Vibration transmission through rolling element bearings in geared rotor system, part 1

A mathematical model is proposed to examine the vibration transmission through rolling element bearings in geared rotor systems. Current bearing models, based on either ideal boundary conditions for the shaft or purely translational stiffness element description, cannot explain how the vibratory motion may be transmitted from the rotating shaft to the casing. This study clarifies this issue qualitatively and quantitatively by developing a comprehensive bearing stiffness matrix of dimension 6 model for the precision rolling element bearings from basic principles. The proposed bearing formulation is extended to analyze the overall geared rotor system dynamics including casing and mounts. The bearing stiffness matrix is included in discrete system models using lumped parameter and/or dynamic finite element techniques. Eigensolution and forced harmonic response due to rotating mass unbalance or kinematic transmission error excitation for a number of examples are computed

Propagation and reflection of pulse waves in flexible tubes and relation to wall properties

This thesis was submitted for the degree of Docter of Philosophy and awarded by Brunel University.The wall properties of the arteries play an important role in cardiovascular function. Stiffness of large artery is predictive of cardiovascular events. To understand the function of the cardiovascular system, special attention should be paid to the understanding of pulse wave propagation, because pulse waves carry information of the cardiovascular function, and provide information which can be useful for the prevention and diagnosis of diseases. This thesis presents a series of in vitro experimental studies of wave propagation, wave reflection and determination of mechanical properties of flexible vessels. In this thesis, several studies have been included: 1) applied and compared foot-to-foot, PU-loop and lnDU-loop methods for determination of wave speed in flexible tubes and calf aortas; 2) investigated the variation of local wave speed determined by PU-loop with proximity to the reflection site; 3) investigated using wave intensity analysis (WIA) as the analytical technique to determine the reflection coefficient; 4) developed a new technique which based on one-point simultaneous measurements of diameter and velocity to determine the mechanical properties of flexible tubes and calf aortas. In the first study, it is found wave speeds determined by PU-loop and lnDU-loop methods are very similar, and smaller than those determined by foot-to-foot method. The timing of arrival time of reflected wave based on diameter and velocity technique highly agreed with the corresponding timing based on pressure and velocity technique. The shapes of forward and backward non-invasive wave intensities based on diameter and velocity are very similar with the corresponding shapes based on pressure and velocity. Although the density term is not part of the equation, the lnDU-loop method for determining local wave speed is sensitive to the fluid density. In the second study, it is found wave speed measured by PU-loop is varied with proximity to the reflection site. The closer the measurement site to the reflection site, the greater the effect upon measured wave speed; a positive reflection caused an increase in measured wave speed; a negative reflection caused a decrease in measured wave speed. Correction iteration process was also considered to correct the affected measured wave speed. In the third study, it is found, reflection coefficient determined by pressure, square roots of wave intensity and wave energy are very close, but they are different from reflection coefficient determined by wave intensity and wave energy. Due to wave dissipation, the closer the measurement site to the reflection site, the greater is the value of the local reflection coefficient. The local reflection coefficient near the reflection site determined by wave intensity and wave energy are very close to the theoretical value of reflection coefficient. In the last study I found that distensibility determined by the new technique which utilising lnDU-loop is in agreement with that determined from the pressure and area which obtained from tensile test in flexible tubes; distensibility determined by the new technique is similar to those determined in the static and dynamic distensibility tests in calf aortas; Young’s modulus determined by the new technique are in agreement with that those determined by tensile tests in both flexible tubes and calf aortas. In conclusion, wave speed determined by PU-loop and lnDU-loop methods are very similar, the new technique lnDU-loop provides an integrated noninvasive system for studying wave propagation; wave speed determined by PU-loop is affected by the reflection, the closer the measurement site to the reflection site, the greater the change in measured wave speed; WIA could be used to determine local reflection coefficient when the measurement site is close to the reflection site; the new technique using measurements of diameter and velocity at one point for determination of mechanical properties of arterial wall could potentially be non-invasive and hence may have advantage in the clinical setting

Compliant aerial manipulation.

The aerial manipulation is a research field which proposes the integration of robotic manipulators in aerial platforms, typically multirotors – widely known as “drones” – or autonomous helicopters. The development of this technology is motivated by the convenience to reduce the time, cost and risk associated to the execution of certain operations or tasks in high altitude areas or difficult access workspaces. Some illustrative application examples are the detection and insulation of leaks in pipe structures in chemical plants, repairing the corrosion in the blades of wind turbines, the maintenance of power lines, or the installation and retrieval of sensor devices in polluted areas. Although nowadays it is possible to find a wide variety of commercial multirotor platforms with payloads from a few gramps up to several kilograms, and flight times around thirty minutes, the development of an aerial manipulator is still a technological challenge due to the strong requirements relative to the design of the manipulator in terms of very low weight, low inertia, dexterity, mechanical robustness and control. The main contribution of this thesis is the design, development and experimental validation of several prototypes of lightweight (<2 kg) and compliant manipulators to be integrated in multirotor platforms, including human-size dual arm systems, compliant joint arms equipped with human-like finger modules for grasping, and long reach aerial manipulators. Since it is expected that the aerial manipulator is capable to execute inspection and maintenance tasks in a similar way a human operator would do, this thesis proposes a bioinspired design approach, trying to replicate the human arm in terms of size, kinematics, mass distribution, and compliance. This last feature is actually one of the key concepts developed and exploited in this work. Introducing a flexible element such as springs or elastomers between the servos and the links extends the capabilities of the manipulator, allowing the estimation and control of the torque/force, the detection of impacts and overloads, or the localization of obstacles by contact. It also improves safety and efficiency of the manipulator, especially during the operation on flight or in grabbing situations, where the impacts and contact forces may damage the manipulator or destabilize the aerial platform. Unlike most industrial manipulators, where force-torque control is possible at control rates above 1 kHz, the servo actuators typically employed in the development of aerial manipulators present important technological limitations: no torque feedback nor control, only position (and in some models, speed) references, low update rates (<100 Hz), and communication delays. However, these devices are still the best solution due to their high torque to weight ratio, low cost, compact design, and easy assembly and integration. In order to cope with these limitations, the compliant joint arms presented here estimate and control the wrenches from the deflection of the spring-lever transmission mechanism introduced in the joints, measured at joint level with encoders or potentiometers, or in the Cartesian space employing vision sensors. Note that in the developed prototypes, the maximum joint deflection is around 25 degrees, which corresponds to a deviation in the position of the end effector around 20 cm for a human-size arm. The capabilities and functionalities of the manipulators have been evaluated in fixed base test-bench firstly, and then in outdoor flight tests, integrating the arms in different commercial hexarotor platforms. Frequency characterization, position/force/impedance control, bimanual grasping, arm teleoperation, payload mass estimation, or contact-based obstacle localization are some of the experiments presented in this thesis that validate the developed prototypes.La manipulación aérea es un campo de investigación que propone la integración de manipuladores robóticos in plataformas aéreas, típicamente multirotores – comúnmente conocidos como “drones” – o helicópteros autónomos. El desarrollo de esta tecnología está motivada por la conveniencia de reducir el tiempo, coste y riesgo asociado a la ejecución de ciertas operaciones o tareas en áreas de gran altura o espacios de trabajo de difícil acceso. Algunos ejemplos ilustrativos de aplicaciones son la detección y aislamiento de fugas en estructura de tuberías en plantas químicas, la reparación de la corrosión en las palas de aerogeneradores, el mantenimiento de líneas eléctricas, o la instalación y recuperación de sensores en zonas contaminadas. Aunque hoy en día es posible encontrar una amplia variedad de plataformas multirotor comerciales con cargas de pago desde unos pocos gramos hasta varios kilogramos, y tiempo de vuelo entorno a treinta minutos, el desarrollo de los manipuladores aéreos es todavía un desafío tecnológico debido a los exigentes requisitos relativos al diseño del manipulador en términos de muy bajo peso, baja inercia, destreza, robustez mecánica y control. La contribución principal de esta tesis es el diseño, desarrollo y validación experimental de varios prototipos de manipuladores de bajo peso (<2 kg) con capacidad de acomodación (“compliant”) para su integración en plataformas aéreas multirotor, incluyendo sistemas bi-brazo de tamaño humano, brazos robóticos de articulaciones flexibles con dedos antropomórficos para agarre, y manipuladores aéreos de largo alcance. Puesto que se prevé que el manipulador aéreo sea capaz de ejecutar tareas de inspección y mantenimiento de forma similar a como lo haría un operador humano, esta tesis propone un enfoque de diseño bio-inspirado, tratando de replicar el brazo humano en cuanto a tamaño, cinemática, distribución de masas y flexibilidad. Esta característica es de hecho uno de los conceptos clave desarrollados y utilizados en este trabajo. Al introducir un elemento elástico como los muelles o elastómeros entre el los actuadores y los enlaces se aumenta las capacidades del manipulador, permitiendo la estimación y control de las fuerzas y pares, la detección de impactos y sobrecargas, o la localización de obstáculos por contacto. Además mejora la seguridad y eficiencia del manipulador, especialmente durante las operaciones en vuelo, donde los impactos y fuerzas de contacto pueden dañar el manipulador o desestabilizar la plataforma aérea. A diferencia de la mayoría de manipuladores industriales, donde el control de fuerzas y pares es posible a tasas por encima de 1 kHz, los servo motores típicamente utilizados en el desarrollo de manipuladores aéreos presentan importantes limitaciones tecnológicas: no hay realimentación ni control de torque, sólo admiten referencias de posición (o bien de velocidad), y presentan retrasos de comunicación. Sin embargo, estos dispositivos son todavía la mejor solución debido al alto ratio de torque a peso, por su bajo peso, diseño compacto y facilidad de ensamblado e integración. Para suplir estas limitaciones, los brazos robóticos flexibles presentados aquí permiten estimar y controlar las fuerzas a partir de la deflexión del mecanismo de muelle-palanca introducido en las articulaciones, medida a nivel articular mediante potenciómetros o codificadores, o en espacio Cartesiano mediante sensores de visión. Tómese como referencia que en los prototipos desarrollados la máxima deflexión articular es de unos 25 grados, lo que corresponde a una desviación de posición en torno a 20 cm en el efector final para un brazo de tamaño humano. Las capacidades y funcionalidades de estos manipuladores se han evaluado en base fija primero, y luego en vuelos en exteriores, integrando los brazos en diferentes plataformas hexartor comerciales. Caracterización frecuencial, control de posición/fuerza/impedancia, agarre bimanual, teleoperación de brazos, estimación de carga, o la localización de obstáculos mediante contacto son algunos de los experimentos presentados en esta tesis para validar los prototipos desarrollados por el auto

Can a continuous mineral foam explain the stiffening of aged bone tissue? A micromechanical approach to mineral fusion in musculoskeletal tissues

Recent experimental data revealed a stiffening of aged cortical bone tissue, which could not be explained by common multiscale elastic material models. We explain this data by incorporating the role of mineral fusion via a new hierarchical modeling approach exploiting the asymptotic (periodic) homogenization (AH) technique for three-dimensional linear elastic composites. We quantify for the first time the stiffening that is obtained by considering a fused mineral structure in a softer matrix in comparison with a composite having non-fused cubic mineral inclusions. We integrate the AH approach in the Eshelby-based hierarchical mineralized turkey leg tendon model (Tiburtius et al 2014 Biomech. Model. Mechanobiol. 13 1003–23), which can be considered as a base for musculoskeletal mineralized tissue modeling. We model the finest scale compartments, i.e. the extrafibrillar space and the mineralized collagen fibril, by replacing the self-consistent scheme with our AH approach. This way, we perform a parametric analysis at increasing mineral volume fraction, by varying the amount of mineral that is fusing in the axial and transverse tissue directions in both compartments. Our effective stiffness results are in good agreement with those reported for aged human radius and support the argument that the axial stiffening in aged bone tissue is caused by the formation of a continuous mineral foam. Moreover, the proposed theoretical and computational approach supports the design of biomimetic materials which require an overall composite stiffening without increasing the amount of the reinforcing material

Computational and experimental time domain, one dimensional models of air wave propagation in human airways

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University.The scientific literature on airflow in the respiratory system is usually associated with rigid ducts. Many studies have been conducted in the frequency domain to assess respiratory system mechanics. Time-domain analyses appear more independent from the hypotheses of periodicity, required by frequency analysis, providing data that are simpler to interpret since features can be easily associated to time. However, the complexity of the bronchial tree makes 3-D simulations too expensive computationally, limiting the analysis to few generations. 1-D modelling in space-time variables has been extensively applied to simulate blood pressure and flow waveforms in arteries, providing a good compromise between accuracy and computational cost. This work represents the first attempt to apply this formulation to study pulse waveforms in the human bronchial tree. Experiments have been carried out, in this work, to validate the model capabilities in modelling pressure and velocity waveforms when air pulses propagate in flexible tubes with different mechanical and geometrical properties. The experiments have shown that the arrival of reflected air waves occurs in correspondence of the theoretical timing once the wave speed is known. Reflected backward compression waves have generated an increase of pressure (P) and decrease of velocity (U) while expansion backward waves have produced a decrease of P and increase of U according to the linear analysis of wave reflections. The experiments have demonstrated also the capabilities of Wave intensity analysis (WIA), an analytical technique used to study wave propagation in cardiovascular system, in separating forward and backward components of pressure and velocity also for the air case. After validating the 1-D modelling in space and time variables, several models for human airways have been considered starting from simplified versions (bifurcation trachea- main bronchi, series of tubes) to more complex systems up to seven generations of bifurcations according to both symmetrical and asymmetrical models. Calculated pressures waveforms in trachea are shown to change accordingly to both peripheral resistance and compliance variations, suggesting a possible non-invasive assessment of peripheral conditions. A favourable comparison with typical pressure and flow waveforms from impulse oscillometry system, which has recently been introduced as a clinical diagnostic technique, is also shown. The results suggested that a deeper investigation of the mechanisms underlying air wave propagation in lungs could be a useful tool to better understand the differences between normal and pathologic conditions and how pathologies may affect the pattern of pressure and velocity waveforms

Human Motor Control and the Design and Control of Backdriveable Actuators for Human-Robot Interaction

The design of the control and hardware systems for a robot intended for interaction with a human user can profit from a critical analysis of the human neuromotor system and human biomechanics. The primary observation to be made about the human control and ``hardware’’ systems is that they work well together, perhaps because they were designed for each other. Despite the limited force production and elasticity of muscle, and despite slow information transmission, the sensorimotor system is adept at an impressive range of motor behaviors. In this thesis I present three explorations on the manners in which the human and hardware systems work together, hoping to inform the design of robots suitable for human-robot interaction. First, I used the serial reaction time (SRT) task with cuing from lights and motorized keys to assess the relative contribution of visual and haptic stimuli to the formation of motor and perceptual memories. Motorized keys were used to deliver brief pulse-like displacements to the resting fingers, with the expectation that the proximity and similarity of these cues to the response motor actions (finger-activated key-presses) would strengthen the motor memory trace in particular. Error rate results demonstrate that haptic cues promote motor learning over perceptual learning. The second exploration involves the design of an actuator specialized for human-robot interaction. Like muscle, it features series elasticity and thus displays good backdrivability. The elasticity arises from the use of a compressible fluid while hinged rigid plates are used to convert fluid power into mechanical power. I also propose impedance control with dynamics compensation to further reduce the driving-point impedance. The controller is robust to all kinds of uncertainties. The third exploration involves human control in interaction with the environment. I propose a framework that accommodates delays and does not require an explicit model of the musculoskeletal system and environment. Instead, loads from the biomechanics and coupled environment are estimated using the relationship between the motor command and its responses. Delays inherent in sensory feedback are accommodated by taking the form of the Smith predictor. Agreements between simulation results and empirical movements suggests that the framework is viable.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120675/1/gloryn_1.pd

Development and characterization of the arterial windkessel and its role during left ventricular assist device assistance

Modeling of the cardiovascular system is challenging, but it has the potential to further advance our understanding of normal and pathological conditions. Morphology and function are closely related. The arterial system provides steady blood flow to each organ and damps out wave fluctuations as a consequence of intermittent ventricular ejection. These actions can be approached separately in terms of mathematical relationships between pressure and flow. Lumped parameter models are helpful for the study of the interactions between the heart and the arterial system. The arterial windkessel model still plays a significant role despite its limitations. This review aims to discuss the model and its modifications and derive the fundamental equations by applying electric circuits theory. In addition, its role during left ventricular assist device assistance is explored and discussed in relation to rotary blood pumps

Acoustical characterization and parameter optimization of polymeric noise control materials

The sound transmission loss (STL) characteristics of polymer-based materials are considered. Analytical models that predict, characterize and optimize the STL of polymeric materials, with respect to physical parameters that affect performance, are developed for single layer panel configuration and adapted for layered panel construction with homogenous core. An optimum set of material parameters is selected and translated into practical applications for validation. Sound attenuating thermoplastic materials designed to be used as barrier systems in the automotive and consumer industries have certain acoustical characteristics that vary in function of the stiffness and density of the selected material. The validity and applicability of existing theory is explored, and since STL is influenced by factors such as the surface mass density of the panel\u27s material, a method is modified to improve STL performance and optimize load-bearing attributes. An experimentally derived function is applied to the model for better correlation. In-phase and out-ofphase motion of top and bottom layers are considered. It was found that the layered construction of the coinjection type would exhibit fused planes at the interface and move in-phase. The model for the single layer case is adapted to the layered case where it would behave as a single panel. Primary physical parameters that affect STL are identified and manipulated. Theoretical analysis is linked to the resin\u27s matrix attribute. High STL material with representative characteristics is evaluated versus standard resins. It was found that high STL could be achieved by altering materials\u27 matrix and by integrating design solution in the low frequency range. A suggested numerical approach is described for STL evaluation of simple and complex geometries. In practice, validation on actual vehicle systems proved the adequacy of the acoustical characterization process