This paper presents the application, and implications of line arrays of light emitting diodes (LEDs) as an illumination source for planar particle image velocimetry (PIV) measurements in large-scale hydraulic laboratories. The use of class 4 lasers, commonly applied as illumination source in these PIV measurements, requires strict safety precautions (i.e. to prevent safety hazards for people working in their vicinity), specifically when applied at hydraulic experimental setups that are not located in a laser lab. To examine the applicability of an alternative light source, differences between LED- and laser-based illumination for PIV are analyzed. A theoretical analysis, in which a so-called motion blur parameter ((Formula presented) ) is introduced, shows that for moderate flow velocities in large-scale setups, image blur can be avoided, even for relatively long (millisecond) pulse widths. The light sheet thickness, width and intensity of a pulsed laser and a line array of both continuous and pulsed LEDs are measured and compared. Based on these properties a safety assessment is made, from which it is concluded that the application of arrays of LEDs for PIV measurements applied in liquid flows requires significantly less safety precautions than in case a class 4 PIV laser is used. Planar (2D) PIV measurements have been performed with both a pulsed and a continuous LED as light source for two testcases in large hydraulic scale-models. Time-averaged velocity field results from the LED-based PIV measurements show good resemblance to both PIV measurements obtained with a class 4 laser as well as to pitot tube measurements. It is shown that the time-averaged PIV vector fields are influenced by motion blur, resulting in a distinct bias towards smaller velocities when increasing motion blur. The two testcases show that linear LED arrays can serve as a suitable alternative illumination source for planar PIV measurements in large-scale hydraulic laboratories in case motion blur remains limited. Specifically, LED line arrays are considered useful for the time-average quantification of predominantly 2D, low to moderate flows in a relatively large domain.

Salt water intrusion through the New Sea Lock of IJmuiden, Netherlands requires mitigation to ensure availability of enough fresh water further inland. For this purpose, a salt screen has been proposed for selective withdrawal of salt water from the Noordzeekanaal in the vicinity of the lock complex. Formulas to assess the withdrawal rate of selective withdrawal are based on idealized layouts and conditions. In the case of IJmuiden, the flow surrounding a salt screen has a strong nonuniform character, such that these formulas are not applicable to predict the correct withdrawal rate and the effectiveness of selective withdrawal accurately. In this case physical scale modeling or computational fluid dynamics (CFD) modeling can be applied. This article discusses the limitations of the formulas for a three-dimensional (3D) flow application near the locks of IJmuiden and presents the use of CFD and physical scale model research to assess the flow patterns around the salt screen and the effectiveness of selective withdrawal. The CFD model was validated against the physical scale model and represented the complex flow fields around the salt screen to within acceptable deviations for both steady and transient states. This gives confidence in applying these more advanced modeling tools for the design and positioning of salt screens in confined complex 3D flow areas.

The NMR relaxivities of the decatungstolanthanoate core-shell nanoparticles, prepared by encapsulating [Ln(W₅O₁₈)₂]⁹⁻ polyoxometalates (LnPOM) within amorphous silica shells (K₉[Ln(W₅O₁₈)₂]@SiO₂), were studied along the Ln series. The relaxivity of GdPOM is slightly higher than for Gd-DTPA due to second-sphere relaxation effects, but the values for the other paramagnetic LnPOMs are much smaller due to the short T_1e values of their Ln³⁺-ions. The NPs have core-shell spherical structures, with LnPOM-containing cores with 9.5–28 nm diameters, and 4.0–11.0 nm thick amorphous silica shells. In water suspensions, the NPs have negative zeta potentials (−32.5 to −40.0 mV) and time-dependent hydrodynamic diameters (31–195 nm) reflecting the formation of aggregates. The relaxivities of GdPOM@SiO₂ NPs suspensions (r₁=10.97 (mM Gd)⁻¹ s⁻¹, r₂=12.02 (mM Gd)⁻¹ s⁻¹, 0.47 T, 25 °C) are considerably larger than for the GdPOM solutions, indicating that their silica shell is significantly porous to water. This increase is limited by the agglomeration of the complexes in the NPs core, limiting their access to water to those at the core surface. Replacing half of the Gd³⁺ ions by Eu³⁺ decreases the NPs r₁ and r₂ relaxivities at 0.47 T to 20 % and 35 % of their initial values, which are still considerable, but does not affect the efficient luminescence properties of the Eu³⁺ centers. This indicates that the mixed NPs have potential as dual modality MRI/optical imaging contrast agents.

This paper investigates the effect of density differences on the forces acting on a moored vessel during lock operations, focusing on the effect of the position of the moored vessel in the lock chamber in the presence of density currents. The extensive scale-model research performed for the new sea lock in IJmuiden, The Netherlands has shown that the combination of density differences and an asymmetric layout of the moored vessel in the lock chamber may lead to high forces on the vessel that can largely exceed the allowable force limit. In particular, as a result of the density currents, forces in the transverse direction build up, pushing the vessel away from the chamber wall, during leveling and after opening the lock gate, leading to higher loads on the mooring lines. The forces caused by the density difference are the dominant forces and the performance of the leveling system cannot be assessed without taking this into account. Based on the results of the performed tests, criteria for achievable leveling times and allowable hydrodynamic forces during leveling are determined for the new sea lock of IJmuiden. Furthermore, the obtained results can be used for calibration or validation of numerical models that are valuable tools for the design of future locks.