Browsing by Author "Rautaheimo, Patrik"

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  • Analyzing vibration sources based on their responses in a large cruise ship
    (2005) Tenovuo, Karno
     Helsinki University of Technology | Master's thesis
    Tutkimuksen tavoitteena on etsiä herätteiden ja vasteiden väliset riippuvuussuhteet isojen risteilylaivojen runkovärähtelyissä. Erityisesti tutkitaan ympäristötekijöiden aiheuttamien herätteiden ja niiden aiheuttamien vasteiden välisiä riippuvuussuhteita rungon ensimmäisille ominaistaajuuksille. Diplomityössä kehitetään erilaisia analysointitapoja värähtelyjen selvittämiseksi ja menetelmä, jolla voidaan arvioida vasteiden avulla herätteen paikka ja tyyppi. Laivojen koko kasvaa vuosi vuodelta ja samalla kasvavat niiltä vaaditut ominaisuudet. Koon kasvaminen saattaa johtaa tiettyjen rakenteiden ja alueiden altistumiseen matalataajuiselle värähtelylle, joka taas puolestaan lisää rungon rasitusta ja vähentää matkustajien mukavuutta. Värähtelyherätteestä tulisi tietää tulevaisuudessa enemmän, jotta runko voitaisiin suunnitella optimaalisesti pienentämään värähtelytasoja. Tavoitteiden saavuttamiseksi tutkittiin useita erilaisia tapoja analysoida herätettä ja vastetta. Nämä tavat perustuvat mm. korrelaatiolaskentaan perustuvaan herätteen paikan selvittämiseen, spektraalianalyysiin, regressiolaskentaan sekä Simulinksimulointimallin käyttöön. Työssä kehitetyt menetelmät vasteen analysointiin sisältävät jonkin verran epävarmuutta, mutta antavat kuitenkin selkeän kuvan herätteen tyypistä, paikasta ja voima4uudesta. Simulointimallilla pystyttiin muodostamaan selkeä käsitys herätteiden ja vasteiden välisistä yhteyksistä. Työssä kehitettiin monta pidemmän aikavälin värähtelytietojen esitystekniikkaa, jotka paljastavat värähtelyn luonteesta erilaisia asioita, kuten värähtelyn hallitsevat taajuudet ja ihmisten tuntemat värähtelytasot.
  • Description of the numerical methodology for the ercoftac test case F3
    (1997) Rautaheimo, Patrik; Ojala, Juha
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: The purpose of thies work is to compare different low-Reynolds-number turbulence models and their suitability for the highly three dimensional return channel with a deswirl cascade. A comparison is made between Chien's k-ε model, Chien's model with a rotational correction, Gatski et al. ARSM and the full Reynolds stress model by Speziale et al. Experiments are provided by Concepts ETI.
  • Description of the numerical methodology for the ercoftac test case F3
    (1997) Rautaheimo, Patrik; Ojala, Juha
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: The purpose of this work is to compare different low-Reynolds-number turbulence models and their suitability for the highly three dimensional return channel with a deswirl cascade. A comparison is made between Chien's k-ε model, Chien's model with a rotational correction, Gatski et al. ARSM and the full Reynolds stress model by Speziale et al. Experiments are provided by Concepts ETI. Main result: Results for the test case F3 in the ERCOFTAC Workshop on Turbomachinery Flow Predictions VI.
  • Developments in turbulence modelling with Reynolds-averaged Navier-Stokes equations
    (2001-04-27) Rautaheimo, Patrik
     Doctoral dissertation (article-based)
    The performance of different low-Reynolds number turbulence models applied to various flows is described. The emphasis is put on Chien's k – ε model, an explicit algebraic Reynolds-stress model by Speziale et al., and a full Reynolds-stress closure. The Reynolds-stress closure of this work has been developed by the author by combining different existing models. Accurate numerical methods are developed to couple the momentum equations and the low-Reynolds number Reynolds-stress equations. Two methods are introduced and these vary depending on how much the source terms are taken into account implicitly. The production of turbulence can be used to couple the inviscid part of the momentum equations and the Reynolds-stress equations in the approximate Riemann solution. As demanding problems are computed, it has been essential to parallelize the computer code. This has been performed via a message passing package. The code shows an excellent parallel performance even in the most complex topologies simulated. In this thesis, validations are presented for ten different fluid dynamic problems. The test cases vary from a simple channel flow to complicated flows in rotating machinery. In the validations it is found that the Reynolds-stress closure generally performs better than the two-equation models in complex flows. Especially streamline curvature is better captured by the Reynolds-stress closure. For the skin friction, the present Reynolds-stress closure does not give satisfactory results, and thus, some further development is needed. For simpler situations the two-equation models give comparable or even better results than the more complex models.
  • Diagonalization of the Reynold's equation by using enthalphy e and density ρ
    (1995) Rautaheimo, Patrik
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: This paper presents an improved method to upwind the Euler part of the uxes with the Reynolds-stress closure model. This new method takes account the anisotropic nature of the Reynolds-stresses. Method uses information of the production of the kinetic energy of turbulence. Resulting eigenvalues shows effect of the anisotropy. The characteristic variables and the right eigenvector matrix are relatively complex. Main result: Possible equations for upwinding.
  • Implementation of the compressibility effect in to dissipation equation of a two equation turbulence model
    (1997) Rautaheimo, Patrik
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: In the k-ε turbulence model the effect of compressibility is generally neglected and an incompressible version of the model is used. However, with high Mach numbers results can be improved by a compressible dissipation. Main result: Correction term owing to compressibility to the turbulent dissipation rate.
  • RANS analyses of cavitating propeller flows
    (2012) Sipilä, Tuomas
     School of Engineering | Licentiate thesis
  • Reynold's stresses in the turbulent fluid flow
    (1995) Rautaheimo, Patrik
     Helsinki University of Technology | Master's thesis
  • Simplified of time averaged Navier-Stokes equations and Reynold's stress equations for an implicit sweep
    (1995) Rautaheimo, Patrik
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: This paper presents an improved method of upwind the Euler part of the uxes with the Reynolds-stress closure model. This new method takes account the anisotropic nature of the Reynolds-stresses. Resulting eigenvalues show effect of the anisotropy. Because the characteristic variables and the right eigenvector matrix are relatively complex, a simplified diagonalization is introduced. Main result: Possible equations for upwinding.
  • Simulation of a free surface flow
    (2000) Rautaheimo, Patrik; Salminen, Esa
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: A numerical model has been developed for a simulation of moving boundaries. The flow field is calculated in one side of the moving interface and pressure is used to determine the boundary condition. The method is based on the moving-grid technique. The flow field is solved by an existing computational fluid dynamics code that uses a finite volume approach. The code uses structured multiblock grids, artificial compressibility method, higher-order discretization and implicit time marching. Main result: Numerical study of a flow around ships.
  • Test Calculations of Various Two-Equation Low Reynolds Number Turbulence Models
    (1996) Rautaheimo, Patrik
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: Purpose of this work is compare different two-equation low Reynolds number turbulence model and their suitability to the different flow situations. There is comparison of old Chien k- ε model, cross-diffusion model and Gatski et al. ARSM. Flow simulations are applied for low Reynolds number channel flow, flow over flat plate, wall jet and curved duct. Main result: Implementation of the different turbulence models.
  • Tilavuuksien ja pinta-alojen laskenta rakenteelliselle hilalle
    (1998) Rautaheimo, Patrik
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Tiivistelmä: FINFLOssa käytetyt algoritmit hilaparametrien laskennassa. Pääkohdat: Tilavuus ja pinta-ala algoritmit.
  • Transportation of FINFLO to a cluster of PCs
    (1999) Rautaheimo, Patrik; Kaurinkoski, Petri
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: For a long time, the UNIX workstations have been superior against to the personal computers as far as computational speed is concerned. However, the gap between the speeds has been decreasing. Today’s personal computers are fast and relatively cheap, whereas the UNIX workstations are expensive. A comparison between the available personal computers and traditional engineering tools like UNIX workstations, servers and also the supercomputers is needed. In this report such a study is made for a cluster of PCs. It will be shown that with ideal cases the speed and parallel performance figures of a cluster of personal computers are competitive with those of the workstation. Main result: Benchmark runs in a cluster of Linux personal computers, and a comparison with different UNIX-platforms.
  • Transportation of FINFLO to a cluster of PCs
    (1999) Rautaheimo, Patrik; Kaurinkoski, Petri
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: For a long time, the UNIX workstations have been superior against to the personal computers as far as computational speed is concerned. However, the gap between the speeds has been decreasing. Today’s personal computers are fast and relatively cheap, whereas the UNIX workstations are expensive. A comparison between the available personal computers and traditional engineering tools like UNIX workstations, servers and also the supercomputers is needed. In this report such a study is made for a cluster of PCs. It will be shown that with ideal cases the speed and parallel performance figures of a cluster of personal computers are competitive with those of the workstation. Main result: Benchmark runs in a cluster of Linux personal computers, and a comparison with different UNIX-platforms.
  • Transportation of FINFLO to CRAY T3D
    (1996) Rautaheimo, Patrik
     Helsinki University of Technology | J Muu elektroninen julkaisu
    Abstract: Explanation of the implementation of FINFLO to the CRAY T3D and also report the benchmark results. Main result: Benchmark runs in CRAY T3D.