Designing Against Capsize in Beam Seas: Recent Advances and New Insights

1997 ◽  
Vol 50 (5) ◽  
pp. 307-325 ◽  
Author(s):  
J. M. T. Thompson
Keyword(s):  
Symmetry Breaking ◽  
Invariant Manifolds ◽  
Damping Ratio ◽  
Historical Review ◽  
Ocean Waves ◽  
Worst Case ◽  
Wide Range ◽  
Wave Slope ◽  
Stiffness And Damping ◽  
Damping Functions

The mechanics of ship capsize under steady and transient conditions is reviewed, focusing on recent applications of global geometrical techniques of nonlinear dynamics. These yield significant new ideas about capsize in waves and its generalization, the escape of a driven oscillator from a potential well. These ideas are robust against gross changes in the forms of the stiffness and damping functions. Fractal basin boundaries in phase and control space yield useful design criteria against transient capsize, which have been applied to real ships. Invariant manifolds are used to explain and predict the sudden loss of safe basin in the space of the starting conditions, and indeterminate resonant jumps to capsize. Further work is concerned with capsize suppression by heave-roll coupling; effects of parametric excitation; and capsize under a propagating wave front. After this historical review, the practical relevance of the results is assessed, and suggestions are made for a standardized transient testing procedure for hulls. A systematic formulation for rolling in beam waves, employing the effective gravitational field perpendicular to the wave surface and the Froude-Krilov assumption, allows the use of the calm-water GZ curve. With general stiffness and damping functions, dimensional analysis offers insights that are often overlooked: for example, the sustainable wave slope is always proportional to the angle of vanishing stability. A degree of quantification is provided by a design formula derived from the displacement magnification of linear resonance. This is validated by Melnikov theory and simulation. It predicts that under worst-case excitation we have: sustainable wave slope = 2 ζθv, where θv is the angle of vanishing stability and ζ is a damping ratio appropriate for heavy roll. So in ocean waves of slope 0.5 (≈30°), a vessel with a θv of one radian needs a damping ratio of about 1/4. Implications for the design of hulls reveal counter-intuitive results: it is the distance of the potential barrier, not its height, that prevents escape or capsize. The formula helps to define a universal capsize diagram. New results on symmetry breaking are finally presented. These show that capsize studies of a symmetric unbiased vessel can give seriously unsafe results. The sustainable wave slope is so sensitive to a symmetry-breaking bias (due to wind or cargo imbalance) that a static heel of 2.5° can halve the sustainable slope over a wide range of sea states. This review article has 112 references.

scholarly journals Observations of Steep Wave Statistics in Open Ocean Waters

2005 ◽  
Vol 22 (3) ◽  
pp. 258-271 ◽  
Author(s):  
Nicholas Scott ◽  
Tetsu Hara ◽  
Edward J. Walsh ◽  
Paul A. Hwang
Keyword(s):  
Wind Speed ◽  
Ocean Waves ◽  
Open Ocean ◽  
Breaking Wave ◽  
Wave Statistics ◽  
Analysis Methodology ◽  
Wide Range ◽  
Wave Slope ◽  
Steep Waves ◽  
Steep Wave

Abstract A new wavelet analysis methodology is proposed to estimate the statistics of steep waves. The method is applied to open ocean wave height data from the Southern Ocean Waves Experiment (1992) and from a field experiment conducted at Duck, North Carolina (1997). Results show that high wave slope crests appear over a wide range of wavenumbers, with a large amount being much shorter than the dominant wave. At low wave slope thresholds, all wave fields have roughly the same amount of wave crests regardless of wind forcing. The steep wave statistic decays exponentially with the square of the wave slope threshold, with a decay rate that is larger for the low wind cases than the high wind cases. Comparison of the steep wave statistic with independent measurements of the breaking wave statistic suggests a breaking wave slope threshold of about 0.12. The steep wave statistic does not scale with the cube of the wind speed, suggesting that other factors besides the wind speed also affect its level. Comparison of the steep wave statistic to the saturation spectrum reveals a reasonable correlation at moderate wave slope thresholds.

Robust Design of a Micro-Electromechanical System in the Presence of Assembly Uncertainty

2010 ◽  
Author(s):  
Choong-Ho Rhee ◽  
Kenn Oldham
Keyword(s):  
Damping Ratio ◽  
Weight Bearing ◽  
Open Loop ◽  
Alignment Error ◽  
Wide Range ◽  
Loop Dynamics ◽  
Out Of Plane ◽  
Micro Electromechanical System ◽  
Stiffness And Damping ◽  
Function Models

Three methods of minimizing error between the transient response of a dynamic system with parameter variation and its nominal open-loop dynamics are tested on a second-order example system of a piezoelectric microactuator. The example system is a piezoelectrically actuated silicon flexure intended for use in micro-robotic systems. Polymer and silicon layers are to be stacked on top of the original flexure to increase out-of-plane weight-bearing capacity, but this process is subject to substantial alignment error. The procedures evaluated in this paper seek target stiffness and damping coefficients that minimize error in open-loop actuator motion. The first method is based on simple damping ratio and natural frequency calculations, while the second and third methods are based on state-space and transfer function models, respectively. All three approaches reduce error in transient dynamics compared to nominal designs based solely on static weight-bearing or fabrication considerations, with the state-based being identified as usable to a wide range of systems, although the ability to reduce sensitivity to model variation in purely open-loop operation is limited.

scholarly journals Harmonic hybrid inflation

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Federico Carta ◽  
Nicole Righi ◽  
Yvette Welling ◽  
Alexander Westphal
Keyword(s):  
Domain Wall ◽  
Symmetry Breaking ◽  
Initial Conditions ◽  
Scalar Potential ◽  
Field Range ◽  
Slow Roll ◽  
Minimal Form ◽  
Wide Range ◽  
Hybrid Inflation ◽  
Type Iib String Theory

Abstract We present a mechanism for realizing hybrid inflation using two axion fields with a purely non-perturbatively generated scalar potential. The structure of the scalar potential is highly constrained by the discrete shift symmetries of the axions. We show that harmonic hybrid inflation generates observationally viable slow-roll inflation for a wide range of initial conditions. This is possible while accommodating certain UV arguments favoring constraints f ≲ MP and ∆ϕ60 ≲ MP on the axion periodicity and slow-roll field range, respectively. We discuss controlled ℤ2-symmetry breaking of the adjacent axion vacua as a means of avoiding cosmological domain wall problems. Including a minimal form of ℤ2-symmetry breaking into the minimally tuned setup leads to a prediction of primordial tensor modes with the tensor-to-scalar ratio in the range 10−4 ≲ r ≲ 0.01, directly accessible to upcoming CMB observations. Finally, we outline several avenues towards realizing harmonic hybrid inflation in type IIB string theory.

scholarly journals Identification of Dynamic Parameters of Pedestrian Walking Model Based on a Coupled Pedestrian–Structure System

2021 ◽  
Vol 11 (14) ◽  
pp. 6407
Author(s):  
Huiqi Liang ◽  
Wenbo Xie ◽  
Peizi Wei ◽  
Dehao Ai ◽  
Zhiqiang Zhang
Keyword(s):  
Negative Correlation ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Field Testing ◽  
The Body ◽  
Structural Vibration ◽  
Pedestrian Dynamics ◽  
Structure Interaction ◽  
Mass Spring ◽  
Stiffness And Damping

As human occupancy has an enormous effect on the dynamics of light, flexible, large-span, low-damping structures, which are sensitive to human-induced vibrations, it is essential to investigate the effects of pedestrian–structure interaction. The single-degree-of-freedom (SDOF) mass–spring–damping (MSD) model, the simplest dynamical model that considers how pedestrian mass, stiffness and damping impact the dynamic properties of structures, is widely used in civil engineering. With field testing methods and the SDOF MSD model, this study obtained pedestrian dynamics parameters from measured data of the properties of both empty structures and structures with pedestrian occupancy. The parameters identification procedure involved individuals at four walking frequencies. Body frequency is positively correlated to the walking frequency, while a negative correlation is observed between the body damping ratio and the walking frequency. The test results further show a negative correlation between the pedestrian’s frequency and his/her weight, but no significant correlation exists between one’s damping ratio and weight. The findings provide a reference for structural vibration serviceability assessments that would consider pedestrian–structure interaction effects.

Influencing Factors on Dynamic Response of Hydrostatic Guideways

2011 ◽  
Vol 418-420 ◽  
pp. 2095-2101 ◽  
Author(s):  
Zhi Wei Wang ◽  
Wan Hua Zhao ◽  
Bing Heng Lu
Keyword(s):  
Film Thickness ◽  
Damping Ratio ◽  
Pressure Ratio ◽  
Settling Time ◽  
Lubricating Oil ◽  
Oil Viscosity ◽  
Supply Pressure ◽  
Maximum Value ◽  
Small Perturbation Method ◽  
Stiffness And Damping

Stiffness and damping of hydrostatic guideways are calculated by small perturbation method based on Reynolds equation in dynamic regime. The hydrostatic guideway is considered as a system which consists of the mass, the spring and the damper. The effects of some main parameters on stiffness, damping and damping ratio are analyzed which include the supply pressure, the film thickness, the pad dimension, the pressure ratio, the lubricating oil volume and the lubricating oil viscosity. The relationships between the settling time of the hydrostatic guideways and these parameters are investigated under a step load. It is shown that the slide block returns to equilibrium without overshooting under a step load, and the amplitude of the block vibration has not a maximum value under a cyclic load, due to the large damping effect( ξ>1). In addition, the settling time can be shorten with the increase of the supply pressure, the film thickness and the lubricating oil volume, and also with the decrease of the pressure ratio and the lubricating oil viscosity. The settling time get the shortest value when recess parameter( α) is 0.55.

A New Type of Gas Turbine Based-Hybrid Propulsion System: Part 1—Concept Development, Definition of Mission Parameters and Preliminary Sizing

2000 ◽  
Author(s):  
Emiliano Cioffarelli ◽  
Enrico Sciubba
Keyword(s):  
Gas Turbine ◽  
Combustion Engine ◽  
Development Program ◽  
Propulsion System ◽  
Medium Size ◽  
Passenger Cars ◽  
Worst Case ◽  
Hybrid Propulsion ◽  
Wide Range ◽  
Definition Of

Abstract A hybrid propulsion system of new conception for medium-size passenger cars is described and its preliminary design developed. The system consists of a turbogas set operating at fixed rpm, and a battery-operated electric motor that constitutes the actual “propulsor”. The battery pack is charged by the thermal engine which works in an electronically controlled on/off mode. Though the idea is not entirely new (there are some concept cars with similar characteristics), the present study has important new aspects, in that it bases the sizing of the thermal engine on the foreseen “worst case” vehicle mission (derived from available data on mileage and consumption derived from road tests and standard EEC driving mission cycles) that they can in fact be accomplished, and then proceeds to develop a control strategy that enables the vehicle to perform at its near–peak efficiency over a wide range of possible missions. To increase the driveability of the car, a variable-inlet vane system is provided for the gas turbine. After developing the mission concept, and showing via a thorough set of energy balances (integrated over various mission profiles), a preliminary sizing of the turbogas set is performed. The results of this first part of the development program show that the concept is indeed feasible, and that it has important advantages over both more traditional (Hybrid Vehicles powered by an Internal Combustion Engine) and novel (All-Electric Vehicle) propulsion systems.

Convulsive Disorders in Children, with Reference to Treatment with Ketogenic Diet

PEDIATRICS ◽  
1964 ◽  
Vol 34 (4) ◽  
pp. 589-590
Author(s):  
CESARE T. LAMBROSO
Keyword(s):  
Antiepileptic Drugs ◽  
Historical Review ◽  
Pediatric Age ◽  
Neonatal Seizures ◽  
General Outline ◽  
Ketogenic Diets ◽  
Wide Range ◽  
Convulsive Disorders ◽  
Page Book ◽  
Insight Into

This 300-page book covers a wide range of so-called convulsive disorders in the pediatric age, such as neonatal seizures, febrile fits, breathholding spells, and "hypsarhythmia," as well as a review of antiepileptic drugs and a series of do and don't questions most often asked by anxious parents, supplied with well-thought-out answers. Some 80 pages are devoted to a historical review, a description of the principles and the actual practice of ketogenic diets, including necessary but often neglected tables. This section, although clearly out of proportion to the general outline of the book, is possibly its greatest contribution, for it not only offers practical aid in a most difficult therapeutic enterprise, but also affords the reader some insight into the author's own experience.

Using Parametric Simulation to Optimize Suspension Design

2003 ◽  
Author(s):  
G. Walter Rosenberger ◽  
Peter E. Klauser ◽  
George P. Binns ◽  
Gary P. Wolf
Keyword(s):  
Control Unit ◽  
Cost Effective ◽  
Parameter Analysis ◽  
Ride Quality ◽  
Worst Case ◽  
Suspension Parameters ◽  
History Of ◽  
Vehicle Response ◽  
Stiffness And Damping ◽  
Test Result

A project to design and implement suspension improvements to Amtrak’s F-40 Non-Powered Control Unit (NPCU) cars is described. The cars, built from former F-40 locomotives, had a history of poor ride quality. Rail Sciences Inc. (RSI) inspected one of the cab cars and measured its ride quality. Peter Klauser modeled the vehicle in NUCARS™ and validated the model against the test data. The vehicle response was primarily in pitch and bounce modes. To optimize the suspension, Klauser simulated vehicle response for a range of four suspension parameters: primary stiffness and damping, and secondary stiffness and damping. Nearly 2600 suspension combinations were considered. Simulation file setup and data analysis were performed automatically using parameter analysis software interacting with NUCARS™. The result was a five-dimensional response contour for each output variable, such as the engineer’s seat vertical and lateral accelerations, and car body acceleration. The most cost effective stiffness and damping parameters were selected from the response contour and translated into component specifications. RSI then provided Amtrak with new axle box springs and dampers, and re-tested the vehicle. The test result closely followed the predicted results from the simulation. Engineer’s seat vertical and cab lateral accelerations improved by 42% and 32% respectively for the worst-case conditions in the test territory.

South Africa at a Turning Point?

2015 ◽  
Vol 53 (3) ◽  
pp. 477-486 ◽  
Author(s):  
Elke Zuern
Keyword(s):  
South Africa ◽  
Turning Point ◽  
Case Scenario ◽  
State Collapse ◽  
Worst Case ◽  
South Africans ◽  
Nelson Mandela ◽  
Wide Range ◽  
Electricity Provision

South Africa is at a crossroads. The state has not adequately addressed dire human development needs, often failing to provide the services it constitutionally guarantees. As a result, citizens are expressing their frustrations in a variety of ways, at times including violence. These serious challenges are most readily apparent in poverty, inequality and unemployment statistics, but also in electricity provision, billing and affordability as well as a recent spate of racially motivated attacks which highlight the tension both among South Africans and between South Africans and darker skinned foreigners. The country has, however, been on the brink before and avoided the worst-case scenario of full-scale civil war and state collapse. Far too often South Africa's past successes have been attributed to the role of one man, Nelson Mandela. While Mandela was indeed an extraordinary human being who rightly deserved the international awards and accolades as well as the deep admiration of so many, South Africa's triumphs as a society and a state are the product of both cooperative and conflicting contributions by a wide range of actors. A central question at the present juncture is how well equipped domestic actors and institutions are to address the crisis. The following pages seek to provide some insights and through the perspectives of three authors to consider causes and possible responses.

scholarly journals Chronic Kidney Disease Prediction using Machine Learning Models

2019 ◽  
Vol 9 (1) ◽  
pp. 6364-6367
Keyword(s):  
Machine Learning ◽  
Chronic Kidney Disease ◽  
Kidney Disease ◽  
Kidney Failure ◽  
Bone Diseases ◽  
Machine Learning Algorithms ◽  
Knowledge Generation ◽  
Good Prediction ◽  
Worst Case ◽  
Wide Range

The field of biosciences have advanced to a larger extent and have generated large amounts of information from Electronic Health Records. This have given rise to the acute need of knowledge generation from this enormous amount of data. Data mining methods and machine learning play a major role in this aspect of biosciences. Chronic Kidney Disease(CKD) is a condition in which the kidneys are damaged and cannot filter blood as they always do. A family history of kidney diseases or failure, high blood pressure, type 2 diabetes may lead to CKD. This is a lasting damage to the kidney and chances of getting worser by time is high. The very common complications that results due to a kidney failure are heart diseases, anemia, bone diseases, high potasium and calcium. The worst case situation leads to complete kidney failure and necessitates kidney transplant to live. An early detection of CKD can improve the quality of life to a greater extent. This calls for good prediction algorithm to predict CKD at an earlier stage . Literature shows a wide range of machine learning algorithms employed for the prediction of CKD. This paper uses data preprocessing,data transformation and various classifiers to predict CKD and also proposes best Prediction framework for CKD. The results of the framework show promising results of better prediction at an early stage of CKD

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