In this study, two ventilation holes were considered to prevent condensation in the circular column supporting the provision crane on a training ship(Saenuri) for Mokpo National Maritime University. The ventilation holes could be understood as the most simple and inexpensive way to prevent condensation because it was formed only by drilling. If sufficient ventilation is provided, the insulation and corrosion of an electric motor can be improved, and a comfortable state can be ensured in the circular column. The circular column had an electric motor for driving the provision crane so that the basic principle was to utilize the kinetic energy for the flow field from a cooling fan in the circular column. The ventilation holes attenuated the low-velocity area in the circular column and contributed to internal flow circulation with updrafts. The results were discussed through numerical analysis based on computational fluid dynamics.

A numerical approach for ventilated disc brake with holes is carried out to investigate the effect of holes on the heat transfer characteristics. The numerical simulation code STAR-CCM+ is utilized to calculate flow and temperature fields with polyhedral meshes. The steady state results show that the holes make the flow velocity on the outer surface increasing, which induce the improvement of convective heat transfer on the outer surface. In the ventilated channel with holes, the convective heat transfer can be reduced due to the inflow of hot air through holes. In unsteady state, the disc has reached the highest temperature in 1,8s since the brake was engaged. The surface of disc without holes has maximum temperatures along the ventilated channels, while the surface temperatures of dis with holes are uniform.

Polycrystalline diamond (PCD) tools possessing high hardness and abrasive wear resistance are particularly suited for drilling of carbon fiber reinforced plastic (CFRP) composites, where tool life and consistent hole quality are important. While PCD presents superior performance when drilling CFRP, it is unclear how it performs when drilling multi-stack materials such as CFRP-titanium (Ti) stacks. This comparative study aims to investigate drilling of a Ti plate stacked on a CFRP panel when using PCD tools. The first sequence of the drilling experiments was to drill 20 holes in CFRP only. CFRP-Ti stacks were then drilled for the next 20 holes with the same drill bit. CFRP holes and CFRP-Ti stack holes were evaluated in terms of machined hole quality. The main tool wear mechanism of PCD drills is micro-fractures that occur when machining the Ti plate of the stack. Tool wear increases the instability and the operation temperature when machining the Ti plate. This results in high drilling forces, large hole diameter errors, high surface roughness, wider CFRP exit thermal damage, and taller exit Ti burrs.

The fracture of mechanical structure is caused by internal cracks in the material. Particularly, the fracture can also be seen to happen under the stress that is lower than yield strength in case of high strength steel because of the crack happening from the defect inside the material. In this study, high strength steel with four holes near the center crack were designed by angle and fatigue experiments, and the simulation analyses to verify the experimental results were carried out. As the results of this study, the crack growth rates are shown to be 0.000485, 0.000434 and 0.000422 respectively at the inclined angles of center crack as 22.5°, 45° and 67.5°. The maximum deformation energies become 0.0848mJ, 0.0603mJ and 0.0582mJ respectively at the inclined angles of center crack as 22.5°, 45° and 67.5°. It is thought that this study result can be utilized as the basic data at the study on the material existing with the defects of crack and hole.

Stainless steel is known as a corrosion-resistant material and this superior ability could be a desired property for a pinhole aperture operated in a corrosive environment and thereby be able to maintain both smoothness and a perfect circular shape in order to achieve precise beam alignment. Laser drilling has widely been preferred when placing holes into stainless steel due to its non-contact method of machining. In addition, this method is capable of performing delicate machining while inducing relatively low amounts of heat in the affected zone in comparison with other traditional machining techniques such as punching. Laser drilling is also beneficial for specimens having a thin thickness since manufacturing tolerances are minimal in this case. In this paper, we have attempted to produce holes of various diameters in 10 m thick stainless steel foil by using a femtosecond laser trepanned method. We have demonstrated these to be of perfect circular shape and adhering to low tolerance manufacturing by adjusting the beam parameters. In addition, holes with various diameters have been made by employing previously selected machining parameters and the viability of pinhole apertures fabricated by laser drilling have been evaluated.