Ograniczanie wyników
Czasopisma
Autorzy
Lata
Preferencje
Język
Widoczny [Schowaj] Abstrakt
Liczba wyników

Znaleziono wyników: 102

Liczba wyników na stronie
Strona / 6
Wyniki wyszukiwania
Wyszukiwano:
w słowach kluczowych:  Monte Carlo
Sortuj według:

Ogranicz wyniki do:
Strona / 6
EN
The light scattering process can be modeled mathematically using the Fredholm integral equation. This equation is usually solved after its discretization and transformation into the system of algebraic equations. Volume integral equations can be also solved without discretization using the Monte Carlo algorithm, but its application to the light scattering simulations has not been sufficiently studied. Here we present the implementation of this algorithm for one and three-dimensional light scattering computations and discuss its applicability in this field. We show that the Monte Carlo algorithm can provide valid and accurate results but, due to its convergence properties, it might be difficult to apply for problems with large volumes or refractive indices of scattering objects.
EN
Various numerical methods were proposed for analysis of the light scattering phenomenon. An important group of these methods is based on solving the volume integral equation describing the light scattering process. The popular method from this group is the discrete dipole approximation. Discrete dipole approximation uses various numerical algorithms to solve the discretized integral equation. In the recent years, the application of the Monte Carlo algorithm as one of them was proposed. In this research, we analyze the application of the Monte Carlo algorithm for two cases: the light scattering by large particles and by random conglomerates of small particles. We show that if proper preconditioning of the numerical problem is applied, the Monte Carlo algorithm can solve the underlying systems of linear equations. We also show that the efficiency of the Monte Carlo algorithm can be increased by reusing performed computations for various incident electromagnetic waves and the applicability of the Monte Carlo algorithm depends on the particular use case. It is unlikely to be used in the case of light scattering by the large particles due to computational times inferior comparing with the other numerical methods but may become useful in the case of light scattering by the random conglomerates of small scattering particles.
EN
The paper shows the application of the Monte Carlo method to the stability analysis of a single-layer shallow (h/d = 0.04) dome modelled with frame elements. Structures of this type are characterized by strong nonlinearity, consequently, they are extremely susceptible to stability loss resulting from the node snap-through. It is necessary to perform a nonlinear stability analysis that allows determination of limit points related to that mode of stability failure. This paper shows that with the reliability analysis methods, it is possible to trace the failure probability level while moving along the load-displacement path towards the limit point.
4
Monte Carlo Study of Triblock Self-Assembly by Cooperative Motion Algorithm
EN
We perform a comprehensive Monte Carlo study of the ABA triblock self-assembly by the Cooperative Motion Algorithm. Our attention is focused on three series of triblocks which are grown from parent AB diblocks of varying asymmetry. Unlike the previous studies in which the total length of the chain varies upon growing the terminal A-block, here we keep the fixed chain length for a given series. Moreover, we determine the order-disorder transition temperature as the τ parameter (being the ratio of the grown A-block to the length of the parent diblock) increases. In this case we find that the order-disorder transition temperature monotonically decreases for two asymmetric series which is different from the non-monotonic depression of TODT reported previously. We also construct a phase diagram which shows a variety of nanostructures as τ is increased.
EN
The modified configuration of the 155 mm rocket assisted projectile equipped with lateral thrusters was proposed. Six degree of freedom mathematical model was used to investigate the quality of the considered projectile. Impact point prediction guidance scheme intended for low control authority projectile was developed to minimize the dispersion radius. Simple point mass model was applied to calculate the impact point coordinates during the flight. Main motor time delay impact on range characteristics was investigated. Miss distance errors and Circular Error Probable for various lateral thruster total impulse were obtained. Monte-Carlo simulations proved that the impact point dispersion could be reduced significantly when the circular array of 15 solid propellant lateral thrusters was used. Single motor operation time was set to be 0.025 s. Finally, the warhead radii of destruction were analyzed.
6
Improving navigation autonomy in mobile robots with Monte-Carlo particle filters
EN
Autonomous Navigation is possible when a vehicle combines internal information about its own state with external information about its environment. A vehicle receives the information as a permanent feed of measurements from its internal sensors (odometry) and from external sensors (ultrasound, cameras, IMUs, radar etc.). The information provided by the sensors is always uncertain and therefore a vehicle cannot estimate its own motion based only on internal sensing (odometry) and cannot plan its trajectory based only on external sensing. For autonomous navigation, all the sensors in a vehicle must be statistically characterized, their accuracy and error margin in a given dynamic range must be available to the vehicle. Using the statistics of all the sensors, a vehicle can take a combined decision that reduces the overall error when estimating its own position and planning a trajectory. Vehicles can use different algorithms to take a decision based on uncertain sensor measurements. One of the most popular algorithms is the Monte Carlo Particle Filter (MCPF). The MCPF uses Bayesian Statistics to reduce the overall uncertainty of a group of uncertain measurements, therefore improving the estimation of the vehicle internal and external states. In this article we give a practical explanation of the meaning of the MCPF. We also present the results of using the MCPF in autonomous navigation of mobile robots.
DE
Autonome Navigation ist möglich, wenn ein Fahrzeug interne Informationen über seinen eigenen Zustand mit externen Informationen über seine Umgebung kombiniert. Ein Fahrzeug erhält die Informationen als permanente Messdatenübertragung von seinen internen Sensoren (Odometrie) und von externen Sensoren (Ultraschall, Kameras, IMUs, Radar usw.). Die von den Sensoren gelieferten Informationen sind immer unsicher und daher kann ein Fahrzeug seine eigene Bewegung nicht nur auf Basis der internen Sensoren (Odometrie) abschätzen und seine Flugbahn nicht nur auf Basis der externen Erfassung planen. Für eine autonome Navigation müssen alle Sensoren in einem Fahrzeug statistisch charakterisiert werden, und ihre Genauigkeit und Fehlertoleranz in einem bestimmten Dynamikbereich muss dem Fahrzeug zur Verfügung stehen. Unter Verwendung der Statistik aller Sensoren kann ein Fahrzeug eine kombinierte Entscheidung treffen, die den Gesamtfehler bei der Schätzung seiner eigenen Position und der Planung einer Trajektorie verringert. Fahrzeuge können unterschiedliche Algorithmen verwenden, um eine Entscheidung basierend auf unsicheren Sensormessungen zu treffen. Einer der beliebtesten Algorithmen ist der Monte-Carlo-Partikelfilter (MCPF). Die MCPF verwendet die Bayes'sche Statistik, um die Gesamtunsicherheit einer Gruppe unsicherer Messungen zu verringern und so die Schätzung der internen und externen Zustände des Fahrzeugs zu verbessern. In diesem Artikel geben wir eine praktische Erklärung der Bedeutung der MCPF. Wir präsentieren auch die Ergebnisse des Einsatzes der MCPF in der autonomen Navigation von mobilen Robotern.
EN
Introduction: Small fields photon dosimetry is associated with many problems. Using the right detector for measurement plays a fundamental role. This study investigated the measurement of relative output for small photon fields with different detectors. It was investigated for three-photon beam energies at SSDs of 90, 95, 100 and 110 cm. As a benchmark, the Monte Carlo simulation was done to calculate the relative output of these small photon beams for the dose in water. Materials and Methods: 6, 10 and 15 MV beams were delivered from a Synergy LINAC equipped with an Agility 160 multileaf collimator (MLC). A CC01 ion chamber, EFD-3G diode, PTW60019 microdiamond, EBT2 radiochromic film, and EDR2 radiographic film were used to measure the relative output of the linac. Measurements were taken in water for the CC01 ion chamber, EFD-3G diode, and the PTW60019. Films were measured in water equivalent RW3 phantom slabs. Measurements were made for 1 × 1, 2 × 2, 3 × 3, 4 × 4, 5 × 5 and a reference field of 10 × 10 cm2. Field sizes were defined at 100cm SSD. Relative output factors were also compared with Monte Carlo (MC) simulation of the LINAC and a water phantom model. The influence of voxel size was also investigated for relative output measurement. Results and Discussion: The relative output factor (ROF) increased with energy for all fields large enough to have lateral electronic equilibrium (LEE). This relation broke down as the field sizes decreased due to the onset of lateral electronic disequilibrium (LED). The high-density detector, PTW60019 gave the highest ROF for the different energies, with the less dense CC01 giving the lowest ROFs. Conclusion: These are results compared to MC simulation, higher density detectors give higher ROF values. Relative to water, the ROF measured with the air-chamber remained virtually unchanged. The ROFs, as measured in this study showed little variation due to increased SSDs. The effect of voxel size for the Monte Carlo calculations in water does not lead to significant ROF variation over the small fields studied.
EN
Monte Carlo and TL dosimetry applied to the characterization of 125I brachytherapy with a different design with other 125I seeds. In a water phantom, lattice configuration simulated with 125I seed in the center and 10 nm gold and gadolinium nan-particle filed voxels. This simulation conducted to the characterization of the nano-particles DEF in low energy and prostate tissue. To study of the prostate brachytherapy, a humanoid computational phantom developed by CT slices applied. KTMAN-2 computational phantom contains 29 organs and 19 skeletal regions and was produced from cross-sectional x-ray computed tomography (CT slices) images. The simulated seed was 125I seed having an average energy of 28.4 keV for photons, a half-life of 59.4 days. DEF factor in the seed radiation energy (28.4 keV) DEF factor was found to be two times higher for the gold nano-particles. It was revealed than gold-nano-particles posing Z about 1.24 times higher than gadolinium led to around 200% DEF increasing in the same conditions and the nano-particles size. It was concluded that in low energy sources brachytherapy, photoelectric is dominant in the presence of relative high element nanoparticles. This leads to a high dose increasing in some micro-meters and causes a dramatic dose gradient in the vicinity of a nano-particle. This dose gradient effectively kills the tumor cells in continuous low energy irradiation in the presence of a high Z material nano-scaled particle. Application of gold nano-particles in low energy brachytherapy is recommended.
EN
103Pd seed is being used for prostate brachytherapy. Additionally, the dose enhancement effect of gold nanoparticles (GNP) has been reported in previous studies. The aim of this study was to characterize the dosimetric effect of gold nanoparticles in brachytherapy with a 103Pd source. Two brachytherapy seeds including 103Pd source was simulated using MCNPX Monte Carlo code. The seeds’ models were validated by comparing the MC with reported results. Then, GNPs (10 nm in diameter) with a concentration of 7mg Au/g were simulated uniformly inside the prostate of a humanoid computational phantom. Additionally, the dose enhancement factor (DEF) of nanoparticles was calculated for both modeled brachytherapy seeds. A good agreement was found between the MC calculated and the reported dosimetric parameters. For both seeds, an average DEF of 23% was obtained in tumor volume for prostate brachytherapy. The application of GNPs in conjunction with 103Pd seed in brachytherapy can enhance the delivered dose to the tumor and consequently leads to better treatment outcome.
EN
Permanent and temporary implantation of I-125 brachytherapy sources has become an official method for the treatment of different cancers. In this technique, it is essential to determine dose distribution around the brachytherapy source to choose the optimal treatment plan. In this study, the dosimetric parameters for a new interstitial brachytherapy source I-125 (IrSeed-125) were calculated with GATE/GEANT4 Monte Carlo code. Dose rate constant, radial dose function and 2D anisotropy function were calculated inside a water phantom (based on the recommendations of TG-43U1 protocol), and inside several tissue phantoms around the IrSeed-125 capsule. Acquired results were compared with MCNP simulation and experimental data. The dose rate constant of IrSeed-125 in the water phantom was about 1.038 cGy·h−1U−1 that shows good consistency with the experimental data. The radial dose function at 0.5, 0.9, 1.8, 3 and 7 cm radial distances were obtained as 1.095, 1.019, 0.826, 0.605, and 0.188, respectively. The results of the IrSeed-125 is not only in good agreement with those calculated by other simulation with MCNP code but also are closer to the experimental results. Discrepancies in the estimation of dose around IrSeed-125 capsule in the muscle and fat tissue phantoms are greater than the breast and lung phantoms in comparison with the water phantom. Results show that GATE/GEANT4 Monte Carlo code produces accurate results for dosimetric parameters of the IrSeed-125 LDR brachytherapy source with choosing the appropriate physics list. There are some differences in the dose calculation in the tissue phantoms in comparison with water phantom, especially in long distances from the source center, which may cause errors in the estimation of dose around brachytherapy sources that are not taken account by the TG43-U1 formalism.
EN
Monte Carlo simulation is widely used in emission tomography, in order to assess image reconstruction algorithms and correction techniques, for system optimization, and study the parameters affecting the system performance. In the current study, the performance of the IRI-microPET system was simulated using the GATE Monte Carlo code and a number of performance parameters, including spatial resolution, scatter fraction, sensitivity, RMS contrast, and signal-to-noise ratio, evaluated and compared to the corresponding measured values. The results showed an excellent agreement between simulated and measured data: The experimental and simulated spatial resolutions (radial) for 18F in the center of the AFOV were 1.81 mm and 1.65 mm, respectively. The difference between the experimental and simulated sensitivities of the system was <7%. Simulated and experimental scatter fractions differed less than 9% for the mouse phantom in different timing windows. The validation study of the image quality indicated a good agreement in RMS contrast and signal-to-noise ratio. Also, system performance was compared with the two available commercial scanners which were simulated using GATE code. In conclusion, the assessment of the Monte Carlo modeling of the IRI-microPET system reveals that the GATE code is a flexible and accurate tool for describing the response of an animal PET system.
EN
A model of REM-2-type chamber was modeled with MCNPX code to study the dose-response to monoenergetic neutrons in wide energy range from thermal to 20 MeV for various compositions of gas in the chamber. The energy dependence of the total dose absorbed in the fi lling gas was compared with the energy dependence of ambient absorbed dose D*(10) and with experimental data. The results of the studies will be useful for designing new, improved generation of recombination chambers.
EN
In the existent world of continuous production systems, strong attention has been waged to anonymous risk that probably generates signiﬁcant apprehension. The forecast for net present value is extremely important for any production plant. The objective of this paper is to implement Monte Carlo simulation technique for perceiving the impact of risk and uncertainty in prediction and forecasting company’s proﬁtability. The production unit under study is interested to make the initial investment by installing an additional spray dryer plant. The expressive values acquied from the Monte Carlo technique established a range of certain results. The expected net present value of the cash ﬂow is $14,605, hence the frequency chart outcomes conﬁrmed that there is the highest level of certainty that the company will achieve its target. To forecast the net present value for the next period, the results conﬁrmed that there are 50.73% chances of achieving the outcomes. Considering the minimum and maximum values at 80% certainty level, it was observed that 80% chances exist that expected outcomes will be between$5,830 and $22,587. The model’s sensitivity results validated that cash inﬂows had a greater sensitivity level of 21.1% and the cash inﬂows for the next year as 19.7%. Cumulative frequency distribution conﬁrmed that the probability to achieve a maximum value of$23,520 is 90 % and for the value of \$6,244 it is about 10 %. These validations suggested that controlling the expenditures, the company’s outﬂows can also be controlled deﬁnitely.
PL
Projektowanie budynków wymaga często zastosowania obliczeń inżynierskich do weryfikacji przyjętych rozwiązań. Powszechnie stosowane są symulacje CFD, w szczególności do oceny skuteczności działania instalacji wentylacji oddymiającej. Obecnie wybór scenariuszy pożarowych, na których opiera się ocena bezpieczeństwa, zależy od inżynierów bezpieczeństwa pożarowego. Niestety bazują oni w zasadzie je- dynie na swoim doświadczeniu, rzadko sięgając do statystyk. Obecnie rutynowym podejściem do oceny bezpieczeństwa pożarowego budynku jest precyzyjne zdefiniowanie parametrów modelu rozwoju pożaru i/lub ewakuacji dla małej liczby, szczegółowo wybranych scenariuszy. Wykorzystanie ilościowej analizy ryzyka do oceny bezpieczeństwa, w znacznym stopniu poprawia jakość oraz zakres tych analiz. Celem artykułu jest przedstawienie możliwości wykorzystania ilościowej analizy ryzyka do wyboru scenariusza pożarowego dla symulacji CFD. Przy opracowaniu artykułu korzystano z metody eksperymentalnej bazującej na modelu komputerowym. Analizowany przypadek wskazuje problemy modelowania CFD, opartego na pojedynczym scenariuszu. Zaproponowano zastosowanie podejścia dwu-modelowego. Zaletą użycia obliczeń wielokrotnych (multisymulacji) w połączeniu z CFD, jest możliwość poznania prawdopodobieństwa poszczególnych scenariuszy i na tej podstawie dokonanie analizy koszt/zysk przy wyborze systemu zabezpieczeń.
EN
Building design often requires the use of engineering calcu- lations to verify the adopted solutions. CFD simulations are commonly used, in particular to assess the effectiveness of smoke ventilation systems. Currently, the choice of fire sce- narios on which the safety assessment is based depends on fire safety engineers. Unfortunately, they are generally only based on their experience and rarely refer to statistics. Cur- rently, a routine approach to fire safety assessment of a build- ing is to define precisely the parameters of the fire develop- ment model and/or evacuation model for a small number of scenarios selected in detail. The use of quantitative analysis of the risk for safety assessment significantly improves the quality and scope of these analyses In this article possibilities of using fire risk analysis for fire scenario selection in the CFD simulation were presented. This article is based on experimental methods and computer models. The analyzed example reveals problems with deterministic fire modelling. The approach based on multiple calculations were shown. This makes it possible to obtain probability of given scenario and making cost/profit analysis.
EN
We studied the relative performance of stochastic heuristics in order to establish the relations between the fundamental elements of their mechanisms. The insights on their dynamics, abstracted from the implementation details, may contribute to the development of an efficient framework for design of new probabilistic methods. For that, we applied four general optimization heuristics with varying number of hyperparameters to traveling salesman problem. A problem-specific greedy approach (Nearest Neighbor) served as a reference for the results of: Monte Carlo, Simulated Annealing, Genetic Algorithm, and Particle Swarm Optimization. The more robust heuristics – with higher configuration potential, i.e. with more hyperparameters – outperformed the smart ones, being surpassed only by the method specifically designed for the task.
16
PL
Kolektory słoneczne są głównymi elementami solarnych systemów grzewczych. Praca tych urządzeń polega na konwersji energii promieniowania słonecznego na ciepło czynnika roboczego. Czynnikiem tym może być zarówno ciecz (glikol lub woda), jak i gaz (powietrze). Ze względu na konstrukcję wyróżnia się kolektory płaskie, próżniowe, próżniowo-rurowe i skupiające. Kolektory płaskie są stosowane przede wszystkim w budynkach, w których potrzeby cieplne są niskie lub średnie, czyli na przykład w gospodarstwach domowych. Rozwój kolektorów został ukierunkowany na zwiększenia wydajności oraz poprawy efektywności ekonomicznej inwestycji. W artykule oceniono wpływ zmiany powierzchni płaskich kolektorów słonecznych na opłacalność ekonomiczną inwestycji. Do analizy wytypowano dom jednorodzinny, zlokalizowany w województwie małopolskim, w którym instalacja przygotowania ciepłej wody użytkowej została rozbudowana o system solarny. System ten składa się z płaskich kolektorów, o łącznej powierzchni absorberów 5,61 m2. Jako czynnik roboczy w instalacji stosowany jest glikol. W celu poprawy efektu ekonomicznego zaproponowano zwiększenie powierzchni absorberów. Na podstawie trzyletnich pomiarów nasłonecznienia oraz efektów cieplnych instalacji, stworzono model ekonomiczny służący do oceny opłacalności zwiększenia powierzchni kolektorów słonecznych. Obliczenia z użyciem modelu promieniowania HDKR wykonano w środowisku Matlab dla lokalizacji Tarnów (najbliższej instalacji). Ponadto na podstawie rzeczywistych pomiarów z tej instalacji, odzwierciedlających wpływ wielu niemierzalnych czynników na efektywność przetwarzania energii słonecznej, wykonano symulacje efektu ekonomicznego dla różnych wielkości zapotrzebowania na ciepło. Otrzymane wyniki uogólniono, co daje możliwość ich wykorzystania w procesie doboru wielkości powierzchni kolektorów w przypadku podobnych instalacji.
EN
Solar collectors are the main components of the solar heating systems. This devices convert radiation from the sun into the heat of distribution medium. The medium can be either (water, glycol) or gas (air). Two types of solar panels can be distinguished on the basis of the construction criterion: flat plate collectors and evacuated tube collectors. Solar collectors development progresses towards improving their efficiency and economic profitability. Flat plate collectors are popular for low and medium heating applications, i.e. in households. In this paper, flat plate collectors with glycol as a distribution medium are investigated. The authors evaluate the impact of changing the size of the solar collectors on the heating economic profitability. A detached house, located in the Malopolskie Province was selected for the analysis. The house was fitted with domestic hot water installation which was extended with the solar system. At present, the collector area amounts to 5.61 m2. In order to improve the economic effect, the authors propose to increase their area. The radiation from the sun, sun exposure and thermal results were collected and calculated for three years. The authors prepared an economic model on the basis of the collected data. This model was created to assess the economic effect in relation to increasing the collector area. Calculations were made with the HDKR radiation model using Matlab software. The authors chose Tarnow as location because the city is the nearest to the tested installation. In addition, the authors created a simulation that allowed the economic effect for different detached houses with different heat demands to be assessed. By using real data an impact of many non-measurable factors on the efficiency of solar energy conversion could be taken into account in the simulation. The obtained results have been generalized and thus can be applied in a similar installation during the process of choosing an appropriate collector area size.
EN
The aim of the article is to present the issue of risk and related management methods, with a particular emphasis on the conditions of investment in energy infrastructure. The work consists of two main parts; the first one is the theoretical analysis of the issue, while the second discusses the application of analysis methods on the example of the investment in an agricultural biogas plant. The article presents the definitions related to the investment risk and its management, with a particular emphasis on the distinction between the risk and uncertainty. In addition, the main risk groups of the energy sector were subjected to an analysis. Then, the basic systematics and the division into particular risk groups were presented and the impact of the diversification of investments in the portfolio on the general level of risk was determined. The sources of uncertainty were discussed with particular attention to the categories of energy investments. The next part of the article presents risk mitigation methods that are part of the integrated risk management process and describes the basic methods supporting the quantification of the risk level and its effects – including the Monte Carlo (MC), Value at risk (VaR), and other methods. Finally, the paper presents the possible application of the methods presented in the theoretical part. The investment in agricultural biogas plant, due to the predictable operation accompanied by an extremely complicated and long-term investment process, was the subject of the analysis. An example of “large drawing analysis” was presented, followed by a Monte Carlo simulation and a VaR value determination. The presented study allows for determining the risk in the case of deviation of financial flows from the assumed values in particular periods and helps in determining the effects of such deviations. The conducted analysis indicates a low investment risk and suggests the ease of similar calculations for other investments.
PL