Sökning: "Lightning"

Visar resultat 1 - 5 av 65 avhandlingar innehållade ordet Lightning.

  1. 1. On the Attachment of Lightning Flashes to Grounded Structures

    Författare :Marley Becerra; Vernon Cooray; Rajeev Thottappillil; Mats Boman; Ivo Gallimberti; Uppsala universitet; []
    Nyckelord :Engineering physics; Lightning; Lightning attachment; Positive leader discharges; Lightning protection; Thunderstorms; Numerical modeling; Teknisk fysik;

    Sammanfattning : This thesis deals with the physical modeling of the initiation and propagation of upward positive leader discharges from grounded structures during lightning strikes. It includes the analysis of upward leaders initiated under the influence of the electric field produced by a dominant negative cloud charge and due to the combined action of a negative thundercloud and a descending downward stepped negative leader. LÄS MER

  2. 2. Electromagnetic Interference in Distributed Outdoor Electrical Systems, with an Emphasis on Lightning Interaction with Electrified Railway Network

    Författare :Nelson Theethayi; Rajeev Thottappillil; Farhad Rachidi; Uppsala universitet; []
    Nyckelord :ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; Electrical engineering; Electromagnetic Compatibility EMC ; Lightning; Lightning Protection; Transmission Lines; Electromagnetic Wave Propagation; Underground Cables; Grounding; Electromagnetic Transients; Electromagnetic Interference; Shielding Effectiveness; Railway Systems; Elektroteknik; elektronik och fotonik; Electrical engineering; electronics and photonics; Elektroteknik; elektronik och fotonik;

    Sammanfattning : This thesis deals with the electromagnetic compatibility (EMC) problems of distributed electrical networks, especially that caused by lightning to electrified railway. Lightning transients were found to damage important devices that control train movements, causing traffic stoppage and delays. LÄS MER

  3. 3. Interaction of Lightning Flashes with Wireless Communication Networks : Special Attention to Narrow Bipolar Pulses

    Författare :Mohd Riduan Ahmad; Vernon Cooray; Mahbubur Rahman; Rajeev Thottappillil; Uppsala universitet; []
    Nyckelord :ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; NATURAL SCIENCES; NATURVETENSKAP; NATURVETENSKAP; TEKNIK OCH TEKNOLOGIER; NATURAL SCIENCES; ENGINEERING AND TECHNOLOGY; Latitude; Lightning; Narrow bipolar pulse; Wireless network.; Engineering Science with specialization in Atmospheric Discharges; Teknisk fysik med inriktning mot atmosfäriska urladdningar;

    Sammanfattning : In this thesis, the features of electric field signatures of narrow bipolar pulses (NBPs) generated by cloud flashes are investigated and their effects on wireless communication systems are studied. A handful amount of NBPs (14.5%) have been observed to occur as part of cloud-to-ground flashes in South Malaysia. LÄS MER

  4. 4. Experimental Observations and Theoretical Modeling of Lightning Interaction with Tall Objects

    Författare :Helin Zhou; Rajeev Thottappillil; Gerhard Diendorfer; Daohong Wang; KTH; []
    Nyckelord :ENGINEERING AND TECHNOLOGY; TEKNIK OCH TEKNOLOGIER; TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Tall objects; Upward lightning initiation; Charge density distribution; Upward positive lightning; Upward bipolar lightning;

    Sammanfattning : This thesis investigates various discharge processes associated with upward lightning initiated from tall objects, both experimentally and theoretically, trying to bridge the knowledge-gap in understanding the mechanisms of the phenomena.Upward lightning initiation has attracted a great deal of interest during recent years due to the proliferation of tall communication towers and wind turbines. LÄS MER

  5. 5. Transient waves in nonstationary media : with applications to lightning and nonlinear media

    Författare :Ingegerd Åberg; Institutionen för elektro- och informationsteknik; []
    Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; lightning; Klein-Gordon; nonlinear; characteristics; wave splitting; imbedding; sources; propagators; Green functions; direct and inverse scattering; Nonstationary; transient; high-frequency switching; Kerr.; Technological sciences; Teknik;

    Sammanfattning : Propagation of transient waves in nonstationary, inhomogeneous, dispersive, stratified media is considered. Waves originating from sources exterior to the scatterer as well as from internal sources are treated. Algorithms are developed and illustrated by computations of wave phenomena in stationary, nonstationary and weakly nonlinear media. LÄS MER