Solar Tracking Using Linear Actuator

Solar trackers make solar panels perpendicular to solar ray to enhance solar power reaping. The relative motion between Sun and Earth has two degrees of freedom. Sun travels from east to west during daytime and also moves north and south due to Earth’s tilt. However, Sun’s daily north-south move is much smaller than its east-west move. Sensor-based solar trackers make solar panels perpendicular to solar ray based on sensor information. Although the existing sensor-based solar trackers increase solar power reaping from solar panels significantly, they also consume considerable power by driving solar trackers. Sensorless solar trackers make solar panels perpendicular to solar ray based on calculated solar location. The performance of sensorless solar trackers is not affected by bad weather. This paper is on sensorless solar trackers. Single-axis solar trackers have one degree of freedom solar tracking motion. They can catch Sun’s daily east-west movement effectively. The Sun’s small north-south movement can be covered for single-axis solar trackers by monthly or seasonal adjustment of their orientations. This research is focused on single-axis sensorless solar trackers that are driven by linear actuators. The advantages of linear actuator driven solar trackers are their self-locking function and high load carrying capacity. Their challenges include limited solar panel motion range, potential interference between an oscillating solar panel and its fixed supporting ground link, and high motor power consumption for solar tracking. The research of this paper is motivated by surmounting the challenges facing sensorless single-axis linear actuator driven solar trackers. In this research, linear actuator driven solar trackers will be designed and analyzed. The models of the designed solar trackers will be developed. The kinematic and dynamic performances of the modeled solar trackers will be analyzed and simulated. The results of this research will provide some guidelines for developing linear actuator driven solar trackers.

Nonlinear Fluid-Elastic Behavior of a Flapping Wing With Low-Order Chord-Wise Flexibility

The present study attempts to capture the fluid-structure interaction dynamics of a chord-wise flexible flapping wing system using a limited mode structural model coupled with a high-fidelity Navier-Stokes (N-S) solver. The wing is modeled as two elliptic rigid foils connected by a non-linear torsional spring that incorporates the chord-wise bending stiffness. The front link is subjected to an active pitching-plunging motion while the rear link undergoes flow-induced passive oscillation. The structural governing equation for the rear link takes the form of a Duffing equation subjected to base excitation and external aerodynamic forcing. The aerodynamic loads on the foil are computed using a discrete forcing Immersed Boundary Method based in-house N-S solver which is coupled with the structural solver by a staggered weak coupling strategy. A bifurcation study is performed considering the free-stream velocity as the control parameter, in the presence of both structural and aerodynamic non-linearities. A dynamical transition in the unsteady flow-field from a periodic reverse-Kármán wake to an aperiodic wake is observed as the flow parameters are varied. The same transition is also reflected in the passive oscillation of the rear foil when analyzed with tools from the dynamical systems theory.

Bearing Housing Design for Vibration Control, Using Tilting Pad Bearings Instead of Lemon-Bore Type on a Gas Turbine

Heavy duty gas turbines are usually equipped with hydrodynamic bearings which are either lemon-bore or tilting pad type. Baker Hughes legacy gas turbines use these two types of bearings, and its selection is based on 1) considering pros & cons from Rotor dynamics, 2) bearing performance, 3) bearing housing stiffness, 4) vibration detection & control. Non-contact probes are used to monitor the vibrations of rotor. Majority of legacy gas turbines are not equipped with these probes. Due to this fact, over the years it resulted in non-detection of dynamics & vibration issue, which caused frequent bearing replacement. As the increase in industry demand to apply and measure vibrations using non-contact probes on bearings, an effort was made by Baker Hughes to implement these on existing fleet units. Also, in order to increase rotor dynamics stability of low-pressure rotor, to improve bearing life and performance, effort was made to replace lemon-bore bearings with tilting pad. This paper demonstrates efforts made to design the titling pad which would fit within envelop of already available bearing housing. Bearing/shaft clearance, bearing performance, modification of bearing retainer clearances are the mandatory tasks which would be dealt in this study. The swap of bearing type, and its effect on whole gas turbine rotor dynamic stability, checking the frequency crossovers with Campbell diagram would also be dealt in this paper. This paper also focuses on assessment on oil passage routing, temperature & proximity probe instrumentation routing design. Re-design is performed by analyzing various configuration, assessing different sensitivity studies & validation of modified bearing housing from structural integrity, ultimate load capability, & split plane oil leakage retention and its comparison with baseline are most important aspects of finalization of this change, which will be showcased in this paper. Instrumentation routing was a critical task when the considering bearing replacement from lemon-bore to tilting pad. As lemon-bore type bearings just have an elliptical inner surface, it’s quite easy to install the thermocouples into a simple hole. But as replacement has tilting pads, the challenge is to instrument the pads without effecting their movement and functionality. Such best practices are also dealt in this paper. Comparison of tilting-pad with lemon-bore, considering the fixed shaft diameter, the retainer outer diameter of tilting pad is higher than lemon-bore. This effect has a change in bearing seat on bearing housing, thereby reducing the effective stiffness of the housing, and the reduced split plane surface. To tackle this situation, several sensitivities were executed, by re-modifying the bolts and bolt holes on the existing housing, without modifying the housing envelop.

Retracted: “Locomotion System Design of an Active Capsule Endoscopy” [ASME 2020 International Mechanical Engineering Congress and Exposition, Volume 7A: Dynamics, Vibration, and Control, Virtual, Online, November 16–19, 2020, Conference Sponsors: ASME, ISBN: 978-0-7918-8454-6, Copyright © 2020 by ASME. Paper No. IMECE2020-23598, V07AT07A012; 6 pages; doi: 10.1115/IMECE2020-23598]

This paper was removed from publication at the author’s request, February 26, 2021. Copyright © 2021 by ASME

Spin Stabilization of an Air Ambulance Litter

This paper proposes a new approach to stabilize the spin of a suspended litter during air ambulance rescue hoist operations. Complex forces generated by the helicopter’s downwash may cause a patient suspended in a rescue litter to spin violently. In severe cases, the spin destabilizes the suspended load, risks injury to the patient, and jeopardizes the safety of the aircrew. The presented design employs an anti-torque device to arrest the spin that is safer and faster than a tagline and is without the tactical constraints of the tagline. The device follows tailored control laws to accelerate a flywheel attached to the litter, thereby generating sufficient angular momentum to counteract the spin and stabilize the suspended litter. An inertial measurement unit (IMU) measures the position, angular velocity, and angular acceleration of the litter and delivers this information to a microcontroller. The research and prototype design were developed under the support of the U.S. Army 160th Special Operations Aviation Regiment (SOAR).

Dynamics of MEMS-Based Angular Rate Sensors Excited via External Electrostatic Forces

This paper investigates the dynamic behavior of rotating MEMS-based vibratory gyroscopes which employs a thin ring as the vibrating flexible element. The mathematical model for the MEMS ring structure as well as a model for the nonlinear electrostatic excitation forces are formulated. Galerkin’s procedure is employed to reduce the equations of motion to a set of ordinary differential equations. Understanding the effects of nonlinear actuator dynamics is considered important for characterizing the dynamic behavior of such devices. A suitable theoretical model to generate nonlinear electrostatic force that acts on the MEMS ring structure is formulated. Dynamic responses in the driving and the sensing directions are examined via time responses, phase diagram, and Poincare’ map plots when the input angular motion and the nonlinear electrostatic force are considered simultaneously. The analysis is envisaged to aid fabrication of this class of devices as well as for providing design improvements in MEMS Ring-based Gyroscopes.

Analysis and Design of an Auxiliary Catching Arm for an Apple Picking Robot

The newly designed 3-dimensional catching robot consists of three revolute joints where the forward linkage is a parallelogram mechanism for keeping the catching end-effector parallel to the picking manipulator’s base. A virtual apple field of 505 apples, designed to test the picking abilities of 7 DOF arm, was used to determine the capabilities of this new catching arm design. The target catching efficiency was 90% for the provided virtual apple field with a maximum drop height of 30 cm. The target coordinates for each virtual apple were found by computer simulation in MATLAB. Geometric parameters were selected such that the catching manipulator could reach every possible drop position in the picking manipulator’s workspace. The design was completed, fabricated, and validated, utilizing the elegant mechanical linkage design. The workspace analysis showed that it had an acceptable 93% catching efficiency, and as the drop height increased, the efficiency approaches 100%. Definitive inverse-kinematics provided exact joint angles required to catch all catchable apples inside of the workspace. Using these angles, the general equation of motion, using Lagrangian mechanics, yielded the required torque outputs of each of the three motors on the arm. Validation of these torques through laboratory experimentation was considered adequate.

Nonlinear Vibrations of Model PWR Fuel Assemblies: Part 2 — Interpretation of Results Using Bilinear Stiffness Model

The experimental response of fuel rods with spacer grids was interpreted using a bilinear hysteresis model. Nonlinear experimental responses of two configurations of rods made out of Zirconium alloy tubes were considered in this paper: one configuration with a single beam and the second configuration with a cluster of beams (stacked in a 3 × 3 matrix formulation). These two configurations were designed to emulate part of the nuclear fuel assembly in Pressurized Water Reactors (PWR). Both configurations were supported by spacer girds at their extremities and were immersed in still water. Spacer grids are grid-like structures made out of thin Zirconium alloy sheets with 17 × 17 cells arranged in a square pattern. Spacer grids provide mechanical support and reduce flow-induced vibration of nuclear fuel rods. They also improve the heat transfer between nuclear fuel rods and the surrounding coolant. The spacer grids impose nonlinear boundary conditions to the beams at the contact points/surface. Specifically, spacer grids present bilinear hysteresis due to their inherent complexity. The bilinear hysteresis shown by spacer grids was measured in terms of force-displacement loops by testing rigid rod inserted in one of its cells. The rigid rod was then excited by external harmonic excitation with excitation frequencies ranging from 5 Hz to 50 Hz in steps of 5 Hz. The bilinear hysteresis model, first studied by Caughey, was modified to include viscous damping and was used to interpret the experimental results. The method of slowly varying parameters was used to solve the equation of motion. First, the measured force-displacement loops of spacer grids were fitted with the numerical model described in the current analysis. Good agreement between the model response and measured loops was found, and the identified parameters allowed the characterization of the nonlinear boundary conditions imposed by spacer grids. Finally, the nonlinear responses of the two configurations under study were interpreted using the bilinear hysteresis model. Excellent agreement between numerical and experimental results was obtained for both configurations.

Capacity Fade Estimation of a Lithium-Ion Battery Through an Integrated Electrochemical Battery Model and Empirical Cycle Aging Model

An electrochemical model based capacity fade estimation method for a Li-Ion battery is investigated in this paper. An empirical capacity fade model for estimating the state of health of a LiFePO4 electric vehicle battery was integrated with electrochemical battery model in Matlab/Simulink platform. This combined model was then validated against experimental data reported in the literature for constant current charge / discharge cycling. An HPPC current profile was then applied to the validated electrochemical-empirical battery prognosis model which reflected a real-time operating condition for charge and discharge current fluctuations in an electric vehicle battery. The combined model was simulated under the two different HPPC current inputs for three different cycle times. Additionally temperature was taken in account in estimating the cycle aging under the applied current profile to assess the present capacity remaining in the battery. The simulation results provided the state of health (SOH) of the battery for these cycling times which were comparable to the published experimental SOH values for constant current charge/discharge profiles. Thus this model can potentially be used to predict the capacity fade status of an electric vehicle battery.

Vibration Suppression of an Elastically Supported Beam With Closely Spaced Natural Frequencies

Vibration suppression of distributed parameter systems is of great interest and has a wide range of applications. The dynamic performance of a primary system can be improved by adding dynamic vibration absorbers (DVA). Although the relevant topics have been studied for decades, the trade-off between capability of suppressing multiple resonant peaks and complexity of absorbers has not been well addressed. In this paper, the vibration suppression problem of a uniform Euler-Bernoulli beam with closely spaced natural frequencies is investigated. To achieve desired vibration reduction, a two-DOF DVA is connected to the beam through a pair of a spring and a dashpot. By introducing a virtual ground spring, the parameters of the absorber are determined via extended fixed point theory. The proposed method only requires univariate optimization and is computationally efficient. Numerical examples conducted verify the viability of the proposed method and the effectiveness of a two-DOF DVA in suppressing double resonances.