A drop tower is a device that produces a microgravity environment by allowing an experiment to free fall for a short period of time, usually less than 10 seconds. Certain types of drop towers are also capable of reproducing the gravitational conditions of other celestial bodies, such as Lunar and Martian gravity. Microgravity environments are often required for many different scientific experiments, such as experiments in material science, fluid dynamics, biological studies and many other fields. Microgravity environments are also often used as a specialized manufacturing method for certain materials. Components and systems that will be used in space or onboard sounding rockets can also be tested and verified using drop towers before launch. There is an ever-present need to conduct experiments in a microgravity environment and thus highlights the importance and relevance of drop towers in research and design verification. Other microgravity facilities such as sounding rockets, parabolic flights and orbital spacecraft typically provide longer microgravity durations, however, come at a considerable cost. This highlights the need for drop towers that are cost-effective as a desirable research device. This thesis consists of a comprehensive, systematic literature review to determine industry standards and the current state of the art in the world of drop towers. The different potential mechanical designs of a drop tower are then analyzed and trade-offs are completed. The most suitable design, that could feasibly be built at Luleå University of Technology (LTU)’s space campus, is chosen and presented later in this thesis. The safety of the drop tower was of utmost concern when deciding on the most suitable design as well as when completing the mechanical design of the drop tower. The slider is a major component of a drop tower, it houses the experiment and is a critical component in determining the achievable microgravity quality. The slider design was also analyzed with a trade-off analysis of the potential existing designs, with the most feasible design being chosen. The drop tower is planned to be installed in the LTU Spacecampus light garden which can accommodate a drop tower of approximately 13m in height. The mechanical design is verified using various Finite Element Analysis (FEA) simulations. The 14m planned and designed drop tower is a non-vacuum, guided design which would provide approximately 3 seconds of microgravity, 5.2 seconds of Martian simulated gravity and 7.8 seconds of Lunar simulated gravity. The drop tower has been designed to accommodate projects that are part of the REXUS program. The towers' considerable size and ease of use would make it suitable for many research institutions and many potential scientific studies.

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The objective of this study was to compare the microstructural response of various DP 600 products subjected to low velocity, dynamic impact tests, typically encountered in a car crash. Since the response of steel is sensitive to its microstructure as controlled by the alloying elements, phase content, and processing; various DP 600 products may respond differently to crashes. The microstructure before and after dynamic impact deformation at 5 and 10 mph was characterized with regards to grain size, morphology, and phase content among vendors A, B, and C to evaluate efficiency in absorbing energy mechanisms during a crash simulated by dynamic impact testing in a drop tower.

Investigations on the design of controllable magnetorheological (MR) fluid devices have focused heavily on low velocity and low frequency applications. The extensive work in this area has led to a good understanding of MR fluid properties at low velocities and frequencies. However, the issues concerning MR fluid behavior in impact and shock applications are relatively unknown. To investigate MR fluid properties in this regime, MR dampers were subjected to impulsive loads. A drop-tower test facility was developed to simulate the impact events. The design includes a guided drop-mass released from variable heights to achieve different impact energies. Five drop-heights and two fundamental MR damper configurations were tested. The two configurations were a double-ended piston and a mono-tube with nitrogen accumulator. To separate the dynamics of the MR fluid from the dynamics of the current source, each damper received a constant supply current before the impact event. A total of five supply currents were investigated for each impact velocity. After reviewing the results, it was concluded that the effect of energizing the MR fluid only leads to "controllability" below a certain fluid velocity for the double-ended design. In other words, until the fluid velocity dropped below some threshold, the MR fluid behaved as if it was not energized, regardless of the strength of the magnetic field. Controllability was defined when greater supply currents yielded larger damping forces. For the mono-tube design, it was shown that the MR fluid was unable to travel through the gap fast enough during the initial impact. Consequently, the damper piston and accumulator piston traveled in unison until the accumulator bottomed out. After which, the fluid was forced through the gap. In conclusion, the two designs were compared and general recommendations on designing MR dampers for impulsive loading were made. Possible directions for future research were presented as well. / Master of Science

Explosives have become increasingly common on the battlefield worldwide. Military personnel and civilians often experience blast loading to the lower extremity due to its direct contact with the ground and floor of vehicles. The pressure and axial loading from these incidents often lead to detrimental injuries. These injuries can be due to a number of mechanisms terming them primary, secondary, tertiary, or quaternary blast injuries. Of these injuries, this study will focus on primary and tertiary injuries, specifically bone fractures, compartment syndrome, and soft tissue disruption which often result from blast loading due to these mechanisms. However, the pressure and load levels causing these injuries are unknown. Currently, the methodologies, which study the injury criteria and design of blast mitigating structures, are limited. The main limitations are the lower rates of testing (automobile), specimen limitation (cadavers, surrogates, etc.), cost, and testing repeatability. Consequently, the goal of this dissertation is to develop a realistic computational model which can be used to improve the injury criteria, personal protective equipment (PPE), and vehicular structure in a cost effective and timely manner. Three Aims were thus pursued. For Specific Aim 1, a standing lower extremity was developed, verified, and simulated with several open-air blast loading conditions. Specific Aim 2 focused on validating the lower extremity model using experimental drop tower test results. In the drop tower simulation, the lower extremity model was successfully converted into a seated posture model and setup with similar loading and boundary conditions as the experiment. Specific Aim 3 involved incorporating a boot into the standing lower extremity model and evaluating its ability to mitigate pressure waves. In summary, Specific Aims 1 and 2 developed, verified, and validated a realistic human lower extremity model for the use in blast simulations. Specific Aim 3 further confirmed the models use in developing PPE.

Football is a much loved sport in the United States. Unfortunately, it is also hard on the players and puts them at very high risk of concussion. To combat this an inventor in Santa Barbara brought a new design to Cal Poly to be tested. The design was tested in small scale first in order to make some preliminary conclusions about the design. In order to fully test the helmet design; however, full scale testing was required. In order to carry out this testing a drop tower was built based on National Operating Committee on Standards for Athletic Equipment, NOCSAE, specification. The drop tower designed for Cal Poly is a lower cost and highly portable version of the standard NOCSAE design. Using this drop tower and a 3D printed prototype the new design was tested in full scale.

This study aims to validate a screw joint simulation model used by BAE Systems in LS-DYNA during blast simulations. It is important that the screw joint simulation model is physically correct, since the simulation results can influence major design decisions. The study provides a short overview on the subject of bolts and screws, material deformation and stress and strain in materials, of the finite element method (FEM) and on some specific numerical methods used in this study. BAE Systems started a validation project of the screw joint simulation model in 2015, but it was not finished due to other priorities. In this older project some drop-tower tests measuring the axial force in a screw joint were conducted. These old tests can now serve as validation data for the screw joint simulation model. The screw joint simulation model used by BAE Systems is dependent on a special kind of finite element formulation; a so called beam element. This study provides a finite element analysis on this simulation model, which is implemented through an established industry FEM solver called LS-DYNA. The validation of the screw joint simulation model is done against three drop-tower experiments performed at 900, 1000 and 1100mm drop height respectively. The drop-tower experiments were replicated in LS-DYNA, with a prescribed velocity on the falling parts rather than simulating a free fall and non-elastic impact. A comparison between the simulation model using beam elements, that is used by BAE Systems, and a similar simulation model using solid elements is presented as part of the validation. To make sure that the result of the study is confident, a local mesh convergence study and a study of the mass scaling numerical method in LS-DYNA is also presented. The results show that the screw joint simulation model using beam elements is valid according to the available experimental data. In one of the experiments, where the drop-test was performed twice, an average maximum force on the screw was measured to be 33.5+-4.8 kN. Simulations of the same case, under the same conditions, using beam elements resulted in a maximum force on the screw of 35.4 kN, well within the experimental result range. In the other two drop-tower experiments, the simulated results showed correlation considering the error sources in the simulation model and the statistical spread that is present in the experimental results. The simulation model using beam elements is also similar to the results using solid elements, which also indicates that the beam model is valid. All in all, it is shown that the beam model can be used to produce safe results that either overestimate or place the simulations of the axial force in the screw in the upper spread of the measurements.

Bereits Galilei untersuchte, ob verschiedene frei fallende Körper im Schwerefeld der Erde gleich stark beschleunigt werden, die sogenannte Universalität des freien Falls. Die Genauigkeit der experimentellen Überprüfungen konnte seitdem beständig gesteigert werden. Einen neuen Ansatz, die Messgenauigkeit noch weiter zu verbessern, bilden quantenmechanische Messmethoden, die auf Materiewelleninterferometrie beruhen. Die dabei genutzten Apparaturen verwenden Laserstrahlung zur Kühlung, Manipulation und Detektion der Atome. Ziel der vorliegenden Arbeit war die Entwicklung des Lasersystems für ein neues Experiment, das erstmals Zwei-Spezies-Atominterferometrie (mit Rb & K) in Mikrogravitation demonstrieren soll. Ein Lasersystem, das sowohl die funktionalen Anforderungen als auch die aus dem Einsatz auf dem Katapult des Fallturms resultierenden Anforderung (Volumen < 44 l, Masse < 35 kg und voll funktionsfähig sofort nach einem Katapultstart mit Beschleunigungen von 30 g) erfüllt, wurde funktional konzipiert und mechanisch designt. Zur Demonstration wurde der Rubidium-Teil des Lasersystems funktional sowie mechanisch qualifiziert. Inzwischen wird er routinemäßig für Experimente am Fallturm eingesetzt. Für das Lasersystem wurden kompakte und robuste schmalbandigen Lasermodule entwickelt. Diese liefern bei einer Grundfläche der optischen Bank von nur 10 mm x 50 mm Ausgangsleistungen von bis zu 3,7 W. Am Arbeitspunkt (1 W Ausgangsleistung) besitzen die Strahlquellen Linienbreiten im Bereich von 100 kHz (Lorentz) bzw. 1 MHz (-3 dB, 10 µs). Zum Nachweis der spektralen Stabilität der Lasermodule wurde ein Messverfahrens zur Charakterisierung des Frequenzrauschens freilaufender Laser entwickelt. Dieses basiert auf einer Schwebungsmessung mit anschließender Analyse der Quadraturkomponenten des Signals im Zeitbereich. Durch den Einsatz geeigneter Filter erlaubt es die Unterdrückung der für Diodenlaser typischen Frequenzdrifts. / Galileo, already, investigated whether different free falling bodies in the gravitational field of the Earth are accelerated at the same rate, the so-called universality of the free fall. The accuracy of the experimental tests has been steadily increased ever since. A new approach to further increase the measurement accuracy is provided by quantum mechanical measurements based on matter wave interferometry. The apparatuses used for this purpose employ laser radiation for cooling, manipulation, and detection of the atoms. The aim of this thesis’ work was the development of the laser system for a new experiment intended to demonstrate two-species atom interferometry (utilizing Rb & K) in microgravity for the first time. A laser system, which fulfills the functional requirements as well as the requirements resulting from the deployment on the catapult of the drop tower (volume < 44 l, mass < 35 kg, and fully functional immediately after a catapult launch with accelerations of 30 g), has been functionally conceived and mechanically designed. For demonstration, the rubidium part of the laser system was functionally and mechanically qualified. By now, it is routinely used for experiments at the drop tower. For the laser system, compact and robust spectrally narrow laser modules have been developed. These provide an output power up to 3.7 W at a footprint of the optical bench of only 10 mm × 50 mm. At the operating point (1 W output power), the radiation sources exhibit linewidths in the range of 100 kHz (Lorentzian) and 1 MHz (−3 dB, 10 μs). To validate the spectral stability of the laser modules a measuring method for the characterization of the frequency noise of free-running lasers has been developed. This method is based on a beat note measurement with subsequent analysis of the quadrature components of the signal in the time domain. By utilizing appropriate filters, it allows for the suppression of the frequency drifts that are typical for diode lasers.

In the automobile industry, there is a big push for the automotive car manufacturers to base engineering decisions on the results of Computer Aided Engineering (CAE) solutions, and to transform the prototyping and testing, from a costly iterative process to a final verification and validation step. The variability in components material properties and environmental conditions together with the lack of knowledge about the underlying physics of complex systems often make it impractical to make reliable predictions based on only deterministic CAE models. One such area is the CAE modelling of cast aluminium components. These cast aluminium components have gained a huge relevance in the automobile industries due to their commendable mechanical properties. The advantage of the cast aluminium alloys are being a well-established alloy system in manufacturing processes, their functional integrity and relatively low weight. However, the presence of pores and micro-voids obtained during the manufacturing process constitutes a specific material behaviour and establishes a challenge in modelling of the cast materials. Furthermore, the low ductility of the materialdemands for the advanced numerical model to predict the failure. The main focus of this master thesis work is to investigate modelling technique of a cast aluminium alloy component, a spring tower, for a drop tower test and validate the predicted behaviour with the physical test results. Volvo Car Corporation currently uses a material model provided by MATFEM for cast aluminium parts which are explored in this thesis work, to validate the material model for component level testing. The methodology used to achieve this objective was to develop a boundary condition to perform component level tests in the drop tower and to correlate these with the obtained results found by using various modelling techniques in the explicit solver LS-DYNA. Therefore, precise and realistic modelling of the drop tower is crucial because the simulation results can be influenced by major design changes. A detailed finite element model for the spring tower has been developed from the observations made during the physical testing. The refined model showed good agreement with the existing model for the spring tower and observations from physical tests.

Atominterferometrie (AI) auf Basis von Lichtpulsen ist ein wichtiges Werkzeug der Präzisionsmesstechnik in Bereichen der inertialen Sensorik oder Fundamentalphysik geworden. Vor allem in Kombination mit ultrakalten, atomaren Quellen, sowie der Verwendung im schwerelosen Raum, werden hohe Sensitivitäten erwartet, die Verletzungen des schwachen Äquivalenzprinzips nachweisen können. QUANTUS-2 ist ein mobiles Atominterferometer, das am ZARM Fallturm in Bremen operiert. Durch seine Atomchip-basierte atomare Rubidiumquelle mit hoher Flussdichte dient es als Vorreiterexperiment für zukünftige Weltraummissionen, bei denen Schlüsseltechnologien wie die Erzeugung von Bose-Einstein Kondensaten (BECs), Delta-Kick Kollimation oder Anwendung verschiedener AI-Geometrien auf sekundenlangen Zeitskalen untersucht werden. Im Rahmen dieser Arbeit wurde ein Kalium-Diodenlasersystem aufgebaut, um die Funktionalität auf Zwei-Spezies Nutzung zu erweitern. Basierend auf dem Design des Rubidium-Diodenlasersystem mit mikrointegrierten Laserdiodenmodulen und kompakter Elektronik, konnte es erfolgreich qualifiziert werden. In einem Machbarkeitsbeweis wurde eine magneto-optische Falle mit Kalium generiert, die die Fähigkeit des Lasersystems zum Fangen von Atomen demonstriert. Mit Rubidium wurden offene Ramsey-Interferometer und Mach-Zehnder Interferometer (MZIs) am Boden und in über 155 Abwürfen untersucht. Die Kombination von unterschiedlich stark Delta-Kick kollimierten BECs und AI in Schwerelosigkeit eröffnete eine neue Methode zur Bestimmung der magnetischen Linsendauer zur optimalen Kollimierung. Asymmetrische MZIs mit Interferometerzeiten von 2T > 1s konnten erfolgreich demonstriert werden. Mit gravimetrischen Untersuchungen am Boden auf Basis von MZIs und einer zusätzlichen Methode der Atomlevitation wurde die lokale Gravitationsbeschleunigung g ermittelt. Die untersuchten Schlüsseltechnologien sind fundamentale Notwendigkeiten, um den Weg für zukünftige Weltraummissionen aufzubereiten. / Light-pulse atom interferometry (AI) is an important tool for high precision measurements in the fields of inertial sensing or fundamental physics. Especially in combination with ultra-cold atomic sources and operation in microgravity, high sensitivities are expected that are necessary for the search for violations of the weak equivalence principle. QUANTUS-2 is a mobile atom interferometer operating at the ZARM drop tower in Bremen. With its high-flux, atom chip-based atomic rubidium source, it serves as a pathfinder for future space missions, examining key technologies like the generation of Bose-Einstein condensates (BECs), implementation of delta-kick collimation or application of various AI geometries. In this thesis, a potassium diode laser system has been built to complete the preordained functionality of dual-species operation. Based on the design of the rubidium laser system with micro-integrated laser diode modules and compact electronics, it successfully passed the qualification tests. In a proof of principle measurement, a potassium magneto-optical trap could be generated to prove the system’s capability of trapping atoms. With rubidium, open Ramsey type interferometers and Mach-Zehnder interferometers (MZIs) were examined on ground and in over 155 drops in microgravity. The combination of variably delta-kicked collimated BECs and AI in microgravity revealed a new technique to determine the magnetic lens duration for optimal collimation. Asymmetric MZIs with interferometry times of 2T > 1s have successfully been demonstrated. Gravimetric examinations on ground with MZIs and by an additional levitation technique have been performed to determine the local gravitational acceleration g. The examined key technologies are fundamental necessities that have to be considered to pave the way for future space missions.