This article examines the effect of friction model on the simulation accuracy of hydraulic cylinders by using three friction models: a steady-state friction model, the LuGre model, and the new modified LuGre model. Hydraulic cylinder’s behaviors are measured under different sinusoidal inputs to the servo valve. Simulations are conducted under the same conditions as the experiments. The comparisons of simulated results with measured ones show that the new modified LuGre model can predict accurately the hydraulic cylinder’s behaviors while the LuGre model may cause high-frequency oscillations in velocity, friction force, and pressures, which are not observed in experiments.

The 6M low speed wind tunnel completed recently at National Aerospace Laboratory, is equipped with a control valve and hydraulic system which ensures an oscillatory change in the air speed in response to any arbitrary command signal in order to simulate the transient state of take off and landing or transition of V/STOL. In the course of its design and construction, the dynamic response of a wind tunnel flow to the movement of the valve was studied theoretically and experimentally.The analogy with an electric circuit was found to be applicable in the theoretical study, and was verified in the latter experiments; a wind tunnel is compared to a first order oscillation system in the lower frequency range. In the higher frequency, however, recognized is a resonant mode due to the oscillatory presure variation accompanied with an insignificant mass motion of the air. A control system to compensate these characteristics was worked out and proved to be successful.