## 8 Impact and Shock Measurements on Critical Structures
In this work, the velocity of the flyer plate was measured by a laser velocity measurement instrument, the pressure of the underwater shock was recorded by a high-range dynamic pressure sensor, and deformation of the target plate was assessed by two high-speed cameras. In terms of the deflection growth due to the crack extension of the target plate, as set according to Table 12, the final bulge height and crack length of the target plate with a small initial crack size were smaller than in the plate with the larger one under the same loading. All the measurement data related to bulge height and crack length are presented in comparative bar charts in Figures 31 and 32. Another result measured is dynamic velocity, and acceleration reflects the characteristic of bending stiffness of the target plates. In the same loading condition, specimen plates with a smaller crack size had a lower velocity and acceleration during the deformation process. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Milestone** & **Author(s)** & **Observational Subject** & **Tools/Instrument** & **Important Remarks** \\ \hline \multirow{6}{*}{2018} & \multirow{6}{*}{[PERSON] et al. [143]} & \multirow{6}{*}{Naval structure subjected to shock trial} & Shock sensor & The values of \(\alpha\) presented in the research are less than the proposed value for DDG-53, while the values of \(\beta\) in this work are greater than the reference. \(\alpha\) and \(\beta\) are the Rayleigh coefficients. \\  & & & Sensor & Polyuria coating had a significant effect on the plastic deformation of the coated plate subjected to the applied loading \\  & & & & \\  
Another work in measurement was conducted by [PERSON] et al. [147], who considers relatively new specimens, i.e., fiber-reinforced polymer (FRP), instead of metallic-based materials. Fiber Bragg grating (FBG) sensors (with a gauge length equal to 10 mm and without coating) were used for performing structural health monitoring (SHM), including spectra analysis and strain measurement. In order to calculate the quality of the sensors, spectra (in stages before and after embedding and loading are conducted) were determined using the Pearson correlation coefficient, as presented in Table 13. The notation set in the table is defined as follows: _F_--free sensor; E\({}_{S}\), E\({}_{F}\)--start and final states of the embedding process on the boat, respectively; _R_--the finished hull of the boat; \(B\)10h, \(B\)80h--boat 10 h and 80 h after the sea trials, respectively. In the next experiment, strain changes (see Figure 33) were summarized based on four FBG sensors installed in the boat hull structures, which was divided into two research group stages:  
* The first group (E\({}_{S}\) and E\({}_{F}\)) was defined as the state related to the construction process while the hull was still in form with a boat shape, and the part with embedded FBG sensors was manufactured. * The second group (_R_, B\({}_{10\text{h}}\), and B\({}_{80\text{h}}\)) was arranged to represent a finished boat mounted in a boat trailer. Figure 31: Measurement results of a specimen after an explosion: final crack length [146]. Figure 32: Recorded results of an explosion test: peak pressure value (left side) and final bulge height (right side) [146]. Besides measuring structural performance, recent work on ship collision was dedicated to improving a genetic algorithm (GA) to execute collision avoidance [148].