In the phase analysis, accuracy can degrade when the intensity of bright and dark lines in interference fringes varies significantly spatially, or when the phase change Delta phi is temporally discontinuous. In this study, we improved the interference fringe analysis method by focusing on a local region in phase analysis and classifying phase inter-frame differences delta phi' in phase unwrapping. The objective of this study is to clarify how to set the threshold for classifying delta phi' and the accuracy of the phase phi and phase change Delta phi obtained by the proposed method. Both experimentally obtained in a microgravity and artificially generated interference fringes were analyzed using the proposed method. As a result, the obtained spatial distribution of Delta phi had a few outliers. In addition, it was revealed that a reliable threshold for classifying delta phi' can be automatically determined by using the total amount of tolerable noise and estimated delta phi'. The phase error and the phase change error were as small as 0.025 pi and 0.034 pi rad, respectively, which is less than one-fifth of the conventional method.
A numerical simulation study was carried out to investigate the relative contributions of thermal and solutal Marangoni convection (thermo-solutal Marangoni convection) on transport structures in a liquid bridge under zero gravity. The liquid bridge in the model represents a three dimensional half-zone configuration of the Floating Zone (FZ) growth system. Three dimensional field equations of the liquid zone, i.e. continuity, momentum, energy, and diffusion equations, were solved by the PISO algorithm. Computations were performed using the open source software OpenFOAM. The numerical simulation results show that the parameter plane spanned by the two Marangoni numbers with an aspect ratio 0.4 can be classified into three main zones: axisymmetric steady flow, steady flow with wave number, and oscillatory flow and the azimuthal wave number depends on the thermal Marangoni number at oscillatory flow zone.
This paper proposes a methodology to determine and validate the local crystal growth rate for vertices of the solid-liquid (S-L) interface at each frame. The crystal growth in levitated Ti and Ti-6Al-4V melts was successfully observed for the first time using a high-speed camera (HSC) installed in the electrostatic levitation furnace in the International Space Station. The displacement of the S-L interface vertices on the sample surface per unit time is defined as the local crystal growth rate. The mathematical equations to geometrically calculate the displacement and error sources were derived, and their parameters were acquired via image analyses. Quantification error, lens distortion, and crystal movement were identified as error sources. Subsequently, the equations for evaluating the error sources were derived. According to the proposed method, the quantification error is dominant under the experimental setup used in this study. For all samples, consequent plots without overlapping error bars exist. Therefore, the variations in the local crystal growth rate are significant. The proposed methodology revealed that the local crystal growth rate decreased at first and then increased during both former and latter halves of the solidification process on the sample surface. These changes in the local crystal growth rate can be attributed to the preferred orientation of crystal growth.
Space agriculture has attracted attention as a solution to the logistical and psychological challenges of long-term missions, such as those planned under the Artemis program. We investigated the effect of soil pressure on the early-stage enlargement of sweet potato root tubers, a promising crop for space agriculture. Growth experiments were conducted under three soil pressure treatments-low, high, and control-in planters filled with different media. Sweet potatoes were grown in a controlled environment, and growth parameters, including the fresh weights of shoots, roots, and root tubers, were measured 40 days after transplanting. Root lengths were analyzed using WinRHIZO software. The results showed a negative correlation between soil pressure and the fresh weight of shoots and roots, whereas root tubers indicated a positive correlation. Total root lengths decreased under the high pressure, while the mass of fine-diameter roots remained relatively unchanged. These findings suggest that moderate soil pressure may be beneficial for storage root development, although it may suppress the growth of other organs. Our study highlights the importance of maintaining appropriate soil pressure in microgravity environments to promote successful sweet potato growth.
This study experimentally evaluated the effect of internal bubbles (void fraction) on the combustion behavior of polypropylene (PP) spheres under microgravity. In previous research, it has been demonstrated that bubble generation during the burning of polymethyl methacrylate (PMMA) spheres clearly affected the burning rate constant. However, because PMMA exhibits unique pyrolysis characteristics -being composed predominantly of monomers- the observed void effect may not necessarily apply to other polymers. In this study, PP spheres with various initial internal void fractions were used as test specimens and burned under microgravity conditions generated using a drop tower test facility. A total of thirteen productive runs were successfully conducted, showing that the burning rate constant of PP spheres exhibited a positive correlation with the initial void fraction in the range of 0-40%, while remaining nearly constant above 40%. This trend indicates that the material-dependent physical properties play a dominant role in the process from bubble growth to bursting. Extrapolation to zero initial void fraction yielded an ideal (with the least initial void effect) burning rate constant of 0.60-0.72 mm2/s (indicating the potential uncertainty range), with the corresponding B-number ranging from 0.42-0.53. These findings suggest that bubble dynamics still significantly influence the burning behavior of PP and confirm the validity of void-fraction-based evaluation methods for identifying the intrinsic burning properties of polymers.
