Gravity Environment Research Articles

Numerical Investigation of Sloshing Characteristics in Long Moving Vessels with Embedded Concave Rigid-ring Baffle in Gravity Environment

Flat Rigid–ring Baffle [1] (FRB) is a common slosh suppression device in Long Moving Vessel (LMV) to mitigate against oscillation-induced instability due to sloshing of its content but, its relative low performance is unacceptable for desirable safety standard thus, necessitating continuous efforts to investigate other baffle configurations. Investigation of Concave Baffles of varying geometries was carried out and analysed with the ANSYS/CFX [2] and the Computational Fluid Dynamics (CFD). Results were post-processed with the help of Mat lab [3-5] in a gravity milieu. This work was therefore designed to study the sloshing characteristics of Water-Carrying Cylindrical (WCC) tank equipped with three baffles. Model governing equations based on conservation of mass and momentum were developed and solved using Finite Element Analysis (FEA) technique. The model was used to evaluate Damping Ratio (DR) from Mile's equation [1] at 72, 66 and 59 percent standard positions, in a 75 percent filled WCC tank with slenderness ratio of 1.5 excited at a frequency of 2 Hz. The investigated baffles were Concave Rigid-ring Baffle-1 (CARB1) 0.02 m pitch, Concave Rigid-ring Baffle-2 (CARB2) 0.04 m pitch and Flat Rigid-ring Baffle, FRB (control). Data were presented in term of non dimensional DR and as the main performance index. Numerical results were obtained and compared with FRB results also obtained numerically. The results showed that, the concave baffles exhibited [better damping characteristics at 72 and 59 percent water-filled positions of the cylinder which mostly the critical states hence, Concave-Rigid-ring Baffle have better damping effectiveness than Flat-Rigid-ring Baffle.

Removing adverse effect of measurement process in flotation method

Ground simulation of space quasi-zero gravity environment is essential in modal testing of space structures. The air flotation method is widely used, in which the air cushion unit is attached to the measured structure. This inevitably increases the total mass of the structure to be tested and leads to the incorrect prediction of modal parameters. And irregular airflow disturbances of the air cushion unit also have negative effects on the test. The fast elimination method is presented to remove the adverse impact in the test data based on measured frequency response functions. Numerical simulations are performed employing the magnetometer structure. Results show that this method effectively removes the adverse mass and the airflow effect.

Spacesuit Center of Gravity Assessments for Partial Gravity EVA Simulation in an Underwater Environment.

The objective is to analytically determine the expected CG and build hardware to measure and verify the suited subject's CG for lunar extravehicular activity (EVA) training in an underwater environment. For lunar EVAs, it is necessary for astronauts to train with a spacesuit in a simulated partial gravity environment. NASA's Neutral Buoyancy Laboratory (NBL) can provide these conditions by producing negative buoyancy for a submerged suited subject. However, it is critical that the center of gravity (CG) for the human-spacesuit system to be accurate for conditions expected during planetary EVAs. An underwater force-transducer system and individualized human-spacesuit model was created to provide real-time measurement of CG, including recommendations for weight placement locations and quantity of weight needed on the spacesuit to achieve a realistic lunar spacesuit CG. This method was tested with four suited subjects. Across tested weighout configurations, it was observed that an aft and high CG location will have large postural differences when compared to low and fore CG locations, highlighting the importance of having a proper CG. The system had an accuracy of ±5lbs of the total lunar weight and within ± 15cm for fore-aft and left-right CG directions of the model predictions. The developed method offers analytical verification of the suited subject's CG and improves simulation quality of lunar EVAs. Future suit design can also benefit by recommending hardware changes to create ideal CG locations that improve balance and mobility. The developed methodology can be used to verify a proper CG location in future planetary EVA simulations such as different reduced gravity training analogs (e.g. active cable offloading systems).

Effect of Water Depth on Heart Rate and Core Temperature During Underwater Treadmill Walking

Exercising using an underwater treadmill (UTM) has become a popular modality; however, few studies have focused on the physiological demands of UTM walking at varying water depths. Thus, the objective of this study was to investigate changes in heart rate (HR) and core temperature (CT) values in college-aged males and females while exercising at different water immersion depths using an UTM. Twenty participants (age = 21.50 ± 2.19 years; height = 169.04 ± 10.85cm; weight = 75.56 ± 22.28kg) walked at water depths of 10cm below the xiphoid process and at the level of the superior iliac crest (I.C.). Each UTM session lasted 15 minutes, consisting of 5-minute bouts at 1, 2, and 3 mph. Polar HR monitors and ingestible thermoregulatory pills were used to measure HR and CT. Results indicated that HR at 1 (p = .305) and 2 mph (p = .864) were not significantly different between water depths. Heart rate was significantly higher at 3 mph (p = .003) at the I.C. water level. No significant differences were found in CT at 1 (p = .919), 2 (p = .392), or 3 mph (p = .310) during either immersion depth. As a result, higher immersion depths resulted in a lower average HR during higher intensity exercise due to the increased buoyancy effects and the reduced gravity environment of the water. Thus, exercising in higher immersion depths allows participants to exercise at a higher intensity with less overall stress placed on the lower extremities.

Ghost of vector fields in compact stars

Spontaneous scalarization is a mechanism that allows a scalar field to go undetected in weak gravity environments and yet develop a nontrivial configuration in strongly gravitating systems. At the perturbative level it manifests as a tachyonic instability around spacetimes that solve Einstein's equations. The endpoint of this instability is a nontrivial scalar field configuration that can significantly modify a compact object's structure and can produce observational signatures of the scalar field's presence. Does such a mechanism exists for vector fields? Here we revisit the model that constitutes the most straightforward generalization of the original scalarization model to a vector field and perform a perturbative analysis. We show that a ghost appears as soon as the square of the naive effective mass squared becomes negative anywhere. This result poses a serious obstacle in generalizing spontaneous scalarization to vector fields.

Surface Shape and Tension Distribution of Static Liquids Near Solid Walls in Different Gravity Environment

Surface Shape and Tension Distribution of Static Liquids Near Solid Walls in Different Gravity Environment

Evaluation of Dynamics of a Bipedal Robot Used in the Moon Base

Humanoid robots are expected to play an important role in the Moon’s exploration. Especially, in the case of robots used inside a room during base operations, the mission of this type of robot is to work with people as well as communicate with them to improve their mood. When developing the control method of this robot moving in a low gravity environment, the dynamics of the robot are necessary. In this paper, evaluation of dynamics derived for this robot was done, comparing with data obtained from the hardware simulator of the robot. First of all, calculation data in the case of walking on earth were compared with that of hardware simulator, and it was confirmed that slip motion didn’t occur. Next, using the same control method, calculation data in the case of the Moon’s environment was compared with data of hardware simulator. At this time, slip motion which was characteristic motion in a low gravity environment was realized in both calculation data and the motion of hardware simulator. From these results, the efficiency of the derived dynamics was shown.

Optimization of Exercise Countermeasures to Spaceflight Using Blood Flow Restriction.

INTRODUCTION: During spaceflight missions, astronauts work in an extreme environment with several hazards to physical health and performance. Exposure to microgravity results in remarkable deconditioning of several physiological systems, leading to impaired physical condition and human performance, posing a major risk to overall mission success and crew safety. Physical exercise is the cornerstone of strategies to mitigate physical deconditioning during spaceflight. Decades of research have enabled development of more optimal exercise strategies and equipment onboard the International Space Station. However, the effects of microgravity cannot be completely ameliorated with current exercise countermeasures. Moreover, future spaceflight missions deeper into space require a new generation of spacecraft, which will place yet more constraints on the use of exercise by limiting the amount, size, and weight of exercise equipment and the time available for exercise. Space agencies are exploring ways to optimize exercise countermeasures for spaceflight, specifically exercise strategies that are more efficient, require less equipment, and are less time-consuming. Blood flow restriction exercise is a low intensity exercise strategy that requires minimal equipment and can elicit positive training benefits across multiple physiological systems. This method of exercise training has potential as a strategy to optimize exercise countermeasures during spaceflight and reconditioning in terrestrial and partial gravity environments. The possible applications of blood flow restriction exercise during spaceflight are discussed herein.Hughes L, Hackney KJ, Patterson SD. Optimization of exercise countermeasures to spaceflight using blood flow restriction. Aerosp Med Hum Perform. 2021; 93(1):32-45.

Experimental results and interfacial lift-off model predictions of critical heat flux for flow boiling with subcooled inlet conditions – In preparation for experiments onboard the International Space Station

This study investigates critical heat flux (CHF) for subcooled flow boiling of n-Perfluorohexane based on results of pre-launch Earth-gravity Mission Sequence Tests (MSTs) of the Flow Boiling and Condensation Experiment (FBCE), which was launched to the International Space Station (ISS) in August 2021. CHF measurements were made in a rectangular channel having a 2.5 mm by 5 mm cross-section and a 114.6-mm long heated segment. Both single-sided and double-sided heating were tested in vertical upflow in Earth gravity for a variety of inlet conditions. The inlet subcooling was varied in the range of 0.4 – 32.0°C and encompassed both near-saturated and highly subcooled conditions. Experimental trends and high-speed video records were investigated to better understand the mechanism of CHF. Overall trends show CHF increases as flow rate and/or inlet subcooling are increased. Flow features from the events around CHF justify the applicability of the Interfacial Lift-off Model and the determination of limiting criteria for its application. The present experimental data are combined with prior databases for various flow orientations with respect to Earth gravity and microgravity data collected on parabolic flights. Predictions are made using the Interfacial Lift-off Model for this consolidated subcooled-inlet FBCE-CHF database. A heat utility ratio was included in the model to capture the effects of subcooling and corresponding thermodynamic non-equilibrium. An overall mean absolute error of 19.04% indicates good predictive capability of the model for both heating configurations, different gravity environments, and a wide range of inlet subcooling.

Numerical Analysis of Smoke Behavior and Detection of Solid Combustible Fire Developed in Manned Exploration Module Based on Exploration Gravity

A fire during manned space exploration can cause serious casualties and disrupt the mission if the initial response is delayed. Therefore, measurement technology that can detect fire in the early stage of ignition is important. There have been a number of works that investigate the smoke behaviors in microgravity as the foundation for a reliable method for sensing a fire during spaceflight. For space missions to the outer planets, however, a strategy of detecting smoke as an indicator of fire should be adjusted to cover the fire scenario that can be greatly affected by changes in gravity (microgravity, lunar, Mars, and Earth gravity). Therefore, as a preliminary study on fire detectors of the manned pressurized module, the present study examined the smoke particle behavior and detection characteristics with respect to changes in gravity using numerical analysis. In particular, the effects of the combination of buoyancy and ventilation flow on the smoke particle movement pattern was investigated to further improve the understanding of the fire detection characteristics of the smoke detector, assuming that a fire occurred in different gravity environments inside the pressurized module. To this end, we modeled the internal shape of Destiny and performed a series of numerical analysis using the Fire Dynamics Simulator (FDS). The findings of this study can provide basic data for the design of a fire detection system for manned space exploration modules.

Instabilities of Scalar Fields around Oscillating Stars

The behavior of fundamental fields in strong gravity or nontrivial environments is important for our understanding of nature. This problem has interesting applications in the context of dark matter, of dark energy physics, or of quantum field theory. The dynamics of fundamental fields has been studied mainly in static or stationary backgrounds, whereas most of our Universe is dynamic. In this Letter we investigate "blueshift" and parametric instabilities of scalar fields in dynamical backgrounds, which can be triggered (for instance) by oscillating stars in scalar-tensor theories of gravity. We discuss possible implications of our results, which include constraints on an otherwise hard-to-access parameter space of scalar-tensor theories.

An analysis on Quantum mechanical Stability of Regular Polygons on a Point Base Using Heisenberg Uncertainty Principle

Abstract: It is a well-known fact in physics that classical mechanics describes the macro-world, and quantum mechanics describes the atomic and sub-atomic world. However, principles of quantum mechanics, such as Heisenberg’s Uncertainty Principle, can create visible real-life effects. One of the most commonly known of those effects is the stability problem, whereby a one-dimensional point base object in a gravity environment cannot remain stable beyond a time frame. This paper expands the stability question from 1- dimensional rod to 2-dimensional highly symmetrical structures, such as an even-sided polygon. Using principles of classical mechanics, and Heisenberg’s uncertainty principle, a stability equation is derived. The stability problem is discussed both quantitatively as well as qualitatively. Using the graphical analysis of the result, the relation between stability time and the number of sides of polygon is determined. In an environment with gravity forces only existing, it is determined that stability increases with the number of sides of a polygon. Using the equation to find results for circles, it was found that a circle has the highest degree of stability. These results and the numerical calculation can be utilized for architectural purposes and high-precision experiments. The result is also helpful for minimizing the perception that quantum mechanical effects have no visible effects other than in the atomic, and subatomic world. Keywords: Quantum mechanics, Heisenberg Uncertainty principle, degree of stability, polygon, the highest degree of stability

Indirect measurement of absolute cardiac output during exercise in simulated altered gravity is highly dependent on the method.

Altered gravity environments introduce cardiovascular changes that may require continuous hemodynamic monitoring in both spaceflight and terrestrial analogs. Conditions in such environments are often prohibitive to direct/invasive methods and therefore, indirect measurement techniques must be used. This study compares two common cardiac measurement techniques used in the human spaceflight domain, pulse contour analysis (PCA-Nexfin) and inert gas rebreathing (IGR-Innocor), in subjects completing ergometer exercise under alteredgravity conditions simulated using a tilt paradigm. Seven subjects were tilted to three different angles representing Martian, Lunar, and microgravity conditions in the rostrocaudal direction. They completed a 36-min submaximal cardiovascular exercise protocol in each condition. Hemodynamics were continuously monitored using Nexfin and Innocor. Linear mixed-effects models revealed a significant bias of [Formula: see text]ml ([Formula: see text]) in stroke volume and [Formula: see text]l/min ([Formula: see text]) in cardiac output, with Nexfin measuring greater than Innocor in both variables. These values are in agreement with a Bland-Altman analysis. The correlation of stroke volume and cardiac output measurements between Nexfin and Innocor were [Formula: see text] ([Formula: see text]) and [Formula: see text] ([Formula: see text]) respectively. There is a poor agreement in absolute stroke volume and cardiac output values between measurement via PCA (Nexfin) and IGR (Innocor) in subjects who are exercising in simulated altered gravity environments. These results suggest that the chosen measurement method and device greatly impacts absolute measurements of cardiac output. However, there is a good level of agreement between the two devices when measuring relative changes. Either of these devices seem adequate to capture cardiac changes, but should not be solely relied upon for accurate measurement of absolute cardiac output.

Preparation and characterization of a specialized lunar regolith simulant for use in lunar low gravity simulation

Lunar in-situ resource utilization (ISRU) has been put on the agenda by many countries. Due to the special material nature and low gravity environment, the lunar regolith demonstrates significantly different behavior from terrestrial geomaterials. However, the systematic understanding of its geotechnical behavior is now seriously restricted by the scarcity of lunar regolith and the difficulty in simulating lunar gravity. A new lunar regolith simulant, termed as China University of Mining and Technology Number One (CUMT-1), has been developed to recover properties of the lunar regolith and simulate the lunar gravity by adopting the recently advanced geotechnical magnetic-similitude-gravity model testing (GMMT) method. The CUMT-1 simulant was prepared by reproducing the in-situ formation and fragmentation of the lunar matrix, which plays a key role in the irregular particle morphology. The mineralogical compositions, particle morphology and gradation, specific gravity, bulk density, void ratio, shear strength, and compressibility were determined. After quantifying the magnetization and magnetic-similitude-gravity characteristics, an application of the cone penetration resistance under low gravity was further given. The obtained results are compared to the values known for lunar regolith samples and other simulants, which demonstrates promising characteristics for use in geotechnical engineering-based and scientific-based applications, especially considering the influence of lunar gravity.

A model to predict the oscillation frequency for drops pinned on a vertical planar surface

Accurate prediction of the natural frequency for the lateral oscillation of a liquid drop pinned on a vertical planar surface is important to many drop applications. The natural oscillation frequency, normalized by the capillary frequency, is mainly a function of the equilibrium contact angle and the Bond number ( $Bo$ ), when the contact lines remain pinned. Parametric numerical and experimental studies have been performed to establish a comprehensive understanding of the oscillation dynamics. An inviscid model has been developed to predict the oscillation frequency for wide ranges of $Bo$ and the contact angle. The model reveals the scaling relation between the normalized frequency and $Bo$ , which is validated by the numerical simulation results. For a given equilibrium contact angle, the lateral oscillation frequency decreases with $Bo$ , implying that resonance frequencies will be magnified if the drop oscillations occur in a reduced gravity environment.

Bio-Inspired Take-Off Maneuver and Control in Vertical Jumping for Quadruped Robot with Manipulator.

The jumping motion of legged robots is an effective way to overcome obstacles in the rugged microgravity planetary exploration environment. At the same time, a quadruped robot with a manipulator can achieve operational tasks during movement, which is more practical. However, the additional manipulator will restrict the jumping ability of the quadruped robot due to the increase in the weight of the system, and more active degrees of freedom will increase the control complexity. To improve the jumping height of a quadruped robot with a manipulator, a bio-inspired take-off maneuver based on the coordination of upper and lower limbs is proposed in this paper. The kinetic energy and potential energy of the system are increased by driving the manipulator-end (ME) to swing upward, and the torso driven by the legs will delay reaching the required peak speed due to the additional load caused by the accelerated ME. When the acceleration of ME is less than zero, it will pull the body upward, which reduces the peak power of the leg joints. Therefore, the jumping ability of the system is improved. To realize continuous and stable jumping, a control framework based on whole-body control was established, in which the quadruped robot with a manipulator was a simplified floating seven-link model, and the hierarchical optimization was used to solve the target joint torques. This method greatly simplifies the dynamic model and is convenient for calculation. Finally, the jumping simulations in different gravity environments and a 15° slope were performed. The jump heights have all been improved after adding the arm swing, which verified the superiority of the bio-inspired take-off maneuver proposed in this paper. Furthermore, the stability of the jumping control method was testified by the continuous and stable jumping.

An LBM-FDM coupled numerical model for ignition and transient downward flame spread over solid fuel

The ignition and subsequent transition to steady-state flame spread behaviors over a vertical solid fuel in normal gravity and static environment were numerically studied in this work. Unlike the general approach based on the NS equation for buoyancy flow, the lattice Boltzmann method (LBM) was employed to solve the velocity field in the gas phase. Elliptic equations of temperature and concentration in gas and solid phases were solved by the finite difference method (FDM). An LBM-FDM coupling model for investigating the downward flame spread over solid fuel was developed. The ignition and the flame propagation behavior can be predicted quantitatively. The results show that a point flame with the shape of a disk appears first at the sheet surface when the vertical solid fuel is ignited. The instantaneous temperature response of ignition lags behind the chemical reaction. The point flame gradually develops into an asymmetric arch-shaped flame with two flame fronts near the sample surface. And then, the flame in the downstream zone is separated from the upstream flame source under the effect of the induced buoyant flow, and eventually disappears at the downstream boundary. Finally, the flame on the upstream gradually develops into a steady downward flame spread. The developed model in this work is validated by comparing the gas-phase temperature and flame spread rate between the predicted results and previous experimental data. This paper provides another method to predict the development of solid flame spread.

Effect of heat source direction on the thermal performance of phase change material (PCM) based thermal control module (TCM) under the influence of low gravity environment

For improving thermal management of electronic components/detectors, a novel phase change material based thermal control module is investigated to analyze the effect of heat source direction on the melting and solidification of PCM in a three-dimensional domain under the influence of low gravity environment. A distinctive method of inverting the PCM-based TCM against gravity is proposed to analyze the direction of heat source in two cases (non-inverted and inverted). The melting of PCM is simulated at different gravitational acceleration values (i.e., g, g/2, g/10, g/20, g/40, g/80) for both the inverted and non-inverted cases. The enthalpy-porosity method is employed to investigate the melting and solidification processes. The results show that inverting the heat source direction significantly affects the thermal performance of the PCM-based TCM. The maximum and minimum difference in the average liquid fraction value between the two cases is observed to be 13.63% and <2% at (g) and (g/80). The difference in the source temperature between the inverted and non-inverted cases varies between 3.3% to 19.68% when the gravitational acceleration increases from g/80 to g. The minuscule discrepancy (< 3%) in average liquid fraction indicates that the solidification of PCM is minimally affected by inverting heat flow direction.

저중력 환경 모사를 위한 낙하 시험 방법 연구

저중력 환경 모사를 위한 낙하 시험 방법 연구

Effects of Simulated Microgravity on the Physiology of Stenotrophomonas maltophilia and Multiomic Analysis.

Many studies have shown that the space environment plays a pivotal role in changing the characteristics of conditional pathogens, especially their pathogenicity and virulence. However, Stenotrophomonas maltophilia, a type of conditional pathogen that has shown to a gradual increase in clinical morbidity in recent years, has rarely been reported for its impact in space. In this study, S. maltophilia was exposed to a simulated microgravity (SMG) environment in high-aspect ratio rotating-wall vessel bioreactors for 14days, while the control group was exposed to the same bioreactors in a normal gravity (NG) environment. Then, combined phenotypic, genomic, transcriptomic, and proteomic analyses were conducted to compare the influence of the SMG and NG on S. maltophilia. The results showed that S. maltophilia in simulated microgravity displayed an increased growth rate, enhanced biofilm formation ability, increased swimming motility, and metabolic alterations compared with those of S. maltophilia in normal gravity and the original strain of S. maltophilia. Clusters of Orthologous Groups (COG) annotation analysis indicated that the increased growth rate might be related to the upregulation of differentially expressed genes (DEGs) involved in energy metabolism and conversion, secondary metabolite biosynthesis, transport and catabolism, intracellular trafficking, secretion, and vesicular transport. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that the increased motility might be associated the upregulation of differentially expressed proteins (DEPs) involved in locomotion, localization, biological adhesion, and binding, in accordance with the upregulated DEGs in cell motility according to COG classification, including pilP, pilM, flgE, flgG, and ronN. Additionally, the increased biofilm formation ability might be associated with the upregulation of DEPs involved in biofilm formation, the bacterial secretion system, biological adhesion, and cell adhesion, which were shown to be regulated by the differentially expressed genes (chpB, chpC, rpoN, pilA, pilG, pilH, and pilJ) through the integration of transcriptomic and proteomic analyses. These results suggested that simulated microgravity might increase the level of corresponding functional proteins by upregulating related genes to alter physiological characteristics and modulate growth rate, motility, biofilm formation, and metabolism. In conclusion, this study is the first general analysis of the phenotypic, genomic, transcriptomic, and proteomic changes in S. maltophilia under simulated microgravity and provides some suggestions for future studies of space microbiology.