Devotions for Lent 2023 Hymns of Lent

This Lent, we will continue reflecting on hymns of faith, namely, some of our most beloved Lenten hymns. 10 such hymns have been chosen to fill the 40(+) days of Lent. Therefore, this devotional, different from previous editions, does not proceed on a weekly basis, but merely flows from one hymn to the next. Also different from previous editions, the devotional reflections are specifically based on the stanzas of the selected hymns. Therefore, each day’s reflection features the text of the hymn stanza, a devotion based on that stanza, a prayer, and then a Scripture passage or passages for further meditation. I pray these reflections may be of edification for you during this Lenten season.https://scholar.csl.edu/osp/1022/thumbnail.jp

Bio-inspired flapper with electromagnetic actuation

The design, construction, and testing of a unique 2.6 gram electromagnetic actuator operated at resonance with the specific application to flapping flight is presented. An initial performance evaluation of a commercially available electromagnetic actuator used for static positioning of control surfaces on toy helicopters paired with a fabricated flapping wing was performed. An alternative wedge shaped electromagnetic actuator fitted with virtual spring magnets was proposed to address the performance issues associated with the commercial actuator. The unique wedge shape of the proposed actuator allows for a maximum stroke amplitude of 120°. without interface through contact by the wing with the sides of the coil. Additional disc magnets attached to the perimeter of the electromagnetic coil were proposed to increase the systems stiffness, adding an energy storage component to the system and creating a virtual spring like effect without the additional of direct mechanical coupling. By selecting the size and quantity of these spring magnets, increases to the stiffness of the system could be manually adjusted increasing the bandwidth of the actuator and allowing for system resonance to be achieved. With the application of a potential difference of alternating polarity across the coil, a driving torque is created by the electromagnetic coil and an opposing counter torque is generated by the displacement of the rotor due to the spring magnets. System resonance could then be achieved by tuning the frequency of the external voltage supply to match that of the primary mode of resonance for the system, resulting in peak amplitudes in the wings stroke dynamics. An analytical model of the system\u27s two degree of freedom dynamics was then derived using a rigid body dynamics, simplified electromagnet relationships based on Maxwells equations, and accepted aerodynamic models for translation and rotational damping of flapping wings. A numerical simulation was then preformed based on these models and used to evaluate the response of the system at multiple voltage frequencies and to gauge the dependency of the coupled system dynamics. A step like response was observed to occur at low voltage frequencies with a steady transition to harmonic motion at higher frequencies near resonance. Simulating a simplified from of the dynamics model, assuming only a single degree of freedom, weak coupling of the systems dynamics near resonance was found by direct comparison of simulated response with the majority of the two degree of freedom model\u27s trajectory and amplitude matching that of simplified model. Independent bench tests preformed on the coil and spring magnets were then used to measure the torque generated for comparison to their derived models. Based on deviation in trends found from this comparison, modifications to the analytical models of the actuator were made to more accurately represent the measured data. Using the simplified model of that actuator dynamics, with modified expressions for the torque generated by the coil and spring magnets, perturbation theory was applied to determine an approximate solution for the maximum stroke of the system operating near resonance finding the amplitude of the stroke dynamics independent of the nonlinear stiffness term. A set of 16 test wings were fabricated for use with the electromagnetic actuator during experimentation. Wing parameters used in to construct these test wings were varied systematically to generate unique wing profiles within the range of parameters of actual biological data. Post fabrication, wing shape parameters were determined using imaging processing software to analyze digital pictures taken of the wings. Compound pendulum experiments then were preformed with the test wing suspended from a fabricated test fixture to determine their period of oscillation resulting from a small perturbation applied to the leading edge. Each test wings center of mass was determined from the intersection of a line along the wing\u27s principle axis and the a reference line defined by balancing the wing on a knife edge. Based on the results of these experiments the moment of inertial for each wing was ascertained and tabulated. Frequency response experiments were conducted on the electromagnetic actuator and wing pair using the entire set of test wings by varying supply voltages and spring configurations. Both course and fine frequency bands of voltage signals were applied to the coil and the response of the wing recorded using a high speed camera to determine the resonance frequency and the maximum stroke amplitude. The results of these test were then compared to the values obtained from approximates solution finding 4.3% error in frequency and 7.2% in amplitude, validating the use of these expressions. With the resonate frequency determined, wing kinematics and mean lift measurements were made for the two best preforming wings operating at resonance, reporting a lift-to-weight ratio of over one at 24V for one of the test wings. (Abstract shortened by UMI.

Principles & Applications of Insect Flight

Insects are the most successful animal on the planet, undergoing evolutionary adaptions in size and the development of flight that have allowed access to vast ecological niches and enabled a means by which to both prey and escape predation. Possessing some of the fastest visual systems on the planet, powerful sets of flight muscles, and mechanosensors tuned to perceive complex environments in high-fidelity, they are capable of performing acrobatic maneuvers at speeds that far exceed that of any engineered system. In turn, stable flight requires the coordinated effort of these highly specialized flight systems while performing activities ranging from evasive flight maneuvers to long-distance seasonal migrations in the presence of adverse flow conditions. As a result, the exceptional flight performance of flying insects has inspired a new class of aerial robots expressly tailored to exploit the unique aerodynamic mechanisms inherent to flapping wings. Over the course of three research studies, I explore new actuation techniques to address limitations in power and scalability of current robot platforms, develop new analytical techniques to aid in the design of insect-inspired robot flapping wings, and investigate attributes of flapping wing aerodynamics that allow insects to overcome the difficulties associated with flight in turbulent flow conditions, in an effort to advance the science of animal locomotion. Recent advancements in the study of insect flight have resulted in bio-inspired robots uniquely suited for the confined flight environments of low Reynolds number flow regimes. Whereas insects employ powerful sets of flight muscles working in conjunction with specialized steering muscles to flap their wings at high frequencies, robot platforms rely on limited sets of mechanically amplified piezoelectric actuators and DC motors mated with gear reductions or linkage systems to generate reciprocating wing motion. As a result, these robotic systems are typically underactuated — with wing rotation induced by inertial and aerodynamic loading — and limited in scale by the efficiency of their actuation method and the electronics required for autonomous flight (e.g., boost converters, microcontrollers, batteries, etc.). Thus, the development of novel actuation techniques addressing the need for scalability and use of low-power components would yield significant advancements to the field of bioinspired robots. As such, a scalable low-power electromagnetic actuator configurable for a range of resonant frequencies was developed. From physics-based models capturing the principles of actuation, improvements to the electromagnetic coil shape and a reconfiguration of components were made to reduce weight and increases overall efficiency. Upon completion of a proof-of-concept prototype, multiple actuators were then integrated into a full-scale robot platform and validated through a series of free flight experiments. Design concepts and modeling techniques established by this study have since been used to develop subsequent platforms utilizing similar forms of actuation, advancing the state-of-art in bio-inspired robotics. With the ability to make instantaneous changes in mid-flight orientation through subtle adjustments in angle-of-attack, the maneuverability of flying insects far exceeds that of any man-made aircraft. Yet, studies on insect flight have concluded that the rotation of insect wings is predominately passive. Coincidentally, bio-inspired flapping wing robots almost universally rely on passive rotational mechanisms to achieve desired angles-of-attack — a compromise between actuator mass and the controllable degrees-of-freedom that results in underactuated flight systems

Data from: Schlieren photography on freely flying hawkmoth

The aerodynamic force on flying insects result from the vortical flow structures that vary both spatially and temporally throughout flight. Due to these complexities and the inherent difficulties in studying flying insects in a natural setting, a complete picture of the vortical flow has been difficult to obtain experimentally. In this paper, Schlieren, a widely used technique for highspeed flow visualization, was adapted to capture the vortex structures around freely flying hawkmoth (Manduca). Flow features such as leading-edge vortex, trailing-edge vortex as well as the full vortex system in the wake was visualized directly. Quantification of the flow from the Schlieren images was then obtained by applying a physics-based optical flow method, extending the potential applications of the method to further studies of flying insects

Flight Characteristics of Flapping Wing Miniature Air Vehicles with Figure-8 Spherical Motion

Hummingbirds and some insects exhibit “Figure-8” flapping motion that allows them to go through a variety of maneuvers including hovering. Understanding the flight characteristics of Figure-8 flapping motion can potentially yield the foundation of flapping wing UAVs that can experience similar maneuverability. In this paper, a mathematical model of the dynamic and aerodynamic forces associated with Figure-8 motion generated by a spherical four bar mechanism is developed. For validation, a FWMAV prototype with the wing attached to a coupler point and driven by a DC servo motor is created for experimental testing. Wind tunnel testing is conducted to determine the coefficients of flight and the effects of dynamic stall. The wing is driven at speeds up to 12.25 Hz with results compared to that of the model. The results indicate good correlation between mathematical model and experimental prototype

Trust: A double-edged sword in combating the COVID-19 pandemic?

We examine the impact of trust in combating the SARS-CoV-2 virus, that can cause COVID-19. Under normal circumstances trust is a crucial component for society to function well, but during a pandemic trust can become a double-edged sword. On the one hand, a high level of trust in society may lead to greater acceptance among citizens for public measures that aim to combat a virus. If people believe that their respective governments implement unbiased and well-informed measures, and people also believe that their fellow citizens will follow these measures, this may lead to a high general compliance in society and less people will be infected. On the other hand, trust may affect people’s perception of risk and hence their behavior. If people believe that most people are trustworthy, they may be less willing to think of everyone else as a potential health threat. If people also trust the government to manage the pandemic in a competent way, their perception of the risks related to the pandemic weaken. Taken together, this may lead people in high trust societies to consider personal protective measures less important, and more people will be infected. The ambiguous effect trust may have on the outcome of a pandemic calls for a closer empirical analysis. Drawing on data from 127 countries we find that the number COVID-19 deaths decrease with trust in government and trust in science, while the number COVID-19 deaths increase with social trust. Implications of these findings for risk communication and management during a pandemic are discussed

Design of Figure-8 Spherical Motion Flapping Wing for Miniature UAV

Hummingbirds and some insects exhibit a “Figure-8” flapping motion, which allows them to undergo variety of maneuvers including hovering. It is therefore desirable to have miniature air vehicle (FWMAV) with this wing motion. This paper presents a design of a flapping-wing for FWMAV that can mimic “Figure-8” motion using a spherical four bar mechanism. In the proposed design, the wing is attached to a coupler point on the mechanism, which is driven by a DC servo motor. A prototype is fabricated to verify that the design objectives are met. Experimental testing was conducted to determine the validity of the design. The results indicate good correlation between model and experimental prototype

Schlieren Setup

Schlieren Setu