| 摘要: | 本研究透過實驗的方式來探討於相同無因次振動強度下，改變不同流體、振動頻率與水高對不同密度比的侵入物(Intruder)在類二維垂直振動床中的巴西豆現象，藉由高速攝影機拍攝照片並利用PTV(Particle Tracking Velocimetry)來分析顆粒的運動行為，並探討侵入物的上升時間與上升速度、顆粒床底部顆粒的水平速度以及侵入物於上升時所受阻力。
當流體為水時，水會影響顆粒的運動，對於尺寸較小的背景顆粒而言，水主導了侵入物與背景顆粒分離的過程，水會使侵入物的上升時間與密度比有依賴性，當密度比趨近背景顆粒的體積佔有率時，侵入物的上升時間最長。透過改變水高可發現，水高越低侵入物上升越慢，這是因為水表面距離顆粒床較近，抑制侵入物的向上運動，而水高較高侵入物上升越快。除了水表面干擾的減少外，增加水高會增加顆粒飛躍時床體的壓力差，進而增加水向下流動的速度，使水更快的側向拖曳背景顆粒填補侵入物底下的空隙，增強巴西豆現象。在水高較低時，頻率越小會使水表面波動施加在顆粒床的干擾更加劇烈，質量與慣性較低的侵入物容易受到影響，輸入的能量越強侵入物的上升時間反而越慢，而在水高較高時，水表面波動對顆粒床的影響減弱，輸入的能量越強可使侵入物的淨向上位移增加，進而增強水驅動的巴西豆現象，使侵入物的上升時間減少。
;This study investigates the Brazil Nut Effect (BNE) in a quasi-two-dimensional vertical vibrated bed by changing different fluid, vibration frequency, and water height to different density ratios of intruders under the same dimensionless vibration intensity through experiments. Take pictures with a high-speed camera and use PTV (Particle Tracking Velocimetry) to analyze the movement of particles, the rise time and velocity of the intruder, the horizontal velocity of the granular bed, and the drag force on the intruder.
When the fluid is water, the water to the particles must be taken into account. For the smaller background particles, the water dominates the size separation process, and the water drag force will make the rise time of the intruder depend on the density ratio. When the density ratio approaches the packing fraction of the small particle, the intruder needs more time to rise. In the case of changing the water height, the lower the water height, the slower the intruder rises, because the water surface close to the granular bed, which affect the upward movement of the intruder. The higher the water height, the faster the intruder rises, increasing the water height will increase the pressure difference of the granular bed, thereby increasing the velocity of the water flowing downward, making the water drag the background particles laterally faster to fill the gap under the intruder, and eventually enhance the BNE. When the water height is low, the smaller the frequency, the more severe the disturbance imposed by the water surface fluctuation on the granular bed, and the intruder with lower mass is easily affected, the stronger the input energy, the slower the rise time of the intruder. When the water height is high, the stronger the input energy can increase the net upward displacement of the intruder, thereby enhancing the water-driven BNE and reducing the rise time of the intruder. |
