Hydraulic components are subject to highly transient loads, limiting their lifetime. For quick market entry, fatigue tests of hydraulic components are often done under rectangular cyclic loading at high frequencies. Hereby, the fluid-structure interaction between the fluid and the crack faces is supposed to significantly affect the fatigue crack propagation rate, especially in the case of high-frequencies pulsations. Due to the different scales and low dampening, the simulation of the fluid-structure interaction is challenging. Cross-section’s height of fatigue cracks range between five and sixty micrometers, whereas the crack’s length can be up to three orders of magnitudes larger. The load pressure reduction and the mechanic structure's elastic relaxation occur in milliseconds, while the oil flow inside the fatigue cracks takes seconds. The low oil compressibility combined with a minimum cross-section provides insignificant damping compared with the high structural resistance. To avoid the enormous computational costs that come with small element sizes and small time steps, we present a simulation approach with reduced physical models, exploiting the specific geometric and fluid-dynamic properties of the problem. The fluid domain is discretized by a one-dimensional finite-difference approach under the assumption of a laminar Couette flow, and a linear-elastic approximation of the crack's deformations replaces the structural simulation of the part. The reduced models are implemented in a forward-Euler simulation, and the simulation results are shown for a test specimen. In addition to the simulation, the specimen was tested on a pulsation test rig, and the mechanical deformation was compared to the reduced simulation. The experimental results demonstrate that the reduced model correctly predicts the fluid-structure interaction's dynamic behavior. Compared to a finite-element and finite-volume representation of the fluid and structural domain, the reduced models decrease computation time significantly, and the lower mode complexity leads to improved stability. Fast and accurate simulation of the fluid-structure interaction provides the groundwork for fatigue predictions under various load conditions.