Icing of Ships, Part 1: Splashing a Ship with Spray (original) (raw)

Estimating the extent of the spraying zone on a sea-going ship

Ocean Engineering, 1988

The maximum extent of ship spraying for a medium-sized fishing trawler (MFV) of Soviet type has been considered. A simple geometrical model for generating the spray due to ship-wave collisions has been applied to determine the maximum height of the spray source above the ship deck. The maximum height of the spray source has been assumed to depend on the ship speed relative to the moving waves and an empirical constant specific to a given type of ship. A unique field data set (Kuzniecov et al., 1971) of the height of the upper limit of ice accretion on the foremast of an MFV has been used to determine the value of the empirical constant for this vessel. For documented air-sea and ship motion parameters, the trajectories of droplets hitting the upper parts of the accretion on the foremast have been calculated using the equation of droplet motion for each reported icing event. The heights of the spray source computed by the trajectory method for each case of icing were compared with the heights of the spray source determined by a correlation involving the ship speed relative to the waves and the vertical extent of spray. The best fit was obtained for an empirical constant value of 0.535. The model performance was tested using an independent data set (Sharapov, 1971) on the spraying zone of an MFV. The tests showed that this model predicts the extent of the spraying zone over the ship with satisfactory accuracy and suggest that it should be incorporated into an integrated ship icing model. Finally, the model was run for several ship speeds, headings and wind speeds to examine the effect of these parameters on the maximum height of the spray hitting the ship's foremast. It was found that this height increases with wind speed and ship speed and is maximum for ship headings of 120-130 ° .

Modeling of Icing on a Planar Surface Due to Sea Spray and Blowing Snow

SSRN Electronic Journal

Two main extensions of the time-dependent two-dimensional sea spray icing model ICEMOD2.1 (Horjen, 2015) is presented. The first extension, called ICEMOD2.2, is the inclusion of heat conduction through the accreted ice. This quantity has been calculated from the temperature distribution in the ice which varies with time. The second extension, called ICEMOD2.3, is the combined effect of sea spray and snow. No other icing models have ever before included this effect. The new models have been applied for some reported icing cases on the nearly vertical wall of the bulkhead of the large Norwegian coast guard vessel KV Nordkapp from 1983 to1997 and three laboratory test results from a cold room at the Memorial University of Newfoundland. Local wind field above the boundary layer, heat loss by forced convection and wind stress have been approximated by using analytical formulas for the wind field around a single plate. The physics of instantaneous freezing of a fraction of supercooled droplets upon impact has been discussed and implemented in the model. The most severe icing conditions in Norwegian Arctic water often occur during polar lows, which are often followed up with heavy snow fall. Due to the inclusion of snow the thermal conductivity of the ice accretion is modified. Using an electrical analogy it is shown that this parameter decreases during snow conditions. Overall ice salinity and density is also affected by the snow.

Modelled and observed sea-spray icing in Arctic-Norwegian waters

Cold Regions Science and Technology, 2017

Hazardous marine icing is a major concern for ships operating in Arctic waters during freezing conditions. Sea spray generated by the interaction between a ship and ocean waves is the most important water source in these dangerous icing events. Although there exist several data sets with observations of ice accretion in conjunction with meteorological and oceanographic parameters, these data sets often have shortcomings and only a few are obtained in Arctic-Norwegian waters. In this study, icing rates from a large coastguard vessel type, the KV Nordkapp class, are used for verification of a newly proposed Marine-Icing Model for the Norwegian COast Guard (MINCOG). Ship observations, NOrwegian ReAnalysis 10 km data (NORA10), and wave data based on empirical statistical relationships between wind and waves are all applied in MINCOG and the results are compared. The model includes two different empirically-derived formulations of spray flux. It is found that in general the best results for different verification scores are obtained by using a combination of observed atmosphere and ocean-wave parameters from the ships, and wave period and direction from NORA10, regardless of the spray-flux formulation applied. Furthermore, the results illuminate that wave parameters derived from formulas based on empirical relationships between the local wind speed and significant wave height and wave period, compared to those obtained from observations or NORA10, considerably worsen icing-rate predictions in Arctic-Norwegian waters when applied in MINCOG.

Understanding spray cloud formation by wave impact on marine objects

Cold Regions Science and Technology, 2016

Wave impacts on vessels and offshore structures can induce significant spray. This process leads to topside icing in sufficiently cold and windy conditions. This paper establishes the current state of the art understanding of the physical behaviour of wave impact and the process of spray cloud formation upstream of a ship or marine structure. Previous work on the behaviour of spray at the bow is extensively reviewed. The process of spray formation is related to several complicated phenomena including wave slamming, jet formation after impact, sheet and droplet breakup, and production of the spray cloud on the top surface of the ship bow. Progress has been made in modeling some of these phenomena, including numerical methods for modeling the free surface, the phenomena of slamming, air entrainment, and water breakup. Field observation methods for measuring characteristic parameters of the spray are also reviewed. Related phenomena, such as wave slamming on a wall and bow waves, are followed from the numerical and experimental point of view. Although direct numerical simulations of spray formation following by wave impacts are not yet a practical option, constituent models for each separate part of this problem (e.g., free surface modeling, slamming on walls, air entrainment, etc.) show promising progress. This work is a guide for researchers of off-deck phenomena in the field of marine icing. The puzzle pieces and the gaps are examined to help design a new research strategy in this field.

Mapping Icing Rates on Sea-Going Ships

Journal of the Meteorological Society of Japan. Ser. II, 1988

Maps for ship icing potential distribution over the oceans are reviewed. Special attention is paid to maps presenting forecast icing rates on ships. The NOAA Experimental Ice Accretion map with a 24-hour categorical forecast of ice growth rate and the AES approach to mapping icing intensity are evaluated. A new mathematical model for the growth of spongy saline ice on a ship's superstructure is presented in detail. This model calculates the icing rates over the entire front face of the ship's superstructure within the zone of spraying. The effect of the salinity of the moving water film and the ice sponginess are both taken into account. The model input is the ship speed and heading, the air temperature, the seawater salinity, the sea surface temperature, and the wind speed and fetch. Computer-produced maps of the icing rates on the ship are produced for the cold waters east of Canada. The first results indicate that our new ship icing model could be applied for operational purposes (hindcasting and forecasting icing rates on ships) if an automated data acquisition system was available.

Review of marine icing and anti-/de-icing systems Review of marine icing and anti-/de-icing systems

The aim of this work is to review the phenomenon of icing in marine operations. The focus is on two main sources of icing, namely atmospheric and sea spray. The literature reveals that sea spray icing is the main contributor to marine icing. This work discusses the available ice accretion prediction models on ships and offshore structures. It also reviews the anti-/de-icing technologies that can be implemented on ships operating in cold climate regions. The significance of ice detection is acknowledged, and a brief review of various ice detection technologies is provided.

Review of marine icing and anti-/de-icing systems

A time-dependent model of marine icing with application of computational fluid dynamics

Cold Regions Science and Technology, 2014

A tool predicting the spatial distribution of ice is required to take precautions against icing in the design of offshore structures. This paper presents a 3-dimensional time-dependent model of icing caused by sea spray, called MARICE. The novelty of MARICE is that a computational fluid dynamics (CFD) solver is used to resolve the details of the airflow and heat transfer from the structure, to track the spray flow in the air, and to calculate the spatial distribution of the ice thickness on the structure. Two case studies illustrate the advantages of MARICE. In the first case study, the heat transfer was calculated on a structure with complex geometry, for which empirical formulas are hardly applicable. In the second, the MARICE, RIGICE04, and ICEMOD icing models predicted the time-series of ice accretion on a 90-m-diameter cylindrical structure. MARICE and RIGICE04 calculated similar total ice loads, which were higher than those calculated by ICEMOD. Both RIGICE04 and ICEMOD underestimated the heat transfer by a factor of 2 -5 compared to MARICE; however, RIGICE04 applies a greater spray flux than the other two models.

Ice Forces and Ship Response to Ice. Consolidated Report

1990

Abstract: Conclusions from this study include:(1) Both peak force and peak pressures during an impact increase with ice severity (ice thickness and ice strength).(2) In arctic regions, operation at higher latitudes increases ice severity and therefore ice loads.(3) Peak pressure during an impact appears to be only weakly dependent on impact speed, and no dependency was discernable from the measured data.(4) Peak force during an impact does increase with impact speed and a linear relationship between them appears reasonable.( ...

Icing of Ships, Part 1: Splashing a Ship with Spray (original) (raw)

Related papers