Department of Aerospace and Ocean Engineering

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50-kHz-rate 2D imaging of temperature and H2O concentration at the exhaust plane of a J85 engine using hyperspectral tomography
Ma, Lin; Li, Xuesong; Sanders, Scott T.; Caswell, Andrew W.; Roy, Sukesh; Plemmons, David H.; Gord, James R. (Optical Society of America, 2013-01-01)
This paper describes a novel laser diagnostic and its demonstration in a practical aero-propulsion engine (General Electric J85). The diagnostic technique, named hyperspectral tomography (HT), enables simultaneous 2-dimensional (2D) imaging of temperature and water-vapor concentration at 225 spatial grid points with a temporal response up to 50 kHz. To our knowledge, this is the first time that such sensing capabilities have been reported. This paper introduces the principles of the HT techniques, reports its operation and application in a J85 engine, and discusses its perspective for the study of high-speed reactive flows. (C) 2013 Optical Society of America
5th International Symposium on Focused Ultrasound
Abounader, Roger; Abraham, Christopher; Adema, Gosse; Agrawal, Punit; Airan, Raag; Aleman, Dionne; Alexander, Phillip; Alkins, Ryan; Alnazeer, Moez; Altman, Michael; Aly, Amirah; Amaral, Joao G.; Amrahli, Maral; Amraoui, Sana; Andarawewa, Kumari; Andriyakhina, Yulia; Angstadt, Mary; Ankou, Bénédicte; Arias, Ana C.; Arvanitis, Costas; Asadnia, Kiana; Aubert, Isabelle; Aubry, Jean-Francois; Aubry, Jean-Francois; Aurup, Christian; Bader, Kenneth; Badr, Lena; Baek, Hongchae; Barbato, Gaetano; Beccaria, Kevin; Bellorofonte, Carlo; Benson, Lee; Bernus, Olivier; Berriet, Rémi; Bertolina, Jim; Beskin, Viktoriya; Bessière, Francis; Bethune, Allison; Bezzi, Mario; Bond, Aaron; Bonomo, Guido; Borowsky, Alexander; Borys, Nicolas; Böttcher, Joachim; Bouley, Donna; Bour, Pierre; Bourekas, Eric; Brenin, David; Brokman, Omer; Brosh, Inbar; Buckner, Andrew; Bullock, Timothy; Cafarelli, Andrea; Cahill, Jessica; Camarena, Francisco; Camelo-Piragua, Sandra; Campbell, Benjamin; Campbell, Fiona; Cannata, Jon; Canney, Michael; Carlson, Roy; Carneiro, Antonio; Carpentier, Alexandre; Catheline, Stefan; Cavin, Ian; Cesana, Claudio; Chabok, Hamid R.; Chamanara, Marzieh; Chang, Jin H.; Chang, Won S.; Changizi, Barbara; Chapelon, Jean Y.; Chaplin, Vandiver; Chapman, Martin; Chaudhary, Neeraj; Chaussy, Christian; Chen, Cherry; Chen, Johnny; Chen, Wohsing; Chen, Xiaoming; Chevalier, Philippe; Chiou, George; Chisholm, Alexander; Christofferson, Ivy; Chung, Hyun H.; Ciuti, Gastone; Clement, Gregory; Cooper, Mark; Corea, Joseph; Corso, Cristiano; Cosman, Josh; Coughlin, Dezba; Crake, Calum; Cunitz, Bryan; Curiel, Laura; Curley, Colleen T.; Czarnota, Gregory; Dababou, Susan; Dallapiazza, Robert; de Bever, Joshua; de Jager, Bram; de Ruiter, Joost; de Senneville, Baudouin D.; Deckers, Roel; Delattre, Jean-Yves; den Brok, Martijn; Dhanaliwala, Ali; Diodato, Alessandro; Dixon, Adam; Donner, Elizabeth; Downs, Matthew; Du, Zhongmin; Dubois, Rémi; Dupre, Aurelien; Eikelenboom, Dylan; Elias, W. J.; Ellens, Nicholas; Endre, Ruby; Eran, Ayelet; Erasmus, Hans-Peter; Everstine, Ashli; Farahani, Keyvan; Farrer, Alexis; Farry, Justin; Federau, Christian; Feng, Xue; Ferrer, Cyril; Ferrera, Vincent; Fishman, Paul; Foley, Jessica; Frenkel, Victor; Fütterer, Jurgen; Gach, H. M.; Gandhi, Dheeraj; Gertner, Michael; Goldsher, Dorit; Gorgone, Alessandro; Greillier, Paul; Griesenauer, Rebekah; Grissom, William; Grondin, Julien; Guha, Chandan; Gulati, Amitabh; Gullapalli, Rao; Guo, Sijia; Gupta, Samit; Gurm, Hitinder; Gwinn, Ryder; Hadley, Rock; Haïssaguerre, Michel; Hammoud, Dima; Hananel, Arik; Hargrove, Amelia; Hatch, Robert; Haworth, Kevin; Hazan, Eilon; He, Ye; Heemels, Maurice; Heerschap, Arend; Hilas, Elaine; Hoang-Xuan, Khe; Hocini, Mélèze; Hodaie, Mojgan; Hofmann, Denis; Holland, Christy; Hoogenboom, Martijn; Hopyan, Sevan; Hossack, John; Houdouin, Alexandre; Hsu, Po-Hung; Hu, Jim; Hurwitz, Mark; Huss, Diane; Hwang, Chang-il; Hwang, Joo H.; Idbaih, Ahmed; Ikeuchi, Masahiko; Ingham, Elizabeth; Ives, Kimberly; Izumi, Masashi; Jackson-Lewis, Vernice; Janát-Amsbury, Margit; Jang, Kee W.; Jedruszczuk, Kathleen; Jiménez-Gambín, Sergio; Jiménez, Noé; Johnson, Sara; Jonathan, Sumeeth; Joy, Joyce; Jung, Hyun H.; Jung, Na Y.; Kahn, Itamar; Kamimura, Hermes; Kamrava, Seyed K.; Kang, Jeeun; Kang, Kook J.; Kang, Soo Y.; Kao, Yi-tzu; Katti, Prateek; Kawasaki, Motohiro; Kaye, Elena; Keupp, Jochen; Kim, AeRang; Kim, Harry; Kim, Hyun-Chul; Kim, Hyuncheol; Kim, Hyungmin; Kim, Min S.; Kim, Namho; Kiyasu, Katsuhito; Kneepkens, Esther; Knopp, Michael; Kobus, Thiele; Koral, Korgun; Kreider, Wayne; Krishna, Vibhor; Krug, Roland; Krupa, Steve; Kuo, Chia-Chun; Kwiecinski, Wojciech; Lacoste, Romain; Lam, Heather; Lamberti-Pasculli, Maria; Lang, Brian; Larner, James; Larrabee, Zachary; Leach, J. K.; LeBlang, Suzanne; Leclercq, Delphine; Lee, Hak J.; Lee, Jong-Hwan; Lehericy, Stéphane; Leighton, Wan; Leung, Steven; Lewis, Bobbi; Lewis, Matthew; Li, Dawei; Linn, Sabine; Lipsman, Nir; Liu, Hao-Li; Liu, Jingfei; Lopes, M. B.; Lotz, Jeff; Lu, Xin; Lundt, Jonathan; Luo, Xi; Lustgarten, Lior; Lustig, Micheal; Macoskey, Jonathan; Madore, Bruno; Maev, Roman; Magat, Julie; Maimbourg, Guillaume; Maimon, Noam; Mainprize, Todd; Malayer, Jerry; Maples, Danny; Marquet, Fabrice; Marrocchio, Cristina; Marx, Mike; Mastorakos, Panagiotis; Mauri, Giovanni; McLean, Hailey; McMichael, John; Mead, Brian P.; Melodelima, David; Melot-Dusseau, Sandrine; Menciassi, Arianna; Merrill, Robb; Meyer, Joshua; Midiri, Massimo; Miga, Michael; Migliore, Ilaria G.; Miller, Eric; Minalga, Emilee; Moon, Hyungwon; Moore, David; Mourad, Pierre; Mouratidis, Petros; Mueller, Michael; Mugler, John; Muller, Sébastien; Namba, Hirofumi; Naor, Omer; Nassar, Maria; Nazai, Navid; Negron, Karina; Negussie, Ayele; Nguyen, Thai-Son; Nicolay, Klaas; Nikolaeva, Anastasia V.; Oetgen, Matthew; Olive, Kenneth; Olumolade, Oluyemi; Orsi, Franco; Owens, Gabe; Ozilgen, Arda; Padegimas, Linas; Palermo, Carmine; Pan, Chia-Hsin; Pandey, Aditya; Papadakis, Georgios; Park, Chang K.; Park, Sang M.; Parker, Jonathon; Parvizi, Mohammad H.; Pascal-Tenorio, Aurea; Patel, Janish; Patz, Sam; Payen, Thomas; Perich, Eloi; Pernot, Mathieu; Perol, David; Perry, James; Pillarisetty, Venu; Pioche, Mathieu; Pizzuto, Matthew; Plaksin, Michael; Plata, Juan; Price, Karl; Prince, Jessica; Przedborski, Serge; Quinones-Hinojosa, Alfredo; Ramachandran, Akhilesh; Ranjan, Ashish; Ravikumar, Vinod; Reichenbach, Juergen; Repasky, Elizabeth; Rezai, Ali; Ritter, Philippe; Rivoire, Michel; Rochman, Carrie; Rosenberg, Jarrett; Rosnitskiy, Pavel B.; Ruiz, Antonio; Sahgal, Arjun; Samiotaki, Gesthimani; Sanghvi, Narendra; Santin, Mathieu D.; Santos, Domiciano; Sasaki, Noboru; Sastra, Steve; Schade, George; Schall, Jeffrey; Schlesinger, Ilana; Schmitt, Paul; Schwaab, Julia; Scionti, Stephen; Scipione, Roberto; Scoarughi, Gian L.; Scott, Serena; Sebeke, Lukas; Seifabadi, Reza; Seo, Jai; Sesenoglu-Laird, Ozge; Shah, Binit; Shahriari, Kian; Shaikh, Sumbul; Shea, Jill; Shi, Jiaqi; Shim, Jenny; Shinkov, Alexander; Shuman, Jillian; Silvestrini, Matthew; Sim, Changbeom; Sin, Vivian; Sinai, Alon; Singh, Manoj; Sinilshchikov, Ilya; Skalina, Karin; Slingluff, Craig; So, Po-Wah; Solomon, Stephen; Son, Keon H.; Sperling, Scott; Stein, Ruben; Stein, Sherman; Stevens, Aaron; Stimec, Jennifer; Storm, Gert; Straube, William; Suelmann, Britt; Sutton, Jonathan; Svedin, Bryant; Takemasa, Ryuichi; Takiguchi, Mitsuyoshi; Tam, Emily; Tan, Jeremy; Tang, Xinyan; Tanter, Mickael; Tebebi, Pamela; Tehrani, Seruz; Temple, Michael; Teofilovic, Dejan; ter Haar, Gail; Terzi, Marina E.; Thueroff, Stefan; Timbie, Kelsie; Tognarelli, Selene; Tretbar, Steffen; Trudeau, Maureen; Tsai, Yi-Chieh; Tsysar, Sergey A.; Tucci, Samantha; Tuveson, David; Ushida, Takahiro; Vaessen, Paul; Vaillant, Fanny; Van Arsdell, Glen; van Breugel, Johanna; Van der Jeugd, Anneke; Van der Jeugd, Anneke; Van der Wall, Elsken; van Diest, Paul; van Stralen, Marijn; Varano, Gianluca; Velat, Manuela; Vidal-Jove, Joan; Vigna, Paolo D.; Vignot, Alexandre; Vincenot, Jeremy; Vykhodtseva, Natalia; Wang, Bin; Wang, Han; Wang, Kevin; Wang, Qi; Wang, Qingguo; Wang, Shengping; Wang, Yak-Nam; Wang, Zhaorui; Wardlow, Rachel; Warren, Amy; Waszczak, Barbara; Watson, Katherine; Webb, Taylor; Wei-Bin, Shen; Wei, Kuo-Chen; Weiss, Steffen; Weissler, Yoni; Werner, Beat; Wesseling, Pieter; Williams, Noelle; Wilson, Emmanuel; Wintermark, Max; Witkamp, Arjen; Wong, Carlos; Wu, Jing-Fu; Wydra, Adrian; Xu, Alexis; Xu, Doudou; Xu, Su; Yang, Georgiana; Yang, Nai-Yi; Yao, Chen; Yarowsky, Paul; Ye, Patrick P.; Yuldashev, Petr; Zaaroor, Menashe; Zachiu, Cornel; Zahos, Peter; Zangos, Stephan; Zhang, Dandan; Zhang, Hua; Zhang, Jimin; Zhang, Junhai; Zhang, Xi; Zhao, Li; Zhong, Pei; Zhuo, Jiachen; Zidowitz, Stephan; Zinke, Wolf; Zorgani, Ali (2016-11-21)
Anisotropic RANS Turbulence Modeling for Wakes in an Active Ocean Environment
Wall, Dylan; Paterson, Eric G. (MDPI, 2020-12-18)
The problem of simulating wakes in a stratified oceanic environment with active background turbulence is considered. Anisotropic RANS turbulence models are tested against laboratory and eddy-resolving models of the problem. An important aspect of our work is to acknowledge that the environment is not quiescent; therefore, additional sources are included in the models to provide a non-zero background turbulence. The RANS models are found to reproduce some key features from the eddy-resolving and laboratory descriptions of the problem. Tests using the freestream sources show the intuitive result that background turbulence causes more rapid wake growth and decay.
Application of the Spectral Element Method in a Surface Ship Far-Field UNDEX Problem
Lu, Zhaokuan; Brown, Alan J. (Hindawi, 2019-07-25)
The prediction of surface ship response to a far-field underwater explosion (UNDEX) requires the simulation of shock wave propagation in the fluid, cavitation, fluid-structure interaction, and structural response. Effective approaches to model the fluid include cavitating acoustic finite element (CAFE) and cavitating acoustic spectral element (CASE) methods. Although the spectral element method offers the potential for greater accuracy at lower computational cost, it also generates more spurious oscillations around discontinuities which are difficult to avoid in shock-related problems. Thus, the advantage of CASE remains unproven. In this paper, we present a 3D-partitioned FSI framework and investigate the application of CAFE and CASE to a surface ship early-time far-field UNDEX problem to determine which method has the best computational efficiency for this problem. We also associate the accuracy of the structural response with the modeling of cavitation distribution. A further contribution of this work is the examination of different nonmatching mesh information exchange schemes to demonstrate how they affect the structural response and improve the CAFE/CASE methodologies.
A Brief History of Aerospace Engineering at the Virginia Polytechnic Institute and State University
Walters, Robert W.; Johnston, Jane Echols (American Institute of Aeronautics and Astronautics, 2004)
This book chapter provides an historical of Aerospace Engineering at Virginia Tech, covering 1913-2004.
Closed-form approximations and series representations for partially saturated ocean acoustic processes
Perakis, Anastassios N.; Nikolaidis, Efstratios; Katzouros, Emmanuel (Acoustical Society of America, 1988-04-01)
An approximate, closed-form expression for the value of the integral encountered in the calculation of the probability density function (PDF) of the envelope of a partially saturated ocean acoustic process is obtained. Furthermore, an expression of this PDF as a series of modified Bessel functions is presented. The results may also be directly applied to the evaluation of the PDF encountered in the structural reliability analysis of rotating machinery components. Numerical applications show that the closed-form expression is always within 1-2% of the exact result. The required computational effort is substantially lower than that required by direct numerical integration. Copyright 1988 Acoustical Society of America
A closed-form method for calculating the angular distribution of multiply scattered photons through isotropic turbid slabs
Sun, Xueqiang; Li, Xuesong; Ma, Lin (Optical Society of America, 2011-11-01)
This paper develops a method for calculating the angular distribution (AD) of multiply scattered photons through isotropic turbid slabs. Extension to anisotropic scattering is also discussed. Previous studies have recognized that the AD of multiply scattered photons is critical for many applications, such as the design of imaging optics and estimation of image quality. This paper therefore develops a closed-from method that can accurately calculate the AD over a wide range of conditions. Other virtues of the method include its simplicity in implementation and its prospective for extension to anisotropic scattering. (C) 2011 Optical Society of America
Corrosion Fatigue Characteristics of 316L Stainless Steel Fabricated by Laser Powder Bed Fusion
Gnanasekaran, Balachander; Song, Jie; Vasudevan, Vijay; Fu, Yao (MDPI, 2021-06-29)
Laser powder bed fusion (LPBF) has been increasingly used in the fabrication of dense metallic structures. However, the corrosion related properties of LPBF alloys, in particular environment-assisted cracking, such as corrosion fatigue properties, are not well understood. In this study, the corrosion and corrosion fatigue characteristics of LPBF 316L stainless steels (SS) in 3.5 wt.% NaCl solution have been investigated using an electrochemical method, high cycle fatigue, and fatigue crack propagation testing. The LPBF 316L SSs demonstrated significantly improved corrosion properties compared to conventionally manufactured 316L, as reflected by the increased pitting and repassivation potentials, as well as retarded crack initiation. However, the printing parameters did not strongly affect the pitting potentials. LPBF samples also demonstrated enhanced capabilities of repassivation during the fatigue crack propagation. The unique microstructural features introduced during the printing process are discussed. The improved corrosion and corrosion fatigue properties are attributed to the presence of columnar/cellular subgrains formed by dislocation networks that serve as high diffusion paths to transport anti-corrosion elements.
A Coupled OpenFOAM-WRF Study on Atmosphere-Wake-Ocean Interaction
Gilbert, John; Pitt, Jonathan (MDPI, 2020-12-30)
This work aims to better understand how small scale disturbances that are generated at the air-sea interface propagate into the surrounding atmosphere under realistic environmental conditions. To that end, a one-way coupled atmosphere-ocean model is presented, in which predictions of sea surface currents and sea surface temperatures from a microscale ocean model are used as constant boundary conditions in a larger atmospheric model. The coupled model consists of an ocean component implemented while using the open source CFD software OpenFOAM, an atmospheric component solved using the Weather Research and Forecast (WRF) model, and a Python-based utility foamToWRF, which is responsible for mapping field data between the ocean and atmospheric domains. The results are presented for two demonstration cases, which indicate that the proposed coupled model is able to capture the propagation of small scale sea surface disturbances in the atmosphere, although a more thorough study is required in order to properly validate the model.
Daily Variability in the Terrestrial UV Airglow
Immel, Thomas J.; Eastes, Richard W.; McClintock, William E.; Mende, Steven B.; Frey, Harald U.; Triplett, Colin C.; England, Scott L. (MDPI, 2020-09-30)
New capability for observing conditions in the upper atmosphere comes with the implementation of global ultraviolet (UV) imaging from geosynchronous orbit. Observed by the NASA GOLD mission, the emissions of atomic oxygen (OI) and molecular nitrogen (N2) in the 133–168-nm range can be used to characterize the behavior of these major constituents of the thermosphere. Observations in the ultraviolet from the first 200 days of 2019 indicate that the oxygen emission at 135.6 nm varies much differently than the broader Lyman-Birge-Hopfield (LBH) emission of N2. This is determined from monitoring the average instrument response from two roughly 1000 km2 areas, well separated from one another, at the same time of each day. Variations in the GOLD response to UV emissions in the monitored regions are determined, both in absolute terms and relative to a running 7-day average of GOLD measurements. We find that variations in N2 emissions in the two separate regions are significantly correlated, while oxygen emissions, observed in the same fixed geographic regions at the same universal time each day, exhibit a much lower correlation, and exhibit no correlation with the N2 emissions in the same regions. This indicates that oxygen densities in the airglow-originating altitude range of 150–200 km vary independently from the variations in nitrogen, which are so well correlated across the dayside to suggest a direct connection to variation in solar extreme-UV flux. The relation of the atomic oxygen variations to solar and geomagnetic activity is also shown to be low, suggesting the existence of a regional source that modifies the production of atomic oxygen in the thermosphere.
Design Optimization Of Slotted Waveguide Antenna Stiffened Structures (Swass)
Kim, Woon Kyung; Canfield, Robert A. (2014-04-15)
The objective of the research is to investigate computational methods for design optimization of a Conformal Load-Bearing Antenna Structure (CLAS) concept. Research centers on investigating computational methods for design optimization of a slotted waveguide antenna stiffened structure (SWASS). The goal of this concept is to turn the skin of aircraft into a radio frequency (RF) antenna. SWASS is a multidisciplinary blending of RF slotted waveguide technology and stiffened composite structures technology. Waveguides provide channels for RF signal transmission, as well as structural stiffening. A SWASS skin or stiffener will have numerous slots that allow the RF energy to radiate to the atmosphere. Slot design for maximum RF performance with minimum structural performance degradation due to the slots will be the multidisciplinary, multiobjective design challenge. Initially, waveguides acting as hat stiffeners were considered in this research; then, waveguides that constituted the core of a sandwich panel were designed for loads in the aircraft skin. The concept design requires parameterization of slot shape, size, location, and spacing in conjunction with stiffener or core sizing and spacing, composite material selection, and laminate layout in order to simultaneously meet desired structural and RF performance.
Detailed flow physics of the supersonic jet interaction flow field
Viti, Valerio; Neel, Reece; Schetz, Joseph A. (American Institute of Physics, 2009-04-01)
The supersonic jet interaction flow field generated by a sonic circular jet with a pressure ratio of 532 exhausting into a turbulent MACH 4.0 cross flow over a flat plate was investigated using numerical simulations. The simulations made use of the three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations coupled with Wilcox's 1998 k-omega turbulence model. The numerical solution was validated with experimental data that include the pressure distribution on the flat plate, with an empirical formula for the height of the barrel shock, and with the Schlieren pictures showing the location and shape of the main shock formations. The simulations correctly captured the location and shape of the main flow features and compared favorably with the experimental pressure distribution on the flat plate. The validated numerical simulation was used to investigate in detail the flow physics. The flow field was found to be dominated by the shock formations and their coupling with the strong vortical structures. Three primary shock formations were observed: a barrel shock, a bow shock, and a separation-induced shock wave. While the general structure of the barrel shock was found to be similar to that of the underexpanded jet exhausting into a quiescent medium, two unique features distinguished the flow field: the concave indentation in the leeside of the recompression (barrel) shock and the folding of the windward side of the barrel shock due to an inner reflection line. The presence of the steep pressure gradients associated with the shocks creates strong vortical motions in the fluid. Six primary vortices were identified: (i) the well-known horseshoe vortex, (ii) an upper trailing vortex, (iii) two trailing vortices formed in the separation region and, aft of the bow shock wave, (iv) two more trailing vortices that eventually merge together into one single rotational motion. The low-pressure region aft of the injector was found to be generated by the combined effect of the concave indentation in the leeside of the barrel shock and the lower trailing vortices. The trailing vortices were found to be the main mechanism responsible for the mixing of the injectant with the freestream fluid.
Diode array velocimeter
(United States Patent and Trademark Office, 1996-05-14)
A velocimeter includes a light source for emitting a light beam through a flow, the flow including particles for scattering light as the light beam passes through the flow, a focussing device for focussing the scattered light into a particle image, a detecting device for detecting the particle image, and a device for timing passage of the particles through a predetermined section of the light beam. The detecting device includes at least one array of photodiodes for receiving light scattered by the particles. The array has a predetermined shape and is positioned so as to control a measurement volume geometry from which light scattered by the particles is received by the photodiodes.
Directive-based GPU programming for computational fluid dynamics
Pickering, Brent P.; Jackson, Ccharles W.; Scogland, Thomas R. W.; Feng, Wu-chun; Roy, Christopher J. (Pergamon-Elsevier, 2015-07-02)
Directive-based programming of graphics processing units (GPUs) has recently appeared as a viable alternative to using specialized low-level languages such as CUDA C and OpenCL for general-purpose GPU programming. This technique, which uses ‘‘directive’’ or ‘‘pragma’’ statements to annotate source codes written in traditional high-level languages, is designed to permit a unified code base to serve multiple computational platforms. In this work we analyze the popular OpenACC programming standard, as implemented by the PGI compiler suite, in order to evaluate its utility and performance potential in computational fluid dynamics (CFD) applications. We examine the process of applying the OpenACC Fortran API to a test CFD code that serves as a proxy for a full-scale research code developed at Virginia Tech; this test code is used to asses the performance improvements attainable for our CFD algorithm on common GPU platforms, as well as to determine the modifications that must be made to the original source code in order to run efficiently on the GPU. Performance is measured on several recent GPU architectures from NVIDIA and AMD (using both double and single precision arithmetic) and the accelerator code is benchmarked against a multithreaded CPU version constructed from the same Fortran source code using OpenMP directives. A single NVIDIA Kepler GPU card is found to perform approximately 20! faster than a single CPU core and more than 2! faster than a 16-core Xeon server. An analysis of optimization techniques for OpenACC reveals cases in which manual intervention by the programmer can improve accelerator performance by up to 30% over the default compiler heuristics, although these optimizations are relevant only for specific platforms. Additionally, the use of multiple accelerators with OpenACC is investigated, including an experimental high-level interface for multi-GPU programming that automates scheduling tasks across multiple devices. While the overall performance of the OpenACC code is found to be satisfactory, we also observe some significant limitations and restrictions imposed by the OpenACC API regarding certain useful features of modern Fortran (2003/8); these are sufficient for us to conclude that it would not be practical to apply OpenACC to our full research code at this time due to the amount of refactoring required.
Dynamic Analysis and Design Optimization of a Drag-Based Vibratory Swimmer
Tahmasian, Sevak; Jafaryzad, Arsam; Bulzoni, Nicolas L.; Staples, Anne E. (MDPI, 2020-03-22)
Many organisms achieve locomotion via reciprocal motions. This paper presents the dynamic analysis and design optimization of a vibratory swimmer with asymmetric drag forces and fluid added mass. The swimmer consists of a floating body with an oscillatory mass inside. One-dimensional oscillations of the mass cause the body to oscillate with the same frequency as the mass. An asymmetric rigid fin attached to the bottom of the body generates asymmetric hydrodynamic forces, which drive the swimmer either backward or forward on average, depending on the orientation of the fin. The equation of motion of the system is a time-periodic, piecewise-smooth differential equation. We use simulations to determine the hydrodynamic forces acting on the fin and averaging techniques to determine the dynamic response of the swimmer. The analytical results are found to be in good agreement with vibratory swimmer prototype experiments. We found that the average unidirectional speed of the swimmer is optimized if the ratio of the forward and backward drag coefficients is minimized. The analysis presented here can aid in the design and optimization of bio-inspired and biomimetic robotic swimmers. A magnetically controlled microscale vibratory swimmer like the one described here could have applications in targeted drug delivery.
Effect of transverse beam size on the wakefields and driver beam dynamics in plasma wakefield acceleration schemes
Bera, Ratan Kumar; Mandal, Devshree; Das, Amita; Sengupta, Sudip (2020-02-01)
In this paper, wakefields driven by a relativistic electron beam in a cold homogeneous plasma are studied using 2D fluid simulation techniques. It has been shown that in the limit when the transverse size of a rigid beam is greater than the longitudinal extension, the wake wave acquires a purely electrostatic form, and the simulation results show a good agreement with the 1D results given by Bera et al. [Phys. Plasmas 22, 073109 (2015)]. In the other limit when the transverse dimensions are equal to or smaller than the longitudinal extension, the wake waves are electromagnetic in nature, and 2D effects play a crucial role. Furthermore, a linear theoretical analysis of 2D wakefields for a rigid bi-parabolic beam has also been carried out and compared with the simulations. It has also been shown that the transformer ratio, which is a key parameter that measures the efficiency in the process of acceleration, becomes higher for a 2D system (i.e., for a beam having a smaller transverse extension compared to the longitudinal length) than the 1D system (i.e., for a beam having a larger transverse extension compared to the longitudinal length). Furthermore, including the self-consistent evolution of the driver beam in the simulation, we have seen that the beam propagating inside the plasma undergoes transverse pinching, which occurs much earlier than the longitudinal modification. Due to the presence of transverse dimensions in the system, the 1D rigidity limit given by Tsiklauri [Phys. Plasmas 25, 032114 (2018)] gets modified. We have also demonstrated the modified rigidity limit for the driver beam in a 2D beam-plasma system.
Experimental Study of Pressure and Velocity Fluctuations Induced by Cavitation in a Small Venturi Channel
Zhang, Linrong; Zhang, Guangjian; Ge, Mingming; Coutier-Delgosha, Olivier (MDPI, 2020-12-08)
The purpose of this paper is to investigate experimentally the influence of the cavitation extent on the pressure and velocity fluctuations in a small convergent–divergent channel. The mean cavity length is determined from high-speed photography images. The mean pressure and the intensity of the pressure fluctuations are obtained from the transient pressure signals recorded by two pressure transducers at the inlet and outlet of the test section. The statistical turbulence quantities are derived from the instantaneous velocity fields measured by the laser-induced fluorescent particle image velocimetry (PIV-LIF) technique. The experimental results show that the decrease of the cavitation number (the increase in the extent of cavitation) leads to a rise in the turbulent fluctuations in the wake region due to the impact of vapour clouds collapsing, while the presence of a vapour phase is found to reduce the streamwise and cross-stream velocity fluctuations in the attached cavity. It might be attributed to two mechanisms: the presence of a vapour phase modifies the vortex-stretching process, and the cavitation compressibility damps out the turbulent fluctuations. Similar effects of cavitation are also observed in the pressure fluctuations.
Final Report: Second Forum on Space Structures
(Virginia Tech, 1984-06)
This document consists of summaries of presentations and discussions from the Forum, which was a meeting for investigators of structural dynamics and control issues in large space structures technology held 11-13 June 1984. The major issues considered are modeling of spacecraft structures, passive and active control techniques, integrated design of structure and control, and experiment and implementation (hardware related) topics, such as sensors, actuators, test techniques, etc. The current status of the technology is reviewed, deficiencies are identified, and recommendations for future research are made.
Force-exerting perpendicular lateral protrusions in fibroblastic cell contraction
Padhi, Abinash; Singh, Karanpreet; Franco-Barraza, Janusz; Marston, Daniel J.; Cukierman, Edna; Hahn, Klaus M.; Kapania, Rakesh K.; Nain, Amrinder S. (2020-07-21)
Aligned extracellular matrix fibers enable fibroblasts to undergo myofibroblastic activation and achieve elongated shapes. Activated fibroblasts are able to contract, perpetuating the alignment of these fibers. This poorly understood feedback process is critical in chronic fibrosis conditions, including cancer. Here, using fiber networks that serve as force sensors, we identify "3D perpendicular lateral protrusions" (3D-PLPs) that evolve from lateral cell extensions named twines. Twines originate from stratification of cyclic-actin waves traversing the cell and swing freely in 3D to engage neighboring fibers. Once engaged, a lamellum forms and extends multiple secondary twines, which fill in to form a sheet-like PLP, in a force-entailing process that transitions focal adhesions to activated (i.e., pathological) 3D-adhesions. The specific morphology of PLPs enables cells to increase contractility and force on parallel fibers. Controlling geometry of extracellular networks confirms that anisotropic fibrous environments support 3D-PLP formation and function, suggesting an explanation for cancer-associated desmoplastic expansion. Padhi et al. employ nanofibers with controlled structure and alignment as an extra-cellular matrix model, on which they study the exertion of forces from adherent fibroblasts. Identifying force exerting 3D perpendicular lateral protrusions, authors describe a mechanism which leads to the contraction of parallel, neighbouring fibers, and the forces needed to move and align the neighbouring fibers. These findings have relevance in understanding cancer-associated desmoplastic expansion.
The Global-Scale Observations of the Limb and Disk (GOLD) Mission
Eastes, R. W.; McClintock, William E.; Burns, A. G.; Anderson, D. N.; Andersson, L.; Codrescu, M.; Correira, J. T.; Daniell, R. E.; England, Scott L.; Evans, J. S.; Harvey, J.; Krywonos, A.; Lumpe, J. D.; Richmond, A. D.; Rusch, D. W.; Siegmund, O. H.; Solomon, S. C.; Strickland, D. J.; Woods, T. N.; Aksnes, A.; Budzien, S. A.; Dymond, K. F.; Eparvier, F. G.; Martinis, C. R.; Oberheide, J. (2017-10)
The Earth's thermosphere and ionosphere constitute a dynamic system that varies daily in response to energy inputs from above and from below. This system can exhibit a significant response within an hour to changes in those inputs, as plasma and fluid processes compete to control its temperature, composition, and structure. Within this system, short wavelength solar radiation and charged particles from the magnetosphere deposit energy, and waves propagating from the lower atmosphere dissipate. Understanding the global-scale response of the thermosphere-ionosphere (T-I) system to these drivers is essential to advancing our physical understanding of coupling between the space environment and the Earth's atmosphere. Previous missions have successfully determined how the "climate" of the T-I system responds. The Global-scale Observations of the Limb and Disk (GOLD) mission will determine how the "weather" of the T-I responds, taking the next step in understanding the coupling between the space environment and the Earth's atmosphere. Operating in geostationary orbit, the GOLD imaging spectrograph will measure the Earth's emissions from 132 to 162 nm. These measurements will be used image two critical variables-thermospheric temperature and composition, near 160 km-on the dayside disk at half-hour time scales. At night they will be used to image the evolution of the low latitude ionosphere in the same regions that were observed earlier during the day. Due to the geostationary orbit being used the mission observes the same hemisphere repeatedly, allowing the unambiguous separation of spatial and temporal variability over the Americas.

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