Sensitivity and regression analysis of acoustic parameters for determining physical properties of frozen fine sand with ultrasonic test
(1) Three-factor analysis of variance (ANOVA) Orthogonal tests are an effective means of multi-factor analysis and lend themselves to assessing the impact of relevant factors (Li Y. et al., 2010; Liu Y.Q. et al., 2016). An orthogonal experiment consisting of nine groups—L9(34)—selected three physical properties of frozen fine sand (temperature, density and water content) as factors to study the sensitivity of three acoustic parameters (wave velocity, attenuation coefficient and dominant frequency) to the physical properties. The values of the factors used for the orthogonal test are given in Table 2. Position for Table 2 (2) Control variable test The control variable test included two types of experiment. One had 16 groups of different levels of water content (4.31, 7.31, 10.31 and 13.31%) at a single level of density (1.87g/cm3) to study the relationships between sensitive acoustic parameters and physical properties (water content and temperature). The other had 16 groups of different levels of density (1.87, 1.8, 1.76 and 1.73g/cm3) under a single level of water content (7.31%) to study the relationships between sensitive acoustic parameters and density. Each group was evaluated three times at four levels of temperature (–5, –10, –15 and –20°C), and the results are mean values of repeated tests.