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SPHERIC newsletter 16th issue – July 2013 SPH European Research Interest Community http://wiki.manchester.ac.uk/spheric/ Contact: david.letouze@ec-nantes.fr

D. Le Touzé, Chairman N. Quinlan, Secretary B. Rogers, Webmaster D. Violeau, Newsletter Steering Committee Ecole Centrale Nantes (France) National University of Ireland, Galway University of Manchester (UK) EDF R&D (France) University of Vigo (Spain) University of Pavia (Italy) ANDRITZ Hydro SAS (France) Hamburg University of Technology (Germany) Technical University of Madrid (Spain) CNR-INSEAN (Italy) ESI-Group Netherlands Technical University of Munich (Germany) Cranfield University (UK) Members University of Plymouth (UK) Ecole Centrale de Lyon (France) CSCS (Switzerland) ANDRITZ Hydro AG (Switzerland) Johns Hopkins University (USA) University of Nottingham (UK) University of Bradford (UK) Technical University of Madrid (Spain) CSIRO Mathematical and Information Sciences (Australia) Ecole Polytechnique Fédérale de Lausanne (Switzerland) Université du Havre (France) Swiss Federal Institute of Technology RSE SpA (Italy) University of Genova (Switzerland) Dublin Institute of Technology (Ireland) Bhabba Atomic Research Center (India) BAE SYSTEMS (UK) University of West Bohemia (Czech Republic) UNISA CUGRI (Italy) Hamburg University of Technology (Germany) City University London (UK) HydrOcean (France) Laboratório Nacional de Engenharia Civil (Portugal) Catholic University Leuven (Belgium) University of Calabria (Italy) University of Ljubljana (Slovenia) Virginia Tech (USA) SINTEF (Norway) Monash University (Autralia) Karlsruhe Institute of Technology (Germany) Sulzer Markets & Technology Ltd (Switzerland) University of Heidelberg (Germany) Amir Kabir University of Technology (Iran) Istituto Nazionale di Geophisica e Vulcanologia (Italy) National Technical University of Athens (Greece) University of Exeter (UK) University of Parma (Italy) Kyoto University (japan) CRS4 (Italy) University of Regina (Canada) University of Auckland (New Zealand) Alstom Hydro (France) MARA University of Technology (Malaysia) Instituto Superior Tecnico (Portugal) Australian Nuclear Science and Technology Organisation (Australia) Eindhoven University of Technology (The Netherlands) The University of Adelaide (Australia) Newcastle University (UK) University of Zanjan (Iran) National Taiwan University (China)

8th International SPHERIC Workshop By Jan Erik OLSEN, head of the Local Organising Committee

The 8th SPHERIC International workshop was arranged in the city of Trondheim (Norway), June 3–6 2013. 95 delegates primarily from Europe, and some from USA and Asia, shared their recent research efforts on SPH. The workshop was hosted by SINTEF at Prinsen Hotel. It began, as usual, with a training day for ca. 20 students, jointly organised by Dr Benedict Rogers and Dr Alex Crespo, with a focus on the DualSPHysics and Paraview PV-meshless softwares. Benjamin Bouscasse and Dr Andrea Colagrossi also presented a lecture on “Nonlinear water wave interaction with floating bodies in SPH”.

During the next 3 days, 57 papers were presented covering a range of topics within numerical aspects of SPH, multiphase, boundary treatment and hardware acceleration (see detailed programme below). Two keynote lectures were given by Prof. Daniel Price (“SPH – How I learnt to stop worrying and love Lagrangians”) and Dr Damien Violeau (“Numerical Stability of SPH for Weakly Compressible Viscous Flows: Optimal Time-Stepping”). The Libersky award for the best student paper was given to Agnes Leroy for her work entitled “Application of the unified semi-analytical wall boundary conditions to incompressible SPH”. Magdalena Neuhauser and Arno Mayrhofer were also highly commended (see picture below). Following the format from the 7th workshop in Prato, a discussion session was organized. This focused on the SPHERIC Grand Challenges on the theoretical progress in SPH, which are presented separately in this Newsletter.

The organizers will make all front pages of the papers, the keynote presentations and some photos available on the SPHERIC Web Pages in the near future.

Contact: Jan.E.Olsen@sintef.no

http://www.sintef.no/Projectweb/SPHERIC-2013/Program-SPHERIC-2013/

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SPHERIC newsletter 16th issue – July 2013

DAY 1: Tuesday 4 June 2013

Keynote lecture: Prof. D.J. Price, Monash University, Melbourne, Australia SPH – How I learnt to stop worrying and love Lagrangians

Session 1: Boundary treatment Chair: D. Le Touzé

• Application of the unified semi-analytical wall boundary conditions to incompressible SPH. A. Leroy, D. Violeau, M. Ferrand & C. Kassiotis

• SPH approximate Zeroth and First-order consistent boundary conditions for irregular boundaries. G. Fourtakas, R. Vacondio & B. D. Rogers

• Consistency analysis of flow field extension models into ghost fluid regions for SPH solid body boundary condition implementations. P.E. Merino-Alonso, F. Macià, A. Souto-Iglesias & A. Colagrossi

• Semi-Analytical Conditions for Open Boundaries in Smoothed Particle Hydrodynamics. C. Kassiotis, M. Ferrand & D. Violeau

Session 2: Theoretical & Numerical aspects of SPH Chair: D. Violeau

• Waves and swimming bodies in a stratified fluid. J.J. Monaghan & J.B. Kajtar

• An improved corrective smoothed particle method approximation for second-order derivatives. S.P. Korzilius, W.H.A. Schilders & M.J.H. Anthonissen

• Pressure-corrected SPH with innovative particle regularization algorithms and non-uniform, initial particle distributions. P. H. L. Groenenboom & B. K. Cartwright

• A Simple and Effective Scheme for Dynamic Stabilization of Particle Methods. N. Tsuruta, A. Khayyer, H. Gotoh & H. Ikari

• An implicit SPH solution of the Burgers equation. L.M. González & J.L. Cercós

Session 3: Multiphase Chair: J.J. Monaghan

• A Novel Error-Minimizing Scheme to Enhance the Performance of Compressible-Incompressible Multiphase Projection-Based Particle Methods. A. Khayyer, H. Gotoh, H. Ikari & N. Tsuruta

• A generalized SPH-DEM discretization for the modelling of complex multiphasic free surface flows. R. Canelas, A. Crespo, J. Domínguez & R.M.L. Ferreira

• Modelling of Phase Decomposition Using a Fourth-Order Derivation for SPH. M. Hirschler, M. Huber, W. Säckel & U. Nieken

• The SPH Modeling of the Deformation of a Droplet under the Effect of Constant External Electric Field. A. Rahmat, M.S Shadloo & M. Yildiz

Session 4: Coupled Methods Chair: P. Groenenboom

• Multi-purpose interfaces for coupling SPH with other solvers. B. Bouscasse, S. Marrone, A. Colagrossi & A. Di Mascio

• Coupling of a SPH-ALE and a Finite Volume Method. M. Neuhauser, F. Leboeuf, J.-C. Marongiu, M. Rentschler, & E. Parkinson

• On the use of particle based methods for cosmological hydrodynamical simulations. M. Schaller, R. G. Bower & T. Theuns

Session 5: Turbulence Chair: A. Colagrossi

• Density diffusion terms and solid wall models in weakly compressible SPH. A. Valizadeh & J.J. Monaghan

• SPH hyperviscosity model for incompressible turbulence. Y.L. Shi, M. Ellero & N.A. Adams

• Direct numerical simulation of 3-D turbulent wall bounded flows with SPH. A. Mayrhofer, D. Laurence, B. D. Rogers, D. Violeau & M. Ferrand

• An algorithm for dusty gas with SPH. G. Laibe, D. J. Price, B. A. Ayliffe

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Discussion: SPHERIC Grand Challenges Working Group Chair: D. Violeau & B.D. Rogers

DAY 2: Wednesday 5 June 2013

Keynote lecture: Dr D. Violeau, Electricité de France Numerical Stability of SPH for Weakly Compressible Viscous Flows: Optimal Time-Stepping

Session 6: Free surface & interface modelling Chair: A. Souto-Iglesias

• SPH modelling of 3D body transport in free surface flows. A. Amicarelli, R. Albano, D. Mirauda, G. Agate, A. Sole, & R. Guandalini

• Application of SPH on study of a deep water plunging wave. M. H. Dao & E. S. Chan

• SPH surface tension model without need for calibration or evaluation of curvature. A.C.H. Kruisbrink, F.R. Pearce, T. Yue, H.P. Morvan & K.A. Cliffe

• Volume reformulation of spatially varying interactions using the example of moving contact lines for a complete surface tension description. M. Huber, W. Säckel, M. Hirschler, U. Nieken & S. M. Hassanizadeh

Session 7: Theoretical & Numerical aspects of SPH Chair: X. Hu

• Several approaches to achieve better accuracy of a single precision SPH code. V. Titarenko, B.D. Rogers & A. Revell

• Measures of Particle Disorder. M. Antuono, A. Colagrossi, S. Marrone & B. Bouscasse

• A Switch for Artificial Resistivity and Other Dissipation Terms. T.S. Tricco & D.J. Price

• Accuracy and performance of implicit projection methods for transient viscous flows using SPH. N. Trask & M. Maxey

• PySPH: A Python framework for SPH. K.Puri, P. Ramachandran, P.Pandey, C.Kaushik & P.Godbole

Session 8: Multi-resolution techniques Chair: B.D. Rogers

• Particle refinement and derefinement procedure applied to Smoothed Particle Hydrodynamics method. D.A. Barcarolo, D. le Touzé, G. Oger & F. de Vuyst

• A multiscale SPH modeling of near-wall dynamics of leukocytes in flow. B. Gholami, A. Comerford & M. Ellero

• Shock interactions with dusty gases using multi-phase RSPH. M.G. Omang & J.K. Trulsen

• SWIFT: Fast algorithms for multi-resolution SPH on multi-core architectures. P. Gonnet, M. Schallery, T. Theunsyz & A.B.G. Chalk

Session 9: High Performance Computing Chair: D.J. Price

• FPM Flow Simulations Using an Adaptive Domain Decomposition Strategy. C. Vessaz, E. Jahanbakhsh, M. Reclari & F. Avellan

• Integration of spring physics with the SPH method for quasi-solid to fluid interaction using GPGPU programming. S.M. Longshaw, B.D. Rogers & P.K. Stansby

• AQUAgpusph, a free 3D SPH solver accelerated with OpenCL. B J.L. Cercos-Pita, A. Souto-Iglesias, L.M. Gonzalez & F. Macià

• Simulating more than 1 billion SPH particles using GPU hardware acceleration. J.M. Domínguez, A.J.C. Crespo, B.D. Rogers & M. Gomez-Gesteira

Session 10: Solids & Structural MechanicsChair Chair: P. Skjetne

• The way to an enhanced Smoothed Particle Hydrodynamics formulation suitable for machining process simulations. F. Spreng & P. Eberhard

• Shock loading of layered materials with SPH. I. Zisis & B. van der Linden

• SPH Simulations of Abrasive Processes at a Microscopic Scale. C. Nutto, C. Bierwisch, H. Lagger & M. Moseler

Steering Committee meeting

DAY 3: Thursday 6 June 2013

Session 11: Maritime applications

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Chair: P.K. Stansby

• SPH modelling of the flow field with spilling generated by a hydrofoil. S. Sibilla, D. di Padova & M. Mossa

• Slam Modelling with SPH: The Importance of Air. S.J. Lind, P.K. Stansby & B.D. Rogers

• Comparison of SPH and VOF simulations with experimental measured wave-induced impact loads due to Green Water Events. C. Pakozdi & SINTEF SPH Team

• Simulation of extreme waves impacts on a FLNG. P.-M. Guilcher, J. Candelier, L. Béguin, G. Ducrozet & D. Le Touzé

Session 12: Multiphase Chair: S. Sibilla

• Modelling Sediment Resuspension in Industrial Tanks using SPH on GPUs. G. Fourtakas, B. D. Rogers & D. Laurence

• GPU Acceleration of 3-D Multi-phase SPH Simulations for Violent Hydrodynamics. A. Mokos, B.D. Rogers, P.K. Stansby & J.M. Dominguez

• SPH Modelling of Bed Erosion for Water/Soil-Interaction. M. Leonardi & T. Rung

• A pool boiling model with SPH . S. Litvinov, D. Gaudlitz, X. Hu & N. Adams

Session 13: Exotic applications and methods Chair: T. Rung

• Application of Modified SPH to Quantum Mechanical Problems. S. Sugimoto & Y. Zempo

• Simulation of particulate suspensions with SPH and application to tape casting processes. P. Polfer & T. Kraft

• SmoothViz: An Interactive Visual Analysis System for SPH Data. V. Molchanov, A. Fofonov, S. Rosswog, P. Rosenthal & L. Linsen

• <MPS> ≡ <SPH>. F. Macià, A. Souto-Iglesias, L. M. González & J.L. Cercos-Pita

Session 14: Turbulence Chair: J.-C. Marongiu

• A transport-velocity formulation for Smoothed Particle Hydrodynamics. S. Adami, X.Y. Hu & N.A. Adams

• SPH simulations of elastic turbulence and mixing in a periodic channel flow. M. Grilli, A. Vazquez-Quesada & M. Ellero

• Simulating 3D turbulence with SPH. S. Adami, X.Y. Hu & N.A. Adams

Session 15: High Performance Computing Chair: A. Khayyer

• Dynamic Load-Balancing for Parallel Smooth Particle Hydrodynamics. P. Godbole, K. Puri & P. Ramachandran

• Effective memory layout and accesses for the SPH method on the GPU. K.O. Lye, C. Dyken, J. Seland & SINTEF SPH Team

• Efficient massive parallelisation for Incompressible Smoothed Particle Hydrodynamics with 108 Particles. X. Guo, S. Lind, B.D. Rogers, P.K. Stansby & M. Ashworth

Closing and awards

Obituary: Prof. Francis Lebœuf Our colleague Professor Francis Leboeuf, from Ecole Centrale de Lyon (ECL, France) left us much too early on May 30th, struck by disease. He spent most of his career as leader of the research group on Turbomachinery at the Laboratory of Fluid Mechanics and Acoustics of ECL. He became Professor in 1989 and was for ten years the Dean of Research and for five years the Dean of Studies. In recent years he was nominated as coordinator of collaborations between China and the five Ecoles Centrales in France. He was also very active in the creation of Ecole Centrale Beijing and became then Director of the International Associated Laboratory on Engineering Sciences.

He also initiated in 2004 research activities on SPH at Ecole Centrale de Lyon, supervising five PhD students and three post-doctoral researchers on the subject of simulating free surface flows in hydraulic turbines. He was one of the founders of the SPHERIC community. Francis was a brilliant researcher, an extraordinary teacher, and a very kind and unique personality. Our thoughts go to his family.

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SPHERIC newsletter 16th issue – July 2013

Application of the unified semi-analytical wall boundary conditions to 2-D incompressible SPH A. Leroy, D. Violeau & C. Kassiotis, Saint-Venant Laboratory for Hydraulics, 6 quai Watier, 78400 Chatou, France M. Ferrand, MFEE, EDF R&D, 6 quai Watier, 78400 Chatou, France

This work received the award for best student paper (Libersky Prize) at the 8th Int. SPHERIC Workshop, Trondheim (Norway), June 2013 (Leroy et al., 2013a).

It was proven that the incompressible SPH method (ISPH) reduces the computational time while providing a better description of the pressure field than the weakly-compressible SPH method (WCSPH). Yet, the problem of the pressure wall boundary condition remains, since most available ISPH models in the literature are based on ghost particles. The latter technique leads to approximate boundary conditions that can hardly be extended to complex geometries. In this work, a new incompressible SPH (ISPH) model is proposed in 2-D: the unified semi-analytical wall boundary conditions (Ferrand et al., 2013) were combined with a classical ISPH model.

The ISPH model chosen was the one proposed by Lind et al. (2012), based on the projection method with a divergence-free velocity field and a stabilizing procedure consisting of particle shifting. The major improvement achieved through the new model is the accurate imposition of boundary conditions on the pressure field to solve the pressure Poisson equation, which allows prescribing the impermeability condition. With the semi-analytical boundary conditions, the SPH interpolation is corrected by a wall renormalization factor that accounts for the kernel truncation near the walls. The discrete SPH operators are then modified. In particular, a boundary term appears in the Laplacian operator, which allows accurate prescription of the impermeability condition.

Figure 1 – Lid-driven cavity for Re = 1000: convergence plots.

The shifting and free-surface detection algorithms were also adapted to the semi-analytical boundary conditions. A way to compute the wall renormalization factor analytically in the frame of these boundary conditions was proposed in order to decrease the computational time with ISPH.

Several validation laminar test-cases were performed: a lid-driven cavity, a water column collapsing on a wedge and a rotating water-wheel, which showed that the

impermeability condition is respected even for violent free-surface flows. Our results were compared to Finite Volume (FV) methods, using VoF in the case of free-surface flows. In general the fields/forces (especially the pressure) obtained with the new ISPH model were more accurate and smoother than with WCSPH using the same boundary conditions. The new ISPH model also presents a higher order of convergence than the WCSPH model, as shown on Figure 1 where a convergence plot obtained for the lid-driven cavity is presented.

The k–ε model was coupled with the proposed ISPH model which allowed modelling of turbulent flows. A turbulent channel flow was chosen as validation case, where an excellent agreement between our results, DNS and FV results was obtained (see Figure 2). Besides, our results were in fairly good agreement with the ones obtained with FV in the case of a turbulent periodic fish-pass.

All the results presented in the paper concerned 2-D flows, but the extension of this work to 3-D does not present any further issues and will be done in a future work in a GPU framework.

Figure 1 – Turbulent Poiseuille channel flow at Reτ = 640: non-dimensional velocity profiles.

Contact: sengaleroy@gmail.com

References

Ferrand, M., Laurence, D.R., Rogers, B.D., Violeau, D., Kassiotis, C. (2013), Unified semi-analytical wall boundary conditions for inviscid, laminar or turbulent flows in the meshless SPH method, J. Num. Meth. Fluids 71:446–472.

Lind, S.J., Xu, R., Stansby, P.K. & Rogers, B.D. (2012), Incompressible smoothed particle hydro-dynamics for free-surface flows: A generalised diffusion-based algorithm for stability and validations for impulsive flows and propagating waves, J. Comp. Phys. 231(4):1499–1523.

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SPHERIC newsletter 16th issue – July 2013

Coupling of an SPH-ALE and a Finite Volume method M. Neuhauser & F. Leboeuf, Ecole Centrale de Lyon, 36 Avenue Guy de Collongue, Ecully, France J.-C. Marongiu, ANDRITZ HYDRO SAS, 13 Avenue Albert Einstein, 69100 Villeurbanne, France M. Rentschler & E. Parkinson, ANDRITZ HYDRO AG, Rue des Deux-Gares 6, 1800 Vevey, Switzerland

This work received the 2nd prize in the competition for the best student paper at the 8th Int. SPHERIC Workshop, Trondeim (Norway), June 2013.

In the following a novel coupling algorithm for Smoothed Particle Hydrodynamics Arbitrary Lagrange Euler (SPH-ALE) and a mesh-based Finite Volume (FV) method is presented, where both methods are discretizing the Navier Stokes equations in an arbitrarily moving frame of reference.

The meshless method SPH-ALE (Vila, 1999 and Marongiu, 2008) is very well adapted for the simulation of highly dynamic flows with moving geometries but has difficulties in correct representation of rapidly changing gradients of the field variables (Neuhauser, 2012). Particle refinement is difficult to implement if particles are moving in Lagrangian motion and the isotropic nature of SPH makes it complicated to refine particles in an anisotropic way, like it is for example done for solving boundary layers with mesh-based methods. FV methods are well established in CFD because of their accuracy and stability, in particular when treating boundary layers. However, they can be tedious for simulations with moving geometries and often necessitate an interface between moving and static parts of the mesh which introduces additional errors.

Figure 1 – Sketch of the coupling algorithm. The information is transferred in two ways, indicated by the arrows. The overlapping FV mesh can be situated any-where in the computational domain.

To overcome the shortcomings of both methods, we propose a coupling, where we use SPH-ALE in the whole computational domain and an overlapping FV mesh in regions where a refined solution is desired. Figure 1 shows that the flow information is transferred in two ways. On the one hand, we use the FV calculation points as SPH neighbours in the parts of the domain where the mesh is overlapping the SPH-ALE particles. On the other hand, the boundary conditions for the FV domain are interpolated from the SPH-ALE particles, similar to what is done in the CHIMERA method of overlapping meshes (Benek, 1983). In contrast to the CHIMERA method, interpolation is not performed on a structured grid but on a set of unstructured points. Hence, an interpolation technique for scattered data like Shepard interpolation or

higher order Moving Least Square (MLS) interpolation is used.

The approach is carefully validated by means of one-dimensional academic test-cases that show very encouraging results, see for example Figure 2. Trans-position of the proposed method in two and three space dimensions is straightforward. Our final aim is the simulation of transient flows in hydraulic machines, where the FV domain(s) will be used to capture boundary layers along turbine blades.

Figure 2 – Velocity of a coupled 1D simulation. A sinusoidal velocity is imposed at the inlet (x = 0), while static pressure is imposed at the outlet (x = 1). The green line indicates the solution obtained by the FV method (0.45 ≤ x ≤ 0.55) and the red points the SPH particles in Lagrangian motion.

Contact: Magdalena.Neuhauser@ec-lyon.fr

References

Vila, J.P. (1999), On particle weighted methods and Smooth Particle Hydrodynamics, Math. Models and Meth. in Appl. Sc. 9:161–209.

Marongiu, J.-C., Leboeuf, F., Parkinson, E. (2008), Riemann solvers and efficient boundary treatments: an hybrid SPH-finite volume numerical method, Proc. 3rd Int. SPHERIC Workshop, Lausanne (Switzerland), pp. 101–108.

Neuhauser, M., Leboeuf, F., Marongiu, J.-C., Rentschler, M., Parkinson, E. (2012), SPH-ALE for simulations of rotor-stator interactions, Proc. 7th Int. SPHERIC Workshop, Prato (Italy), pp. 103–108.

Benek, J.A., Steger, J.L., Dougherty, F.C. (1983), A flexible grid embedding technique with application to the Euler equations, AIAA Paper No. 83–1944.

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SPHERIC newsletter 16 th issue – July 2013

Direct numerical simulation of 3-D turbulent wall bounded flows with SPH A. Mayrhofer, D. Laurence & B. D. Rogers, School of MACE, University of Manchester, United Kingdom D. Violeau, Laboratoire national d'Hydraulique et d'Environnement, EDF R&D, Chatou, France M. Ferrand, Mécanique des Fluides, Energie et Environnement, EDF R&D, Chatou, France

This work received the 3rd prize in the competition for the best student paper at the 8th Int. SPHERIC Workshop, Trondheim (Norway), June 2013 (Mayrhofer et al., 2013a).

Turbulence simulation with SPH is a recent topic of research with several difficulties to be overcome. In this paper we use the unified semi-analytical wall boundary conditions for SPH in 2-D by Ferrand et al. (2012). The key feature is a kernel renormalization factor which does not rely on the standard SPH quadrature rule. Additionally, the SPH differential operators are defined without neglecting the boundary terms which enables the correct imposition of boundary conditions. Several modifications by Mayrhofer et al. (2013b) are applied and investigated in the present context.

The first part of the present paper deals with the validation of SPH as an accurate Navier-Stokes solver, in particular demonstrating the extension of the unified semi-analytical wall boundary conditions to 3-D as proposed by Mayrhofer et al. (2013c). A novel algorithm for initializing the kernel correction factor is proposed and tested for stability in a simulation with a highly complex gemetry. The 3-D Poiseuille flow is used to demonstrate the proper imposition of the shear stress at walls.

Figure 1 – Snapshot of the minimal flow unit.

The main simulation of this paper is a Direct Numerical Simulation (DNS) of the minimal flow unit first proposed by Jiménez and Moin (1991). This test case (see Figure 1) is the smallest computational box to study the turbulent flow in an infinite channel which contains exactly one large scale turbulent structure at each wall and captures the relevant flow physics of smaller scale fluctuations. Two different resolutions of the channel are investigated showing that a resolution equal to the spectral one on structured grids by Jiménez and Moin (1991) is not sufficient. The simulation with twice the resolution and over 107 particles shows good agreement with the reference data.

Eulerian statistics are investigated using a binning technique for the interpolation to the grid. The mean velocity and turbulent intensities are compared to the results by Jiménez and Moin (1991). The main deviation from the reference data occurs close to the wall where the wall normal intensity is significantly overpredicted (Figure 2). The two-point autocorrelations close to the wall show the same defect indicating numerical noise as the source of the issue.

Preliminary Lagrangian statistics, naturally available with SPH, are presented and compared to the results by Choi et al. (2004).

Figure 2 – Minimal flow unit: normalised standard deviation of vertical velocity fluctuations on log scale.

Contact: arno.m@gmx.at

References

Choi, J.-I., Yeo, K., Lee, C. (2004), Lagrangian statistics in turbulent channel flow, Phys Fluid 16:779.

Ferrand, M., Laurence, D., Rogers, B. D., Violeau, D., Kassiotis, C. (2012), Unified semi-analytical wall boundary conditions for inviscid, laminar or turbulent flows in the meshless SPH method, Int. J. Numer. Meth. Fluids 71-4:446.

Jiménez, J., Moin, P. (1991), The minimal flow unit in near-wall turbulence, J. Fluid Mech. 225:213.

Maryhofer, A., Laurence, D., Rogers, B.D., Violeau, D., Ferrand, M. (2013a), Direct numerical simulation of 3-D turbulent wall bounded flows with SPH, Proc. 8th SPHERIC Int. Workshop, pp. 130–138.

Maryhofer, A., Rogers, B. D., Violeau, D., Ferrand, M. (2013b), Investigation of wall bounded flows using SPH and the unified semi-analytical wall boundary conditions, Comput. Phys. Commun. [accepted for publication, arXiv:1304.3692]

Maryhofer, A., Ferrand, M., Kassiotis, C., Violeau, D. and Morel, F.-X. (2013c), Unified semi-analytical wall boundary conditions in SPH: analytical extension to 3-D, Numer. Algorithms: [under review].

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SPHERIC newsletter 16 th issue – July 2013

SPHERIC Grand Challenge Working Group D. Violeau, Laboratoire national d'Hydraulique et d'Environnement, EDF R&D, Chatou, France B. D. Rogers, School of MACE, University of Manchester, United Kingdom

Today SPH is considered as a promising method but still suffers from a lack of broad recognition both from the scientific community and industry as a serious candidate to become tomorrow's numerical tool. One of the main reasons is that SPH still has unknown characteristics where numerous questions remain unanswered, many on purely theoretical grounds. Although recent progress has been made, a huge amount of theoretical work remains to be addressed.

Convergence, numerical stability, boundary condi-tions, kernel properties, time marching, existence and properties of solutions, etc., are just a short list of the key issues that need to be addressed in order to advance SPH to be a mature method. In order to make progress in the development of the above mentioned problems, SPHERIC has created a Working Group on SPH numerical development, named the SPHERIC Grand Challenge Working Group (GCWG).

Four Grand Challenges (GCs) have been identified by the SPHERIC Steering Committee:

� GC#1: Convergence Leaders: J.J. Monaghan and D.J. Price

� GC#2: Numerical stability Leaders: D. Violeau and R. Vignjevic

� GC#3: Boundary conditions Leaders: A. Souto-Iglesias and J.-C. Marongiu

� GC#4: Adaptivity Leaders: B.D. Rogers and R. Vacondio

Ideally, the GCWG should clarify the most important problems remaining in these GCs, list the most significant publications on each topic, keep aware of the state-of-the-art and identify active research teams and foster cooperation through a living network. Sharing knowledge and clarifying the needs will be our main motivation. So far, since the GCWG is under construction no clear agenda has emerged, but the more we are open and discuss the issues, the quicker SPH will make progress and become widely accepted and used as a viable numerical tool. It is open to all volunteers and contributions with suggestions from all areas welcome.

PhD and postdoctoral fellows are particularly welcome to join this Group. Their contributions to the improvement of SPH will be of great help, and the Group aims at fostering their cooperation with other institutes.

A SPHERIC Grand Challenge Award will reward future publications of particular merit in the

abovementioned fields. It will be given by the SC according to recent relevant publications.

Now, what can YOU do? Below is a list of suggestions:

� Contribute to the GC sections below by adding references (contact: benedict.rogers@manchester.ac.uk)

� Contribute to the GCs with your own work

� If you do so, inform the corresponding GC leaders

� Take advantage of the SPHERIC community and Workshops to share knowledge

� Propose publications to be nominated for the GC Award

� Propose new GCs?

During the last SPHERIC Workshop in Trondheim (see p. 1), a discussion session was chaired by Dr B.D. Rogers in order to start discussion and stimulate ideas. The discussion rapidly focused on consistency, convergence and boundary conditions. This sort of informal discussion session is planned to take place in the future Workshops.

The present information, as well as further details and references about the GCs, is available on the SPHERIC website through the following link:

https://wiki.manchester.ac.uk/spheric/index.php/SPH_Theory_Working_Group