We study the problem of dynamically controlling the shape of a cable that is fixed at one end and attached to an actuated robot at another end. This problem is relevant to unmanned aerial vehicles (UAVs) tethered to a...We study the problem of dynamically controlling the shape of a cable that is fixed at one end and attached to an actuated robot at another end. This problem is relevant to unmanned aerial vehicles (UAVs) tethered to a base. While rotorcrafts, such as quadcopters, are agile and versatile in their applications and have been widely used in scientific, industrial and military applications, one of the biggest challenges with such UAVs is their limited battery life that make the flight time for a typical UAVs limited to twenty to thirty minutes for most practical purposes. A solution to this problem lies in the use of cables that tether the UAV to a power outlet for constant power supply. However, the cable needs to be controlled effectively in order to avoid obstacles or other UAVs. In this paper, we develop methods for controlling the shape of a cable using actuation at one end. We propose a discrete model for the spatial cable and derive the equations governing the cable dynamics for both force controlled system and position controlled system. We design a controller to control the shape of the cable to attain the desired shape and perform simulations under different conditions. Finally, we propose a quasi-static model for the spatial cable and discuss the stability of this system and the proposed controller.展开更多
A systematic, accurate and robust evaluating method for fine pitch printed circuit board (PCB) positioning assessment in testing fixture is developed. Targeting reliability of bed-of-nails tester is successfully eva...A systematic, accurate and robust evaluating method for fine pitch printed circuit board (PCB) positioning assessment in testing fixture is developed. Targeting reliability of bed-of-nails tester is successfully evaluated by the 2D pattern transform. Probe offset vector with its Weibull and Gaussian distribution estimates are obtained for further investigation about the causes of misalignment on the basis of a batch tests for same kind of PCBs.展开更多
The damage properties of Focused Ion Beam(FIB) milling Si3N4 thin film are investigated by the detailed analyzing images of nanoholes and simulation of Monte Carlo. The damage depth in the Si3N4 thin film for two diff...The damage properties of Focused Ion Beam(FIB) milling Si3N4 thin film are investigated by the detailed analyzing images of nanoholes and simulation of Monte Carlo. The damage depth in the Si3N4 thin film for two different ion species(Gallium and Arsenic) under various parameters(ion energy, angle of incidence) are investigated by Monte Carlo method. The simulations show the damage depth increases with the increasing ion energy, the damage depth is dependent on the angle of incident ion, the curves of the damage depth for Ga ion and As ion at 30 keV nearly superpose, while the damage depth for Ga with 90 keV ion is more than that for As ion with the same energy.展开更多
Vibration issues of a five-stand tandem cold rolling mill were found in the steel production practice,and the experimental observation and numerical analysis indicated that the vibrations were related to the back-up r...Vibration issues of a five-stand tandem cold rolling mill were found in the steel production practice,and the experimental observation and numerical analysis indicated that the vibrations were related to the back-up roll bearing.The results were validated by replacing the back-up roll bearing with the new bearing resulting in 30%decline in vibration amplitude.Models describing the four-row cylindrical roller bearing and the vertical system of the cold rolling mill including the bearing were established.Moreover,the mechanisms of periodic excitation and amplified vibrations of fault-free bearing were explained theoretically,along with the analysis of bifurcation behaviors of the motion states of the roller bearing and rolling mill system.It is found that the energy transmitted between vibrations with different frequencies if multiple excitation frequencies in the rolling mill system were close.展开更多
An overview is provided of CFDShip-Iowa modeling, numerical methods and high performance computing (HPC), including both current V4.5 and V5.5 and next generation V6. Examples for naval architecture highlight capabi...An overview is provided of CFDShip-Iowa modeling, numerical methods and high performance computing (HPC), including both current V4.5 and V5.5 and next generation V6. Examples for naval architecture highlight capability and needs. High fidelity V6 simulations for ocean engineering and fundamental physics describe increased resolution for analysis of physics of fluids. Uncertainty quantification research is overviewed as the first step towards development stochastic optimization.展开更多
Zinc is generally considered to be one of the most promising materials to be used in biodegradable implants,and many zinc alloys have been optimized to improve implant biocompatibility,degradation,and mechanical prope...Zinc is generally considered to be one of the most promising materials to be used in biodegradable implants,and many zinc alloys have been optimized to improve implant biocompatibility,degradation,and mechanical properties.However,long-term degradation leads to the prolonged presence of degradation products,which risks foreign body reactions.Herein,we investigated the in vivo biocompatibility and degradation of a biodegradable Zn-Mg-Fe alloy osteosynthesis system in the frontal bone,mandible,and femur in beagles for 1 year.Results of the routine blood,biochemical,trace element,and histological analyses of multiple organs,peripheral blood CD4/CD8a levels,and serum interleukin 2 and 4 levels showed good biocompatibility of the Zn-Mg-Fe alloy.Zinc content analysis revealed zinc accumulation in adjacent bone tissue,but not in the liver,kidney,and spleen,which was related to the degradation of the Zn-Mg-Fe alloy.The alloy demonstrated a uniform slowing degradation rate in vivo.No degradation differences in the frontal bone,mandible,and femur were observed.The degradation products included zinc oxide[ZnO],zinc hydroxide[Zn(OH)_(2)],hydrozincite[Zn_(5)(OH)_(6)(CO_(3))_(2)],and hopeite[Zn_(3)(PO_(4))_(2)⋅4H_(2)O].The good biocompatibility and degradation properties of the Zn-Mg-Fe alloy render it a very attractive osteosynthesis system for clinical applications.展开更多
Over 200,000 Americans have peripheral nerve injuries annually that result in a loss of function and a compromised quality of life.Of these,a significant percent involves unsuccessful repair of peripheral nerve gaps t...Over 200,000 Americans have peripheral nerve injuries annually that result in a loss of function and a compromised quality of life.Of these,a significant percent involves unsuccessful repair of peripheral nerve gaps that occur due to traumatic limb injury or collateral damage to peripheral nerves during tumor resection.展开更多
We briefly summarized how to design and fabricate an insect-mimicking flapping-wing system and demonstrate how to implement inherent pitching stability for stable vertical takeoff. The effect of relative locations of ...We briefly summarized how to design and fabricate an insect-mimicking flapping-wing system and demonstrate how to implement inherent pitching stability for stable vertical takeoff. The effect of relative locations of the Center of Gravity (CG) and the mean Aerodynamic Center (AC) on vertical flight was theoretically examined through static force balance considera- tion. We conducted a series of vertical takeoff tests in which the location of the mean AC was determined using an unsteady Blade Element Theory (BET) previously developed by the authors. Sequential images were captured during the takeoff tests using a high-speed camera. The results demonstrated that inherent pitching stability for vertical takeoff can be achieved by controlling the relative position between the CG and the mean AC of the flapping system.展开更多
In recent decades, the take-off mechanisms of flying animals have received much attention in insect flight initiation. Most of previous works have focused on the jumping mechanism, which is the most common take-off me...In recent decades, the take-off mechanisms of flying animals have received much attention in insect flight initiation. Most of previous works have focused on the jumping mechanism, which is the most common take-off mechanism found in flying animals. Here, we presented that the rhinoceros beetle, Trypoxylus dichotomus, takes offwithout jumping. In this study, we used 3-Dimensional (3D) high-speed video techniques to quantitatively analyze the wings and body kinematics during the initiation periods of flight. The details of the flapping angle, angle of attack of the wings and the roll, pitch and yaw angles of the body were investigated to understand the mechanism of take-off in T. dichotomus. The beetle took off gradually with a small velocity and small acceleration. The body kinematic analyses showed that the beetle exhibited stable take-off. To generate high lift force, the beetle modulated its hind wing to control the angle of attack; the angle of attack was large during the upstroke and small during the downstroke. The legs of beetle did not contract and strongly release like other insects. The hind wing could be con- sidered as a main source of lift for heavy beetle.展开更多
An emerging chalcogenide perovskite,CaZrSe_(3),holds promise for energy conversion applications given its notable optical and electrical properties.However,knowledge of its thermal properties is extremely important,e....An emerging chalcogenide perovskite,CaZrSe_(3),holds promise for energy conversion applications given its notable optical and electrical properties.However,knowledge of its thermal properties is extremely important,e.g.for potential thermoelectric applications,and has not been previously reported in detail.In this work,we examine and explain the lattice thermal transport mechanisms in CaZrSe_(3) using density functional theory and Boltzmann transport calculations.We find the mean relaxation time to be extremely short corroborating an enhanced phonon-phonon scattering that annihilates phonon modes,and lowers thermal conductivity.In addition,strong anharmonicity in the perovskite crystal represented by the Grüneisen parameter predictions.展开更多
Magnetic microswimmers are useful for navigating and performing tasks at small scales. To demonstrate effective control over such microswimmers, we implemented feedback control of the three-bead achiral microswimmers ...Magnetic microswimmers are useful for navigating and performing tasks at small scales. To demonstrate effective control over such microswimmers, we implemented feedback control of the three-bead achiral microswimmers in both simulation and experiment. The achiral microswimmers with the ability to swim in bulk fluid are controlled wirelessly using magnetic fields generated from electromagnetic coils. The achirality of the microswimmers introduces unknown handedness resulting in uncertainty in swimming direction. We use a combination of rotating and static magnetic fields generated from an approximate Helmholtz coil system to overcome such uncertainty. There are also movement uncertainties due to environmental factors such as unsteady flow conditions. A kinematic model based feedback controller was created based on data fitting of experimental data. However, the controller was unable to yield satisfactory performance due to uncertainties from environmental factors; i.e., the time to reach target pose under adverse flow condition is too long. Following the implementation of an integral controller to control the microswimmers' swimming velocity, the mieroswimmers were able to reach the target in roughly half the time. Through simulation and experiments, we show that the feedback control law can move an achiral microswimmer from any initial conditions to a target pose.展开更多
A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO_(2) turbine expansion electric power generation system was proposed in this paper.Assisted by this integrat...A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO_(2) turbine expansion electric power generation system was proposed in this paper.Assisted by this integrated model,thermo-economic and optimization analyses for the key design parameters of the whole system including the geothermal well pattern and operational conditions were performed to obtain a minimal levelized cost of electricity(LCOE).Specifically,in geothermal heat extraction simulation,an integrated wellbore-reservoir system model(T2Well/ECO_(2)N)was used to generate a database for creating a fast,predictive,and compatible geothermal heat mining model by employing a response surface methodology.A parametric study was conducted to demonstrate the impact of turbine discharge pressure,injection and production well distance,CO_(2) injection flowrate,CO_(2) injection temperature,and monitored production well bottom pressure on LCOE,system thermal efficiency,and capital cost.It was found that for a 100 MWe power plant,a minimal LCOE of$0.177/kWh was achieved for a 20-year steady operation without considering CO_(2) sequestration credit.In addition,when CO_(2) sequestration credit is$1.00/t,an LCOE breakeven point compared to a conventional geothermal power plant is achieved and a breakpoint for generating electric power generation at no cost was achieved for a sequestration credit of $2.05/t.展开更多
Three-dimensional(3D)bioprinting has emerged as a promising approach for engineering functional tissues and organs by layer-by-layer precise positioning of biological materials,living cells,and biochemical components....Three-dimensional(3D)bioprinting has emerged as a promising approach for engineering functional tissues and organs by layer-by-layer precise positioning of biological materials,living cells,and biochemical components.Compared with nonbiological printing,3D bioprinting involves additional complexities and technical challenges owing to the processing of living cells,such as the appropriate biomaterials that fulfill the requirements for both printability and functionality.In this review,we first introduce the development course of 3D bioprinting,highlighting innovative forms of living building blocks and advances in enabling techniques of 3D bioprinting.We then summarize the state-of-the-art advancements in 3D bioprinting for biomedical applications,including macroscale tissue or organ bioprinting,disease modeling,microphysiological systems,biobots,and bioprinting in space.Despite the rapid development of 3D bioprinting over the past decades,most 3D bioprinted tissue or organ constructs are still far from being suitable for clinical translation,and it is necessary for the field of bioprinting to shift its focus from shape mimicking towards functionality development.Therefore,we provide our perspectives on this burgeoning field with an emphasis on functional maturation post printing and translational applications at the bedside.展开更多
文摘We study the problem of dynamically controlling the shape of a cable that is fixed at one end and attached to an actuated robot at another end. This problem is relevant to unmanned aerial vehicles (UAVs) tethered to a base. While rotorcrafts, such as quadcopters, are agile and versatile in their applications and have been widely used in scientific, industrial and military applications, one of the biggest challenges with such UAVs is their limited battery life that make the flight time for a typical UAVs limited to twenty to thirty minutes for most practical purposes. A solution to this problem lies in the use of cables that tether the UAV to a power outlet for constant power supply. However, the cable needs to be controlled effectively in order to avoid obstacles or other UAVs. In this paper, we develop methods for controlling the shape of a cable using actuation at one end. We propose a discrete model for the spatial cable and derive the equations governing the cable dynamics for both force controlled system and position controlled system. We design a controller to control the shape of the cable to attain the desired shape and perform simulations under different conditions. Finally, we propose a quasi-static model for the spatial cable and discuss the stability of this system and the proposed controller.
基金This project is supported by US Pennsylvania Dept. of Community & Economic Development(No.20-906-0015)National Natural Science Foundation of China(No.50390064, No.50575230)National Basic Research Program of China(973 Program, No.2003CB716202).
文摘A systematic, accurate and robust evaluating method for fine pitch printed circuit board (PCB) positioning assessment in testing fixture is developed. Targeting reliability of bed-of-nails tester is successfully evaluated by the 2D pattern transform. Probe offset vector with its Weibull and Gaussian distribution estimates are obtained for further investigation about the causes of misalignment on the basis of a batch tests for same kind of PCBs.
基金Science Foundation of Yunnan Province , China(2004A00229 M)
文摘The damage properties of Focused Ion Beam(FIB) milling Si3N4 thin film are investigated by the detailed analyzing images of nanoholes and simulation of Monte Carlo. The damage depth in the Si3N4 thin film for two different ion species(Gallium and Arsenic) under various parameters(ion energy, angle of incidence) are investigated by Monte Carlo method. The simulations show the damage depth increases with the increasing ion energy, the damage depth is dependent on the angle of incident ion, the curves of the damage depth for Ga ion and As ion at 30 keV nearly superpose, while the damage depth for Ga with 90 keV ion is more than that for As ion with the same energy.
文摘Vibration issues of a five-stand tandem cold rolling mill were found in the steel production practice,and the experimental observation and numerical analysis indicated that the vibrations were related to the back-up roll bearing.The results were validated by replacing the back-up roll bearing with the new bearing resulting in 30%decline in vibration amplitude.Models describing the four-row cylindrical roller bearing and the vertical system of the cold rolling mill including the bearing were established.Moreover,the mechanisms of periodic excitation and amplified vibrations of fault-free bearing were explained theoretically,along with the analysis of bifurcation behaviors of the motion states of the roller bearing and rolling mill system.It is found that the energy transmitted between vibrations with different frequencies if multiple excitation frequencies in the rolling mill system were close.
基金supported by research Grants from the Office of Naval Research (ONR), with Dr. Patrick Purtell, Dr. Ki-Han Kim, Dr. Thomas Fu, Ms. Kelly Cooper, Dr. Roshdy Barsoum, and Dr. Robert Brizzolara as the program managers
文摘An overview is provided of CFDShip-Iowa modeling, numerical methods and high performance computing (HPC), including both current V4.5 and V5.5 and next generation V6. Examples for naval architecture highlight capability and needs. High fidelity V6 simulations for ocean engineering and fundamental physics describe increased resolution for analysis of physics of fluids. Uncertainty quantification research is overviewed as the first step towards development stochastic optimization.
基金This work was supported by Science and Technology Development Fund[grant number 2020JZ005]National Key R&D Program of China[grant number 2018YFB1107100]and Research project of National Key Laboratory[grant number 2018ZA04].
文摘Zinc is generally considered to be one of the most promising materials to be used in biodegradable implants,and many zinc alloys have been optimized to improve implant biocompatibility,degradation,and mechanical properties.However,long-term degradation leads to the prolonged presence of degradation products,which risks foreign body reactions.Herein,we investigated the in vivo biocompatibility and degradation of a biodegradable Zn-Mg-Fe alloy osteosynthesis system in the frontal bone,mandible,and femur in beagles for 1 year.Results of the routine blood,biochemical,trace element,and histological analyses of multiple organs,peripheral blood CD4/CD8a levels,and serum interleukin 2 and 4 levels showed good biocompatibility of the Zn-Mg-Fe alloy.Zinc content analysis revealed zinc accumulation in adjacent bone tissue,but not in the liver,kidney,and spleen,which was related to the degradation of the Zn-Mg-Fe alloy.The alloy demonstrated a uniform slowing degradation rate in vivo.No degradation differences in the frontal bone,mandible,and femur were observed.The degradation products included zinc oxide[ZnO],zinc hydroxide[Zn(OH)_(2)],hydrozincite[Zn_(5)(OH)_(6)(CO_(3))_(2)],and hopeite[Zn_(3)(PO_(4))_(2)⋅4H_(2)O].The good biocompatibility and degradation properties of the Zn-Mg-Fe alloy render it a very attractive osteosynthesis system for clinical applications.
文摘Over 200,000 Americans have peripheral nerve injuries annually that result in a loss of function and a compromised quality of life.Of these,a significant percent involves unsuccessful repair of peripheral nerve gaps that occur due to traumatic limb injury or collateral damage to peripheral nerves during tumor resection.
基金Basic Science Research Program through the National Research Foundation of Korea (NRF),The Ministry of Education,Science and Technology,The New & Renewable Energy R&D program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP),The Korea government Ministry of Knowledge Economy,M.J.Kim appreciates the financial support from National Science Foundation
文摘We briefly summarized how to design and fabricate an insect-mimicking flapping-wing system and demonstrate how to implement inherent pitching stability for stable vertical takeoff. The effect of relative locations of the Center of Gravity (CG) and the mean Aerodynamic Center (AC) on vertical flight was theoretically examined through static force balance considera- tion. We conducted a series of vertical takeoff tests in which the location of the mean AC was determined using an unsteady Blade Element Theory (BET) previously developed by the authors. Sequential images were captured during the takeoff tests using a high-speed camera. The results demonstrated that inherent pitching stability for vertical takeoff can be achieved by controlling the relative position between the CG and the mean AC of the flapping system.
文摘In recent decades, the take-off mechanisms of flying animals have received much attention in insect flight initiation. Most of previous works have focused on the jumping mechanism, which is the most common take-off mechanism found in flying animals. Here, we presented that the rhinoceros beetle, Trypoxylus dichotomus, takes offwithout jumping. In this study, we used 3-Dimensional (3D) high-speed video techniques to quantitatively analyze the wings and body kinematics during the initiation periods of flight. The details of the flapping angle, angle of attack of the wings and the roll, pitch and yaw angles of the body were investigated to understand the mechanism of take-off in T. dichotomus. The beetle took off gradually with a small velocity and small acceleration. The body kinematic analyses showed that the beetle exhibited stable take-off. To generate high lift force, the beetle modulated its hind wing to control the angle of attack; the angle of attack was large during the upstroke and small during the downstroke. The legs of beetle did not contract and strongly release like other insects. The hind wing could be con- sidered as a main source of lift for heavy beetle.
基金The work was supported,in part,by the National Science Foundation(NSF)through award CMMI-1753770.
文摘An emerging chalcogenide perovskite,CaZrSe_(3),holds promise for energy conversion applications given its notable optical and electrical properties.However,knowledge of its thermal properties is extremely important,e.g.for potential thermoelectric applications,and has not been previously reported in detail.In this work,we examine and explain the lattice thermal transport mechanisms in CaZrSe_(3) using density functional theory and Boltzmann transport calculations.We find the mean relaxation time to be extremely short corroborating an enhanced phonon-phonon scattering that annihilates phonon modes,and lowers thermal conductivity.In addition,strong anharmonicity in the perovskite crystal represented by the Grüneisen parameter predictions.
基金This work was funded by National Science Foundation (DMR 1306794), Korea Institute of Science Technology (K-GRL program), Army Research Office (W911NF- 11-1-0490), and Ministry of Trade, Industry, and Energy (MOTIE) (NO. 10052980) awards to Min Jun Kim.
文摘Magnetic microswimmers are useful for navigating and performing tasks at small scales. To demonstrate effective control over such microswimmers, we implemented feedback control of the three-bead achiral microswimmers in both simulation and experiment. The achiral microswimmers with the ability to swim in bulk fluid are controlled wirelessly using magnetic fields generated from electromagnetic coils. The achirality of the microswimmers introduces unknown handedness resulting in uncertainty in swimming direction. We use a combination of rotating and static magnetic fields generated from an approximate Helmholtz coil system to overcome such uncertainty. There are also movement uncertainties due to environmental factors such as unsteady flow conditions. A kinematic model based feedback controller was created based on data fitting of experimental data. However, the controller was unable to yield satisfactory performance due to uncertainties from environmental factors; i.e., the time to reach target pose under adverse flow condition is too long. Following the implementation of an integral controller to control the microswimmers' swimming velocity, the mieroswimmers were able to reach the target in roughly half the time. Through simulation and experiments, we show that the feedback control law can move an achiral microswimmer from any initial conditions to a target pose.
基金funded by the Mexican National Council of Science and Technology(CONACYT in Spanish),under the Sectorial Fund for Energy Sustainability,CONACYT-Secretaiy of Energy(No.S0019-2012-04).
文摘A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO_(2) turbine expansion electric power generation system was proposed in this paper.Assisted by this integrated model,thermo-economic and optimization analyses for the key design parameters of the whole system including the geothermal well pattern and operational conditions were performed to obtain a minimal levelized cost of electricity(LCOE).Specifically,in geothermal heat extraction simulation,an integrated wellbore-reservoir system model(T2Well/ECO_(2)N)was used to generate a database for creating a fast,predictive,and compatible geothermal heat mining model by employing a response surface methodology.A parametric study was conducted to demonstrate the impact of turbine discharge pressure,injection and production well distance,CO_(2) injection flowrate,CO_(2) injection temperature,and monitored production well bottom pressure on LCOE,system thermal efficiency,and capital cost.It was found that for a 100 MWe power plant,a minimal LCOE of$0.177/kWh was achieved for a 20-year steady operation without considering CO_(2) sequestration credit.In addition,when CO_(2) sequestration credit is$1.00/t,an LCOE breakeven point compared to a conventional geothermal power plant is achieved and a breakpoint for generating electric power generation at no cost was achieved for a sequestration credit of $2.05/t.
基金supported by National Natural Science Foundation of China(Grant No.U21A20394)National Key Research and Development Program of China(Grant No.2018YFA0703004)+2 种基金National Natural Science Foundation of China(Grant No.52105306)New Faculty Start-up Funding Provided by Tsinghua University(Grant No.012-53330200421,L.O.)China Postdoctoral Science Foundation(Grant No.2021TQ0184).
文摘Three-dimensional(3D)bioprinting has emerged as a promising approach for engineering functional tissues and organs by layer-by-layer precise positioning of biological materials,living cells,and biochemical components.Compared with nonbiological printing,3D bioprinting involves additional complexities and technical challenges owing to the processing of living cells,such as the appropriate biomaterials that fulfill the requirements for both printability and functionality.In this review,we first introduce the development course of 3D bioprinting,highlighting innovative forms of living building blocks and advances in enabling techniques of 3D bioprinting.We then summarize the state-of-the-art advancements in 3D bioprinting for biomedical applications,including macroscale tissue or organ bioprinting,disease modeling,microphysiological systems,biobots,and bioprinting in space.Despite the rapid development of 3D bioprinting over the past decades,most 3D bioprinted tissue or organ constructs are still far from being suitable for clinical translation,and it is necessary for the field of bioprinting to shift its focus from shape mimicking towards functionality development.Therefore,we provide our perspectives on this burgeoning field with an emphasis on functional maturation post printing and translational applications at the bedside.