Wyniki wyszukiwania - BazTech

1

The impact of initial and boundary conditions on severe weather event simulations using a high-resolution WRF model. Case study of the derecho event in Poland on 11 August 2017

Figurski Mariusz J., Nykiel Grzegorz, Jaczewski Adam, Bałdysz Zofia, Wdowikowski Marcin

Meteorology Hydrology and Water Management. Research and Operational Applications

|

2022

|

Vol. 10, Iss. 2

60--87

EN

Precise simulations of severe weather events are a challenge in the era of changing climate. By performing simulations correctly and accurately, these phenomena can be studied and better understood. In this paper, we have verified how different initial and boundary conditions affect the quality of simulations performed using the Weather Research and Forecasting Model (WRF). For our analysis, we chose a derecho event that occurred in Poland on 11 August 2017, the most intense and devastating event in recent years. High-resolution simulations were conducted with initialization at 00 and 12 UTC (11 August 2017) using initial and boundary conditions derived from the four global models: Global Forecast System (GFS) from the National Centers for Environmental Prediction (NCEP), Integrated Forecast System (IFS) developed by the European Center for Medium-Range Weather Forecasts (ECMWF), Global Data Assimilation System (GDAS) and ERA5. For the last, we made separate calculations using data at the pressure and model levels. The results were evaluated against surface and radar data. We found that the simulations that used data from the GDAS and GFS models at 12 UTC were the more accurate, while ERA5 gave the worst predictions. However, all models were characterized by a low probability of detection and a high number of false alarms for simulations of extreme precipitation and wind gusts.

2

Motion characteristics after ricochet: an experimental investigation

Chen Guoming, Hu Junhua, Liu An, Feng Jinfu, Hu Qingqing

Polish Maritime Research

|

2020

|

nr 2

4--10

EN

The ricochet behaviour of the air–water trans-media vehicle (AWTMV) during water-entry crossing was experimentally investigated. Three types of small-scale AWTMV including cone, ogive, and flat nose were used in the test. The underwater trajectory, velocity, and inclination angle of projectiles during the ricochet process were obtained using a high-speed camera. The angle change of the AWTMV and the ratio of the residual velocity are introduced. Based on this result, the relationship between the ricochet responses and initial conditions was derived. The results of this study show that (1) a small incident angle and great velocity make the occurrence of ricochet behaviour easier, (2) the stability of the trajectory of projectiles with cone, ogive, and flat nose weakened in turn at the same initial conditions, (3) the angle change and the ratio of the residual velocity are linear functions of the incident angle and velocity.

3

Role of initial density distribution in simulations of bone remodeling around dental implants

Nutu E.

Acta of Bioengineering and Biomechanics

|

2018

|

Vol. 20, no. 4

23--31

EN

In this paper, the effect of initial density distribution upon the predicted density via numerical simulations of bone remodeling was evaluated. The main purpose was to correlate the numerical results with clinical data according to which the initial bone quantity is an essential factor for long term survival of dental implants. Methods: Two-strain energy density-based bone remodeling theories were employed, one which accounts for overload resorption and the second one, which does not. The remodeling parameters were derived from the mechanostat theory. Bone remodeling around an osseointegrated dental implant was simulated based on finite element method using a generic mandible plane model. A variable time step was introduced to increase the speed of the remodeling simulations by keeping the truncation errors small. The simulations were performed for several initial density distributions correlated with values from clinical classifications of bone quality. For each density value, the occlusal load was defined in two ways so that to consider normal and overload mastication forces, respectively. Results: The results showed that the initial density distribution influences the predictions of bone remodeling simulations. For the analyzed model, the remodeling algorithm predicted overload resorption only in the case of low initial density, which can be associated with low bone quality, which, from clinical perspective, may probably lead to implant loss. Conclusions: The paper demonstrated that when simulating bone remodeling around dental implants using finite element method, it is important to account for initial density distribution in correlation with the bone quantity.

4

Określanie warunków początkowych do symulacji lotu pocisków artyleryjskich

Baranowski L., Surma Z.

Problemy Mechatroniki : uzbrojenie, lotnictwo, inżynieria bezpieczeństwa

|

2014

|

Vol. 5, Nr 1 (15)

51-58

PL

W artykule przedstawiono wyniki badań poligonowych rejestracji przebiegu strzelania ze 120 mm moździerza pociskiem odłamkowo-burzącym OF-483A, mające na celu umożliwienie określenia warunków początkowych wylotu pocisku z lufy moździerza, niezbędnych do przeprowadzenia symulacji komputerowej lotu pocisku moździerzowego. Wyniki rejestracji ruchu zarówno pocisków, jak i moździerza posłużyły do opracowania doświadczalnej metody wyznaczania prędkości wylotowej pocisku oraz kąta rzutu (tzn. kąta pochylenia wektora prędkości pocisku w chwili opuszczania przekroju wylotowego lufy moździerza). W badaniach poligonowych do rejestracji zjawisk szybkozmiennych wykorzystano kamerę Phantom v12, natomiast do wyznaczenia prędkości lotu pocisku oraz przemieszczania się lufy moździerza wykorzystano oprogramowanie TEMA Motion, służące do opracowywania wyników rejestracji kamerą Phantom v12. W celu określenia wpływu parametrów rejestracji na ewentualną jakość rejestrowanego obrazu i tym samym dokładność określenia prędkości wylotowej pocisku, stosowano różne ustawienia kamery uwzględniające szybkość filmowania i rozdzielczość zdjęć.

EN

The results of field tests of 120 mm mortar have been presented in this paper. Tests were conducted with using the mortar projectile type OF-483A. The main task of investigations was experimental determination of muzzle velocity and throwing angle, which are initial conditions for numerical simulation of the mortar projectile flight. Muzzle velocity and throwing angle were determined on the basis of accomplished results of motion the projectile as well as the mortar. The high-speed camera Phantom v12 was used during the field tests. The projectile velocity and the movement of the mortar barrel were calculated by means of TEMA Motion program.

5

Comparison of methods for initializing EM algorithm for estimation of parameters of gaussian, multi-component, heteroscedastic mixture models

Sokół R., Polański A.

Studia Informatica

|

2013

|

Vol. 34, nr 1

49--73

EN

A basic approach to estimation of mixture model parameters is by using expectation maximization (EM) algorithm for maximizing the likelihood function. However, it is essential to provide the algorithm with proper initial conditions, as it is highly dependent on the first estimation (“guess”) of parameters of a mixture. This paper presents several different initial condition estimation methods, which may be used as a first step in the EM parameter estimation procedure. We present comparisons of different initialization methods for heteroscedastic, multi-component Gaussian mixtures.

PL

Algorytm EM (ang. expectation-maximization) jest szeroko stosowanym rozwiązaniem problemu estymacji parametrów mieszanin rozkładów prawdopodobieństwa poprzez maksymalizację wiarygodności. Istotne znaczenie dla działania algorytmu mają parametry początkowe, stanowiące pierwsze przybliżenie badanej mieszaniny. Publikacja przybliża kilka metod wyznaczania warunku początkowego dla iteracji algorytmu EM oraz porównuje ich skuteczność dla przypadku heteroscedastycznych, wieloskładnikowych mieszanin rozkładów normalnych.

6

Wpływ warunków początkowych na stabilność przekształtnikowych napędów trakcyjnych

Stobiecki A, Dudek R.

Maszyny Elektryczne : zeszyty problemowe

|

2013

|

Nr 1(98)

95-100

PL

Postęp w dziedzinie projektowania i produkcji w pełni sterowalnych elementów półprzewodnikowych dużej mocy umożliwia zwiększenie częstotliwości pracy przekształtników układów napędowych pojazdów trakcyjnych. Przy zwiększonej częstotliwości pracy i określonych dopuszczalnych wahaniach napięcia i prądu sieci trakcyjnej zmniejszone mogą być pojemność i indukcyjność filtru wejściowego. Znaczne zmniejszenie wartości tych parametrów może być jednak niedopuszczalne, między innymi ze względu na konieczność zapewnienia stabilnej pracy układu napędowego. Stabilność pracy napędu trakcyjnego zależy od parametrów systemu trakcyjnego, takich jak rezystancja i indukcyjność sieci trakcyjnej i filtru, wartość napięcia zasilania, moc napędu i pojemność kondensatora filtru. W układzie nieliniowym także wartości początkowego prądu dławika i napięcia kondensatora filtru wpływają na warunki stabilnej pracy napędu. Na podstawie uproszczonego modelu zastępczego systemu trakcyjnego, obejmującego źródło zasilania, sieć trakcyjną, filtr wejściowy i układ napędowy pojazdu z regulatorami momentu i prędkości zbadano wpływ napięcia początkowego kondensatora i prądu początkowego dławika filtru na warunki stabilnej pracy napędu. Badania wykonano z wykorzystaniem programu Maple, a ich wyniki zweryfikowano modelując analizowany układ w programie IsSpice.

EN

Advance in a field of design and production of fully controllable high-power semiconductor devices enables increase of operating frequency of traction vehicle converter-based drive systems. Due to increased operating frequency and at determined allowable fluctuations of voltage and current in a traction network, the capacitance and inductance of an input filter can be significantly decreased. However, the significant change of the parameter values of these elements might be unacceptable, among other things due to necessity to ensure the stable operation of the drive system. Stability of the traction drive operation depends on parameters of the traction system such as resistance and inductance of traction network and input filter, supply voltage value, drive power and capacitance of the input filter capacitor. In a non-linear system, the initial values of input filter capacitor voltage and inductor current can also influence the conditions of the stable drive operation. On the basis of a simplified traction system model, consisting of an energy source, traction network, input filter and pulse-mode controlled drive system with speed and torque controllers, the analysis of influence of initial values of filter capacitor voltage and filter inductor current on conditions of stable drive operation was carried out. Necessary calculations were made using the Maple program and obtained results were verified by modelling the analysed system in IsSpice program.

7

Time-efficient removal of power-line noise from EMG signals using IIR notch filters with non-zero initial conditions

Piskorowski J.

Biocybernetics and Biomedical Engineering

|

2013

|

Vol. 33, no. 3

171--178

EN

Power-line interference is always a problem when biopotential signals are recorded. This paper presents a technique for time-efficient power-line interference suppression from EMG signals using digital IIR (Infinite Impulse Response) notch filters with reduced transient response. The reduction of the transient response is obtained by finding optimal non-zero initial conditions for the considered notch filters. Simulations verifying the effectiveness of the proposed technique are presented and compared with the performance of the traditional notch filters with zero initial conditions using EMG signal with unwanted sinusoidal interferences as a study case.

8

Realizacja sprawdzenia warunków brzegowych optymalizacji doboru technologii produkcji energii i surowców energetycznych w systemie doradczym

Pietkiewicz P, Nalepa K, Miąskowski W

Mechanik

|

2012

|

R. 85, nr 7CD

697--704

PL

W pracy przedstawiono sposób realizacji sprawdzenia warunków brzegowych przy tworzeniu podzbioru technologii pozyskiwania surowców energetycznych na potrzeby konkretnego kompleksu agroenergetycznego. Przedstawiono graficznie źródła danych wykorzystanych do stworzenia niezbędnych mechanizmów oraz zapis mechanizmów realizujących wybór podzbioru spełniającego warunki brzegowe

EN

The way of initial conditions test realization, while the creation of the subset of energetic raw materials acquiring technology for the specific agroenergy complex, were presented in this paper. Data sources used for the indispensable actions formation and record of mechanisms which realize the choice of the subset satisfying initial conditions, were shown graphically.

9

Modeling of the propagation and evolution of nonlinear waves in a wave train

Sulisz W., Paprota M.

Archives of Mechanics

|

2011

|

Vol. 63, nr 3

311-311

EN

A theoretical approach is applied to predict the propagation and evolution of nonlinear water waves in a wave train. A semi-analytical solution was derived by applying an eigenfunction expansion method. The solution is applied to study the evolution of nonlinear waves in a wave train and the formation of freak waves. The analysis focuses on the changes of wave profile and wave spectrum due to the interaction of wave components in a wave train. The results indicate that for waves of very low steepness, the changes of wave profile and wave spectrum are of secondary importance and weakly nonlinear wave theories can be applied to describe wave propagation in a wave train. For waves of low and moderate steepness, the nonlinear terms in the free-surface boundary conditions are becoming more and more important and weakly nonlinear wave theories cannot be applied to describe substantial changes in wave profile. A train of basically sinusoidal waves may drastically change its form within a relatively short distance from its original position and freak waves are often formed. The interaction between waves in a wave train and significant wave evolution has substantial effects on a wave spectrum. A train of initially very narrow-banded spectrum changes its simple one-peak spectrum to a broad-banded and often multi-peak spectrum in a fairly short period of time. The analysis shows that these phenomena cannot be described properly by the nonlinear Schrödinger equation or its modifications. Laboratory experiments were conducted in a wave flume to verify theoretical approaches. The free-surface elevation recorded by a system of wave gauges was compared with the results provided by the semi-analytical solution. Theoretical results are in a fairly good agreement with experimental data. A reasonable agreement between theoretical results and experimental data is observed, even for complex changes of long wave trains.

10

Application of the BEM using discretization in time for numerical solution of 3D parabolic equation

Kałuża G.

Prace Naukowe Instytutu Matematyki i Informatyki Politechniki Częstochowskiej

|

2010

|

Vol. 9, nr 2

83-90

EN

The 3D parabolic equation supplemented by adequate boundary and initial conditions is considered. This equation is solved using the combined variant of the boundary element method. The numerical model for constant boundary elements and constant internal cells is presented. In the final part of the paper the examples of computations are shown.

11

Dynamika i zależność od warunków początkowych w pewnych układach z uderzeniami

Okniński A., Radziszewski B.

Przegląd Mechaniczny

|

2009

|

nr 1

32-36

12

Warunki początkowe drgań okresowych nieliniowych układów dynamicznych

Radwański M.

Zeszyty Naukowe. Mechanika / Akademia Techniczno-Rolnicza w Bydgoszczy

|

2002

|

Z. 53(241)

209-214

PL

W artykule stwierdza się, że dla każdego układu dynamicznego tłumionego, wymuszanego okresowo istnieją warunki początkowe drgań okresowych tego układu. Można je wyznaczyć drogą obliczeń cyfrowych. Przedstawiono przykład działania takiego układu.

EN

The article demonstrates that for each dynamic system, damped and periodically forced, there exist initial conditions for periodic vibrations of the system. They can be determined by numerical calculations. An example of how such a system works was shown.