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  • 101. Qureshi, A.
    et al.
    Peters, Christopher
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Apperly, I.
    How does varying gaze direction affect interaction between a virtual agent and participant in an on-line communication scenario?2014Ingår i: 6th International Conference on Virtual, Augmented and Mixed Reality, VAMR 2014 - Held as Part of 16th International Conference on Human-Computer Interaction, HCI International 2014, 2014, Vol. 8525, nr PART 1, s. 305-316Konferensbidrag (Refereegranskat)
    Abstract [en]

    Computer based perspective taking tasks in cognitive psychology often utilise static images and auditory instructions to assess online communication. Results are then explained in terms of theory of mind (the ability to understand that other agents have different beliefs, desires and knowledge to oneself).The current study utilises a scenario in which participants were required to select objects in a grid after listening to instructions from an on-screen director. The director was positioned behind the grid from the participants' view. As objects in some slots were concealed from the view of the director, participants needed to take the perspective of the director into account in order to respond accurately. Results showed that participants reliably made errors, attributable to not using the information from the director's perspective efficiently, rather than not being able to take the director's perspective. However, the fact that the director was represented by a static sprite meant that even for a laboratory based experiment, the level of realism was low. This could have affected the level of participant engagement with the director and the task. This study, a collaboration between computer science and psychology, advances the static sprite model by incorporating head movement into a more realistic on-screen director with the aim of a.) Improving engagement and b.) investigating whether gaze direction affects accuracy and response times of object selection. Results suggest that gaze direction can influence the speed of accurate object selection, but only slightly and in certain situations; specifically those complex enough to warrant the participant paying additional attention to gaze direction and those that highlight perspective differences between themselves and the director. This in turn suggests that engagement with a virtual agent could be improved by taking these factors into account.

  • 102. Qureshi, A.
    et al.
    Peters, Christopher
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Apperly, I.
    Interaction and engagement between an agent and participant in an on-line communication paradigm as mediated by gaze direction2013Ingår i: Proceedings of the 2013 Inputs-Outputs Conference: An Interdisciplinary Conference on Engagement in HCI and Performance, Association for Computing Machinery (ACM), 2013, s. 2557603-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Computer based perspective taking tasks in cognitive psychology often utilise static images to assess on-line communication [1] explaining results in terms of theory of mind (the ability to understand that other agents have different beliefs, desires and knowledge to oneself [10]). The current study utilises the method used in [1] in which participants are required to respond correctly to instructions from an on-screen director by taking the perspective of the director into account. Results showed that participants reliably made errors, attributable to not using the information from the director's perspective efficiently, rather than not being able to take the director's perspective. However, the fact that the director was represented by a static sprite could mean that participant engagement with the director and the task was low. This study, a collaboration between computer science and psychology, advances this model by incorporating head movement into a more realistic on-screen director [9], potentially improving engagement. Whether the gaze direction of the director facilitated or hindered participants in object selection was investigated, and results will be discussed in terms of the level of engagement shown by the participant with the director, as measured by their efficiency in object selection, and how this varied with gaze direction. Further adaptations of the model (body movement, blinking) will also be discussed as ways of improving engagement.

  • 103.
    Ramos Carretero, Miguel
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Qureshi, Adam
    Peters, Christopher
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Evaluating the perception of group emotion from full body movements in the context of virtual crowds2014Ingår i: Proceedings of the ACM Symposium on Applied Perception, SAP 2014, ACM Digital Library, 2014, s. 7-14Konferensbidrag (Refereegranskat)
    Abstract [en]

    Simulating the behavior of crowds of artificial entities that have humanoid embodiments has become an important element in computer graphics and special effects. However, many important questions remain in relation to the perception of social behavior and expression of emotions in virtual crowds. Specifically, few studies have considered the role of background context on the perception of the full-body emotion expressed by sub-constituents of the crowd i.e. individuals and small groups. In this paper, we present the results of perceptual studies in which animated scenes of expressive virtual crowd behavior were rated in terms of their valence by participants. The behaviors of a task-irrelevant crowd in the background were altered between neutral, happy and sad in order to investigate effects on the perception of emotion from task-relevant individuals in the foreground. Effects of the task irrelevant background on ratings of foreground characters were found, including cases that accompanied negatively valenced stimuli.

  • 104. Rehg, J. M.
    et al.
    Abowd, G. D.
    Rozga, A.
    Romero, Mario
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Clements, M. A.
    Sclaroff, S.
    Essa, I.
    Ousley, O. Y.
    Li, Y.
    Kim, C.
    Rao, H.
    Kim, J. C.
    Presti, L. L.
    Zhang, J.
    Lantsman, D.
    Bidwell, J.
    Ye, Z.
    Decoding children's social behavior2013Ingår i: 2013 IEEE Conference on Computer Vision and Pattern Recognition (CVPR), IEEE Computer Society, 2013, s. 3414-3421Konferensbidrag (Refereegranskat)
    Abstract [en]

    We introduce a new problem domain for activity recognition: the analysis of children's social and communicative behaviors based on video and audio data. We specifically target interactions between children aged 1-2 years and an adult. Such interactions arise naturally in the diagnosis and treatment of developmental disorders such as autism. We introduce a new publicly-available dataset containing over 160 sessions of a 3-5 minute child-adult interaction. In each session, the adult examiner followed a semi-structured play interaction protocol which was designed to elicit a broad range of social behaviors. We identify the key technical challenges in analyzing these behaviors, and describe methods for decoding the interactions. We present experimental results that demonstrate the potential of the dataset to drive interesting research questions, and show preliminary results for multi-modal activity recognition.

  • 105. Restante, A. L.
    et al.
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Lapenta, G.
    Intrator, T.
    Geometrical investigation of the kinetic evolution of the magnetic field in a periodic flux rope2013Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 20, nr 8, s. 082501-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Flux ropes are bundles of magnetic field wrapped around an axis. Many laboratory, space, and astrophysics processes can be represented using this idealized concept. Here, a massively parallel 3D kinetic simulation of a periodic flux rope undergoing the kink instability is studied. The focus is on the topology of the magnetic field and its geometric structures. The analysis considers various techniques such as Poincare maps and the quasi-separatrix layer (QSL). These are used to highlight regions with expansion or compression and changes in the connectivity of magnetic field lines and consequently to outline regions where heating and current may be generated due to magnetic reconnection. The present study is, to our knowledge, the first QSL analysis of a fully kinetic 3D particle in cell simulation and focuses the existing QSL method of analysis to periodic systems.

  • 106.
    Romero, Mario
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). Georgia Institute of Technology.
    Hasselqvist, Hanna
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Svensson, Gert
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Supercomputers Keeping People Warm in the Winter2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present the design and evaluation of the heat recovery system for KTH's Lindgren, Stockholm's fastest supercomputer, a Cray XE6. Lindgren came into service in 2010 and has since been primarily used for complex numeric simulations of fluid mechanics and computational chemistry and biology. The heat exchange system collects the wasted heat from Lindgren's 36,384 CPU cores and transfers it via the standard district heating and cooling system to a neighboring building which houses the Chemistry laboratories. We analyze the impact of Lindgren's heat recycle system as a function of outside temperature and we estimate the system's carbon emission savings. Since the original installation of Lindgren in 2010, it has become common practice to use water cooling systems for supercomputers, as water is a better heat transfer medium than air. We discuss the relevant design lessons from Lindgren as they relate to practical and sustainable waste heat recovery designs for today's platforms. Finally, we estimate that the recovered heat from Lindgren reduced the carbon emissions by nearly 50 tons over the 2012-13 winter, the sample period of our analysis.

  • 107.
    Romero, Mario
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Beräkningsvetenskap och beräkningsteknik (CST).
    Thuresson, Björn
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Peters, Christopher
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Kis, Filip
    KTH, Skolan för datavetenskap och kommunikation (CSC), Medieteknik och interaktionsdesign, MID.
    Coppard, J.
    Andrée, Jenny
    KTH.
    Landázuri, N.
    Augmenting PBL with large public presentations: A case study in interactive graphics pedagogy2014Ingår i: ITICSE 2014 - Proceedings of the 2014 Innovation and Technology in Computer Science Education Conference, 2014, s. 15-20Konferensbidrag (Refereegranskat)
    Abstract [en]

    We present a case study analyzing and discussing the effects of introducing the requirement of public outreach of original student work into the project-based learning of Advanced Graphics and Interaction (AGI) at KTH Royal Institute of Technology. We propose Expo-Based Learning as Project-Based Learning augmented with the constructively aligned goal of achieving public outreach beyond the course. We promote this outreach through three challenges: 1) large public presentations; 2) multidisciplinary collaboration; and 3) professional portfolio building. We demonstrate that the introduction of these challenges, especially the public presentations, had lasting positive impact in the intended technical learning outcomes of AGI with the added benefit of learning team work, presentation skills, timeliness, accountability, self-motivation, technical expertise, and professionalism.

  • 108. Ruhland, Kerstin
    et al.
    Andrist, Sean
    Badler, Jeremy B.
    Peters, Christopher E.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Badler, Norman I.
    Gleicher, Michael
    Mutlu, Bilge
    McDonnell, Rachel
    Look me in the Eyes: A Survey of Eye and Gaze Animation for Virtual Agents and Artificial Systems2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    A person's emotions and state of mind are apparent in their face and eyes. As a Latin proverb states: ''The face is the portrait of the mind; the eyes, its informers.''. This presents a huge challenge for computer graphics researchers in the generation of artificial entities that aim to replicate the movement and appearance of the human eye, which is so important in human-human interactions. This State of the Art Report provides an overview of the efforts made on tackling this challenging task. As with many topics in Computer Graphics, a cross-disciplinary approach is required to fully understand the workings of the eye in the transmission of information to the user. We discuss the movement of the eyeballs, eyelids, and the head from a physiological perspective and how these movements can be modelled, rendered and animated in computer graphics applications. Further, we present recent research from psychology and sociology that seeks to understand higher level behaviours, such as attention and eye-gaze, during the expression of emotion or during conversation, and how they are synthesised in Computer Graphics and Robotics.

  • 109.
    Ruhland, Kerstin
    et al.
    Trinity College Dublin.
    Peters, Christopher E.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Andrist, Sean
    University of Wisconsin–Madison.
    Badler, Jeremy B.
    Université catholique de Louvain.
    Badler, Norman I.
    University of Pennsylvania.
    Gleicher, Michael
    University of Wisconsin–Madison.
    Mutlu, Bilge
    University of Wisconsin–Madison.
    McDonnell, Rachel
    Trinity College Dublin.
    A Review of Eye Gaze in Virtual Agents, Social Robotics and HCI: Behaviour Generation, User Interaction and Perception2015Ingår i: Computer graphics forum (Print), ISSN 0167-7055, E-ISSN 1467-8659, Vol. 34, nr 6, s. 299-326Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    A person's emotions and state of mind are apparent in their face and eyes. As a Latin proverb states: ‘The face is the portrait of the mind; the eyes, its informers’. This presents a significant challenge for Computer Graphics researchers who generate artificial entities that aim to replicate the movement and appearance of the human eye, which is so important in human–human interactions. This review article provides an overview of the efforts made on tackling this demanding task. As with many topics in computer graphics, a cross-disciplinary approach is required to fully understand the workings of the eye in the transmission of information to the user. We begin with a discussion of the movement of the eyeballs, eyelids and the head from a physiological perspective and how these movements can be modelled, rendered and animated in computer graphics applications. Furthermore, we present recent research from psychology and sociology that seeks to understand higher level behaviours, such as attention and eye gaze, during the expression of emotion or during conversation. We discuss how these findings are synthesized in computer graphics and can be utilized in the domains of Human–Robot Interaction and Human–Computer Interaction for allowing humans to interact with virtual agents and other artificial entities. We conclude with a summary of guidelines for animating the eye and head from the perspective of a character animator.

  • 110.
    Schliephake, Michael
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Laure, Erwin
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Performance Analysis of Irregular Collective Communication with the Crystal Router Algorithm2015Ingår i: Solving software challenges for exascale, 2015, s. 130-140Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to achieve exascale performance it is important to detect potential bottlenecks and identify strategies to overcome them. For this, both applications and system software must be analysed and potentially improved. The EU FP7 project Collaborative Research into Exascale Systemware, Tools & Applications (CRESTA) chose the approach to co-design advanced simulation applications and system software as well as development tools. In this paper, we present the results of a co-design activity focused on the simulation code NEK5000 that aims at performance improvements of collective communication operations. We have analysed the algorithms that form the core of NEK5000's communication module in order to assess its viability on recent computer architectures before starting to improve its performance. Our results show that the crystal router algorithm performs well in sparse, irregular collective operations for medium and large processor number but improvements for even larger system sizes of the future will be needed. We sketch the needed improvements, which will make the communication algorithms also beneficial for other applications that need to implement latency-dominated communication schemes with short messages. The latency-optimised communication operations will also become used in a runtime-system providing dynamic load balancing, under development within CRESTA.

  • 111.
    Schliephake, Michael
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Laure, Erwin
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Heisey, Katherine
    Argonne National Laboratory.
    Fischer, Paul
    Argonne National Laboratory.
    Design, implementation and use of mampicl, the multi-algorithm MPI collective library2013Konferensbidrag (Övrigt vetenskapligt)
  • 112. Stasiewicz, K.
    et al.
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Eliasson, B.
    Strumik, M.
    Yamauchi, M.
    Acceleration of solar wind ions to 1 MeV by electromagnetic structures upstream of the Earth's bow shock2013Ingår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 102, nr 4, s. 49001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present measurements from the ESA/NASA Cluster mission that show in situ acceleration of ions to energies of 1MeV outside the bow shock. The observed heating can be associated with the presence of electromagnetic structures with strong spatial gradients of the electric field that lead to ion gyro-phase breaking and to the onset of chaos in ion trajectories. It results in rapid, stochastic acceleration of ions in the direction perpendicular to the ambient magnetic field. The electric potential of the structures can be compared to a field of moguls on a ski slope, capable of accelerating and ejecting the fast running skiers out of piste. This mechanism may represent the universal mechanism for perpendicular acceleration and heating of ions in the magnetosphere, the solar corona and in astrophysical plasmas. This is also a basic mechanism that can limit steepening of nonlinear electromagnetic structures at shocks and foreshocks in collisionless plasmas.

  • 113. Valero-Lara, P.
    et al.
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    A Non-uniform Staggered Cartesian Grid approach for Lattice-Boltzmann method2015Ingår i: Procedia Computer Science, Elsevier, 2015, nr 1, s. 296-305Konferensbidrag (Refereegranskat)
    Abstract [en]

    We propose a numerical approach based on the Lattice-Boltzmann method (LBM) for dealing with mesh refinement of Non-uniform Staggered Cartesian Grid. We explain, in detail, the strategy for mapping LBM over such geometries. The main benefit of this approach, compared to others, consists of solving all fluid units only once per time-step, and also reducing considerably the complexity of the communication and memory management between different refined levels. Also, it exhibits a better matching for parallel processors. To validate our method, we analyze several standard test scenarios, reaching satisfactory results with respect to other stateof-the-art methods. The performance evaluation proves that our approach not only exhibits a simpler and efficient scheme for dealing with mesh refinement, but also fast resolution, even in those scenarios where our approach needs to use a higher number of fluid units.

  • 114. Vapirev, A. E.
    et al.
    Lapenta, G.
    Divin, A.
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Parallelldatorcentrum, PDC.
    Henri, P.
    Goldman, M.
    Newman, D.
    Formation of a transient front structure near reconnection point in 3-D PIC simulations2013Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, nr 4, s. 1435-1449Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Massively parallel numerical simulations of magnetic reconnection are presented in this study. Electromagnetic full-particle implicit code iPIC3D is used to study the dynamics and 3-D evolution of reconnection outflows. Such features as Hall magnetic field, inflow and outflow, and diffusion region formation are very similar to 2-D particle-in-cell (PIC) simulations. In addition, it is well known that instabilities develop in the current flow direction or oblique directions. These modes could provide for anomalous resistivity and diffusive drag and can serve as additional proxies for magnetic reconnection. In our work, the unstable evolution of reconnection transient front structures is studied. Reconnection configuration in the absence of guide field is considered, and it is initialized with a localized perturbation aligned in the cross-tail direction. Our study suggests that the instabilities lead to the development of finger-like density structures on ion-electron hybrid scales. These structures are characterized by a rapid increase of the magnetic field, normal to the current sheet (Bz). A small decrease in the magnetic field component parallel to the reconnection X line and the component perpendicular to the current sheet is observed in the region ahead of the front. The instabilities form due to fact that the density gradient inside the front region is opposite to the direction of the acceleration Lorentz force. Such density structures may possibly further develop into larger-scale earthward flux transfer events during magnetotail reconnection. In addition, oscillations mainly in the magnetic and electric fields and the electron density are observed shortly before the arrival of the main front structure which is consistent with recent THEMIS observations. Key PointsThree dimensional particle-in-cell simulation of reconnection in the magnetotailEvolution of dipolarization front at reconnection and associated plasma flowDevelopment of instabilities in the plasma population

  • 115.
    Vencels, Juris
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Delzanno, G. L.
    Johnson, A.
    Peng, I. Bo
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Laure, Erwin
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Markidis, Stefano
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Spectral solver for multi-scale plasma physics simulations with dynamically adaptive number of moments2015Ingår i: Procedia Computer Science, Elsevier, 2015, nr 1, s. 1148-1157Konferensbidrag (Refereegranskat)
    Abstract [en]

    A spectral method for kinetic plasma simulations based on the expansion of the velocity distribution function in a variable number of Hermite polynomials is presented. The method is based on a set of non-linear equations that is solved to determine the coefficients of the Hermite expansion satisfying the Vlasov and Poisson equations. In this paper, we first show that this technique combines the fluid and kinetic approaches into one framework. Second, we present an adaptive strategy to increase and decrease the number of Hermite functions dynamically during the simulation. The technique is applied to the Landau damping and two-stream instability test problems. Performance results show 21% and 47% saving of total simulation time in the Landau and two-stream instability test cases, respectively.

  • 116.
    Vilela De Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Towards the development of adaptive finite element methods for internal flow aeroacoustics2013Ingår i: 19th AIAA/CEAS Aeroacoustics Conference, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    We report the latest results obtained in the development of an adaptive finite element method for computational aeroacoustics (CAA). The new methodology is based on the General Galerkin (G2) method, which has been successfully used for the computation of incompressible, turbulent flow. Here, we simulate the flow past an in-duct mixer plate and compare the results with available experimental data. The comparisons include mean velocity profiles and frequency content of the turbulent signal. No direct simulation of sound or sound wave propagation has been performed; instead, simple analogy arguments have been used to extract acoustic results from incompressible simulations by assuming a direct correlation between the computed pressure drop signal and the sound at the far field. We were able to reproduce the sound signal from experiments with our incompressible simulation and our results compared well with both the level and the broadband frequency peak of the measured sound. We suggest that the methodology presented here is mainly suitable for the prediction of sound in low Mach number pipe flows.

  • 117.
    Vilela de Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Adaptive Computation of Aeroacoustic Sources for a Rudimentary Landing Gear2014Ingår i: International Journal for Numerical Methods in Fluids, ISSN 0271-2091, E-ISSN 1097-0363, Vol. 74, nr 6, s. 406-421Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present our simulation results for the benchmark problem of the flow past a rudimentary landing gear using a General Galerkin FEM, also referred to as adaptive DNS/LES. In General Galerkin, no explicit subgrid model is used; instead, the computational mesh is adaptively refined with respect to an a posteriori error estimate of a quantity of interest in the computation, in this case, the drag force on the rudimentary landing gear. Turbulent boundary layers are modeled using a simple wall-layer model with the shear stress at walls proportional to the skin friction, which here is assumed to be small and, therefore, can be approximated by zero skin friction. We compare our results with experimental data and other state of the art computations, where we find good agreement in sound pressure levels, surface velocities, and flow separation. We also compare with detailed surface pressure experimental data where we find largely good agreement, apart from some local differences for which we discuss possible explanations.

  • 118.
    Vilela de Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Computation of Aeroacoustic Sources for a Gulfstream G550 Nose Landing Gear Model Using Adaptive FEMManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    This work is a direct comparison of our unsteady, turbulent flow simulations with measurements performed using a Gulfstream G550 Nose Landing Gear Model. The experimental campaign, which was carried out by researchers from the NASA Langley Research Center, provided a series of detailed, well documented wind-tunnel measurements for comparison and validation of computational fluid dynamics (CFD) and computational aeroacoustics (CAA) methodologies. Several computational efforts were collected and presented at the Benchmark for Airframe Noise Computation workshops, BANC-I and II. For our simulations, we used a General Galerkin finite element method (G2), where no explicit subgrid model is used, and where the computational mesh is adaptively refined with respect to a posteriori error estimates for a quantity of interest. The mesh is fully unstructured and the solutions are time-resolved, which are key ingredients for solving relevant, industrial applications in the field of aeroacoustics. The comparisons presented here are an attempt to quantify the accuracy of our models, methods and assumptions, and the results, although not perfect, are of relevant quantitative quality. We present several results containing both time-averaged and unsteady flow quantities, always side by side with its corresponding experimental values. The main finding is that we are able to simulate such a complex, unsteady flow problem as the flow past a nose landing gear using a parameter-free methodology for high Reynolds numbers (Re), external aerodynamics and aeroacoustics applications.

  • 119.
    Vilela de Abreu, Rodrigo
    et al.
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz). KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Jansson, Niclas
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Hoffman, Johan
    KTH, Skolan för datavetenskap och kommunikation (CSC), High Performance Computing and Visualization (HPCViz).
    Computation of aeroacoustic sources for a Gulfstream G550 nose landing gear model using adaptive FEM2016Ingår i: Computers & Fluids, ISSN 0045-7930, E-ISSN 1879-0747, Vol. 124, s. 136-146Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work presents a direct comparison of unsteady, turbulent flow simulations with measurements performed using a Gulfstream G550 nose landing gear model. The experimental campaign, which was carried out by researchers from the NASA Langley Research Center, provided a series of detailed, well documented wind-tunnel measurements for comparison and validation of computational fluid dynamics (CFD) and computational aeroacoustics (CAA) methodologies. Several computational efforts were collected and presented at the Benchmark for Airframe Noise Computation workshops, BANC-I and II. For our simulations, we used a General Galerkin finite element method (G2), where no explicit subgrid model is used, and where the computational mesh is adaptively refined with respect to a posteriori estimates of the error in a quantity of interest, here the source term in Lighthill's equation. The mesh is fully unstructured and the solution is time-resolved, which are key ingredients for solving problems of industrial relevance in the field of aeroacoustics. Moreover, we choose to model the boundary layers on the landing gear geometry with a free-slip condition for the velocity, which we previously observed to produce good results for external flows at high Reynolds numbers, and which considerably reduces the amount of cells required in the mesh. The comparisons presented here are an attempt to quantify the accuracy of our models, methods and assumptions; to that end, several results containing both time-averaged and unsteady flow quantities, always side by side with corresponding experimental values, are reported. The main finding is that we are able to simulate a complex, unsteady flow problem using a parameter-free methodology developed for high Reynolds numbers, external aerodynamics and aeroacoustics applications.

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