Although machining accuracy is always focused on by researches of manufacturing technology, the scale difference has been hardly discussed in conventional manufacturing fields. In recent industrial researches, additive manufacturing (AM), so-called 3D printer, gathers attention as a new technology for complex-shape fabrication. Although the accuracy has been determined by the performance of positioning control for tools and machined objects in conventional manufacturing, the shape of AM products is strongly influenced by the melting and solidifying processes, i.e., fluid dynamics in fabricated materials. Therefore, if the scaling in fluid dynamics during AM could be small, AM would achieve the drastic enhancement in fabrication accuracy and efficiency. This paper explains a new aspect to discuss the relation between the scaling factors and physical phenomena in AM. Considering that the gravity acceleration is a factor strongly influencing on AM process, the new analogy in different gravitational fields is clarified for improving the performance of AM in this study.

SFX (special effects) frequently used in Science Fiction (SF) films shall include rich example of scale model experiments. Technicians and staffs of SFX put extra-ordinal efforts to reproduce unrealistic scene (yet it looks very real) by “Kufu” based on empirical experiences, so called “know-how”, based on their professional sense. This work is to provide the strategies to understand how such “Kufu(s)” works to reproduce the “unrealistic” catastrophe in SFX using the concept of scale modeling. Through the strategy, professional sense can be written as certain formula of engineering law. To do so, melting-collapse of pylons subjected to extremely hot gas jet (so called “atomic breath”) by Godzilla is used as the case study. The actual treatment applied in the past SFX is recalled and discussed its feasibility. Improved method based on scale model concept is newly introduced and discussed.

This paper discusses the effects of gravity on the combustion-wave propagation through a dust cloud. Two models, continuum and point-source models, are developed by extending the models of Goroshin et al. to consider gravity effects. The continuum model treats a particle cloud as a continuum phase, while the point-source model considers heat generation from individual particles; hence, the latter model better represents the actual phenomenon. Both the models have three dimensionless parameters: dimensionless reaction time, 𝜏_c, dimensionless ignition temperature, 𝜃_ign, and dimensionless terminal velocity of particles, 𝑈_g. It is first confirmed that the continuum model is a good approximation of the point-source model when 𝜏_c ≳1, whereas their differences are apparent when 𝜏_c ≲1. Evaluating the values of 𝜏_c for the propagation through a cloud of aluminum particles shows that 𝜏_c is less than unity in conditions of interest. The point-source model is therefore applied to assessing the gravity effect, revealing that the extinction condition (minimum explosive concentration, MEC) is significantly influenced by gravity even for particles as small as 10 μm.