Christian F Janßen

Altair Engineering GmbH

We report on the development and validation of a 3D hybrid Lattice Boltzmann Model (LBM), with Large Eddy Simulation (LES), to simulate the interactions of incompressible turbulent flows with ocean structures. The LBM is based on a perturbation method, in which the velocity and pressure are expressed as the sum of an inviscid flow and a viscous per...

The lattice Boltzmann method (LBM) sees a growing popularity in the field of atmospheric sciences and wind energy, largely due to its excellent computational performance. Still, LBM large-eddy simulation (LES) studies of canonical atmospheric boundary layer flows remain limited. One reason for this is the early stage of development of LBM-specific...

The trend of increasing rotor diameters and tip-speeds has brought about concerns of non-negligible compressibility effects in wind turbine aerodynamics. The investigation of such effects on wakes is particularly difficult when using actuator line models (ALM). This is because crucial regions of the flow, i.e. the direct vicinity of the blade, are...

In this work, we report on the development and initial validation of a new hybrid numerical model for the simulation of incompressible flow. A kinetic Lattice Boltzmann method (LBM) model using a reduced domain is nested within an inviscid flow field to provide increased simulation fidelity where desired, while leveraging the computational efficien...

This paper presents numerical simulations of the natural laminar-turbulent transition in a flat plate boundary layer. Natural transition occurs in low disturbance environments and is triggered by the growth of boundary layer instabilities or disturbances. This contribution specifically aims at investigating the interaction of multiple disturbances...

Most computational fluid dynamics (CFD) simulations require massive computational power, which is usually provided by traditional high-performance computing (HPC) environments. Often, simulations are executed on a massive number of CPU cores (O(1000)) that are hosted in a remote supercomputing center or an in-house supercomputing facility. Due to s...

This webinar discusses how NVIDIA GPUs and NVIDIA CUDA can enable high-fidelity Computational Fluid Dynamics for Higher Education and Research. Flow field computations for transient and turbulent flow problems are very compute-intensive and time-consuming. Popular existing numerical techniques often compromise on the underlying physics or require...

The present research project comprises the development of innovative hydrodynamic design methods for ice-going ships for the investigation and optimization of the propulsion efficiency. It can be stated that there is an urgent need for rational simulation-based techniques in order to reliably analyze the ship motions in ice-covered areas that have...

This paper presents a new and efficient algorithm for the calculation of sub-grid distances in the context of a lattice Boltzmann method (LBM). LBMs usually operate on equidistant Cartesian grids and represent moving geometries by either using immersed boundary conditions or dynamic fill algorithms in combination with slip or no-slip boundary condi...

In this work, we present the innovative commercial GPU-based Computational Fluid Dynamics (CFD) solver ultraFluidX. The software is based on the Lattice Boltzmann Method (LBM), which is explicit in time, hence inherently transient and which only requires nearest-neighbor information for each point of the computational grid. Therefore, LBM is a perf...

In this paper, the scaling properties of the commercial Computational Fluid Dynamics (CFD) solver ultraFluidX are analyzed. The solver is based on the Lattice Boltzmann Method (LBM), is explicit in time, inherently transient and only requires next-neighbor information on the computational grid. ultraFluidX thus highly benefits from the computationa...

Highlights • Modeling of wave-structure interaction, particularly for studying forces on ships, is presented using a hybrid viscid-inviscid approach and overlapping domains • Fully nonlinear potential flow provides the inviscid solution, solved with a boundary element approach, using cubic B-spline elements, and accelerated with the parallel fast m...

This contribution addresses the applicability of an efficient lattice Boltzmann-based single-phase free-surface model for the simulation of wave impact on the side walls of 2-D containers. The computational efficiency of the method is known to allow for very short turnaround times, but wave impact simulations have not been investigated in detail ye...

simulation of the complex dynamics response of ships in waves is typically modeled by nonlinear potential flow theory, usually solved with a higher order BEM. In some cases, the viscous/turbulent effects around a structure and in its wake need to be accurately modeled to capture the salient physics of the problem. Here, we present a fully 3D model...

This article gives an overview of the diverse range of teaching applications that can be realized using an interactive lattice Boltzmann simulation tool in fluid mechanics instruction and outreach. In an inquiry-based learning framework, examples are given of learning scenarios that address instruction on scientific results, scientific methods or t...

The paper reports on the predictive performance of Lattice Boltzmann methods in turbulent channel flows. Attention is confined to model-free (direct) numerical simulations at ReTau=180 using essentially different collision models, i.e. the Bhatnagar-Gross-Krook (BGK), the Multiple-Relaxation-Time (MRT) and the Cumulant model. The three approaches a...

The contribution is devoted to a novel grid refinement technique for GPU-accelerated Lattice Boltzmann Method (LBM) dedicated to free surface flow simulations in marine applications. LBM implementations are mostly based on homogeneous isotropic Cartesian discretizations of the computational domain. Challenges occur when a refined spatial and tempor...

This paper reports on the adaptation of a Lattice Boltzmann based free surface flow solver to the simulation of complex fluid-ship-ice interactions in marine engineering. The analysis is restricted to the interaction of already broken ice floes and the ship hull, aiming at the optimization of a ship hull’s capability to clear the ice and keep it aw...

In recent years, the Lattice Boltzmann Method (LBM) has gained importance in CFD applications in the field of industrial and maritime engineering. Many associated fluid dynamic problems as for instance, propellers, sloshing tanks or wind turbines need to account for moving geometries. A simple but often occurring case is a geometry that is only mov...

It’s out of the question that the Lattice Gas Method (LGM) has rapidly become obsolete in practical applications since the Lattice Boltzmann Method (LBM) has been established in the late 1980s. But by now, the LGM has made its comeback by rediscovering its benefits in teaching applications. Lattice Gas Cellular Automata (LGCA) have turned out to pr...

Fluid mechanics is the branch of physics that studies the behavior of fluids and that is used to solve challenges related to fluids in mechanical engineering, water management, energy management, or meteorology. Typical applications include the design of components that fluids will flow through or around, and the simulation of dissemination and wav...

This contribution presents a GPU-accelerated simulation tool for turbulent flows. The tool is based on LBM implementations on Cartesian grids with local grid refinement. The turbulent characteristics of the under-resolved high Reynolds number flows are either modeled by Large Eddy models, e.g. Smagorinsky LES, or by the LBM collision operator itsel...

The Poster was presented on the 13th International Conference for Mesoscopic Methods in Engineering and Science in Hamburg. It gives an overview of a research project on the numerical simulation of ship-ice interaction under consideration of ice breaking.

A numerical model to predict the interaction between floating objects and the surrounding level ice is presented. Attention is restricted to breaking of level ice due to bending. Emphasis is given to modeling the process by contact forces between floating objects, i.e. the vessel, the level ice and the ice floes, in the framework of a physics engin...

This contribution addresses the efficient numerical simulation of wave impact on the side walls of two-dimensional containers. For the flow field calculations, an efficient Lattice Boltzmann Method (LBM) is used. Whilst modeling essentially similar physics as classical continuum mechanics procedures, LBM features a number of performance-related adv...

Real-time rendering in the realm of computational fluid dynamics (CFD) in particular and scientific high performance computing (HPC) in general is a comparably young field of research, as the complexity of most problems with practical relevance is too high for a real-time numerical simulation. However, recent advances in HPC and the development of...

This contribution is dedicated to demonstrating the high potential and manifold applications of state-of-the-art computational fluid dynamics (CFD) tools for free-surface flows in civil and environmental engineering. All simulations were performed with the academic research code elbe (efficient lattice boltzmann environment, http://www.tuhh.de/elbe...

Dive deep into the fascinating world of real-time computational fluid dynamics. We present details of our GPU-accelerated flow solver for the simulation of non-linear violent flows in marine and coastal engineering. The solver, the efficient lattice boltzmann environment elbe, is accelerated with recent NVIDIA graphics hardware and allows for three...

This paper reports on the applicability of the Lattice Boltzmann based free surface flow solver elbe to the simulation of complex ship-ice interactions in marine engineering. In order to model the dynamics of these colliding rigid multi-body systems, elbe is coupled to the ODE physics engine. First, basic validations of the ODE collision and fricti...

We perform Direct Numerical Simulation (DNS) of three-dimensional (3D) turbulent flows in a rectangular channel, with a Lattice Boltzmann Method (LBM), efficiently implemented on heavily parallel General Purpose Graphical Processor Units (GPGPUs). After validating the method for a single fluid, for standard boundary layer problems, we study changes...

This paper presents a fast surface voxelization technique for the mapping of tessellated triangular surface meshes to uniform and structured grids that provide a basis for CFD simulations with the lattice Boltzmann method (LBM). The core algorithm is optimized for massively parallel execution on graphics processing units (GPUs) and is based on a un...

Abstract We report on the development, implementation and validation of a new Lattice Boltzmann method (LBM) for the numerical simulation of three-dimensional multiphase flows (here with only two components) with both high density ratio and high Reynolds number. This method is based in part on, but aims at achieving a higher computational efficienc...

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The paper reports the extension of a Lattice Boltzmann model for the nonlinear viscous shallow water equations (NSW) and its application to the simulation of internal flood water dynamics. The solver is accelerated with the help of NVIDIAs CUDA framework to access the computational power of graphics processing units (GPGPUs). The model is validated...

A new Lattice Boltzmann method (LBM) is developed to efficiently simulate multiphase flows with high density ratios, in order to study complex air-sea interaction problems, such as wind wave breaking and related sea-spray generation. In this method, which builds and improves on the method proposed earlier by [1], the motion of (diffusive) interface...

In this paper, we present extensions, extensive validations and applications of our previously published hybrid volume-of-fluid-based (VOF) model for the simulation of free-surface flow problems. For the solution of the flow field, the lattice Boltzmann method is used, where the free surface is represented by a VOF approach. The advection equation...

This work investigated the validity and efficiency of the coupling of the Lattice Boltzmann Method with finite element schemes as well as rigid body approaches to model fluid-structure interaction (FSI). The results on two- and three-dimensional benchmark configurations are very promising and show that an explicit coupling scheme is able to produce...

Underwater landslides may be triggered by the reduction in soil strength caused by excess inter-granular pore pressures resulting from seismic loading. Our goal is to study micro-mechanical processes responsible for such excess pore pressure build up in soils, by way of microfluidics technologies and numeric al modeling. Thus, small-scale experimen...

We present an efficient implementation of the Lattice Boltzmann method (LBM) for the numerical simulation of the propagation of long ocean waves (e.g., tsunamis), based on the Nonlinear Shal-low Water (NSW) wave equation. The LBM solution of NSW equations is fully nonlinear and it is assumed that the surface el-evation is single-valued (hence, wave...

In this paper, we present the implementation of a volume-of-fluid-(VOF)-based algorithm for the simulation of free-surface flow problems on general purpose graphical processing units (GPGPUs). For the solution of the flow field and the additional advection equation for the VOF fill level, the lattice Boltzmann method on the basis of an MRT collisio...

This contribution discusses extended physical interface models for fluid–structure interaction problems and investigates their phenomenological effects on the behavior of coupled systems by numerical simulation. Besides the various types of friction at the fluid–structure interface the most interesting phenomena are related to effects due to additi...

In the recent years we investigated the validity and efficiency of coupling high order finite elements schemes for mechanics with the Lattice Boltzmann Method. The results on two dimensional and three dimensional benchmark configurations are very promising and show that an explicit coupling scheme is able to produce results which agree with referen...

In this work, we report on the development and initial validation of a new hybrid numerical model for strongly nonlinear free surface flows, including wave breaking and wave-structure interactions. Specifically, a two-dimensional numerical wave tank (NWT) based on Fully Non-linear Potential Flow (FNPF) theory, and a higher-order Boundary Ele-ment M...

In this paper, we present a hybrid volume-of-fluid-based algorithm for the simulation of free-surface-flow problems. For the solution of the flow field, the lattice Boltzmann method is used. The additional advection equation for the volume-of-fluid (VOF) fill level is discretized with a classical finite volume method. For the interface reconstructi...

In this contribution the authors address recent advances of modelling and simulating flow problems related to Environmental and Civil Engineering using Lattice-Boltzmann methods (LBM) and present results documenting the potential of this kinetic approach. After a short introduction to theoretical aspects of the method, we address extensions of the...

Kurzfassung: Strömungsberechnungen auf Basis der Lattice Boltzmann (LB) Methode haben sich als Alternative zu klassischen Finite Volumen (FV) Verfahren auf Grundlage der Navier-Stokes Gleichungen etabliert. Auch die Simulation von Strömungen mit frei-en Oberflächen ist möglich. Hierbei ist zur Verfolgung der Grenzfläche zwischen den beteiligten Pha...