bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Supply Systems Based on Micro Gas Turbines for Industrial Applications
Authors: Bach Inger , Widell Karl Erik , Schmidt Geert V.
Published: November 2021

Denmark has a well-developed natural gas distribution grid and during the last decade a large number of decentralised CHP-plants (> 2000 MW total capacity) have been built around the country for industrial applications and district heating. The largest small scale CHP has an installed electrical capacity of 99 MW, while most of the plants have capacities from some hundred kW to 10 MW. The larger plants are all based on gas turbines while the smaller plants predominantly use lean-burn reciprocating engines. On the whole this development has been very successful and is supported by tax incitements for small power producers. Lean-burn engines have, however, some problems, e.g. with regard to UHC, so the emergence of small and micro-gas turbines from a number of producers offers an interesting possibility to extend the use of gas turbines down to the smaller plant sizes.

Two cases have been investigated involving smaller industries with a process steam demand.

The energy systems investigated are based on a 100 kW recuperated gas turbine (Turbec T100) and a 600 kW simple cycle gas turbine (Volvo Aero VT600). The steam and hot water is produced in a Waste Heat Recovery boiler (WHR). To obtain the sufficient steam production and sufficient steam quality it is necessary to use supplementary firing.

The analysis shows that a recuperated gas turbine has no particular advantages for industrial steam production plants. The low exhaust temperature after the recuperator is not sufficient to produce steam of proper quality.

When comparing a CHP plant with a natural gas fired steam boiler, it is found that a simple cycle gas turbine is more suitable for steam producing industrial energy supply systems.

Even if the net electric efficiency is lower for a simple cycle gas turbine, one can get a quite high, marginal net electric efficiency of about 60% (LHV) when replacing a gas fired boiler with a steam producing industrial CHP-plant. The marginal net electric efficiency is based on comparing the actual CHP plant with an existing gas fired steam producing boiler with an efficiency of 90% (LHV). This is a very high net electric efficiency compared to a centralised power plant.

The study shows that there is little doubt that CHP systems based on gas turbines are functional, efficient and environmentally friendly, but it is very difficult to achieve a satisfactory economy with the present relations between gas costs, electricity prices and gas turbine prices.
Computational Code for the Management of a Deregulated Power Generation System
Authors: Bianchi M. , Gadda E. , Peretto A.
Published: November 2021

The European electric market is going to be fully liberalized moving the problems, related to the minimization of the electric energy production cost, to the Independent Power Producers.

In the present paper, a computational code, developed by the Authors, to discover the management strategy permitting to minimize the total variable cost (in terms of fuel consumption) required by a power generation system to face a specific load demand, is described.

Subsequently, the code has been applied to an existing power generation system comparing the fuel consumption in different management strategies.

It has also emerged that the code may represent an useful advice in the power generation system upgrading feasibility, calculating the fuel saving obtainable with the addition of new or repowered units.
Effects of Variation of the Overall Heat Transfer Coefficient in the Feedwater Heaters on the Thermodynamic and Economic Performance of Power Stations
Authors: Portacha Józef , Elfeituri Idris A. , Smyk Adam , Fiszdon Jerzy K.
Published: November 2021

This paper examines the effect of the variation of the overall heat transfer coefficient (U) in feedwater heaters on the thermodynamic and economic performance of a coal-fired steam power plant. The changes in the values of U are caused by the heat transfer surface fouling or by errors in the power plant design. These errors often result from the use of approximate heat transfer equations when selecting power plants elements.

Low and high pressure feedwater heaters of a power plant equipped with a condensing turbine and a natural circulation steam generator with one reheat stage are considered in this work.

The research was conducted using the overall heat transfer coefficients from 50% to 150% of the nominal value. The thermodynamic and economic effects on the power plant were calculated using the mathematical model of the power plant. The power plant components’ mathematical models evaluate the influence of the changes in the heaters’ overall heat transfer coefficient on the thermodynamic (especially exergetic) losses and economic effects. They take into account off-design operating conditions. The decomposition method and multi-level iterative process was used to solve the problem.

The research proved that, during operation, the capacity of the power plant might change by up to 2% due to above-mentioned variations. For a 600 MW power plant that means variation of the electric power delivery of approximately 12 MW and increase of the operating costs of up to 4 million dollars per year.

The obtained results are particularly useful in the decision-making process in planning renovation and feedwater heaters’ replacement periods.
Two-Phase Flow and Transport in the Interdigitated Air Cathode of Proton Exchange Membrane Fuel Cells
Authors: Wang Z. H. , Wang C. Y.
Published: November 2021

The two-phase flow and transport in an interdigitated air cathode is studied numerically by applying the multiphase, multicomponent transport model previously developed for conventional air cathodes. A computational fluid dynamics (CFD) technique is used to solve the two-dimensional model for the interdigitated air cathode, and the contours of oxygen concentration, water vapor concentration and liquid water saturation as well as the velocity vector fields of gas and liquid phases are obtained. A polarization curve is presented which includes both the single- and two-phase operating regimes. It is found that the threshold critical current density at which the two-phase zone begins to appear inside the porous cathode is higher than that of the conventional air cathode. The maximum liquid water saturation is found to be about 0.045 for a dry inlet at an average current density of 2.07A/cm2. Both gas diffusion and convection play significant roles in oxygen supply and water removal. A higher inlet relative humidity produces a more extensive two-phase zone in the interdigitated air cathode.
Computation of the Spectral Signature Behind a Jet Engine Using the Finite Volume Method
Authors: Badinand Thomas , Tamvel Heino , Fransson Torsten H.
Published: November 2021

A method is developed to compute the infrared signature behind a jet engine. The radiative transfer equation is solved with the Finite Volume Method (FVM) based on a double discretization of the spatial and the directional domain. Then, by solving step-by-step for different wave numbers for all directions, the value of the intensity received by a point placed at infinity looking at the computational domain with a defined angle and at a defined wave number is obtained. The resulting values of the intensity for a jet engine plume case compared very well with results from a validated ray-tracing model. A sensibility analysis has been carried out to assess the influence of the spatial and directional mesh, as well as the composition of the gas mixture on the results. The method appeared to be a very powerful and practical tool to study the spectral radiative signature created by a flow with arbitrary geometry.
An Introductory Course in Thermal Fluid Engineering
Authors: Sorensen I. , Ellis M. , Dancey C. , Vick B. , Jaasma D. , Diller T.
Published: November 2021

Experiences related to a new sophomore level course, “Introduction to Thermal Fluid Engineering,” are described. Several hundred students have taken the course and are currently enrolled in the follow-on courses in thermodynamics, fluid mechanics, and heat transfer. The introductory course is structured as a two-hour per week lecture with a laboratory that meets three times during the semester. Although thermodynamics, fluid mechanics, and heat transfer subjects are introduced sequentially during the course, the overlap and inter-relationships between topics are emphasized. It has been beneficial both for students and the faculty teaching the course to see the bigger picture of the three courses as a whole rather than as separate topics. The open laboratories are manned by a graduate student or senior who guides the students through hands-on experiments. Each of the three simple experiments is designed to illustrate important principles and reinforce the computational skills of the students. A web site has been established to help guide the students in preparing the written portion of the laboratory report. Team teaching of some sections has been tried and compared to the standard one teacher per section approach. Feedback from the students indicated a surprising acceptance of having several teachers for a course when they were well coordinated. One advantage mentioned by the students was to introduce them to more of the mechanical engineering faculty early in their studies. Because this is the first course requiring engineering analysis taught by the mechanical engineering faculty, it provides the opportunity to direct them in their problem solving and organizational skills that will be useful throughout the rest of their courses. Student evaluations are included as part of the results presented.
Unsteady Mixed Convection Over Spinning Isothermal Bodies With Blowing and Suction
Authors: Öztürk Ayşegül , Ece Mehmet C.
Published: November 2021

Initial development of the laminar thermal boundary-layer flow over an impulsively started translating and spinning axisymmetrical isothermal body with blowing and suction in the case of mixed convection is investigated. Velocity components and temperature are expanded in series in powers of the square root of time. Leading, first and second order functions are obtained analytically and the third, forth and fifth order functions are determined numerically. Application of the general results to a sphere shows that buoyancy driven aiding and opposing flows help surface suction in retarding and surface blowing in facilitating the onset of flow separation respectively. Surface heat flux is increased near the front stagnation point due to the axial inflow created by the body spin and enhanced by the circulating flow inside the separated region. Surface suction is found to increase the heat transfer while the surface blowing decreases it. Aiding and opposing flows increase the surface heat flux around the front and rear stagnation points respectively.
Basic Research Towards the Development of a Noninvasive Cardiac Pressure Monitor Using an Imaging Modality
Authors: Oakley Barbara A. , Stiles David
Published: November 2021

The complex electrical permittivity of heparinized whole human blood was studied as a function of frequency between 50 MHz to 20 GHz at both atmospheric pressure (97.7 kPa absolute) and at 300 mm Hg gauge pressure (137.3 kPa absolute). Complex permittivity was found to decrease throughout much of the frequency range with this relatively small increase in pressure. Subsequent depressurization and repressurization of the same blood sample showed no change in permittivity with pressure, leading the authors to hypothesize that changes in permittivity seen with the first pressurization of the blood may be related potentiation of an unknown factor with pressure, which may be reversed in vivo but not in vitro.
Internal Heat Transfer to Power-Law Fluid Flows Through Porous Media
Authors: Rao B. K. , McDevitt J. P. , Vetter D. L.
Published: November 2021

Heat transfer and pressure drop were measured for flow of aqueous solutions of Carbopol 934 through a vertical tube filled with porous media. The heated stainless steel test section has an inside diameter of 2.25 cm, and is 200 diameters long. The porosity was varied from 0.32 to 0.68 by using uniform spherical glass beads. Uniform heat flux thermal boundary condition was imposed bypassing direct electric current through the tube wall. Over a range of the parameters: 45 < Rea < 7,000, 21 < Pra < 58, 0.62<n (power-law exponent)<0.80, 0.22 < d/D < 0.6, and the polymer concentration from 250 to 500 parts per million, the friction factor data for power-law fluids agreed with the Newtonian predictions. Heat transfer to power-law fluids increases with increasing Rea and Prw and decreasing porosity. A new correlation was proposed for predicting heat transfer to power-law fluid flows through confined porous media.
Binary Fluid Mixture and Thermocapillary Effects on the Wetting Characteristics of a Heated Curved Meniscus
Authors: Pratt David M. , Kihm Kenneth D.
Published: November 2021

An investigation of the thermocapillary effects on a heated, evaporating meniscus formed by binary fluid mixtures of wetting liquids in a vertical capillary pore system has been conducted. Experiments were conducted to primarily observe the wetting characteristics of the binary fluid mixture and how they are affected by the dynamics associated with the heating of and evaporation from a meniscus. The results have demonstrated that interfacial thermocapillary stresses arising from liquid-vapor interfacial temperature gradients that degrade the ability of the liquid to wet the pore can be counteracted by introducing naturally occurring concentration gradients associated with distillation in binary fluid mixtures without affecting the heat transport capacity of the system.
High Temperature Microscale Reactor Analysis Using a Counterflow Heat Exchanger Model
Authors: Peterson Richard B. , Vanderhoff John A.
Published: November 2021

A microscale reactor model, with axial conduction and radiation heat loss, has been developed for predicting the thermal performance of high temperature systems. The model considers: 1.) flow loss due to non-unity effectiveness, 2.) thermal conduction along the axial direction, and 3.) radiation surface loss to the environment. A system of three coupled differential equations were developed where two of the equations modeled the temperature variation in the fluid streams and the third equation gave the temperature of the wall. The wall equation contained a highly non-linear term linked to radiation surface loss. This study is unique in several ways. First, the boundary conditions for the problem modeled a micro reactor attached to a substrate at ambient temperature while the hot end was free to assume a wall temperature half way between the two fluid temperatures. Next, surface radiation was treated explicitly as a heat loss term. At elevated temperatures, the overall thermal performance of the micro reactor was significantly impacted by this loss mechanism. Finally, an implicit method is described capable of solving the non-linear coupled differential equations. The results of the study are presented in the form of normalized total heat loss curves for each of the three loss mechanisms. A scaling study is presented showing what contributions to heat loss are important as the characteristic length scale of the device is reduced. This study demonstrates that both conduction and surface radiation losses are significant in high temperature micro reactors. Furthermore, the heat loss (in normalized form) by radiation is significant for larger scale devices but the ultimate size limits for a micro reactor will be governed by conduction losses through the structure. For high temperature micro reactor technology to be practical, this study demonstrates that devices must be designed with low thermal conductivity materials, high aspect ratio geometries, and low effective surface emissivities.
Feedback Thermal Control in Microscale Heat Transport
Authors: Tzou D. Y. , Monda E.
Published: November 2021

Feedback thermal control in ultrafast heating processes is studied in this work. The emphasis is placed on the desirable rate of heating that avoids the thermal instability developed during the short-time transient. Physical parameters characterizing the thermal instability and effects of thermalization and relaxation on the desirable heating rate are identified in the ultrafast process of heat transport.
Scanning Thermal Microscopy of Carbon Nanotubes
Authors: Shi Li , Plyasunov Sergei , Bachtold Adrian , McEuen Paul L. , Majumdar Arunava
Published: November 2021

This paper reports the use of scanning thermal microscopy (SThM) for studying heat dissipation and phonon transport in nanoelectronic circuits consisting of carbon nanotubes (CNs). Thermally designed and batch fabricated SThM probes were used to resolve the phonon temperature distribution in the CN circuits with a spatial resolution of 50 nm. Heat dissipation at poor metal-CN contacts could be readily found by the thermal imaging technique. Important questions regarding energy transport in nanoelectronic circuits, such as where is heat dissipated, whether the electrons and phonons are in equilibrium, how phonons are transported, and what are the effects of mechanical deformation on the transport and dissipation properties, are addressed in this work.
Mass/Heat Transfer in Rotating Dimpled Turbine-Blade Coolant Passages
Authors: Acharya Sumanta , Zhou Fuguo
Published: November 2021

Naphthalene sublimation measurements are made in a rotating dimpled square coolant flow passage with radially-outward flow. The coolant flow passage represents a typical internal cooling channel of a turbine blade. The dimples are in the form of hemispherical depressions and are arranged in staggered rows. In the present study, only the leading and trailing surfaces are dimpled. Measurements are made at a Reynolds number of 7,000 and 21,000 and for Rotation number of 0.2. The measurements indicate that dimples enhance surface mass transfer by a factor of about two compared to a smooth surface. With rotation, the trailing wall mass transfer is increased to nearly twice that of the leading wall mass transfer. Peak mass transfer occurs immediately downstream of the dimples, while the minimum mass transfer occurs in the dimple region itself. Higher mass transfer is also observed along the lateral edges of the dimple. The locations of the Sherwood number peaks suggest the existence of streamwise vortical structures generated from the leading and lateral edges of the dimples.
Non-Linear Numerical Analysis in Transient Cutting Tool Temperatures
Authors: Jen Tien-Chien , Gutierrez Gustavo , Eapen Sunil
Published: November 2021

A numerical analysis, using a control volume approach, is conducted to study the transient cutting tool temperatures with temperature dependent thermal properties. With temperature dependent thermal properties, the governing conduction equation is non-linear and thus, the standard analytical solutions are no longer valid. In any cutting processes, the temperature distribution is intrinsically three-dimensional and very steep temperature gradient may be generated in the vicinity of the tool-chip interface. In this region, where the maximum temperature occurs, the effect of variable thermal properties may become important. The full three-dimensional non-linear transient heat conduction equation is solved numerically to study these non-linear effects on cutting tool temperatures. The extremely small size of the heat input zone (tool-chip interface), relative to the tool insert rake surface area, requires the mesh to be dense enough in order to obtain accurate solutions. This usually requires very intensive computational efforts. Due to the size of the discretized domain, an efficient algorithm is desirable in the solution of the problem. Four different iterative schemes are explored, and an optimized numerical scheme is chosen to significantly reduce the required computing time. This numerical model can be used for process development in an industrial setting. The effect of two different heat flux input profiles, a spatially uniform plane heat flux and a spatially non-uniform plane heat flux at the tool-chip interface, on the tool temperatures are also investigated in the present study. Some recommendations are given regarding the condition when these non-linear effects can not be ignored.
Numerical Simulation of Condensation on a Capillary Grooved Structure
Authors: Zhang Yuwen , Faghri Amir
Published: November 2021

Condensation in a capillary grooved structure is investigated using the Volume of Fluid (VOF) model. The governing equations are written in a generalized form and are applicable to both liquid and vapor phases. Condensation on the fin top and at the meniscus is modeled by introducing additional source terms in the continuity, VOF, and energy equations. The effects of temperature drop, contact angle, surface tension, and fin thickness on the condensation heat transfer are investigated.
On the Potential for Homogeneous Nucleation in Aqueous Salt Solutions at Elevated Temperatures and Pressures
Authors: Smith Kenneth A. , Hodes Marc , Griffith Peter
Published: November 2021

Recent studies have experimentally and theoretically examined the rate of salt deposition by natural convection on a cylinder heated above the solubility temperature corresponding to the concentration of salt in the surrounding solution at conditions typical of the Supercritical Water Oxidation (SCWO) process (Hodes et al., 2000A; Hodes, 1998). The total deposition rate of salt on the cylinder is the sum of the rates of deposition at the salt layer-solution interface (SLSI) formed on the cylinder and within the porous salt layer. The rate of deposition at the SLSI can not be accurately computed without determining whether or not salt nucleates homogeneously in the adjacent (natural convective) boundary layer. A methodology to determine whether or not homogeneous nucleation in the boundary layer is possible is presented here. This is accomplished by computing the temperature and concentration profiles in the boundary layer under the assumption that homogeneous nucleation does not occur. If, under this assumption, supersaturation does not occur, homogeneous nucleation is impossible. If supersaturation is present, homogeneous nucleation may or may not occur depending on the amount of metastability the solution can tolerate. It is shown that the Lewis number is the critical property in determining whether or not homogeneous nucleation is possible and a simple formula is developed to predict the Lewis number below which homogeneous nucleation is impossible for a given solubility boundary and set of operating conditions.
Heat Transfer Correlations for Air-Water Two-Phase Flow of Different Flow Patterns in a Horizontal Pipe
Authors: Kim Dongwoo , Kim Jae-yong , Ghajar Afshin J. , Dougherty Ronald L.
Published: November 2021

New heat transfer correlations were developed for two-phase heat transfer in a horizontal pipe for different flow patterns. Flow patterns were observed in a transparent circular pipe (2.54 cm I.D. and L/D = 96) using an air/water mixture. Visual identification of the flow patterns was supplemented with photographic data, and the results were plotted on the flow regime map proposed by Taitel and Dukler and agreed quite well with each other. A two-phase heat transfer experimental setup was built for this study and a total of 150 two-phase heat transfer data with different flow patterns were obtained under a uniform wall heat flux boundary condition. For these data, the superficial Reynolds number ranged from 640 to 35,500 for the liquid and from 540 to 21,200 for the gas. Our previously developed robust two-phase heat transfer correlation for a vertical with modified constants predicted the horizontal pipe air-water heat transfer experimental data with good accuracy. Overall the proposed correlations predicted the data with a mean deviation of 1.0% and an rms deviation of 12%.
Metal Monoxide Diagnostics in Particle Synthesis Flames
Authors: Chen Yijia , Colibaba-Evulet Andrei , Glumac Nick G.
Published: November 2021

Recent measurements of metal monoxides in powder producing flames are reviewed and discussed. While the mole fraction profiles of species such as SiO, AlO, and TiO can in principle be used to infer useful information about metalorganic decomposition in flames, the dominant features of these profiles appear to be due to the partial pressure of the solid product. Most monoxides do serve as good markers of the flame zone, but are no better than emission profiles of key excited intermediates. Monoxide profiles may, however, be of significant value in validating future comprehensive multiphase models of the synthesis process.
The Mathematical Modeling of Utility Boilers at IST
Authors: Coelho P. J. , Azevedo J. L. T. , Coelho L. M. R.
Published: November 2021

The mathematical modeling of utility boilers is a difficult problem due to the multiplicity of physical phenomena involved and to the interaction between different phenomena. However, reliable models are extremely useful since they can be used to design new equipment, and to optimize and retrofit units in operation. In this paper a survey of the work carried out at Institute superior Técnico (IST) in Lisbon is reported. Only the work based on comprehensive models, i.e., those accounting for all the relevant physical phenomena taking place in the combustion chamber is addressed. The models employed are briefly outlined. Then, four examples of application are given, two of them for coal-fired boilers where the effect of low NOx burners and coal over coal reburning is investigated, and the other two for oil-fired boilers where parallelization of the code and simulation of the convection chamber are reported.
Structural Acoustic Optimization of a Composite Cylindrical Shell Using FEM/BEM
Authors: Johnson W. M. , Cunefare K. A.
Published: November 2021

A finite element/boundary element design tool is used to perform a structural acoustic optimization on an eight-ply graphite epoxy cylindrical shell. The shell is subject to two external monopole sources vibrating at a single frequency. The goal of the optimization is the minimization of the sum of the squared pressure amplitudes within the enclosed acoustic cavity. The ply angles serve as the design variables in optimization. The optimal design was obtained after 15 iterations with a 2 dB reduction in the average interior sound pressure level. The ply angle orientation shifted from an initially symmetric lay-up to an unsymmetric lay-up in the final design.
Micro-Scale Acoustic Streaming Pump Performance Characteristics
Authors: Frampton Kenneth D. , Martin Shawn E.
Published: November 2021

Acoustic streaming theory, applied to micro-scale pumps is presented. A mathematical model based on streaming equations and Mason’s model [9] of the piezoelectric transducer is described. Using this model, the effect of geometric scaling, frequency variation, and excitation amplitude on head and flow rate are examined. The significance of high body forces in the AC boundary layer are demonstrated, along with their effect on mass flow rates for small geometries. It is shown that flow velocities are inversely proportional to the flow tube diameter for small sizes. Experimental data for a macro-scale pump is provided and used to corroborate the static head versus excitation relationship predicted by the model. Compression wave acoustic streaming pumps are shown to have potential viability for micro-scale applications.
Silicon Micromachined Ultrasonic Transducers
Authors: Khuri-Yakub Butrus T. , Cheng Ching-Hsiang , Degertekin Fahrettin-Levent , Ergun Sanli , Hansen Sean , Jin Xue-Cheng , Oralkan Omer
Published: November 2021

This paper reviews capacitor micromachined ultrasonic transducers (cMUTs). Transducers for air-borne and immersion applications are made from parallel-plate capacitors whose dimensions are controlled through traditional integrated circuit manufacturing methods. Transducers for airborne ultrasound applications have been operated in the frequency range of 0.1–11 MHz, while immersion transducers have been operated in the frequency range of 1–20 MHz. The Mason model is used to represent the cMUT and highlight the important parameters in the design of both airborne and immersion transducers. Theory is used to compare the dynamic range and the bandwidth of the cMUTs to piezoelectric transducers. It is seen that cMUTs perform at least as well if not better than piezoelectric transducers. Examples of single-element transducers, linear-array transducers, and two-dimensional arrays of transducers will be presented.
Flow Noise Predictions for Automotive Air Rush Noise
Authors: Howell James , Humbad Niranjan G. , Hargrove Jeff , Porada Robert A.
Published: November 2021

Noise from automotive air handling systems is an important issue for driver comfort. This study was undertaken to quantify the noise from the air handling system and to develop a predictive model for the noise level and spectrum at the drivers right ear location. Tests were conducted on six vehicles to develop the predictive model and then four more vehicles were tested and used to verify the prediction model. All vehicles tested were production level designs ranging from small economy cars to large luxury trucks. The study shows that the noise generated by the air handling system can be modeled with the parameters of static pressure across the blower (ΔP) and system air flow rate (Q). When the measured noise levels were compared to the predicted noise levels, there was a mean error of −0.03 dBA with a standard deviation of 1.31 dBA for all vehicles and for various modes of operation. This model can be used in the early stages of design using CFD/CAE analysis, or in evaluating the effects of design changes on the sound pressure level and spectrum.
Cepstral Analysis Applied to Identification of Longitudinal Vibration in Timber Piles
Authors: Pardue Sally J. , Renfro Michael W. , Ramsagar Prasanna
Published: November 2021

A method for field measurement of timber pile length in bridge foundations is possible by determining the natural frequency spacing between consecutive resonant peaks in the longitudinal frequency response function (FRF) as well as experimental determination of the longitudinal wave speed. The measurement procedure relies on vibration modes excited through the attachment of small actuators driven with random input and the recorded response of attached accelerometers.

The identification of natural frequencies in timber piles is complicated by the inhomogeneous nature of wood and the location of measurement points at possible longitudinal nodes along the pile. Missing peaks and corrupted spectrums are common in the experimental data collected during the testing of timber piles. A form of cepstral analysis using the FRF shows promise towards overcoming some of the inherent difficulties in identifying the natural frequency spacing between resonant peaks in the spectrum.

The details of the signal processing and natural frequency spacing identification are presented and demonstrated on a laboratory aluminum bar and typical timber pile data.
New Algorithms to Improve Noise Source Location Using a Microphone Array
Authors: Darvennes Corinne M. , Bhatt Tarun K.
Published: November 2021

Several algorithms are presented to improve noise source location using a microphone array. The estimation of the source location is essentially a two step process: first, time delays of arrivals (TDOA’s) are calculated using the unwrapped phase (UP) method; then the TDOA estimates are used to determine the coordinates of the source. The first algorithm was developed to calculate TDOA’s automatically by removing the data points with low coherence from the unwrapped phase and by using a delay error rather than a mean square error to choose the best distance estimate. A simplex algorithm was then implemented to evaluate source coordinates from the TDOA’s. Finally, a pruning algorithm was devised to remove unreliable data from the source coordinate calculations. Experimental data is presented to illustrate the use and benefits of these algorithms.
Comparison of Static and Dynamic Stiffness for Beams Undergoing Flexural and Torsional Loading With an Intermediate Mass
Authors: Garcia Arnoldo , Lumsdaine Arnold , Yao Ying X.
Published: November 2021

Many studies have been performed to analyze the natural frequency of beams undergoing both flexural and torsional loading. For example, Adam (1999) analyzed a beam with open cross-sections under forced vibration. Although the exact natural frequency equation is available in literature (Lumsdaine et al), to the authors’ knowledge, a beam with an intermediate mass and support has not been considered. The models are then compared with an approximate closed form solution for the natural frequency. The closed form equation is developed using energy methods. Results show that the closed form equation is within 2% percent when compared to the transcendental natural frequency equation.
A Study on Gradient Polymer Materials Used as Damping Coatings: Focus on Free Damping Coatings
Authors: Remillat C. , Tomlinson G. R.
Published: November 2021

This paper discusses the damping capabilities of polymer materials with mechanical characteristics which vary through the thickness. The case studied is that of a beam coated with a single layer of this material, which can be classified as a free layer damping coating. A simple mechanical model of the system is proposed, together with a suitable modelling of the gradient material. Simulation results based on realistic cases are presented for different types of distribution through the thickness and their damping performance is assessed.
On the Exploitation of Thermoelectric Coupling for Characterization of Inclusions in Metals
Authors: Nayfeh Adnan H. , Carreon Hector , Nagy Peter B.
Published: November 2021

It was recently discovered that inclusions and other types of inhomogeneities can be nondestructively detected by thermoelectric measurements in an entirely non-contact way by using high-sensitivity magnetometers to sense the weak thermoelectric currents around the affected region when the specimen is subjected to directional heating or cooling. This paper presents theoretical models capable of predicting the magnetic field produced by thermoelectric currents around inclusions under external thermal excitation. We investigated how the magnetic signal to be detected depends on (i) the relevant physical properties of the host and the inclusion, (ii) the size of the inclusion, (iii) the polarization of the magnetometer, (iv) the lift-off distance of the magnetometer from the specimen, and the (v) direction and (vi) strength of the external heating or cooling applied to the specimen. The presented analytical model is numerically evaluated for comparison to experimental results that were obtained by measuring the magnetic field produced by thermoelectric currents around surface-breaking spherical tin inclusions in copper under external thermal excitation for different lift-off distances between the sensor and the surface of the specimen. The diameter of the inclusions and the lift-off distance varied from 2.4 to 12.7 mm and from 12 to 20 mm, respectively. A fairly modest 0.7 °C/cm temperature gradient in the specimen produced peak magnetic flux densities ranging from 1 to 250 nT, that could be easily measured by a commercial fluxgate magnetometer. The experimental results were found to be in very good agreement with our analytical predictions.
Understanding Stage Matching of a High-Efficiency Multi-Stage Centrifugal Gas Compressor
Authors: Cave Michael J. , David Tim
Published: November 2021

A series of closed loop development tests were conducted on a new high-efficiency, multi-stage gas compressor. Using the test data and a 1-D compressor analysis software program, stage characteristics were modeled for each of the six stages. Overall stage results from the 1-D model were compared to development test data to validate the model. Once the model was validated, it was used to understand stage-to-stage matching at design and off-design conditions.
Hybrid System Stability and Capacitive Shunting of Piezoelectric Stiffness
Authors: Kurdila Andrew J. , Feng Yunfei , Lesieutre George A.
Published: November 2021

Recent research demonstrated that an actively-switched capacitive shunt circuit across a piezoceramic stiffness element can provide the basis for a frequency-tunable solid state vibration absorber. From a theoretical standpoint, the stability characteristics of such a design are amenable to conventional mechanical systems analysis when the shunt circuit operates in quasi-steady manner. However, when active tracking of a disturbance is desired to enhance broadband disturbance attenuation, the conditions for closed loop stability of the electromechanical system are not clear. In the present research, a simplified mechanical model of a switch-shunted piezoceramic was first developed. This model was amenable to study as a hybrid or Witsenhausen switching system. Using the method of multiple Lyapunov functions, the simplified model was shown to be unstable for some switching strategies. Subsequently, a coupled electromechanical model was developed and used as the basis for numerical performance simulation. In this model, all switching strategies evaluated resulted in stable systems, although some exhibited considerably higher effective damping than others. These results indicate the importance of retaining electrical states in dynamical models of switched piezoelectric systems.
Nonlinear Coupled Piezoelectric-Mechanical Model of Smart Composites
Authors: Thornburgh Robert P. , Chattopadhyay Aditi
Published: November 2021

A completely coupled piezoelectric-mechanical theory which includes the nonlinear piezoelectric effects is developed for composite plates with embedded or surface bonded actuators and sensors. A higher order laminate theory is used to describe the displacement field in order to accurately capture the effects of transverse shear in moderately thick laminates. The coupling between the piezoelectric effect and mechanical response allows for mutual influence of multiple actuators and transformation of energy between the electrical and the mechanical fields. A new fourth order distribution of electric potential is used to develop an electrical model completely compatible with the assumed higher order strain field. The behavior of actuators subjected to large electric fields is captured using the nonlinear piezoelectric-mechanical coupling terms. The resulting model shows good correlation with available experimental data.
A Generalized Laminate Model for Electro-Mechanical Plates and Shells
Authors: Sealing C. S. , Dasgupta A.
Published: November 2021

A coupled finite element formulation is developed to address heterogeneous electro-mechanical plates and shells whose properties vary through the thickness. The goal is to better approximate the through-thickness variation of the mechanical and electrical fields, without incurring the computational burden of a fully layer-wise theory. This formulation uses a special constraint condition, which makes the transverse gradients of the field variables proportional to the gradation of the material properties through the thickness. The formulation is implemented into a commercial finite element code and used to solve simple test cases. Results are compared with other known methods.
Linear Parametric Models of Tensegrity Structures
Authors: Sultan Cornel , Skelton Robert E.
Published: November 2021

In this paper we derive the linear equations of motion for tensegrity structures around arbitrary equilibrium solutions and cast them in vector second order form. For certain tensegrity structures which yield particular equilibrium configurations easily parameterized we present the corresponding linear models and identify the structure of the linear models matrices in terms of the geometrical and inertial parameters of these structures. Analytical and numerical evidence is presented which shows that these equilibria are stable.
Energy Minimization-Based Vibration Control of a Bridge Using Magneto-Rheological Fluid Dampers
Authors: Liu Yanming , Gordaninejad Faramarz , Evrensel Cahit A. , Wang Xiaojie , Hitchcock Gregory
Published: November 2021

This paper presents vibration control of a scaled two-span bridge structure. Magneto-rheological fluid (MRF) dampers are utilized as the semi-active energy absorbing devices and a bridge vibration control system is developed. Closed-loop control system based on the total energy minimization is used to suppress the bridge deck motion under simple harmonic and simulated earthquake excitation. It is experimentally demonstrated that this closed-loop control system can effectively control the relative displacement and the absolute acceleration of the bridge deck.
Genetic Spatial Optimization of Active Elements on an Aeroelastic Delta Wing
Authors: Richard Robert E. , Rule John A. , Clark Robert L.
Published: November 2021

Reduced-order models of potential-flow aerodynamics have been developed and greatly facilitate the analysis and design of aeroelastic systems in the early design phase. Models capturing 95% of the physics with 8% of the modeling effort can be realized to evaluate various active and passive design considerations. A delta wing model has been developed to determine the most effective locations and shapes for transducers required to provide flutter control. The basic design philosophy is presented based upon an analytical model of the structure. A genetic algorithm was used to determine the optimal transducer locations and shapes required to provide effective flutter control based upon an open-loop performance metric. The genetic algorithm and performance metric essentially provide loop shaping through the adaptive structure design. An experimental model was developed based upon the optimal transducer designs. Wind tunnel tests were performed to demonstrate closed-loop performance for flutter control. Results from this study indicate that a single sensor/actuator pair can be designed to extend the flutter boundary and selectively couple to only those modes required to control the response.
Design of a Piezoelectric Point Actuated Active Aperture Antenna
Authors: Angelino Marc , Washington Greg
Published: November 2021

In this research, the design of a piezoelectric point actuated active aperture antenna is introduced. The antenna consists of numerous piezoelectric point actuators placed perpendicular to the doubly curved aperture. The point actuators are comprised of a piezoelectric element and a stick-slip mechanism used to generate motion. A specially designed code that takes into account the mechanical and electromagnetic effects is used to determine the desired shape of the aperture. The final shape of the aperture is verified using stereo photogrammetry.
Design and Modeling of a Piezoelectric Actuator for Minimally Invasive Surgery
Authors: Edinger Ben , Frecker Mary , Koopmann Gary H.
Published: November 2021

A small-scale piezoelectric actuator has been designed for use in minimally invasive surgery. The actuator is designed to actuate a compliant suture needle grasper as part of a telerobotic surgical system. The actuator consists of a single piezoceramic stack and a slider-crank mechanism which acts as a mechanical stroke amplifier. The main focus of this paper is on the design of the actuator and fabrication and test of a prototype as a proof of concept. The design and fabrication of the prototype actuator is discussed as well as experimental results measuring its performance. A quasi-static model of the actuator which predicts the mechanical amplification and force response is also discussed. Results from laboratory bench-top experiments are presented, and the actuator together with the compliant gripper are shown to grasp and hold a standard suture needle.
Mechanical Models for Insect Locomotion: Parameter Studies
Authors: Schmitt John
Published: November 2021

Motivated by experimental studies of insects, we develop a three-degree-of-freedom, energetically conservative, rigid body model with a pair of elastic legs in intermittent contact with the ground. The resulting piecewise-holonomic mechanical system exhibits periodic gaits whose neutral and asymptotic stability characteristics are due to intermittent foot contact, and are largely determined by geometrical criteria. We study how dynamics depend on physical parameters such as mass, moment of inertia, leg length, leg stiffness, and leg touchdown angle. We develop exact and approximate scaling relations that predict gait scaling in response to individual parameter changes, and suggest that the model is relevant to the understanding of locomotion dynamics across species.
Predictive Control of Nonlinear Mechanical Systems Using a Short-Term Prediction Method Based on Chaos Theory: Applications to a Forced Pendulum
Authors: Masumoto Noriyasu , Yamakawa Hiroshi
Published: November 2021

In this paper, an active vibration control method for nonlinear mechanical systems is presented. The control forces are determined by the future values obtained by a short-term prediction method based on chaos theory and the authors call such a control method a predictive control method. The predictive control method is applied to a system for a pendulum forced by a sinusoidal torque at the supported point. The equation of motion for the pendulum becomes nonlinear when the swing angle is large. It is also known that chaotic behaviors occur in such a nonlinear pendulum model under some conditions. Here, a predictive control method to get the control forces using the angular displacements near future is discussed. In addition, a method is presented to find the optimum sampling period to take samples from the response which is continuous with respect to time. The ideas of forward and backward horizons, defined by the authors before, are also taken to the nonlinear pendulum system, and the effectiveness of the control method is examined numerically.
Relative Stability Analysis for Vibration Absorbers With Multiple Delayed Feedback
Authors: Huang Chang , Olgac Nejat
Published: November 2021

A novel tuning methodology for active vibration absorption is discussed. The underlying proposition is to use partial state feedback with multiple unrelated time delays. The objective of this tuning is to combat excitation forces with multiple frequencies, which are time varying. It is shown that the required control parameters can be evaluated on-line rather rapidly. The system stability aspect however, needs to be resolved a priori to the control actuation. This is the challenge facing this procedure due to the presence of multiple (and mostly “unrelated”) time delays. A new stability assessment methodology, the Directional Stability Chart method, is presented. The outcome of this procedure is used to determine the local stability levels and preferred operating zones in the domain of the multiple excitation frequencies. The method is also expanded to assess the relative stability level of the tuned absorber. Example case is taken from a PZT actuated active absorber. Desirability of the operating points are compared based on the relative stability levels, and the observations are verified by simulations.