Yigit Yazicioglu

Acoustic radiation from a fluid-filled, subsurface vascular tube with internal turbulent flow due to a constriction.

The vibration of a thin-walled cylindrical, compliant viscoelastic tube with internal turbulent flow due to an axisymmetric constriction is studied theoretically and experimentally. Vibration of the tube is considered with internal fluid coupling only, and with coupling to internal-flowing fluid and external stagnant fluid or external tissue-like viscoelastic material. The theoretical analysis includes the adaptation of a model for turbulence in the internal fluid and its vibratory excitation of and interaction with the tube wall and surrounding viscoelastic medium. Analytical predictions are compared with experimental measurements conducted on a flow model system using laser Doppler vibrometry to measure tube vibration and the vibration of the surrounding viscoelastic medium. Fluid pressure within the tube was measured with miniature hydrophones. Discrepancies between theory and experiment, as well as the coupled nature of the fluid-structure interaction, are described. This study is relevant to and may lead to further insight into the patency and mechanisms of vascular failure, as well as diagnostic techniques utilizing noninvasive acoustic measurements.

MODELING THE COMPLIANCE OF A VARIABLE STIFFNESS C-SHAPED LEG USING CASTIGLIANO'S THEOREM

This paper discusses the application of Castigliano’s Theorem to a half circular beam intended for use as a shaped, tunable, passively compliant robot leg. We present closed-form equations characterizing the deflection behavior of the beam (whose compliance properties vary along the leg) under appropriate loads. We compare the accuracy of this analytical representation to that of a Pseudo Rigid Body (PRB) approximation in predicting the data obtained by measuring the deflection of a physical half-circular beam under the application of known static loads. We briefly discuss the further application of the new model for solving the dynamic equations of a hexapod robot with a C-shaped leg.Copyright

Task oriented kinematic analysis for a legged robot with half-circular leg morphology

In this paper, we study the kinematics of a legged robot with half-circular leg morphology. In particular, our focus is on the RHex hexapod platform. A new kinematic model for RHex is developed considering the leg shape and its consequences, which was over simplified in the previous models seen in literature. The formulation is an accurate kinematic representation of the robot in the sagittal plane that is based on a four-link mechanism analogy. When only pure rolling motion of the legs are considered, it is found that when front and rear pairs of legs are in contact with the ground, the robot becomes a one degree-offreedom mechanism and position of the middle pair of legs are redundant. The problem is solved in two steps; the first one being the determination of the initial configuration of the leg angular positions which defines the initial value of the variable distance of the front and rear leg and ground contact ponts. After the initial configuration of the system is set, pitch angle of the robot body can be manipulated by controlling one of the leg angular positions and the results are presented on an example case; positioning a body fixed unactuated sensor by controlling robot body pitch angle through the actuation of one of the legs. The results are a good display of the multi-functional aspect of the legs in addition to their use for locomotion.

A fuzzy logic controlled Anti-lock Braking System (ABS) for improved braking performance and directional stability

A simple and effective fuzzy logic controller is designed for an Anti-Lock Braking System (ABS) to improve the braking performance and directional stability of an automobile during braking, and steering-braking manoeuvres on uniform and nonuniform (µ-split) friction surfaces. The system consists of two controllers working in tandem. The first controller works on the longitudinal slip, and the second controller is responsible for the side-slip motion control of the vehicle. The fuzzy logic controller is implemented on a four-wheel nonlinear vehicle model with nonlinear tyre behaviour. Simulations are carried out and comparisons are made using the vehicle model with and without the fuzzy logic controlled ABS to assess controller performance.

A comparative evaluation of adaptive and non-adaptive Sliding Mode, LQR & PID control for platform stabilization

During the uniform locomotion of compliant legged robots and other terrain vehicles, the body of the robot often exhibits complex oscillations which may have a disturbing effect on onboard sensors. For a camera mounted on such a robot, due to perspective projection, the effects of angular disturbances are particularly pronounced as compared to translational disturbances. This paper is motivated by the particular problem of legged robots exhibiting angular body motions and attempts to evaluate the performance of baseline and state-of-the-art controllers for compensating this undesired motion. For this comparative evaluation, a simplified planar camera platform is considered in a Matlab-Simulink based simulation environment but motion disturbances are collected on a physical experimental robot platform. Although the full stabilization problem is in 3D with three independent axes of rotation, we currently consider a planar case on the pitch axis with a kinematic structure very similar to many parallel actuated 3D platforms. We believe that despite the simplified analysis, the presented performance evaluation provides significant insight into the general problem. The work consist of the derivation of the planar platform model followed by the implementation and comparative testing of 4 different controllers, namely Proportional-Integral-Derivative (PID), Linear Quadratic Regulator (LQR), Sliding Mode (SMC) and Adaptive Sliding Mode (ASMC) controllers. Experimental setup, disturbance collection and finally, the controller performance test results are presented and discussed.

A multimode sonic and ultrasonic diagnostic imaging system with application to peripheral vascular characterization

Ultrasound (US) medical imaging technology is enhanced by integrating a simultaneous noninvasive audible frequency measurement of biological sounds that could be indicative of pathology. Measurement of naturally‐occurring biological acoustic phenomena can augment conventional imaging technology by providing unique information about material structure and system function. Sonic phenomena of diagnostic value are associated with a wide range of biological functions, such as breath sounds, bowel sounds, and vascular bruits. The initial focus of this multimode technology was to provide an improved diagnostic tool for common peripheral vascular complications that result in transitional or turbulent blood flow, such as associated with arteriovenous (AV) grafts and stenoses in common carotid and other arteries due to plaque buildup. We review: (1) the development the multimode system by combining a commercial US system with a novel sonic sensor array and associated instrumentation, and (2) the evaluation of its c...

Lagrangian based mathematical modeling and experimental validation of a planar stabilized platform for mobile systems

Typical operating conditions for mobile sensor systems, and in particular mobile robots, exhibit a wide range of mechanical disturbances due their ego-motion. Sensor systems mounted on these mobile platforms often suffer to varying degrees from these disturbances. The quality of acquired data is degraded as a result. For instance, the quality of captured video frames from an onboard camera greatly depends on the angular velocity of the body on which the camera is mounted. Motion blur degradation results if large angular motions are present. In order to compensate for such disturbances, stabilization platforms are used. A common approach is measuring body movements using inertial sensors and attempting their cancellation with actuators and control systems. Design of high performance control systems often requires analytical system models. In this article, a planar stabilization platform is considered, to develop and study its kinematic and simple-to-complex dynamic model. The mathematical derivation of the model is presented with and without neglect of the actuator mass components as well as friction effects. This is followed by the comparative validation of these model alternatives against a realistic numerical model fitted to physical experimental data. The results demonstrate that the analytical model, in particular with the actuator mass and friction components included, provides a high degree of fit to the actual behavior.

Effects of Aircraft Aeroelastic Deformations on External Store Separation Dynamics

Store separation analyses are carried out in order to estimate the safe separation envelope for external stores carried on military aircrafts by varying the flight/ejection conditions. Typical separation analysis considers either only the store motion beyond the end-of-stroke (EoS), or solves the EoS conditions with predefined ejection forcing that are assumed to be unaltered with respect to flight/ejection conditions. There exists a gap in the literature in modeling the EoS conditions and precise ejection loads. Data from ground and flight tests show that, dynamic responses of a store differ beyond acceptable limits where aerodynamics and aircraft elasticity are the two main sources of this miscorrelation. In order to have a reliable mathematical model that modifies the ground test data to have a reasonable correlation with the real ejection case, not only ejector and store dynamics but also store aerodynamics, aircraft aerodynamics, aircraft rigid body dynamics, aircraft elasticity should be considered. To show the effects of aircraft deformation on the EoS store conditions, first of all, a methodology that can be used to estimate the ejection loads and EoS conditions of the store more precisely is presented. For the purpose of visualizing the aeroelastic effects on store ejection dynamics, various virtual test cases are handled by changing wing torsional stiffness values and store mounting station positions along aircraft longitudinal axis. The acceleration responses of the store, obtained with and without the inclusion of aeroelastic effects, are used to emphasize the effects of aeroelasticity on ejection.Copyright

Modeling of aircraft effects on external store ejection

Modern fighter aircraft, together with their interceptor roles, are utilized as aerial bomb and long-/short-range missile carriers. Separation of those external stores from aircraft is still a challenge where the external store has to clear the carrier aircraft following the ejection process. Aircraft and store aerodynamics coupled with their individual flight conditions may result in an unsafe ejection where the store may interfere with the carrier aircraft instead of a clear separation. Store ejection is the initial phase of the launching process, which dominates the separation of the store by generating the initial conditions. Any error introduced to the store separation analysis during this phase will propagate to the complete trajectory solution, which is used for determining whether the store separation is safe or not. The objective of this paper is to present a computational methodology that includes not only the store aerodynamics but also the interactions of the store with aircraft rigid body motions and deformations, together with ejector dynamics. In this study, store aerodynamics, aircraft aerodynamics, aircraft aeroelasticity, and pylon elasticity are used to characterize the ejector dynamics for determining the ejection end-of-stroke parameters.

Flow-induced vibration analysis of constricted artery models with surrounding soft tissue

Arterial stenosis is a vascular pathology which leads to serious cardiovascular diseases. Blood flow through a constriction generates sound and vibration due to fluctuating turbulent pressures. Generated vibro-acoustic waves propagate through surrounding soft tissues and reach the skin surface and may provide valuable insight for noninvasive diagnostic purposes. Motivated by the aforementioned phenomena, vibration of constricted arteries is investigated employing computational models. The flow-induced pressure field in an artery is modeled as broadband harmonic pressure loading based on previous studies in the literature and applied on the inner artery wall. Harmonic analysis is performed for determining radial velocity responses on the outer surface of the models. Results indicate that stenosis severities higher than 70% lead to significant increase in response amplitudes, especially at high frequencies between 250 and 600 Hz. The findings agree well with experimental and theoretical results in the literature considering bending mode frequencies, amplitude scales, and mainly excited frequency ranges. It is seen that artery vibration is sensitive to the phase behavior of pressure loading but its effect becomes less significant with the presence of surrounding tissue. As the surrounding tissue thickness increases, radial velocity response amplitudes decrease but the effect of changes in tissue elastic modulus is more pronounced.