Interactions between irregular wave fields and sea ice: A physical model for wave attenuation and ice breakup in an ice tank

Irregular, unidirectional surface water waves incident on model ice in an ice tank are used as a physical model of ocean surface wave interactions with sea ice. Results are given for an experiment consisting of three tests, starting with a continuous ice cover and in which the incident wave steepness increases between tests. The incident waves range from causing no breakup of the ice cover to breakup of the full length of ice cover. Temporal evolution of the ice edge, breaking front, and mean floe sizes are reported. Floe size distributions in the different tests are analyzed. The evolution of the wave spectrum with distance into the ice-covered water is analyzed in terms of changes of energy content, mean wave period, and spectral bandwidth relative to their incident counterparts, and pronounced differences are found between the tests. Further, an empirical attenuation coefficient is derived from the measurements and shown to have a power-law dependence on frequency comparable to that found in field measurements. Links between wave properties and ice breakup are discussed

SEM Image

This photograph originally appeared in the 2017 Research student photography and image competition held to celebrate National Science Week (18 August - 8 September 2017). Blurb: The image is about the successful confirmation of conductive Platinum-Polydopamine-Graphene composite synthesis using Scanning Electron Microscopy (SEM), in particular. The SEM image A is the view of the as-prepared composite at the magnification of 20 micrometer. A lot of Platinum and Polydopamine particles uniformly decorated on Graphene sheets surface. The SEM image B is the closer view of the composite at the magnification of 1 micrometer. It can be seen that both Platinum nanoclusters with cauliflower shapes and spherical Polydopamine clusters successfully anchored on wrinkle surfaces of Graphene sheets. The SEM image C is the closer view of the cauliflower shaped Platinum nanoclusters at the magnification of 200 nanometer, which is very similar with a natural cauliflower in shape. With different interesting shapes of each component, the as-prepared conductive composite shows a great potential for electrochemical detection purposes

Wave-ice interaction

This photograph originally appeared in the 2017 Research student photography and image competition held to celebrate National Science Week (18 August - 8 September 2017). Blurb: I investigate the interaction between ice and waves of Polar regions (Arctic and Antartic) to find out how the wave will be changed when face an ice cover, and how the ice cover will behave when an incident wave approaches

Case Study on Water Quality Improvement in Xihu Lake through Diversion and Water Distribution

Eutrophication in lakes and reservoirs is a serious environmental problem that has damaged ecosystem health worldwide. Water diversion is one of the most popular methods for improving the water quality in shallow lakes, as it dilutes pollutants in and diverts them out of the lake. However, simple diversion without rational water distribution cannot significantly enhance water exchange in the entire lake because dead water zones always exist. This paper illustrates a case study on water quality improvement in Xihu Lake by diversion and water distribution. Based on theoretical calculation, the diversion water discharge was determined and rationally distributed into four different locations. According to the field observations after the implementation of the diversion and water distribution project, the average velocity over the dead water zones increased approximately 50 times over that of prior to the project. The average water exchange period reduced from 68 days to 22.5 days. The average turbidity was 8.8% and 12.4% lower than before after two and four months of diversion, respectively. The maximum turbidity reduced from the original 27.5 NTU (Nephelometric Turbidity Unit) to 20.1 NTU after two months of diversion, then to 16.1 NTU after four months of diversion. It shows that this diversion and rational water distribution eliminates most of the dead water zones and achieves a favorable flow field, thus reducing the turbidity and increasing water transparency, which is conducive to the improvement of water quality

Discretization of Multidimensional Mathematical Equations of Dam Break Phenomena Using a Novel Approach of Finite Volume Method

This paper was concerned to simulate both wet and dry bed dam break problems. A high-resolution finite volume method (FVM) was employed to solve the one-dimensional (1D) and two-dimensional (2D) shallow water equations (SWEs) using an unstructured Voronoi mesh grid. In this attempt, the robust local Lax-Friedrichs (LLxF) scheme was used for the calculating of the numerical flux at cells interfaces. The model named V-Break was run under the asymmetry partial and circular dam break conditions and then verified by comparing the model outputs with the documented results. Due to a precise agreement between those output and documented results, the V-Break could be considered as a reliable method for dealing with shallow water (SW) and shock problems, especially those having discontinuities. In addition, statistical observations indicated a good conformity between the V-Break and analytical results clearly

A physical model of wave attenuation in pancake ice

A physical model is discussed that mimics the interaction between ocean waves and a multitude of loose pancake ice floes, which form the outer edge of the Arctic and Antarctic marginal ice zones during winter sea ice formation. The pancakes were modeled by using ice cubes with different concentrations, while waves were generated mechanically. The ice cubes had a dimension of a few centimeters, which was two orders of magnitude smaller than the dominant wavelength. Experiments consisted of tracking the propagation of regular and irregular wave fields along the flume as they crossed the ice cover to measure the rate of ice-induced wave attenuation. Results indicate that wave attenuation increases with ice concentration with only 30% of energy allowed to pass through high-density covers. Wave energy is attenuated across the entire spectral domain and is strongest at high frequencies. This results in a downshift of the spectral peak

An experimental model of wave attenuation in pancake ice

In the winter, when the Antarctic sea ice cover is expanding, the far edge of the marginal ice zone is populated by small floes with characteristic diameters much smaller than ocean wavelengths and known as pancake ice. This form of sea ice was once only typical of Antarctic waters, but it is now observed in the Arctic due to the intensification of the wave action following ice retreat. Despite recent studies, the governing physics controlling how waves propagate through pancake ice is not understood. To cast new light on the propagation of waves in ice. an experimental model was setup in the Sea Ice Wind Wave Interaction (SIWWI) flume at the University of Melbourne, which allows operations at sub-zero temperatures. To simulate pancakes, the ice cover was modelled using ice cubes with characteristic dimension of a few centimeters (much smaller than the generated wavelength) and different concentrations. Experiments consisted of tracking the propagation of regular and irregular wave fields along the flume to monitor the dissipative effect of the ice cover. Results indicate that wave attenuation depends on ice concentration, with as low as 20 - 40% of energy going through high density covers. Although observations reveal that the ice cover attenuates wave energy over the entire spectrum, energy attenuation is more effective at high frequencies, inducing a significant downshift of the spectral peak

CFD analyses on the water entry process of a freefall lifeboat

The launch of lifeboats is commonly completed through freefall dropping from a considerable height, where the lifeboat is released from an inclined skid so that it can obtain a forward speed after being launched. The drop is followed by a water entry process that can induce high impact forces on the hull, which gives a significant risk of structural damages. Ascertaining the water entry impact is therefore a key step of lifeboat design; however, conventional methods have linear assumptions and assess the water impact following a quasi-static manner, which causes these methods to be not fully accurate and ignore some important details. To address this gap, this work developed a model based on Computational Fluid Dynamics to holistically simulate and analyse the process. An overset mesh technique was incorporated to reproduce the entire series of drop, water entry and resurfacing, in which the pressure distribution on the whole hull was obtained and recorded with a sampling frequency of 1000 Hz to ensure the peak impacts can be captured. Full-scale measurements were used to confirm the accuracy of the present computational model. Subsequently, a systematic series of simulations were performed to investigate how the water entry process is influenced by the inclined angle and height at which the lifeboat is dropped. The results show that a higher dropping angle can reduce the pressure impacts, but the dropping angle also dictates the lifeboat\u27s motion pattern during the water entry. It was demonstrated that the best dropping angle is around 70\ub0 for the investigated case, since an either too low or too high dropping angle would cause the lifeboat to appear in an undesirable after-launch status. This indicates the great importance to assess the optimal dropping angle for every potential freefall lifeboat launch, and the present work proved an effective approach to perform the task

Wave propagation in continuous sea ice:An experimental perspective

Ocean waves penetrate hundreds of kilometres into the icecovered ocean. Waves fracture the level ice into small floes, herd floes, introduce warm water and overwash the floes, accelerating ice melt and causing collisions, which concurrently erodes the floes and influences the large-scale deformation. Concomitantly, interactions between waves and the sea ice cause wave energy to reduce with distance travelled into the ice cover, attenuating wave driven effects. Here a pilot experiment in the ice tank at Aalto University (Finland) is presented to discuss how the properties of irregular small amplitude (linear) waves change as they propagate through continuous model sea ice. Irregular waves with a JONSWAP spectral shape were mechanically generated with a very low initial wave steepness to avoid ice break up and maintain a consistent continuous ice cover throughout the experiments. Observations show an exponential attenuation of wave energy with distance. High frequency components attenuated more rapidly than the low frequency counterparts, in agreement with a frequency-cubed power-law. The more effective attenuation in the high frequency range induced a substantial downshift of the spectral peak, stretching the dominant wave component as it propagates in ice