Stephan Ulrich

Characterization of Step Response Time and Bandwidth of Electrorheological Fluids

The dynamic behavior of the commercially used electrorheological fluid RheOil3.0 is measured under well-defined conditions. Measurements were carried out in shear mode as well as in flow mode using flow channels that provide similar flow conditions to many electrorheological applications. The response times of the change in flow behavior upon a changed electric field are measured. Measurements were carried out in time domain (single step response) as well as in frequency domain (sinusoidal frequency sweep). In most flow conditions, the observed dynamic behavior is characterized by two leading response times of which the fast one is in the millisecond range. Under stable flow or constant shear rate conditions, ionic conductivity is found to be a limiting factor for a quick step response.

Scale effects of the rheological properties of electrorheological suspensions

The knowledge about the rheological behavior of electrorheological suspensions in all prevalent conditions is essential for the design process of applications. Of particular importance is the dependence of fluid viscosity on the electric field strength, the temperature, and the shear rate. Previous research has pointed out the difficulties in determining the relevant rheological parameters independent from the geometry and flow conditions. For example, experimental results obtained using a capillary rheometer are different from the results gained in flow channel experiments. Even the results from one flow channel could not easily be used to predict the performance of a channel with, for example, a different distance between the electrodes. Some possible effects such as wall slip, interactions of the particles with the surface of the electrodes, or scale effects based on the particle size distribution in relation to the dimension of the flow channel may complicate the determination of the rheological parameters. To investigate these effects, a flow channel test rig that allows systematic changes to the flow conditions was developed. The distance of the electrodes can continuously be changed from 0.02 to 1 mm with an apparent shear rate from 100 to 10,000 s−1. The electrodes can easily be replaced to determine the influence of surface structure. This article will first discuss the design of the flow channel followed by the experimental results obtained under different test conditions. The aim of this research is to gain insight into the scale effects of electrorheological suspensions in order to develop microfluidic applications.

Extending the operation range of electrorheological actuators for vibration control through novel designs

Electrohydraulic actuators with electrorheological fluids were lately introduced for active vibration decoupling. They are suited especially for active isolation of heavy machines and apparatuses. Compared to conventional electrodynamic or hydraulic actuators, these electrorheological systems have considerable advantages because of very high force density and broad frequency range. However, the potential of the electrorheological technology does not remain used up to now completely. In this study, new designs are introduced, which extend the operation borders of the electrorheological actuators for vibration decoupling by utilization of hydrostatic as well as to hydrodynamic forces. The theoretically determined dynamic behaviors of the new actuator principles form the basis for the choice and adaptation of the electrohydraulic systems to special vibration isolation problems and show the advantages to conventional hydraulic actuators.

High-pressure electrorheological valve with full pQ-functionality for servohydraulic applications

Stationary and mobile hydraulic systems require switching increasing velocity, power and efficiency. Usually, their performance mainly faces physical constraints by the valves. These are in particular electrical and magnetic losses as well as various flow saturation effects. Compared to conventional valves, some of these physical constraints do not appear in electrorheological valves. However, electrorheological valves being employed as valves in conventional hydraulic systems were previously unimaginable due to the small controllable pressure differences. The presented new kind of electrorheological valve obtains a significant performance enhancement by combining the potential of conventional and electrorheological systems.

Electrorheological Self-Amplifiying Microvalve

This paper presents the design structure of an electrorheological self-amplifying microvalve for electrorheological fluids. This self-amplifying valve can thereby be devided into two main parts, the steering valve and the self-amplifying unit. The first step - combining a conventional electrorheological valve with a self-amplifying unit is one very important aspect and already induced to a promising result in the past. In a next step the conventional electrorheological valve is replaced by an electrorheological microvalve. Smaller dimensions are the final result. The simulation results of the whole system based on measurement results of the electrorheological microvalve are presented in this paper.