沙中的波动游泳：沙鱼蜥蜴的地下运动
Undulatory Swimming in Sand: Subsurface Locomotion of the Sandfish Lizard
AI总结：
研究沙漠沙鱼蜥蜴的地下运动，发现其靠波动行波推进，开发经验模型预测其游泳速度，揭示其非惯性游泳发生在摩擦流体中。
摘要：
栖息于沙漠的沙鱼蜥蜴（Scincus scincus）可在干燥沙子中移动，沙子兼具固体与类流体行为。高速X射线成像显示，在地表以下，该蜥蜴不再用肢体推进，而是通过沿身体传播波动行波产生推力以克服阻力。尽管粘性流体动力学可预测水等流体中的游泳速度，但尚无针对颗粒阻力的等效理论。为预测沙鱼的游泳速度，我们开发了经验模型，测量小圆柱体在相对于位移方向不同角度下的颗粒阻力，并沿动物运动轮廓对这些力求和。模型与实验的一致性表明，这种非惯性游泳发生在摩擦流体中。
英文摘要：
The desert-dwelling sandfish (Scincus scincus) moves within dry sand, a material that displays solid and fluidlike behavior. High-speed x-ray imaging shows that below the surface, the lizard no longer uses limbs for propulsion but generates thrust to overcome drag by propagating an undulatory traveling wave down the body. Although viscous hydrodynamics can predict swimming speed in fluids such as water, an equivalent theory for granular drag is not available. To predict sandfish swimming speed, we developed an empirical model by measuring granular drag force on a small cylinder oriented at different angles relative to the displacement direction and summing these forces over the animal movement profile. The agreement between model and experiment implies that the noninertial swimming occurs in a frictional fluid.
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