Hydraulic transport pipelines in the dredging, mining and deep sea mining are designed using steady-state methods. However, these methods cannot predict density wave formation. Density waves form a risk for pipeline blockages, therefore there is a need to understand and preferably be able to model the process. The density waves studied in this research are caused by a stationary sediment deposit in the pipeline. This article explores the development of a new transient design model, based on 1-dimensional-two-layer Driftflux CFD. The two layers model the exchange of sediment between the turbulent suspension, and a stationary bed layer, and can therefore model density wave amplification. An empirical erosion-sedimentation closure relationship is applied to model the sediment exchange between the two layers, and is calibrated using experiments. The final model is also validated against a second experiment, specifically for density wave amplification. The experiments and the model show good agreement on the erosion of a stationary bed layer and the growth rate of a density wave and the amplitude of the density wave.

Self-amplifying density waves in hydraulic transport pipelines is a scarcely researched topic. Density waves are in essence the result of a spatial redistributing effect and clustering of solids in hydraulic transport pipelines. Self-amplifying density waves are very undesirable for practical applications, as these waves increasing the risk of pipeline blockages. The two available experimental studies (Talmon et al., 2007; Matoušek and Krupička, 2013) report conflicting properties of the density waves, such as wave length and wave celerity. This new experimental research aims to shed light on the reported differences, by broadly varying particle size and concentration in a new dedicated experiment. The main highlight of this research is that two separate mechanisms were identified that can cause density waves, and Talmon et al. (2007) and Matoušek and Krupička (2013) in hindsight were studying the two different mechanism respectively. Both wave type mechanisms come into effect at mixture velocities close to the deposit limit velocity, and require a stationary bed layer to initiate. The first mechanism is caused by an imbalance of erosion and sedimentation of the bed layer, which is predominant for fine sand particles (∼242μm and ∼308μm in this research). The second mechanism occurs when the bed layer starts sliding, instead of being eroded, and is specific for larger sand sizes (∼617μm and ∼1.08mm in this research). These two mechanisms are clearly distinguishable, having different wave lengths, celerity, amplitudes and amplification rates. The results also show a clear relationship between the mean concentration of a density wave, the wave amplitude and wave celerity specific for each of the two mechanisms.

Density wave amplification in hydraulic transport pipelines forms a high risk to operational continuity, as density waves can lead to system blockages or centrifugal pump drive failures. Recent experimental research, in pipelines which contain long vertical sections, has shown that density waves can amplify at velocities far exceeding the deposit limit velocity, previously thought to be a limiting condition for amplification. The typical design methodology of hydraulic transport pipelines is based on a steady-state philosophy, which assumes that the mixture velocity and sediment concentration are constant in time and space. However, these variations can lead to the amplification of density waves. This article discusses the cause of a new type of density wave amplification mechanism, which is related to slurry dynamics in a pipeline containing vertical sections. This research also presents a 1D Driftflux CFD model which models the aforementioned slurry dynamics and can predict density wave amplification.

This paper presents an improvement on a previous model for predicting the Marsh funnel (MF) test that is used in slurry shield tunneling for evaluating the rheological properties of bentonite slurries. The improvement focuses on the prediction of the dynamic part for fluids with small MF times. The velocity profile of the Herschel-Bulkley fluid in a laminar pipe flow condition is first investigated and a correction factor is introduced in the improved model. Comparisons of results from experiments and calculations with the previous model confirm the improved performance over the existing model. The rheological parameters obtained from the improved model show good resemblance to those obtained from a laboratory viscometer. The work also provides a reference to similar applications such as fluid transportation through pipelines where dynamic pressure dominates and therefore should be correctly predicted considering its velocity profile in a laminar condition.

The hydraulic transport of sediments in sediment–water multiphase mixtures is an important process in nature and many industrial applications. The flows are characterized by complex transient phenomena, in which the overall system scale and the particle scale are equally important. Experimental research into dense mixture flows is focused on measurement of flowrates, differential pressures and concentrations of the suspended sediments. Concentration measurements are especially challenging in the case of coarse particles (beyond millimeter size scale) flowing in dense mixtures, limiting the range of available sensors for accurately measuring the in-situ solids concentrations. For the investigation of transient processes, a quick sensor response is required, which makes concentration measurement based on mixture conductivity an interesting option. This study is focused on combined concentration and pressure measurements in dense sediment–water mixtures with coarse particles in a vertically oriented closed conduit, using differential pressure sensors over the vertical segments and conductivity probes for measuring the mixture concentration. We experimentally investigated the dispersion process of an initially densely packed batch of sand and gravel by measuring the concentration on different segments of the conduit, resulting in data on mixture wall shear stresses for different sand and gravel mixtures and data of attenuation of concentration gradients in vertical upward and downward flow, in the conduit horizontal top section and in the centrifugal pump. We describe in the detail the sensor calibration and data processing method, giving a best practice for the use of conductivity concentration sensors in dense coarse particle mixtures, and we suggest a novel method for analysis of density wave amplification and attenuation based on concentration measurements in general, which allows for the detailed analysis of transient multiphase flow phenomena at pipe system component level.

Hydraulic two-phase transport applied in the dredging, mining, and deep-sea mining industries involves the transportation of sand, gravel, polymetallic nodules, or other particulate tailings as a solids phase and water as a liquid phase. Regardless of the type or size of the granular material, the slurry flow is always subject to transient behavior. Most transient behavior can be attributed to the centrifugal pump as variations in pump pressure and mixture velocity over time, but transients can also be caused by microscopic slurry mechanisms, specifically the amplification of density waves in a pipeline. Density wave amplification in horizontal pipelines at mixture velocities just above the deposition limit velocity was reported and researched in the 1990s. New experiments showing a density wave amplification in a system with combined vertical and horizontal pipelines and at mixture velocities far above the deposition limit suggest that another type of density wave amplification mechanism exists. The newly proposed density wave amplification mechanism is hypothesized to be caused by a change in average particle velocity as the slurry flows from a vertical pipe into a horizontal pipe. Density waves that grow too large cause system blockages or possibly a failure of the pump drive. This article considers centrifugal pump-induced transients and density wave amplification effects separately and how these effects influence each other. Three case studies showing density wave amplification are analyzed, one from the literature and two from new data sets. Furthermore, the causes of these transients are discussed, and where possible, solutions are proposed to avoid these undesirable instabilities.

The mining of polymetallic nodules from the seafloor at depths down to 6000m requires the excavation of nodules with a seafloor mining tool, the transport of nodules as a slurry through a jumper hose connecting the mining tool to a vertical hydraulic transport system and the transport of the nodules through the vertical lifting pipe. We focus on a concept with conventional hydraulic transport, using a series of centrifugal pump booster stations. The nodules will be transported in different flow regimes, ranging from a sliding bed (in the jumper hose) to a homogeneous suspension (vertical flow). Each regime gives rise to degradation of the nodules in a different way. It is important to understand the degradation mechanisms in detail in order to predict the particle size distribution of the slurry leaving the riser. This particle size distribution is a key design parameter for design of processing equipment and for environmental impact assessment. In this article we present the results of experimental work on abrasive wear (particle-wall interaction) and attrition (particle-particle interaction) of polymetallic nodules from the Clarion Clipperton Zone and we discuss its applicability to engineering practice.

Channel formation is a common feature in the deposition of tailings. It is unknown how this initiates. It is investigated if channel formation in laminar flow can originate from hydrodynamics only. An analytical linearised approach is followed in order to establish a theoretical basis and a reference for further developments. It shows that thixotropy can govern pattern formation. Observations in tailings deposition flume testing are applied for reference. It is concluded that sidewall friction influences system behaviour in a similar way, and is here held responsible for meandering.

During hydraulic transport for deep sea mining, polymetallic nodules are transported in various ascending inclined pipes located at the sea floor. These inclined pipes can constantly change their angle of inclination due to moving excavation equipment attached to these pipes. Flow assurance during transport requires a safe transport velocity which takes into account all inclination angles. A study was conducted into safe transport velocities of slurries composed of gravel sized material in ascending inclined pipes. Experimental research was conducted with 4.6, 6.3 and 12 mm diameter gravel in a 100 mm experimental flow loop up to an inclination angle of 52 degrees. Measured parameters include pressure losses, mixture velocity, delivered concentration, deposit limit velocity and velocity profiles from high speed camera footage. During this research, various literature sources have been studied for definitions and models of transition velocities between safe and unsafe transport. These definitions and models are discussed in terms of their relevance for coarse slurries. With these definitions in mind and with the experimental data a recommendation is given for a transportation velocity of coarse slurries in inclined pipes.

Self-formed channel profiles on tailings beaches are determined by rheology, settling solids and flow conditions. A model is described for the width of subaereal tailings channels with settling solids flowing at onset of turbulence. Early transition of open channel with viscous Non-Newtonians is taken into account building on the homogenous slurry open channel data set of Haldenwang. Free formed channels measured in on-site tilting flume tests by Pirouz et al. are analysed. It is confirmed that a number of these channels is at onset of transition and that their width/depth ratio is reasonably well predicted. Other channels in this data set are at low Re laminar flow at minimal width-depth ratio, settling solids apparently being discharged.