When transporting large volumes of technical liquids, for example, oil in large tanks and other chemicals, operators often encounter uncontrolled internal resonant flows, the so-called splashes, which, due to the large mass of the liquid, form systematic force effects on the tanks walls and other internal structures. The presented material presents the results of numerical modeling flows of a viscous liquid during its resonant oscillations in tanks. As a result of numerical studies, it can be concluded that the total moment of inertia of the liquid can form significant (up to 450 kg) impact effects on the walls of the tank and can change over time due to the existence of a vertical floating baffles. New modeling results allow quantitative determination of the force effects of oscillating fluid on the tank walls. When analyzing the flows hydrodynamic mechanism under consideration, it is important to identify the force effects of the liquid bulk on the tank walls, as well as internal floating near-surface baffles. Due to the presence and systematic migration of liquid moving masses within the tank, significant instabilities arise, as well as shock pressures on the walls and internal structures, which in turn leads to deformation and even destruction of power structures. The presented material provides examples of the distribution and development of inertial flows from the point of force effects view on internal structures, taking into account the effect of floating near-surface baffles.