326,489 research outputs found
The influence of the ship's speed and distance to an arbitrarily shaped bank on bank effects
A displacement vessel obviously displaces a (large) amount of water. In open and deep navigation areas this water can travel almost without any restriction underneath and along the ship's hull. In restricted and shallow waterways, however, the displaced water is squeezed under and along the hull. These bathymetric restrictions result in increased velocities of the return flow along the hull. The resulting pressure distribution on the hull causes a combination of forces and moments on the vessel. If generated because of asymmetric flow due to the presence of a bank, this combination of forces and moment is known as bank effects.
By far the most comprehensive and systematic experimental research program on bank effects has been carried out in the Towing Tank for Manoeuvres in Shallow Water (cooperation Flanders Hydraulics Research Ghent University) at Flanders Hydraulics Research (FHR) in Antwerp, Belgium. The obtained data set on bank effects consists of more than 14 000 unique model test setups. Different ship models have been tested in a broad range of draft to water depth ratios, forward speeds and propeller actions. The tests were carried out along several bank geometries at different lateral positions between the ship and the installed bank.
The output consists of forces and moments on hull, rudder and propeller as well as vertical ship motions. An analysis of this extensive database has led to an increased insight into the parameters which are relevant for bank effects.
Two important parameters are linked to the relative distance between ship and bank and the ship's forward speed. The relative position and distance between a ship and an arbitrarily shaped bank is ambiguous. Therefore a definition for a dimensionless distance to the bank will be introduced. In this way the properties of a random cross section are taken into account without exaggerating the bathymetry at a distance far away from the ship or without underestimating the bank shape at close proximity to the ship.
The dimensionless velocity, named the Tuck number (Tu), considers the water depth and blockage, and is based on the velocity relative to the critical speed. The latter is dependent on the cross section (and thus the bank geometry) of the waterway
Analisis Faktor Pembentuk Urban Heat Island di Kota Bitung
Urban Heat Island (UHI) is a phenomenon where urban areas experience hotter temperatures than the surrounding rural areas. Changes in land cover that occur include the establishment of buildings and infrastructure that replace open areas and vegetation, where the land cover that was originally permeable and moist has changed to impermeable and dry as a result of urban development which led to the formation of the Urban Heat Island. UHI is formed by various factors such as weather, geographic location, vegetation, materials, geometry and anthropogenic heat. Bitung city experienced population growth from 2008-2017 of 2.12% per year as well as various land use changes resulting in decreased open space and vegetation which led to an increase in surface temperature. Therefore this research was conducted to identify the distribution of surface temperature in the Bitung city and its forming factors. This study aims to find out how the surface temperature in the city of Bitung and the conditions of land use, building materials and urban geometry at high surface temperatures. The data analysis used is in the form of spatial analysis with GIS software in the form of ArcGIS 10.3. In determining the surface temperature, data from Landsat 8 imagery is used. From image processing in Bitung city, it was found that the lowest surface temperature was 15.47 ºC and the highest surface temperature was 43.34 ºC. The highest average surface temperature in the city of Bitung is in the sub-districts of Girian, Madidir, and Maesa with land use for housing, trade, industry and services; with the use of zinc roofing material and concrete walls and a building distance of 0.82m to 8.47m. Keyword: Urban heat island; Land use; Building materials; Urban geometr
Influence of bench geometries on rockfall behaviour in open pit mines
Faculty of Engineering and Built Enviroment
School of Mining Engineering
0315711f
[email protected] are a significant risk in open pit mines. Once movement of a rock perched
on the top of a slope (bench) has been initiated, the most important factor controlling
its fall trajectory is the geometry of the slope (bench). The best possible knowledge of
rockfall trajectories and energies is important in order to determine accurate risk
zoning and for the design and construction of adequate defence systems near the
threatened areas.
This study attempts to determine the influence of bench geometries, and the
coefficient of restitution of rock, on rockfall behaviour. A study of literature was
carried out to review previous studies and other relevant information on rockfalls and
their analysis. The literature may be divided into two categories: experimental
methods involving physical modelling, and computer models involving rockfall
analyses using computers analysis methods. Rockfall computer simulation is
considered to be applicable, quick to carry out and reproducible. The accuracy of the
results depends on the knowledge of site conditions and slope geometry. The use of
the Modified Ritchie criterion for the design of catch benches in open pit mines was
also investigated.
The assessment of bounce height, maximum run-out distance and kinetic energy
achieved during the fall of rocks on the catch bench were the bases of the evaluation
of the results obtained in this project. The computer program, Rocfall Version 4, was
used for the purposes of the research. The following parameter variables were
considered in the analyses: three types of rock; slopes with three stack configurations;
four bench heights; and four bench face angles.
The results show that, for all stack configurations and rock types, the maximum runout
distance and maximum bounce height increase as functions of bench height at a
specific bench face angle. A single bench configuration provides a maximum run-out
distance of falling rocks larger than the value determined using the Modified Ritchie
criterion for all rock types and bench face angles. Multiple bench stack configurations
provide maximum run-out distances less than the value determined using the
Modified Ritchie criterion only for the 90o bench face angle in all rock types; those
with 60o, 70o and 80o bench face angle provide a larger maximum run-out distance.
Therefore, the validity of the Modified Ritchie criterion for the design of catch bench
widths in open pit mines with inclined benches must be questioned.
According to Ritchie’s study (1963), rocks that fall in trajectory (free fall) seldom
give high bounces after impact on a catch bench. This project shows that this finding
is valid for rocks with low coefficients of normal restitution. Rocks with lower
coefficients of normal restitution provide larger run-out distances with flatter bench
face angles compared with rocks with higher coefficients. In contrast, rocks with
higher coefficients provide larger run-out distances than those with lower coefficients
for steeper angles.
The consideration of the influence of geometry (shape) of falling rocks on rockfall
behaviour showed that, for a flatter slope, as could logically be expected, the
maximum run-out distance is greatest for rounder rocks and smallest for flatter slabby
iv
rocks. This is due to the fact that on a flatter slope, the mode of falling of rounder
rocks is rolling down the slope. This mode provides essentially no resistance to
motion, resulting in largest maximum run-out distance. In contrast, for long flat slabs,
the mode of movement will be sliding, which results in a smaller maximum run-out
distance. The maximum run-out distance as function of rock shape reduces as the
normal coefficient of restitution increases.
For all rock types, the maximum bounce height reduces as a function of the friction
angle for flatter slopes. This is due to the fact that rocks are in contact with the slope
during the rockfall. As the coefficient of normal restitution increases, an increase in
the maximum bounce height results
Use of sonic tomography to detect and quantify wood decay in living trees.
Premise of the studyField methodology and image analysis protocols using acoustic tomography were developed and evaluated as a tool to estimate the amount of internal decay and damage of living trees, with special attention to tropical rainforest trees with irregular trunk shapes.Methods and resultsLiving trunks of a diversity of tree species in tropical rainforests in the Republic of Panama were scanned using an Argus Electronic PiCUS 3 Sonic Tomograph and evaluated for the amount and patterns of internal decay. A protocol using ImageJ analysis software was used to quantify the proportions of intact and compromised wood. The protocols provide replicable estimates of internal decay and cavities for trees of varying shapes, wood density, and bark thickness.ConclusionsSonic tomography, coupled with image analysis, provides an efficient, noninvasive approach to evaluate decay patterns and structural integrity of even irregularly shaped living trees
The COST IRACON Geometry-based Stochastic Channel Model for Vehicle-to-Vehicle Communication in Intersections
Vehicle-to-vehicle (V2V) wireless communications can improve traffic safety
at road intersections and enable congestion avoidance. However, detailed
knowledge about the wireless propagation channel is needed for the development
and realistic assessment of V2V communication systems. We present a novel
geometry-based stochastic MIMO channel model with support for frequencies in
the band of 5.2-6.2 GHz. The model is based on extensive high-resolution
measurements at different road intersections in the city of Berlin, Germany. We
extend existing models, by including the effects of various obstructions,
higher order interactions, and by introducing an angular gain function for the
scatterers. Scatterer locations have been identified and mapped to measured
multi-path trajectories using a measurement-based ray tracing method and a
subsequent RANSAC algorithm. The developed model is parameterized, and using
the measured propagation paths that have been mapped to scatterer locations,
model parameters are estimated. The time variant power fading of individual
multi-path components is found to be best modeled by a Gamma process with an
exponential autocorrelation. The path coherence distance is estimated to be in
the range of 0-2 m. The model is also validated against measurement data,
showing that the developed model accurately captures the behavior of the
measured channel gain, Doppler spread, and delay spread. This is also the case
for intersections that have not been used when estimating model parameters.Comment: Submitted to IEEE Transactions on Vehicular Technolog
Analyzing urban sprawl patterns through fractal geometry: the case of Istanbul metropolitan area
Over the last decade, there has been a rapid increase in the amount of literature on the measurement of urban sprawl. Density gradients, sprawl indexes which are based on a series of measurable indicators and certain simulation techniques are some quantitative approaches used in previous studies. Recently, fractal analysis has been used in analyzing urban areas and a fractal theory of cities has been proposed. This study attempts to measure urban sprawl using a sprawl index and analyses urban form through fractal analysis for characterizing urban sprawl in Istanbul which has not been measured or characterized yet.
In this study, measures of sprawl were calculated at each neighborhood level and then integrated within sprawl index through “density” and “proximity” factors. This identifies the pattern of urban sprawl during six periods from 1975 to 2005, and then the urban form of Istanbul is quantified through fractal analysis in given periods in the context of sprawl dynamics. Our findings suggest that the fractal dimension of urban form is positively correlated with the urban sprawl index score when urban growth pattern is more likely “concentrated”. However, a negative relationship has been observed between fractal dimension and sprawl index score when the urban growth pattern changes from the concentrated to the semi-linear form
Applications of finite geometry in coding theory and cryptography
We present in this article the basic properties of projective geometry, coding theory, and cryptography, and show how
finite geometry can contribute to coding theory and cryptography. In this way, we show links between three research areas, and in particular, show that finite geometry is not only interesting from a pure mathematical point of view, but also of interest for applications. We concentrate on introducing the basic concepts of these three research areas and give standard references for all these three research areas. We also mention particular results involving ideas from finite geometry, and particular results in cryptography involving ideas from coding theory
A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles
In recent years, there has been a dramatic increase in the use of unmanned
aerial vehicles (UAVs), particularly for small UAVs, due to their affordable
prices, ease of availability, and ease of operability. Existing and future
applications of UAVs include remote surveillance and monitoring, relief
operations, package delivery, and communication backhaul infrastructure.
Additionally, UAVs are envisioned as an important component of 5G wireless
technology and beyond. The unique application scenarios for UAVs necessitate
accurate air-to-ground (AG) propagation channel models for designing and
evaluating UAV communication links for control/non-payload as well as payload
data transmissions. These AG propagation models have not been investigated in
detail when compared to terrestrial propagation models. In this paper, a
comprehensive survey is provided on available AG channel measurement campaigns,
large and small scale fading channel models, their limitations, and future
research directions for UAV communication scenarios
Examining trade-offs between social, psychological, and energy potential of urban form
Urban planners are often challenged with the task of developing design solutions which must meet multiple, and often contradictory, criteria. In this paper, we investigated the trade-offs between social, psychological, and energy potential of the fundamental elements of urban form: the street network and the building massing. Since formal methods to evaluate urban form from the psychological and social point of view are not readily available, we developed a methodological framework to quantify these criteria as the first contribution in this paper. To evaluate the psychological potential, we conducted a three-tiered empirical study starting from real world environments and then abstracting them to virtual environments. In each context, the implicit (physiological) response and explicit (subjective) response of pedestrians were measured. To quantify the social potential, we developed a street network centrality-based measure of social accessibility. For the energy potential, we created an energy model to analyze the impact of pure geometric form on the energy demand of the building stock. The second contribution of this work is a method to identify distinct clusters of urban form and, for each, explore the trade-offs between the select design criteria. We applied this method to two case studies identifying nine types of urban form and their respective potential trade-offs, which are directly applicable for the assessment of strategic decisions regarding urban form during the early planning stages
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