Compared to open water, the presence of ice floes in ice-covered water may pose additional challenges tothe towing operations of offshore platforms. This paper proposes a numerical model for analyzing coursestability of a gravity-based structure during towing operation in managed ice fields, considering coupledmotions of tugs, towed platform, and ice floes. A discrete element method is applied to simulateinteraction between drifting ice floes and structures, and verified by existing model tests. The motions oftug and towed platform are coupled through a catenary towline model. A proportional-differentialcontroller is employed to adjust heading and lateral position of tug. The effects of main factors, such astugs’ number, towline length, ice concentration, rudder area and controller gains on course stability arediscussed through numerical case studies. The presented numerical approach is expected to providepractical guidance for towing design, and ensure safety of towing operation.

This article focuses on design of an Artificial Neural Network (ANN) model to estimate ship resistance in ice-covered water by using suitable ship and ice parameters. In order to develop a reliable model, as much ice resistance test data as from the ship sea trials and model test measurements are collected to train the neural network. Different features (ship design parameters and ice mechanic properties) are explored to find a suitable combination of input features. Several algorithms are tested and compared to select a good model for resistance prediction. It turns out that seven features and the Radial Basis Function - Particle Swarm Optimization algorithm (RBF-PSO) can provide a reasonable generalization model. This study shows that the ice resistance predicted by the ANN correlates well with the measured data. The model developed herein can be used as an ice resistance prediction tool with high accuracy compared to the conventional semi-empirical formulae used in polar ship design.

Inland waterway (IWW) shipping is a sustainable opportunity to reduce traffic on, in many times very congested, roads and railways. This is especially true for cities and urban areas. However, for an operator, the ship Operation Time Window (OTW) is important in order to predict possible business cases, especially for regions with long-term winter seasons with icy conditions. The OTW indicates the probable number of navigable days for the ship. The operability is in relation with ship speed, ice thickness, whereas the ship resistance is of significant relevance. This study proposes a model to investigate the possibility of a certain operating condition for ice-going ships based on an Artificial Neural Network (ANN) model and a statistical model. To demonstrate the proposed method for calculating the ship OTW of an IWW, a case study is performed. Ice condition in Lake Mälaren (in Sweden) and an IWW ship designed to maximise its dimension restrictions are used for this case. The Radial Basis Function-Particle swarm optimization (RBF-PSO) ANN model is used to predict ice resistance in level ice conditions. Given the ice resistance prediction, a statistical analysis is further conducted regarding to the ice thickness distribution and the operational ship speed distribution to obtain ship OTW. Comparisons are made between semi-empirical ice resistance prediction methods and the ANN model. The influence of different ship speed distribution profiles is investigated by performing a parametric study. The OTW model can be used to evaluate ship operational scenarios in ice-covered waters for ship designers and owners.

With increasing interest in utilizing the inland waterways (IWW) in European countries, the design of IWW vessels gains attention both from a transport efficiency and an emission control point of view. Usually, IWW ships are designed without ice operation concerns and are structurally weaker than ships designed according to ice-class notifications from the classification societies. It poses a potential danger for countries with long winter seasons and frozen waterways. Designing such ships requires particular concerns since there are no strict requirements regarding ice-class notifications for IWW ships. Among all the design issues, the primary challenge is to estimate the ship resistance and impact load on the ship hull structure.

To consolidate the design challenges for IWW ice-going ships, Lake Mälaren is selected. The mechanical properties of ice have a significant influence on the ice load. Ice conditions, e.g. ice type and concentration, and ice data, e.g. thickness and flexural strength, are extracted and analyzed for the ice load estimation. Ice characteristics are studied based on empirical formulae and calibrated by reference data.

Determination of the ice impact load is the first vital step in designing a lightweight structure. A deterministic approach and a probabilistic approach are used to predict the ice loads. The Finnish Swedish Ice Class Rule (FSICR) is the deterministic approach used for the first-year freshwater ice conditions. The probabilistic approach includes a probabilistic and a numerical method. The probabilistic method simplifies the ice pressure in relation to the contact area between the ice and the ship hull. The numerical method investigates the idealized ship-ice impact model regarding the ice failure process, ice conditions, and ship geometry. Given the impact load, a lightweight panel is designed, and it saves almost 83.5% weight compared to a stiffened steel panel. This is achieved by using a sandwich structure with a composite face and PVC core.

Ship resistance in ice-covered water plays a significant role in assessing the operational scenario. It is essential for ship owners and operators to evaluate ship economics. In order to estimate ship resistance in ice-covered water, an Artificial Neural Network (ANN) model is developed by using suitable ship and ice parameters. A statistical model is designed to account for the most important ship operation variables, i.e. ship speed and ice thickness. Combined, the two models provide a very promising way to estimate a ship's Operation Time Window.

Med ökande intresse för att använda de inre vattenvägarna (IVV) i europeiska länder uppmärksammas IVV-fartyg både ur transporteffektivitets- och utsläppssynvinkel. Vanligtvis är IVV-fartyg konstruerade utan hänsyn till is och är strukturellt svagare än fartyg designade med isklass från klassificeringssällskapen. Det utgör en potentiell fara i länder med lång vintersäsong. Utveckling av IVV-fartyg för nordiska förhållanden kräver därför speciella hänsyn eftersom det inte finns några strikta krav på isklass för IVV-fartyg. Bland alla designfrågor är den primära utmaningen att uppskatta fartygets motstånd och belastningen på skrovet vid gång i is. 

 För att konkretisera designproblemen för isgående IVV-fartyg väljs Mälaren. Isens mekaniska egenskaper har stort inflytande på belastningarna. Isförhållanden (som istyp och koncentration) och isdata (som istjocklek och isens böjhållfasthet) extraheras och analyseras för isbelastningsberäkningarna. Isens karakteristika studeras med hjälp av empiriska formler som kalibreras med referensdata.

Att bestämma ispåverkansbelastningen på strukturer är det första viktiga steget i utformningen av en lätt struktur. En deterministisk metod och en probabilistisk metod används för att bestämma islasterna. Den finsk-svenska isklassen (FSICR) är den deterministiska metod som används för förstaårs-isförhållanden i sötvatten. Den probabilistiska metoden inkluderar både en probabilistisk och en numerisk metod. Den probabilistiska metoden förenklar istrycket i förhållande till kontaktområdet. Den numeriska metoden undersöker den idealiserade fartyg-is-interaktionssmodellen och inkluderar isens skademoder, isförhållanden och skrovgeometri. Med den givna slagbelastningen så designas en lättviktspanel som sparar närmare 83.5% vikt jämfört med en stålpanel. Denna lättviktpanel består av en sandwichstruktur vilken har en kompositytskikt och en kärna av PVC-material.

Fartygsmotstånd i is spelar en viktig roll i bedömningen av operabiliteten. Det är viktigt för fartygsägare och operatörer att utvärdera fartygsekonomin. För att uppskatta fartygsmotstånd i istäckt vatten med hjälp av lämpliga fartygs- och isparametrar utvecklas en modell baserad på ett artificiellt neuralt nätverk (ANN). En statistisk modell är utformad för att ta hänsyn till de viktigaste driftsvariablerna, vilka är fartygets hastighet och istjockleken. Dessa två modeller utgör tillsammans ett mycket lovande verktyg att uppskatta framtida fartygs driftsfönster.

For polar ship operating in ice-covered areas, numerical prediction and relevant research on maneuverability are particularly important. In this paper, a numerical method considering circumferential crack fracture of level ice based on former research is applied to calculate ice load and predict motion of ship turning in level ice. The difference between bending failure and crushing failure are also taken into consideration during the turning simulation, meanwhile crushing failure pattern is validated with measured data. The turning performance of icebreaker AHTS/IB Tor Viking Ⅱ based on present method is analyzed and compared with full scale measurement. The simulated icebreaking capability of the ship is also validated with sea trials and previous work. The results show that good agreement is achieved and the accuracy of the numerical prediction is improved by including crushing failure into previous research.

A simplified numerical model is introduced to predict ice impact force acting on the ship hull in level ice condition. The model is based on ice-hull collision mechanisms and the essential ice breaking characteristics. The two critical ice failure modes, localized crushing and bending breaking, are addressed. An energy method is used to estimate the crushing force and the indentation displacement for different geometry schemes of ice-ship interaction. Ice bending breaking scenario is taken as a semi-infinite plate under a distributed load resting on an elastic foundation. An integrated complete ice-hull impact event is introduced with ice failure modes and breaking patterns. Impact location randomness and number of broken ice wedges are considered in order to establish a stochastic model. The analysis is validated by comparison with the model ice test of a shuttle passenger ferry performed in May 2017 for SSPA Sweden AB at Aker Arctic Technology Inc. Good agreement is achieved with appropriate parameter selection assumed from the model test and when ice bending failure is dominant. This model can be used to predict the ice impact load and creates a bridge between design parameters (ice properties and ship geometry) and structure loads.

For ships running on ice-covered waters, the ice impact load on ship structure shall be carefully considered. This paper proposes an analytical model which takes two most important ice failure modes, localized crushing and bending breaking, into consideration. The energy method is introduced to estimate the crushing force and the indentation displacement for different scenarios. Ice bending breaking scenario is simplified as a semi-infinite plate under a distributed load resting on an elastic foundation. The two ice failure modes are assumed to share the same contact area. This model is useful to predict the ice impact load and creates a bridge between design parameters (ice properties and ship geometry) and structure loads. 

There has been an increased awareness of the benefits of utilizing inland waterways (IWW) from a transport efficiency and an emission control point of view. However, due to presence of ice in water bodies, vessels designed for non-ice river operations cannot operate during the winter months. This paper analyses a grillage representative of barge’s bow region using non-linear finite element analysis (NL FEA) and assesses survivability in comparison with load limits prescribed by latest Finnish Swedish Ice Class Rules (FSICR) 2017 rules, International Association of Classification Societies (IACS) Polar Cass 6 (PC6) rules and simplified plastic collapse limit states calculated by Daley (2002). The NLFEA study included strength contributions from strain hardening and membrane stress and it was found that the limit state described by rupture stress was significantly larger. It was found that allowance for plasticity can reduce structural scantling requirements for fresh water ice operating vessels. The study also validated latest FSIRCR 2017 requirements.

With increasing need to utilize inland waterways (IWW), the design for IWW vessels gains attention both from a transport efficiency and an emission control point of view. The primarily issue is to estimate the ice pressure acting on the ship hull for inland waterways. Ice information for Lake Malaren is extracted and analysed in this work. Since the ice properties have great influence on the impact load, they are studied based on empirical formulae and are calibrated by reference data. The ice impact is then predicted for an inland water barge. Probabilistic method is selected to derive the load based on available field test data. Several parent datasets are chosen, and different design strategies are implemented to evaluate the ice impact load and investigate the influences from exposure factors. The paper finds that the design curve of alpha = 0.265a(-0.57) can be used for Lake Malaren. The approach itself introduces a possible way to investigate loads on ice affected IWW.