COMSOL Multiphysics is a very suitable tool for analysis of wave propagation in phononic crystals. In the thesis, I give the steps for two kind of simulations in COMSOL Multiphysics. KEY WORDS：Phononic Crystals, FEM, Eigenfrequencies, Frequency Response Analysis, Band Gap, Euler-Bernoulli Beam, Spring Resonator. At very shallow flow depths, such as a hydraulic depth of 1 foot or less, the Mannings roughness coefficient will often diverge significantly from its value for the same channel at a deeper flow. Thus, if the user determines n value from guidance that has not specifically taken into account shallow flow, it should not be assumed to apply toThe MIMO channel between the tri-directional coil antennas are characterized under the complex influences from the water absorption as well as the surface reflection and lateral waves. To validate the channel model, we compare the theoretical results with simulations derived by the COMSOL Multiphysics simulation tool.