## 8 Impact and Shock Measurements on Critical Structures  
Structures in the marine environment are subject to various loadings during their building and manufacture processes due to the harsh environment, which contributes to a number of loading forms, such as nonlinear wave patterns and crack-induced corrosion. Besides these, impact phenomena also threaten the structures. The events can be triggered in almost unlimited scenarios, i.e., dust and methane explosions in a mining site, underwater explosion, and shock due to a torpedo attack in warfare state, until collision and grounding hull interaction with obstructions. Such conditions will cause severe damage  
Figure 30: The hardware architecture of Sparrow, an autonomous robot [135]. Figure 29: An overview of Sparrow, a robotic system [135]. to the structures and lead to immense casualties. Considering the critical influences delivered by explosions, shocks, and collision and grounding, a series of research studies have been dedicated to quantifying structural responses and loading behavior in the form of experimental tests and trials. In these, sensors are deployed to sense and record the occurred response and behavior from both the target structure and the induced impact phenomenon. In 2010, [PERSON] et al. [136] conducted an experiment in coal dust using a large-scale tube as the medium for explosion set-up. The values measured by 16 pressure sensors, which were mounted on the wall of the tube (along the axial direction) in the experiment, were later recorded by a data acquisition (DAQ) system with a sampling frequency of 1 MHz. Primarily, pressure sensors were used to measure the pressure histories at different points along the tube during the explosion experiment. According to the recorded measurements, propagation of the pressure wave occurs in the range of 370-420 m/s, with the maximum overpressure of the explosion being between 50 and 72 kPa. A year later, similar work was performed, but with a different explosion medium. Methane-air mixtures (with methane purity of 99.995%) were considered another possible ignition cause in a coal mine [137]. In realizing the explosion, an explosion vessel was deployed that was mounted to a pressure sensor to record the pressure variation that occurred when the ignition grew. A camera was installed on the experiment site to observe the flame structure and fireball growth. Based on the experimental observation, it was concluded that the explosion of the mixture was divided into two stages, namely, the pressure rise stage (in this state, the released energy level from the combustion reaction is higher than the heat loss to the environment) and the pressure decline stage (the reaction energy is less than the energy loss to the environment). Besides mining sites, impact and shock phenomena in sub-zero regions, i.e., the Arctic, have also received attention. The opening of the Northern Sea Route (NSR) has led to ships from Asia passing through this region to reach the European and American continents since the mid-2000s. The motive behind this was found to be the reduced sailing time, lower fuel consumption, and lower risk of pirating activities compared to the Southern Sea Route (SSR) through the Gibraltar strait. Scholars from Finland tried to quantify ice-crushing pressure on a ship hull during interaction with ice [138]. Instead of a piezoelectric pressure sensor, the experimental research used I-Scan 210 tactile sensors, in which sensing elements were installed in 44 by 44 grids with a sample rate of 50 Hz along the ship hull (in bow shoulder, midship, aft shoulder, and aft locations for the general cargo ship; and bow, bow shoulder, midship, and aft shoulder for the ice-breaker ship). Evaluation of the test results indicated that the number of contact elements is set as the number of adjacent elements with a pressure higher than the threshold (in this case, 20 kPa).