to the advancements in Internet-of-things applications. These devices operate in environments that have limited resources. To ensure security, stream ciphers are implemented on hardware due to their speed and simplicity. Amongst different stream ciphers, the eSTREAM ciphers stand due to their frugal implementations. This work probes the effect of unrolling on the efficiency of eSTREAM ciphers, including Trivium, Grain (Grain 80 and Grain 128) and MICKEY (MICKEY 2.0 and MICKEY-128 2.0). It addresses the question of optimal unrolling for designing high-performance stream ciphers. The increase in the area consumption is also bench-marked. The analysis is conducted to identify efficient design principles for ciphers. We experimentally show that the resulting performance after unrolling may disagree with the theoretical prediction when the effects of technology library are considered. We report pre-layout synthesis results on 65 and 130 nm ASIC technology as well as synthesis results for Xilinx FPGA platform in support of our claim. Based on our findings, cipher design and implementation suggestions are proposed to aid hardware designers. Furthermore, we explore why and where area-efficiency for these ciphers saturate.


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