bluuebunny/crossref_metadata_2025 huggingface dataset:
Ethiopian Christians on the margins: Symbolic blackness in Filippino Lippi's Adoration of the Magi and Miracle of St Philip
Authors: Nelson Jonathan K.
Published: February 2021

New identifications of prominent but overlooked black figures in two major works by Filippino Lippi enrich our understanding of how Africans were seen in late Quattrocento Florence. The African in the Adoration of the Magi, neither king nor attendant, represents the first gentiles who accepted Christ, as discussed in St Augustine’s Epiphany sermons. The black man in the Miracle of St Philip fresco, in the Strozzi Chapel of Santa Maria Novella, represents (or alludes to) the Ethiopian eunuch baptised by St Philip. These and other Florentine paintings from the 1490s, by various artists, shows black Africans as recent or future Christian converts. This hitherto unnoticed phenomenon reflects an increased awareness of Ethiopian Christians, who visited Italy repeatedly in the Quattrocento. Many Italians saw these African coreligionists as different from themselves: both insiders and outsiders. Filippino used various visual strategies to express both inclusion and alterity. Specifically, he depicts both black figures on the margins, both literally and symbolically: they stand at the edge of the miracle scenes.
Around Logical Perfection
Authors: Cruz Morales John A. , Villaveces Andrés , Zilber Boris
Published: February 2021

In this article we present a notion of “logical perfection”. We first describe through examples a notion oflogical perfectionextracted from the contemporary logical concept of categoricity. Categoricity (in power) has become in the past half century a main driver of ideas in model theory, both mathematically (stability theory may be regarded as a way of approximating categoricity) and philosophically. In the past two decades, categoricity notions have started to overlap with more classical notions of robustness and smoothness. These have been crucial in various parts of mathematics since the nineteenth century. We postulate and present the category of logical perfection. We draw on various notions of perfection from mathematics of the 19th and 20th centuries and then trace the relation to the concept of categoricity in power as a logical notion of what a “mathematically perfect” structure is.
Optimization or Bayesian Strategy? Performance of the Bhattacharyya Distance in Different Algorithms of Stochastic Model Updating
Authors: Bi Sifeng , Beer Michael , Zhang Jingrui , Yang Lechang , He Kui
Published: February 2021

The Bhattacharyya distance has been developed as a comprehensive uncertainty quantification metric by capturing multiple uncertainty sources from both numerical predictions and experimental measurements. This work pursues a further investigation of the performance of the Bhattacharyya distance in different methodologies for stochastic model updating, and thus to prove the universality of the Bhattacharyya distance in various currently popular updating procedures. The first procedure is the Bayesian model updating where the Bhattacharyya distance is utilized to define an approximate likelihood function and the transitional Markov chain Monte Carlo algorithm is employed to obtain the posterior distribution of the parameters. In the second updating procedure, the Bhattacharyya distance is utilized to construct the objective function of an optimization problem. The objective function is defined as the Bhattacharyya distance between the samples of numerical prediction and the samples of the target data. The comparison study is performed on a four degrees-of-freedom mass-spring system. A challenging task is raised in this example by assigning different distributions to the parameters with imprecise distribution coefficients. This requires the stochastic updating procedure to calibrate not the parameters themselves, but their distribution properties. The second example employs the GARTEUR SM-AG19 benchmark structure to demonstrate the feasibility of the Bhattacharyya distance in the presence of practical experiment uncertainty raising from measuring techniques, equipment, and subjective randomness. The results demonstrate the Bhattacharyya distance as a comprehensive and universal uncertainty quantification metric in stochastic model updating.
Serviceability Assessment of Footbridges Via Improved Interval Analysis
Authors: Santoro Roberta , Sofi Alba , Tubino Federica
Published: February 2021

This paper studies the propagation of uncertainties on serviceability assessment of footbridges in unrestricted traffic condition based on a nondeterministic approach. Multipedestrian loading is modeled as a stationary Gaussian random process through the equivalent spectral model which yields analytical expressions of the spectral moments of the footbridge dynamic response. The uncertain pedestrian-induced loading parameters and structural dynamic properties are modeled as interval variables. An approximate analytical procedure, based on the improved interval analysis, is introduced as an efficient alternative to classical optimization in order to propagate interval uncertainties. The presented procedure allows us to derive closed-form expressions of the bounds of the spectral moments of the response, as well as of the expected value and cumulative distribution function of the maximum footbridge acceleration. Two strategies are proposed to assess footbridges' serviceability. The first one leads to the definition of a range of comfort classes. The second strategy enables us to estimate an interval of probability of reaching at least a suitable comfort level.
Enhanced Specific Heat of Molten Salt Nano-Eutectic Via Nanostructural Change
Authors: Tiznobaik Hani , Pournorouz Zahra , Seo Joohyun , Mostafavi Amirhossein , Shin Donghyun
Published: February 2021

In this study, the specific heat of molten salt nano-eutectic (Li2CO3-K2CO3 doped with SiO2 nanoparticles) was theoretically and computationally investigated. The effective specific heat of a nano-eutectic can be significantly enhanced by the formation of needlelike nanostructures by salt eutectic. To investigate the effect of the formed nanostructure, its specific heat was theoretically calculated by a theoretical model. The mass fraction of the formed nanostructure was estimated by matlab. The theoretical prediction made a good agreement with the measured specific heat values from the literature with an error less than 3%. Additional verification of the proposed model was performed by a Molecular Dynamics simulation study. The simulated specific heat of pure molten salt eutectic made a good agreement with the literature value (1.6 kJ/kg °C with an error less than 1.7%). The simulated specific heat of nano-eutectic was 2.017 kJ/kg °C. The error between the theoretical prediction and the simulation is only 3.4% and the value made a good agreement with the experiment (1.9% max. error). The result shows that the enhanced specific heat of a nano-eutectic can be explained by the contribution of the formed nanostructures.
The Effects of Upstream Wall Roughness on the Spatio-Temporal Characteristics of Flow Separations Induced by a Forward-Facing Step
Authors: Kumahor Sedem , Fang Xingjun , Tachie Mark F.
Published: February 2021

Separating and reattaching turbulent flows induced by a forward-facing step submerged in thick oncoming turbulent boundary layers (TBL) developed over smooth and rough upstream walls were investigated using time-resolved particle image velocimetry. The examined upstream walls resulted in smooth, transitionally rough, and fully rough wall conditions. The upstream boundary layer thicknesses were 4.3 and 6.7 times the step height in the smooth and rough wall cases, respectively. The Reynolds number based on the step height and freestream velocity was 7800. The effects of upstream wall roughness on the mean flow characteristics, Reynolds stresses defined in both Cartesian and curvilinear coordinate systems, as well as the unsteadiness of the turbulent separation bubbles were critically examined. The results show that upstream wall roughness increases the boundary layer thickness and turbulence intensity and consequently, promotes early mean flow reattachment over the step. Distinct regions of significantly elevated vertical Reynolds normal stress and Reynolds shear stress were observed upstream of the step in the fully rough wall case compared to the smooth wall case. Proper orthogonal decomposition (POD) and the reverse flow area over the step were employed to investigate the unsteadiness of the separation bubbles. The first POD mode coefficient and the reverse flow area over the step were strongly correlated and exhibited the same dominant frequency.
Development of a Phase-Field Method for Phase Change Simulations Using a Conservative Allen–Cahn Equation
Authors: Tamura Akinori , Katono Kenichi
Published: February 2021

Two-phase flows including a phase change such as liquid–vapor flows play an important role in many industrial applications. A deeper understanding of the phase change phenomena is required to improve the performance and safety of nuclear power plants. For this purpose, we developed a phase change simulation method based on the phase-field method (PFM). The low computational efficiency of the conventional PFM based on the Cahn–Hilliard equation is an obstacle in practical simulations. To resolve this problem, we presented a new PFM based on the conservative Allen–Cahn equation including a phase change model. The wettability also needs to be considered in the phase change simulation. When we apply the conventional wetting boundary condition to the conservative Allen–Cahn equation, there is a problem that the mass of each phase is not conserved on the boundary. To resolve this issue, we developed the mass correction method which enables mass conservation in the wetting boundary. The proposed PFM was validated in benchmark problems. The results agreed well with the theoretical solution and other simulation results, and we confirmed that this PFM is applicable to the two-phase flow simulation including the phase change. We also investigated the computational efficiency of the PFM. In a comparison with the conventional PFM, we found that our proposed PFM was more than 100 times faster. Since computational efficiency is an important factor in practical simulations, the proposed PFM will be preferable in many industrial simulations.
Design of Condensation Heat Transfer Experiment to Evaluate Scaling Distortion in Small Modular Reactor Safety Analysis
Authors: Bhowmik Palash K. , Schlegel J. P. , Kalra V. , Mills C. , Usman S.
Published: February 2021

Designing a novel scaled modular test facility as a part of an experiment for condensation heat transfer (CHT) in small modular reactors (SMRs) is the main focus of this study. This facility will provide data to evaluate models' scalability for predicting heat transfer in the passive containment cooling system (PCCS) of SMR. The nuclear industry recognizes SMRs as future candidates for clean, economic, and safe energy generation. However, licensing requires proper evaluation of the safety systems such as PCCS. The knowledge gap from the literature review showed a lack of high-resolution experimental data for scaling of PCCS and validation of computational fluid dynamics tools. In addition, the presently available test data are inconsistent due to unscaled geometric and varying physics conditions. These inconsistencies lead to inadequate test data benchmarking. To fill this research gap, this study developed three scaled (different diameters) condensing test sections with annular cooling for scale testing and analysis. This facility considered saturated steam as the working fluid with noncondensable gases like nitrogen and helium in different mass fractions. This facility also used a precooler unit for inlet steam conditioning and a postcooler unit for condensate cooling. The high fidelity sensors, instruments, and data acquisition systems are installed and calibrated. Finally, facility safety analysis and shakedown tests are performed.
Numerical Simulation of Container Breach and Airborne Release of Solids Due to Mechanical Insults
Authors: Louie David L. Y. , Le San , Gilkey Lindsay N.
Published: February 2021

Throughout U.S. Department of Energy (DOE) complexes, safety engineers employ the five-factor formula to calculate the source term (ST) that includes parameters of airborne release fraction (ARF), respirable fraction (RF) and damage ratio (DR). Limited experimental data on fragmentation of solids, such as ceramic pellets (i.e., PuO2), and container breach due to mechanical insults (i.e., drop and forklift impact), can be supplemented by modeling and simulation using high fidelity computational tools to estimate these parameters. This paper presents the use of Sandia National Laboratories' SIERRA solid mechanics (SM) finite element code to investigate the behavior of the widely utilized waste container (such as 7A Drum) subject to a range of free fall impact and puncture scenarios. The resulting behavior of the container is assessed, and the estimates are presented for bounding DRs from calculated breach areas for the various accident conditions considered. This paper also describes a novel multiscale constitutive model recently implemented in SIERRA/SM that simulates the fracture of brittle materials such as PuO2 and determines ARF during the fracture process. Comparisons are made between model predictions and simple bench-top experiments.
Simple Graphical Method for Detection of a Partial Blockage or Leak in a Single Pipeline
Authors: Kumar Prabhat , Mohapatra P. K.
Published: February 2021

Transient-based methods in the frequency domain are used for fault detection in pipes. However, the required measurements are performed with a large number of valve frequencies. Sometimes the number of frequencies in traditional frequency-domain methods can be in the hundreds. More runs are required with higher harmonics when the required number of frequencies is more. The current study aims to overcome this difficulty of requirement of higher number of frequencies. The location and the size of a single leak or a single discrete blockage are proposed to be predicted using two appropriately chosen low frequencies. isopressure frequency responses (IPFRs) are generated by performing numerical experiments with these two low frequencies enabling determination of the fault. The methodology is demonstrated through various numerical examples. The results show that the procedure is quite accurate, with a high level of agreement between the actual and the predicted fault parameters. The error in the result is of the order of the chosen discretization. An uncertainty analysis is performed to illustrate that the prediction error caused by the error in the measurements of the pressure frequency responses (PFRs) depends on the location and the size of the fault itself. The error in prediction results is analyzed in uncertainty analysis with 0.10%, 0.15%, and 0.20% error in the peak head measurement. For the same error in the PFR measurement, the fault lying in a thin density of the contours would lead to a higher error in the final solution.
A Comparative Study on Thermal-Hydraulic Performance of Different Non-Newtonian Nanofluids Through an Elliptical Annulus
Authors: Zainith Prabhakar , Mishra Niraj Kumar
Published: February 2021

This paper presents a numerical investigation on heat transfer and flow behavior for non-Newtonian nanofluids with different nanoparticles (Al2O3 and CuO) and carboxymethyl cellulose (CMC) with water as a base fluid. The analysis has been carried out in an elliptical tube. Power-law model is adopted to depict the non-Newtonian nature of nanofluid. The present study has been done with a range of nanosized particles 0–4% by volume, and the variation of Reynolds number is kept under the laminar condition. The physical model covers two concentric tubes used to create an annular space. The effects of volume fraction, particle type, and base fluid have been investigated at different Reynolds numbers numerically. Also, the effect of pressure and heat transfer coefficient on the flow behavior of non-Newtonian nanofluids is analyzed. The results concluded that Al2O3 particles showed 219% and CuO particles give 195% higher heat transfer coefficient as compared with pure water.
Temperature Elevation in the Human Eye Due To Intraocular Projection Prosthesis Device
Authors: Gongal Dipika , Thakur Siddhant , Panse Ashay , Stark John A. , Yu Charles Q. , Foster Craig D.
Published: February 2021

Corneal opacity is a leading cause of blindness worldwide. Corneal transplantation and keratoprosthesis can restore vision but have limitations due to the shortage of donor corneas and complications due to infection. A proposed alternative treatment using an intraocular projection prosthesis device can treat corneal disease. In this study, we perform a transient thermal analysis of the bionic eye model to determine the power the device can produce without elevating the eye tissue temperature above the 2°C limit imposed by the international standard for implantable devices. A 3D finite element model, including blood perfusion and natural convection fluid flow of the eye, was created. The device was placed 1.95 mm from the iris, which experienced less than 2°C rise in the tissue temperature at a maximum power dissipation of LED at 100 mW and microdisplay at 25 mW.
Using Private Industry Based Projects to Teach an Air Conditioning Technical Elective Course
Authors: Anderson Kevin R.
Published: February 2021

This paper presents the use of private industry based projects to augment the teaching of a senior level thermal design Heating Ventilation Air Conditioning and Refrigeration (HVAC/R) technical elective. The projects describe herein are used to augment the laboratory portion of the course, and act a synthesizing agents allowing students to experience real-world problem solving first hand. The industry based projects are solicited form local industry representatives, whereby mentors from the engineering company are assigned to direct a team of students to complete a given set of action items during the duration of a semester concluding in an end of semester customer design review. The key to this type of learn-by-doing is the active engagement and willingness on behalf of the industry mentors to take time to guide the students via biweekly face to face or web based tag up meetings. This type of experience is invaluable for the students, since it demonstrates the importance of establishing a network of mentors in order to foster life-long learning in the students chosen field of study.
Experimental Study of Direct Metal Laser Sintering: High Cycle Fatigue Life and Process Parameters
Authors: Seyffert Riley , Kaul Sudhir
Published: February 2021

Direct Metal Laser Sintering (DMLS) is a relatively new manufacturing process in additive manufacturing (AM) that fuses powdered metal by using a high-powered laser. Although this process allows manufacturing prototypes without requiring specific tooling, it is challenging to use this process for manufacturing high volume production parts since complex shapes can take a significant amount of build time. Furthermore, manufactured parts also need some amount of post-processing to remove the support material that may be required due to the layer-by-layer build process. This study investigates three process parameters that could be optimized to substantially reduce production time. These three parameters are as follows: build layer thickness, laser scan speed, and laser hatch distance. In order to evaluate the influence of these parameters, manufactured parts made of AISI 316L Stainless Steel are tested for fatigue life and static strength. A three-point bending test is used as per ASTM E466. While none of the three parameters is seen to significantly influence ultimate tensile strength, results indicate that build layer thickness is a significant process parameter that directly affects fatigue life. Furthermore, the interaction between build layer thickness and laser scan speed is found to be statistically significant for high cycle fatigue. However, laser scan speed and laser hatch distance are seen to be statistically insignificant for fatigue life. The initial results of this study indicate that process parameters of DMLS need to be selected judiciously in order to minimize build time while maintaining structural integrity.
Pragmatic Approach to Teaching Introduction to Machine Design
Authors: Anderson Kevin R. , Stover Clifford M.
Published: February 2021

This paper presents examples of teaching Mechanical Design using a pragmatic approach. The pedagogy used herein embeds real-world experience and projects into the curriculum by taking representative case studies from industry and creating course projects. The approach focuses on using sanity checks using free-body diagrams and hand-calculations, materials specification and proliferate used of commercial off the shelf parts supplier catalog data. Case studies from course projects are presented demonstrating the above skill set reinforcement. The assessment of the student work is presented as it is related to the ABET learning outcomes of the mechanical design curriculum track.
Experimental and Numerical Investigation Into Vertical Axis Water Turbine Self-Starting Phenomenon
Authors: Rivera Marcos , Shook Daniel , Foust Emine
Published: February 2021

In rural areas and isolated regions of the world, it is often difficult to obtain reliable access to electricity. A solution often exploited is the use of diesel generators to power homes but that has its negative effects on climate change. In this study, an alternative solution is being investigated, which involves the use of water turbines. For low head applications such as rivers, hydrokinetic turbines are used to harness the kinetic energy in rivers. There are two types of hydrokinetic turbines: horizontal and vertical axis water turbines. The turbine studied in this paper is the Darrieus type vertical axis water turbine (VAWT) which has three straight blades. Darrieus type VAWT primarily use lift forces to operate. Advantages of vertical axis water turbines are simple construction, low cost, and being able to self-orient. However, the Darrieus VAWT has several disadvantages like self-starting problem, low coefficient of performance, shaking, debris accumulation, and cavitation.

In this study, the effect of using thermoplastic polyurethane blades with varying levels of flexibility have been investigated to remedy the self-starting problem. For blade profile, S1046 airfoil is selected. 3-D numerical models were created by using time-accurate Reynolds-averaged Navier Stokes (RANS) commercial solver (ANSYS Fluent 2019 R3). Experimental results show that turbine with lower blade hardness starts to rotate at 0.34m/s while the turbine with higher blade hardness experiences rotation at 0.51m/s.
2 DOF Compliant 3D-PLE System Demonstrating Fundamentals of Vibrations and Passive Vibration Isolation
Authors: Giannakakos Niko , Tekes Ayse , Utschig Tris
Published: February 2021

Mechanical engineering students often learn the fundamentals of vibrations along with the time response of underdamped, critically damped, and overdamped systems in machine dynamics and vibrations courses without any validation or visualization through hands-on experimental learning activities. As these courses are highly theoretical, students find it difficult to connect theory to practical fundamentals such as modeling of a mechanical system, finding components of the system using experimental data, designing a system to achieve a desired response, or designing a passive vibration isolator to reduce transmitted vibrations on a primary system. Further, available educational laboratory equipment demonstrating vibrations, dynamics and control is expensive, bulky, and not portable. To address these issues, we developed a low-cost, 3D printed, portable laboratory equipment (3D-PLE) system consisting of primary and secondary carts, rail, linear actuator, Arduino, and compliant flexures connecting the carts. Most of the educational systems consist of a mass limited to 1DOF motion and multi-degrees of freedom systems can be created using mechanical springs. However, in real-world applications oscillations in a system are not necessarily due to mechanical springs. Anything flexible, or thin and long, can be represented by a spring as seen in torsional systems. We incorporated 3D printed and two monolithically designed rigid arms connected with a flexure hinge of various stiffness. The carts are designed in a way such that two flexible links can be attached from both sides and allow more loads to be added on each cart. The system can be utilized to demonstrate fundamentals of vibrations and test designs of passive isolators to dampen the oscillations of the primary cart.
Designing Composites for Graceful Failure
Authors: Micheal Amany , Bahei-El-Din Yehia , Abd El-Latief Mahmoud E.
Published: February 2021

When inevitable, failure in composite laminates is preferred to occur gracefully to avoid loss of property and possibly life. While the inherent inhomogeneity leads to slow dissipation of damage-related energy, overall failure is fiber-dominated and occurs in a rather brittle manner. Multidirectional plies usually give a more ductile response. Additionally, stiffness and strength as well as cost are important factors to consider in designing composite laminates. It is hence desirable to optimize for high mechanical properties and low cost while keeping graceful failure.

Designing composite laminates with hybrid systems and layups, which permit gradual damage energy dissipation, are two ways proposed in this work to optimize for mechanical properties while avoiding catastrophic failure. In the hybrid system design, combining the less expensive glass reinforced plies with carbon reinforced plies offers a cost-effective product, marginal mechanical properties change and ductile profile upon failure. Hybrid glass/carbon composite laminates subjected to three-point bending showed strain to failure which is double that measured for carbon composite specimens, without affecting the ultimate load.

Energy dissipation mechanisms were also created by building laminates which were intentionally made discontinuous by introducing cuts in the fibers of the interior plies. This created a longer path for damage before cutting through the next ply resulting in double failure strain with marginal reduction in load. The effect of fiber discontinuity in terms of spacing and distribution are among the factors considered.
Mechanical Component’s Dimension Design With Required Reliability by the Monte Carlo Method
Authors: Le Xiaobin
Published: February 2021

Since the main design parameters in a mechanical component design have some uncertainties and should be treated as random variables, the reliability of a component is a better measurement of the safe status of a component. A component will not be reliable unless it is designed with specified reliability. Therefore, the mechanical component design should be a dimension design with the required reliability. The fundamental concept of the Monte Carlo method is to plug-in randomly generated numerical values into the governing equation of a design problem to get a trial result. The Monte Carlo method has become so powerful numerical simulation approach in almost every field such as optimization, numerical integration, and reliability calculation. But for reliability engineering, most of the literature shows how to use the Monte Carlo method to calculate the reliability of a component. This paper will propose the modified Monte Carlo method to determine a component dimension with required reliability. This paper first discusses and establishes typical limit state functions of a component under static loads. These limit state functions cover two failure modes including the failure mode due to strength and the failure mode due to excessive deformation. Then, the procedure and the flowchart of the modified Monte Carlo method will be explained in detail. The provided procedure and the flowchart are easy to be followed for compiling a MATLAB program to conduct a dimension design with required reliability. Two examples will show how to implement the proposed new method for conducting a dimension design with required reliability.
Global Warming Potential Estimations of a Gas Turbine Engine and Effect of Selected Design Parameters
Authors: Dinc Ali , Gharbia Yousef
Published: February 2021

Anthropogenic global warming is a result of greenhouse gas emissions from many human activities such as industry, power generation, transportation etc. Burning fossil fuels generates gas emissions and those emissions should be minimized by careful designs and operations for a sustainable world. The gas turbines are typically used in many applications to generate power and propulsion which require burning of liquid fuel, natural gas etc. In this study, Global Warming Potential (GWP) calculations of a 43 MW class gas turbine engine have been performed. Global warming potential values were calculated for a range of selected design parameters such as turbine inlet temperature, compressor pressure ratio, compressor efficiency, turbine efficiency etc. Those design input parameters were changed ± 5% from an assumed baseline to investigate their effects on the total GWP values due to emissions of CO2, H2O and NOx. The results presented a good guide on the selection of design input parameters in order to cut the emissions down from the design perspective of gas turbine engines. A range of reductions in GWP between 0.46% and 5.86% were estimated by the calculations in this study.
Comparison of Fluid Structure Interaction Capabilities in Finite Volume and Finite Element Based Codes
Authors: Lu Qiyue , Santiago Alfonso , Koric Seid , Cordoba Paula
Published: February 2021

Fluid-Structure Interaction (FSI) simulations have applications to a wide range of engineering areas. One popular technique to solve FSI problems is the Arbitrary Lagrangian-Eulerian (ALE) method. Both academic and industry communities developed codes to implement the ALE method. One of them is Alya, a Finite Element Method (FEM) based code developed in Barcelona Supercomputing Center (BSC). By analyzing the application on a simplified artery case and compared to another commercial code, which is Finite Volume Method (FVM) based, this paper discusses the mathematical background of the solver for domains, and carries out verification work on Alya’s FSI capability. The results show that while both codes provide comparable FSI results, Alya has exhibited better robustness due to its Subgrid Scale (SGS) technique for stabilization of convective term and the subsequent numerical treatments. Thus this code opens the door for more extensive use of higher fidelity finite element based FSI methods in future.
An Eigensystem Realization Algorithm for Modal Parameter Identification of a Vertical-Shaft High-Speed Centrifugal Machine
Authors: Piramoon Sina , Ayoubi Mohammad A.
Published: February 2021

In this paper, we utilize the observer/Kalman filter identification (OKID) and the eigensystem realization algorithm (ERA) techniques to identify the modal parameters of a centrifugal machine. To this end, we use an experimental setup to generate a pseudo-impulse input and collect output measurements which are corrupted by noise. We use the pseudo-impulse input and the OKID to find the Markov parameters of the system. Then we form the Hankel matrix of the system and determine the singular values of the system. A minimum-order, state-space model of the system is realized through the Markov parameters and then the natural frequency, damping ratio, mode shapes, and modal amplitudes at the sensor location are estimated by the ERA. We find three models for three separate cases and validate all the three identified models with the measured data and the Waterfall plot. The identified models are useful for designing passive or active vibration suppression control and fault detection systems. The results confirm that OKID/ERA is a reliable time-domain method for identifying the modal parameters of vertical centrifuge machines.
Robustness Analysis of Parallel Feedforward Control With Derivative (PFCD) Method
Authors: Noury Keyvan , Yang Bingen
Published: February 2021

In this paper, the authors represent the robustness capabilities of their previously implemented parallel feedforward compensator configuration, applicable to nonminimum-phase (NMP) systems. In the previous papers, it was shown how a paralleled feedforward compensator can stabilize a general purpose NMP system with ease. However, the robustness analysis was postponed for a later study. Thus, herein, the robustness capabilities of the proposed configuration in the presence of noise and disturbance are investigated. It will be shown that the main idea behind the stability of the parallel feedforward compensation with derivative (PFCD) methodology comes handy when trying to test for the robustness purposes. At the end, a simulation example is brought to represent the ballparks of the methodology.
Exergoeconomic Analysis in a Cement Production Plant
Authors: Fajardo J. , Mendoza A. , Barreto D. , Valle H.
Published: February 2021

A dry-type Cement Production Plan of 151 Tons per hour was taken as a case of study to implement an exergoeconomic analysis. In this paper, the exergy destruction and the investment costs of the system’s units were calculated to obtain accurate information about the performance of the process, from the exergoeconomic factor and the relative difference cost.

Conventional exergoeconomic analysis showed that the total cost of exergy destruction is 4206537 USD/h. The Calciner and the Rotary Kiln cause 62% of the total cost of the exergy destruction. The lowest values of the exergoeconomic factor were calculated for Calciner (0.01%), Clinker Cooler (0.01%), Rotary Kiln (0.02%), and Raw Mill (0.04%). The significant difference in relative cost was calculated for Calciner (42%) and Rotary Kiln (54.21%). The above implies that this equipment should be considered for an investment that allows the decrease of the exergy destruction cost and the increase of the exergetic efficiency.
Modeling Transient Heat Transfer and Dry-Out Phenomena in Heat Pipes Using Finite Element Analysis
Authors: Özçatalbaş Mustafa , Sezmen Ramazan Aykut
Published: February 2021

Heat pipes are passive two-phase heat transfer devices that used in various heat transport applications because of their high thermal conductance capacities with low temperature differences. One of these applications is aerospace avionics that heat pipes are exposed to transient heat loads. Although heat pipes have been one of the heat removal alternatives for compact electronic devices, they have some restrictions during the usage in such high heat flux areas. In order to use heat pipes as effective heat removal devices, operating heat load range should not be exceeded during the operation of avionics or electronic devices. Out of these operating range, heat pipes no longer perform as effective heat removal devices because of phenomena called dry-out.

In this study, a novel Finite Element (FE) Analysis Method was developed to model transient heat transfer behavior in heat pipes including dry-out phenomenon. Transient heat transfer analysis using Finite Element Method (FEM) was conducted to investigate heat pipe thermal performance considering heat flux dependent thermal conductivity under randomly varying heat inputs, which were assumed as heat dissipation of an electronic device. Validation of the FE model was done by using the results given in the literature.

Heat pipe was made of Al with a length of LHP = 200 mm. Heat flux and convective heat transfer boundary conditions were used at the evaporator and condenser sections, respectively. Effective thermal conductivity of heat pipe, keff, was calculated by using the heat input depended thermal resistance, Rth, values given in literature. Under transient heat loads, heat flux dependent effective thermal conductivity was defined using user defined subroutines to simulate the dry-out. The transient heat transfer analysis was conducted using ABAQUS commercially available software. Temperature differences between evaporator and condenser sections, ΔT = Te−Tc, and thermal resistance, Rth, values are calculated for varying heat input values and compared with the results that provided in literature.
Maximum Condensable Pressure in a Sealed Container With Arbitrary Temperature Distribution
Authors: Watjen J. I. , Schifano M. T. , Sexton M. N.
Published: February 2021

Pressure vessels and sealed canisters are designed to maintain seal integrity under a maximum internal pressure. When the temperature inside the canister rises, the internal pressure rises accordingly. The presence of condensable liquid-vapor mixtures can create a strong relationship between the pressure and temperature. An isothermal container admits a straightforward thermodynamic pressure calculation; however, large temperature gradients inside the container require complex multiphase conjugate heat transfer calculations to predict accurate pressures. A simplified prediction using the peak internal temperature to find the saturated pressure of the condensable fluid may introduce unrealistic pressures when significant fluid mass exists in a cooler location of the container.

This work presents methodology to calculate the pressure of a condensable fluid in a sealed container with large internal temperature differences using a two-temperature approach to predict saturated boiling and superheating of the vapor phase. An arbitrary temperature distribution allows for pressure calculations by considering the expected location of the liquid mass and the peak internal temperature. An enthalpy balance provides the effects of the temperature distribution and the peak pressure condition is easily predicted using the proposed method. This work provides a means to calculate the maximum internal pressure of a sealed container with a condensable fluid without the need for complex multiphase computer modeling.
Kit Based Motion Generator for a Soft Walking Robot
Authors: Schiller Lars , Maruthavanan Duraikannan , Seibel Arthur , Schlattmann Josef
Published: February 2021

In order to control high-level goals such as walking speed and direction or position of legged robots, a locomotion controller is required. This complicated task can be solved in many different ways. The approach presented here selects the optimal gait pattern from a discrete, predefined set of possibilities to get closer to a given target position. The method is based on an off-line component: elementary gait patterns are generated by trajectory optimization using a simulation model, and an on-line component: for given robot and target positions the optimal next elementary gait pattern is chosen based on a minimization problem, and the joint space references are derived from it. To ensure feasible subsequent poses, the elementary patterns always begin and end with one and the same pose, so that they can be placed on top of each other like Lego bricks. A great advantage of this method is a straightforward transition between different motion modes, such as switching from trotting to crawling. It is discussed how many different elementary patterns are needed to ensure a stable locomotion control. Finally, in simulation and experiment, it is shown that the robot can master any obstacle course using the proposed locomotion controller.
Augmentation of Fixed Gain Controlled Infinite Dimensional Systems With Direct Adaptive Control
Authors: Balas Mark J.
Published: February 2021

Linear infinite dimensional systems are described by a closed, densely defined linear operator that generates a continuous semigroup of bounded operators on a general Hilbert space of states and are controlled via a finite number of actuators and sensors. Many distributed applications are included in this formulation, such as large flexible aerospace structures, adaptive optics, diffusion reactions, smart electric power grids, and quantum information systems.

In this paper, we focus on infinite dimensional linear systems for which a fixed gain linear infinite or finite dimensional controller is already in place. We augment this controller with a direct adaptive controller that will maintain stability of the full closed loop system even when the fixed gain controller fails to do so. We prove that the transmission zeros of the combined system are the original open loop transmission zeros, and the point spectrum of the controller alone. Therefore, the combined plant plus controller is Almost Strictly Dissipative (ASD) if and only if the original open loop system is minimum phase, and the fixed gain controller alone is exponentially stable. This result is true whether the fixed gain controller is finite or infinite dimensional. In particular this guarantees that a controller for an infinite dimensional plant based on a reduced -order approximation can be stabilized by augmentation with direct adaptive control to mitigate risks.

These results are illustrated by application to direct adaptive control of general linear diffusion systems on a Hilbert space that are described by self-adjoint operators with compact resolvent.
Prediction of Surface Profile in Friction Stir Welding Using Coupled Eulerian and Lagrangian Method
Authors: Das Debtanay , Bag Swarup , Pal Sukhomay , Amin M. Ruhul
Published: February 2021

Friction stir welding (FSW) is widely accepted by industry because of multiple advantages such as low-temperature process, green technology, and capable of producing good quality weld joints. Extensive research has been conducted to understand the physical process and material flow during FSW. The published works mainly discussed the effects of various process parameters on temperature distribution and microstructure formation. There are few works on the prediction of defect formation from a physics-based model. However, these models ignore chip formation or surface morphology and material loss during the FSW process. In the present work, a fully coupled 3D thermo-mechanical model is developed to predict the chip formation and surface morphology during welding. The effects of various process parameters on surface morphology are also studied using the current model. Coupled Eulerian-Lagrangian (CEL) technique is used to model the FSW process using a commercial software ABAQUS. The model is validated by comparing the results in published literature. The current model is capable of predicting the material flow out of the workpiece and thus enables the visualization of the chip formation. The developed model can extensively be used to predict the surface quality of the friction stir welded joints.
Ten Years of Positive Feedback on Project-Based Learning From First-Year Engineering Students’ Perspective
Authors: Alves Anabela C. , Moreira Francisco , Leão Celina P. , Fernandes Sandra
Published: February 2021

Project-Based Learning (PBL) is an active student-centered learning methodology. Several schools (of varying degrees of education) have implemented, in different ways, PBL, having as common strands that the student learns in teams, and being challenged in the context of a case-scenario. In Portugal, a PBL methodology has been implemented, in the first year of an Industrial Engineering and Management (IEM) program, for more than 15 years. This represents a total number above 700 students of IEM enrolled in PBL during the reported timeframe. A continuous improvement process of the PBL activities was relentlessly pursued during such period. Grounded on end-of-term on-line PBL process satisfaction questionnaires, as well as on results of each PBL edition final workshops, this paper studies and reports on a number of such achievements and shortcomings. Thus, this paper presents the analysis of the results of ten academic years of PBL evaluation process, grounded on the compiled results obtained from 2009/10 to 2019/20. Also, a synthesis of the effective findings (either positive or negative), systematically pointed out by the students, will be presented. Altogether, the PBL implementation in the IEM program has been very positive for students and teachers and worth for others to follow.
Dynamic Simulation and Ground Testing of the Autonomous Vertical Air-Launch Sled Concept
Authors: Lee Peter , Sarigul-Klijn Nesrin
Published: February 2021

A unique towed air-launch concept called the vertical air-launch sled is studied using a 1/32nd scale vehicle. The sled allows a launch vehicle carried by it to be towed to an altitude by a mother aircraft using a standard towline. The focus was to design and test autonomous tow taxi and takeoff phase of flight using simulations and flight tests. In order to study the scaling validity, experimental flight test data was compared to the theoretically predicted dynamic response of the scaled system, as well as compared to a theoretically predicted dynamic response of the full-scale system. The towing aircraft is a 1/11th scale T-28 remotely piloted aircraft. Lateral stability, runway centerline following ability as well as tautness of the tow line are studied as measures of performance of the autonomous system designed. Test results are reported showing that the tow aircraft was able to tow the vehicle along the correct path. It is identified that the rudder servos were saturated in adjusting the trajectory and future flight tests will include implementing front wheel steering into the system to alleviate the rudder servos saturation. Duration of the flight tests will be increased to better evaluate the automatic controller.
Vibration Suppression for Large-Scale Flexible Structures Using Deep Reinforcement Learning Based on Cable-Driven Parallel Robots
Authors: Sun Haining , Tang Xiaoqiang , Wei Jinhao
Published: February 2021

Specific satellites with ultra-long wings play a crucial role in many fields. However, external disturbance and self-rotation could result in undesired vibrations of flexible wings, which affects the normal operation of the satellites. In severe cases, the satellites will be damaged. Therefore, it is imperative to conduct vibration suppression for these flexible structures. Utilizing deep reinforcement learning (DRL), an active control scheme is presented in this paper to rapidly suppress the vibration of flexible structures with quite small controllable force based on a cable-driven parallel robot (CDPR). To verify the controller’s effectiveness, three groups of simulation with different initial disturbance are implemented. Besides, to enhance the contrast, a passive pre-tightening scheme is also tested. First, the dynamic model of the CDPR that is comprised of four cables and a flexible structure is established using the finite element method. Then, the dynamic behavior of the model under the controllable cable force is analyzed by Newmark-ß method. Furthermore, the agent of DRL is trained by the deep deterministic policy gradient algorithm (DDPG). Finally, the control scheme is conducted on Simulink environment to evaluate its performance, and the results are satisfactory, which validates the controller’s ability to suppress vibrations.