A two-dimensional hydraulic servo valve is an innovative servo control element that provides hydraulic systems with a high power-to-weight ratio, great anti-pollution potential, and superior static and dynamic characteristics. The spool of such a valve is subject to two degrees of freedom: rotation around and sliding along the spool axis, to accomplish both pilot control and flow amplifier functions. The structure of the spool at the main stage is similar to that of a traditional slide valve wherein the asymmetrical distribution of the oil paths manufactured in the valve body produces circumferential unevenness in the radial flow force to the spool at the annular orifice, in line with the momentum theory. Three-dimensional computational fluid dynamics analysis of the flow field revealed that the radial flow force at the annular orifice increases sharply with inlet flow velocity and decreases as the orifice opening grows, while changes in outlet pressure do not affect the levels or distribution of this force. Also, net radial force at the annular orifice increases with both inlet velocity and opening size. The paper presents results demonstrating that the net radial force from fluid flow through the orifice could increase friction resistance and cannot be safely ignored, especially under high-flow-rate conditions.

The hydraulic sliding-spool valve is a key component to control the flow rates and thus pressures in different hydraulic volumes. The lateral force on the spool is one of the important effects resulting from moving resistance. This paper presents research aimed at understanding the effects of radial flow force and static pressure upon the lateral force. The radial flow force is calculated from three types of control surfaces labelled with square land, 45° conical, and round curved surfaces, for discovering the effects of control profile, combined with inlet and outlet control conditions. The pressure difference effect is analyzed along with six cases under the same orifice opening, and the radial flow force is found to vary linearly with the pressure difference. The results also indicate that the radial force for the inlet control mode is less than that of the outlet control mode. The jet angle is discovered to not only be related to the annular orifice opening and gap clearance, but is also influenced by the flow direction and control surface profile. The static pressure is the predominant factor in the lateral force compared to the radial flow force. The results indicate that the static pressure variation on the surface of the cylindrical spool shoulder increased linearly with the inlet pressure; and two stagnation points can be observed in the case of the valve cavity with oil passages on the same section, and square land control edge profile. The lateral force on the spool increases with the pressure, and could reach to the maximum of 300 N, implying that this force should be taken into account in the selection of an actuator, especially in high pressure applications.

In this study, the flexoelectric and piezoelectric distributed sensing signal of the toroidal shell is discussed. By considering the curvature radii and Lamé parameters of the toroidal shell, dynamic strains are derived based on the double-curvature shell. Flexoelectric and piezoelectric distributed sensing models of the toroidal shell are established. Based on the direct flexoelectric effect and direct piezoelectric effect, the flexoelectric/piezoelectric distributed sensing signal is evaluated respectively. The local neural sensing signal is discussed while the flexoelectric and piezoelectric sensor patches approach to infinitesimal. The neural sensing signal is made of different signal components, and the components effects are discussed to elaborate the difference between the flexoelectric and piezoelectric sensing signal. The results indicate that the membrane-induced signal components and bending-induced signal components both affect the piezoelectric sensing signal, while only the bending-induced signal components affect the flexoelectric sensing signal. To elaborate the significance of the components in different directions, signal induced by different strains in different directions are discussed. The signal induced by the meridional bending strain dominates for the flexoelectric sensing while signal induced by the meridional membrane strain is dominant for piezoelectric sensing.