Changki Mo - Academia.edu (original) (raw)

Papers by Changki Mo

: The gas turbine-burner engine was first proposed by Professors Liu and Sirignano in 1999. A det... more : The gas turbine-burner engine was first proposed by Professors Liu and Sirignano in 1999. A detail exergic analysis was performed on this engine. A turbofan engine core was used as a study system for this analysis. The first and second principles of thermodynamics were applied to each component of the system. An exergy balance was derived for each component of the system. An exergetic analytic study was performed to each component and the results were compared. Results show the combustor having the highest exergetic value. A comparison of the exergy of the conventional and the turbine-burner engines was completed based on ideal gas and reversible process assumption. Results shows less than 5% increase in the exergetic value of the turbine-burner to the conventional turbine.

Thesis (M.S.)--University of Oklahoma, 1992. Includes bibliographical references (leaves 55-56).

International Journal of Vehicle Autonomous Systems, 2003

Smart Structures and Materials 2006 Smart Structures and Integrated Systems, Mar 16, 2006

This paper presents a study in which clamped unimorph rectangular piezoelectric diaphragms are an... more This paper presents a study in which clamped unimorph rectangular piezoelectric diaphragms are analyzed to determine the importance of electrode patterning. There has been a great deal of interest in getting increased deflection out of smaller piezoelectric devices with lower input power. In previous work, it has been shown that a clamped circular diaphragm can generate much increased deflection in response to an electric loading when the electrode has a "regrouped" pattern. Regrouping refers to the process of segmenting the electrodes into regions that are electrically disconnected so that the corresponding polarity can be set in opposite directions. The rectangular diaphragm actuator is studied in this paper to determine the effects of electrode patterns and the shape of the piezoelectric layer on the actuator's static displacement. From the analytical results, it is shown that regrouping the electrode pattern on a rectangular actuator can increase deflection, and subsequently volumetric displacement, by many times.

Energy Research Journal, 2015

Journal of Engineering Mechanics, 1998

Journal of Vibration and Acoustics, 2011

Journal of Sound and Vibration, 1998

ABSTRACT A mechanistic model of a seat cushion is developed. The work relates the kinematic motio... more ABSTRACT A mechanistic model of a seat cushion is developed. The work relates the kinematic motion of the seat to the geometric and constitutive properties of the cellular foam used in the seat. The model includes the influence of pneumatic damping caused by friction between the gas within the open-celled foam and matrix polymer. A continuous shape function is introduced to characterize the piecewise continuous stress–strain characteristic of flexible open–celled foam. After some simplification, a non-linear dynamic automotive seat cushion model is derived, which relies explicitly on the constitutive properties of polyurethane foams and on the geometry of the seat cushion. Experimental and analytical models of the two automotive seats are compared to verify the model. The comparisons indicate that the new model is able to predict the dynamic performance of an automotive seat cushion with fidelity.

ASME 2011 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, Volume 2, 2011

Proceedings of SPIE - The International Society for Optical Engineering

This paper presents experimental results that demonstrate energy generating performance of circul... more This paper presents experimental results that demonstrate energy generating performance of circular piezoelectric diaphragm harvesters for use in implantable medical devices. The piezoelectric energy generators are designed to transfer internal biomechanical forces into electrical energy that can be stored and used to power other in vivo devices. Such energy harvesters can eliminate complicated procedures for replacement of batteries in active implants by possibly increasing the longevity or capacity of batteries. Experimental results indicated that the PZT circular diaphragm harvesters generated enough power to meet requirements for specific implantable medical devices. It is also found that edge condition, thickness of bonding layer, and a degree of symmetry in fabrication for the unimorph circular diaphragms affect the energy generating performance significantly.

In order to predict the thermomechanical behavior of Shape Memory Polymers (SMPs), a one-dimensio... more In order to predict the thermomechanical behavior of Shape Memory Polymers (SMPs), a one-dimensional rheological thermomechanical constitutive model was adopted and a numerical simulation of this model was developed using a finite element software ABAQUS. The one-dimensional model was selected due to its undemanding material constant requirements which are practical for engineering industrial applications. The model was expanded to a three-dimensional isotropic model and then simulated by means of a user-defined subroutine. The methods of three-dimensional expansion and numerical implementation are presented in this work. Evolution of the internal loads was conducted by making use of the backward difference scheme, which was applied to all quantities within the model, including the material properties. A comparison of the numerical simulation results was carried out with the available experimental data. The Model shows good correlation with experimental results with the capability t...

Volume 1: Development and Characterization of Multifunctional Materials; Modeling, Simulation and Control of Adaptive Systems; Structural Health Monitoring, 2012

ABSTRACT This paper presents the development of a bimorph piezoelectric cymbal energy harvester t... more ABSTRACT This paper presents the development of a bimorph piezoelectric cymbal energy harvester that is particularly useful for extracting energy from the vibrating systems of relatively high compressive load. The bimorph cymbal harvester can be used to charge a capacitor or a battery through the piezoelectric layers fitted within the metal end caps under repeated compression or deformation.In this work, feasibility of a bimorph piezoelectric cymbal harvester in series operation is investigated through theoretical analysis and experimental validation. The bimorph cymbal uses a composite disc of two piezoelectric layers and a steel substrate between metal end caps.Theoretical modeling to quantify the generated energy by using bimorph cymbal design is first conducted. A parametric study is then performed to optimize generated energy with the dominant design parameters influencing energy harvesting performance for the cymbal structure. The parameters such as thickness of the end caps, radius ratio of the apex to the cavity of the end caps, cavity depth, and thickness ratio of the piezoelectric to the steel substrate are considered. Based on the optimized dimension, a cymbal harvester was fabricated and tested to validate analytically predicted open-circuit voltage on a hand jack type test rig.Experimental result indicates that the measured open-circuit voltage from the bimorph cymbal harvester is less than that of analytically predicted. However, it shows that the bimorph piezoelectric cymbal structure is an alternative cymbal design that is useful for harvesting energy from the source of relatively high load.

Smart Structures and Materials 2005: Smart Structures and Integrated Systems, 2005

ABSTRACT This paper presents a study in which clamped unimorph piezoelectric diaphragms are teste... more ABSTRACT This paper presents a study in which clamped unimorph piezoelectric diaphragms are tested to determine the importance of the pattern of the electrodes that supply the driving charge to the actuator. In previous work, it has been shown that such a diaphragm, when used as an energy harvesting device, can generate a much increased charge in response to an applied pressure when the electrode has a "regrouped" pattern. Regrouping refers to the process of segmenting the electrodes into regions that are electrically disconnected and then reconnecting those regions such that some have reversed polarity. The circular diaphragm actuator studied in this paper works somewhat the opposite of an energy harvester. That is, applied charge is used to generate diaphragm deflection as opposed to applied pressure generating charge. Four unimorph diaphragm actuators, with different electrode patterns, were tested in this work. According to analytical and experimental results, it is shown that a factor of seven increase in diaphragm deflection can be obtained with regrouping.

Smart Structures and Materials 2006: Smart Structures and Integrated Systems, 2006

Active and Passive Smart Structures and Integrated Systems 2011, 2011

ABSTRACT Harvesting wasted energy and converting it into electrical energy to use as needed is an... more ABSTRACT Harvesting wasted energy and converting it into electrical energy to use as needed is an emerging technology area. In this work, a new design of a cymbal energy harvester is developed and tested to validate analytical energy generating performance. Cymbal transducers have been demonstrated to be beneficial as energy harvesters for vibrating systems under modest load and frequency. In this paper a new design is adopted using a unimorph circular piezoelectric disc between the metal end caps to deal with higher loads. Simple analysis for the new cymbal design to predict voltage output was first conducted. The new cymbal design, 25.4 mm diameter and 8.2 mm thickness, was then fabricated and tested on the load frame with up to 324 lb load and 1 Hz frequency to measure output voltages. This device could be used in numerous applications for potentially self sustaining sensors or other electronic devices. By changing the structure between the metal end caps of cymbal harvesters the new design could be extended in higher load applications.

2013 1st IEEE Conference on Technologies for Sustainability (SusTech), 2013

ABSTRACT This paper reviews energy harvesting technologies for structural health monitoring appli... more ABSTRACT This paper reviews energy harvesting technologies for structural health monitoring applications. Structural health monitoring (SHM) is the process of damage detection in machinery, aerospace, and civil structures. There is a great deal of interest across a broad section of industries in obtaining technology that can be used to monitor the health of machinery and structures. In particular, the need for autonomous monitoring of structures has been ever-increasing in recent years. Autonomous SHM systems typically include embedded sensors, data acquisition, wireless communication, and energy harvesting systems. Among all of these components, this paper focuses on the energy harvesting technologies. Since low-power sensors and wireless communications are used in most recent SHM systems, a number of researchers have recently investigated techniques to extract energy for such stand-alone, self-powered systems from the local environment. Ambient energy sources could be vibration, thermal gradient, sun, wind, pressure, etc. If the structure has a rich enough loading, then it may be possible to extract the needed power directly from the structure itself. Harvesting energy using piezoelectric materials by converting applied stress to electricity is most common. In a structural health monitoring application, the piezoelectric material would be stressed due to vibrations or direct loading in a structure. Other methods to harvest energy such as electromagnetic, magnetostrictive, or thermoelectric generator is also reviewed. Lastly, an energy harvester with frequency tuning capability is demonstrated.

Smart Materials Research, 2014

Volume 1: 20th Biennial Conference on Mechanical Vibration and Noise, Parts A, B, and C, 2005

A great amount of research has been done to determine whether piezoelectric materials can be used... more A great amount of research has been done to determine whether piezoelectric materials can be used as power generators for a variety of portable and low power consuming devices. Among the possibilities for energy harvesters, the 31-type cantilever piezoelectric benders ...