Mixture transport from a seabed mining vehicle to a buffer is a key procedure in deep-sea mining. Dynamic performances of the particle–seawater mixture in a single-peak flexible riser were numerically investigated using computational fluid dynamics and the discrete element method. Both the time-averaged local characteristics and the instantaneous flow behaviors in the riser are presented. The effects of key parameters, such as feeding concentration and mixture transport velocity, were evaluated by a sensitivity analysis. Large local concentration accompanied by small particle velocity occurs in the ascending sections and increases the risk of blockage. The particle–wall contact reaches the maximum value at both the peak and trough of the single-peak riser. A small feeding concentration would reduce both particle–wall contact, and hydraulic gradient, whereas a moderate mixture transport velocity may be appropriate for the transport in terms of operation safety and energy efficiency. In addition, the mixture transport in a double-peak riser was simulated to examine which configuration is better for engineering applications. The lower maximum local concentration, particle–wall contact and hydraulic gradient and the larger minimum particle velocity indicate that a double-peak flexible riser may be more suitable for the mixture transport.

As one of the most widely used types of deepwater offshore platforms, the Tension Leg Platform (TLP) has shown excellent motion performance in waves; however, a detailed evaluation of their performance under tendon failure condition is vital and necessary. In this study, numerical simulations were conducted in both time and frequency domains using the commercial software HydroD and OrcaFlex, respectively. The numerical results were validated by a series of wave basin model tests. The motions of the TLP, with one tendon failure, and loads on the effective tendons, were studied in dynamic analyses to evaluate the potential adverse impact of tendon failure. Moreover, sensitivity studies of TLP performance under tendon failure were also conducted with various quantities of hull ballast. The relation between the response of the TLP and quantities of ballast were established and some advices were provided about lowering the risks of the loss of TLP stability under one-tendon failure condition.