Experimental Research on Cavitation Evolution and Movement Characteristics of the Projectile during Vertical Launching

Aiming at the problem of unsteady cavitation during a projectile’s vertical water-exit process, scaled model experiments were carried out based on the self-designed underwater launch platform and high-speed cameras, which focus on changes in cavitation shape and projectile posture. In this paper, the general process of the cavitation evolution and projectile’s movement is described; the relationship between the re-entry jet, local cavitation number and cavitation stability is discussed. Meanwhile, the effect of head forms and launch speeds on the cavitation evolution and movement characteristics is analyzed, including 60° cone, 90° cone and hemispherical head with velocity of 16.8 m/s, 18.5 m/s and 20.0 m/s, whose launch cavitation number is 0.714, 0.589 and 0.504. The results show that the attached cavities fall off from the bottom up under the influence of the end-re-entry jet and the shedding frequency declines when the launch cavitation number decreases. The cavitation growth of 60° cone is easily disturbed by the air mass near the launcher, the cavitation development of 90° cone is characterized by small-scale and high-frequency growth and shedding, while the hemispherical head is not prone to cavitation. Moreover, increasing the speed can improve the stability of cavitation development and the projectile’s movement.

Zenius Stimulation during a Pandemic: Framing of Republika.co.id and Liputan6.com on Distance Learning Issues in the Pandemic Era

Indonesia’s education sector has also been affected by the Covid-19 pandemic. The learning process has changed from conventional to online learning. Many students find it challenging to capture and understand their knowledge because they are accustomed to the learning process through face-to-face interactions with teachers. Teachers need to create a teaching system that is more efficient than just completing the curriculum. Regarding this problem, Zenius, as an educational application from Indonesia, issued the “Zenius Untuk Guru” platform, which helps teachers create learning systems. The product launch attracted influential online media in Indonesia, Liputan6.com and Republika.co.id. The interesting point about the launch platform is that these two online media display the related news with different framing. This research using Entman’s framing theory to describe how the two media perceive the platform. The results show that Liputan6. com frames Zenius commercially, while Republika.co.id communicates Zenius as a problem solver to improve teacher literacy in less technologically literate areas. Zenius also helps Indonesia in equalizing education to remote areas of Indonesia.

Efficiency in Carrying Cargo to Earth Orbits: Spaceports Repositioning

Space flights are in these days not any more question of technology, but more question of costs. One way how to decrease cost of launch is change of home spaceport. Change of home spaceport for different rockets is a way to achieve more efficient launches to space. The reason is different acceleration achieved from Earth rotation. We added several mathematical calculations of missions to Low Earth Orbit and Geostationary Earth Orbit to show bonuses from Earth rotation and effect of atmospheric drag on specific rockets used these days. We discussed only already used space vessels. Namely Arianne 5, Delta 4 heavy, Proton-M, Zenit and Falcon9. For reaching GEO we discuss possibility of using Hohmman transfer, because none of aforementioned vessels is available for direct GEO entry. As possible place for launch we discussed spaceports Baikonur, Kennedy Space center, Guyana Space center and Sea Launch platform. We present results in form of additional acceleration for each spaceport, and we also project this additional acceleration in means payload increase. In conclusion we find important differences between vessel effectivity based on spaceport used for launch. Change of launch location may bring significant cost decrease for operators.