Longitudinal waves longitudinal wave 2 Acoustic surface wave devices 1 Acoustic wave analysis 1 Acoustic waves 1 Circular cross-sections 1 Complex algorithms 1 Containers 1 Discrete elements method 1 Dispersion (waves) 1 Dispersion curves 1 Elastic wave propagation 1 Elastic waves 1 Filling 1 Filling levels 1 Finite difference method 1 Finite element method 1 Guided electromagnetic wave propagation 1 Longitudinal acoustic waves 1 Longitudinal elastic wave 1 Measurements of 1 Method model 1 Model and simulation 1 Noninvasive technique 1 Numerical methods 1 Sensitive techniques 1 Sensor systems 1 Small filling level 1 Steel rod 1 Surface acoustic waves 1