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

Znaleziono wyników: 65

Liczba wyników na stronie
first rewind previous Strona / 4 next fast forward last
Wyniki wyszukiwania
Wyszukiwano:
w słowach kluczowych:  finite volume method
help Sortuj według:

help Ogranicz wyniki do:
first rewind previous Strona / 4 next fast forward last
1
Content available remote Problemy dotyczące modelowania obciążenia wiatrem obiektów budowlanych
PL
Im bardziej skomplikowany kształt obiektu budowlanego, tym trudniej prognozować, jak będą na niego oddziaływały masy powietrza podczas przepływu. Problem jest istotny z uwagi na niezawodność obiektów budowlanych. Analizy numeryczne oraz badania doświadczalne pozwolą w przyszłości zmodyfikować wytyczne normowe, przyczyniając się do poprawy bezpieczeństwa obiektów budowlanych.
EN
The more complex the shape of a building object, the more difficult it is to predict how air masses will affect it during flow. The problem is important for the reliability of buildings. Numerical analyses and experimental studies will allow future modification of the standard guidelines, contributing to the improvement of the safety of buildings.
EN
Natural convection characteristics of Al2O3-water nanofluid in a cavity is investigated numerically under the influence of a inclined magnetic field. The bottom wall is partially heated, and the top wall is cooled and the remaining regions of the cavity are kept adiabatic. An isothermally heated square blockage of the different rectangular size is placed at the centre of the cavity. The schematic model is converted into mathematical form, and the non-dimensional equations are discretized by the finite volume method using power law scheme and solved by Semi-Implicit Method for Pressure Linked Equation algorithm. The relevant parameters such as Rayleigh number (104-106), Hartmann numer (10-500), size of blockage ratio (0.25-0.75), length of the heat source (0.25-1.0) and inclination angle of the magnetic field (0°-90° on the flow and temperature fields are examined. Results are presented in terms of streamlines, isotherms, velocity profile, local and average Nusselt number. It was found that for low Hartmann numbers, the average heat transfer rate attained the maximum at the inclined magnetic field of γ = 45°. In addition, the blockage ratio of B = 0.75 enhanced the higher heat transfer rate for all values of γ.
EN
In this work, we develop and analyze an explicit finite volume scheme for a one-dimensional nonlinear, degenerate, convection–diffusion equation having application in petroleum reservoir. The main difficulty is that the solution typically lacks regularity due to the degenerate nonlinear diffusion term. We analyze a numerical scheme corresponding to explicit discretization of the diffusion term and a Godunov scheme for the advection term. L∞ stability under appropriate CFL conditions and BV estimates are obtained. It is shown that the scheme satisfies a discrete maximum principle. Then we prove convergence of the approximate solution to the weak solution of the problem, and we mount convergence results to a weak solution of the problem in L1 . Results of numerical experiments are presented to validate the theoretical analysis.
EN
Numerical studies on detonation wave propagation in rotating detonation engine and its propulsive performance with one- and multi-step chemistries of a hydrogen-based mixture are presented. The computational codes were developed based on the three-dimensional Euler equations coupled with source terms that incorporate high-temperature chemical reactions. The governing equations were discretized using Roe scheme-based finite volume method for spatial terms and second-order Runge-Kutta method for temporal terms. One-dimensional detonation simulations with one- and multi-step chemistries of a hydrogen-air mixture were performed to verify the computational codes and chemical mechanisms. In two-dimensional simulations, detonation waves rotating in a rectangular chamber were investigated to understand its flowfield characteristics, where the detailed flowfield structure observed in the experiments was successfully captured. Three-dimensional simulations of two-waved rotating detonation engine with an annular chamber were performed to evaluate its propulsive performance in the form of thrust and specific impulse. It was shown that rotating detonation engine produced constant thrust after the flowfield in the chamber was stabilized, which is a major difference from pulse detonation engine that generates repetitive and intermittent thrust.
PL
Przedstawiono badania numeryczne propagacji fali detonacyjnej w wirującym silniku detonacyjnym oraz jego wydajności pędnej z jedno- i wielostopniową mieszanką chemiczną na bazie wodoru. Kody obliczeniowe opracowano w oparciu o trójwymiarowe równania Eulera w połączeniu z pojęciami źródłowymi, które obejmują wysokotemperaturowe reakcje chemiczne. Obowiązujące równania zostały zdyskredytowane przy użyciu metody skończonej objętości opartej na schemacie Roe'a dla terminów przestrzennych oraz metody Runge-Kutta drugiego rzędu dla terminów czasowych. W celu weryfikacji kodów obliczeniowych i mechanizmów chemicznych przeprowadzono jednowymiarowe symulacje detonacji z jedno- i wieloetapowymi chemikaliami mieszaniny wodoru i powietrza. W symulacjach dwuwymiarowych badano fale detonacyjne obracające się w komorze prostokątnej w celu zrozumienia jej charakterystyki pola przepływu, gdzie udało się uchwycić szczegółową strukturę pola przepływu zaobserwowaną w doświadczeniach. Przeprowadzono trójwymiarowe symulacje dwufalowego wirującego silnika detonacyjnego z komorą pierścieniową w celu oceny jego właściwości pędnych w postaci ciągu i impulsu właściwego. Wykazano, że wirujący silnik detonujący wytwarza stały ciąg po ustabilizowaniu się pola przepływu w komorze, co stanowi istotną różnicę w stosunku do silnika detonującego impulsowo, który wytwarza powtarzalny i przerywany ciąg.
EN
In this paper, the characteristics of the flow and forced heat transfer of power law non-Newtonian fluids that flow around a quadrilateral and rectangular cylinder that are located in a 2D channel are investigated by use of the finite volume method (FVM) in a steady state flow regime. To this accomplishment, in the constant temperature, the effects of a different obstruction ratio, aspect ratio and Reynolds number are investigated. The Reynolds number in the range 5 ≤ Re ≤ 40, the power index in the range 0.5 ≤ n ≤ 1.4, the aspect ratio in the range 0.5 ≤ a ≤ 2, and the obstruction ratio in the range 0.125 ≤ b ≤ 0.5 were selected. By surveying the drag coefficient profiles, it’s concluded that as the obstruction ratio increases, the drag coefficient is increased, while an increase in the Reynolds number causes the lower drag coefficient. In addition, the drag coefficient is strongly increased by aspect ratio enhancements.
EN
This paper deals with the numerical simulation of a turbulent flow around two-dimensional bodies by the finite volume method with non-orthogonal body-fitted grid. The governing equations are expressed in Cartesian velocity components and solution is carried out using the SIMPLE algorithm for collocated arrangement of scalar and vector variables. Turbulence is modeled by the turbulence model and wall functions are used to bridge the solution variables at the near wall cells and the corresponding quantities on the wall. A simplified pressure correction equation is derived and proper under-relaxation factors are used so that computational cost is reduced without adversely affecting the convergence rate. The numerical procedure is validated by comparing the computed pressure distribution on the surface of NACA 0012 and NACA 4412 hydrofoils for different angles of attack with experimental data. The grid dependency of the solution is studied by varying the number of cells of the C-type structured mesh. The computed lift coefficients of NACA 4412 hydrofoil at different angles of attack are also compared with experimental results to further substantiate the validity of the proposed methodology.
PL
W artykule przedstawiono analizę wpływu parametrów symulacji przepływu czynnika ściśliwego przez zwężkę Venturiego na dokładność uzyskiwanych rezultatów, z wykorzystaniem programu Ansys 2019 R2. Analiza została przeprowadzona w oparciu o wzorzec za jaki uznano wyniki obliczeń przepływu wg. normy PN-EN ISO 51674:2005. Rozważono wpływ modelu gazu i modelu turbulencji. Symulacji podlegała całość układu pomiarowego włącznie z przewodami impulsowymi.
EN
The article presents the analysis of the impact of the compressor flow simulation parameters through the Venturi tube on the accuracy of the obtained results. The Ansys 2019 R2 program was used for analysis. The analysis was carried out on the basis of the pattern for which the results of flow calculations according to standards PN-EN ISO 5167-4: 2005. The influence of the gas model and turbulence model was considered. The entire measurement system, including impulse lines, was subject to simulation.
8
Content available Symulacja prostego silnika magnetohydrodynamicznego
PL
Silnik magnetohydrodynamiczny jest maszyną elektryczną, w której elementem bezpośrednio wprawianym w ruch jest płyn znajdujący się w polu magnetycznym. W opisanym przykładzie taką rolę pełni osolona woda przewodząca prąd znajdująca się w zewnętrznym polu magnetycznym pochodzącym od magnesu ferrytowego. W artykule zawarto model matematyczny zjawisk pozwalający na przewidywanie zachowania się płynu oraz wykorzystany model numeryczny, który wstępnie zweryfikowano na modelu fizycznym w laboratorium. Omawiane urządzenie wprawia w ruch obrotowy wodę znajdującą się w szalce Petriego, której zewnętrzna ścianka wyłożona jest taśmą miedzianą. Na dnie szalki położony jest magnes ferrytowy w kształcie pierścienia. Całość zasilana jest prądem stałym przepływającym poprzez płyn z umieszczonej centralnie elektrody wykonanej z miedzianego drutu do znajdującej się na zewnątrz elektrody utworzonej z taśmy miedzianej, którą wyłożona jest zewnętrzna ścianka.
EN
Magnetohydrodynamic drive is a type of electric drive, where force acts directly on fluid without mechanical moving parts. The fluid in most cases conducts electric current in magnetic field creating force. Article includes mathematical model allowing to predict fluid behavior together with incorporated numerical model, which was preliminary verified on physical model on test rig. In described example salty water conducts direct current from central electrode made of copper wire to external electrode made of thin copper sheet covering external wall of Petri dish. External magnetic field is provided by ferrite magnet located on the bottom of the vessel. In result water spins in directions according to forces created in conductor exposed to magnetic field.
PL
Jedną z uniwersalnych a zarazem prostych metod dla numerycznego rozwiązywania zadań nieustalonego przewodzenia ciepła w obudowie budynku jest metoda objętości skończonych. Jednak, przy sformułowaniu jawnym konieczne jest dobranie kroku czasowego, gwarantującego stabilność rozwiązania. W tym artykule wartość takiego kroku czasowego została określona z warunku zerowej różnicy pomiędzy teoretycznym a numerycznym rozwiązaniem dla danej geometrii ściany. Rozpatrzono wpływ współczynnika przewodzenia ciepła ściany na długość kroku. Warunki brzegowe przyjęte w artykule odpowiadały obciążeniom ogniowym ściany schronu.
EN
One of the most simple and versatile method for numeric solving of the problems of transient heat conduction in the building envelope is the finite volume method. In explicit scheme however there is a problem of assuming correct time step for solution stability. In this article stable step value was determined from the condition of zero difference between the theoretical and numerical solution for the particular geometry of the wall. The influence of the thermal conductivity on the step length has been evaluated. Condition for the correctness of solutions obtained from the analysis in this article is sharper than the condition of equations stability according to the literature. For the boundary conditions adopted solution can be applied to the study of resistance of buildings shelters to long fire.
10
EN
This article concerns the widespread matter of biophysical comfort. In this work, 10 double-layer knitted fabrics with potential application in multilayer garments addressed to a specific group of users, such as newborns, were investigated. The materials were constructed with the following raw materials: cotton, polypropylene, polyester, polyamide, bamboo, and viscose. The textiles with a comparable geometrical structure and different composition were tested for their air permeability. In the experimental part, the materials were tested in specific constant ambient conditions using an air permeability tester. In the simulation part, 3D models of actual textiles were designed and air permeability based on the performed simulations using finite volume method was calculated. Both measurements and simulations yielded comparable results and showed that the air permeability of the knitted fabric strongly depends on the thickness and geometrical parameters of yarn.
EN
In this study, a finite volume method (FVM) is suitably used for solving the problem of a fully coupled fluid flow in a rectangular domain with slip boundary conditions. Numerical solutions for the flow variables, viz. velocity, and pressure have been computed. The FVM, with an upwind scheme, has been implemented to discretize the governing equations of the present problem. The well known SIMPLE algorithm is employed for pressure-velocity coupling. This was executed with the aid of a computer program developed and run in a C-compiler. Computations have been performed for unknown variables with Reynolds numbers (Re) = 50, 100, 250, 500, 750 and 1000. The behavior of steady-state solutions of velocity and pressure of the fluid along horizontal and vertical through geometric center of the rectangular domain have been illustrated. We observed that, with the increase of the Reynolds number, the absolute value of velocity components decreases whereas the pressure value increases.
EN
The aim of this paper is to build and validate a class of energy-preserving schemes for simulating a complex modified Korteweg–de Vries equation. The method is based on a combination of a discrete variational derivative method in time and finite volume element approximation in space. The resulting scheme is accurate, robust and energy-preserving. In addition, for comparison, we also develop a momentum-preserving finite volume element scheme and an implicit midpoint finite volume element scheme. Finally, a complete numerical study is developed to investigate the accuracy, conservation properties and long time behaviors of the energy-preserving scheme, in comparison with the momentum-preserving scheme and the implicit midpoint scheme, for the complex modified Korteweg–de Vries equation.
13
EN
This paper presents the patient-specific simulations of the aortic valve based on the proposed geometric model. A structural analysis is performed by using the finite element method to determine the stress-strain state of the aortic valve. The study is focused on the investigation of various turbulence models crucial for the appropriate description of the flow in the deceleration phase, following the peak systole. A comparative study of the flow solution without a turbulence model and the numerical results obtained by using various turbulence models is also performed. The results yielded by the shear-stress transport k-ω model supplemented with the intermittency transition equation most closely match those of numerical simulations without a turbulence model.
EN
Theoretical and numerical modeling of flow transients in pipelines is a challenging field of research. The governing flow equations constitute a system of nonlinear hyperbolic partial differential equations enforcing the conservation laws for mass, momentum and energy. The application of these mathematical models might be limited due to the absence of complete knowledge about the physical phenomena and uncertainties. Information about the initial and boundary conditions is usually obtained from measurements. The presence of noise and inaccuracies, as well as inexactness of the flow model and numerical approximations for solving the full model can lead to predictions that differ from reality. In this paper, we deal with the problem of extracting information about states of the system in real time given noisy measurements. We solved the isothermal flow model during a hydraulic shock while using the extended Kalman filter to estimate the hidden state variables. To avoid spurious oscillations in the solution, the flow model in conservative form was solved using Roe’s flux limiter within the finite volume framework to ensure the total variation diminishing property. Numerical approximation of the Jacobian was done with an adaptive routine and showed that most entries in the matrix are zero and therefore sparse. The robustness of the extended Kalman filter was examined by varying the noise statistics. In most of the situations, we can conclude that the extended Kalman filter was successful in estimating the rapid transients of natural gas.
EN
The article concerns the wide issue which is thermal comfort. In the paper investigations on the textile thermal insulation problem are presented. Materials tested were multi-layer systems with potential application in uniforms addressed to firefighters. Thermal insulation was tested both experimentally (using a thermal imaging camera) and by modelling (by means of simulations of heat transfer phenomena on 3-D models of real textiles). The materials investigated were constructed with the following raw materials: Kevlar, Nomex, ePTFE, PU and carbon fiber. Textiles with a comparable geometric structure and similar composition were tested for their thermal insulation. In the experimental part temperature, the change in specific constant ambient conditions was obtained using a thermal imaging camera. In the simulation part 3-D models of actual textiles were designed and the temperature change was calculated on the basis simulations of the real experiment performed . For each multi-layer system two models were designed, with varying degree of mapping the structure of the yarn in the fabrics. The main goal of the work was experimental verification of both models. As a result of the simulation performed on a model characterised by a more accurate mapping of the yarn structure, comparable results were obtained with experimental data and a strong relationship of thermal insulation textiles from the composition of raw materials and the geometric structure was confirmed.
PL
Artykuł dotyczy szeroko pojętego problemu jakim jest komfort cieplny. W pracy zostały przedstawione wyniki badań dotyczące termoizolacyjności tekstyliów. Przedmiotem analiz były układy wielowarstwowe (składające się z tkanin, włóknin i folii) o potencjalnym zastosowaniu w odzieży ochronnej przeznaczonej dla straży pożarnej. Termoizolacyjność materiałów została przebadana zarówno eksperymentalnie (za pomocą kamery termowizyjnej) jak i teoretycznie (w wyniku symulacji zjawiska transportu ciepła przeprowadzonych na trójwymiarowych modelach rzeczywistych tekstyliów). Przeanalizowane układy tekstylne (wykonane z następujących surowców: Kevlar, Nomex, ePTFE, PU, włókno węglowe) charakteryzowały się porównywalnym składem oraz strukturą geometryczną. W części eksperymentalnej dla wszystkich układów został wyznaczony gradient temperatury w ściśle określonych stałych warunkach otoczenia. W części teoretycznej gradient temperatury został obliczony na podstawie symulacji rzeczywistego eksperymentu. Dla każdego układu zostały zaprojektowane dwa modele, o różnym stopniu odwzorowania struktury przędzy w tkaninach. Głównym celem pracy była weryfikacja eksperymentalna obu modeli. W wyniku symulacji przeprowadzonych na modelu charakteryzującym się dokładniejszym odwzorowaniem struktury przędzy zostały otrzymane rezultaty porównywalne z danymi eksperymentalnymi i potwierdziły silny związek termoizolacyjności tekstyliów z ich składem surowcowym oraz strukturą geometryczną.
EN
A new very high-order finite volume method to solve problems with harmonic and biharmonic operators for one-dimensional geometries is proposed. The main ingredient is polynomial reconstruction based on local interpolations of mean values providing accurate approximations of the solution up to the sixth-order accuracy. First developed with the harmonic operator, an extension for the biharmonic operator is obtained, which allows designing a very high-order finite volume scheme where the solution is obtained by solving a matrix-free problem. An application in elasticity coupling the two operators is presented. We consider a beam subject to a combination of tensile and bending loads, where the main goal is the stress critical point determination for an intramedullary nail.
EN
This paper concerns numerical modelling of the Yb:YAG laser beam welding process. Numerical algorithms are developed for the analysis of thermal phenomena in a laser welded joint taking into account the motion of the liquid material in the welding pool. The model describing the laser beam heat source power distribution is developed on the basis of the kriging method. The heat source model uses the real laser beam profile obtained from experimental measurements of the beam emitted from a Trumpf D70 laser head performed on UFF100 analyzer. On the basis of developed numerical algorithms computer simulations of a Yb:YAG laser beam welding are carried out used to analyze the influence of the thermal load model on the shape and size of the weld.
PL
W pracy przedstawiono symulacje numeryczne wyciskania profili nieosiowosymetrycznych. Ze względu na bardzo duże zmiany kształtu obrabianego materiału podejście Lagrangea, typowe dla zadań mechaniki ciała stałego, nie jest efektywne. W obliczeniach numerycznych zastosowano podejścia bazujące na sformułowaniu Eulera: metodę objętości skończonych oraz sprzężoną analizę Eulera-Lagrangea. Jako kryterium poprawności obliczeń numerycznych przyjęto siłę wyciskania, której wartość porównano z wynikami badań eksperymentalnych.
EN
Numerical simulations of extrusion of non-axisymmeric profiles is presented in this paper. Extreme changes of the shape of processed material exclude application of Lagrangian approach typical for solving the solid mechanics problems. In the numerical simulations two approaches based on Eulerian approach are applied, namely: finite volume method and coupled Eulerian-Lagrangian. The punch force is chosen as the criterion of numerical computations reliability – numerically derived punch force was compared to the results of experimental investigations.
EN
Various methods for steady-state and transient analysis of temperature distribution and efficiency of continuous-plate fins are presented. For a constant heat transfer coefficient over the fin surface, the plate fin can be divided into imaginary rectangular or hexangular fins. At first approximate methods for determining the steady-state fin efficiency like the method of equivalent circular fin and the sector method are discussed. When the fin geometry is complex, thus transient temperature distribution and fin efficiency can be determined using numerical methods. A numerical method for transient analysis of fins with complex geometry is developed. Transient temperature distributions in continuous fins attached to oval tubes is computed using the finite volume - finite element methods. The developed method can be used in the transient analysis of compact heat exchangers to calculate correctly the heat flow rate transferred from the finned tubes to the fluid.
EN
This short article presents all basic “closures” that are needed to supplementation the general set of balance equations in form characteristic for the Finite Volume Method. In subsequent chapters the equation of state, viscous molecular stress tensor, turbulent stress tensor, molecular heat flux, turbulent heat flux and momentum and energy sources were described. This article is a second part of a cycle dedicated for the mathematical basis of Finite Volume Method. The motivation for writing the article follows from the observation that the Finite Volume Method is usually described in greater detail in monographic books, or very briefly in the basic books dedicated to fluid mechanics. This article is an attempt to center justifications of these approaches, so that in the simplest way show the readers the basic knowledge of the so-called Computational Fluid Mechanics. For this reason this article can be treated as a literature review.
first rewind previous Strona / 4 next fast forward last
JavaScript jest wyłączony w Twojej przeglądarce internetowej. Włącz go, a następnie odśwież stronę, aby móc w pełni z niej korzystać.