Academic literature on the topic 'Actice force measurement'

Active magnetic bearings (AMBs) have the unique capability to act concurrently as support bearings and load cells for measuring shaft forces. Current state-of-the-art methods for force measurement rely on models with limited accuracy due to effects which are difficult to characterize such as fringing, leakage, and variations in material properties. In addition, these effects may be a function of actual air gaps which are difficult to determine in a dynamic operating environment. This paper discusses a new force measurement methodology that inherently accounts for these types of effects and other system uncertainties by utilizing multiple sets of current pairs in opposing actuators, in conjunction with a calculation algorithm, to accurately determine the force applied by the AMB. This new multipoint methodology allows for the determination of bearing forces from information on basic actuator geometry and control currents only, with no knowledge of actual operating air gaps required. The inherent nature of the methodology accounts for model uncertainties such as fringing, leakage, and other system unknowns. Initial static experimental test results are presented demonstrating 3% error in measuring the nominal determined bearing load, and a variation in calculated forces of less than 5% in most cases (8% in one case) when the location of the rotor within the bearing stator is modified. For the analogous conventional single-point measurements, the results show 15% error and 23% variation.

A research pump intended for both flow visualization studies and direct measurement of hydrodynamic radial and axial forces has been developed. The impeller and the volute casing are constructed from Plexiglas which facilitates optical access for laser velocimetry measurements of the flow field both inside the impeller and in the volute casing. The pump housing is designed for flexibility allowing for each interchange of impellers and volute configurations. The pump rotor is supported by three radial magnetic bearings and one double acting magnetic thrust bearing. The magnetic bearings have been calibrated to characterize the force versus coil current and air gap relationship for each bearing type. Linear calibration functions valid for rotor eccentricities of up to 2/3 of the nominal bearing clearances and force level of ±58 N (13 lbf) and ±267 N (60 lbf) for the radial and axial bearings, respectively, were found. A detailed uncertainty analysis of the force calibration functions was conducted such that meaningful uncertainty bounds can be applied to in situ force measurements. Hysteresis and eddy current effects were quantified for each bearing such that their effect on the in situ force measurements could be assessed. By directly measuring the bearing reaction forces it is possible to determine the radial and axial hydraulic loads acting on the pump impeller. To demonstrate the capability of the magnetic bearings as active load cells representative hydraulic force measurements for a centered 4 vane 16 degree log spiral radial flow impeller operating in a single tongue spiral volute casing were made. At shut-off a nondimensional radial thrust of 0.084 was measured. A minimum nondimensional radial thrust of about 0.007 was observed at the nominal design flow. The nondimensional radial thrust increased to about 0.019 at 120 percent of design flow. The nondimensional axial thrust had a maximum at shut-off of 0.265 and decreased steadily to approximately 0.185 at 120 percent of design flow. Two regions of increasing axial thrust, in the flow range 75 to 100 percent of design flow, were observed. The measurements are compared to radial and axial force predictions using classical force models. The direct radial force measurements are compared to a representative set of radial force measurements from the literature. In addition, the directly measured radial force at design flow is compared to a single representative radial force measurement (obtained from the literature) calculated from the combination of static pressure and net momentum flux distribution at the impeller exit.

Entropy production is the hallmark of nonequilibrium physics, quantifying irreversibility, dissipation, and the efficiency of energy transduction processes. Despite many efforts, its measurement at the nanoscale remains challenging. We introduce a variance sum rule (VSR) for displacement and force variances that permits us to measure the entropy production rate σ in nonequilibrium steady states. We first illustrate it for directly measurable forces, such as an active Brownian particle in an optical trap. We then apply the VSR to flickering experiments in human red blood cells. We find that σ is spatially heterogeneous with a finite correlation length, and its average value agrees with calorimetry measurements. The VSR paves the way to derive σ using force spectroscopy and time-resolved imaging in living and active matter.

Abstract This article reviews the surface forces measurement as a novel tool for materials science. The history of the measurement is briefly described in the Introduction. The general overview covers specific features of the surface forces measurement as a tool for studying the solid-liquid interface, confined liquids and soft matter. This measurement is a powerful way for understanding interaction forces, and for characterizing (sometime unknown) phenomena at solid-liquid interfaces and soft complex matters. The surface force apparatus (SFA) we developed for opaque samples can study not only opaque samples in various media, but also electrochemical processes under various electrochemical conditions. Electrochemical SFA enables us to determine the distribution of counterions between strongly bound ones in the Stern layer and those diffused in the Gouy-Chapman layer. The shear measurement is another active area of the SFA research. We introduced a resonance method, i.e. the resonance shear measurement (RSM), that is used to study the effective viscosity and lubricity of confined liquids in their thickness from μm to contact. Advantages of these measurements are discussed by describing examples of each measurement. These studies demonstrate how the forces measurement is used for characterizing solid-liquid interfaces, confined liquids and reveal unknown phenomena. The readers will be introduced to the broad applications of the forces measurement in the materials science field.

Hydrodynamic diffusion in the absence of Brownian motion is studied via active microrheology in the ‘pure-hydrodynamic’ limit, with a view towards elucidating the transition from colloidal microrheology to the non-colloidal limit, falling-ball rheometry. The phenomenon of non-Brownian force-induced diffusion in falling-ball rheometry is strictly hydrodynamic in nature; in contrast, analogous force-induced diffusion in colloids is deeply connected to the presence of a diffusive boundary layer even when Brownian motion is very weak compared with the external force driving the ‘probe’ particle. To connect these two limits, we derive an expression for the force-induced diffusion in active microrheology of hydrodynamically interacting particles via the Smoluchowski equation, where thermal fluctuations play no role. While it is well known that the microstructure is spherically symmetric about the probe in this limit, fluctuations in the microstructure need not be – and indeed lead to a diffusive spread of the probe trajectory. The force-induced diffusion is anisotropic, with components along and transverse to the line of external force. The latter is identically zero owing to the fore–aft symmetry of pair trajectories in Stokes flow. In a naïve first approach, the vanishing relative hydrodynamic mobility at contact between the probe and an interacting bath particle was assumed to eliminate all physical contribution from interparticle forces, whereby advection alone drove structural evolution in pair density and microstructural fluctuations. With such an approach, longitudinal force-induced diffusion vanishes in the absence of Brownian motion, a result that contradicts well-known experimental measurements of such diffusion in falling-ball rheometry. To resolve this contradiction, the probe–bath-particle interaction at contact was carefully modelled via an excluded annulus. We find that interparticle forces play a crucial role in encounters between particles in the hydrodynamic limit – as they must, to balance the advective flux. Accounting for this force results in a longitudinal force-induced diffusion $D_{\Vert }=1.26aU_{S}{\it\phi}$, where $a$ is the probe size, $U_{S}$ is the Stokes velocity and ${\it\phi}$ is the volume fraction of bath particles, in excellent qualitative and quantitative agreement with experimental measurements in, and theoretical predictions for, macroscopic falling-ball rheometry. This new model thus provides a continuous connection between micro- and macroscale rheology, as well as providing important insight into the role of interparticle forces for diffusion and rheology even in the limit of pure hydrodynamics: interparticle forces give rise to non-Newtonian rheology in strongly forced suspensions. A connection is made between the flow-induced diffusivity and the intrinsic hydrodynamic microviscosity which recovers a precise balance between fluctuation and dissipation in far from equilibrium suspensions; that is, diffusion and drag arise from a common microstructural origin even far from equilibrium.

In this paper, we explore the use of end forces for vibration control in structural elements. The process involves vibration measurement and observer-based estimation of modal amplitudes, which are used to determine when to apply an end load such that it will remove vibration energy from the structure. For this study, we consider transverse vibration of a cantilever beam with a buckling-type end load that can be switched between two values, both of which are below the buckling load. The stability of the control system is proven using Lyapunov stability theory and its effectiveness is demonstrated using simulations and physical experiments. It is shown that the effectiveness of the approach is affected by the bandwidth of the actuator and the attendant characteristics of the filter, the level of the control force, and the level of bias in the end force. The experiments employ a beam fitted with a cable mechanism and motor for applying the end force, and a piezoelectric patch for taking vibration measurements. It is shown that the first two modes of the beam, whose natural frequencies are less than the bandwidth of the motor, are very effectively controlled by the proposed scheme.

Generally, a combination of kinematic, electromyographic (EMG), and force measurements are used to understand how an organism generates and controls movement. The chicken embryo has been a very useful model system for understanding the early stages of embryonic motility in vertebrates. Unfortunately, the size and delicate nature of embryos makes studies of motility during embryogenesis very challenging. Both kinematic and EMG recordings have been achieved in embryonic chickens, but two-dimensional force vector recordings have not. Here, we describe a dual-axis system for measuring force generated by the leg of embryonic chickens. The system employs two strain gauges to measure planar forces oriented with the plane of motion of the leg. This system responds to forces according to the principles of Pythagorean geometry, which allows a simple computational program to determine the force vector (magnitude and direction) generated during spontaneous motor activity. The system is able to determine force vectors for forces >0.5 mN accurately and allows for simultaneous kinematic and EMG recordings. This sensitivity is sufficient for force vector measurements encompassing most embryonic leg movements in midstage chicken embryos allowing for a more complete understanding of embryonic motility. Variations on this system are discussed to enable nonideal or alternative sensor arrangements and to allow for translation of this approach to other delicate model systems.

Giant magnetostrictive actuator (GMA) are commonly used in active vibration isolation domain for hight frequency response and large output force. GMA has a nonlinear displacement output when disturbed by vibrations. In order to compensate for the nonlinearity and improve the precision of the system, the critical process is the measurement of external disturbances which can be realized with a bridge circuit based on a traditional equivalent circuit model. However, the sensitivity is restricted because of the integral relationship between the force and the open circuit voltage. In this paper, the conception of the dynamic inductance is proposed to optimize the equivalent circuit model that is based on coupled linear magneto-mechanical constitutive equations. Then the measurement for external forces becomes effective with the improvement in the sensitivity through measuring the dynamic inductance. A dynamic simulation is carried out to test the performance of GMA based on the equivalent circuit model. The external dynamic forces can be accurately detected by calculating the impedances in the self-sensing effect of the Terfenol-D.

Active magnetic bearings (AMBs) have the ability to act concurrently as support bearings and as load sensing measurement tools. Previous work in the area of AMB force measurement has relied upon basic magnetic equations requiring knowledge of coil currents and air gap lengths. Some researchers have utilized magnetic flux probes to eliminate the need for air gap measurements, but these are limited by physical size constraints and require complex hardware. This thesis presents a new method for measuring forces with AMBs that utilizes multiple current pairs with no gap measurement to provide accurate and precise force predictions. Previous methods for force measurement with AMBs rely on the controlled environment of a laboratory setting for accurate measurements. The goal of this work is to develop a robust force measurement procedure for use in industrial and field applications, as well as the laboratory. The harsh environment of a factory floor makes air gap measurements difficult, which limits the use of current-based force equations. Additionally, the flexibility of AMB-equipped thrust measurement systems (TMSs) to measure many types of forces with little to no reconfiguration or calibration makes them appealing. The multi-point method provides predictions of both shaft force and rotor position using only current pairs without air gap measurements. Static and dynamic load scenarios were investigated to determine the feasibility of this new approach to force measurement. For both, the effects of bearing load and rotor position within the bearing were analyzed. Under dynamic loading, different amounts of unbalance as well as various rotor speeds were used to provide multiple test cases. The multi-point predictions of rotor position were analyzed and compared with the measured rotor positions. It was shown that this new multiple-point method for measuring bearing loads with AMBs provides equivalent or better force predictions to analogous single-point methods for static loads while eliminating the need for measuring rotor position.
Master of Science

Many processes involving rotating machinery could benefit from the continuous feedback of force applied to the bearings that support the machinery. Such a system could be used to provide diagnostics for process monitoring in a manufacturing application or to provide information for machine health monitoring. Active Magnetic Bearings (AMBs) have the capability to act concurrently as a shaft force sensor and support bearing. This capability stems from the AMB's control system, which is designed to maintain a specific rotor position, regardless of forces acting on the rotor. Researchers have demonstrated the force sensing ability of AMBs; current state of the art methods typically rely on a direct measurement of magnetic flux density as provided by a Hall probe inserted in the magnetic field. In this work, a system identification approach to force measurement is proposed; the proposed approach is applicable to all active magnetic bearings and does not require Hall probes. Recent developments in system identification of bearing forces (Kasarda et al., 2000) indicate that a different approach is feasible. In the work of Marshall (Marshall et al., 2001), a variety of perturbations are applied to an AMB while the AMB controller signals are interrogated, no outside instrumentation such as force transducers or Hall probes are required. The work of Kasarda and Marshall is the starting point for the work presented here. The initial work was expanded to include a general characterization of air gap for any rotor position. Although this characterization relies on static testing to identify system parameters, the identified parameters can then be used in the measurement of dynamic forces. The identification procedure provides a measurement of effective air gap length. Effective gap length is used to infer the effective position of the rotor with respect to the stator. This measurement is made for several specific rotor locations. The relationship between the effective rotor positions provided by the identification and the rotor positions reported by the AMB system sensors establishes a coordinate transformation. The procedure is also applied at different shaft rotation angles. In this way rotor runout can be identified.
Ph. D.

Existing thrust measurement systems (TMSs) at NASA Stennis Space Center use strain gauges and flux plates to measure forces produced by a test article. Alignment and calibration can take two weeks or more every time a piece of hardware or test article is changed. Cross axis loading is also problematic because it is impossible to perfectly align the flex plates and strain gauges in the thrust direction. In response to these problems, a magnetically levitated thrust measurement system has been proposed and a 300lb capacity demonstrator has been designed and built. In this design, the magnetic bearings work concurrently as support bearings and force measurement devices. The demonstrator consists of a floating frame that is completely levitated within a fixed frame by four support bearings carrying loads in the x- and y-direction and seven thrust bearings carrying loads in the z- or thrust direction. Joe Imlach of Imlach Consulting Engineering designed the demonstrator and magnetic bearing components, while Virginia Tech's role has been the application of the multipoint calibration technique including code development, the implementation of a 128-channel data acquisition system, and the overall test verification of the TMS demonstrator.A turnbuckle assembly and magnetostrictive actuator are used in series with a conventional load cell for static and dynamic testing, respectively. Both current based and flux based force equations were used to measure the reaction forces at the bearings. The static results using the current based equations including the current based fringing equations resulted in accuracies of 93% of full load, while the static results using the flux based equations including the flux based fringing equations resulted in accuracies of 99.5% of full load. These accuracies can be compared to accuracies of 83-90% seen in previous work using magnetic bearings to measure forces by monitoring currents and to accuracies of about 99% in previous work using magnetic bearings to measure forces by monitoring fluxes. All of the improved accuracies were made possible through the implementation of a calibration technique known as the multipoint method and the implementation of a gap dependent fringing correction factor developed by Joe Imlach. The demonstrator was not outfitted with accelerometers so the inertia of the floating frame could not be accounted for, limiting the scope of dynamic testing. However, the tests confirmed the ability of the demonstrator to measure dynamic loads in general.
Master of Science

Directional control valves are widely used in hydraulic systems to control the flow direction and the flow rate. In order to design an actuator for such a valve a preliminary analysis of forces acting on the spool is necessary. The dominant axial force is the so called steady flow force, which is analysed within this study. For this purpose a 2/2-way spool valve with a sharp control edge was manufactured and investigated. CFD simulations were carried out to visualize the fluid flow inside the valve. The measured and simulated axial forces and pressure drops across the test valve are compared and show good qualitative correlation. However, the simulated values of axial forces are in average by 32 % lower compared with the measured ones. Therefore, the components of the axial force were scrutinized revealing a dominancy of the pressure force acting on ring areas in the spool chamber. Although CFD simulations are preferably used to save resources, the results of this study emphasise the importance of the experiments.

Aktionskräfte stellen wesentliche Risikofaktoren für die Entstehung von Erkrankungen im Finger-, Hand- und Armbereich dar. Daher ist die Erfassung und Analyse von Aktionskräften ein wichtiger Bestandteil der ergonomischen Bewertung von Arbeitsplätzen. Zur Erfassung von Aktionskräften, insbesondere in der Automobilproduktion, existiert bisher jedoch weder eine einheitliche noch eine systematische Vorgehensweise. Es mangelt an konkreten Forschungserkenntnissen über den Messaufbau, die Messdurchführung und die Messauswertung von Kraftfällen. In der vorliegenden Arbeit wird deshalb ein erster Schritt unternommen, um die Erfassung von Aktionskräften auf Basis wissenschaftlich gestützter Erkenntnisse zu standardisieren. Hierzu werden insgesamt vier empirische Untersuchungen (zwei Vorstudien und zwei empirische Laborstudien) durchgeführt. In der ersten Studie (Kapitel 4) erfolgt eine Identifizierung der vorhandenen Arten von Kraftaufwendungen in verschiedenen Fertigungsbereichen der Automobilproduktion im Rahmen einer Dokumentenanalyse. In der zweiten Studie (Kapitel 5) wird der bedeutendste Fertigungsbereich ausgewählt, um darin eine Auszählung der Kraftaufwendungen anhand einer standardisierten Beobachtung definierter Arbeitsprozesse durchzuführen. Die dritte Untersuchung (Kapitel 6) ist als empirische Laborstudie konzipiert. Darin wird die technische Erfassung von Aktionskräften unter idealisierten Bedingungen ohne menschlichen Einfluss erprobt. In der vierten Untersuchung (Kapitel 7), ebenfalls als empirische Laborstudie konzipiert, werden spezifische Kraftaufwendungen im Labor systematisch durch Probanden nachgestellt und gemessen. Dabei wird das Vorgehen zur Durchführung und Auswertung von praxisnahen Kraftmessungen unter menschlichem Einfluss evaluiert. Die Erkenntnisse der Arbeit helfen dabei, bestehende Forschungsdefizite aufzuarbeiten und zu beheben. Sie stellen ferner eine Handlungshilfe für betriebliche Kraftanalysen sowie eine Orientierung für zukünftige Forschungsarbeiten dar
Action forces have been identified as risk factors. Therefore, the collection and analysis of action forces is an essential part of the ergonomic evaluation. Up to now, there was a lack of a standardized and systematic approach to evaluate action forces, especially in the automotive production. Thus, in the present thesis a methodical approach is described to evaluate action forces systematically. The thesis is divided into four studies. The first study contains the identification of the variety of action forces in the different manufacturing areas of automotive production. The second study describes the detailed analysis of action forces in the assembly shop, which is the manufacturing area with the highest count of action forces in the automotive production. The third study describes the direct measurement of action forces in laboratory conditions. The action forces are applied by a testing machine. The fourth study consists of the direct measurement of action forces, which are applied by subjects. Thereby, the methodical approach to perform direct measurements has been evaluated. The findings of the thesis can be used as a guideline, to evaluate action forces in the automotive production. Also the findings highlight the potential for further research projects

Die selbständige, gerichtete Bewegung von biologischen Zellen ist eine der grundlegendsten und komplexesten Erscheinungen der Natur. In höher entwickelten Lebewesen spielt die Zellbewegung eine wichtige Rolle, z.B. bei der Entwicklung des Organismus, bei der Funktion des Immunsystems aber auch bei der Metastase von Krebszellen. Die physikalischen Prozesse die dieser Fähigkeit zugrunde liegen, sind im Fokus dieser Arbeit. Um besser zu verstehen welche Prozesse im Einzelnen und in welcher Kombination den Zellen erlauben sich gerichtet fortzubewegen, wurde in der vorliegenden Arbeit ein representatives Modellsystem von motilen Zellen untersucht. Fischkeratozyten bewegen sich in vitro regelmäßig und gleichförmig, relativ schnell über die Substratfläche, und stellen aus physikalischer Sicht eine optimierte, sich selbständig bewegende Polymermaschine dar. Um Kräfte in der Bewegungsebene der Zellen zu untersuchen, wurde in der vorliegenden Arbeit eine neuartige, auf dem Rasterkraftmikroskop (RKM) basierende Methode entwickelt. Zusätzlich wurden hochaufgelöste, mit dem Phasenkontrastmikroskop aufgenommene Bilderserien analysiert und die Geschwindigkeitsverteilung in der Zelle durch Korrelationsalgorithmen bestimmt. Die Struktur des Polymernetzwerkes wurde in mit Fluoreszenzfarbstoff markierten Zellen untersucht, und elastische Eigenschaften wurden mit rheologischen RKM-Messungen bestimmt. Traktionskraftmessungen an elastischen Substraten runden das umfassende Bild ab. Durch Veränderung der molekularen Strukturen mit verschiedenen Chemikalien, die unterschiedliche Prozesse im Gesamtsystem stören, konnte nun ein Phasenraum der Kraftgenerierungsprozesse untersucht und unterschiedliche Effekte verschiedenen Prozessen eindeutig zugeordnet werden. Es wurde somit erstmalig experimentell bewiesen, dass die Polymerisation von Aktin die treibende Kraft am vorderen Rand der Zelle ist. Darüber hinaus wurde das Verhalten des Kraftaufbaus mit einem Model beschrieben, das Aufschluss über die Funktionsweise der darunterliegenden Aktinpolymerstrukturens gibt. Desweiteren wurde in der Mitte der Zelle, zwischen vorderem Rand und Zellkörper, erstmalig eine rückwärtsgerichtete Kraft gemessen, die wichtig ist um ein Kräftegleichgewicht zu erstellen. Ein Model das auf entropischen Kräften im Polymersystem basiert, beschreibt diese kontraktilen Kräfte und ordnet sie der Depolymerisation von Aktin zu. Die Bewegung des Zellkörpers wiederum basiert auf dem Zusammenspiel dieser beiden Mechanismen, sowie der Kontraktion von Aktin und Aktinbündeln durch molekulare Motoren. Eine umfassendes Charakterisierung über verschiedene lokale Mechanismen und ihrer Wechselwirkungen konnte somit erstellt werden, und damit das Verständnis der Kraftgenerierung zur Zellbewegung vertieft.

Les propriétés mécaniques des nanotubes membranaires (sans la présence du cytosquelette), en particulier la force nécessaire pour les former et les maintenir, sont maintenant bien comprises. Par contre, bien que dans la cellule les nanotubes soient souvent couplés à l’actine, son mécanisme d’action sur de telles structures est inconnu. L’objectif de cette thèse est donc de comprendre comment la dynamique de polymérisation de l’actine affecte la croissance et la stabilité des nanotubes de membrane et contribue à leur scission. Le projet consistera à adresser deux questions principales : - comment la force pour maintenir un nanotube de membrane évolue en présence du cytosquelette d’actine ? - comment la structure du réseau d’actine (taille de la maille, composition, dynamique) détermine les effets mécaniques observés ? La dynamique de l’actine stabilise-t-elle le nanotube ? Les forces générées par la polymérisation peuvent-elles provoquer une scission des nanotubes ? La structure du réseau d’actine permet-elle d’expliquer ces deux effets opposés ? Quel est l’effet de l’ajout de myosines, moteurs moléculaires capables de faire coulisser les filaments d’actine entre eux et de créer une contrainte mécanique supplémentaire dans le réseau ? Ces questions indissociables seront étudiées en collaboration entre les équipes de C. Sykes à l’Institut Curie (Paris), et de C. Campillo et S. Labdi au LAMBE (Evry)
The mechanics of membrane nanotubes (without the presence of the cytoskeleton), especially the force needed to form and maintain a nanotube, are now well understood. But, although in the cell the nanotubes are often coupled with actin, its action mechanism on such structures is unknown. The objective of this thesis is to understand how actin polymerization dynamics affect the growth and stability of membrane nanotubes and may contribute to their scission. The project will address two main questions: - How the force to maintain a membrane nanotube evolves in presence of a reconstituted actin cytoskeleton? - How the structure of the actin network (mesh size, composition, dynamic) determines its mechanical effect on the nanotube? Does actin dynamics stabilize the nanotube? Are the forces generated by actin polymerization able to cut nanotubes? Does the structure of the actin network explain these two opposite effects? What is the effect of adding myosins, molecular motors able to create additional mechanical stress in the network? These inseparable issues will be studied in collaboration between the teams of C. Sykes at the Institut Curie (Paris), and C. Campillo and S. Labdi in LAMBE (Evry)

La thématique étudiée dans ce mémoire est axée sur la préservation de la stabilité dynamique de véhicules évoluant en environnement naturel. En effet, la mobilité en milieu tout-terrain est une activité particulièrement pénible et dangereuse en raison de la nature difficile de l'environnement de conduite et de la reconfigurabilité des machines. Le caractère changeant et incertain des interactions rencontrées entre des véhicules à dynamique complexe et variable et leur environnement entraîne régulièrement des risques accrus de renversement et/ou de perte de contrôle (dévalement, dérapage déclenché par une perte soudaine d'adhérence) pour le conducteur. Une forte accidentalité mortelle est, en effet, recensée dans ce secteur, en particulier, dans le milieu agricole ou le renversement de véhicule est classé comme étant la première cause de mortalité au travail. A l'heure actuelle, les approches existantes sur la stabilité d'engins agricoles sont qualifiées à juste titre de passives car elles ne permettent pas d'éviter que les accidents ne se produisent. Par ailleurs, la transposition directe des solutions de sécurité active du secteur de l'automobile (ABS, ESP) s'est révélée inadaptée aux véhicules tout-terrain a cause des hypothèses simplificatrices (routes plates et homogènes, conditions d'adhérence constantes, etc.) dont souffre la conception de ces dispositifs. Ainsi, le développement de systèmes actifs de sécurité prenant en compte les spécificités de la conduite en milieu tout-terrain se révèle être la meilleure voie d'amélioration à suivre. Eu égard à ces circonstances, ce projet se propose d'adresser cette problématique en étudiant des métriques de stabilité pertinentes permettant d'estimer et d'anticiper en temps réel les risques afin de permettre des actions correctives pour la préservation de l'intégrité des machines tout-terrain. Afin de faciliter l'industrialisation du dispositif actif de sécurité conçu, l'une des contraintes sociétales et commerciales de ce projet a été l'utilisation de capteurs compatibles avec le coût des machines visées. L'objectif ambitieux de cette étude a été atteint par différentes voies. En premier lieu, une approche de modélisation multi-échelle a permis de caractériser l'évolution dynamique de véhicules en milieu tout-terrain. Cette approche à dynamique partielle a offert l'avantage de développer des modèles suffisamment précis pour être représentatifs du comportement réel de l'engin mais tout en présentant une structure relativement simple permettant la synthèse d'asservissements performants. Puis, une étude comparative des avantages et des inconvénients des trois grandes familles de métriques répertoriées dans la littérature a permis de mettre en exergue l'intérêt des métriques analytiques à modèle dynamique par rapport aux catégories de critères de stabilité dits statiques et empiriques. Enfin, l'analyse approfondie des métriques dynamiques a facilité le choix de trois indicateurs (Lateral and Longitudinal Load Transfer (LLT), Force Angle Stability Measurement (FASM) et Dynamic Energy Stability Measurement (DESM)) qui sont représentatifs d'un risque imminent de renversement du véhicule. La suite du mémoire s'appuie sur la théorie d'observation pour l'estimation en ligne des variables non directement mesurables en milieu tout-terrain telles que les rigidités de glissement et dérive du pneumatique. Jumelée aux différents modèles dynamiques du véhicule, la synthèse d'observateurs a permis donc d'estimer en temps réel les efforts d'interaction pneumatiques-sol nécessaires à l'évaluation des indicateurs d'instabilité. Le couplage de ces modèles multi-échelles à la théorie d'observation a ainsi constitué un positionnement original à même de briser la complexité de la caractérisation de la stabilité de véhicules à dynamiques complexes et incertaines. (...)
This work is focused on the thematic of the maintenance of the dynamic stability of off-road vehicles. Indeed, driving vehicles in off-road environment remains a dangerous and harsh activity because of the variable and bad grip conditions associated to a large diversity of terrains. Driving difficulties may be also encountered when considering huge machines with possible reconfiguration of their mechanical properties (changes in mass and centre of gravity height for instance). As a consequence, for the sole agriculture sector, several fatal injuries are reported per year in particular due to rollover situations. Passive protections (ROllover Protective Structure - ROPS) are installed on tractors to reduce accident consequences. However, protection capabilities of these structures are very limited and the latter cannot be embedded on bigger machines due to mechanical design limitations. Furthermore, driving assistance systems (such as ESP or ABS) have been deeply studied for on-road vehicles and successfully improve safety. These systems usually assume that the vehicle Center of Gravity (CG) height is low and that the vehicles are operating on smooth and level terrain. Since these assumptions are not satisfied when considering off-road vehicles with a high CG, such devices cannot be applied directly. Consequently, this work proposes to address this research problem by studying relevant stability metrics able to evaluate in real time the rollover risk in order to develop active safety devices dedicated to off-road vehicles. In order to keep a feasible industrialization of the conceived active safety device, the use of compatible sensors with the cost of the machines was one of the major commercial and societal requirements of the project. The ambitious goal of this study was achieved by different routes. First, a multi-scale modeling approach allowed to characterize the dynamic evolution of off-road vehicles. This partial dynamic approach has offered the advantage of developing sufficiently accurate models to be representative of the actual behavior of the machine but having a relatively simple structure for high-performance control systems. Then, a comparative study of the advantages and drawbacks of the three main families of metrics found in the literature has helped to highlight the interest of dynamic stability metrics at the expense to categories of so-called static and empirical stability criteria. Finally, a thorough analysis of dynamic metrics has facilitated the choice of three indicators (Longitudinal and Lateral Load Transfer (LLT), Force Angle Stability Measurement (FASM) and Dynamic Energy Stability Measurement (DESM)) that are representative of an imminent rollover risk. The following of the document is based on the observation theory for estimating online of variables which are not directly measurable in off-road environment such as slip and cornering stiffnesses. Coupled to the dynamic models of the vehicle, the theory of observers has helped therefore to estimate in real time the tire-soil interaction forces which are necessaries for evaluating indicators of instability. The coupling of these multiscale models to the observation theory has formed an original positioning capable to break the complexity of the characterization of the stability of vehicles having complex and uncertain dynamics. (...)

Dissertation is focused on the application of optical measurement methods using techniques of optical microscopy and fluorescence microscopy in measurements of electromechanical characteristics of isolated cardiac cells and clusters of differentiated cardiomyocytes. The first proposed method uses a practical combination of fluorescence microscopy equipped with fluorescent fast and high-resolution camera and atomic force microscopy for simultaneous measurement of calcium transients and contraction of cardiomyocyte clusters. The signals obtained undergoes filtration, processing and analysis. Result function parameters obtained by analyzing signals after application of caffeine are evaluated by comparison with functional parameters obtained during the control measurement. The second proposed method is applied to the cardiomyocyte clusters for the purpose of cardiomyocyte contraction signals measurement. The signals obtained by optical methods are analyzed and compared with the reference signal obtained using atomic force microscopy. Optical measurement method of cell contractins based on detection of cell ends using adjusting of microscopy images by re-sharpening and fluorescence method for cardiomyocyte contractions measurements were designed to increase realiability in simultaneous measurement of cell contractions simultaneously with calcium transients in isolated cardiomyocytes experiments.

The diploma thesis is focused on the measurement of forces acting between the tire and the road. There is an outline of tire and tire models problematic in the opening part. In the following part, the rear right suspension of the formula student car was mounted with strain gauges and the data logging system was described. There is also a multi-body model of the rear axle created in Adams/Car and SAMS software, that is able to calculate forces acting between the tire and the road, taking the measured forces in the suspension, rocker position, and throttle position into consideration. After a series of calibrations and verification measurements, the measurement on the test track was made, with data analysis focused on forces acting between the tire and the road.

We present a comprehensive overview of microrheology, emphasizing the underlying theory, practical aspects of its implementation, and current applications to rheological studies in academic and industrial laboratories. Key methods and techniques are examined, including important considerations to be made with respect to the materials most amenable to microrheological characterization and pitfalls to avoid in measurements and analysis. The fundamental principles of all microrheology experiments are presented, including the nature of colloidal probes and their movement in fluids, soft solids, and viscoelastic materials. Microrheology is divided into two general areas, depending on whether the probe is driven into motion by thermal forces (passive), or by an external force (active). We present the theory and practice of passive microrheology, including an in-depth examination of the Generalized Stokes-Einstein Relation (GSER). We carefully treat the assumptions that must be made for these techniques to work, and what happens when the underlying assumptions are violated. Experimental methods covered in detail include particle tracking microrheology, tracer particle microrheology using dynamic light scattering and diffusing wave spectroscopy, and laser tracking microrheology. Second, we discuss the theory and practice of active microrheology, focusing specifically on the potential and limitations of extending microrheology to measurements of non-linear rheological properties, like yielding and shear-thinning. Practical aspects of magnetic and optical tweezer measurements are preseted. Finally, we highlight important applications of microrheology, including measurements of gelation, degradation, high-throughput rheology, protein solution viscosities, and polymer dynamics.

This chapter examines how wider social forces, including globalization, neo-liberal economics, and widening participation in higher education shape government policies, and how much space these allow for academics to pursue meaningful and socially useful research. It assesses how various research evaluation schemes can be made more effective and meaningful, and how they may encourage more relevant research in the social sciences. The chapter addresses the use of bibliometrics (citations indices) and measurements aimed at assessing the impact of academic research. It also examines how teaching may be restored as in its rightful place as a core meaningful activity for social science academics. Teaching must once again anchor the identities and practices of academics, whether they see themselves as research-active or inactive, as long as they seek to maintain active scholarly identities.

Bones are multifunctional passive organs of movement that supports soft tissue and directly attached muscles. They also protect internal organs and are a reserve of calcium, phosphorus and magnesium. Each bone is covered with periosteum, and the adjacent bone surfaces are covered by articular cartilage. Histologically, the bone is an organ composed of many different tissues. The main component is bone tissue (cortical and spongy) composed of a set of bone cells and intercellular substance (mineral and organic), it also contains fat, hematopoietic (bone marrow) and cartilaginous tissue. Bones are a tissue that even in adult life retains the ability to change shape and structure depending on changes in their mechanical and hormonal environment, as well as self-renewal and repair capabilities. This process is called bone turnover. The basic processes of bone turnover are: • bone modeling (incessantly changes in bone shape during individual growth) following resorption and tissue formation at various locations (e.g. bone marrow formation) to increase mass and skeletal morphology. This process occurs in the bones of growing individuals and stops after reaching puberty • bone remodeling (processes involve in maintaining bone tissue by resorbing and replacing old bone tissue with new tissue in the same place, e.g. repairing micro fractures). It is a process involving the removal and internal remodeling of existing bone and is responsible for maintaining tissue mass and architecture of mature bones. Bone turnover is regulated by two types of transformation: • osteoclastogenesis, i.e. formation of cells responsible for bone resorption • osteoblastogenesis, i.e. formation of cells responsible for bone formation (bone matrix synthesis and mineralization) Bone maturity can be defined as the completion of basic structural development and mineralization leading to maximum mass and optimal mechanical strength. The highest rate of increase in pig bone mass is observed in the first twelve weeks after birth. This period of growth is considered crucial for optimizing the growth of the skeleton of pigs, because the degree of bone mineralization in later life stages (adulthood) depends largely on the amount of bone minerals accumulated in the early stages of their growth. The development of the technique allows to determine the condition of the skeletal system (or individual bones) in living animals by methods used in human medicine, or after their slaughter. For in vivo determination of bone properties, Abstract 10 double energy X-ray absorptiometry or computed tomography scanning techniques are used. Both methods allow the quantification of mineral content and bone mineral density. The most important property from a practical point of view is the bone’s bending strength, which is directly determined by the maximum bending force. The most important factors affecting bone strength are: • age (growth period), • gender and the associated hormonal balance, • genotype and modification of genes responsible for bone growth • chemical composition of the body (protein and fat content, and the proportion between these components), • physical activity and related bone load, • nutritional factors: – protein intake influencing synthesis of organic matrix of bone, – content of minerals in the feed (CA, P, Zn, Ca/P, Mg, Mn, Na, Cl, K, Cu ratio) influencing synthesis of the inorganic matrix of bone, – mineral/protein ratio in the diet (Ca/protein, P/protein, Zn/protein) – feed energy concentration, – energy source (content of saturated fatty acids - SFA, content of polyun saturated fatty acids - PUFA, in particular ALA, EPA, DPA, DHA), – feed additives, in particular: enzymes (e.g. phytase releasing of minerals bounded in phytin complexes), probiotics and prebiotics (e.g. inulin improving the function of the digestive tract by increasing absorption of nutrients), – vitamin content that regulate metabolism and biochemical changes occurring in bone tissue (e.g. vitamin D3, B6, C and K). This study was based on the results of research experiments from available literature, and studies on growing pigs carried out at the Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences. The tests were performed in total on 300 pigs of Duroc, Pietrain, Puławska breeds, line 990 and hybrids (Great White × Duroc, Great White × Landrace), PIC pigs, slaughtered at different body weight during the growth period from 15 to 130 kg. Bones for biomechanical tests were collected after slaughter from each pig. Their length, mass and volume were determined. Based on these measurements, the specific weight (density, g/cm3) was calculated. Then each bone was cut in the middle of the shaft and the outer and inner diameters were measured both horizontally and vertically. Based on these measurements, the following indicators were calculated: • cortical thickness, • cortical surface, • cortical index. Abstract 11 Bone strength was tested by a three-point bending test. The obtained data enabled the determination of: • bending force (the magnitude of the maximum force at which disintegration and disruption of bone structure occurs), • strength (the amount of maximum force needed to break/crack of bone), • stiffness (quotient of the force acting on the bone and the amount of displacement occurring under the influence of this force). Investigation of changes in physical and biomechanical features of bones during growth was performed on pigs of the synthetic 990 line growing from 15 to 130 kg body weight. The animals were slaughtered successively at a body weight of 15, 30, 40, 50, 70, 90, 110 and 130 kg. After slaughter, the following bones were separated from the right half-carcass: humerus, 3rd and 4th metatarsal bone, femur, tibia and fibula as well as 3rd and 4th metatarsal bone. The features of bones were determined using methods described in the methodology. Describing bone growth with the Gompertz equation, it was found that the earliest slowdown of bone growth curve was observed for metacarpal and metatarsal bones. This means that these bones matured the most quickly. The established data also indicate that the rib is the slowest maturing bone. The femur, humerus, tibia and fibula were between the values of these features for the metatarsal, metacarpal and rib bones. The rate of increase in bone mass and length differed significantly between the examined bones, but in all cases it was lower (coefficient b <1) than the growth rate of the whole body of the animal. The fastest growth rate was estimated for the rib mass (coefficient b = 0.93). Among the long bones, the humerus (coefficient b = 0.81) was characterized by the fastest rate of weight gain, however femur the smallest (coefficient b = 0.71). The lowest rate of bone mass increase was observed in the foot bones, with the metacarpal bones having a slightly higher value of coefficient b than the metatarsal bones (0.67 vs 0.62). The third bone had a lower growth rate than the fourth bone, regardless of whether they were metatarsal or metacarpal. The value of the bending force increased as the animals grew. Regardless of the growth point tested, the highest values were observed for the humerus, tibia and femur, smaller for the metatarsal and metacarpal bone, and the lowest for the fibula and rib. The rate of change in the value of this indicator increased at a similar rate as the body weight changes of the animals in the case of the fibula and the fourth metacarpal bone (b value = 0.98), and more slowly in the case of the metatarsal bone, the third metacarpal bone, and the tibia bone (values of the b ratio 0.81–0.85), and the slowest femur, humerus and rib (value of b = 0.60–0.66). Bone stiffness increased as animals grew. Regardless of the growth point tested, the highest values were observed for the humerus, tibia and femur, smaller for the metatarsal and metacarpal bone, and the lowest for the fibula and rib. Abstract 12 The rate of change in the value of this indicator changed at a faster rate than the increase in weight of pigs in the case of metacarpal and metatarsal bones (coefficient b = 1.01–1.22), slightly slower in the case of fibula (coefficient b = 0.92), definitely slower in the case of the tibia (b = 0.73), ribs (b = 0.66), femur (b = 0.59) and humerus (b = 0.50). Bone strength increased as animals grew. Regardless of the growth point tested, bone strength was as follows femur > tibia > humerus > 4 metacarpal> 3 metacarpal> 3 metatarsal > 4 metatarsal > rib> fibula. The rate of increase in strength of all examined bones was greater than the rate of weight gain of pigs (value of the coefficient b = 2.04–3.26). As the animals grew, the bone density increased. However, the growth rate of this indicator for the majority of bones was slower than the rate of weight gain (the value of the coefficient b ranged from 0.37 – humerus to 0.84 – fibula). The exception was the rib, whose density increased at a similar pace increasing the body weight of animals (value of the coefficient b = 0.97). The study on the influence of the breed and the feeding intensity on bone characteristics (physical and biomechanical) was performed on pigs of the breeds Duroc, Pietrain, and synthetic 990 during a growth period of 15 to 70 kg body weight. Animals were fed ad libitum or dosed system. After slaughter at a body weight of 70 kg, three bones were taken from the right half-carcass: femur, three metatarsal, and three metacarpal and subjected to the determinations described in the methodology. The weight of bones of animals fed aa libitum was significantly lower than in pigs fed restrictively All bones of Duroc breed were significantly heavier and longer than Pietrain and 990 pig bones. The average values of bending force for the examined bones took the following order: III metatarsal bone (63.5 kg) <III metacarpal bone (77.9 kg) <femur (271.5 kg). The feeding system and breed of pigs had no significant effect on the value of this indicator. The average values of the bones strength took the following order: III metatarsal bone (92.6 kg) <III metacarpal (107.2 kg) <femur (353.1 kg). Feeding intensity and breed of animals had no significant effect on the value of this feature of the bones tested. The average bone density took the following order: femur (1.23 g/cm3) <III metatarsal bone (1.26 g/cm3) <III metacarpal bone (1.34 g / cm3). The density of bones of animals fed aa libitum was higher (P<0.01) than in animals fed with a dosing system. The density of examined bones within the breeds took the following order: Pietrain race> line 990> Duroc race. The differences between the “extreme” breeds were: 7.2% (III metatarsal bone), 8.3% (III metacarpal bone), 8.4% (femur). Abstract 13 The average bone stiffness took the following order: III metatarsal bone (35.1 kg/mm) <III metacarpus (41.5 kg/mm) <femur (60.5 kg/mm). This indicator did not differ between the groups of pigs fed at different intensity, except for the metacarpal bone, which was more stiffer in pigs fed aa libitum (P<0.05). The femur of animals fed ad libitum showed a tendency (P<0.09) to be more stiffer and a force of 4.5 kg required for its displacement by 1 mm. Breed differences in stiffness were found for the femur (P <0.05) and III metacarpal bone (P <0.05). For femur, the highest value of this indicator was found in Pietrain pigs (64.5 kg/mm), lower in pigs of 990 line (61.6 kg/mm) and the lowest in Duroc pigs (55.3 kg/mm). In turn, the 3rd metacarpal bone of Duroc and Pietrain pigs had similar stiffness (39.0 and 40.0 kg/mm respectively) and was smaller than that of line 990 pigs (45.4 kg/mm). The thickness of the cortical bone layer took the following order: III metatarsal bone (2.25 mm) <III metacarpal bone (2.41 mm) <femur (5.12 mm). The feeding system did not affect this indicator. Breed differences (P <0.05) for this trait were found only for the femur bone: Duroc (5.42 mm)> line 990 (5.13 mm)> Pietrain (4.81 mm). The cross sectional area of the examined bones was arranged in the following order: III metatarsal bone (84 mm2) <III metacarpal bone (90 mm2) <femur (286 mm2). The feeding system had no effect on the value of this bone trait, with the exception of the femur, which in animals fed the dosing system was 4.7% higher (P<0.05) than in pigs fed ad libitum. Breed differences (P<0.01) in the coross sectional area were found only in femur and III metatarsal bone. The value of this indicator was the highest in Duroc pigs, lower in 990 animals and the lowest in Pietrain pigs. The cortical index of individual bones was in the following order: III metatarsal bone (31.86) <III metacarpal bone (33.86) <femur (44.75). However, its value did not significantly depend on the intensity of feeding or the breed of pigs.

AbstractThe dynamics of histone-DNA interactions govern chromosome organization and regulates the processes of transcription, replication, and repair. Accurate measurements of the energies and the kinetics of DNA binding to component histones of the nucleosome under a variety of conditions are essential to understand these processes at the molecular level. To accomplish this, we employ three specific single-molecule techniques: force disruption (FD) with optical tweezers, confocal imaging (CI) in a combined fluorescence plus optical trap, and survival probability (SP) measurements of disrupted and reformed nucleosomes. Short arrays of positioned nucleosomes serve as a template for study, facilitating rapid quantification of kinetic parameters. These arrays are then exposed to FACT (FAcilitates Chromatin Transcription), a non-ATP-driven heterodimeric nuclear chaperone known to both disrupt and tether histones during transcription. FACT binding drives off the outer wrap of DNA and destabilizes the histone-DNA interactions of the inner wrap as well. This reorganization is driven by two key domains with distinct function. FD experiments show the SPT16 MD domain stabilizes DNA-histone contacts, while the HMGB box of SSRP1 binds DNA, destabilizing the nucleosome. Surprisingly, CI experiments do not show tethering of disrupted histones, but increased rates of histone release from the DNA. SI experiments resolve this, showing that the two active domains of FACT combine to chaperone nucleosome reassembly after the timely release of force. These combinations of single-molecule approaches show FACT is a true nucleosome catalyst, lowering the barrier to both disruption and reformation.

Abstract.Myosin 10 (Myo10) is an actin-based molecular motor that is essential for filopodia formation and likely senses tension through interactions with integrins in filopodial tips. It possesses a single α-helical (SAH) domain at the end of its canonical lever, which amplifies the movement of the motor. We have shown the SAH domain can contribute to lever function and possesses the properties of a constant force spring. Here we investigate whether the SAH domain plays a role in tension sensing and whether it becomes extended under load at the filopodial tip. Previously, we found that removing the entire SAH domain and short anti-parallel coiled coil (CC) region at the C-terminal end of the SAH does not prevent Myo10 from moving to filopodial tips in cells. Exploiting this, we generated recombinant forms of Myo10, in which a tension-sensing module (TSMod), comprising a FRET-pair YPet and mCherry separated by a linker sequence of amino acids was then inserted between the Myo10 motor and tail domains, so as to replace the SAH domain and CC region. The linker sequence comprised either a portion of the native SAH domain, or control sequences that were either short (x1: stiff) or long (x5: flexible) repeats of “GPGGA”. As additional controls we also placed the TSMod construct at the N-terminus, where it should not experience force. Our FRET measurements indicate that the SAH domain of Myo10 may become extended at when the protein is stalled at the filopodial tips, so the SAH domain may therefore act as a force sensor.

In turbomachinery, seals are used to prevent fluid leakage. At seal part, rotordynamic fluid force (RD fluid force), which causes whirling motion of rotor, is generated. Under certain conditions, the RD fluid force may contribute to instability of the machine. There are several cases that the whirling is accompanied by eccentricity due to the influence of gravity, or the whirling orbit becomes elliptical due to the influence of the bearing support anisotropy. In these cases, mathematical modeling of the RD fluid forces becomes increasingly complex. As a result, the RD fluid force measurement is more preferable. To improve the measurement and evaluation technology of the RD fluid force, a method to arbitrarily control whirling of the orbit is required. In this paper, RD fluid force measurement by controlling the shape of the orbit using an active magnetic bearing (AMB) is proposed. A contact type mechanical seal is used as a test specimen. When the rotating shaft is whirling, the RD fluid force due to hydrodynamics lubrication and the frictional force due to contact occur on the sliding surface. The resultant force of these forces is taken as the reaction force of mechanical seal and the measurement is performed. The measured reaction force of the mechanical seal is compared with simulation results and the validity of the proposed measurement method is confirmed.

Active magnetic bearings (AMBs) have the unique capability to act concurrently as support bearings and load cells for measuring shaft forces. Current state-of-the-art methods for force measurement rely on models with limited accuracy due to effects which are difficult to characterize such as fringing, leakage, and variations in material properties. In addition, these effects may be a function of actual air gaps which are difficult to determine in a dynamic operating environment. This paper discusses a new force measurement methodology that inherently accounts for these types of effects and other system uncertainties by utilizing multiple sets of current pairs in opposing actuators, in conjunction with a calculation algorithm, to accurately determine the force applied by the AMB. This new multi-point methodology allows for the determination of bearing forces from information on basic actuator geometry and control currents only, with no knowledge of actual operating air gaps required. The inherent nature of the methodology accounts for model uncertainties such as fringing, leakage, and other system unknowns. Initial static experimental test results are presented demonstrating 3% error in measuring the nominal determined bearing load, and a variation in calculated forces of less than 5% in most cases (8% in one case) when the location of the rotor within the bearing stator is modified. For the analogous conventional single-point measurements, the results show 15% error and 23% variation.

Abstract Force guided assembly is a control scheme to guide a workpiece based on a stored map from forces to a correction of motion. Based on the geometry of the workpiece and its kinematic behavior in interacting with the environment, the functional map relating the correction of motion to force measurements is generated and stored as a control law. Central to the design of force guided control is how to synthesize this functional map. Although these explicit force-guided controls are a useful concept, particularly for the monitoring of assembly processes, there are inherent difficulties in applying it to real world problems. In real assembly lines, pipe insertion task, for instance, has been performed only by human workers. Skilled workers insert pipes by perturbing the pipes in order to avoid jamming as well as to determine which way to correct the motion. According to them, the skilled workers monitor obstructing forces in response to the applied perturbation, and modify their motion accordingly. The proposed perturbation/correlation method was motivated by this human perception and action : perturbing the pipe, observing the reaction to the perturbation and correcting the trajectory. In this paper, we propose a novel technique for acquiring effective force information despite sensor noise and friction. Instead of simply receiving force signals from the process, we give perturbation to the robot and measure the reaction forces to the perturbation. By taking the correlation between the perturbation signal and the reaction forces, reliable and useful information for guiding the robot would be extracted. It is expected that this perturbed force measurement provides much richer force information than that of stationary measurement. The perturbation/Correlation method presented in this paper is not only effective for reducing friction, but also effective for obtaining useful information for guiding the robot towards a desired direction. Preliminary experimental results with one directional perturbation are shown in this paper. Extensive mathematical analysis shows the potential application to assemblies in higher dimension.

Under contact-free levitation, rotors supported by active magnetic bearings have many advantages such as allowing near frictionless rotation and high rotational speeds. They also provide the designer the capability to achieve increased machine power density. However, magnetic bearings possess limited load capacity and operate under active control. Under certain operational conditions, the load capacity may be exceeded or a transient fault may occur. The rotor may then make contact with touchdown bearings and the ensuing rotor dynamics may result in transient or sustained contact dynamics. The magnetic bearings may have the capability to restore contact-free levitation, though this will require appropriate control strategies to be devised. An understanding of the contact dynamics is required, together with the relationship between these and applied magnetic bearing control forces. This paper describes the use of a contact force measurement system to establish the force relationship. The contact force components measured by the system are calibrated against forces applied by an active magnetic bearing. The data generated can be used to validate non-linear dynamic system models and aid the design of control action to minimize or eliminate contact forces.

Active Magnetic Bearings (AMBs) can be used concurrently as support bearings and as load cells for the measurement of support forces. This paper discusses the preliminary design for a test rig to simulate a full-scale rocket thrust measurement system utilizing AMBs and procedures that have been developed to enhance the use of AMBs in this application. These enhancements include the development of a model of the effect of fringing on force measurements and an on-line calibration procedure. The fringing effect model is based on actuator geometry and has been verified through finite element analyses. On-line calibration procedures for a magnetic thrust bearing arrangement have also been developed and verified through finite element analyses. Since the rocket thrust measurement system is not rotating, planar magnetic bearings will also be used for vertical support and will utilize the same calibration procedure, resulting in force and torque measurements in all six degrees of freedom.

Abstract The in-plane (stream-wise) fluid-elastic instability of triangular tube arrays caused tube-to-tube wear indications as observed in the U-bend regions of tube the bundles of San Onofre Unit-3 steam generators. To understand the in-plane FEI characteristics, stability analysis using unsteady fluid forces is quite helpful. However, taking measurements of unsteady fluid forces in the in-plane direction is quite challenging as the fluid coupling forces of the surrounding tubes must be measured simultaneously for the in-plane stability analysis. In particular, taking measurements under a high pressure and high temperature steam-water conditions, similar to an SG operating condition, is extremely difficult. Recently we have been able to successfully measure unsteady fluid force using a specially designed test equipment. In the meantime, random excitation forces acting on heat transfer tubes were also measured. We calculated the stability boundary of the in-plane FEI using the unsteady fluid force measurement with this special equipment.

The surface force technique, whereby the forces acting between two solid surfaces immersed in liquids or in adhesive contact are directly measured, represents a novel approach for both fundamental and application-oriented studies of the surface and colloid science of papermaking. The nature and measurement of surface forces are briefly discussed, and some results reported for mica surfaces are reviewed in order to illustrate the surface chemical information obtainable using a conventional Israelachvili-type surface force apparatus. In the case of cellulose surfaces immersed in water and aqueous electrolyte solutions the measured force vs. distance profile is characterized by three regimes. Significantly, conventional DLVO theory cannot explain the interaction forces measured between cellulose surfaces. Electrostatic double-layer forces, as anticipated, dominate the long-range interactions. However, as the two cellulose surfaces begin to “contact” each other, there is an interplay of steric and electrostatic forces due to dangling tails of cellulose chains. The observed force curves, therefore, are interpreted in terms of a new model — the “dangling tail” model — of the cellulose surface, namely, the water-swollen cellulose surface has long and weakly charged cellulose chains or “molecularfibrils” which extend into the aqueous solution. In addition, the application of the surface force technique to basic problems in the adsorption of polymers, both cationic polyelectrolytes and hemicelluloses, and the colloidal stability of kaolin suspensions is illustrated. The advantages of using a new type of surface force apparatus in future studies of surface and physicochemical phenomena relevant to paper manufacturing, coating and recycling are also briefly discussed.

Abstract Low Pressure Turbine (LPT) blades encounter highly stressed forced vibrations driven by centrifugal force and steady/unsteady aerodynamic loads. To prevent the blades from failure due to high cycle fatigue (HCF), the amplitude of these vibrations must be estimated and reduced. Friction damping devices like under-platform dampers, shrouds and snubbers are usually implemented to lessen these blade vibration amplitudes. For adjacent shrouded blades coupled to each other at the blade tips, the blade vibration levels are strongly affected by the three-dimensional periodic contact forces at shrouds resulting in energy dissipation due to friction. Therefore, to experimentally validate the numerical contact models that predict nonlinear forced response of shrouded blades, it is equally important to measure the contact forces acting at the shrouds. This study outlines the development and commissioning of an experimental test rig that allows the measurement of three-dimensional shroud contact forces and the forced response of the shrouded blade simultaneously. Firstly, the design requirements of the experimental setup that were considered while deciding the test rig components, are highlighted. The test rig comprises of a pair of tri-directional contact force transducers in contact with the two shroud ends of a dummy blade and includes a blade twisting mechanism for the application of the normal preload. The employed tri-directional contact force transducers consist of three uniaxial strain gauge-based force sensors, arranged in a tripod configuration, and attached to a reference block that accommodates the shroud. The calibration and the decoupling procedure of the tri-directional contact force measurement system is then briefly described. This is followed by the details of the experimental process to acquire the forced response and three-dimensional shroud contact forces simultaneously for a specified frequency range determined by a prior experimental modal analysis of the blade and test rig. Subsequently, the effects of the variation in shroud normal preload and excitation force on measured response and shroud contact forces are also discussed. Finally, the results demonstrate how the proposed experimental test rig provides a thorough understanding of the dynamic response of the shrouded blade and shroud contact forces which will lead to a more reliable experimental validation of simulation tools and its effect on system dynamics.

Proper actuator sizing and valve-stem guide selection requires accurate knowledge of the thrust requirements for linear valves. For globe valves, the flow-induced forces acting on the disc can be a substantial part of the total required thrust that the actuator is required to overcome. The flow-induced forces acting on the globe valve disc are decomposed into the rejection (or axial) force and the transverse (or side load) force. The axial force acts along the disc stem axis and the transverse force acts perpendicular to the disc stem axis. The axial force generally lends itself to simple analytical models or experimental measurement, making force predictions straight forward. The nature of the transverse force and globe valve design however, make predicting or experimentally measuring the transverse force nontrivial. An experimental test matrix was developed to better understand the behaviour and dependencies of the axial and transverse force on key factors, including the valve geometry and flow state (cavitating and noncavitating). In addition to the experimental investigation, numerical predictions using a 3-D model were performed to better understand and correlate the flow-induced forces with valve design and operating conditions. To facilitate the experimental study of the axial and transverse forces acting on a globe valve disc under cavitating and noncavitating conditions, a full model of a 2" Plexiglas globe valve was used to perform experimental testing so that visual observations of the formation and location of cavitation could be made. The disc stem was specially machined and instrumented so that the flow-induced forces and moments acting on the disc could be measured. The valve model was installed in a flow loop and the operating conditions and flow state were controlled using flow rate and downstream pressure. The flow loop was designed so that the pressure downstream of the valve could be sub atmospheric to provide accurate control over the level of cavitation. Experimental testing was conducted for a large set of cavitation conditions, fluid flows and disc opening positions. The CFD predictions were performed using ANSYS CFX 11.0 on a SGI ALTIX 330. The CFD predictions were performed using non-cavitating water. The flow field was assumed to be fully turbulent and the turbulence was modelled using the k-ε RNG model. Based on the experimental testing, it is found that the transverse force can reach the intensity of the axial force. Because the transverse force directly affects the guide friction force and other performance factors, the transverse force should be accurately quantified and included to determine the total required actuator thrust. It was also found that the transverse force depends very weakly on the severity of cavitation. The experimental results and visual observations provided a more complete understanding of the behaviour and significance of cavitation with respect to the flow-induced forces. CFD simulations provide insights into the resulting flow field allowing for a greater understanding of the relationship between the valve differential pressure and the flow-induced forces. CFD predictions were generally in good agreement with experimental results.

The paper discusses a system for the measurement and calibration of nanonewton forces and force vs. deformation curves of micro force sensors such as AFM Cantilevers. The system bases on an electromagnetic compensated microbalance whereas its control loop was modified to generate and measure the force at the same time without the need of an additional actuator. Thus, the concept is similar to the NIST Electrostatic Force Balance where the force is generated and measured based on a capacitor. To probe the micro force sensor under calibration, the balance pan is moved by feeding a defined current through the balance internal coil. Thereby the current is proportional to the acting force which was calibrated with milligram mass artifacts before. The movement of the balance pan as well as the position of the micro force sensor under test is measured with a special triple beam interferometer. Hence, the calibration of forces and force vs. deformation curves is traceable to the SI units mass and length. To compare our concept of force generation to the concept of PTB and KRISS an additional piezo actuator was integrated in the setup. Thus, we can alternatively push the micro force sensor under test onto the balance pan using the piezo. Measurement and calibration results will be presented and discussed. A standard deviation of < 1 nN is achieved for the measurement of constant forces. The stiffness (force vs. deformation curve) of a contact mode AFM cantilever was calibrated to be 0.26 N/m with a repeatability of 0.25 %. Thereby linearity deviations of < 1 nN were observed for this measurement. Due to the uncertainty of the contact parameters (contact angle and position as well as friction) between the AFM tip and the stylus mounted on the balance pan the combined uncertainty of the calibration is in the range 3 %.

The underlying similarity between soils, grains, fertilizers, concentrated animal feed, pellets, and mixtures is that they are all granular materials used in agriculture. Modeling such materials is a complex process due to the spatial variability of such media, the origin of the material (natural or biological), the nonlinearity of these materials, the contact phenomenon and flow that occur at the interface zone and between these granular materials, as well as the dynamic effect of the interaction process. The lack of a tool for studying such materials has limited the understanding of the phenomena relevant to them, which in turn has led to energy loss and poor quality products. The objective of this study was to develop a reliable prediction simulation tool for cohesive agricultural particle materials using Discrete Element Modeling (DEM). The specific objectives of this study were (1) to develop and verify a 3D cohesionless agricultural soil-tillage tool interaction model that enables the prediction of displacement and flow in the soil media, as well as forces acting on various tillage tools, using the discrete element method; (2) to develop a micro model for the DEM formulation by creating a cohesive contact model based on liquid bridge forces for various agriculture materials; (3) to extend the model to include both plastic and cohesive behavior of various materials, such as grain and soil structures (e.g., compaction level), textures (e.g., clay, loam, several grains), and moisture contents; (4) to develop a method to obtain the parameters for the cohesion contact model to represent specific materials. A DEM model was developed that can represent both plastic and cohesive behavior of soil. Soil cohesive behavior was achieved by considering tensile force between elements. The developed DEM model well represented the effect of wedge shape on soil behavior and reaction force. Laboratory test results showed that wedge penetration resistance in highly compacted soil was two times greater than that in low compacted soil, whereas DEM simulation with parameters obtained from the test of low compacted soil could not simply be extended to that of high compacted soil. The modified model took into account soil failure strength that could be changed with soil compaction. A three dimensional representation composed of normal displacement, shear failure strength and tensile failure strength was proposed to design mechanical properties between elements. The model based on the liquid bridge theory. An inter particle tension force measurement tool was developed and calibrated A comprehensive study of the parameters of the contact model for the DEM taking into account the cohesive/water-bridge was performed on various agricultural grains using this measurement tool. The modified DEM model was compared and validated against the test results. With the newly developed model and procedure for determination of DEM parameters, we could reproduce the high compacted soil behavior and reaction forces both qualitatively and quantitatively for the soil conditions and wedge shapes used in this study. Moreover, the effect of wedge shape on soil behavior and reaction force was well represented with the same parameters. During the research we made use of the commercial PFC3D to analyze soil tillage implements. An investigation was made of three different head drillers. A comparison of three commonly used soil tillage systems was completed, such as moldboard plow, disc plow and chisel plow. It can be concluded that the soil condition after plowing by the specific implement can be predicted by the DEM model. The chisel plow is the most economic tool for increasing soil porosity. The moldboard is the best tool for soil manipulation. It can be concluded that the discrete element simulation can be used as a reliable engineering tool for soil-implement interaction quantitatively and qualitatively.

The Menzingen Verification Experiment described in this report was designed to test practical procedures for verifying the absence of nuclear weapons at a storage site. The experiment, which was conducted on 8 March 2023, was organized by UNIDIR in partnership with the Swiss Armed Forces, Spiez Laboratory, Princeton University’s Program on Science and Global Security, and the Open Nuclear Network. The project was supported by the Governments of the Kingdom of the Netherlands, Norway, and Switzerland. The experiment modelled an on-site inspection of a nuclear weapons storage site, represented by a former air defence site near Menzingen, Switzerland. In preparation for the experiment, UNIDIR developed a model protocol governing the inspection activities. Together with its partners, it designed procedures to confirm the non-nuclear nature of the inspected items, including radiation measurements with active sources, and arranged for the acquisition of satellite imagery of the site. The scenario developed for the experiment assumed that the inspection was conducted as part of an agreement that requires the parties to remove all nuclear weapons from storage sites associated with military bases that host nuclear-capable delivery systems. The inspection procedures used in the experiment were modelled on those developed for the Conventional Forces in Europe Treaty and New START. The Menzingen Verification Experiment demonstrated in practice the viability of the approach to nuclear disarmament based on removing nuclear weapons from their delivery systems. It provided an opportunity to test in practice specific verification procedures and techniques, provided valuable insights into the challenges that can be encountered during an on-site inspection, and identified promising new approaches to verification that can create political space for arms control and disarmament initiatives.