scholarly journals Development of small-scale unmanned hydrofoil boats

2020 ◽  
pp. 1-12
Author(s):  
Noah T. Thompson ◽  
Phillip R. Whitworth ◽  
Konstantin I. Matveev
Keyword(s):  
Small Scale ◽  
Empirical Correlations ◽  
Unmanned Surface Vehicles ◽  
High Speeds ◽  
Carbon Fiber Cloth ◽  
Measuring Module ◽  
Design Calculations ◽  
Semi Empirical ◽  
Maritime Community

Unmanned boats have gained a lot of interest in the maritime community during the last decade. Most hydrodynamic platforms employed for unmanned boats are based on traditional relatively simple hulls. In the present study, small-scale hydrofoil-assisted unmanned boats (0.6–0.7 m in length and 3.5–5.5 kg in mass) have been developed and tested. Design calculations using a hydrodynamic transverse-strip engineering method with semi-empirical correlations were applied to determine suitable dimensions for hydrofoil systems. The boat hulls and hydrofoils were fabricated by laying up carbon-fiber cloth sheets on foam cores or 3-D printed profiles. The boats were instrumented with outboard propulsors and electronic equipment for operations in both remote control and autopilot modes. In addition, an in-situ thrust-measuring module was designed and installed at the hull sterns to gather thrust data at GPS-measured speeds in the range between 0 and 11 m/s. The developed boats proved to be robust platforms capable of going over 600 m distances at high speeds while autonomously following preset paths. The presented methods and results can assist engineers developing unmanned surface vehicles that utilize advanced hydrodynamic concepts.

scholarly journals Upscaling THM modeling from small-scale to full-scale in-situ experiments in the Callovo-Oxfordian claystone

2021 ◽  
Vol 144 ◽  
pp. 104582
Author(s):  
D.M. Seyedi ◽  
C. Plúa ◽  
M. Vitel ◽  
G. Armand ◽  
J. Rutqvist ◽  
...  
Keyword(s):  
Full Scale ◽  
Small Scale ◽  
In Situ Experiments

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.

Predicting pressure piling by semi-empirical correlations

2005 ◽  
Vol 40 (3) ◽  
pp. 282-298 ◽  
Author(s):  
A. Di Benedetto ◽  
E. Salzano ◽  
G. Russo
Keyword(s):  
Empirical Correlations ◽  
Semi Empirical

Coupled Thermo-Hydro-Geochemical Models of Engineered Barrier Systems: The Febex Project

2000 ◽  
Vol 663 ◽  
Author(s):  
J. Samper ◽  
R. Juncosa ◽  
V. Navarro ◽  
J. Delgado ◽  
L. Montenegro ◽  
...  
Keyword(s):  
Large Scale ◽  
Reference Model ◽  
Numerical Models ◽  
Full Scale ◽  
Small Scale ◽  
Model Parameters ◽  
In Situ Test ◽  
Wide Range ◽  
Engineered Barrier

ABSTRACTFEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository (HLWR). It includes two main experiments: an situ full-scale test performed at Grimsel (GTS) and a mock-up test operating since February 1997 at CIEMAT facilities in Madrid (Spain) [1,2,3]. One of the objectives of FEBEX is the development and testing of conceptual and numerical models for the thermal, hydrodynamic, and geochemical (THG) processes expected to take place in engineered clay barriers. A significant improvement in coupled THG modeling of the clay barrier has been achieved both in terms of a better understanding of THG processes and more sophisticated THG computer codes. The ability of these models to reproduce the observed THG patterns in a wide range of THG conditions enhances the confidence in their prediction capabilities. Numerical THG models of heating and hydration experiments performed on small-scale lab cells provide excellent results for temperatures, water inflow and final water content in the cells [3]. Calculated concentrations at the end of the experiments reproduce most of the patterns of measured data. In general, the fit of concentrations of dissolved species is better than that of exchanged cations. These models were later used to simulate the evolution of the large-scale experiments (in situ and mock-up). Some thermo-hydrodynamic hypotheses and bentonite parameters were slightly revised during TH calibration of the mock-up test. The results of the reference model reproduce simultaneously the observed water inflows and bentonite temperatures and relative humidities. Although the model is highly sensitive to one-at-a-time variations in model parameters, the possibility of parameter combinations leading to similar fits cannot be precluded. The TH model of the “in situ” test is based on the same bentonite TH parameters and assumptions as for the “mock-up” test. Granite parameters were slightly modified during the calibration process in order to reproduce the observed thermal and hydrodynamic evolution. The reference model captures properly relative humidities and temperatures in the bentonite [3]. It also reproduces the observed spatial distribution of water pressures and temperatures in the granite. Once calibrated the TH aspects of the model, predictions of the THG evolution of both tests were performed. Data from the dismantling of the in situ test, which is planned for the summer of 2001, will provide a unique opportunity to test and validate current THG models of the EBS.

scholarly journals On the short-term variability of turbulence and temperature in the winter mesosphere

2018 ◽  
Vol 36 (4) ◽  
pp. 1099-1116
Author(s):  
Gerald A. Lehmacher ◽  
Miguel F. Larsen ◽  
Richard L. Collins ◽  
Aroh Barjatya ◽  
Boris Strelnikov
Keyword(s):  
Attitude Control ◽  
Large Scale ◽  
Lower Thermosphere ◽  
Density Fluctuations ◽  
Large Temperature ◽  
Small Scale ◽  
Spatial And Temporal Variability ◽  
Temperature Structure ◽  
Wind Shears

Abstract. Four mesosphere–lower thermosphere temperature and turbulence profiles were obtained in situ within ∼30 min and over an area of about 100 by 100 km during a sounding rocket experiment conducted on 26 January 2015 at Poker Flat Research Range in Alaska. In this paper we examine the spatial and temporal variability of mesospheric turbulence in relationship to the static stability of the background atmosphere. Using active payload attitude control, neutral density fluctuations, a tracer for turbulence, were observed with very little interference from the payload spin motion, and with high precision (<0.01 %) at sub-meter resolution. The large-scale vertical temperature structure was very consistent between the four soundings. The mesosphere was almost isothermal, which means more stratified, between 60 and 80 km, and again between 88 and 95 km. The stratified regions adjoined quasi-adiabatic regions assumed to be well mixed. Additional evidence of vertical transport and convective activity comes from sodium densities and trimethyl aluminum trail development, respectively, which were both observed simultaneously with the in situ measurements. We found considerable kilometer-scale temperature variability with amplitudes of 20 K in the stratified region below 80 km. Several thin turbulent layers were embedded in this region, differing in width and altitude for each profile. Energy dissipation rates varied between 0.1 and 10 mW kg−1, which is typical for the winter mesosphere. Very little turbulence was observed above 82 km, consistent with very weak small-scale gravity wave activity in the upper mesosphere during the launch night. On the other hand, above the cold and prominent mesopause at 102 km, large temperature excursions of +40 to +70 K were observed. Simultaneous wind measurements revealed extreme wind shears near 108 km, and combined with the observed temperature gradient, isolated regions of unstable Richardson numbers (0<Ri<0.25) were detected in the lower thermosphere. The experiment was launched into a bright auroral arc under moderately disturbed conditions (Kp∼5).

scholarly journals Microwave snow emission modeling uncertainties in boreal and subarctic environments

2015 ◽  
Vol 9 (5) ◽  
pp. 5719-5773
Author(s):  
A. Roy ◽  
A. Royer ◽  
O. St-Jean-Rondeau ◽  
B. Montpetit ◽  
G. Picard ◽  
...  
Keyword(s):  
Grain Size ◽  
Spatial Variability ◽  
Boreal Forest ◽  
Frozen Soil ◽  
Microwave Emission ◽  
Small Scale ◽  
Radiometric Measurements ◽  
Snow Properties ◽  
Modeling Uncertainties

Abstract. This study aims to better understand and quantify the uncertainties in microwave snow emission models using the Dense Media Radiative Theory-Multilayer model (DMRT-ML) with in situ measurements of snow properties. We use surface-based radiometric measurements at 10.67, 19 and 37 GHz in boreal forest and subarctic environments and a new in situ dataset of measurements of snow properties (profiles of density, snow grain size and temperature, soil characterization and ice lens detection) acquired in the James Bay and Umijuaq regions of Northern Québec, Canada. A snow excavation experiment – where snow was removed from the ground to measure the microwave emission of bare frozen ground – shows that small-scale spatial variability in the emission of frozen soil is small. Hence, variability in the emission of frozen soil has a small effect on snow-covered brightness temperature (TB). Grain size and density measurement errors can explain the errors at 37 GHz, while the sensitivity of TB at 19 GHz to snow increases during the winter because of the snow grain growth that leads to scattering. Furthermore, the inclusion of observed ice lenses in DMRT-ML leads to significant improvements in the simulations at horizontal polarization (H-pol) for the three frequencies (up to 20 K of root mean square error). However, the representation of the spatial variability of TB remains poor at 10.67 and 19 GHz at H-pol given the spatial variability of ice lens characteristics and the difficulty in simulating snowpack stratigraphy related to the snow crust. The results also show that for ground-based radiometric measurements, forest emission reflected by the surface leads to TB underestimation of up to 40 K if neglected. We perform a comprehensive analysis of the components that contribute to the snow-covered microwave signal, which will help to develop DMRT-ML and to improve the required field measurements. The analysis shows that a better consideration of ice lenses and snow crusts is essential to improve TB simulations in boreal forest and subarctic environments.

scholarly journals VERIFICAÇÃO DO DESEMPENHO DAS ESTACAS INJETADAS AUTOPERFURANTES EXECUTADAS EM SOLOS ARENOSOS PARA CONSTRUÇÃO DE USINA EÓLICA

2017 ◽  
Vol 13 (2) ◽  
Author(s):  
Rodrigo Cerqueira Rogerio
Keyword(s):  
Structural Characteristics ◽  
Load Capacity ◽  
The Self ◽  
Executive Processes ◽  
Empirical Methods ◽  
Deep Drilling ◽  
Load Tests ◽  
Different Diameters ◽  
Semi Empirical

RESUMO: Apresenta-se neste trabalho a solução adotada para execução das fundações do Parque de Usina Eólica localizado no Ceará, com a utilização das estacas injetadas autoperfurantes, executadas em presença de solos arenosos. No qual consiste em perfurar o solo com altíssima velocidade por rotação e “pull down”, através da injeção simultânea de nata de cimento com medias pressões. Ocasionando na estaca um diâmetro final que pode obter o dobro do bit de perfuração, de acordo com o tipo de solo, gerado pelo efeito do jato da nata de cimento. Detalhando os processos executivos, verificando os aspectos técnicos e operacionais, para melhor compreender as características estruturais deste elemento. De forma a verificar “in situ” o desempenho deste novo tipo de fundação profunda, foram realizadas provas de carga, em estacas com diferentes diâmetros e comprimentos, realizadas em perfis estratigráficos de solos arenosos, para melhor avaliação de sua capacidade de carga. Analisando-se os ensaios das provas de carga interpretados a base da extrapolação da curva carga versus recalque e das previsões da capacidade de carga, obtidas por meio dos métodos semi-empíricos de correlação com ensaios de penetração (SPT), avaliando os padrões de execução desta tipologia de estaca injetada para comunidade geotécnica. ABSTRACT: This paper aims to establish the selected solution to except the foundations of the Wind Energy Park in Ceará (Brazil), with an executive methodology of the self-drilling injection piles framed in loco in Sandy soil. In which the soil drilling is done with the highest speed by rotation and pull down, through the simultaneous injection of grouting with medium pressures. This kind of drilling causes in the pile a final diameter that can get the double bore bit, according to the type of soil, done by the grouting blast. The executive processes are detailed as a whole, and also presenting the pile materials composition, in order to understand the structural characteristics of this element. To verify the performance of this new kind of deep drilling, instrumentations were done: settlement control and load tests in constructions with different structural characteristics, in self-drilling injected piles with different diameters and length, done in stratigraphical sandy, for a better evaluation of its load capacity. Analyzing the essays of load tests interpreted in the basis of curve extrapolation load versus settlement and the previsions of the load capacity, obtained by semi-empirical methods correlating with the penetrations methods (SPT), offering information to the geotechnical community.

scholarly journals A Case Study of Clear-Air Turbulence at Upper Levels

2021 ◽  
Author(s):  
Léo Rogel ◽  
Didier Ricard ◽  
Eric Bazile ◽  
Irina Sandu
Keyword(s):  
Turbulent Flow ◽  
Partial Information ◽  
Weather Prediction ◽  
Turbulent Fluxes ◽  
Small Scale ◽  
Mixing Length ◽  
Vertical Resolution ◽  
Stable Conditions ◽  
Study Results

&lt;p&gt;Because of the technical difficulties of achieving measurements at high altitudes, it is not clear how well turbulent phenomena are represented in the upper levels of current Numerical Weather Prediction (NWP) operational models.&lt;br&gt;Indeed, turbulence in strongly stable conditions near the tropopause is known to be particularly difficult to correctly parameterize. The constraining buoyancy forces on the vertical lead to anisotropic turbulence, potentially inhibiting turbulent production in NWP models.&lt;br&gt;Partial information for high altitude turbulence events is nonetheless available in the form of in-situ measurements from aircrafts. However, it only allows for qualitative comparisons with model outputs.&lt;br&gt;This study focuses on a turbulent episode induced by a winter upper-level jet above east Belgium on January 27, 2018, for which in-situ EDR (Eddy Dissipation Rate) reports indicate moderate-or-greater turbulence levels. Numerical simulations are performed with the M&amp;#233;t&amp;#233;o-France operational model AROME, and with the mesoscale research model MesoNH (Laero/CNRM), at the same horizontal grid resolution (1.3km). These two models also use the eddy-diffusivity turbulence scheme of Cuxart et al (2000), a 1.5 order closure scheme based on a prognostic Turbulent Kinetic Energy (TKE) evolution equation, with a diagnostic computation of the mixing length.&lt;br&gt;TKE budgets, as well as stability indices and gradient-based quantities (Richardson number, vertical wind shear) are computed from the model outputs, and qualitative comparison with in-situ data is presented. Time evolution of the turbulent event over Belgium is well captured by both models, agreeing with EDR data.&lt;br&gt;Several sensitivity tests on the vertical resolution, on the mixing length formulation and on the parameters of the TKE equation are then performed. Most notably, the use of an increased vertical resolution near the tropopause greatly enhances the turbulent fluxes in both operational and research models. Secondly, comparison of various expressions of the mixing length shows that the Bougeault and Lacarrere (1989) formulation produces the higher amount of subgrid TKE and turbulent mixing. A decreased turbulent dissipation parameter also significantly increases the amount of subgrid TKE. On the contrary, the use of a 3D turbulence scheme appears to have very limited impacts on the turbulent flow at this kilometer-scale horizontal resolution.&lt;br&gt;On a second part of this study, results from ongoing Large Eddy Simulations (LES) will be presented. These simulations aim at representing small-scale features of the turbulent flow. They will be used as a reference for the computation of turbulent fluxes at kilometer-scale resolution using a coarse-graining method, allowing for a comparison with the parameterized fluxes from the turbulence scheme. In particular, the dissipation term of the TKE equation will be examined. These results are expected to give insight on the leading turbulent mechanisms for which the current turbulence parameterization can be improved in stable conditions.&lt;/p&gt;

scholarly journals A STUDY INTO ICE BUILD-UP AND MELTING ON VERTICAL COOLED PIPES

2016 ◽  
Vol 52 (3) ◽  
Author(s):  
Y. Zasiadko ◽  
O. Pylypenko ◽  
A. Forsiuk ◽  
R. Gryshchenko
Keyword(s):  
Thermal Energy ◽  
Experimental Unit ◽  
Ice Thickness ◽  
Ice Melting ◽  
Empirical Correlations ◽  
Time Intervals ◽  
Ice Accumulation ◽  
Time Periods ◽  
Semi Empirical

The use of cold accumulators based on the principle of ice build up on the cooled surfaces during off-peak periods and ice melting during on-peak periods is an effective method of electricity bills reduction. Within comparatively short periods of on-peak demand a noticeable amount of thermal energy related to ice melting is to be released, it becomes clear that not only sizing of ice accumulators based on balance calculations is actual, but also the determination of time periods of ice accumulation becomes critical. This work presents experimental unit for obtaining data on the ice build-up on the vertical cooled pipes and later on to continuously register data on the ice thickness diminishing at the regimes of ice melting when cooling of pipe stops. The data for ice build-up and melting for some regimes have been presented and analyzed. The data form the base for deriving semi-empirical correlations allowing to determine a time intervals necessary to generate of ice layers of a given thickness.

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