During tissue retraction with a laparoscopic grasper, tissue-damaging pressures can occur. Past research suggests that peak pressures can be considerably reduced by rounding the edges or covering the tip of the end effector with a silicon sleeve. To identify grasping methods that limit tissue damage, the effects of (a) Young's modulus of the end effector, (b) curvature of the end effector, and (c) angle with which the tissue is pulled relative to the plane of the end effector, on the pressure generated on the tissue were investigated. Artificial skin was placed between two non-serrated jaws, a pressure-sensitive film was interposed between the skin and upper jaw, and the end effector was loaded with 13 N. End effectors with Young's moduli of 0.09, 0.67, 1.49 MPa, and 69 GPa, and with non-rounded and 5 mm rounded edges were tested under pulling angles of 25°, 50°, and 75°. For non-rounded end effectors, the maximum pressure and the area across which pressure exceeded the safety threshold for tissue damage increased with Young's modulus and pulling angle. For rounded end effectors, maximum pressure did not increase monotonically with Young's modulus. Instead, the end effector with the second lowest Young's modulus yielded significantly lower maximum pressure than the end effector with the lowest Young's modulus. For rounded end effectors, pressures were below the safety threshold for all Young's moduli. This indicates that to prevent tissue damage, soft graspers may not be needed; rounding the edges of metal graspers could suffice for preventing tissue damage.
This paper presents the results of a systematic validation of numerical simulation of reflection and transmission of rubble-mound breakwater structures. The aim of the study is to provide a body of validation measurements for increasingly complex situations, starting simple and building up the complexity in terms of breakwater geometry, wave conditions and numerical simulation models. The predictions from a set of three different numerical models were compared against measurements from small scale physical model tests. The results of the comparison and the achieved level of accuracy are reported. Finally, a hypothetical application for the design of rubble-mound breakwaters is presented.
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