Evaluation of Existing Semi-Empirical Models of Scour at a Submarine System

2018 ◽  
Author(s):  
Valeria S. Rego ◽  
Claudia M. P. M. Santos
Keyword(s):  
Experimental Data ◽  
Empirical Models ◽  
Small Scale ◽  
Scour Depth ◽  
Simplified Models ◽  
Practical Applications ◽  
Survey Statistics ◽  
Evaluation Of Data ◽  
Semi Empirical ◽  
Noncohesive Sediments

Assessment of scour below pipelines and gravity based structures in a submarine system is revisited with evaluation of data from two inspections and results for semi-empirical simplified models. Usually semi-empirical models are based on small scale experimental data that normally consider uniform and noncohesive sediments and have been questioned as to their practical applications. Recent local metocean data is used to revisit predictions of onset of scour and scour depth for the system, which are compared to survey statistics.

Current Affairs: Model Tests, Semi-Empirical Predictions and CFD Computations for Current Coefficients of Semi-Submersibles

2009 ◽  
Author(s):  
Guilherme Vaz ◽  
Olaf J. Waals ◽  
Harald Ottens ◽  
Fahd Fathi ◽  
Tim Le Soue¨f ◽  
...  
Keyword(s):  
Experimental Data ◽  
Empirical Models ◽  
Model Tests ◽  
Numerical Errors ◽  
Current Affairs ◽  
Rounded Corner ◽  
Model Predictions ◽  
Modeling Accuracy ◽  
Key Issues ◽  
Semi Empirical

Current loads on stationary vessels have been investigated as part of the Current Affairs Joint Industry Project (JIP). Model-tests, semi-empirical models and CFD methods were used to predict these loads. This paper examines one configuration out of the eight tested in the JIP; an idealized semi-submersible consisting of two square rounded-corner columns connected with a pontoon. The model experiments, empirical model predictions and CFD results are presented and discussed. ‘Blind’ and ‘Improved’ CFD computations (with and without knowledge of the experimental results) have been carried out by the JIP participants. Comparisons between these results are made, deviations from the experimental data are quantified and conclusions are drawn. Two key issues for modeling accuracy are identified and discussed; the location of the transition to turbulent flow and the control of the numerical errors.

scholarly journals Prediction of Seabed Scour Induced by Full-Scale Darrieus-Type Tidal Current Turbine

2019 ◽  
Vol 7 (10) ◽  
pp. 342 ◽  
Author(s):  
Sun ◽  
Lam ◽  
Dai ◽  
Hamill
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Tidal Current ◽  
Full Scale ◽  
Scale Model ◽  
Small Scale ◽  
Scour Depth ◽  
Equilibrium Scour Depth ◽  
Tidal Current Turbine ◽  
Current Turbine

Scour induced by a Darrieus-type tidal current turbine was investigated by using a joint numerical and experimental method with emphasis on the scour process of a full-scale turbine. This work proposes a new numerical method to estimate turbine scour developments, followed by model validation through experimental data in the initial stage. The small-scale numerical model was further extended to a full-scale model for the prediction of turbine scour. The numerical model consists of (1) k-ω turbulence closure, (2) a sediment transport model, and (3) a sediment slide model. The transient-state model was coupled with a morphologic model to calculate scour development. A dynamic mesh updating technique was implemented, enabling the autoupdate of data for the grid nodes of the seabed at each time step. Comparisons between the numerical results and the experimental measurements showed that the proposed model was able to capture the main features of the scour process. However, the numerical model underestimated about 15%–20% of the equilibrium scour depth than experimental data. An investigation of the temporal and spatial development of seabed scour around a full-scale Darrieus-type tidal current turbine is demonstrated. This work concludes that the proposed numerical model can effectively predict the scour process of tidal current turbines, and the rotating rotor has a significant impact on the equilibrium scour depth for full-scale turbines.

scholarly journals Voltage dependent models of the formative time delay in argon

2017 ◽  
Vol 15 (2) ◽  
pp. 81-93
Author(s):  
Suzana Stamenkovic ◽  
Vidosav Markovic ◽  
Aleksandar Jovanovic ◽  
Marjan Stankov
Keyword(s):  
Experimental Data ◽  
Data Analysis ◽  
Time Delay ◽  
Breakdown Voltage ◽  
Empirical Models ◽  
Formative Time ◽  
Voltage Dependent ◽  
Semi Empirical ◽  
Empirical Corrections ◽  
Good Agreement

Measurements of the formative time delay tf at different working voltages U in argon at low pressure are presented. The well-known decreasing voltage behavior of the formative time delay is theoretically described by different empirical and semi-empirical models. In addition to the introduced empirical models, some models from the literature are applied to elucidate experimentally obtained tf (U) dependence. However, the models from the literature show a good agreement with the experimental data only at low overvoltages ?U(?U=U-Us where Us is the static breakdown voltage). Therefore, empirical corrections are made based on data analysis, and good compatibility is achieved in a whole range of working voltages.

Diagnostics of metal samples using the results of experimental and theoretical study of positively charged microparticles formed upon sample destruction

2018 ◽  
Vol 84 (10) ◽  
pp. 23-28
Author(s):  
D. A. Golentsov ◽  
A. G. Gulin ◽  
Vladimir A. Likhter ◽  
K. E. Ulybyshev
Keyword(s):  
Experimental Data ◽  
Early Stage ◽  
Experimental Studies ◽  
Material Model ◽  
Total Charge ◽  
Cross Sectional ◽  
Practical Applications ◽  
Mechanical And Electrical Properties ◽  
Order Of Magnitude ◽  
Using Data

Destruction of bodies is accompanied by formation of both large and microscopic fragments. Numerous experiments on the rupture of different samples show that those fragments carry a positive electric charge. his phenomenon is of interest from the viewpoint of its potential application to contactless diagnostics of the early stage of destruction of the elements in various technical devices. However, the lack of understanding the nature of this phenomenon restricts the possibility of its practical applications. Experimental studies were carried out using an apparatus that allowed direct measurements of the total charge of the microparticles formed upon sample rupture and determination of their size and quantity. The results of rupture tests of duralumin and electrical steel showed that the size of microparticles is several tens of microns, the particle charge per particle is on the order of 10–14 C, and their amount can be estimated as the ratio of the cross-sectional area of the sample at the point of discontinuity to the square of the microparticle size. A model of charge formation on the microparticles is developed proceeding from the experimental data and current concept of the electron gas in metals. The model makes it possible to determine the charge of the microparticle using data on the particle size and mechanical and electrical properties of the material. Model estimates of the total charge of particles show order-of-magnitude agreement with the experimental data.

Force field for in-plane vibrations of terephthalonitrile

1989 ◽  
Vol 54 (1) ◽  
pp. 18-27 ◽  
Author(s):  
Juan F. Arenas ◽  
Juan I. Marcos ◽  
Francisco J. Ramírez
Keyword(s):  
Experimental Data ◽  
Force Field ◽  
Normal Coordinates ◽  
Internal Coordinates ◽  
Isotopic Shifts ◽  
Quadratic Force Field ◽  
Semi Empirical

The general quadratic force field for the in-plane vibrations of terephthalonitrile was calculated by the semi-empirical MINDO/3 method. This force field was refined to the frequencies observed experimentally for terephthalonitrile and isotopic shifts of terephthalonitrile-[15N2]. The refined frequencies reproduce the experimental data with errors less than 0.5%. The normal coordinates and the force field in internal coordinates were also calculated from the refined field.

scholarly journals 2D Nanomaterials for Effective Energy Scavenging

2021 ◽  
Vol 13 (1) ◽  
Author(s):  
Md Al Mahadi Hasan ◽  
Yuanhao Wang ◽  
Chris R. Bowen ◽  
Ya Yang
Keyword(s):  
Large Scale ◽  
Waste Heat ◽  
Material Selection ◽  
Power Supplies ◽  
Small Scale ◽  
Energy Scavenging ◽  
Power Sources ◽  
Practical Applications ◽  
2D Nanomaterials ◽  
Self Powered

AbstractThe development of a nation is deeply related to its energy consumption. 2D nanomaterials have become a spotlight for energy harvesting applications from the small-scale of low-power electronics to a large-scale for industry-level applications, such as self-powered sensor devices, environmental monitoring, and large-scale power generation. Scientists from around the world are working to utilize their engrossing properties to overcome the challenges in material selection and fabrication technologies for compact energy scavenging devices to replace batteries and traditional power sources. In this review, the variety of techniques for scavenging energies from sustainable sources such as solar, air, waste heat, and surrounding mechanical forces are discussed that exploit the fascinating properties of 2D nanomaterials. In addition, practical applications of these fabricated power generating devices and their performance as an alternative to conventional power supplies are discussed with the future pertinence to solve the energy problems in various fields and applications.

The effects of wind on the flame characteristics of individual leaves

2011 ◽  
Vol 20 (5) ◽  
pp. 657 ◽  
Author(s):  
Wesley J. Cole ◽  
McKaye H. Dennis ◽  
Thomas H. Fletcher ◽  
David R. Weise
Keyword(s):  
Froude Number ◽  
Flame Length ◽  
Flame Height ◽  
Combustion Model ◽  
Small Scale ◽  
Single Leaf ◽  
Small Branch ◽  
Flame Burner ◽  
Broadleaf Species ◽  
Semi Empirical

Individual cuttings from five shrub species were burned over a flat-flame burner under wind conditions of 0.75–2.80 m s–1. Both live and dead cuttings were used. These included single leaves from broadleaf species as well as 3 to 5 cm-long branches from coniferous and small broadleaf species. Flame angles and flame lengths were determined by semi-automated measurements of video images. Additional data, such as times and temperatures corresponding to ignition, maximum flame height and burnout were determined using video and infrared images. Flame angles correlated linearly with wind velocity. They also correlated with the Froude number when either the flame length or flame height was used. Flame angles in individual leaf experiments were generally 50 to 70% less than flame angles derived from Froude number correlations reported in the literature for fuel-bed experiments. Although flame angles increased with fuel mass and moisture content, they were unaffected by fuel species. Flame lengths and flame heights decreased with moisture contents and wind speed but increased with mass. In most cases, samples burned with wind conditions ignited less quickly and at lower temperatures than samples burned without wind. Most samples contained moisture at the time of ignition. Results of this small-scale approach (e.g. using individual cuttings) apply to ignition of shrubs and to flame propagation in shrubs of low bulk density. This research is one of the few attempts to characterise single-leaf and small-branch combustion behaviour in wind and is crucial to the continued development of a semi-empirical shrub combustion model.

A Critical Review of NOx Correlations for Gas Turbine Combustors

1975 ◽  
Author(s):  
D. A. Sullivan ◽  
P. A. Mas
Keyword(s):  
Experimental Data ◽  
Data Base ◽  
Gas Turbine ◽  
Critical Review ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
Empirical Correlations ◽  
Gas Turbine Combustors ◽  
Semi Empirical ◽  
Adequate Data

The effect of inlet temperature, pressure, air flowrate and fuel-to-air ratio on NOx emissions from gas turbine combustors has received considerable attention in recent years. A number of semi-empirical and empirical correlations relating these variables to NOx emissions have appeared in the literature. They differ both in fundamental assumptions and in their predictions. In the present work, these simple NOx correlations are compared to each other and to experimental data. A review of existing experimental data shows that an adequate data base does not exist to evaluate properly the various NOx correlations. Recommendations are proposed to resolve this problem in the future.

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