André Pohlmann

Numerical computation can save life: FEM simulations for the development of artificial hearts

Cardiovascular diseases are the major cause of death worldwide. In conjunction with the restricted heart transplants due to the limited number of donor hearts, artificial hearts (AH) are the only therapy available for terminal heart diseases. Starting from the first design of an AH to its implantation into a human body, the AH has to pass several clinical trials, which result in redesigns and optimizations respectively. During this process, the dimensions, the weight and the required electromagnetic forces of the AH as well as blood damage, caused e.g. by shear forces or overheating, have to be considered. Thus, a coupling of analytical and numerical approaches permits an accurate design process to investigate force characteristics and losses of the drive. This contribution will give an example of an existing AH and provides exemplary the adoption of analytical and numerical approaches for the design of an AH developed by the authors. The presented heart prototype was already in operation during clinical animal tests.

Mathematical description and control design for the simultaneous levitation and propulsion of a conveyor vehicle

Magnetic levitation is still an important issue for industry and research. Wherever high dynamics, position accuracy, high reliability and low mechanical wear are required, magnetic levitation is an effective alternative to conventional technologies. Conventional systems with mechanical guiding have shown to be limited in speed. For transporting goods over long distances, levitation can thus lead to a significant saving in time and cost. This paper describes a control design for an autonomous magnetically levitated conveyor vehicle with a linear direct drive for propulsion. Based on a mathematical description as a 2-rigid-body system with elastic coupling in torsion, a simulation environment for the vehicle is created. After that, a degree-of-freedom control is designed for the levitation operation, whereas a conventional PI control is used for the propulsion. This control design is based on the representation of the system as a 2-body system as well. The combination of control and simulation environment offers the opportunity for extensive testing and optimization before the control is applied to a test bench. By intensive analysis the stable and efficient operation of the vehicle is determined. An assortment of measurement results is presented and discussed in this paper.

Comparative Study on the Optimization Methods for a Motor Drive of Artificial Hearts

Worldwide cardiovascular diseases are the major cause of death. Beside heart transplants, which is a limited option due to the available number of human donor hearts, artificial hearts are the only therapy available for terminal heart diseases. For various reasons a total implantable artificial heart is desirable. But the limited space in the human thorax sets rigorous restrictions regarding the weight and the dimensions of the device. Nevertheless the appropriate functionality of the artificial heart must be ensured and blood damage must be prevented. These requirements set further restrictions to the drive of this device. In this paper two optimization methods, which are manual parameter variation and Differential Evolution (DE) algorithm, are presented, to match the specifications of an artificial heart.

Simulation based efficiency prediction of a Brushless DC drive applied in Ventricular Assist Devices

Ventricular Assist Devices (VADs) are mechanical blood pumps that support the human heart in order to maintain a sufficient perfusion of the human body and its organs. During VAD operation blood damage caused by hemolysis, thrombogenecity and denaturation has to be avoided. One key parameter causing the bloods denaturation is its temperature which must not exceed 42°C. As a temperature rise can be directly linked to the losses occuring in the drive system, this paper introduces an efficiency prediction chain for Brushless DC (BLDC) drives which are applied in various VAD systems. The presented chain is applied to various core materials and operation ranges, providing a general overview on the loss dependencies.

Drive optimization of a pulsatile total artificial heart

Purpose – Total artificial hearts (TAHs) are required for the treatment of cardiovascular diseases. In order to replace the native heart a TAH must provide a sufficient perfusion of the human body, prevent blood damage and meet the implantation constraints. Until today there is no TAH on the market which meets all constraints. So the purpose of this paper is to design a drive in such a way that the operated TAH meets all predefined constraints. Design/methodology/approach – The drive is designed in terms of weight and electric losses. In setting up a cost function containing those constraints, the drive design can be included in a optimization process. When reaching the global minimum of the cost function the optimum drive design is found. In this paper the optimization methods manual parameter variation and differential evolution are applied. Findings – At the end of the optimization process the drives weight amounts to 460 g and its mean losses sum up to 10 W. This design meets all predefined constrain...

Design of an BLDC drive with iron core to improve the efficiency of Ventricular Assist Devices

Single sided Brushless DC (BLDC) drives with axial flux have the advantage of a flat design and high torque. This makes them a good choice for operating less invasive implantable Ventricular Assist Devices (VADs), which can be applied for the therapy of cardio vascular diseases. The disadvantage of such drives is the occurrence of high axial forces. In order to avoid axial forces some VAD drives have air gap windings. Their torque generation completely relies on magnetic stray fluxes. Therefore an increase in efficiency is expected when using iron teeth with single tooth windings. As iron losses have to be considered now, a study is performed to identify the key parameters for iron and copper losses. From this study an efficient VAD drive design is deduced.

Validation of the electromagnetic design of a total artificial heart under physical load conditions

Purpose – The purpose of this paper is to introduce the RWTHs total artificial heart, ReinHeart, focusing on the design of the unique drive system.Design/methodology/approach – The force characteristics of the drive have been simulated in a finite element (FE) approach. Additionally the coppler losses within the motor coils have been predicted based on the FE‐simulation. Both results are compared to laboratory measurements of a prototype to validate the design.Findings – The presented results show a good correlation between simulation and measurement and proof the applicability of the new design drive system.Research limitations/implications – The used hydraulic models of the cardiovasular system used as a load for the device are not fully validated with data from living organisms. Therefore, further in vivo trials are needed.Originality/value – The high force density of the drive allows its integration into a fully implantable, total artificial heart, in order to significantly improve durability. This h...

Algorithm‐based, drive design for a ventricular assist device

Purpose – The purpose of this paper is to describe a design process for a drive of a ventricular assist device (VAD) under the consideration of constraints given by the application. In this case, these constraints are the possibility to implant the VAD system, providing a sufficient perfusion of the human body and cutting down development costs.Design/methodology/approach – In the described approach an optimization algorithm is integrated in the initial stage of the design process for a drive system.Findings – During simulations the optimum drive design under the implantation constraints of the given VAD system is found. The key constraints of this design, which are torque, axial force and losses, are validated during initial test bench measurements of a drive prototype.Practical implications – The described design process enables an optimum drive design from the beginning of a VAD development. This reduces the time to initial and chronic in vivo test, which are required to be approved for the market late...