Ice breaking by a high-speed water jet impact

Ice breaking has become one of the main problems faced by ships and other equipment operating in an ice-covered water region. New methods are always being pursued and studied to improve ice-breaking capabilities and efficiencies. Based on the strong damage capability, a high-speed water jet impact is proposed to be used to break an ice plate in contact with water. A series of experiments of water jet impacting ice were performed in a transparent water tank, where the water jets at tens of metres per second were generated by a home-made device and circular ice plates of various thicknesses and scales were produced in a cold room. The entire evolution of the water jet and ice was recorded by two high-speed cameras from the top and front views simultaneously. The focus was the responses of the ice plate, such as crack development and breakup, under the high-speed water jet loads, which involved compressible pressure ${P_1}$ and incompressible pressure ${P_2}$ . According to the main cause and crack development sequence, it was found that the damage of the ice could be roughly divided into five patterns. On this basis, the effects of water jet strength, ice thickness, ice plate size and boundary conditions were also investigated. Experiments validated the ice-breaking capability of the high-speed water jet, which could be a new auxiliary ice-breaking method in the future.

A Coupled Model of Temperature and Pressure for Managed Pressure Cementing in Deep-Water Region

The narrow density window in deep-water environment brought great challenges to well drilling and completion by causing well control issues. Managed Pressure Cementing (MPC) is a new technology developed from Manage Pressure Drilling (MPD), which can precisely control the annular fluid pressure profile. Accurate calculation of wellbore temperature and pressure is the key to MPC. This paper focus on coupled models of temperature and pressure for MPC in deep-water region. The well cementing process can be divided into two stages: fluid displacement stage and cement setting stage, which displays different characteristics. During the cementing displacement stage, the cement is in a flowable slurry state and is circulated into the annulus. During this process, the rheology of fluids if effected by temperature in wellbore. On basis of the fluid rheology model, a coupled model of temperature and pressure in wellbore is established considering the transient flow characteristics during cementing displacement stage. During cement setting stage, the cement slurry stops flowing and the significant cement hydration reaction starts. A large amount of hydration heat and obvious pressure reduction can be observed. On basis of the cement hydration kinetics model, a coupled model of temperature and pressure in wellbore during cementing setting stage is established. Based on the models established in this paper, a series of numerical simulations are conducted using a deep-water well. Simulation results show that neglecting the complicated interactions between temperature and pressure can cause a big error. During the cementing displacement stage, higher temperature in the deep part of wellbore reduces the fluid viscosity, which leads to a smaller friction. On the contrary, larger friction is observed near seabed as a result of the low temperature in deep-water environment. The pressure in wellbore changes frequently due to the coexistence of multiple fluids in wellbore. Therefore, a frequent control of annular fluid pressure is required using the MPC technology. During the cement setting stage, an obvious temperature increase is observed as a result of cement hydration heat. The pressure decreases with the depending of cement hydration. An addition back pressure at wellhead has to be added using the MPC technology. The transient temperature and pressure have impact on the rate of cement hydration in turn. Cement in the deep part of wellbore have a faster rate of cement hydration. The low temperature at mudline slows the cement hydration process. Considering the complicated interactions between temperature, pressure, cement hydration and fluid rheology, coupled models between temperature and pressure based on hydration kinetics during well cementing in deep-water region is established in the manuscript. The new model established in this paper plays an important role in the MPC technology.

Population dynamics of anchovy pekto (Stolephorus waitei) in the waters of Malacca Strait, North Sumatra, Indonesia

Mulya MB, Jhon AH, Harahap ZA. 2021. Population dynamics of anchovy pekto (Stolephorus waitei) in the waters of Malacca Strait, North Sumatra, Indonesia. Biodiversitas 22: 2693-2698. Anchovy pekto or Stolephorus waitei (Engraluidae: Clupeiformes) is one of the fish in the eastern coastal part of North Sumatra, occupying the waters of Malacca Strait. This research presents the population dynamics of S. waitei following its age, growth, mortality, and recruitment pattern based on the length-frequency data. Fork length (FL) and total weight (TW) data of S. waitei were collected at three sites from April to September 2018. A total of 1994 specimens with FL from 4.0 to 6.7 cm and TW from 0.2 to 2.3 g with the length-weight relationship of TW = 0.073FL3.0046 (R2=0.765) indicated a near isometric and positive allometric growth in the water region. The relative condition factor (Kn) ranged from 1.01 to 1.02, indicating an estimate of good condition of the fishes. The growth parameters based on von Bertalanffy was 6.56 cm (L?) with the growth coefficient (K) of 0.34 yr-1 and t0 (anchovy age at zero length ) of 0.6506. The total mortality (Z), natural mortality (F), and catch mortality (M) of S. waitei were 0.64, 1.39, and 0.75 yr-1 respectively, which suggest that the fishing activities of S. waitei are still in normal intensity. The recruitment pattern of S. waitei was stable between April and August with its peak in June by 14.21%. The fishing activities may then be limited during the spawning months (May to June) of S. waitei to maintain their population in the Strait of Malacca.

Characteristics of morphodynamic conditions in the shallows of Puck Bay (southern Baltic Sea)

Puck Bay is an unusual and thus interesting coastal water region, as it combines two different environments – a lagoon and the sea. They differ from each other in their seabed morphology, salinity, dynamics and water exchange. Their common elements are the extensive shallows and the vicinity of the Hel Peninsula. The shallows of Puck Bay have developed at various stages of its evolution, which began several thousand years ago and continues to this day. They have been shaped by varying morphogenetic factors resulting from changes in sea level and accompanying evolution phases of sand barriers, e.g. washover fans, as well as the intensity and directions of sediment transport. At present, the shallows cover more than 35% of the seabed area and are influenced by hydrodynamic factors and availability of sediments. The study area was divided into five fields, taking into account morphological and genetic criteria as well as recent hydrodynamic conditions. This study provides an updated map with classification and distribution of surface sediments and describes grain size parameters for sediment samples collected in the selected fields. Based on a comprehensive assessment of grain size parameters, lithodynamic equilibrium zones were determined and areas of sediment deposition and redeposition were identified.

Impact of Highest Maximum Sustained Wind Speed and Its Duration on Storm Surges and Hydrodynamics Along Krishna-Godavari Coast

The storm surge and hydrodynamics along the Krishna-Godavari (K-G) basin are examined based on numerical experiments designed from assessing the landfalling cyclones in Bay of Bengal (BoB) over the past 38 years with respect to its highest maximum sustained wind speed and its duration. The model is validated with the observed water levels at the tide gauge stations at Visakhapatnam during Helen (2013) and Hudhud (2014). Effect of gradual and rapid intensification of cyclones on the peak water levels and depth average currents are examined and the vulnerable locations are identified. The duration of intensification of a rapidly intensifying cyclone over the continental shelf contributed to about 10-18 % increase in the peak water levels, whereas for the gradually intensifying cyclone the effect is trivial. The inclusion of the wave-setup increased the peak water levels up to 39% compared to those without wave-setup. In the deep water region, only rapidly intensifying cyclones affected the peak MWEs. Intensification over the continental slope region significantly increases the currents along the shelf region and coast. The effect on peak maximum depth averaged current extends up to 400 km from the landfall location. Thus, it is necessary to consider the effect of various combinations of the highest cyclone intensity and duration of intensification for identifying the worst scenarios for impact assessment of coastal processes and sediment transport. The study is quite useful in improving the storm surge prediction, in preparedness, risk evaluation, and vulnerability assessment of the coastal regions in the present changing climate.

A decadal perspective on north water microbial eukaryotes as Arctic Ocean sentinels

The North Water region, between Greenland and Ellesmere Island, with high populations of marine birds and mammals, is an Arctic icon. Due to climate related changes, seasonal patterns in water column primary production are changing but the implications for the planktonic microbial eukaryote communities that support the ecosystem are unknown. Here we report microbial community phenology in samples collected over 12 years (2005–2018) from July to October and analysed using high throughput 18S rRNA V4 amplicon sequencing. Community composition was tied to seasonality with summer communities more variable than distinct October communities. In summer, sentinel pan-Arctic species, including a diatom in the Chaetoceros socialis-gelidus complex and the picochlorophyte Micromonas polaris dominated phytoplankton and were summer specialists. In autumn, uncultured undescribed open water dinoflagellates were favored, and their ubiquity suggests they are sentinels of arctic autumn conditions. Despite the input of nutrients into surface waters, autumn chlorophyll concentrations remained low, refuting projected scenarios that longer ice-free seasons are synonymous with high autumn production and a diatom dominated bloom. Overall, the summer sentinel microbial taxa are persisting, and a subset oceanic dinoflagellate should be monitored for possible ecosystem shifts as later autumn ice formation becomes prevalent elsewhere.