Mathematical Models for the Assessment of the Composite Structures of Cylindrical Floating Elements Level of Performances, Used in Brackish Seas.

Abstract

The safety of life and navigation in the areas with high risk potential adjacent parts to the coast, the fight against pollution with oil fractions, as well as the protection of marine biodiversity, all represent the central objective of this research action. One of the critical points was to statistically assess and decide the performance level of the composite structures of the modular systems with a cylindrical form, designed for the sustainable development of biodiversity and aquatic ecosystems. For this purpose, a database that includes two independent variables related to the physical-mechanical/physical-chemical values of the used raw materials was created. There were considered 1000 values associated to the: i) mass per surface unit; ii) maximum breaking force in the warp; iii) elongation at break in the warp; iv) tearing force in the warp and batting; v) film type. Moreover, 800 values related to the raw material were included for the determination of the length density, resistance and elongation at break, torsion, resistance and elongation at the knot, resistance and elongation at the loop. Descriptive statistics were used for the: a) determination of the parameters that evidence the homogeneity degree of the analysed data; b) assessment of the coefficients of variability that demonstrate the extent to which the data groups are homogeneous or heterogeneous; c) histograms of each variable, which highlight the asymmetry of the distribution, with the predominance of frequencies or variables. The statistical data analysis enabled the prediction of the asymmetries of the data series, related to Skewness and Kurtosis. The links between the considered variables were established according to the values of the correlation coefficients for each of the composite structures studied. The regression equations were developed to express the influence on the resistance to tearing for the transverse/longitudinal system of: mass, resistance and elongation at break of the composite material and resistance to knot breaking of the yarn from composite matrix structure. It was shown that for the prediction of the value of the composite element’s resistance to tearing, the values of this characteristic in the warp should be preferentially considered. In the weft direction, the introduction of additional independent variables is necessary. The two tested variants of composite material were differentiated by the fibrous composition and structure of the reinforcement matrix, for the longitudinal and transversal systems (45//55%PES//PA6.6, ratio: 1:1/100//100 PES//PES, ratio 2:1). Four mathematical models that are approximately normally distributed and follow the cumulative percentage line described by the normal curve were created. The mathematical models demonstrated that, in the design stage, for dynamic conditions (impact factor 2.5), the tear resistance value should be considered in both systems.