Methodology for simulation of unsteady flows to determine the time-dependent interference between stationary and moving boundaries

A new methodology is developed to simulate unsteady flows about prescribed and aerodynamically determined moving boundary problems. The method couples the fluid dynamics and rigid-body dynamics equations to capture the time-dependent interference between stationary and moving boundaries. The unsteady, compressible, inviscid (Euler) equations are solved on dynamic, unstructured grids by an explicit, finite-volume, upwind method. For efficiency, the grid adaptation is performed within a window around the moving object. The Eulerian equations of the rigid-body dynamics are solved by a Runge-Kutta method in a non-inertial frame of reference. The two-dimensional flow solver is validated by computing the flow past a sinusoidally-pitching airfoil and comparing these results with the experimental data. The overall methodology is used for two two-dimensional examples: the flow past an airfoil which is performing a three-degrees-of-freedom motion in a transonic freestream, and the free-fall of a store after separation from a wing-section. Then the unstructured mesh methodology is extended to three-dimensions to simulate unsteady flow past bodies in relative motion, where the trajectory is determined from the instantaneous aerodynamics. The flow solver and the adaptation scheme in three dimensions are validated by simulating the transonic, unsteady flow around a wing undergoing a forced, periodic, pitching motion, and comparing the results with the experimental data. To validate the trajectory code, the six-degrees-of-freedom motion of a store separating from a wing was computed using the experimentally determined force and moment fields, then comparing with an independently generated trajectory. Finally, the overall methodology was demonstrated by simulating the unsteady flowfield and the trajectory of a store dropped from a wing. The methodology, its computational cost notwithstanding, has proven to be accurate, automated, easy for dynamic gridding, and relatively efficient for the required man-hours

O električnoj susceptibilnoj masi u A3IIB2V poluvodičima pri proizvoljnoj orijentaciji kvantizirajućeg magnetskog polja

An attempt is made to investigate the electric susceptibility mass of electrons in A3IIB2V materials under arbitrary magnetic quantization by including the influence of spin and broadening of Landau levels, respectively. It is found, taking n-Cd3P2 as an example, that the same mass oscillates with inverse quantizing magnetic field and also with the angle of orientation of the same field. Besides, the same mass increases with increasing carrier degeneracy and the crystal field splitting parameter enhances the numerical magnitudes in all the three variations. The corresponding results for the three-band Kane model, the two-band Kane model and that of parabolic energy bands have also been obtained as special cases of our generalized derivation.Razmatrana je električna susceptibilna masa elektrona u AII 3 B V 2 materijalima uz proizvoljnu magnetsku kvantizaciju ukjučujući utjecaj spina i širenja Landauovih nivoa. Nađeno je, koristeći n-Cd3P2 kao primjer, da masa oscilira s inverzom magnetskog polja te također s kutom orijentacije polja. Pored toga, masa raste porastom degeneracije nosilaca naboja. Parametar cijepanja kristalnog polja povećava brojčanu vrijednost u sve tri varijacije. Kao posebni slučajevi općenitog razmatranja rezultati su primijenjeni na Kaneov model s dvije i tri vrpce, te na model paraboličnih energetskih vrpci

Jednostavna analiza termoelektrične snage u kvantnim žicama neparaboličnih poluvodiča u prekriženom električnom i magnetskom polju

In this paper a study is made of the thermoelectric power of electrons in quantum wires of nonparabolic semiconductors in the presence of crossed electric and magnetic fields on the basis of a newly derived electron dispersion law considering all types of anisotropies of the energy spectrum. It is found, taking n-CdGeAs2 as an example, that the thermopower increases with increasing film thickness, magnetic field and electric field, respectively. The crystal field splitting enhances the thermopower with respect to all physical variables. In addition, the corresponding expressions for quantum wires of parabolic semiconductors have also been obtained from our generalized analysis under certain limiting conditions.Razmatrana je termoelektrična snaga elektrona u tzv. kvantnim žicama neparaboličnih poluvodiča u prekriženom električnom i magnetskom polju koristeći nedavno dobiven zakon disperzije za energiju elektrona koji uzima u obzir sve tipove anizotropije u energetskom spektru. Uzevši n-CdGeAs2 kao primjer, nadeno je da termoelektrična snaga opada porastom debljine filma, te jakošću električnog i magnetskog polja. Isto tako, kristalno polje jača termoelektričnu snagu u odnosu na sve fizikalne parametre

Termoelektrična sila u kvantnim točkama polumetala u prisustvu jakog magnetskog polja

We study the thermoelectric power of the carriers in quantum dots of semimetals under large magnetic field, taking Bi as an example. The numerical results are presented for McClure and Choi, hybrid, Cohen, Lax and ellipsoidal parabolic energy band models of Bi. It is observed that the thermopower increases with decreasing electron concentration, increasing magnetic field and increasing film thickness, respectively. The oscillations of the TPM in Bi, in accordance with McClure and Choi model, show up much more significantly as compared to other models. In addition, the corresponding well-known expression for the thermoelectric power in the presence of a classically strong magnetic field in bulk specimens of parabolic semiconductors has been obtained as a special case of our generalized expressions.Razmatrana je termoelektrična sila u kvantnim točkama u prisustvu jakog magnetskog polja. Kao primjer uzet je Bi. Prikazani su numerički rezultati za nekoliko modela energetskih vrpci Bi. Opaženo je da termonapon raste s padom koncentracije nosilaca naboja, porastom magnetskog polja te povećanjem debljine filma

Dynamic Unstructured Method for Prescribed and Aerodynamically Determined Relative Moving Boundary Problems

A new methodology is developed to simulate unsteady flows about prescribed and aerodynamically determined moving boundary problems. The method couples the fluid dynamics and rigid-body dynamics equations to capture the time-dependent interference between stationary and moving boundaries. The unsteady, compressible, inviscid (Euler) equations are solved on dynamic, unstructured grids by an explicit, finite-volume, upwind method. For efficiency, the grid adaptation is performed within a window around the moving object. The Eulerian equations of the rigid-body dynamics are solved by a Runge-Kutta method in a non-inertial frame of reference. The two-dimensional flow solver is validated by computing the flow past a sinusoidally-pitching airfoil and comparing these results with the experimental data. The overall methodology is used for two two-dimensional examples: the flow past an airfoil which is performing a three-degrees-of-freedom motion in a transonic freestream, and the free-fall of a store after separation from a wing-section. Then the unstructured mesh methodology is extended to three-dimensions to simulate unsteady flow past bodies in relative motion, where the trajectory is determined from the instantaneous aerodynamics. The flow solver and the adaptation scheme in three-dimensions are validated by simulating the transonic, unsteady flow around a wing undergoing a forced, periodic, pitching motion, and comparing the results with the experimental data. To validate the trajectory code, the six-degrees-of-freedom motion of a store separating from a wing was computed using the experimentally determined force and moment fields, then comparing with an independently generated trajectory. Finally, the overall methodology was demonstrated by simulating the unsteady flowfield and the trajectory of a store dropped from a wing. The methodology, its computational cost notwithstanding, has proven to be accurate, automated, easy for dynamic gridding, and relatively efficient for the required man-hours

Utjecaj kvantnog zasužnjenja na toplinski kapacitet grafita

In this paper an attempt is made to investigate theoretically the heat capacity in graphite having quantum confinement in one, two and three dimensions such as quantum wells, quantum wires, quantum dots and magneto-sized quantization of band states. The appropriate density of states functions are deduced, taking into account various types of anisotropies of the energy band constants. It has been found that the heat capacity oscillates with the film thickness, magnetic film and doping in various manners. The heat capacity is largest in quantum dots and smallest in quantum wells. The theoretical analysis is in agreement with the experimental results.Pokušava se objasniti toplinski kapacitet grafita u kojem postoji kvantno zasužnjenje u jednoj, dvije ili tri dimenzije, tj. u kvantnim jamama, kvantnim žicama, kvantnim točkama, te sistemima s magnetski-ograničenom kvantizacijom stanja vrpci zaključivanjem o odgovarajućem obliku funkcije gustoće stanja. Pri tome se uzimaju u obzir razni oblici anizotropije konstanti energetskih vrpci. Nadeno je da toplinski kapacitet titra kao funkcija debljine sloja, magnetskog polja i dopiranja. Toplinski kapacitet je najveći u kvantnim točkama, a najmanji u kvantnim jamama. Teorijska analiza u skladu je s rezultatima mjerenja

Jednostavna teorijska analiza kapacitancije magnetskih vrata u MOS strukturi p-kanalnog inverzijskog sloja na teluru

An attempt is made to study the gate capacitance of MOS structure of p-channel inversion layers on tellurium in the presence of a quantizing magnetic field by considering all types of anisotropies of the valence bands of tellurium within the framework of k^→ · p^→ theory. We have derived an analytical expression of the surface electron concentration in low electric field limit in the presence of a quantizing magnetic field. We have then formulated a model expression of the magneto-gate capacitance with the proper use of the electron concentration. For the purpose of relative comparison, we have also derived the same capacitance by including the broadening effects and without any approximations of low or high electric field limits. It has been observed that the gate capacitance of p-channel inversion layers on tellurium exhibits spiky oscillations with changing magnetic field. The corresponding well-known results for p-channel inversion layers on parabolic energy bands have also been obtained under certain limiting conditions from the generalized expressions.Proučavaju se kapacitancija vrata MOS strukture p–kanalnih inverzijskih slojeva na teluru u magnetskom polju na osnovi k^→ · p^→ teorije. Pokazuje se da kapacitancija vrata mijenja periodički s rastućim magnetskim poljem. Dobiveni rezultati svode se u modelu paraboličkih vrpci, uz određene uvjete, na poznate izraze

Einsteinova relacija u superrešetkama poluvodiča s ne-paraboličnim vrpcama i neoštrim međuplohama kod magnetske kvantizacije

We study the Einstein relation under magnetic quantization in III-V, II-VI, PbSnTe/PbTe, strained layer and HgTe/CdTe superlattices with graded interfaces and compare the same with that of the corresponding bulk specimens of the constituent materials. It is found, taking GaAs/Ga1-xAlxAs, CdS/CdTe, PbTe/PbSnTe, InAs/GaSb and HgTe/CdTe superlattices with graded interfaces as examples, that the Einstein relation exhibits oscillatory dependence with the inverse quantizing magnetic field due to the Shubnikov-de Haas effect, and increases with increasing electron concentration in an oscillatory manner in all the cases. The ratio of diffusivity to mobility in graded superlattices is greater than that of constituent bulk materials. The oscillations in HgTe/CdTe superlattices show up much more significantly as compared to other systems. In addition, we have suggested an experimental method of determining the Einstein relation in degenerate materials having arbitrary dispersion laws.Razmatrana je Einsteinova relacija kod magnetske kvantizacije u superrešetkama s neoštrim međuplohama III-V i II-VI poluvodiča, PbSnTe/PbTe, HgTe/CdTe te slojeva s napetošću, te je usporedena s onom u volumnim uzorcima gradbenih materijala. Nadeno je, uzevši GaAs/Ga1−xAlxAs, CdS/CdTe, PbTe/PbSnTe, InAs/GaAs i HgTe/CdTe superrešetke s neoštrim međuplohama kao primjer, da Einsteinova relacija pokazuje oscilatornu zavisnost o inverznim kvantizirajućim magnetskim poljima kao posljedica Shubnikov-de Haas efekta te raste oscilatorno s porastom koncentracije elektrona u svim slučajevima. Omjer difuzivnosti i pokretnosti je veći nego u volumnim uzorcima gradbenih materijala. Oscilacije u HgTe/CdTe superrešetkama su izrazitije nego u drugim uzorcima. Također, predložena je eksperimentalna metoda određivanja Einsteinove relacije u degeneriranim materijalima s proizvoljnim zakonom disperzije