Sensitivity of Rogue Wave Prediction to the Oceanic Stratification

2015 ◽  
Author(s):  
Qiuchen Guo ◽  
M.-Reza Alam
Keyword(s):  
State Of The Art ◽  
Rogue Wave ◽  
Rogue Waves ◽  
Offshore Structures ◽  
High Accuracy ◽  
Current State ◽  
Spatial Domains ◽  
The Waves ◽  
Very High ◽  
Accurate Wave

Oceanic rogue waves are short-lived very large amplitude waves (a giant crest typically followed or preceded by a deep trough) that appear and disappear suddenly in the ocean causing damage to ships and offshore structures. Assuming that the state of the ocean at the present time is perfectly known, then the upcoming rogue waves can be predicted via numerically solving the equations that govern the evolution of the waves. State of the art radar technology can now provide accurate wave height measurements over large spatial domains and when combined with advanced wave-field reconstruction techniques together render deterministic details of the current state of the ocean (i.e. surface elevation and velocity field) at any given moment of time with a very high accuracy. The ocean density is, however, stratified (mainly due to the salinity and temperature differences). This density stratification, with today’s technology, is very difficult to measure accurately. As a result, in most predictive schemes these density variations are neglected. While the overall effect of the stratification on the average state of the ocean may not be significant, here we show that these density variations can strongly affect the prediction of oceanic rogue wave. Specifically, we consider a broadband oceanic spectrum in a two-layer density stratified fluid and study, via extensive statistical analysis, the effects of the strength of the stratification (difference between densities) and the depth of the thermocline on the prediction of upcoming rogue waves.

Loads on Ships and Offshore Structures

2007 ◽  
Author(s):  
P. Temarel
Keyword(s):  
State Of The Art ◽  
Fatigue Loading ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Green Water ◽  
Vortex Induced Vibrations ◽  
Ice Loads ◽  
Offshore Industry ◽  
Multi Body ◽  
Wave Induced

The Loads Committee of the International Ship and Offshore Structures Congress (ISSC) critically reviews the state of the art of environmental and operational loads. Amongst these, elements more relevant to the offshore industry will be presented in this paper. These comprise wave-induced loads, including linear and nonlinear methods, multi-body interactions, slamming, green water, sloshing and rogue waves, cables and risers, vortex-induced vibrations, ice loads, fatigue loading and, verification and validation.

scholarly journals Current State of Development of Ship Structural Design and Optimization Methods

2020 ◽  
Vol 3 (3) ◽  
pp. 171-187
Author(s):  
Marin Palaversa ◽  
Pero Prebeg ◽  
Jerolin Andrić
Keyword(s):  
Sensitivity Analysis ◽  
Support System ◽  
Structural Design ◽  
State Of The Art ◽  
Optimization Methods ◽  
Offshore Structures ◽  
Engineering Practice ◽  
Design And Optimization ◽  
Current State ◽  
Design Support System

This paper presents state-of-the-art methodologies and methods used in the rationally-based structural design of ships and offshore structures, namely design support system, structural optimization, surrogate modelling and sensitivity analysis. It demonstrates their application in structural design of a platform support vessel. It ends with a list of benefits that a structural designer may expect when the presented methods/methodologies are used. It also shows the obstacles to their full implementation in the engineering practice.

scholarly journals Numerical modelling of extreme waves by Smoothed Particle Hydrodynamics

2011 ◽  
Vol 11 (2) ◽  
pp. 419-429 ◽  
Author(s):  
M. H. Dao ◽  
H. Xu ◽  
E. S. Chan ◽  
P. Tkalich
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Wave Crest ◽  
Extreme Waves ◽  
Coastal Structures ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
The Impact ◽  
The Waves

Abstract. The impact of extreme/rogue waves can lead to serious damage of vessels as well as marine and coastal structures. Such extreme waves in deep water are characterized by steep wave fronts and an energetic wave crest. The process of wave breaking is highly complex and, apart from the general knowledge that impact loadings are highly impulsive, the dynamics of the breaking and impact are still poorly understood. Using an advanced numerical method, the Smoothed Particle Hydrodynamics enhanced with parallel computing is able to reproduce well the extreme waves and their breaking process. Once the waves and their breaking process are modelled successfully, the dynamics of the breaking and the characteristics of their impact on offshore structures could be studied. The computational methodology and numerical results are presented in this paper.

Design Potentials of External Gear Machines With Asymmetric Tooth Profile

2013 ◽  
Author(s):  
Ram Sudarsan Devendran ◽  
Andrea Vacca
Keyword(s):  
Design Principle ◽  
State Of The Art ◽  
Design Method ◽  
Optimization Procedure ◽  
Tooth Profile ◽  
Design Parameters ◽  
Simulation Tool ◽  
Performance Potentials ◽  
Current State ◽  
Very High

This paper describes the design, optimization and the performance potentials of external gear machines with asymmetric tooth profiles. Conventionally, the design of these machines is entirely based on symmetric involute profile. A design method has been developed to derive the tooth profiles based on a modified rack-cutter profile which is assumed to be used for manufacturing the gears with asymmetric involute surfaces and trochoidal fillet profiles. The study is based on the simulation tool HYGESim (HYdraulic GEar machines Simulator) which is being developed and has been validated by the authors’ research group to accurately analyze the performance of the machine. For the purpose of this research, HYGESim was adapted to simulate the particular case of non-symmetric gear profiles. A specific optimization procedure based on genetic algorithm was implemented to find the maximum performance of the new design, in terms of volumetric efficiency, fluid borne noise, internal pressure peaks and localized cavitation acting on the design parameters that characterize the tooth profile. The results of the optimization process are compared to the current state of the art for external gear machines. This comparison show very high potentials for this new design principle, particularly concerning the reduction of the fluid borne noise.

scholarly journals Rogue waves in 2006–2010

2011 ◽  
Vol 11 (11) ◽  
pp. 2913-2924 ◽  
Author(s):  
I. Nikolkina ◽  
I. Didenkulova
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Rogue Wave ◽  
World Ocean ◽  
Rogue Waves ◽  
Shallow Waters ◽  
Extreme Waves ◽  
Significant Wave ◽  
The World ◽  
The Waves

Abstract. The evidence of rogue wave existence all over the world during last five years (2006–2010) has been collected based mainly on mass media sources. Only events associated with damage and human loss are included. The waves occurred not only in deep and shallow zones of the World Ocean, but also at the coast, where they were manifested as either sudden flooding of the coast or high splashes over steep banks or sea walls. From the total number of 131 reported events, 78 were identified as evidence of rogue waves (which are expected to be at least twice larger than the significant wave height). The background significant wave height was estimated from the satellite wave data. The rogue waves at the coast, where the significant wave height is unknown or meaningless, were selected based on their unexpectedness and hazardous character. The statistics built on the selected 78 events suggests that extreme waves cause more damage in shallow waters and at the coast than in the deep sea and can be used for hazard assessment of the rogue wave phenomenon.

scholarly journals Metamaterials-Enabled Sensing for Human-Machine Interfacing

Sensors ◽  
2020 ◽  
Vol 21 (1) ◽  
pp. 161
Author(s):  
Fei Li ◽  
Run Hu
Keyword(s):  
State Of The Art ◽  
Recent Decade ◽  
High Accuracy ◽  
Electric Machines ◽  
Future Directions ◽  
Daily Lives ◽  
The Future ◽  
Working Principle ◽  
Very High ◽  
The Way

Our modern lives have been radically revolutionized by mechanical or electric machines that redefine and recreate the way we work, communicate, entertain, and travel. Whether being perceived or not, human-machine interfacing (HMI) technologies have been extensively employed in our daily lives, and only when the machines can sense the ambient through various signals, they can respond to human commands for finishing desired tasks. Metamaterials have offered a great platform to develop the sensing materials and devices from different disciplines with very high accuracy, thus enabling the great potential for HMI applications. For this regard, significant progresses have been achieved in the recent decade, but haven’t been reviewed systematically yet. In the Review, we introduce the working principle, state-of-the-art sensing metamaterials, and the corresponding enabled HMI applications. For practical HMI applications, four kinds of signals are usually used, i.e., light, heat, sound, and force, and therefore the progresses in these four aspects are discussed in particular. Finally, the future directions for the metamaterials-based HMI applications are outlined and discussed.

scholarly journals Bayesian U-Net: Estimating Uncertainty in Semantic Segmentation of Earth Observation Images

2021 ◽  
Vol 13 (19) ◽  
pp. 3836
Author(s):  
Clément Dechesne ◽  
Pierre Lassalle ◽  
Sébastien Lefèvre
Keyword(s):  
Deep Learning ◽  
Satellite Images ◽  
State Of The Art ◽  
Qualitative Evaluation ◽  
Semantic Segmentation ◽  
High Accuracy ◽  
Earth Observation ◽  
Current State ◽  
Learning Techniques ◽  
Reference Databases

In recent years, numerous deep learning techniques have been proposed to tackle the semantic segmentation of aerial and satellite images, increase trust in the leaderboards of main scientific contests and represent the current state-of-the-art. Nevertheless, despite their promising results, these state-of-the-art techniques are still unable to provide results with the level of accuracy sought in real applications, i.e., in operational settings. Thus, it is mandatory to qualify these segmentation results and estimate the uncertainty brought about by a deep network. In this work, we address uncertainty estimations in semantic segmentation. To do this, we relied on a Bayesian deep learning method, based on Monte Carlo Dropout, which allows us to derive uncertainty metrics along with the semantic segmentation. Built on the most widespread U-Net architecture, our model achieves semantic segmentation with high accuracy on several state-of-the-art datasets. More importantly, uncertainty maps are also derived from our model. While they allow for the performance of a sounder qualitative evaluation of the segmentation results, they also include valuable information to improve the reference databases.

Study on Influence of Wave-Current Interaction on Prediction of Rogue Wave Taking Viscous Effect Into Account

2013 ◽  
Author(s):  
Bo Peng ◽  
Ning Ma ◽  
Xiechong Gu
Keyword(s):  
Numerical Model ◽  
Viscous Flow ◽  
Wave Height ◽  
Rogue Wave ◽  
Rogue Waves ◽  
Offshore Structures ◽  
Wave Generation ◽  
Group Method ◽  
Linear Wave ◽  
Current Interaction

Wave-current interaction is a common phenomenon in real sea and has significant influence on sea conditions, thus threatening the safety of offshore structures. Waves countering current is one of the main reasons for occurrence of rogue waves, which imperils offshore structures and is of much importance for research. Based on Computational Fluid Dynamics (CFD), the simulation of viscous flow for wave generation in a Circulating Water Channel (CWC) has been carried out. In the calculation model, the motion of an oscillating flap type wave maker is simulated to generate specified waves by controlling movement of dynamic mesh in numerical model. Smoothing and local refreshing of dynamic meshes have been done to adapt meshes. Then, viscous flow simulation of wave generation among current in numerical tank is accomplished by using Reynolds-Averaged-Navier-Stokes (RANS) equation, renormalization group method based (RNG-based) k-ε turbulence model and Volume of Fluid (VOF) method as treatment of free surface. Both waves propagating along and against current have been investigated. To validate the numerical model, a part of calculation results are compared with the experimental results in CWC for regular wave propagating along current. Furthermore, calculations based on linear wave theory and modified nonlinear Schrödinger Equation (mNLS) are also performed. For further investigation of occurrence of rogue wave in deep water, focusing technique is adopted by using transient water wave. Results show that wave height and group velocity of wave sequence would change notably when wave propagates along preexisting large-scale current. Wave height decreases as the velocity of uniform current increases and wave sequence arrives at given position earlier when propagating on faster current. On the other hand, on a counter current, waves are steepened and wave height increases dramatically. Based on the numerical results, several characteristics and principal values such as wave height and asymmetry have been discussed. The effects of viscous flow and wave-current interaction on prediction of rogue waves are analyzed and evaluated. Accordingly, some concluding remarks on improving of numerical model of rogue wave are given.

scholarly journals A Review of Elastic–Plastic Contact Mechanics

2017 ◽  
Vol 69 (6) ◽  
Author(s):  
Hamid Ghaednia ◽  
Xianzhang Wang ◽  
Swarna Saha ◽  
Yang Xu ◽  
Aman Sharma ◽  
...  
Keyword(s):  
State Of The Art ◽  
Asperity Contact ◽  
Elastic Plastic ◽  
Single Asperity ◽  
Current State ◽  
Metallic Contacts ◽  
Contact Models ◽  
Rough Surface Contact ◽  
Elastic And Plastic Deformation ◽  
Very High

In typical metallic contacts, stresses are very high and result in yielding of the material. Therefore, the study of contacts which include simultaneous elastic and plastic deformation is of critical importance. This work reviews the current state-of-the-art in the modeling of single asperity elastic–plastic contact and, in some instances, makes comparisons to original findings of the authors. Several different geometries are considered, including cylindrical, spherical, sinusoidal or wavy, and axisymmetric sinusoidal. As evidenced by the reviewed literature, it is clear that the average pressure during heavily loaded elastic–plastic contact is not governed by the conventional hardness to yield strength ratio of approximately three, but rather varies according to the boundary conditions and deformed geometry. For spherical contact, the differences between flattening and indentation contacts are also reviewed. In addition, this paper summarizes work on tangentially loaded contacts up to the initiation of sliding. As discussed briefly, the single asperity contact models can be incorporated into existing rough surface contact model frameworks. Depending on the size of a contact, the material properties can also effectively change, and this topic is introduced as well. In the concluding discussion, an argument is made for the value of studying hardening and other failure mechanisms, such as fracture as well as the influence of adhesion on elastic–plastic contact.

scholarly journals Using Social Signals to Predict Shoplifting: A Transparent Approach to a Sensitive Activity Analysis Problem

Sensors ◽  
2021 ◽  
Vol 21 (20) ◽  
pp. 6812
Author(s):  
Shane Reid ◽  
Sonya Coleman ◽  
Philip Vance ◽  
Dermot Kerr ◽  
Siobhan O’Neill
Keyword(s):  
Signal Processing ◽  
State Of The Art ◽  
High Accuracy ◽  
Black Box ◽  
Social Signals ◽  
Social Signal Processing ◽  
Legal Cases ◽  
Current State ◽  
Social Signal ◽  
High Degree

Retail shoplifting is one of the most prevalent forms of theft and has accounted for over one billion GBP in losses for UK retailers in 2018. An automated approach to detecting behaviours associated with shoplifting using surveillance footage could help reduce these losses. Until recently, most state-of-the-art vision-based approaches to this problem have relied heavily on the use of black box deep learning models. While these models have been shown to achieve very high accuracy, this lack of understanding on how decisions are made raises concerns about potential bias in the models. This limits the ability of retailers to implement these solutions, as several high-profile legal cases have recently ruled that evidence taken from these black box methods is inadmissible in court. There is an urgent need to develop models which can achieve high accuracy while providing the necessary transparency. One way to alleviate this problem is through the use of social signal processing to add a layer of understanding in the development of transparent models for this task. To this end, we present a social signal processing model for the problem of shoplifting prediction which has been trained and validated using a novel dataset of manually annotated shoplifting videos. The resulting model provides a high degree of understanding and achieves accuracy comparable with current state of the art black box methods.

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