Uwe Janoske

Partitioned fluid-solid coupling for cardiovascular blood flow: left-ventricular fluid mechanics.

We present a 3D code-coupling approach which has been specialized towards cardiovascular blood flow. For the first time, the prescribed geometry movement of the cardiovascular flow model KaHMo (Karlsruhe Heart Model) has been replaced by a myocardial composite model. Deformation is driven by fluid forces and myocardial response, i.e., both its contractile and constitutive behavior. Whereas the arbitrary Lagrangian–Eulerian formulation (ALE) of the Navier–Stokes equations is discretized by finite volumes (FVM), the solid mechanical finite elasticity equations are discretized by a finite element (FEM) approach. Taking advantage of specialized numerical solution strategies for non-matching fluid and solid domain meshes, an iterative data-exchange guarantees the interface equilibrium of the underlying governing equations. The focus of this work is on left-ventricular fluid–structure interaction based on patient-specific magnetic resonance imaging datasets. Multi-physical phenomena are described by temporal visualization and characteristic FSI numbers. The results gained show flow patterns that are in good agreement with previous observations. A deeper understanding of cavity deformation, blood flow, and their vital interaction can help to improve surgical treatment and clinical therapy planning.

Detection of position and orientation of flying cylinder shaped objects by distance sensors

A new approach considers in-plant transportation of objects by throwing them in direct hits into a capturing device. Therefore, trajectories of the thrown objects have to meet it in a certain position as well as in a defined angular orientation. Due to high sensitivity, for instance to environmental effects, a trajectory is fairly hard to predict precisely via simulation models. Furthermore, repeatability may be poor due to uncertainties in launch angle and launch velocity. If the trajectory does not meet the capturing device accurately, its position and orientation has to be adapted accordingly. Deviations between predicted and actual trajectory have therefore to be detected by a sensor system. This paper presents an algorithm for the detection of position and orientation of thrown cylinders during flight. This algorithm uses measured points on the lateral surface of the cylinder. These data are collected by distance sensors, which are located along the trajectory.

Automated throwing and capturing of cylinder-shaped objects

A new approach for transportation of objects within production systems by automated throwing and capturing is investigated. This paper presents an implementation, consisting of a throwing robot and a capturing robot. The throwing robot uses a linear and the capturing robot a rotary axis. The throwing robot is capable of throwing cylinder-shaped objects onto a target point with high precision. The capturing robot there smoothly grips the cylinders during flight by means of a rotational movement. In order to synchronize the capturing robot and the cylinders pose and velocity, its trajectory has to be modeled as well as the motion sequences of both robots. The throwing and capturing tasks are performed by the robots automatically without the use of any external sensor system.

Holistic Modeling of Trajectories for Cylinder-Shaped Objects

A new approach for the transportation of objects within production systems by throwing and capturing is investigated. For the purpose of throwing objects in direct hits into a capturing device, the trajectory has to meet it in a predefined position. Therefore, the corresponding trajectory has to be simulated and appropriately controlled by the required launch angle as well as launch velocity. This paper presents a holistic approach for the modeling of trajectories for cylinder-shaped objects. The calculation of the position and orientation of the cylinder for each point of time during the flight is enabled by this approach. Furthermore, an algorithm for the determination of the launch parameters in order to meet the capturing device in a predefined position as well as angular orientation is presented.

Implicit Partitioned Cardiovascular Fluid–Structure Interaction of the Heart Cycle Using Non-newtonian Fluid Properties and Orthotropic Material Behavior

Although image-based methods like MRI are well-developed, numerical simulation can help to understand human heart function. This function results from a complex interplay of biochemistry, structural mechanics, and blood flow. The complexity of the entire system often causes one of the three parts to be neglected, which limits the truth to reality of the reduced model. This paper focuses on the interaction of myocardial stress distribution and ventricular blood flow during diastole and systole in comparison to a simulation of the same patient-specific geometry with a given wall movement (Spiegel, Strömungsmechanischer Beitrag zur Planung von Herzoperationen, 2009). The orthotropic constitutive law proposed by Holzapfel et al. (Philos. Trans. R. Soc. Lond. Ser. A, 367:3445–3475, 2009) was implemented in a finite element package to model the passive behavior of the myocardium. Then, this law was modified for contraction. Via the ALE method, the structural model was coupled to a flow model which incorporates blood rheology and the circulatory system (Oertel, Prandtl—Essentials of Fluid Mechanics, 3rd edn, Springer Science + Business Media, 2010; Oertel et al., Modelling the Human Cardiac Fluid Mechanics, 3rd edn, Universitätsverlag Karlsruhe, 2009). Comparison reveals a good quantitative and qualitative agreement with respect to fluid flow. The motion of the myocardium is consistent with physiological observations. The calculated stresses and the distribution are within the physiological range and appear to be reasonable. The coupled model presented contains many features essential to cardiac function. It is possible to calculate wall stresses as well as the characteristic ventricular fluid flow. Based on the simulations we derive two characteristics to assess the health state quantitatively including solid and fluid mechanical aspects.

An Application of a Gradient Theory With Dissipative Boundary Conditions to Fully Developed Turbulent Flows

The paper presents a complete gradient theory of grade two, including new dissipative boundary conditions based on an axiomatic conception of a nonlocal continuum theory for materials of grade n. The total stress tensor of rank two in the equation of linear momentum contains two higher stress tensors of rank two and three. In the case of isotropic materials, both the tensors of rank two and three are tensor valued functions of the second order strain rate tensor and its first gradient. So the vector valued differential equation of motion is of order four, where the necessary dissipative boundary conditions are generated by using porosity tensors. An application to hydrodynamic turbulence by a linear theory is shown, whereby fully developed steady turbulent channel flows with fixed walls and one moving wall are also examined. The velocity distribution parameters are identified by a numerical optimization algorithm, using experimental data of velocity profiles of channel flow with fixed walls from the literature. These profiles were compared with others given in the literature. With these derived parameters, the predicted velocity gradient of a channel flow agrees well with data from the literature. In addition all simulations were successfully carried out using the finite difference method.

Numerical Simulation of the Fluid Flow and the Separation Behavior in a Single Gap of a Disk Stack Centrifuge

Using physicomathematical modeling and numerical simulation, a disk stack centrifuge was examined. With these tools it was possible to derive criteria for the stability of the flow behavior. Subsequently, this knowledge led to regularities describing the separation efficiency which can be written in dimensionless laws. The theoretical and numerical results were proven by experiments.

Dewatering behavior of sewage screenings

Screenings from municipal sewage treatment plants have increased in importance in recent years, particularly in Germany, where laws prohibit depositing of screenings in landfill. This paper presents basic investigations of sewage screenings, especially the structure and dewatering behavior. Two standard experiments are conducted. First, the relationship between pressure and water content is determined. Secondly the flow resistance as a function of pressure is evaluated. The results help to derive simulation models in order to understand how the material behaves inside a wash press.

Hydrodynamic Investigations on the Separation Behavior of Suspensions in a Gap of a Disk Stack Centrifuge with Caulks

By means of physicomathematical modeling it was possible to calculate the flow processes and the separation behavior in a gap of a disk stack centrifuge with caulks. We carried out experiments to validate the separation efficency in the range of laminar flow. The experiment and the calculation correspond well. Furthermore, different forms of flow which resulted in the gap were determined in experiments. The transition from laminar to turbulent was determined in experiments and shown as a function of characteristic numbers. There was a clear stabilization of the flow field when compared to a gap without caulks. A variation of the number of caulks did not have a significant influence on the onset of instabilities.

Experimental Study Of Water Drop Motions Induced By Superposition Of Vibrations And Shear Flows

Droplet motion induced by mechanical vibrations and superposed shear flows has not yet been investigated in detail, despite its major importance in many applications. The current study introduces a novel experimental setup for this purpose. Furthermore, droplet motion measurements on acrylic glass surfaces are presented. This study observes mechanical vibrations and shear flows separately as well as in combination. Measurements with sinusoidal vibrations show that the droplets overcome the force due to contact angle hysteresis, when vibrational acceleration is increased above a certain threshold. Consequently, droplets experience a lateral motion, particularly if the vibrational frequency matches their natural frequency. Separate experiments with shear flows indicate that droplet motions are initiated when a critical flow velocity is reached. The flow velocity required to initiate drop motions decreases when increasing droplet volume. Superposing vibration with the shear flow results in an inconvenient droplet contour and motion, the shaking slip motion. Additionally, the required flow velocity for droplet motion reduces noticeably. Furthermore, the influence of vibrations on the initial droplet motion increases with higher droplet volume. The study concludes that the mobility of water droplets on acrylic glass surfaces increases significantly when a superposition between vibrational forces and shear flows exists.