bluuebunny/crossref_metadata_2025 huggingface dataset:
A Discrete Cell Model for Shape Control of Precision Membrane Antennae and Reflectors
Authors: Kalanovic V. D. , Padmanabhan K. , Jenkins C. H.
Published: December 2021

The potential for placing large precision reflectors in space is currently being investigated through the use of inflatable membrane structures. Their capacity for reducing launch mass and stowed volume is being exploited. However, on-orbit performance will require an understanding of the various influences on the deployment, inflation, and service of the membrane, and the associated effects on reflector surface precision.

Nonlinear controllers developed to improve performance of such systems are often dependent on state estimation and parameter identification procedures. The existence of these procedures, within the control strategy, increases the size of the algorithms, limiting the system performance in real-time. The research presented has as a main objective to create an intelligent controller, based on feedback error learning, which is capable of extracting performance information from precision large membrane deployables, and subsequently using this information to achieve maximum surface precision.

This paper presents a method to spatially discretize a doubly-curved membrane model into N = m × n spring-mass-damper cells. A recursive algorithm is developed and used in a simulator to predict the surface profile of the membrane. Each cell is connected to a feedback error learning controller in order to extract local state estimations. Simulation results are then compared to finite element predictions. The discrete cell model is shown to be simple enough for real-time control strategies, and potential methods for sensing/actuating to close the loop are discussed.
Development of a Test Bed for Evaluating Electron Gun Shape Correction of Distributed Structures
Authors: Martin Jeffrey W. , Main John A. , Nelson George C.
Published: December 2021

Electron gun control of distributed structures is an emerging technology that needs to be further characterized. Due to the experimental demands of this technique a unique testing apparatus must be developed. This equipment must meet the demands of high precision and high range measurement for use in “real-time” closed loop control applications. This system is further complicated in that these measurements must be done remotely, external to the bulky experimental apparatus. The system and issues concerning its use are discussed.
Active and Passive Vibration Control of Landing Gear Components
Authors: Kwak Seung-Keon , Washington Gregory , Yedavalli Rama K.
Published: December 2021

In this paper, we address a way to absorb the vibrations of large scaled heavy aircraft structures such as landing gear components, using the combination of active and passive controls. A steel tube, which is equivalent to Boeing 747 landing gear break rod, is selected as a test bed. The expected goal of this study is to dissipate the fundamental mode of the tube. A Beam type dynamic absorber and a constrained layer damping method are used for passive vibration controls. Both Matlab simulations and experimental results are provided for the dynamic absorber case. A fuzzy logic based controller with an acceleration measurement using piezoelectric actuators (PZT) is implemented in dSPACE for the active vibration control of the system. The integrated controller with passive and active components absorb the fundamental mode of the system according to the experimental results.
Structural Health Monitoring Applications Using Piezo-Dielectric Effects
Authors: Vipperman Jeffrey S.
Published: December 2021

A new method of sensing structural integrity using piezoceramic transducers is presented. Capacitance values of piezoceramic patches are dependent upon the prescribed mechanical boundary conditions. This dependence can be exploited to monitor the rudimentary health of a structure by monitoring the capacitance of an attached piezoceramic patch. An adaptive piezoelectric sensoriactuator is used because of its inherent ability to monitor the capacitance of piezoelectric transducers in real-time. A simple experiment is performed where the device is used to successfully detect a change in boundary conditions for a composite beam piezostructure.
Bioactive and Degradable Composite Microcarriers for 3-D Bone Tissue Engineering in Simulated Microgravity
Authors: Qiu Qing-Qing , Ducheyne Paul , Ayyaswamy Portonovo S.
Published: December 2021

Microcarriers currently used in cell and tissue cultures in microgravity environment simulated by rotating-wall bioreactors are primarily biocompatible polymers. For bone cell cultures and tissue formation, bioactive glasses and ceramics have unique advantages, such as bone bonding ability and stimulation of bone cell functions.1 However, they are difficult to be processed into spherical microcarriers and have not been used in simulated microgravity environment until recently.2 In this study, we developed composite microspheres by incorporating bioactive glasses and ceramics into a polymer microsphere to combine the osteoconductivity of bioactive glasses and ceramics with the ease of polymer processing. In addition, the wide range of mechanical and biological properties of polymer offers the possibility of making composite microspheres with various desired properties, such as biodegradation.

Another important factor in the microsphere design is the density of the microcarrier. Previous numerical analysis of the particle dynamics in a rotating-wall bioreactor has revealed that the shear stress imparted to a microcarrier increases with the density difference between the microcarrier and the culture medium.34 Solid ceramic particles would experience a high shear stress due to their high density and, as a results, affect cell attachment and cause cell damage.4 To alleviate the problem, microcarriers with a density close to that of the culture medium are desired. By combining biodegradable polymer with bioactive glasses and ceramics, the density of the composite microsphere could be adjusted and significantly reduced in comparison to solid ceramic microspheres.

In this study, we report development and characterization of novel bioactive and degradable composite microspheres for 3-D bone tissue engineering in simulated microgravity environment.
Using Encapsulation to Improve the Viability of Cryopreserved Cells
Authors: Matsumoto Yoshifumi , Morinaga Yukihiro , Ujihira Masanobu , Oka Kotaro , Tanishita Kazuo
Published: December 2021

The purpose of this study is to clarify whether encapsulated cells have an advantage over suspended cells in cryopreservation. Rat pheochromocytoma (PC12) cells were selected for test biological cell and microencapsulated in alginate-polylysine-alginate membranes. Microencapsulated PC12 cells were frozen with differential scanning calorimetry (DSC) at a cooling rate of 0.5 to 10°C/min, their latent heat was measured among the freezing process over the temperature range 4 to −80°C. Their post-thaw viability were evaluated by dye exclusion assay and dopamine release. As a result, latent heat of encapsulated cells was lower than that of suspended cells at a cooling rate of 0.5 and l°C/min. This is because extra-capsule was frozen and intra-capsule unfrozen, as ice crystals forms in extra-capsule space. Post-thaw viability of microencapsulated PC12 cells was improved at 0.5 and l°C/min compared with that of suspended cells. Therefore, in microencapsulated PC12 cells, achievement of intra-capsule unfrozen condition during freezing leads to reducing the solution effect and improving the viability.
The Effect of Heat Induced Changes in Microwave Tissue Properties on Microwave Thermal Therapy for Prostate Cancer
Authors: Sherar M. D. , Chin L. , Kolios M. C. , Gladman A. S.
Published: December 2021

The delivery of heat to the prostate using microwave antennas is being investigated as an experimental treatment for prostate cancer. Tissue temperatures can be calculated by solving the bioheat equation with the volumetric power deposition of the antenna as an input. This heating pattern is expected to change during heating due to changes in the electrical properties of the prostate. We have measured the microwave properties of rat prostate as a function of temperature and time and applied these parameters to the solution of the bioheat equation. We describe the nature of the changes in prostate tissue properties with heating. In addition, we present simulations of microwave heating in prostate tissue which illustrate the significance of including heat induced changes in tissue properties for this thermal therapy application. The prostate tissue measurements were performed using a loaded coaxial cable technique where the tissue sample could be rapidly heated as measurements were taken. Prostate treatment simulations were performed using a finite element approach to the bioheat equation.
An Apparatus for Measuring the Effective Thermal Conductivity of the Body Surface
Authors: Cheng Shuxia , Zhang Hongbo , Luo Dawei , Gao Dayong
Published: December 2021

To prevent body from injury during the hyper- and hypo-thermic therapy, knowledge of the temperature distribution in the body surface (e.g. skin or tissue) close to the therapy location is needed. In order to predict, by calculation, the correct temperature field, it is essential to input meaningful values of the thermal properties of the body surface into numerical and analytical simulation models of its behavior during heating or cooling. A simple experimental apparatus for measuring effective thermal conductivity of the body surface has been developed. It differs from the previously developed apparatus. In experiments, a fine platinum wire (0.01 mm in diameter) with electrical resistance R (0.4Ω)is embedded between a tested specimen (body surface) and a silicone rubber. When the wire, specimen and rubber are in thermal equilibrium, and a constant electrical power is applied to the wire, the temperature increase of the wire against logarithm time in predetermined time interval was measured. The kinetics of this temperature rising is related to the thermal conductivity of the tested specimen and silicone rubber. The thermal conductivity of the silicone rubber is known from reference or measured. So the thermal conductivity of tested specimen can be calculated by measuring the temperature rise of platinum wire at predetermined time interval. It is assumed that (1) the wire is infinite long and the heat source is steady, (2) the tested medium (e.g. the tested specimen and the silicone rubber) are infinite large in space, and contact resistance between the fine wire and soft medium is negligible.

The apparatus’ validity has been demonstrated by the following tests. First, as the standard specimen, thermal conductivity of glycerol and fused quartz glass (99.9% SiO2) were respectively measured using the apparatus. The relative errors between measured thermal conductivity and data provided by Thermophysical Properties Research Center (TPRC) are less than 0.7%. The validity of the theory model was also confirmed using several inorganic specimens and biological materials (e.g. rabbit sin, in vivo). Conditions and prerequisites for application of the technique and apparatus to measuring thermal conductivity of biomaterials (in vivo) were discussed.
Dynamic Behavior of Aircraft Wings Modeled as Doubly-Tapered Composite Thin-Walled Beams
Authors: Na Sungsoo , Librescu Liviu
Published: December 2021

A study of the dynamical behavior of aircraft wings modeled as doubly-tapered thin-walled beams, made from advanced anisotropic composite materials, and incorporating a number of non-classical effects such as transverse shear, and warping inhibition is presented.

The supplied numerical results illustrate the effects played by the taper ratio, anisotropy of constituent materials, transverse shear flexibility, and warping inhibition on free vibration and dynamic response to time-dependent external excitations. Although considered for aircraft wings, this analysis and results can be also applied to a large number of structures such as helicopter blades, robotic manipulator arms, space booms, tall cantilever chimneys, etc.
Assessing Creativity in Engineers
Authors: Larson Michael C. , Thomas Benjamin H. , Leviness Peter O.
Published: December 2021

This study investigates how well certain popular psychological written tests aimed at assessing creativity relate to the performance of undergraduate mechanical engineering students engaged in a design competition. There is a growing awareness of the need to stimulate creativity in students. A valid standardized test would be useful for educators to develop curricular components aimed at bolstering student creativity and to measure the success of efforts to instill creativity. The Myers-Briggs Type Indicator1, the Torrance Tests of Creative Thinking2, and the Revised Minnesota Paper Form Board Test3 were administered to students enrolled in a sophomore-level engineering design course at Tulane University. In addition, a modified Ypma’s Biographical Questionnaire4 was used to gather personal data from each student. The design competition served as a basis for evaluating the individual’s applied creativity in an open-ended, yet constrained, engineering design activity.

For the particular group tested, the three tests were poor indicators of the engineering creativity embodied in the students’ designs. It may be that the attributes which contribute to creativity in an engineering exercise differ from those which contribute to creativity in a more general sense, for example in art and literature, and which are measured by the tests. Responses to the biographical questionnaire suggest that, while the whole class shares a similar socioeconomic background, the students judged to be creative in the design activity possess certain qualities which distinguish them from the rest of the group. Noteworthy in this regard is the difference in the self-perception of creative ability — the creative students see themselves as being less creative than the other students see themselves. It may be worthwhile to follow up this small-sample investigation and undertake a larger study using the biographical questionnaire to collect information about personal experiences (presumably something that can be addressed in an engineering curriculum). This present study, although limited in scope, indicates that great care should be taken before the engineering community embraces a diagnostic test for creative potential.
Teaching Tools for Teachers: An Engineering Design Project to Enhance Science and Mathematics Education for Middle/High School Students
Authors: Nagchaudhuri Abhijit , Conway Harold M.
Published: December 2021

With the approach of the new millennium and the emergence of the global market, significant restructuring of university education in general, and science and engineering education in particular, is taking place with the objective of preparing the students for the new social and economic order.

The paradigm shift and emerging trends in engineering education demand a holistic integration of “soft” and “technical” skills. There is also an emphasis on “educational outcomes” as evidenced by student design projects and other outcome evaluation criteria. “Service-Learning”, an approach that endeavors to integrate “community service” and “student learning” has found wide acceptance in the Humanities and Social Sciences. Implemented in a novel and creative fashion, it may well provide an effective pedagogical tool consistent with the new paradigm of engineering education.

The design project described in this paper integrates both “Service-Learning” and “Design Project” requirements in the first course in “Engineering Mechanics” offered at the University of Maryland Eastern Shore (UMES), Engineering Program. One of the desired “outcomes” of the course is that the student not only understands the theory as discussed in class but also learns to apply the knowledge to develop and design engineering products useful for the society. The project demonstrates the development of a device that visually reinforces concepts related to Newton’s laws of motion and mechanical advantage in simple machines (lever arms, pulley systems, and springs), in consultation with a science and mathematics teacher in a local high school. In the future, the device will be utilized in the school and benefit education efforts not only at the high school level but also in the elementary and middle schools. It is anticipated that it will also help introduce the field of Engineering to school students.

During the implementation of the project, other learning outcomes were accomplished in concert with the demonstration of application of engineering mechanics and providing service to the community. The student has reflected that the project has helped him in realizing the “role” of the customer in engineering design, developing a clear perception of constraints in space, time and budget in implementing projects, and improving communication skills. It has also given him a better appreciation of the role of engineering in society and helped his inner growth as an individual and a citizen.
Reverse Engineering of Free-Form Surfaces: Data Reduction When Using an On-Line Contact Probe
Authors: Wong K. , Krishnan K. K. , Bahr B. , Chowdhury P. P.
Published: December 2021

When reverse engineering free-form surfaces a perennial question is the limit on the number of points to be measured and the size of the grid in which the points are measured. The size of the grid can be determined only after an analysis of the surface is performed. However, the data required for analysis is not available. Hence, a continuous scanning technique or scanning at very close intervals is necessary. When using continuous scanning techniques for reverse engineering free-form surfaces a large number of points are generated. The transfer of these points into a CAD system to generate a NURBS surface requires a large database. Fitting a surface through a limited set of points and performing a geometric analysis of the surface to determine the complexity of the surface can reduce the excessive number of points. The complexity of the surface will be determined by using such parameters as radius of curvature. Additional points can be measured at necessary location based on the analysis. This research describes the development of an integrated reverse engineering system that will measure a free-form surface using a scanning contact probe and determine the location points on the surface to be measured. The developed system reduces the number of data points that are measured and stored. The software has been developed using ACIS and C++.
Dynamics of Metalcutting
Authors: Isakov Edmund
Published: December 2021

A practical engineering method of calculating tangential cutting force in milling is proposed. The method is based on the ultimate tensile strength of a work material, cross-sectional area of uncut chip, the number of inserts in cut, and a machinability factor of a workpiece material. Milling tests of high shear cutters with torque dynamometer were carried out at a wide range of the cutting conditions and various workpiece materials to verify the concept. Proposed method provides the accuracy of ± 15% or better for calculating tangential cutting force, torque, and power consumption in relationship with machining conditions and work material mechanical properties.
Development of a Cutting Direction and Sensor Orientation Independent Monitoring Technique for End-Milling
Authors: Roth John T. , Pandit Sudhakar M.
Published: December 2021

In the authors’ previous work, univariate models were fit to acceleration data to predict impending tool failure. Numerous end-milling life tests, conducted under a wide variety of cutting conditions, demonstrated that the method could consistently warn of impending failure between 6 inches (15 cm) and 8 inches (20 cm) prior to the actual event. This paper presents an improved method that increases the warning time and allows the technique to function independent of the cutting direction or sensor orientation. Using multivariate autoregressive models fit to tri-axial accelerometer signals, monitoring indices are developed, verified and the results are compared with those from the univariate models. The multivariate models detected impending failure 30 inches (76 cm) prior to its occurrence, 23.5 inches (60 cm) earlier than with the univariate models. Furthermore, the multivariate models are able to monitor the condition of the tool, regardless of the cutting direction or sensor orientation.
Modeling Oscillations During Conduction Mode Laser Welding
Authors: Smith Elizabeth T. , Schultz William W. , Kannatey-Asibu Elijah
Published: December 2021

Thermal, optical, and acoustic signals are generated during laser welding by the many physical phenomena which govern the laser beam-material interactions involved in welding. The objective of this study is to analyze one potential source of these signals — oscillations of the molten weld pool. Weld pool oscillations are modeled as gravity-capillary waves in a partially penetrating, conduction mode weld pool. The weld pool is assumed to be stationary and cylindrical, containing inviscid, incompressible, irrotational liquid metal. Dynamic and kinematic boundary conditions are imposed at the free surface of the pool, with impenetrability providing a boundary condition at solid boundaries. Two different edge conditions are examined. First, the free surface is assumed to meet the boundary orthogonally. Second, the contact line is assumed to remain fixed during pool motion. Solution of the governing equations subject to the boundary conditions provides the natural frequencies of oscillation and mode shapes governing pool motion. Results from the analytic model agree well with preliminary experimental data. The dominant mode of oscillation can be characterized as a sloshing of material from the front to the back of the pool, occurring at approximately 700Hz for the conditions examined.
High Precision Cutting and High Speed Interrupted Cutting of Hardened Steel With PCBN Tools
Authors: Yoshida Katsuhito , Kukino Satoru , Harada Takashi , Fukaya Tomohiro , Shiraishi Junichi , Nakai Tetsuo
Published: December 2021

PCBN (Polycrystalline Cubic Boron Nitride) cutting tools have become very familiar in the industries for cutting hardened steel parts and the demand for PCBN tools is growing rapidly. One of the reasons for this is the trend of replacing grinding processes with cutting. Although the trend of processing is to use more cutting, there still remains grinding in many processing fields. High precision machining and high speed interrupted machining have been such fields. In this study it has been verified that a novel cutting method can be applied to high precision machining with the smoothness of Rz 0.8 μm and that a new PCBN has sufficient reliability against tool failure in high speed (< 250m/min) interrupted cutting. Thus cutting has become applicable to those machining and the trend of replacement of grinding with cutting will be enhanced. Those new technologies will be introduced in this report.
Modal Analysis and Modeling of a Parallel Kinematic Machine
Authors: Hardage David S. , Wiens Gloria J.
Published: December 2021

This paper presents the results of a mini-modal survey on the Hexel Tornado 2000, a parallel kinematic machine tool located at Sandia National Laboratories, and discusses the finite element model that is used to simulate the structural dynamics of this machine. Preliminary data suggests a dependency of resonant frequency and stiffness characteristics on machine configuration.
Study of Edge Effects in Laser Bending
Authors: Bao Jiangcheng , Yao Y. Lawrence
Published: December 2021

Laser forming has not been widely used due to limited understanding of its mechanism and immaturity of processing technology. In the study of single axis laser bending of plates, edge effects affect accuracy of the bending. Experimental and numerical studies are carried out to study the mechanism of the edge effects. Temperature dependency of material properties and strain-rate dependency of yield stress are considered in numerical simulation. Numerical results match well with experimental results. Patterns of edge effects are examined in terms of bending angle variation and curved bending edge under different conditions. A more complete explanation for the mechanism of the edge effects is given.
Frequency Domain Analysis of Vibrations in Liquid-Filled Piping Systems
Authors: Jiao Zongxia , Hua Qing , Yu Kai
Published: December 2021

In the analysis of liquid-filled piping systems there are Poisson-coupled axial stress waves in the pipe and liquid column, which are caused by the dilation of the pipe. In some conditions the influence of viscous friction that is usually frequency-dependent should not be omitted, which in fact is another kind of coupled form. It directly influences the amplitude of vibration of piping systems to some degree. The larger the viscosity of the liquid is, the greater the influence will be. Budny (1991) included the viscous friction influence in time domain analysis of fluid-structure interaction, but did not give frequency domain analysis. Lesmez (1990) gave the model analysis liquid-filled piping systems without considering friction. If the friction is not included in frequency domain analysis, the vibration amplitude will be greater than that when friction is included, especially at harmony points, cause large errors in the simulation of fluid pipe network analysis, although it may have little influence on the frequency of harmony points. The present paper will give detail solutions to the transfer matrix that represents the motion of single pipe section, which is the basis of complex fluid-structure interaction analysis. Combined with point matrices that describe specified boundary conditions, overall transfer matrix for a piping system can be assembled. Corresponding state vectors can then be evaluated to predict the piping and liquid motion. At last, a twice-coordinate transformation method is adopted in joint coupling. Consequently, the vibration analysis of spatial liquid-filled piping systems can be carried out. It is proved to be succinct, valid and versatile. This method can be extended to the simulation of the curved spatial pipeline systems.
A Modified Tustin Transformation for Improved Controller Performance With Application to the Electrohydraulic Actuator
Authors: Kim Dean H. , Moulton Shawn J. , Tsao Tsu-Chin
Published: December 2021

This paper presents a modified Tustin transformation which can be used in the design process to improve controller performance significantly by reducing control input fluctuations caused by unfavorable controller pole locations. An important application is the design of robust performance controllers, which can exhibit control input fluctuations due to the rigidity of the known optimal solutions. This modified Tustin transformation utilizes a scaling factor to map the stability region of the continuous domain to a region in the discrete domain which excludes the undesirable points near z = −1. In comparison to the standard Tustin transformation, this scaling factor affects the mapping of only the points in the continuous domain corresponding to high frequencies. Hence, a critical feature of this modified transformation is that it preserves the mapping from the origin in the continuous domain to point z = 1 in the discrete domain, because this pole location corresponds to integral control. This modified Tustin transformation is applied to the robust performance controller designs for the electrohydraulic actuator. The objective is to perform a number of controller designs with different scaling factors and then determine the design which provides the best compromise between improved controller performance and achieved system performance. The simulation results and experimental data demonstrate that a scaling factor equal to 1.2 improves controller performance and maintains system performance when compared to the controller design using the standard Tustin transformation. Specifically, the control input signal energy is reduced by 53%, the system overshoot is reduced by 47%, and the settling time is reduced by 42%.
Adaptive Robust Precision Motion Control of Single-Rod Hydraulic Actuators With Time-Varying Unknown Inertia: A Case Study
Authors: Bu Fanping , Yao Bin
Published: December 2021

This paper studies the precision motion control of single-rod hydraulic actuators with time-varying unknown inertia loads. The swing motion control of a robot arm driven by a single-rod hydraulic actuator (a scaled down version of industrial backhoe loader arm) is used as a case study. During the swing motion, the effective mass acting on the hydraulic actuator varies greatly with the swing angle and thus time-varying. Furthermore, due to the change of the load of the robot arm in operations, the effective mass is also unknown. A discontinuous projection based adaptive robust controller is constructed to take into account this strong dependence of the effective mass on the fast changing swing angle and the unknown payload of the arm. The resulting ARC controller is able to take into account not only the effect of parametric uncertainties coming from the payload and various hydraulic parameters but also the effect of uncertain nonlinearities such as uncompensated friction forces and external disturbances. The ARC controller guarantees a prescribed output tracking transient performance and final tracking accuracy while achieving asymptotic output tracking in the presence of parametric uncertainties. In addition, the zero output tracking error dynamics for tracking a large class of time-varying trajectories is shown to be globally uniformly asymptotically stable. Comparative experimental results are presented to show the effectiveness and the high performance nature of the proposed control algorithm.
Modeling and Optimization of Fixture for Handling Compliant Sheet Metal Parts
Authors: Ceglarek D. , Li H. F. , Tang Y.
Published: December 2021

Material handling of compliant parts is one of the most critical and underresearched problems in the sheet metal stamping industry. The fundamental shortcoming of currently studied material handling systems for sheet metal stamping is the lack of analysis of its impact on part dimensional quality and production throughput.

This paper addresses this problem by development of a generic methodology for modeling and optimization of part holding end-effector fixture layout in order to minimize part dimensional deformation during handling operations. The methodology extends the design of “N-2-1” fixturing layout by adding part movability conditions. It considers part CAD model, handling direction and motion kinematic parameters to determine the best end effector layout. This methodology is realized by integrating FEM part and loading modeling with the optimization algorithm. It can be implemented into the design stage of a stamping line so that the trial and error process, which is current industrial practice, can be greatly shortened and the production throughput increased. Experimental results verify the proposed part holding end-effector layout methodology.
A Steady-State Model for the High-Pressure Side of Unitary Air-Conditioners
Authors: Petit Pascale J. , Meyer Josua P.
Published: December 2021

A steady-state model was developed to predict the performance of the high-pressure side of vapour-compression air-conditioning systems. The model consists of two segments; the compressor model and condenser model. The compressor model consists of a single empirical equation, for reciprocating compressors, operating with R-22, and having a cooling capacity from 2.6 to 3.5 kW. An important advantage of the approach is that the compressor performance indexes are based on operating conditions. The condenser model displays an exact method to determine physical dimensions of heat exchangers, and a simple, accurate manner to calculate the heat transfer variables. The correctness of the condensing temperature is obtained by an iterative procedure, using terms from both the compressor and condenser studies. The feasibility of the proposed model is demonstrated via a comparison with experimental data and a simulation study. Results indicate a good correlation between the mathematical model and its counterparts.
Extension of the Definition of Entropy and Temperature for Thermodynamic Systems Defined by More Than Two Independent Variables
Authors: Kouremenos Demetrius A.
Published: December 2021

In a previous paper [1] by the same author, it has been shown how to define the entropy and temperature of a thermodynamic system by using a system of two differential equation. This way of definition concerned thermodynamic system that can be described by only two independent variables such as volume v and internal energy u. By the present work this definition is shown to be valid even for more complicated systems described by more than two independent variables such as the ones that include chemical reactions, burning processes or any other. From the mathematical point of view, the extension of definition of entropy and temperature to thermodynamic systems with more than two independent variables is equivalent to finding an integrating factor for Pffafian forms having more than two independent variables. This mathematical problem is not generally solved, if such a solution is possible at all. But for the case concerned here, the special differential forms defining the entropy and temperature can deliver solutions of the problem, as it is shown in the paper. In this way, after having obtained these special solutions there is no need to prove the mathematical existence of solutions for this system of differential forms.
Development of a Space-Rated Proton Exchange Membrane Fuel Cell Powerplant
Authors: Hoffman William C. , Vasquez Arturo , Lazaroff Scott M. , Downey Michael G.
Published: December 2021

Power systems for human spacecraft have historically included fuel cells due to the superior energy density they offer over battery systems depending on mission length and power consumption. As space exploration focuses on the evolution of reusable spacecraft and also considers planetary exploration power system requirements, fuel cells continue to be a factor in the potential system solutions.

Substantial efforts are currently underway in the commercial markets to produce a proton exchange membrane (PEM) fuel cell capable of meeting terrestrial power demands in residential, commercial, and automotive applications. However, there are unique characteristics of spaceflight that can only be dealt with through specific engineering solutions.

From a systems perspective, removing product water from the cell stack and separating the water from the oxygen gas stream in a PEM fuel cell are two critical functions. One method to remove product water from the cell stack and subsequently separate the product water from the oxygen involves using components with no moving parts — a gas ejector and membrane gas-water separator. Tests are currently underway at the Johnson Space Center to evaluate and refine gas ejectors to satisfy the fuel cell requirement to circulate cathode reactant gas (oxygen) at 1 to 3 times the stoichiometric consumption flow rates in order to adequately remove water from the cathode. A gas-water separator utilizing hydrophobic and hydrophilic materials is also being evaluated to perform the function of separating the water from the oxygen gas stream. Analytical and experimental evaluations are continuing on the fuel cell components, including cell stacks, with the goal of developing a comprehensive design basis for a fuel cell powerplant capable of delivering 20 kW at approximately 28 VDC. Through the select critical component refinement in work at the Johnson Space Center, engineers are improving the readiness and reducing the technical and cost risks of a PEM fuel cell capable of operating in a space environment.
Three Phases of Applications of Thermodynamics to Process System Synthesis
Authors: Ishida Masaru
Published: December 2021

Process system synthesis is a very creative work. It has been thought that only experts can create a new system. In this paper, we discuss the procedure for process system synthesis systematically and show that applications of thermodynamics are possible in three different phases of process system synthesis.

(1) Concept generation

(2) Creation of functional structures

(3) Effective utilization of energy

The roles of each phase in the course of process system synthesis are discussed and the key tools for each stage are presented.
Thermodynamic Analysis of Various Heat Generation Methods
Authors: Smyk Adam , Portacha Józef , Fiszdon Jerzy K.
Published: December 2021

Various methods of heat generation including cogeneration, district heating, and several types of individual heaters are considered together with a variety of fuels. Performance characteristics for these systems, including fuel use, and thermal and exergetic efficiency are evaluated. Specifically, a complex thermodynamic model of the cogeneration system is presented. In this model the conditions of the surroundings vary with the surroundings temperature. Calculated efficiencies include losses in all components from the sources to the consumer (i.e. in the boiler, the turbine, the heat exchangers, and the whole transmitting network). Exergetic efficiencies vary from as low as 3% for electric heaters to more than 14% for large cogeneration plants. This result places the cogeneration systems as the most effective technology for heating. This technology produces the biggest fuel savings (four times less than for electric heating), and is therefore more environmentally friendly.
Nontraditional Striker Impact
Authors: Goldsmith Werner
Published: December 2021

More than 95% of published investigations involving projectile collisions can be classified as “standard”, defined as the orthogonal impact of purely translating strikers on stationary solid targets; non-standard impacts are all other cases that invariably occur in the field in one form or another. Impingement of projectiles has been studied since the 1700’s; for the first 150 years, only empirical results were obtained. Since about 1890, semi-empirical and quasi-rational approaches have been developed. This century has seen the enormous growth of phenomenological modeling, computational analysis — which provides for both spatial and temporal discretization and relies on material behavior description, including failure — and extended test methodologies due to the vast improvement of observation and measuring devices. Basically, whether standard or otherwise, impingement of a striker on a target can result in embedment, perforation or ricochet.
Lamb Wave Inspection of Concrete Beams
Authors: Jung Y. C. , Kundu T. , Ehsani M.
Published: December 2021

The feasibility of detecting defects in concrete beams using Lamb waves is investigated in this paper. The traditional ultrasonic methods for inspecting defects in concrete use the reflection and scattering of longitudinal waves by internal defects. Signal amplitude and time of flight measurements provide information about the internal defects in concrete. However, these methods are time consuming and often fail to detect honeycombs, closed cracks and small defects. In this paper the potential of the Lamb wave technique to detect those defects in large concrete beams is investigated. The Lamb wave technique is found to be reliable for detecting such defects in concrete beams.
Application of Joint-Time Frequency Analysis Methods for Nondestructive Evaluation
Authors: Nam Ki-Woo , Lee Kun-Chan , Oh Jeong-Hwan
Published: December 2021

Application of signal processing techniques to nondestructive evaluation (NDE) in general and acoustic emission (AE) studies in particular has become a standard tool in determining the frequency characteristics of the signals and relating these characteristics to the integrity of the structure under consideration. Recent studies have shown that the frequency characteristics of ultrasonic signals from evolving damage during cyclic (fatigue) and dynamic loads change with time; in other words, the signals are nonstationary, and that these changes can be related to the nature of the damage taking place during loading. A joint time-frequency analysis such as Short Time Fourier Transform (STFT) and Wigner-Ville distribution (WVD), can in principle be used to determine the time dependent frequency characteristics of nonstationary signals in presence of background noise. In this study these techniques are applied to analyze AE signals from fatigue crack propagation in 5083 aluminum alloys and ultrasonic signals in degraded austenitic 316 stainless steels, to study the evolution of damage in these materials. It is demonstrated that the nonstationary characteristics of both AE and ultrasonic signals could be analyzed effectively by these methods. STFT was found to be more effective in analyzing AE signals, and WVD was more effective for analyzing the attenuation and frequency characteristics of degraded materials through ultrasonics. It is indicated that the time-frequency analysis methods should also be useful in evaluating crack propagation and final fracture process resulting from various damages and defects in structural members.
Stiffness and Strength Properties for Basic Sandwich Material Core Types
Authors: Kim Beomkeun , Christensen Richard M.
Published: December 2021

Three basic core material types for sandwich structure applications are studied. The three two-dimensional pattern types are: honeycomb, triangular cells, and a new configuration involving star type cells. The specific critical properties of stiffness and strength type are identified and studied, both theoretically and experimentally.
Measure of Test Fidelity of Analytical Crash Pulses
Authors: Riesner M. , Low E. K.
Published: December 2021

In this paper, the test fidelity measure of analytical crash pulses is defined by the magnitude of an energy-momentum, (E-M), metric distance of an analytical pulse with respect to a reference, (test), pulse. The energy-momentum metric is defined and applied to calculate (E-M) metric distance of three analytical crash pulses from each other and from the test pulse. The pulses are for 35 mph. 90° rigid barrier front crash event for an identical vehicle. The three analytical pulses are generated by finite element analysis, FEA, using three different finite element models, FEM, and different solution techniques. The (E-M) metric distance of the pulses is shown to be a measure of the test fidelity of the analytical pulses. The test fidelity of the analytical pulses is defined as the ability of an analytical pulse to predict the occupant injury predictions close to the ones measured in the actual hardware test. It is shown that the crash pulse with the smallest (E-M) metric distance from the test will yield the occupant injury predictions closest to the ones yielded by the test. The test fidelity of analytical pulse will, in turn, allow to evaluate the ability of an FEM to produce high fidelity crash pulses. It is shown that high test fidelity crash pulses can be obtained by using relatively simple finite element models.
Crashworthiness Studies of Locomotive Wide Nose Short Hood Designs
Authors: Tyrell David C. , Martinez Eloy E. , Wierzbicki Tomasz
Published: December 2021

This paper investigates the parameters that influence the structural response of typical wide nose locomotive short hoods involved in offset collisions. This accident scenario was chosen based upon the railway collision that occurred in Selma, North Carolina, on May 16, 1994. A raised overhanging intermodal trailer on a freight car struck the front of the oncoming passenger locomotive. The objective of the study is to determine the current baseline level of crashworthiness of locomotive hood structures and the potential effectiveness of stronger corner structures. The key issues addressed are: degree of overlap, material and thickness combinations, obliquity, and crush response dependence on initial impacting speed. For a raised offset collision where the intruding body is far away from any support structures, an analytical expression is developed to predict the mean crush force. Comparisons of the results with finite element calculation are favorable. The scenarios involving obliquity, and different initial impacting speeds are investigated using non-linear large deformation finite element analyses. Key results are: obliquity has little effect on the mean crush force for short penetration distances; increased material thickness improves crashworthiness performance; initial impacting speed does not dramatically alter mean crush loads predicted for large offsets away from supports; and the distances from supporting structures have a significant effect of the predicted mode of failure and hence predicted mean crush loads. The results of the study show that it is possible to dramatically increase the crashworthiness responses of short hood structures with minor increases in weight while staying within the original design volume envelope.
Convective Heat Transfer at Minimum Fluidization Velocity for Gas-Solid Fluidized Beds
Authors: Sharma Kal R.
Published: December 2021

Experimentally measured values for the minimum fluidization velocities and time averaged local surface heat transfer coefficients are provided for 16 different cases of fluidizing conditions for gas-solid dense fluidized beds. Semi-empirical Correlations for the minimum fluidization velocity and the heat transfer coefficient at minimum fluidization velocities are provided. The implications of the Peclet number dependence in terms of diffusion and convection is discussed.
Determination of Air-Water Interfacial Area for Drainage and Imbibition in Unsaturated Porous Media
Authors: Schaefer Charles E. , DiCarlo David A. , Roberts Paul V. , Blunt Martin J.
Published: December 2021

A new experimental method was developed to measure air-water interfacial area as a function of capillary pressure and water saturation in unsaturated porous media. The surfactant sodium dodecyl benzene sulfonate (SDBS) was used in equilibrium column adsorption experiments to determine the air-water interfacial area for water saturations (ml water/ml pore space) ranging from 0.05 to 1.0, and pressures ranging from 0 to 20 cm of water. A comparison was made between columns which were equilibrated under gravity drainage, versus columns equilibrated under secondary imbibition. Gravity drainage experiments showed the air-water interfacial area decreased linearly with saturation, while imbibition experiments showed a more complex non-monotonic relation to the saturation.
The Influence of Boundary Condition on Solidification of Binary Solution in Rectangular Cavity
Authors: Pradeep N. , Kang H. J. , Lin C. X. , Ebadian M. A.
Published: December 2021

The solidification of a binary mixture of ammonium chloride and water flow cooling in rectangular cavities was investigated experimentally under different boundary conditions. Two cavities measuring 63.5 × 180 × 165 mm and 76 × 120 × 96 mm were employed in this study. For the first cavity, its three surfaces (i.e., two side surfaces and one bottom surface) were cooled. For the second cavity, however, only two side surfaces were cooled (i.e., the bottom surface was adiabatic). The influence of the change of boundary was studied. All investigations were carried out in the surface temperature range from −15 to −30°C under a constant refrigerant temperature of −22°C. The effect of cooling boundary condition had a great effect on the heat transfer process during the solidification process. The advanced Particle Image Velocimetry (PIV) technique was used to catch the velocity profiles during the solidification process.