Normal flow past flat plates at high Reynolds numbers appears in various engineering contexts. To accurately model such flows for slender plates in Computational Fluid Dynamics requires scale-resolving rather than scale-modelling methods. The present paper uses Detached-Eddy Simulation to investigate the influence of plate corner curvature on global flow quantities such as the time-averaged drag coefficient. The effect of corner curvature is mapped and collated with the literature. Solution verification is carried out to quantify the numerical uncertainty. The time-averaged drag coefficient increases significantly between semi-cylindrically rounded (〈𝐶〉=2.28) and sharp-cornered (〈𝐶〉=2.42) plates.
Scrubbers have gained importance in the maritime sector following recent tightening of the emission legislation regarding sulphur. In this work, a model framework based on an Eulerian-Eulerian multiphase model for a packed bed marine scrubber has been developed. The framework account for both dispersed droplets and a packed bed, where sub-models for interfacial forces and heat- and mass transfer are applied for the respective regions. Additionally, a chemistry model and boundary conditions for the nozzles injecting seawater into the scrubber are also implemented. The model framework is calibrated using data from an ocean-going vessel, where the model predictions were within 3% of the measured pressure loss while the discrepancy in the gas and liquid temperatures were between 0.5% and 3.5%. The sulphur concentration predicted by the model varies between − 24% and 25%. However, the concentrations were within 5 ppm of the measured values for all but a single data set.
With increasing demand for renewable energy resources, the development of alternative concepts is still ongoing. The wave energy sector is still in vast development on the way to contribute to the energy production world wide. The present study presents the development of the Exowave wave energy converter made so far. A numerical model has been established supported by wave flume tests performed at Aalborg University during the first phase of the development. Furthermore, a successful open sea demonstration has been performed on 7 meters of water at Blue Accelerator, Belgium, from which the concept has been proven. As part of the ongoing research, verification of the numerical model will be made through experimental testing in the wave tank of Aalborg University, and an open sea demonstration at 14 meters of water depth will be executed off the coast of Hanstholm, Denmark.
Coupled mooring analysis using CFD with dynamic mooring models is becoming an established field. This is an important step for better predictions of responses of moored marine structures in extreme sea states and also for capturing the low-frequency response correctly. The coupling between the CFD and mooring solvers are most often carried out by exchanging the fairlead/anchor points and fairlead forces. In this paper we will discuss the effects of using (i) viscous fluid flow on a mooring component level (submerged buoys and clump weights) and (ii) the fluid-structure coupling between the viscous fluid solver and the mooring system.
The influence of directional spreading of waves is significant for wave-induced loads, wave breaking and nonlinearity of the waves. For physical model testing performed at test facilities such as the Ocean and Coastal Engineering Laboratory at Aalborg University, it is crucial to validate if the test conditions match the target sea states by measurement and analysis of the generated directional wave field. Most of the existing methods assume a double summation sea state to be present which is valid in the prototype. However, waves in the laboratory are usually generated by single summation. The current paper presents a method to analyze short-crested waves generated by the single summation method. Compared to similar methods oblique reflections are considered instead of only in-line reflections. The results show that the method successfully decomposes the incident and reflected wave fields in the time domain. Thus, for example the incident wave height distribution may be obtained. The sensitivity of the new method to additional reflective directions, noise, calibration errors and positional errors of the wave gauges was found small.
This report provides a current assessment on the prospects for aerial drone applications onboard ships. Three use cases are each forecasted to their time to implementation and evaluated as an opportunity for the maritime and offshore industries. The report's findings are based on respondents' answers to surveys about the three use cases. The data for this report is based on desk research and an analysis of survey responses. The report is produced by the PERISCOPE network.
We investigate piston-mode fluid resonance within the narrow gap formed by two identical fixed barges in a side-by-side configuration, utilizing a two-dimensional fully nonlinear numerical wave tank. The focus is on examining the effects of uniform and shear currents. Under ‘wave+uniform-current’ conditions, a certain current speed is identified, beyond which the gap resonance reduces dramatically and monotonically with the current speed. This reduction is attributed to a stronger increase in damping compared to wave excitation, qualitatively explained by a linearized massless damping lid model. Furthermore, we study the effects of waves propagating on shear currents, maintaining an identical ambient current speed at the gap depth. Complementary to previous studies on this topic, our study reveals that the velocity profile of the studied shear current has an insignificant effect on the resonant gap amplitudes. The ambient current velocity at the gap depth is a more important key parameter to consider when assessing wave-induced gap responses, leading to a non-negligible increase in the resonant gap response. Consequently, disregarding the influence of currents in engineering practices is not a conservative approach.
The present numerical study aims to assess the performance of an Eulerian Stochastic Field (ESF) model in simulating spray flames produced by three fuel injectors with different nozzle diameters of 100 µm, 180 µm and 363 µm. A comparison to the measurements shows that although the simulated ignition delay times are consistently overestimated, the relative differences remain below 28%. Furthermore, the change of the averaged pressure rise with respect to the variation of nozzle diameter is captured by the model. The simulated flame lift-off lengths also agree with the measurements, with a maximum relative difference of 13%. The spray flame produced by a larger nozzle diameter has a fuel-richer premixed core region despite the longer lift-of length, indicating that the higher fueling rate used with the larger nozzle diameter is a more dominating factor than the lift-off length is in influencing the air entrainment into the upstream of the spray flames. In addition, the simulated normalised flame lengths are found to decrease when the nozzle diameters increase. These predictions are in good qualitative agreement with the experimental observation. This work proves that the ESF model can serve as an important tool for the simulation of spray flames in marine diesel engines, where fuel injectors with different nozzle diameters are applied for pilot and main injections.
A numerical study on effects of the injection direction of the pilot diesel fuel on combustion and emissions under two-stroke dual-fuel marine engine-like conditions is presented in this paper. It is found that the injection direction of the pilot fuel has significant effects on the methane start of combustion as well as flame propagation direction which leads to different heat transfer trends to combustion chamber walls and flame- wall interaction. Furthermore, the injection direction of the pilot fuel changes the methane combustion intensity which leads to different trends for emission formation.
A major challenge in next-generation industrial applications is to improve numerical analysis by quantifying uncertainties in predictions. In this work we present a formulation of a fully nonlinear and dispersive potential flow water wave model with random inputs for the probabilistic description of the evolution of waves. The model is analyzed using random sampling techniques and nonintrusive methods based on generalized polynomial chaos (PC). These methods allow us to accurately and efficiently estimate the probability distribution of the solution and require only the computation of the solution at different points in the parameter space, allowing for the reuse of existing simulation software. The choice of the applied methods is driven by the number of uncertain input parameters and by the fact that finding the solution of the considered model is computationally intensive. We revisit experimental benchmarks often used for validation of deterministic water wave models. Based on numerical experiments and assumed uncertainties in boundary data, our analysis reveals that some of the known discrepancies from deterministic simulation in comparison with experimental measurements could be partially explained by the variability in the model input. Finally, we present a synthetic experiment studying the variance-based sensitivity of the wave load on an offshore structure to a number of input uncertainties. In the numerical examples presented the PC methods exhibit fast convergence, suggesting that the problem is amenable to analysis using such methods.