Search results for "Tau"

Estimates of the Distance to Exact Solutions of the Stokes Problem with Slip and Leak Boundary Conditions

2019

We deduce a posteriori error estimates of functional type for the stationary Stokes problem with slip and leak boundary conditions. The derived error majorants do not contain mesh dependent constants and are valid for a wide class of energy admissible approximations that satisfy the Dirichlet boundary condition on a part of the boundary. Different forms of error majorants contain global constants associated with Poincaré type inequalities or the stability (LBB) condition for the Stokes problem or constants associated with subdomains (if a domain decomposition is applied). It is proved that the majorants are guaranteed and vanish if and only if the functions entering them coincide with the r…

Designing a graphics processing unit accelerated petaflop capable lattice Boltzmann solver: Read aligned data layouts and asynchronous communication

2016

The lattice Boltzmann method is a well-established numerical approach for complex fluid flow simulations. Recently, general-purpose graphics processing units (GPUs) have become available as high-performance computing resources at large scale. We report on designing and implementing a lattice Boltzmann solver for multi-GPU systems that achieves 1.79 PFLOPS performance on 16,384 GPUs. To achieve this performance, we introduce a GPU compatible version of the so-called bundle data layout and eliminate the halo sites in order to improve data access alignment. Furthermore, we make use of the possibility to overlap data transfer between the host central processing unit and the device GPU with com…

Virtauslaskenta traktorien tuotekehityksessä

2016

This work describes the deployment of the current fluid flow simulation software, Star-CCM+, at Valtra Inc. The text also gives a brief introduction to computational fluid dynamics and its role in the product development process for an engineer at the company. Two computational test cases are also described. A simpler case of the simulation of an engine air intake channel flow is shown first. The results show better agreement with the measured values than the outsourced simulation that was used as a reference. The second case is the so called underhood analysis which is a flow simulation of the whole Valtra N-series front end, including fan and heat exchangers. It is a steady state simulati…

Numeerista virtauslaskentaa hila-Boltzmann-simulointimenetelmällä

2006

Spin Pumping and Torque Statistics in the Quantum Noise Limit

2017

We analyze the statistics of charge and energy currents and spin torque in a metallic nanomagnet coupled to a large magnetic metal via a tunnel contact. We derive a Keldysh action for the tunnel barrier, describing the stochastic currents in the presence of a magnetization precessing with the rate Ω. In contrast to some earlier approaches, our result is valid for an arbitrary ratio of ℏΩ/kBT. We illustrate the use of the action by deriving spintronic fluctuation relations, the quantum limit of pumped current noise, and consider the fluctuations in two specific cases: the situation with a stable precession of magnetization driven by spin transfer torque, and the torque-induced switching betw…

Smoothed particle hydrodynamics virtausmekaniikan simulaatioissa

2016

Tässä opinnäytetyössä käsittelemme Smoothed Particle Hydrodynamics -menetelmää (SPH) virtausmekaniikan simulaatioissa. Aluksi johdamme nesteen liikettä kuvaavat differentiaaliyhtälöt. Määrittelemme SPH:n diskreetit divergenssi-, gradientti- sekä Laplace-operaattorit avaruuden diskretisoimiseksi. Lisäksi tutkimme SPH:n toimivuutta rajoitetuissa virtauksissa ja esittelemme menetelmiä rajoituksista seuraavien ongelmien korjaamiseksi tutkien erityisesti SPH:n renormalisaatiota. Lopulta käsittelemme ajan diskretisointia, simulaatiototeutuksessa tarvittavia tietorakenteita ja reunaehtoja sekä esittelemme simulaatiotuloksia sekä analyyttisesti ratkeaville Couette- ja Poiseuille -virtauksille sekä …

Unstable thin film spreading of volatile binary mixtures

2013

This Thesis discusses the fluid mechanics of thin films, with emphasis on dynamical instabilities observed in some situations. The theoretical part first presents the main theory of thin-film flow, and then advances to discuss the problems associated with incorporation of evaporative effects and binary mixtures in the model. In the experimental part, measurements related to spreading of certain class of binary mixtures are presented. The studied mixtures have a volatile component with low surface tension and a less volatile component with high surface tension. The main example of such a mixture is the water-isopropanol system. Tämän opinnäytteen aiheena on ohuiden nestekalvojen virtausmekan…

Accountability for disinformation in times of covid-19

2022

Nelabvēlīgās informācijas plašais tvērums liek vairumam sabiedrībā ar vien uzmanīgāk vērtēt informāciju sociālajos tīklos un masu mēdijos, bet arī nekritiski domājošā sabiedrības daļa ir jāpasargā no šādas bīstamas informācijas it īpaši globālās pandēmijas laikā, kad plašie pamattiesību ierobežojumi un ikdienas saasinājumi vājina uzticību valdībai. It īpaši nelabvēlīgas informācijas izplatīšanas ierobežojumi ir nepieciešama virtuālajā vidē, jo 21. gs. ir pavēris jaunas iespējas daļēji vai pilnīgi nepatiesas informācijas ātrai izplatīšanai. Pašlaik Latvijā nav skaidri izveidota doktrīna, kā efektīvi aizsargāt nelabvēlīgās informācijas aizskartās cilvēktiesības, jo to traucē plašais aizsardzī…

Characterizing the bacterial fish pathogen Flavobacterium columnare, and some factors affecting its pathogenicity

2010

Flavobacterium columnare is a bacterial pathogen of fresh water fish causing lethal columnaris disease worldwide. At Finnish fish farms, columnaris disease has occurred since the early 1980s, and is a serious problem in salmonid farming in Finland. Currently, the only effective treatment is with antibiotics. Factors related to the pathogenicity of F. columnare, transmission of columnaris disease and the immunity of salmonids to columnaris infections are poorly known. F. columnare strains isolated from Finnish fish farms were characterized geno- and phenotypically, virulence and transmission experiments were conducted, and the efficacy of two immunostimulants against columnaris infections in…

Publiskā iepirkuma un valsts atbalsta regulējumu problemātika Eiropas Savienības tiesībās

2017

Attiecības starp publiskā iepirkuma un valsts atbalsta regulējumiem ES tiesības ir neskaidra. Vai praksē visos gadījumos darbojas nostiprinātā prezumpcija, ka atbilstoši ES publiskā iepirkuma direktīvām organizēts iepirkums izslēdz iespēju, ka tiks piešķirts valsts atbalsts? Situāciju vēl vairāk sarežģī, tas ka valsts atbalsta regulējuma kontekstā ir aplūkojams arī vispārējas tautsaimnieciskas nozīmes pakalpojumu institūts ES tiesībās. Ja tiek norādīts, ka atbilstoši ES normatīvajiem aktiem rīkots publiskais iepirkums izslēdz valsts atbalsta iespējamību, vai gadījumā ja publiskais iepirkums rīkots neatbilstoši iepirkuma direktīvām būtu prezumējams valsts atbalsts? Darbā tika analizēta ES no…