# An Attempt to Model the Surface Pressures of Apples Using the Finite Element Method
## 3 Results and Discussion
Figure 6 presents the effect of the drop height on experimental and model values of surface pressures, \(p\). It can be observed that model values start from a lower value, by about 0.04 MPa from the experimental values and their increase with height increase occurs faster than in the experimental results, and reaches most of them. [PERSON] et al. (2019), in his studies, pointed out that, for a wood-type substrate, with a 10 mm drop height, damage occurs, so higher values obtained at higher drop heights do not have any effect, because, even at lower values, damage occurs. As previously stated, these results are within the error limit (10%) and should be considered as very good due to the value of the coefficient of determination R\({}^{2}\) = 0.99 obtained from the power model. The results are presented in Figure 6.  
In Figure 7, a comparison of contact area \(A\) for experimental and model values is presented. The obtained values differ to a small extent, as evidenced by the presented trend lines for their courses, where determination coefficients are close to unity and are R\({}^{2}\) = 0.96 for experimental results and R\({}^{2}\) = 0.98 for model results. Based on the results of the contact surface, it can be concluded that the proposed model is a very good representation of reality. Figure 6: Influence of drop height on the experimental and model values of surface pressure, for wood type substrates. _pm_—means model surface pressure, _pe_—means experimental surface pressure. Error bars represent mean \(\pm\) SD (standard deviation). Figure 7: Influence of the drop height on the experimental and model contact surface, for wood type substrates. _Am_—means model contact surface, _Ac_—means experimental contact surface. Error bars represent mean \(\pm\) SD (standard deviation). In Figure 8, a comparison of the obtained force \(F\) values for experimental and model values is presented. It can be observed that the strength values are close to each other and are characterised by an equal fast build-up rate as the height increases; the trend lines for both runs are characterised by a high coefficient of determination close to unity. In Figure 9, the effect of drop height on experimental and model values of surface pressures is presented. It can be observed that model values start from a lower value, around 0.1 MPa from the experimental values, and their increase with the drop height increase occurs faster than in the experimental results, but reaches a similar maximum value. However, as previously stated, these results were within the error \(\pm\)10% compared to the base value calculated. In Figure 10, a comparison of contact area \(A\) for experimental and model values is presented. The obtained values differ to a small extent; bigger values were obtained in the model tests. On the other hand, the increases in contact area values are similar and have a similar course. Figure 8: Influence of the drop height on the experimental and model force value, for wood type substrates. _Fm_—means model force, _Fe_—means experimental force. Error bars represent mean \(\pm\) SD (standard deviation). Figure 9: Influence of drop height on the experimental and model values of surface pressure, for concrete type substrates. _pm_—means model surface pressure, _pe_—means experimental surface pressure. Error bars represent mean \(\pm\) SD (standard deviation). In Figure 11, a comparison of the obtained force \(F\) values for experimental and model values is presented. It can be observed that the force values are similar to each other and are characterised by a comparable rate of increase in speed, as the drop height increases to 70 mm, while from the drop height of 80 mm, the model values are characterised by a greater increase in force, \(F\). The trend lines for both runs have high determination factors.