Sökning: "Upward positive lightning"

Visar resultat 1 - 5 av 7 avhandlingar innehållade orden Upward positive 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

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

   Författare :Helin Zhou; Rajeev Thottappillil; Gerhard Diendorfer; Daohong Wang; KTH; []
   Nyckelord :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

4. 3. Some Properties of Lightning Flashes to a Tall Tower on a Mountain Top

   Författare :Helin Zhou; Rajeev Thottappillil; Gerhard Diendorfer; Farhad Rachidi; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; NATURVETENSKAP; NATURAL SCIENCES; tall tower; mountain top; effective height; field enhancements; upward lightning initiation; upward positive lightning; upward bipolar lightning;

   Sammanfattning : .... LÄS MER

5. 4. Features of the Electric Fields Generated by Lightning with Special Attention to Positive Ground Flashes

   Författare :Dalina Johari; Vernon Cooray; Mahbubur Rahman; Fridolin Heidler; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; positive ground flashes; preliminary breakdown pulses; multiple-trains PBPs; positive leader; bidirectional leader; negative leader branch; subsequent return strokes; distant lightning; Engineering Science with specialization in Atmospheric Discharges; Teknisk fysik med inriktning mot atmosfäriska urladdningar;

   Sammanfattning : This thesis focuses on the main processes in positive ground flashes and the distant lightning environment for both positive and negative ground flashes. It presents the characteristics of the preliminary breakdown pulses (PBPs), the characteristics of the electric field pulses observed during leader propagation, and the characteristics of the electric fields produced by the first and the subsequent return strokes. LÄS MER

7. 5. Numerical Simulations of Long Spark and Lightning Attachment

   Författare :Liliana Arevalo; Vernon Cooray; Dan Windmar; Uppsala universitet; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; breakdown; discharge; leader channel; lightning attachment; negative discharge; positive discharge; streamer; Electrical engineering; Elektroteknik; Engineering Science with specialization in Atmospheric Discharges; Teknisk fysik med inriktning mot atmosfäriska urladdningar;

   Sammanfattning : The research work presented here is concerned with numerical simulations of two different electrical phenomena: Long gap electrical discharges under switching impulses and the lightning attachment process associated with positive upward leaders. The development of positive upward leaders and the progression of discharges in long gaps are attributable to two intertwined physical phenomena, namely, the leader channel and the streamer zone. LÄS MER