11 research outputs found
PARALLEL VISIBILITY AND FRESNEL-ZONES CALCULATION USING GRAPHICS PROCESSING UNITS
Delo opisuje inovativno metodo izračuna vidnosti [61, 62] in Fresnelovih con na digitalnih
zemljevidih z uporabo grafično procesnih kartic CUDA NVIDIA. Izdelani so trije
vzporedni algoritmi:
• modificiran vzporedni algoritem R2 za računanje vidnosti (R2-P),
• algoritem za izračun zakrivanj Fresnelovih con (FZC),
• algoritem za izračun prečnega preseka Fresnelovih con med oddajnikom in sprejemnikom
(FZTI).
Na osnovi uveljavljenega sekvenčnega algoritma R2 za računanje vidnosti je razvit modificiran
vzporedni algoritem R2-P, ki za pohitritev izračuna poleg večnitenja izkorišča še
druge uporabne lastnosti grafične procesne enote. Združen dostop do globalnega pomnilnika
pripomore k hitrejšemu pretoku podatkov in s tem k hitrejšemu izračunu. Izmenjava
informacij med nitmi v času računanja igra ključno vlogo pri pohitritvi. Izračun vidnosti
na poljubno velikih podatkih je omogočeno s segmentacijo digitalnega zemljevida.
Modificiran vzporedni algoritem R2 je primerjan z že implementiranimi algoritmi za
izračun vidnosti v smislu točnosti izračuna in časa izračuna. Izkaže se, da je novi algoritem
enako točen kot že uveljavljeni sekvenčni algoritem R2, hkrati pa omogoča bistveno
pohitritev izračuna. Čas izračuna je skrajšan iz reda nekaj minut na red nekaj sekund.
To pa v praksi pomeni možnost interaktivnega dela.
Pri načrtovanju radijskega pokrivanja je poleg vidnosti zelo uporaben podatek o zakrivanju
Fresnelovih con. Pri algoritmu za izračun zakrivanj Fresnelovih con se izbere
lokacijo radijskega oddajnika, višino oddajnika, opazovano višino sprejemnika nad terenom
in valovno dolžino radijskega valovanja. Algoritem za vsako točko terena izračuna,
katera Fresnelova cona je zakrita. Rezultat je digitalni zemljevid z izrisanimi območji
zakrivanj Fresnelovih con, kar o radijskem signalu na terenu pove precej več kot izračun
vidnosti. Predvsem na področjih, kjer je prva Fresnelova cona povsem zakrita, se v primerjavi
z izračunom vidnosti pridobi v praksi zelo uporabna informacija. Algoritem ima
tudi možnost upoštevanja rabe tal, kjer se višina terena poveča v odvisnosti od rabe tal
(npr. za gozdno površino reda 15 m). Z modifikacijami, kot sta vpeljava Friisove enačbe in upoštevanje smernega diagrama
anten, postane algoritem enostaven propagacijski model in tako primeren za izračun radijskega
pokrivanja. Izračun radijskega signala se primerja z izmerjenimi vrednostmi na
terenu za frekvence 90 Mhz (FM), 800 MHz (LTE) in 1800 MHz (LTE). Za različne
vhodne parametre enostavnega propagacijskega modela se izračuna standardna deviacija
sprememb med izmerjenimi in izračunanimi vrednostmi in se jih prikaže na grafih. Tako se
pridobijo najbolj optimalne vrednosti vhodnih parametrov za vsako frekvenčno področje
posebej.
Algoritem za izračun prečnega preseka Fresnelovih con med oddajnikom in sprejemnikom
izračuna sliko Fresnelovih con, ki predstavlja matematični presek vseh skaliranih
prečnih presekov Fresnelovih con vzdolž radijske poti. Rezultat je vizualna slika, ki pokaže
lastnosti radijske (linkovske) zveze v smislu zakritja posameznih Fresnelovih con. V
praksi bi algoritem najbolj koristil pri načrtovanju radijskih linkov, kjer bi lahko preverili,
koliko in kateri del Fresnelovih con manjka zaradi ovir (terena).
Vsi trije algoritmi so implementirani kot moduli GRASS GIS in se lahko uporabljajo
na vsakem osebnem računalniku, ki ima vgrajeno grafično procesno enoto CUDA NVIDIA
in naloženo ustrezno prosto dostopno programsko opremo.The work describes an innovative method with which to calculate the visibility [61, 62]
and Fresnel zones on digital maps using graphics processing NVIDIA CUDA cards. Three
parallel algorithms were formulated:
• modified R2 parallel algorithm for calculating visibility (R2-P),
• algorithm for calculating Fresnel zone clearance (FZC),
• algorithm for calculating Fresnel zone transverse intersection between the transmitter
and the receiver (FZTI).
The R2 parallel algorithm was developed based on the established R2 sequential algorithm
for computing visibility. Aside from threading, other useful features of the graphics
processing unit were used to speed up calculation time. Coalesced access to the global
memory helps speed up the flow of information and thus also speeds up the calculation.
Exchange of information between threads during computation plays a key role in the
speedup. The segmentation of the digital map enables the calculation of visibility for
huge data sets.
The modified parallel R2 algorithm was compared with the already implemented algorithms
for the viewshed calculation in term of accuracy and duration of the calculation.
It turned out that the new algorithm R2-P had the same accuracy as the already established
sequential algorithm R2, although the former also makes it possible to significantly
speed up the calculation. Calculation time is reduced from the order of a few minutes to
the order of a couple of seconds. This, in practice, means that there is a possibility of
interactive work.
In addition to the viewshed, Fresnel zone clearance is very useful for planning the radio
coverage. Algorithm FZC starts with the location of the radio transmitter, the height of
the transmitter, the receiver observation height above terrain, and the wavelength of
the radio waves. The algorithm for each point of the terrain calculates the first clear
Fresnel zone. The result is a digital map with the plotted areas of Fresnel zone clearance.
This map provides better information about the radio signal than just a calculation of the
viewshed. Indeed areas where the first Fresnel zone is completely obscured are particularly
good for providing very useful information. The algorithm also has the ability to take
into account land use, where the height of the terrain is raised as a function of land use
(eg. For the forest area, raising can be 15 m).
With modifications, such as the introduction of the Friis transmission equation and
consideration of the radiation pattern, the algorithm becomes a simple radio propagation
model and thus is suitable for the calculation of radio coverage. Calculation of the radio
propagation is compared with the measured values on a field for frequencies of 90 MHz
(FM), 800 MHz (LTE) and 1800 MHz (LTE). For a variety of input parameters, the
standard deviation of changes between the field measurements and calculated propagation
is presented in graphs. In this way, the optimal values of the input parameters for each
frequency band can be obtained.
The algorithm for calculating Fresnel zone transverse intersection between the transmitter
and the receiver produces an image of Fresnel zones, which represents the mathematical
section of all scale cross-sectional Fresnel zones along the transmission path. The
result is a visual image that shows the characteristics of the radio link in terms of masking
individual Fresnel zones. In practice, the algorithm is most useful in the design of radio
links, where man can check how much and which part of the Fresnel zone is missing due
to terrain obstacles.
All three algorithms were implemented as GRASS GIS modules and can be used on any
PC with an integrated GPU NVIDIA CUDA and loaded with the appropriate free-access
software
Analysis of fluid flow around a beating artificial cilium
Biological cilia are found on surfaces of some microorganisms and on surfaces of many eukaryotic cells where they interact with the surrounding fluid. The periodic beating of the cilia is asymmetric, resulting in directed swimming of unicellular organisms or in generation of a fluid flow above a ciliated surface in multicellular ones. Following the biological example, externally driven artificial cilia have recently been successfully implemented as micropumps and mixers. However, biomimetic systems are useful not only in microfluidic applications, but can also serve as model systems for the study of fundamental hydrodynamic phenomena in biological samples. To gain insight into the basic principles governing propulsion and fluid pumping on a micron level, we investigated hydrodynamics around one beating artificial cilium. The cilium was composed of superparamagnetic particles and driven along a tilted cone by a varying external magnetic field. Nonmagnetic tracer particles were used for monitoring the fluid flow generated by the cilium. The average flow velocity in the pumping direction was obtained as a function of different parameters, such as the rotation frequency, the asymmetry of the beat pattern, and the cilium length. We also calculated the velocity field around the beating cilium by using the analytical far-field expansion. The measured average flow velocity and the theoretical prediction show an excellent agreement
Measurement of fluid flow generated by artificial ciliaa
We observed and measured the fluid flow that was generated by an artificial cilium. The cilium was composed of superparamagnetic microspheres, in which magnetic dipole moments were induced by an external magnetic field. The interaction between the dipole moments resulted in formation of long chains—cilia, and the same external magnetic field was also used to drive the cilia in a periodic manner. Asymmetric periodic motion of the cilium resulted in generation of fluid flow and net pumping of the surrounding fluid. The flow and pumping performance were closely monitored by introducing small fluorescent tracer particles into the system. By detecting their motion, the fluid flow around an individual cilium was mapped and the flow velocities measured. We confirm that symmetric periodic beating of one cilium results in vortical motion only, whereas asymmetry is required for additional translational motion. We determine the effect of asymmetry on the pumping performance of a cilium, verify the theoretically predicted optimal pumping conditions, and determine the fluid behaviour around a linear array of three neighbouring cilia. In this case, the contributions of neighbouring cilia enhance the maximal flow velocity compared with a single cilium and contribute to a more uniform translational flow above the surface
Self-assembled artificial cilia
Due to their small dimensions, microfluidic devices operate in the low Reynolds number regime. In this case, the hydrodynamics is governed by the viscosity rather than inertia and special elements have to be introduced into the system for mixing and pumping of fluids. Here we report on the realization of an effective pumping device that mimics a ciliated surface and imitates its motion to generate fluid flow. The artificial biomimetic cilia are constructed as long chains of spherical superparamagnetic particles, which self-assemble in an external magnetic field. Magnetic field is also used to actuate the cilia in a simple nonreciprocal manner, resulting in a fluid flow. We prove the concept by measuring the velocity of a cilia-pumped fluid as a function of height above the ciliated surface and investigate the influence of the beating asymmetry on the pumping performance. A numerical simulation was carried out that successfully reproduced the experimentally obtained data
Dynamic Assembly of Magnetic Colloidal Vortices
Magnetic
colloids in external time-dependent fields are subject
to complex induced many-body interactions governing their self-assembly
into a variety of equilibrium and out-of-equilibrium structures such
as chains, networks, suspended membranes, and colloidal foams. Here,
we report experiments, simulations, and theory probing the dynamic
assembly of superparamagnetic colloids in precessing external magnetic
fields. Within a range of field frequencies, we observe dynamic large-scale
structures such as ordered phases composed of precessing chains, ribbons,
and rotating fluidic vortices. We show that the structure formation
is inherently coupled to the buildup of torque, which originates from
internal relaxation of induced dipoles and from transient correlations
among the particles as a result of short-lived chain formation. We
discuss in detail the physical properties of the vortex phase and
demonstrate its potential in particle-coating applications
Magnetically driven omnidirectional artificial microswimmers
We present an experimental realisation of two new artificial microswimmers that swim at low Reynolds number. The swimmers are externally driven with a periodically modulated magnetic field that induces an alternating attractive/repulsive interaction between the swimmer parts. The field sequence also modulates the drag on the swimmer components, making the working cycle non-reciprocal. The resulting net translational displacement leads to velocities of up to 2 micrometers per second. The swimmers can be made omnidirectional, meaning that the same magnetic field sequence can drive swimmers in any direction in the sample plane. Although the direction of their swimming is determined by the momentary orientation of the swimmer, their motion can be guided by solid boundaries. We demonstrate their omnidirectionality by letting them travel through a circular microfluidic channel. We use simple scaling arguments as well as more detailed numerical simulations to explain the measured velocity as a function of the actuation frequency