Offshore cranes are less frequently used than onshore cranes. Because of the reasons, fatigue analysis of offshore crane has often been ignored or performed with a nominal stress approach based on FEM1,001. Recently, ultra-high tensile steel has been used for crane structure and the speed of cargo handling has been increased. Fatigue has become a major design parameter. Recently owners require a detailed fatigue analysis using a proper load spectrum model. Except API-RP, it is almost hard to find regulations that define load spectrum models. The load spectrum model in API-RP is difficult to apply to the modern cranes. In order to solve the problem, a load spectrum model is presented in this study. The load spectrum model is based on the data recorded in three offshore cranes for three years. The data were statistically analyzed, and a proper load spectrum model was derived. ABBREVIATION API: American Petroleum Institute DNV: Det Norske Veritas EN: European Norm FEM1,001: Federation Europeenne de la Manutention FEA: Finite Element Analysis HMC: Heerema Marine Contractor GL: Germanischer Lloyd SWL: Safety Working Load RP: Recommended Practice INTRODUCTION When the environmental conditions deteriorate, cranes do not work and are supported by boom rest. In order to remove the loads resulted from platform's (or hull, hereinafter collectively referred to as platform) deformation or motion, crane structure is designed with a statically determinant system in general. Because of the reasons, stresses due to environmental loads are less than 10% of those resulted by working loads. Thus, environmental loads are generally ignored in fatigue analysis of crane (FEM1,001, 1998; GL, 2012; DNV, 2011) and fatigue loads of cranes are working loads. One load cycle is a process in which a cargo is lifted at a spot, moved to a target spot and unloaded at the spot. It is assumed that the process is quasi-static. The stress range occurred in the process is considered in fatigue analysis. A load spectrum is a function which defines the relation between cargo weight and cycle. It is the basis of fatigue analysis for crane structures, life evaluation and reliability calculation, having an important engineering significance. Except API-RP (API, 2007), other offshore rule and regulations do not provide any guidance for the load spectrum. This has often created wasteful arguments between builder, class and owner. In order to avoid the wasteful arguments, the objective of the study is to provide load spectrum models and guidance. In general, load spectrum model is defined by owner. According to author experience, while some owners are well define a load spectrum, the others do not.

Ice load is an important factor in ship structure design and safe navigation. In view of the advantages of Discrete Element Method (DEM) in dealing with the problem of discontinuous medium, the ice resistance of ships in flat ice area is analyzed by using DEM, and the resistance of water body is simulated by using Computational Fluid Dynamics(CFD). In the discrete element simulation of ship ice breaking process, flat ice is composed of spherical particles. At the same time, the influence of buoyancy, drag and added mass force on ice element is considered. During the interaction between ice and ship, the adhesion between particles will be destroyed. The resistance characteristics of the hull under the ice water coupling are analyzed, and the action load of ice on the hull in the process of ice breaking is determined. INTRODUCTION In recent years, affected by global warming, the Arctic ice cover area has decreased year by year. There is a possibility of navigation in the Arctic channel. In addition, the Arctic channel can greatly shorten the navigation time, which is of great strategic significance to China. At the same time, the Arctic is rich in oil and gas resources, accounting for 13% of the world's proven crude oil reserves and 30% of the world's natural gas reserves. In view of the above situation, China conducted an investigation on the navigation possibility of the Arctic channel in 2012, and actively carried out research in related fields. In the process of ship navigation in ice area, due to the comprehensive influence of ice type, ship type, driving mode and other factors, the process of ship and ice becomes very complex. It is generally believed that when ice acts on a ship's hull, it will undergo three processes: bending, breaking, overturning and sliding, with the accumulation and overlapping of ice in the bow. In the research process of ship ice load, the research methods such as real ship measurement, model test, empirical formula, theoretical analysis and numerical simulation are generally used to analyze the action mechanism of ice and ship hull and determine the specific resistance value. The numerical simulation method can reflect the damage and deformation of ice and the change of resistance in the middle of the ship at any time. It is an important means to study the ice interaction of ships.

Ice-Mas is a simulator used for design of offshore structures interacting with ice combining a variety of models and approaches. It was initiated by TechnipFMC with a joint-cooperation with Cervval and Bureau Veritas. This paper present overall functionalities of Ice-Mas. It will then focus on the modelling approach used for a semi-submersible platform, the calculation of the different ice load and ‘shielding effect’ according to the ice incidence angle. The time series of load will be applied to moored submersible to calculate the motion response and tension force. The result can be used as a reference for design of semi-submersible. INTRODUCTION In the Arctic ocean, significant part of resources remains to be recovered especially in deep-water area. For further exploitation in Arctic area, the design of floating units is necessary. The design of floating structure in ice covered ocean faces a number of challenges due to complex phenomenon of ice failure and interaction with structures. The interaction between a structure and sea ice is a complex process. Ice failure caused by interacting with offshore structure has been investigated by many scientists using analytical and empirical techniques and numerical methods (FEM, DEM, CEM, etc). T.D.Ralston (1980) proposed the plastic limit analysis method to investigate the forces imposed on conical-shaped structures by moving ice sheets. D.E.Nevel (1992) obtained the analytical solutions for the failure of an infinite ice wedge beam on an elastic foundation. The solution then finds application in the calculations of ice breaking loads for various types of sloping structure. Lubbad and Løset (2011). and Konuk, Gürtner et al. (2009) combing different numerical models to predict the ice failure due to the interaction between sea ice and structures. These methods mentioned above are widely used in modelling ice behavior and calculating ice loads exerted on structures in ice covered ocean. However, failure modes of ice can be quite different depending on the shape of structure, ice type, ice thickness and interaction velocity etc.. Even with methods mentioned above, the prediction of ice loads is still a challenge. Especially in the case of semi-submersible units, the geometry of the interacting structure with ice is widely variable. The number of columns and the intruding angle of ice sheet and also size and depth of the pontoon are important parameters in the calculations. The broken ice from ice sheet will accumulate around the legs and contributes a non-negligible part of ice load on structure. This force is also affected by parameters mentioned above.

Until 2019 the Rules of Russian Maritime Register of Shipping (RS) had only regulated design ice impact loads on inclined hull sides. These regulations are based on a hydrodynamic model of ship hull/ice interaction. At present large-size vessels operating in the Arctic seas have full hull lines with vertical sides extending over the entire hull entrance or even bulbous bows. Such vessels may have an ice class up to Arc7. The hydrodynamic model does not provide sufficiently simple analytical relations for class rules to estimate impact ice loads on vertical sides in way of forebody entrance in case of ship collisions with a floe or ice channel edge. This paper suggests a method for regulation of impact ice loads on vertical sides using the tools of experiment design theory in numerical simulations. The numerical experiment is ice load computation based on a physical hull/ice interaction model. The suggested method is implemented in application to the hydrodynamic hull/ice interaction model. Relationships of ice impact loads versus ice class, hullform parameters and ship mass are obtained in the form of regression formulas. Design relationships are developed to determine parameters of ice loads on vertical sides. These relationships are included in RS Rules of 2019. INTRODUCTION Modern ice class vessels may be designed with bulbous bows to ensure good seakeeping in open water. The current Rules of Russian Maritime Register of Shipping (RS Rules) allow this design for the ice-going vessels of Ice1 to Arc7 inclusive (RMRS, 2020). In particular, the bulbous bow is typical for double- acting ships (DAS), i.e. when the ship stern is designed for stern-first operation in ice conditions, while the bow is optimized for open-water sailing (Aleksandrov, Platonov and Tryaskin, 2018). Under the current RS Rules the design ice loads on ice belt in the forebody of an ice-class vessel are determined depending on the ice strengthening class and parameters of the hull form at the ice load waterline 1 . Ships with bulbous lines in way of the ice waterline (and often ballast waterline) will typically have a vertical side portion where the frame angle is very small or zero. Non-arctic vessels of Ice1-Ice3 may have a long part of vertical-side forebody extending from the fore perpendicular to the parallel middle body (Platonov and Tryaskin, 2019a). It was impossible to estimate ice loads according to current RS Rules for these ship design cases.

In this paper, based on the idea of two-parameter model of bond-based peridynamics (BB-PD), the formulas of bond force is derived, and the tension and simple shear of plate are simulated by the derived form of bond force. Then the time step and the corresponding parameters of the model under the quasi-static algorithm and dynamic relaxation algorithm are derived,respectively. The two algorithms are applied to the simulations, respectively. By conducted two typical simulations It is proved that the two-parameter model can solve the problem of fixed Poisson's ratio, and the correctness of formulas of bond force and parameters in calculation. INTRODUCTION When dealing with the crack problems, the peridynamics (PD) is calculated by the integral equation, which avoids the shortcomings of discontinuity equation of the traditional continuum mechanics at the crack (Silling,2000; Silling and Askari,2005). However, BB-PD is only related to bulk modulus when simulating linear elastic materials, so that the Poisson's ratio is fixed to 1/ 3 for plane stress problems, and 1/ 4 for plane strain and 3D problems. It is impossible to accurately simulate problems with the arbitrary Poisson's ratios. The fixed Poisson's ratio has so much limits, when solving the practical problem. Therefore, the state-based peridynamic was proposed (Silling, Epton, Weckner, Xu, and Askari,2007). There is no problem of the fixed Poisson's ratio in the state base. However, the state-based peridynamic is more complicated than the bond-based peridynamic. Therefore, domestic and foreign researchers have done a lot of research on solving the problem of fixed Poisson's ratio. Gerstle, Sau and Silling (2007) proposed the micro-polar model, which adds a pair of moments based on the original bond force. However, the model needs to process a large amount of calculation in actual use, and it does not give a clear potential energy function. Prakash and Seidel (2015) proposed the twoparameter linear elastic peridynamic model. Two coefficients of springs were introduced to describe the displacements in the normal and tangential directions to solve the fixed Poisson's ratio problem. Similarly, Zhu and Ni (2017) considered the shear deformation in the BB-PD model of the bond. By introducing the rotation effect of the bond, the bond force between the two material points can be decomposed into normal and tangential components, and the energy of the bond can also be divided into tensile energy and shear energy. In fact, the twoparameter models proposed by Prakash and Seidel (2015) and Zhu and Ni (2017) are the same models in theory, except that the definitions of the potential energy functions are different, which resulted in the different final forms of coefficients. Diana and Casolo (2019) summarized several theoretical hypotheses of bond and proposed corresponding solutions. And a micro-polar model considering shear deformation of bond and failure criteria for shear deformation was proposed.

This paper presents the results from wind load CFD calculations performed on a truss leg of a typical GustoMSC designed drilling jack-up rig. The CFD model is constructed using the STAR-CCM+ software package from Siemens. The performance of two numerical models Unsteady RANSE and Delayed DES are investigated. A number of flow angles are considered. The wind force is computed using a constant and uniform flow field at the inlet boundary of the computational domain. In order to investigate the scale effects, the calculations are performed at model-scale as well as at full-scale. The results of the CFD calculations are compared with the results that can be obtained on the basis of the recommended drag force coefficients by the SNAME which are developed largely based on wind tunnel measurements. It was found that the scale effects are present for the drag force acting on truss legs due to the Reynolds number dependency of the cylindrical components. CFD results at full-scale show that the SNAME recommendation method is on the conservative side. Based on the results of the CFD calculations at model-scale and full-scale, this paper discusses the scale effects of wind drag force acting on a truss jack-up leg. INTRODUCTION A typical drilling jack-up rig consists of a buoyant platform standing on three independent truss legs, with a large forward accommodation block, several large structures and equipment, a drilling derrick and several cranes on the deck. The truss shaped leg consists of three chords with racks connected with each other through cylindrical shaped bracings and spanbreakers. Fig. 1 shows a typical GustoMSC designed drilling jack-up with three truss legs. The design of a jack-up rig requires the prediction of the forces generated by wind on the truss legs for the transit condition. In the early design stage of a jack-up, the wind forces are usually estimated by empirical methods which are given by standards such as the SNAME (2008) and ISO (2016). The standards are based on the building block approach. The total wind force on the truss leg is estimated by summing up the forces of the chords and cylindrical members considering the projected area, orientations and flow angles. This method is efficient and fast but usually the level of detail is low and shielding effects and flow interactions by the leg components are not considered. When high accuracy is required at the design stage, wind tunnel measurements are commonly carried out. However, the wind tunnel measurements are performed at model-scale and must be carefully performed to ensure that appropriate Reynolds numbers are reached for the truss legs, since scaling effects can be significant for truss legs, due to the Reynolds number dependency on the cylindrical shape components. Predicting the drag force using Computational Fluid Dynamics (CFD) is therefore of particular interest. Because, in CFD not only the drag force can be predicted, but also valuable insight can be obtained into the flow behavior through visualization of the flow field.

Subsea production system and topside processing systems are coherent system in real field but simulators are separated into two independent program, multiphase flow simulator "OLGA" and topside process simulator "HYSYS". It requires labor to transfer the values between two simulators especially in transient cases, where step time is less than 1 second, which blocks fluent transient simulation. So integrator has been developed to automatically transferring values in two-way and controlling timesteps of both integrators. Algorithms were developed to give control between simulators, and systematic approaches were optimized for two programs using DCOM configuration and OPC DA specifications. To verify the integrator, some case studies were designed and done using pre-built simulation models. Also other modules were added to analyze the integrated simulation with in-house source code. INTRODUCTION Delivering values between the different simulators needs technical implementation and also need theoretical assurance of its consistency. To accomplish the integration of dynamic simulation in whole production field, link has been accomplished for several simulation programs like OLGA, HYSYS, PIPESIM… etc. Simulation results has been drawn with this dynamic integration, although yet not fully reliable. This paper will focus on the linkage between two specific program, one is dynamic multiphase flow simulator OLGA and the other is process simulator HYSYS. OLGA is strong in computation of multiphase flow, but not in chemical processing. On the other hand, HYSYS is strong in chemical processing but not in calculation of flow dynamics. These two programs are coupled to simulate large offshore field with subsea pipelines and topside platform more accurately. To achieve the integration, programming has been done to develop the in-house code with C# and user interface (Fig.1) with Winform. Using OPC DA library and HYSYS library (Peltoniemi et al., 2001), Automation of value delivery of selected point for each timestep were implemented satisfying mass continuity. Also, on-off control on simulators were made with this integrator with master timestep. Since the scheme of time discretization is different between two, synchronization between two simulators were loosely set and controlled. Difference by master timestep has been measured for given case study, where both simulation cases of OLGA and HYSYS can be described as chaotic system. with case study consists of different length of ramp-up cases, for fixed flowrate for single process train. Verification of integrator has been also checked within this case study.

The critical incidents of the brash ice accumulation are considered using the port of Sabetta as an example. The heat volume, required for the keeping the certain thickness of the brash ice layer is determined using a thermodynamic simulation. The simulation results determine the power capacity of the required heat producing generator. The various methods, that can be used to reduce the energy consumption costs are described, such as: scheduling of the vessels traffic, change of the vessel movement scheme, optimization of the location of the bubbling lines and discharge points of the heated water. INTRODUCTION Currently, active development of the Arctic coast of Russia is under way. Mining companies developed the vigorous activities for development of oil, gas, gas-condensate and other fields. A maritime transport plays an important role in these works. It delivers consumables, machinery and ready-made structures to the Arctic to build the infrastructure. The developed fields begin to supply the raw materials (hydrocarbons and other) to markets by sea. The largest economic activity is observed in the Ob-Yenisei region. It includes the construction of ports and other hydraulic facilities. The port of Dudinka has long operated on the Yenisei River. It provides a transportation of finished products from Norilsk mining and metallurgical plant. The port of Sabetta and the terminal "Arctic Gate" in the Ob' bay had already built for LNG and oil offloading. The design and construction of other facilities, mainly in the northern part of the Ob' bay, continues. The "Utrennyi" terminal is being built on the Gydan Peninsula and it is part of the port of Sabetta. The LNG carrier vessels will be loaded with liquefied natural gas at this terminal. The development of the region is causing a transfer from seasonal sea transportations to year-round traffic. In the Yenisei Gulf, a regular winter sea navigation from the port of Dudinka is carried out since 2008. In the Ob'Bay, a regular winter navigation is carried out from the port of Sabetta since 2013 and from the oil terminal "Arctic Gate" near Kamennyi Cape since 2015. During this time, a sea traffic, for example, in Sabetta, has grown from single calls to several hundred vessels per season.

The unsteady motion of a slender body in liquid under an ice cover is considered. The ice cover is modelled as an elastic plate. To simulate the motion of the slender body, a source-sink system moving in the fluid with a free surface is used. The strength of the source and sink and the distance between them depend on body length and central cross-section area. The solution is carried out using known integral and asymptotic methods. The effects of an ice sheet thickness, its lateral stress, water depth, submergence depth on wave resistance and lift force of slender body is analyzed. INTRODUCTION Operating of submarines in ice cover conditions requires to analyze ice sheet influences on hydrodynamic forces that are experienced by a submarine transiting near the surface. It is known that the closeness of the free surface adjusts the wave resistance and lift acting on the slender body moving in fluid. Many theoretical and experimental investigations devoted to submarine resistance and lift were published in the twentieth century (Havelock, 1917, 1931a, 1931b; Kinoshita and Inui, 1953; Farell, 1973; and so on). Havelock obtained analytical formulae for wave resistance of a sphere (Havelock, 1917), for prolate and oblate spheroids (Havelock, 1931a), and for an ellipsoid (Havelock, 1931b). In these works, Havelock used distributed parallel doublets to describe the body and determine a solution that satisfied the body boundary conditions. However, more recent work, most notably by Farell (1973) and Doctors and Beck (1987), has shown that these early results were not accurate and did not adequately capture the wave resistance at low Froude numbers. Wigley (1953) investigated the wave resistance, lift force and pitching (trimming) moment acting on a submerged spheroid with a length-to-diameter ratio of 20. Wigley (1953) observed that at the slow speeds the lift force generated by the interaction of the body and the free-surface acts to push the body upwards and closer to the surface. At the high speeds the lift force acts to push the body away from the free-surface

The creation of offshore wind power plants capable of operating in the Arctic marine conditions is a difficult task. Usually, in the Arctic zones, there is no developed industrial infrastructure and there are no skilled workers. In these conditions, it is difficult to build and maintain complex technical devices. Arctic Wind Power Plants should have high reliability in severe operating conditions, use suitable materials for these conditions, installation and assembly technology. This paper contains a review of conceptual design of offshore stationary wind power installations capable of operating in the Arctic conditions. The analysis of available constructional typologies, the evaluation of external loads on these possible options and, finally, the suggestion of approach how to choose installed power capacity of wind turbine which will provide economic expediency of its construction and operation in Arctic marine conditions. INTRODUCTION Centralized energy supply does not exist almost everywhere in Russian Arctic zone. Diesel power plants, which are used now in this area, produce quite expensive electric energy. Besides, the task to provide them with fuel is connected with complex logistic problems. Therefore, it appeals to use offshore wind power plants there, which are delivered and constructed during the summer navigation period. The main parameter, that determines the price of produced energy, is the cost of construction of these wind power plants. It is obvious that the development of offshore wind energy is possible only when arctic offshore wind power plants will have an acceptable cost to compete with other sources of energy. The amount of used metal and the cost of offshore wind power plants depend on the power capacity of installed generator and the external loads, which are affecting the supporting structure and rotor. Structure of offshore wind power installations significantly depends on the sea depth. At relatively shallow depths, stationary structures are usually used. With the increase of sea depth, it becomes more appealing to install wind turbines on a floating base. Conceptual design of floating wind power plants for Arctic zone has been described in previous article written by authors (Bolshev et al., 2019). This paper is dedicated to the various conceptual design options of stationary offshore wind power plants in Arctic zone.

The main factor affecting the operating conditions and the reliability of offshore structures in the production of exploratory drilling in the Russian Arctic is the ice regime of the water area. The problems of exploration drilling in the Arctic are among the most pressing issues in the development of offshore hydrocarbon deposits in the Arctic. The article considers a new approach to assessing the exploration time of offshore drilling rigs in ice conditions and the possibility of their extension in a mode that ensures their normal (safe) operation in such conditions. As an example, the article considers the interaction of ice formations in the form of flat ice fields and their fragments with the legs of the Jack- Up platform, and their geometric parameters (area and thickness) are determined at which the ultimate state of the marine engineering structure does not occur. NOMENCLATURE ODP – offshore drilling platform JUP - Jack-Up platform INTRODUCTION Issues of reconnaissance drilling in water areas with ice regimes remain relevant for economic activities in the Arctic, as traditional drilling platforms such as Jack-Up, Semisubmersible and Drilling Rig, which are widely used in world practice for drilling offshore wells, are wave-resistant, i.e. not designed to work in ice conditions. In this regard, experts are developing new types of ice-resistant offshore drilling platforms to work in difficult ice conditions (For example, Urycheva and Gudmestad, 2014; Toropov, Mokhov, Semenov and Livshits, 2013). One of the most important indicators for assessing the effectiveness of the use of such drilling platforms in the freezing sea is the duration of the navigation period. In the Arctic, the duration of the navigation period is usually insufficient for the construction of one well. Therefore, an urgent problem is the creation of a technology for managing the timing of drilling exploration work in ice conditions based on the management of the geometric parameters of ice formations in the water area using icebreakers. Such technology should include the destruction of drifting ice fields into fragments of controlled sizes and methods for assessing the reliability of a drilling platform depending on the size of ice formations. This technique is applicable to estimating the duration of the drilling season in ice conditions for both existing drilling platforms and newly developed drilling platforms. A description of the methodology for assessing the duration of drilling operations in order to ensure the minimum required drilling time under given ice conditions is given by the example of a Jack-Up platform.

The authors have been developing an autonomous underwater glider which equips an OBEM (Ocean Bottom Electromagnetometer). That is a hopeful instrument for the ocean floor resources explorations. The autonomous vehicle has an ability to achieve a continuous resource exploration autonomously for a long term. The buoyancy and attitude control mechanism of the vehicle enable to move to the next measurement point by gliding. The vehicle which has a blended wing body measures the slight variation of electromagnet wave on the sea bottom and the landing point for the measurement must be precisely controlled by the motion control system. In the landing stage, it is predicted that surface effect of the sea bottom affects the hydrodynamic characteristics of the vehicle, and it might cause some problems on the motion control system of the vehicle. The authors attempt to make clear the characteristics of the flow field around the vehicle in the vicinity of a sea bottom. The motion control system for landing of the vehicle was investigated in the previous study (Yamaguchi and Sumoto, 2019). In this report, hydrodynamic performance of the vehicle in landing is examined by CFD calculations. The surface effect by a sea bottom which affects the lift and drag of the wings of the glider is studied and the characteristics of the blended wing body near a sea bottom is discussed. INTRODUCTION Development of sea floor resources gathers attention from wide area recently. Ocean floor resources such as sea-floor hydrothermal deposit, methane hydrate and manganese nodule are promising resources in the near future. Moreover, it is becoming apparent that certain amount of these resources deposit near Japan by recent research and various researches were started for the development. Several kinds of exploration methods such as seismic exploration, a multi-beam echo sounder and a sub-bottom profiler which are equipped with a survey ship or an underwater vehicle are used for the resource explorations in the ocean (Yoshida, Hyakudome, Ishibashi et al ., 2013). In these instruments, the OBEM is a device which measures the slight variation of the electromagnetic field on a sea floor and the structure under the seabed can be analyzed using gathered data. Ocean development is expanded to deeper sea area nowadays and OBEM is a promising method for the ocean resources exploration. The OBEM needs to repeat measurements many times to acquire the information of the structure under the seabed and the high cost and long cruise time of the system are serious problems because a usual OBEM cannot move to the next observation point by itself.

To ensure safety of marine operations during ice management in arctic seas, it is essential to understand an iceberg's stability. Stable icebergs can be towed away from offshore facilities using standard vessels and procedures. Unstable icebergs create high risks and can easily capsize during the vessel's maneuvering and towing. As is known, an iceberg capsize event could lead to iceberg destruction into several pieces. The total danger from the parts often would exceed the initial one. Especially dangerous are large icebergs that may capsize and damage the towing vessel. Due to interaction with the seawater, the icebergs have their natural oscillations, which under certain environmental conditions can significantly complicate the towing process due to resonance phenomena. We should also notice that during the melting, icebergs will change form and motion characteristics. The paper presents calculations of icebergs' stability criteria (metacentric height) based on iceberg towing experiments conducted in 2016–2017 in the Barents and Kara seas. Longitudinal and roll oscillations of various icebergs are considered. The appearance of resonance phenomena during iceberg drift is studied for characteristic periods of waves of the Kara and Laptev seas. Periods of natural oscillations are defined using 3D models of icebergs constructed from aerial and sonar surveys. The results obtained show the dependencies of the iceberg's stability criteria on the iceberg's above-water parameters – and demonstrate that unstable icebergs may be identified without sonar surveys. INTRODUCTION Due to significant mass of icebergs and sophisticated underwater geometries that are hard to determine, aspects of icebergs stability significantly affect the tactics of ice management operations. On the one hand, an iceberg can overturn during towing (Efimov et al., 2019) or even while a tow rope or net is being deployed requiring prompt vessel maneuvering, and in the worst case, causing some damage to a towing vessel. On the other hand, an unstable iceberg may breakup due to wave action from the vessel without direct contact with vessel or rope (Kornishin et al., 2019).

In this paper, based on CFD method, the virtual propeller disk of volume force method is used to replace the real propeller to provide propulsive force. Combined with global moving mesh and overset mesh technology, 3DOF is released at the same time. The mesh size used for calculation is tested for irrelevance. Finally, a 20 million mesh is used to complete the zigzag steering test in which the submarine dynamically changed the rudder angle during self-propelled state. The results show that compared with C-rudder submarine, X-rudder submarine has about 34% less zigzag steering period and 38.5% less overshoot time. The rotation index K is large, and the stability index T is small. Therefore, it can be considered that the X-rudder submarine has good steering ability and stability. INTRODUCTION In the actual operation of a submarine, a complete steady rotation is extremely rare. More often, it is repeatedly steered with a small rudder angle during the process of adjusting the attitude of the submarine. This involves an important maneuverability index of the submarine--the rudder performance. Determination of rudder performance can be done by zigzag maneuvering test. The zigzag maneuvering test is a kind of standard test to evaluate the maneuverability of ship’s horizontal plane. It was first proposed by Kempf in 1934, mainly through changing the rudder angle regularly, simulating the situation of small rudder angle steering on the left and right of the ship, to determine the rudder performance of the ship (SHI Shengda, 1995). However, the rudder force and propeller thrust torque during the maneuvering process can be obtained through theself-propelled model test, which not only needs high requirements of test environment and instruments, but also the test method is not mature(Khanfir, S , Hasegawa, K , Nagarajan, V , Shouji, K , and Lee, SK, 2011). In recent years, with the rapid development of computer technology, CFD methods have made significant progress in the field of ships (WANG Huaming and ZHOU Zaojian, 2006). The CFD method has the advantages of low cost, high accuracy, and easy implementation. Biguang Hong used the CFD method to carry out numerical simulation Corresponding author.

Minimal structures of jacket platforms are commonly applied in development of marginal offshore oil and gas fields. It is subjected to continuous cyclic wave loads during services, causing fatigue damage to the platform structures. In design of this kind of structures, assessments of fatigue damage become particularly important. Spectral fatigue analysis approach is a computationally efficient method to describe the random nature of environmental ocean wave conditions during calculating wave loads on the offshore jacket structures and subsequently structural responses. However, its fundamental theory is based on the assumption of linearity of both structural system and wave loading mechanism,but it has still been widely utilized for the design and assessment of shallow water jacket platforms with strong nonlinear mechanism. Therefore, the paper focuses on the studies on the improvement of the accuracies of the fatigue calculations by a new technical approach that can reduce the errors in the spectral fatigue analysis of shallow water platforms. This new approach can reasonably reflect the individually local sea state data by using wave height-period joint probability density function, the discussions of comparisons between the improved approach and the design code oriented method carry out by means of the analysis results. In addition, the wave probability density function which is employed for computing the fatigue damage in the existing design software is only effective for the narrow band spectra, and it causes additional errors for the broadband spectra during the computation of the fatigue damage. The appraisal on improving the calculation of the fatigue damage for the broadband spectra also carries out in the paper. INTRODUCTION Fatigue analysis plays an important role and has become compulsory in the design of offshore jacket platforms since fatigue failure is one of the major reasons causing the welding joint defects of offshore jacket platforms(Bishop, Sherratt, 1989). According to the international authoritative institutions in offshore platform, joint damage of the structures, about 70% above is caused by fatigue. The spectral fatigue analysis method has many advantages compared with other fatigue analysis methods, such as deterministic fatigue analysis and time history fatigue analysis etc(Pierson, Mosskowitz, 1964). The major reason that the spectral fatigue analysis method is recommended is computationally efficient, assessing structures where the response can be assumed to be linear, Gaussian, stationary and random.

In this paper, the numerical model of level ice is developed in the framework of finite elements and the water is considered by SPH method, the numerical method is established by adopting the contact algorithm to calculate the contact forces between finite elements and water particles. Then the icebreaking process of the polar tanker is calculated and its navigation in open water simulated by CFD numerical simulation based on viscous theory. The resistance of a polar tanker under multiple load cases is predicted. INTRODUCTION The melting speed of ice in Arctic region is accelerating because of the changes in climate, which makes the marine transportation in Arctic region possible. The polar tanker will play an important role and its full route includes both ice area and open water area. And the demand of the polar tanker with self-icebreaking ability is increasing recently. For a polar tanker, the comprehensive performance in both of the ice area and the open water area should be considered in the design phase. In the resistance prediction of ice-breaking, finite element method is a commonly used numerical calculation methods. Compared with the oversimplification of the model in the empirical formula and the long period and high cost of the model test, it can take into account the effects of sea ice failure modes and more ship form parameters. The Cohesive Zone Model (CZM) has found great attention in the applied numerical fracture literature to solve problems of multiple cracking brittle and quasi-brittle solids during impacts and failure loading. Then the CZM was extended into sophisticated numerical algorithms in the framework of finite elements, termed the Cohesive Element Model (CEM), for the simulation of ice-structure interactions, (Konuk et al, 2009). Arne Gürtner et al. (2009) used the numerical method to simulate the action to a lighthouse, the simulation results indicate that the numerical method captures many of the qualitative observation as well as quantitatively derives comparable global ice loads to the lighthouse to those of the selected ice event. Wang et al. (2008) developed a collision model of crushable ice based on nonlinear dynamic finite element and analyze the ice load of a FLNG ship using commercial code DYTRAN. Yang et al. (2008) adopted the method of fluid-structure interaction and established the nonlinear finite element model of collision between ship and ocean platform by taking sea ice as medium.

The floating wind turbine system is subjected to a combination of aerodynamic forces, wave forces and mooring forces during operation. In this study, the computational fluid dynamics method is used to analyze the wind load of the wind turbine system, and the wind force model is established by the NARMAX theory. The pitching motion of the tower and blades is taken into account in the calculation. This paper will give the load and flow field of the wind turbine under constant wind and pulsating wind, and establish a more optimized wind load forecasting model based on NARMAX theory. INTRODUCTION Wind energy currently has important prospects as a pollution-free renewable energy source. In pursuit of higher efficiency and higher average wind speeds, offshore floating wind turbines are rapidly increasing in order to adapt to the trend towards the deep sea. Offshore floating wind turbines (FOWT) require offshore wind turbines to be mounted on floating structures, which can generate electricity in deep sea locations where bottom-fixed support structures cannot be installed. At present, research on offshore wind power technology has been extensively carried out. The analysis of the coupled motion of offshore wind turbines under the combined action of wind and waves is a difficult point in current calculations. As shown in Fig.1, due to the dynamic excitation of the waves, the motion of the FOWT will include 6 degrees of freedom: three translational components (heave, sway, and surge) and three rotational components (yaw, pitch, and roll). The effect of these coupled motions transmitted to the wind turbine on the performance of the wind turbine is worthy of study. In addition, unsteady numerical tools are used in the simulation of the coupled motion. The FAST code developed by the US National Renewable Energy Laboratory (NREL) can already perform coupled time-domain dynamic analysis of FOWT (2009). However, the BEM method still has doubts about the prediction accuracy of unsteady aerodynamic loads, and it has theoretical limitations. For cross-computation verification, a new unsteady numerical method is needed.

This paper describes the hull form optimization method of an icebreaker. The objective function is resistance in ice which is calculated by ICHM (Ice-Covered Hull Model) we developed. A genetic algorithm is adopted as the numerical optimizer. We optimize a hull form which has the same hull form parameters as the preliminary designed hull form as an application example. As the optimization result, the hull form which has smaller ice resistance than the preliminary designed hull form is obtained. INTRODUCTION In the development of an icebreaker, we design a hull form which meets the performance requirements at its navigating sea area in both ice-covered and open water conditions. For evaluation of icebreaker’s performance in ice, ice tank tests are needed. These tests take longer time than general open water tests, because they need to make model ice for each test. Therefore, to develop an icebreaker’s hull form with better performance within a limited development period, it is important to preliminarily design a hull form whose performance is close to the requirement before ice tank tests. For a conventional hull form, many optimization methods using CFD, Rankine source methods or other resistance estimation methods have been studied for minimizing resistance in open water. However, when an icebreaker navigates in ice fields, its dominant resistance components come from ice breaking phenomena and hull-ice interaction. Thus, for the first step to the development of hull form optimization system for icebreakers, an optimization method for minimizing resistance in level ice is devised. Moreover, optimization performed only around the bow because bow form is dominant in ice resistance. The optimization problem of an icebreaker was investigated by Edwards, Major, Kim, German, Lewis and Miller (1976). In that paper, the principal particulars of an icebreaker were optimized with the focus on ice resistance, costs and maneuverability in ice. However, since ice resistance and maneuverability in ice were calculated based on the results of parametric ice tank tests, it could not optimize a hull form in detail. On the other hand, the other calculation methods commonly used for estimating resistance in ice (Lindqvist, 1989; Ionov, 1988) employ hull form parameters around the planned water line. Hence, these methods can hardly consider underwater hull geometry. In the present study, to optimize a hull form in detail, we use ICHM (Ice-Covered Hull Model) (Anzai, Yamauch and Mizuno, 2019) in which, ice resistance is decomposed into ice breaking resistance, resistance due to ice buoyancy and clearing ice pieces and each resistance component is calculated by estimating ice pieces distribution on hull surface.

Due to the hull characteristics of small waterplane area twinhull( SWATH) ship, seakeeping software based on traditional single and catamaran potential flow theory cannot be directly applied to SWATH ship seakeeping prediction, because the longitudinal motion of SWATH must also consider the effects of viscosity and fin lift. The experiments of SWATH ship are carried out in this paper, and different stabilized fin angles and ship speeds are studied. The CFD method is used to perform numerical simulation calculations on SWATH ship, by using STARCCM + software based on the RANS equation. This example is a multilayer encryption of the free liquid surface and the grid surrounding the hull, and is dedicated to building a computational model that can be used for numerical simulation of this ship shape. By comparing the numerical calculation results with the experiment results, the accuracy of the numerical calculations is verified. The numerical simulation results in the higher wave frequencies are highly consistent with the model experiment results. This study can provide a numerical calculation method for the research of SWATH ships. INTRODUCTION The biggest advantage of SWATH ship in terms of performance is its excellent seakeeping. It is necessary to estimate the seakeeping in the early stages of ship design. The seakeeping software based on the traditional single and double-body potential flow theory cannot be directly applied to the seakeeping prediction of SWATH ships, because the longitudinal movement of SWATH must also consider the effects of viscosity and fin lift. Due to the special type of SWATH ship, the transverse section of the submerged part is much larger than the transverse section of the pillar part, and non-linear forces will be generated when the ship is moving longitudinally. Therefore, the influence of viscosity cannot be ignored in the seakeeping prediction If we ignore the effect of viscosity and simply use slice theory to calculate, the frequency response function curve will be too large. This theoretical result is verified by comparing the previous experimental results with the calculated results. Brizzolara, Stefano (2013) used the CFD method to make in-depth research on the design direction of small waterplane area twin-hull ship in terms of its hull concept, such as transforming hull dimensions and optimizing hydrodynamic performance. Mao Xiaofei (2005), based on the slice theory, adopted a complete set of hydrodynamic calculation formulas for SWATH ship, and applied it to extend the seakeeping prediction program of conventional catamarans, and wrote a WAVMOSWATH program in order to calculate and forecast the seakeeping of the SWATH ship, this paper also uses the 390t oilfield small waterline surface transportation ship as the calculation object. The ship's shape under various sea conditions in regular waves and irregular waves is calculated. The longitudinal motion was calculated and analyzed, and the influence of setting the stabilized fin on the seakeeping was compared. The calculation shows that the setting of the stabilized fin greatly reduces the peak frequency response of the longitudinal motion. Based on the CFD uncertainty analysis procedure recommended by ITTC, Deng Lei, Peng Hongyu (2016) conducted an uncertainty analysis of the calculation results of the longitudinal motion in the SWATH ship wave based on the RANS equation, which verified the mesh convergence of the calculation model and the Convergence. Based on the determination of the longitudinal stability of SWATH, Gao Zhansheng, Cai Yan, Hou Jianjun (2014) analyzed the influence and their laws of parameters such as the installation position and fin area of the stabilized fin on the longitudinal stability of SWATH at different speeds.

As an indispensable tool for polar resource development, the research on the seakeeping performance of icebreakers becomes more necessary. This article takes the 153-meter icebreaker as the research object. The motion response of the icebreaker is calculated using Maxsurf software based on strip theory. The effect of different heading angles and sea conditions on the seakeeping performance of ship is analyzed. The calculation results show that the seakeeping performance is excellent and meets the demand of residential comfort. In addition, the dangerous heading angles during the navigation are also listed, which can help to improve the sailing safety. INTRODUCTION The main function of the icebreaker is to serve as a tool for opening ice channels, science surveys and emergency rescue. Since icebreakers need to navigate in open water and ice areas, more factors need to be considered to ensure their navigation safety. Especially for countries far away from the polar region, their icebreakers need to sail in a variety of complex sea conditions, so good seakeeping performance is a key factor to ensure safe hull navigation. The seakeeping performance of a ship during sailing is determined by a variety of factors, including the movement of the six degrees of freedom and linear (accelerated) or angular (accelerated) speed of ship. In addition, when encountering severe weather incidents, some events such as the green water, slamming and emergence probability of the screw will also affect its seakeeping performance. The theory of wave resistance of modern ships originates from the 1950s. Among them, the strip theory proposed by Korvin-Kroukovsk (1955) based on the slender body theory in aerodynamics has become an effective method for predicting the wave resistance of ships. In the subsequent development process, Korvin-Kroukovsky and Jacobs (1957) developed and perfected this theory, finally they proposed the ordinary strip method (O.S.M), which is the first theory that can effectively calculate the motion response of ships on waves, but it is only suitable for solving the heave and pitch motion responses in the head seas conditions. Later, Vossers (1962) and Joosen (1964) further reasoned the strip theory based on the slender body hypothesis. Gerrisma, J. and W. Beukelman (1967) proposed to use a modified slice theory (M.S.T) to perform theoretical calculations of ship motion on waves and wave loads. The calculated results are in good agreement with the experimental results in head seas conditions. Later, Tasai (1967), Grim and schenzle (1969) based on the slice theory to predict the lateral motion response of ship under inclined waves. Ogilvie and Tuck (1969) proposed the Reasonable Slice Method (R.S.T), which illustrates the slice theory through magnitude analysis, but it is also only applicable to heave and pitch responses. Salvesen, Tuck and Faltinsen (1970) proposed the STF theory, which can be used to predict the motion response of ships in five degrees of freedom (yaw, sway, pitch, heave, roll) other than surge. At the same time, this method is also suitable for solving the motion response in inclined waves.The strip theory is based on the assumption of low speed and high frequency, which is not suitable for the prediction of high speed ships. Due to the high calculation efficiency of the strip theory, it has a good agreement with model tests at medium and low speeds, and it is still an important tool for studying the seakeeping performance of ships. Besides, its scope of application can be extended to many other complex conditions: Prediction of the seakeeping performance of ships with limited water depth; Prediction of ship motion response under complex boundary conditions (He, 1998).