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Cosimulation is known for simulation of processeswith more or less similar time scales by means of significant changes in the same distance in time. Chemical reactions generally are fast and so are fluid dynamics. Time scales might be between seconds and minutes. This is why commercial tools for calculation of fluid dynamics often include modules for chemical reactions. Biological systems are much slower. Typical time scales are between hours and days. In computational fluid dynamics there is currently no way to calculate several hours real time for relevant problems in adequate time. Simulating the hydrodynamics on sufficiently resolved grids in small time-steps causes a demand on computing power such that cosimulation of hydrodynamics and growth cannot be done in adequate time. Sequential cosimulation is proposed as solution sequentially calculating hydrodynamics and growth. For the simulation of hydrodynamics the reactors are discretized into a few hundred thousand finite volume elements. Due to computational restrictions the number of elements used for simulating growth has to be reduced to several thousands. with maximum inter point distances at the same time. Related values are adjusted correspondingly. The calculations have shown that simulations of entire cultivations of biological systems can be performed. The method is especially useful for slow biological systems where the time scale very much differs from the time scale of fluid dynamics. The method solves the problem of not having been able so far to simulate reactor systems for which perfectmixing cannot be claimed. This holds true for all kind of industrial scale systems and especially for those with static gassing systems. The most obvious advantage of the proposed method is the consideration of mass transfer related to fluid dynamics. Thereby, system characteristics directly influence growth. In most biological systems oxygen plays an important role but the oxygen carrying gas does not have constant oxygen content due to prior consumption. The described effect can be termed the history effect of the gas. In order to assess the system performancewith respect to used reactors and gassing systems the consideration of this effect is a must. The effect influences the liquid side saturation concentration as well as the mass transfer. Evenly spaced sequences in time with long distances provide sufficient results. Artefacts as described for the liquid side oxygen concentration at the very beginning can be avoided in two ways. One way to solve the problem is to reduce the distance in time such that even significant gradients are calculated with adequate resolution.