Maladen Ryan D, Ding Yang, Li Chen, Goldman Daniel I
Interdisciplinary Bioengineering Program, Georgia Institute of Technology, Atlanta, GA 30332, USA.
Science. 2009 Jul 17;325(5938):314-8. doi: 10.1126/science.1172490.
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.
生活在沙漠中的沙鱼（Scincus scincus）在干燥的沙子中移动，沙子这种物质兼具固体和类似流体的特性。高速X射线成像显示，在沙子表面以下，这种蜥蜴不再用四肢推进，而是通过沿着身体传播起伏的行波来产生推力以克服阻力。尽管粘性流体动力学可以预测在水等流体中的游动速度，但目前还没有适用于颗粒阻力的等效理论。为了预测沙鱼的游动速度，我们通过测量一个相对于位移方向成不同角度的小圆柱体上的颗粒阻力，并将这些力在动物运动轮廓上进行求和，从而建立了一个经验模型。模型与实验结果的吻合表明，这种非惯性游动发生在一种摩擦流体中。
