| 摘要: | 為什麼音響玩家總是在音響支撐架填充鋼珠或石英砂來改善音響的聲音品質？這有趣的物理機制至今尚未深入研究與釐清。本研究採用離散元素法與有限元素法雙向耦合方法 (Two-way Couple DEM-FEM Approach) 模擬在市售音響支撐架中填充顆粒體的動態反應，進行對應的物理實驗驗證模擬結果，並進一步探討顆粒間摩擦係數、顆粒與邊壁間的摩擦係數、顆粒間恢復係數及顆粒楊氏模數對音響支撐架動態反應的影響，並作為音響業界選擇顆粒體的參考。本研究使用阻尼因子，摩擦消能效率，碰撞消能效率與總消能效率量化系統減振效果，並創新引入顆粒體傳輸性質(包括局部平均速度、擾動速度分佈及粒子溫度)探討顆粒體的減振效果。研究結果顯示：(1)消能效率呈現振幅相依性，隨著外力振幅增加，主導的消能機制由接觸阻尼消能機制轉變為摩擦消能機制。(2)顆粒性質影響減振效果，其中以顆粒楊氏模數的影響效果最為顯著，在一定的楊氏模數範圍顆粒體內部將出現調諧質量阻尼器，此時存在最佳減振效果。(3)當摩擦係數較低及楊氏模數與恢復係數較高時，系統產生較高的摩擦消能效率，當外力振幅增加，摩擦消能效率增加而碰撞消能效率降低，且兩者的變化量造成總消能效率下降。(4)模擬與實驗皆證實填充顆粒體能降低所有頻率的振動，尤其在1kHz以上的頻率特別顯著，並改變了音響1kHz以上的頻率響應。(5)填充較大楊氏模數的顆粒體能增加1kHz以上頻率的減振效果，卻降低1kHz以下頻率的減振效果。(6)減振效果與顆粒體軸向局部平均速度、擾動速度分佈及粒子溫度具有顯著的相關性。;Why do sound experts always fill the loudspeaker stands with steel beads or quartz sand to improve the sound quality of the loudspeaker? The mechanism of this interesting physical phenomenon has not yet been thoroughly studied and clarified. In this study, two-way Couple DEM-FEM Approach was employed to model the dynamic response of commercially available loudspeaker stands equipped with damping particles, and the corresponding physical experiments were performed to validate the proposed numerical model. The effect of particle properties, such as the inter-particle friction coefficient, the particle-wall friction coefficient, the inter-particle restitution coefficient, and the Young′s modulus of particles, on the dynamic response of the loudspeaker stands was further explored, and the outcome can guide the audio industry to select the appropriate particles. This study used damping factors, friction energy dissipation efficiency, collision energy dissipation efficiency and total energy dissipation efficiency to quantify the system′s vibration reduction effect, and innovatively introduced particle transport properties (including local average velocity, fluctuation velocity distribution and granular temperature) to explore the performance of vibration reduction effect. The main findings are highlighted below: (1) As the external force amplitude increases, the dominant energy dissipation mechanism transforms from the damping dissipation mechanism to the friction dissipation mechanism; (2) The particle properties affect the damping effect. Among them, the Young′s modulus of the particles exhibits the most significant effect. In a certain range of Young’s modulus, a tuned mass damper occurs inside the granular solid, leading to the best damping effect; (3) The condition with smaller friction coefficients and larger Young’s modulus and restitution coefficients provides higher friction energy dissipation efficiency. As the external force amplitude increases, the friction dissipation efficiency increases while the collision dissipation efficiency decreases. The resultant effect from both mechanisms causes the total energy dissipation efficiency to decrease. (4) Both simulations and experiments confirmed that filling particles into the loudspeaker stands can attenuate vibrations for the frequencies studied here, especially at frequencies above 1kHz, and change the frequency response of the sound above 1kHz. (5) Filling particles with a larger Young′s modulus can increase the damping effect at frequencies above 1kHz, but decrease the damping effect at frequencies below 1kHz. (6) The damping effect has a significant correlation with the local average vertical velocity, fluctuation velocity distribution and granular temperature of particles. |
