Free-fall Experiments Research Articles

Experimental and numerical analysis of the fluid flow behavior of a tank corner impacting a water surface

The interaction of a tank impacting a water surface is an extremely complex nonlinear multiphase flow phenomenon. In this study, experiments and numerical simulations are used to systematically investigate the flow physics and load characteristics of a tank corner impacting a water surface. Free surface flow at different fall heights (200–800 mm) and inclination angles (0°–15°) was obtained through free fall experiments. The volume of fluids method and overset grid technology were used to simulate the water impact process of a three-dimensional structure accurately. For typical bubble flows, the numerical and experimental results agree well. On the basis of the three-dimensional flow characteristics and pressure distribution, flow behaviors, such as fluid climbing, corrugation disturbances, and air cavity effects, are analyzed. Bubble flow has a significant effect on the behavior mode of the impact load. In particular, the bubbles at the upper wall play a key role in the load characteristics at different locations. In addition, the influences of corrugations inside the tank's corner and the impact velocity on fluid flow were investigated. These results provide beneficial references for an in-depth understanding of the fluid flow and load characteristics between a tank and fluid.

Influence of Long-Term Use of American Football Helmets on Concussion Risk.

In this study, to discuss the influence of concussion risk from the long-term use of American football helmets on collegiate teams, accident cases during the game are replicated based on game videos by simulations using whole-body numerical models and helmeted finite element human head models. The concussion risks caused by collisions were estimated using the mechanical parameters inside the skull obtained from finite element analyses. In the analyses, the different material properties of helmets identified by free-fall experiments using headform impactor-embedded helmets were used to represent brand-new and long-term-use helmets. After analyzing the five cases, it was observed that wearing a new helmet instead of a long-term-use one resulted in a reduction in the risk of concussion by 1 to 44%. More energy is attenuated by the deformation of the liners of the brand-new helmet, so the energy transferred to the head is smaller than that when wearing the long-term-use helmet. Thus, the long-term use of the helmet reduces its ability to protect the head.

Improved Accuracy in Determining the Acceleration Due to Gravity in Free Fall Experiments Using Smartphones and Mechanical Switches

This study presents an innovative methodology to augment the accuracy of gravitational acceleration (g) measurements in free fall experiments. Employing smartphones and integrating mechanical switches, our approach utilizes a built-in microphone for precise time measurements during the initiation of free fall. A meticulously designed mechanical switch controls the release of a steel sphere, triggering the timer upon the initiation of descent. Our experimental outcomes showcase a commendable congruence between the calculated g value and the locally accepted reference value, pinpointing g at 9.8274 ± 0.01 m/s2. A salient feature of our method is the utilization of the smartphone’s onboard microphone sensor, offering superior convenience to conventional sensor-based methodologies that require additional equipment. Additionally, our study introduces the seamless integration of open-source software on smartphones, facilitating the direct display and analysis of sound parameters. This integration streamlines the experimental process, contributing to the ongoing endeavors aimed at enhancing accuracy in free fall experiments. Our findings underscore the potential of smartphones and mechanical switches as accessible and effective tools in advancing physics education and scientific investigations.

A novel microwave Doppler method for mass estimation of machine-picked seed cotton

Obtaining information on cotton yields and creating a spatial map of cotton production is the starting point for implementing precision agriculture. Microwave technology has been used for yield estimation in China for crops such as corn and soybeans and has shown strong applicability. However, research on cotton yield estimation using microwave technology is weak. Therefore, this paper proposes a method for seed cotton mass estimation based on the microwave Doppler method and designs bench tests to prove the feasibility of the method. First, a seed cotton speed estimation model was established based on the microwave Doppler effect and fast Fourier transform. On this basis, a seed cotton velocity estimation experiment was designed to study the effects of sensor installation angle and position, pipe collision friction, air resistance, and the interaction force between the seed cotton on the seed cotton movement velocity. The power spectral density (PSD) of the acquired microwave data is then estimated using the modified periodogram method. The least squares method was used to establish a linear regression model between seed cotton mass and the corresponding PSD, and finally the free-fall mass experiment and pneumatic conveying mass experiment yielded that the estimation errors of seed cotton mass were 7.30% and 6.17%, respectively. The experimental results show that the estimation error is small when using microwave technology for seed cotton mass estimation, which meets the requirements of actual operation.

Effects of collision shock on semi-buoyant fish egg hatchings in high-speed streams

During downstream drifting in high-speed steams, semi-buoyant fish eggs can run onto rocks, boats, and other surfaces. This will result in the abrupt and severe collision shock to the fish eggs, causing damage to fish eggs and potentially leading to their death. For protection of fish stocks and river management, it is crucial to understand the impact of collision shock on their hatching and to clarify the upper threshold of collision velocity. Through an indoor free-fall experiment, we quantified the influences of collision shock on semi-buoyant fish eggs. We discovered that, when fish eggs collided with a rock at a speed of 4.4 m/s, about 70% of the eggs did not successfully hatch. Forty-five percent of the egg envelopes were broken when the collision velocity was 4.4 m/s and collided with water. Development stage, particularly when the eggs were at the cell cleavage stage, was the most susceptible factor to collision shock. Our results offer new insights for preserving fish stocks in high-speed streams and can be used to inform river management strategies.

Modification of Space Debris Trajectories through Lasers: Dependence of Thermal and Impulse Coupling on Material and Surface Properties

Environmental pollution exists not only within our atmosphere but also in space. Space debris is a critical problem of modern and future space infrastructure. Congested orbits raise the question of spacecraft disposal. Therefore, state-of-the-art satellites come with a deorbit system in cases of low Earth orbit (LEO) and with thrusters for transferring into the graveyard orbit for geostationary and geosynchronous orbits. No practical solution is available for debris objects that stem from fragmentation events. The present study focuses on objects in LEO orbits with dimensions in the dangerous class of 1 to 10 cm. Our assumed method for the change of trajectories of space debris is laser ablation for collision avoidance or complete removal by ground-based laser systems. Thus, we executed an experimental feasibility study with focus on thermal and impulse coupling between laser and sample. Free-fall experiments with a 10 ns laser pulse at nominally 60 J and 1064 nm were conducted with GSI Darmstadt’s nhelix laser on various sample materials with different surfaces. Ablated mass, heating, and trajectory were recorded. Furthermore, we investigated the influence of the sample surface roughness on the laser-object interaction. We measured impulse coupling coefficients between 7 and 40 µNs/J and thermal coupling coefficients between 2% and 12.5% both depending on target fluence, surface roughness, and material. Ablated mass and changes in surface roughness were considered via simulation to discriminate their relevance for a multiple shot concept.

One setup for many experiments: enabling versatile student-led investigations

This article presents an experimental setup capable of conducting various experiments. The setup is used to accurately determine the acceleration due to gravity using either the pendulum or free fall experiment, as well as to allow students to conceive and conduct their own experiment. We discuss the design of the setup and the experiments conducted with it, highlighting the versatility and potential use for open inquiry. We include students’ perception on this particular experiment and how it led to an interesting and educational open inquiry.

Drag Coefficient Estimation of Low Density Objects by Free Fall Experiments

Abstract The present article investigates whether the drag coefficient of low density objects can be determined by free fall experiments with sufficient accuracy. Among other things, the drag coefficient depends on the flow velocity, which can be controlled in wind channels experiments. Free fall experiments do not offer an experimental environment with constant flow velocity. Especially the later part of the movement gets relevantly influenced by air drag deceleration. We theoretically estimate an average sphere drag coefficient for the relevant part of the movement of falling spheres. The results are verified by examining the drag coefficient from experimental data. Finally, we determine the drag coefficient of a model rocket, which is compared to the result of the corresponding wind channel experiment.

Searching for Ultralight Scalar Dark Matter with Muonium and Muonic Atoms.

Ultralight scalar dark matter may induce apparent oscillations of the muon mass, which may be directly probed via temporal shifts in the spectra of muonium and muonic atoms. Existing datasets and ongoing spectroscopy measurements with muonium are capable of probing scalar-muon interactions that are up to 12 orders of magnitude more stringent than astrophysical bounds. Ongoing free-fall experiments with muonium can probe forces associated with the exchange of virtual ultralight scalar bosons between muons and standard-model particles, offering up to 5 orders of magnitude improvement in sensitivity over complementary laboratory and astrophysical bounds.

Large Displacement Detection Using Improved Lucas–Kanade Optical Flow

Displacement is critical when it comes to the evaluation of civil structures. Large displacement can be dangerous. There are many methods that can be used to monitor structural displacements, but every method has its benefits and limitations. Lucas-Kanade (LK) optical flow is recognized as a superior computer vision displacement tracking method, but it only applies to small displacement monitoring. An upgraded LK optical flow method is developed in this study and used to detect large displacement motions. One motion controlled by a multiple purpose testing system (MTS) and a free-falling experiment were designed to verify the developed method. The results provided by the upgraded LK optical flow method showed 97 percent accuracy when compared with the movement of the MTS piston. In order to capture the free-falling large displacement, the pyramid and warp optical flow methods are included in the upgraded LK optical flow method and compared with the results of template matching. The warping algorithm with the second derivative Sobel operator provides accurate displacements with 96% average accuracy.

Calibration and Testing of Discrete Element Modeling Parameters for Fresh Goji Berries

This paper aims at the standard grading of fresh goji berries and develops a variable gap-type fresh goji berry grading machine. To establish a complete simulation model, the discrete element parameters of the model were calibrated by a combination of physical experiments and simulation experiments. The outline of the goji berry was extracted by the SFM-CMVS technique, and a goji berry model was obtained using the multi-spherical particle model filling method in the EDEM software. By designing the free-fall, suspension collision, slope slip, and slope rolling experiments, we obtained the discrete element simulation parameters: the inter-particle collision restitution coefficient was 0.158, the collision restitution coefficient of fresh goji berry–silicone rubber material was 0.195, the static friction coefficient of fresh goji berry–silicone rubber material was 0.377, and the rolling friction coefficient of fresh goji berry–silicone rubber material was 0.063. By designing the steepest ascent search and central composite design experiments with the angle of repose (AoR) value obtained from the physical experiment as the target value (31.27°), we determined the inter-particle static friction coefficient to be 0.454 and the inter-particle rolling friction coefficient to be 0.037. Validation tests were conducted on the calibrated discrete element modeling parameters, and the results showed that the established fresh goji berry model and the optimally calibrated parameter combination are effective for discrete element studies on fresh goji berries.

Role of resistance forces in Galileo’s experiments

We apply fluid resistance and rolling resistance analysis to the free fall and projectile experiments described in Galileo Galilei’s 1638 Dialogues Concerning Two New Sciences (Discorsi), and his unpublished folio 116v experiment in the Codex 72 collection. Both air resistance and rolling resistance affect the horizontal projection distance in the folio 116v experiment. Newton’s second law and the two combined resistance forces can quantitatively explain Galileo’s observations. The analysis is also applied to replication experiments made by Naylor in 1974. Quantitative agreement is achieved. Resistance forces remove a small discrepancy between observed and theoretical horizontal projectile distances that is present when air resistance and rolling resistance are ignored. The result is significant because it shows that, contrary to prior studies, resistance forces cannot be ignored when one models the folio 116v experiment. Air drag forces due to acceleration (added mass and Basset history) are negligible, but quasi-steady drag and Magnus lift are not. This exercise provides an historical perspective to the description of basic body motion: constant acceleration, uniformly increased velocity, constant inertial motion, and decomposition of two-dimensional motion into orthogonal coordinates. It also serves to give specific examples of significant ‘real-world’ effects, such as steady drag, added mass, Basset history, rolling resistance, spin drag, and Magnus lift that complicate what appears to be a simple experiment. Finally, it shows that a quantitative test of a seemingly obvious assumption can yield new insights.

Design study of an antiproton trap for the GBAR experiment

The GBAR (Gravitational Behaviour of Antihydrogen at Rest) experiment at CERN has been proposed to measure the gravitational acceleration of the ultracold antihydrogen atoms. This experiment produces antihydrogen ions through interactions between antiprotons and positronium atoms. Then, antihydrogen atoms are produced for the free-fall experiment after the photo-detachment of an excess positron from the cold antihydrogen ions. The energy of the antiproton beam before the positronium target chamber will be in the range of 1–10 keV. The cross-section for the reaction between the antiprotons and positroniums depends mainly on the energy of the antiprotons. Hence, to maximize the productivity of antihydrogen ions, a sufficient number of antiprotons should be provided with well-controlled energy. In this regard, an antiproton trap is considered to accumulate and slow down antiproton beams, and cool them utilizing the electron cooling technique. This trap is designed based on the Penning-Malmberg trap, which consists of a superconducting solenoid magnet and a series of ring electrodes including high-voltage electrodes to trap antiprotons. In addition, a set of extraction electrodes and optics for beam transport are used. Each electrode has been designed and optimized using the WARP PIC simulations. In this study, the design and simulation results of each trap component are presented.

High-precision velocity measurement method based on high frame rate image processing

The traditional drop-weight impact velocity measurement is affected by the measurement distance of the sensor and the measurement environment, and the accuracy is difficult to guarantee. Aiming at this problem, this paper proposes a high-precision velocity measurement method based on high frame rate image. Firstly, a measurement scheme based on high frame rate image is designed, the position information is obtained by processing the image of the marked point, and the target impact velocity is obtained according to the time difference between frames; Then an error model is established, and the sources of errors and solutions are analyzed; Then by improving the subpixel edge and other methods to improve the feature extraction accuracy of the marking point image, thereby improving the velocity measurement accuracy. Finally, the measurement accuracy is verified by the actual drop-weight free-fall experiment. The experimental results show that the method proposed in this paper is better than 0.5% in the measurement of the impact velocity of the drop weight, which meets the needs of practical applications, and the measuring process is visualized and traceable, which has high application value.

Investigation of the influence of impact velocity and liquid bridge volume on the maximum liquid bridge length

Several models exist to predict the capillary forces due to liquid bridges during static particle contacts. However, for dynamic impacts, there is still a lack of knowledge to accurately describe the geometry and rupture of liquid bridges. This is essential in order to calculate correctly the energy dissipation in numerical models. Therefore, the liquid bridge volume during the rebound phase of collision, the restitution coefficient, the rupture time and the maximum liquid bridge length were analyzed for a wide range of contact velocities from 0.0001to4.0 m∙s−1. To perform experiments at different velocities three experimental setups were developed. First, free-fall experiments with spherical particles colliding on a glass pane covered with a water layer were performed at different impact velocities from 0.3 to 1.5 m∙s−1 and water layer thicknesses. Secondly, a pneumatic setup was developed for investigating the maximum liquid bridge length at constant liquid bridge volume and contact velocities from 0.3 to 4.0 m∙s−1. A third setup was used to investigate the liquid bridge behavior during low velocities from 0.0001 to 0.04 m∙s−1. Based on the experimental results, a new model is presented to account for the significant influence of impact velocity on the maximum liquid bridge length.

Measurement of Physical Properties of Sorghum Seeds and Calibration of Discrete Element Modeling Parameters

This study aimed to improve the measurement accuracy of the discrete element method (DEM) simulation parameters of sorghum seeds for enhanced model accuracy. We measured the intrinsic and contact parameters of sorghum seeds, extracted the outline of the seeds by 3D scanning, and used the multi-spherical particle model filling method in the EDEM (Version 2020) software to obtain the simulation model of the seeds. By simulating the free-fall, slope slip, slope rolling, and rolling experiments of sorghum seeds–photosensitive resin material, we calibrated the collision restitution coefficient of the sorghum seeds–photosensitive resin material to 0.690, static friction coefficient to 0.345, and rolling friction coefficient to 0.040. Through the steepest ascent search and central composite design experiments, we calibrated the collision restitution coefficient of sorghum seeds–sorghum seeds to 0.400, the static friction coefficient to 0.450, and the rolling friction coefficient to 0.043. The angle of repose of the parameter combination and the angle of repose of the physical experiment (33.82°) were verified, and the relative errors of the coefficients were 0.7%, 0.25%, and 0.3%, respectively, indicating that the established model had a high simulation accuracy and reliability. These results show that the established sorghum seeds model and the optimally calibrated parameter combination are effective for DEM studies on sorghum seeds.

Serbest Düşüş Deneyi İçin Bir Deney Cihazı ve Mobil Kontrol Uygulamasının Tasarımı ve Gerçeklenmesi

In this study, a device for free fall experiment has developed and implemented. A mobile Android
 application is developed in order to control the device via Bluetooth connection and see results of
 experiments in terms of measured time values, squares of measured time values and their graphs.
 Furthermore, a method is developed and implemented on embedded software in order to make it
 possible for more than one person groups to experiment using machine without interrupting each
 other’s work or taking each other’s pre-defined turn. Experimental results and comparison with
 theoretical calculations provided.

Collective-Mode Enhanced Matter-Wave Optics.

In contrast to light, matter-wave optics of quantum gases deals with interactions even in free space and for ensembles comprising millions of atoms. We exploit these interactions in a quantum degenerate gas as an adjustable lens for coherent atom optics. By combining an interaction-driven quadrupole-mode excitation of a Bose-Einstein condensate (BEC) with a magnetic lens, we form a time-domain matter-wave lens system. The focus is tuned by the strength of the lensing potential and the oscillatory phase of the quadrupole mode. By placing the focus at infinity, we lower the total internal kinetic energy of a BEC comprising 101(37) thousand atoms in three dimensions to 3/2 k_{B}·38_{-7}^{+6} pK. Our method paves the way for free-fall experiments lasting ten or more seconds as envisioned for tests of fundamental physics and high-precision BEC interferometry, as well as opens up a new kinetic energy regime.

Antimatter Free-Fall Experiments and Charge Asymmetry

We propose a method by which one could use modified antimatter gravity experiments in order to perform a high-precision test of antimatter charge neutrality. The proposal is based on the application of a strong, external, vertically oriented electric field during an antimatter free-fall gravity experiment in the gravitational field of the Earth. The proposed experimental setup has the potential to drastically improve the limits on the charge-asymmetry parameter ϵ¯q of antimatter. On the theoretical side, we analyze possibilities to describe a putative charge-asymmetry of matter and antimatter, proportional to the parameters ϵq and ϵ¯q, by Lagrangian methods. We found that such an asymmetry could be described by four-dimensional Lorentz-invariant operators that break CPT without destroying the locality of the field theory. The mechanism involves an interaction Lagrangian with field operators decomposed into particle or antiparticle field contributions. Our Lagrangian is otherwise Lorentz, as well as PT invariant. Constraints to be derived on the parameter ϵ¯q do not depend on the assumed theoretical model.

Measurement of Aerodynamic Characteristics Using Cinder Models through Free Fall Experiment

Rocks ejected from a volcanic eruption often cause loss of lives and structures. Aerodynamic characteristics are needed for evaluating motions of volcanic rocks for the reduction of damage. Falling motions of volcanic rock were measured by using models imitated the configuration of cinders collected at the site of the experiment, Sakurajima volcano. Two types, one with sharp edges and one without sharp edges, were selected as representative of cinder and a sphere was selected as reference model. The falling motions of the models dropped down from a drone were recorded by video camera and a stand-alone measuring system that included a pressure sensor, acceleration and angular velocity sensors in the models. The motion, posture, velocity and acceleration of the model were obtained in order to measure the three-dimensional falling trajectory. The drag and the deviation angle between relative wind direction and wind force direction were examined. The variation of the drag coefficient and the deviation angle with Reynolds number was clarified.