In approaching the design of an electrorheology-based, semi-active suspension, the electrorheological component (ER damper) can be built as either a flow-mode, shear-mode, or mixed-mode type of damper. The source of damping force in the flow-mode is exclusively from flow-induced pressure drop across a valve, while that in the shear-mode is purely from the shear stress on a sliding surface. The dynamics of the fluid flow are included in the derivation of the zero-field damping forces. The control effectiveness is found to be strongly related to the dynamic constant (which is proportional to the square root of the vibration frequency) and, for shear-and flow-mode dampers, the ratio of the piston area to the cross-section of the ER control gap. To achieve the same performance, a flow-mode ER damper is not as compact and efficient as a shear-mode ER damper. With the same ER damping force, a mixed-mode damper is more compact than a shear-mode damper. However, the mixed-mode damper does not have as a low zero-field damping force as the shear-mode damper. The analysis is based on the assumption that the ER fluid is Bingham plastic.

An analysis was performed to determine the error that results from the estimation of the wall shear rates based on linear and quadratic curve-fittings of the measured velocity profiles. For steady, fully developed flow in a straight vessel, the error for the linear method is linearly related to the distance between the probe and the wall, dr1, and the error for the quadratic method is zero. With pulsatile flow, especially a physiological pulsatile flow in a large artery, the thickness of the velocity boundary layer, delta is small, and the error in the estimation of wall shear based on curve fitting is much higher than that with steady flow. In addition, there is a phase lag between the actual shear rate and the measured one. In oscillatory flow, the error increases with the distance ratio dr1/delta and, for a quadratic method, also with the distance ratio dr2/dr1, where dr2 is the distance of the second probe from the wall. The quadratic method has a distinct advantage in accuracy over the linear method when dr1/delta << 1, i.e. when the first velocity point is well within the boundary layer. The use of this analysis in arterial flow involves many simplifications, including Newtonian fluid, rigid walls, and the linear summation of the harmonic components, and can provide more qualitative than quantitative guidance.

A two-dimensional numerical model was developed to determine the effect of the non-Newtonian behavior of blood on a pulsatile flow at the aortic bifurcation. The blood rheology was described by a weak-form Casson equation. The successive-over-relaxation (SOR) method was used to solve both the vorticity and Poisson equations numerically. It was disclosed that the non-Newtonian property of blood did not drastically change the flow patterns, but caused an appreciable increase in the shear stresses and a slightly higher resistance to both flow separations and the phase shifts between flow layers.

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The increasing concerns of air pollution and energy usage led to the electrification of the vehicle powertrain system in recent years. On the other hand, internal combustion engines were the dominant vehicle power source for more than a century, and they will continue to be used in most vehicles for decades to come; thus, it is necessary to employ advanced technologies to replace traditional mechanical systems with mechatronic systems to meet the ever-increasing demand of continuously improving engine efficiency with reduced emissions, where engine intake and the exhaust valve system represent key subsystems that affect the engine combustion efficiency and emissions. This paper reviews variable engine valve systems, including hydraulic and electrical variable valve timing systems, hydraulic multistep lift systems, continuously variable lift and timing valve systems, lost-motion systems, and electro-magnetic, electro-hydraulic, and electro-pneumatic variable valve actuation systems.