發送短信 : Head-on collisions of vortex rings upon round cylinders

  ____       ___     _____     _    _     _  __  
 |  _ \\    / _ \\  |  __ \\  | || | ||  | |/ // 
 | |_| ||  | / \ || | |  \ || | || | ||  | ' //  
 | .  //   | \_/ || | |__/ || | \\_/ ||  | . \\  
 |_|\_\\    \___//  |_____//   \____//   |_|\_\\ 
 `-` --`    `---`    -----`     `---`    `-` --`