Density waves inhibit the stability of (long) pipelines, which cannot be predicted using current day design tools. Density waves are formed due to an inverse relationship between sand eroding and settling in a pipeline. By designing and building a dedicated flow loop, an experimental study on how the erosion and sedimentation of sand in a pipe is influenced by particle size and concentration is conducted. Moreover, it is determined whether the erosion and sedimentation process can be modeled numerically using existing analytical pick-up functions. This could be applied for predicting density waves in horizontal pipelines. From the experimental study it is found that at higher concentrations, the caterpillar-like movements of the bed, associated with the sedimentation and erosion unbalance at high concentrations, were observed more and more frequently. The influence of the mean grain size diameter can be characterised as the ability of the mixture to trigger amplifying density waves in the horizontal measurement section. Only the coarser sands used in the experiments were found to experience the sliding-stopping behaviour. Implementing different analytical pick-up functions to simulate the experimental study resulted in sufficiently accurate results. Depending on the pick-up function on how much calibration was required the measurements could be simulated adequately.

This study is the first to experimentally show two wave mechanisms regarding density wave amplification with long horizontal slurry transport. There is bed-driven and suspended-driven density wave amplification, in which the grain size determines which mechanism is dominant. Density wave amplification in hydraulic pipeline transport causes significant risk during operation with the consequences of blockage. Current design methodology for pipeline transport considers mixture velocity and density constant over space and time. However, these conditions are only possible in laboratory circuits where conditions can be controlled carefully. In real-world conditions, concentration varies significantly over time due to the natural dredging process in which a dredging vessel takes slurry from the seabed. Density wave amplification can be differentiated into two different flow categories. Both long horizontal transport and a combination of vertical and horizontal transport. With the first category, there are two main theories that explain the amplification of density waves: 'erosion and sedimentation imbalance' and 'the unstable slip point of the bed'. Here, density wave amplification only occurs in the presence of a bed.  In the second category, there is one theory called the: 'transient accumulation theory' which is applicable to a combination of horizontal and vertical transport. With this density wave, amplification can occur far above the deposit limit velocity. Mixture velocities change when density waves travel from horizontal to vertical orientation and vice versa. When mixture velocity changes density will change. The influence of grain size, concentration and the centrifugal pump on density wave amplification has not been researched yet. A test loop has been built with an inner diameter of 46mm and a length of 46 meters. The goal of this laboratory circuit is to investigate the mechanisms that result in the amplification of density waves. Two types of density waves were measured: bed-driven density waves occurring with coarse sediments (Dorsilit 7: d50=1040 μm and Dorsilit 8: d50=619 μm) and suspended-driven density waves occurring with fine sediments (Dorsilit 9: d50=316 μm and Zilverzand: d50=240 μm). With bed-driven density waves, there is fast amplification and multiple sharp waves which can result in areas where no concentration is left. With suspended-driven density waves, there is one smooth wave, and amplification takes multiple loop lengths.

In recent decades, a significant amount of the research into deep sea polymetallic nodule mining has been conducted on the collecting vehicle and the riser system accommodating transport from the seabed to the mining support vessel. The topside operation, however, is less commonly described in the literature. This part of the operation deserves attention because it significantly impacts project risk and cost. After initial investigation the main research question was formed: What is the effect of moisture on the granular characteristics of polymetallic nodules in the context of bulk handling? Royal IHC provided a container with around 50 kg of polymetallic nodules from the Clarion Clipperton Zone. These nodules have been used in earlier research, focused on the degradation of nodules in transport from the seabed to the sea surface. Resulting in broken and damaged nodules. Therefore these are a good representation of nodules coming from the vertical transport system. The degraded nodules provide an unique opportunity to gain an understanding of the bulk behaviour of the nodules once they have arrived on the ship. Four experimental setups were used to understand the granular characteristics of degraded polymetallic nodules in a non-destructive manner. In the first setup, particle properties such as density, porosity, and water content have been measured. The second setup identifies the shape of degraded nodules. The third setup measures the angle of repose for different nodule sizes and water content. The last setup measures the friction factor for different nodule sizes and water content, while changing the sliding surface between steel or rubber. Lastly, clay has been added to the sliding surface experiment. Considering the angle of repose tests and the sliding and rolling friction angle, it is evident that the difference between dry and fully saturated nodules is minimal. For the friction angle: The maximum deviation between dry, saturated and CCZ clay is 8 % on steel and 9 % on rubber, corresponding to 2 degrees. For the angle of repose, the difference between dry and saturated is negligible. It is concluded that the moisture content only contributes minimal level to bulk behaviour of nodules.