Browsing by Author "Jokinen, Juha"

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  • Development of hydrostatic jacking unit for sleeve bearings in high voltage diesel generators
    (2017-06-12) Jaakkola, Esa
     Insinööritieteiden korkeakoulu | Master's thesis
    High voltage diesel generators are used in ships, power plants, and other facilities where they produce power to the electrical grid. It is of utmost importance that they work reliably at all times, and considerable technical efforts are undertaken to ensure this outcome. One area of importance is the control of friction between the rotating part of the machine, the rotor, and the sleeve bearings. This is challenging during slow speed operation, such as in starting and stopping, because the hydrodynamic oil film that forms between the surfaces is not sufficiently thick to separate them. In these cases, it is possible to utilize a hydrostatic jacking unit, a device that separates the surfaces regardless of the running speed. This greatly improves the service life of the sleeve bearings and consequently, the reliability of the generator. The main objective of this thesis was to develop a new design for the hydrostatic jacking unit. The development focused on reducing the existing units’ total cost of ownership and improving their structural rigidity. These had been identified as the most important characteristics of the devices, which have become an integral part of most high voltage diesel generators. As an outcome of this thesis, two detailed hydrostatic jacking unit designs were developed for two product platforms of high voltage diesel generators. The new designs are modular and they utilize the same components and subassemblies, which improves their cost-effectiveness. Additional cost reductions result from the reassessment of the system parameters and functional requirements, which allowed scaling down and/or optionalizing of components. A third source of cost savings arises from the change in the design ownership, which improves the product management capabilities. To ensure that the new structures are sufficiently rigid, a finite element modal analysis was performed on the structures. According to the results, the new units are – depending on the mounting configuration – either significantly more rigid or equally rigid compared to the existing units. This increase in the rigidity of the unit should improve its structural integrity considerably in demanding engine-generator applications.
  • A framework for solving data mapping problems in message-based integration
    (2012) Rintaniemi, Ari-Heikki
     School of Electrical Engineering | Master's thesis
  • Mikrorakoilu kalliomurskeessa
    (1990) Jokinen, Juha
     Helsinki University of Technology | Licentiate thesis
  • Modeling of rotor bar swaging process
    (2024-05-20) Sammalkorpi, Vili
     Insinööritieteiden korkeakoulu | Master's thesis
    This thesis studies the rotor bar swaging i.e. locking process in electric motor pro-duction. Main focus of the thesis was developing a model to analyse the rotor bar deformation and locking into the rotor core grooves with simulating dynamic strikes of a high frequency pneumatic hammer. Many previous swaging analyses have used static loading to simulate the hammer strikes, and statically modeling a dynamic impact can lead to unrealistic results. Rotor bars with proper locking greatly reduce the risk of rotor bar breakage due to motor vibrations and thermal bow of rotor. Tightly locked rotor bars can also help avoid permanent rotor residual unbalance changes, and therefore the better the locking, the more reliable the results. Ansys was used to create transient structural analysis models. The effectiveness of swaging was considered for different bar shapes, sizes, materials and swaging depths. Other swaging parameters investigated were non-centricity of swaging, different rotor core groove openings and comparison to a static swaging analysis. Main findings of the analyses were that most of the rotor bars do not lock into the bottom of the rotor core grooves and most of those that do, lock only with 3 mm swaging depths. 1 mm swages were found to provide insufficient locking and highly varied contact forces were seen at top corner of the rotor core grooves between 2 mm and 3 mm swages, some copper and aluminium bar 3 mm swages suggesting double as high contact forces. Contact forces at bottom of the rotor core groove vary massively between bars with bottom contact and no proper bottom contact, bars that locked into the bottom inflicted from 20 to up to 2000 times higher contact forces when inspecting 2 mm and 3 mm swages. The groove opening value was up to 3 times higher in 3 mm than 2 mm swages which results in tighter locking of subjacent bars. Other parameters including non-centricity of swaging and initial groove mouth width were found not to have a major effect on results of the swage. Based on the results of this thesis, swaging depth, groove shape, rotor bar material and bottom contact have the most significant role on success of the swaging. With the rotor bar locking models developed, bar shape designs of API-machines are suggested to be optimized and 3 mm swage depth set as the aim to reach the most reliable locking with bottom contact.
  • Tahtikoneen kestomagneettinavan lujuusanalyysi elementtimenetelmällä
    (2007) Jokinen, Juha
     Helsinki University of Technology | Master's thesis
    Tässä diplomityössä tehtiin lujuusanalyysi kestomagneeteilla magnetoidun tahtikoneen naparakenteelle, jota ympäröi muovikomposiittikuori. Naparakenne perustui muinaisten etruskien kehittämän holvaustekniikan hyödyntämiseen. Tahtikoneen rakenteen esittämisen jälkeen työssä kerrotaan kestomagneettimateriaalille tehdyistä puristuskokeista. Tuloksien hajonnan ja tarvittavien materiaaliarvojen puuttumisen takia päädyttiin siihen, ettei materiaalia voida kuormittaa korkealle tasolle. Navan lujuuslaskenta aloitettiin analyyttisellä tarkastelulla. Laskennalla muodostettiin kokonaiskuva rakenteen käyttäytymisestä koneen pyöriessä ja laskettiin naparuuveille tarvittavat esikiristysvoimat. Analyyttisen laskennan perusteella rakenteesta voitiin muodostaa malli elementtimenetelmällä. Malli ratkaistiin voima-askelmenetelmällä epälineaarisena kontaktianalyysinä. Laskelmien perusteella magneettien jännitykset kasvavat liian suureksi, napojen välinen kiila on lähes mahdoton suunnitella ja muovikomposiittikuoren ominaisuuksia ei ole käytetty optimaalisesti hyväksi. Tämän takia diplomityön aikana käynnissä olleessa tuotekehitysprojektissa kehitettiin yhdessä projektiryhmän kanssa paranneltu rakenneversio navasta, jossa edellä mainitut ongelmat on poistettu.
  • Taivekartongin käyristyminen ja sen hallinta
    (1994) Jokinen, Juha
     Helsinki University of Technology | Master's thesis
  • Valuation analysis of technology companies in venture capital investments
    (2000) Jokinen, Juha
     School of Business | Master's thesis