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Paper presented at the The 28th International Ocean and Polar Engineering Conference, June 10–15, 2018
Paper presented at the The 28th International Ocean and Polar Engineering Conference, June 10–15, 2018
Paper presented at the The 28th International Ocean and Polar Engineering Conference, June 10–15, 2018
Paper presented at the The 27th International Ocean and Polar Engineering Conference, June 25–30, 2017
Paper presented at the The 27th International Ocean and Polar Engineering Conference, June 25–30, 2017

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Proceedings Papers

Paper presented at the The 30th International Ocean and Polar Engineering Conference, October 11–16, 2020

Paper Number: ISOPE-I-20-2137

... model

**expression**reservoir simulation ship tail end different time china university upstream oil & gas posture coefficient cable equation propeller rotary speed steady motion mass method towed system dynamical equation order runge-kutta method Numerical simulation of 3 DOF...
Abstract

A dynamic model was proposed with the features of high precision and fast response. The dynamical equations of the flexible cable were established by using Newton's second law. Lumped mass method was used to discretize equilibrium equation and continuity equation. The motion excitation was input at the head or tail end of the cable. The model equations were iteratively solved by fourth order Runge-Kutta method. Four cases of simulation of a towed system were presented to prove feasibility and effectiveness of the model, including equilibrium state in different currents, sailing with constant propeller rotary speed, turning motion and the spiral descending motion of the submersible. INTRODUCTION A towed system is an efficient device for underwater measurement, oceanic detection and submarine mapping, which usually consists of a mother ship, a cable and a submersible. Since reliable and rapid motion prediction can ensure good operation and prolong service life, it is necessary to accurately establish a reasonable dynamic model of a towed system. Usually, discrete model is the most important part in the modeling process. Finite difference method, finite element method and lumped mass method are the common discrete methods. Therein, lumped mass method is the most acceptable one because of its simple theory and concise form. Walton and Polachek (1960) firstly proposed lumped mass method in solving the nonlinear partial differential equations governing 2D transient motion of a cable. Delmer and Stephens (1983) utilized lumped mass method to analysis the breaking process subsequent behavior of a cable under excessive load. The computed results show a fine consistency with the experimental ones. Huang (1994) considered the linear elasticity of the cable materials and promoted lumped mass method in discretizing a 3D dynamic model. The new model enabled larger time step and faster iteration time. Driscoll and Lueck (2000) used lumped mass method analyze the motion and load characteristics of a deep-sea ROV system, which consist of a ship, a cage, a remotely operated vehicle (ROV) and towed cables. Results prove that the model is effective and rapid for the prediction of snap loads. Liu (2012) and Wang (2012) further studied the dynamic model of towed systems on the basis of the previous work. In their research, bending and torsional moments were added to the elastic cable segment divided by lump mass method. Besides, the cable in Wang's (2012) investigation was covered streamlined sleeves to reduce the drag force, which lead to a steady axial rotation of the cable. Thus, a 4D dynamic model was successfully developed.

Proceedings Papers

Paper presented at the The 29th International Ocean and Polar Engineering Conference, June 16–21, 2019

Paper Number: ISOPE-I-19-548

... only eliminate the error of the physical model itself, but also be convenient for modeling and analyzing as a multibody system(Choi, Sohn, 2013) together with the floating body. subproblem denote artificial intelligence mooring system anchor ring anchor chain

**expression**ground chain...
Abstract

ABSTRACT In order to describe the multibody system of the anchor chain with both the catenary and the ground chain under the environment of no special added equation or determinant condition, the optimization equation, i.e., the minimum potential energy equation, was proposed in this paper to represent the state of the static multibody system of anchor chain. This method was compared with the traditional catenary equation and the general mechanical equation of the multibody system of the anchor chain. The results showed that this method proposed in this paper need not the complex analysis involving forces. The form of the equation is simple and the physical meaning is clear and explicit. The computational results were consistent with the predictions from the traditional methods and this method in this paper can calculate the mixture of catenary and ground chain under the unified framework. INTRODUCTION When the force analysis on anchor chain was carried out, it was reasonable to ignore the connection between the anchor rings and simplify the anchor chain as a catenary if the length of the anchor ring is small enough compared with the length of the overall anchor chain(Liu, Wang, 2011). The catenary equations derived from the differential equation of mechanics(Hu, Tang, 2004) could be applied to determine the parameters of the anchor chain and complete the selection of mooring equipment (Wang, Liu, 2007) in engineering. In addition, it was often used in the mooring of deep-water semisubmerged platform(Tong, Yang, et al., 2008) and FPSO (Floating Production Storage and Offloading)(Ting, Hong, et al., 2013), multicomponent catenary mooring system (Zhu, Yin, et al., 2015), the intelligent active mooring system(Jamie, Simon, et al., 2016) and the design of mooring system(Zhu, Wang, et al., 2017). There is no escape from occurrence of error in its physical model when simplifying the discrete multi-body system of anchor chain connected by anchor rings to a continuous catenary. Utilizing the multi-body dynamic equation to solve the state of the anchor chain system(Kreuzer, Wilke, 2013) could not only eliminate the error of the physical model itself, but also be convenient for modeling and analyzing as a multibody system(Choi, Sohn, 2013) together with the floating body.

Proceedings Papers

Paper presented at the The 29th International Ocean and Polar Engineering Conference, June 16–21, 2019

Paper Number: ISOPE-I-19-581

... approximately a third of the spudcan diameter above the clay-sand interface. A simplified

**expression**is proposed to predict the spudcan penetration resistance between the depth at which the squeezing prevails and the clay-sand interface. clay layer spudcan penetration spudcan foundation footing...
Abstract

ABSTRACT Safe installation of mobile jack-up platforms requires accurate prediction of the vertical load-penetration curves of their large ∼20 m diameter spudcan footings. Difficulties can arise due to a change of soil strength from a soft to a stiff layer. A substantial increase in the ultimate bearing capacity occurs when a spudcan penetrates vertically through a soft clay layer towards a sand layer. This is because the softer soil that is trapped beneath the spudcan base starts to be squeezed horizontally as the vertical load begins to be borne by the stronger underlying sand layer. The theoretical solution of the bearing capacity of a soil layer on a rigid base has conventionally been used to predict the spudcan penetration resistance in soft over strong layers. However, recent centrifuge experimental studies suggested that the design approaches recommended by current industry guidelines ISO (2016) and SNAME (2008) are not adequately accurate in predicting the sharp increase in the resistance prior to penetration into the sand layer. In this paper, large deformation finite element (LDFE) analyses that capture the evolving soil failure mechanisms during spudcan penetration in a clay layer overlying sand, and explore relationships for the penetration resistance, are reported. The Coupled Eulerian-Lagrangian method was used to simulate the continuous penetration of the spudcan foundation. The clay layer was modelled with the elastic perfectly plastic Tresca model, while the sand layer was modelled by the Mohr-Coulomb model using a nonassociated flow rule. The findings show that the increased capacity is associated with the squeezing mechanism, which starts at the depth where the bottom of the soil failure mechanism first touches the underlying sand layer. This is approximately a third of the spudcan diameter above the clay-sand interface. A simplified expression is proposed to predict the spudcan penetration resistance between the depth at which the squeezing prevails and the clay-sand interface.

Proceedings Papers

Paper presented at the The 28th International Ocean and Polar Engineering Conference, June 10–15, 2018

Paper Number: ISOPE-I-18-008

... linearization artificial intelligence extreme load return value procedure maxima wind energy loading history extrapolation value distribution derivative subsea system platform design load case renewable energy wind turbine

**expression**equation block length offshore projects planning and...
Abstract

ABSTRACT In this paper we show how a new idea for how to calculate the derivatives of extrapolated 50-year return values, used in extreme load safety criteria, can be used to estimate the uncertainty in these return values resulting from uncertainty in the simulations and in the load extrapolation procedure itself. The method yields uncertainty estimates with a high degree of accuracy. Additionally, to highlight one of the subtler uncertainties involved in this setting, we also make a small study of how changing the block size used in the extraction of maxima from load time series affects the 50-year return value. INTRODUCTION Finding ways to reduce the cost of offshore wind turbine support structures is one of the main objectives of current research on this topic. One of the main challenges involved in cost reduction of structures is the balance between measures that reduce the resistance to loading (like e.g. lighter designs) and the safety requirements. A primary reason for the difficulty posed by this balance is the large amount of uncertainties in the analysis. On the load side there are a lot of uncertainties coming from various sources such as measurements, local variations within windfarms and simplified modeling of the environment. In the structure there are uncertainties such as those related to the production of components and to simplified structural models. The usual solution to this issue is to make designs that are very conservative, scaling preliminary designs as dictated by analysis by large safety factors. Hence, increased knowledge about uncertainty could potentially enable designers to be less conservative and make more economical choices. Extreme load, or Ultimate Limit State (ULS), criteria present a particular challenge for uncertainty analysis due to the way these are evaluated. Chiefly, this is because of the requirement (Det Norske Veritas, 2014) that extreme loads should be the 50-year return values calculated from the loads obtained by simulations. While this is a standard procedure in the design of wind turbines, it is not trivial. It entails fitting the short term maximum loads to extreme value distributions and then extrapolating from these distributions to the 50-year return value. A considerable amount of work has gone into the study of various aspects of the load extrapolation procedure for wind turbines. A comparison of three different approaches, including a process model, was made by Cheng (2002). A study of the effect of turbulence level on the predicted extreme load was performed by Moriarty et al. (2002). A report discussing, among other things, several aspects of extreme load extrapolation, including selection of threshold values, the statistical uncertainty of the fits, details of both short term and long term statistics and possibilities for model simplification was made by Moriarty et al. (2004). Further studies and discussion of various standard and alternative methods for short term fitting and long term extrapolation methods, as well as details of uncertainty, can be found in, e.g., Saranyasoontorn and Manuel (2006), Ragan and Manuel (2007), Agarwal and Manuel (2007), Fogle et al. (2008), Toft and Sørensen (2009), Agarwal and Manuel (2010) and Dimitrov (2016).

Proceedings Papers

Paper presented at the The 28th International Ocean and Polar Engineering Conference, June 10–15, 2018

Paper Number: ISOPE-I-18-118

... coordinate system matrix equation postnov generalized displacement fluctuation

**expression**module-element method artificial intelligence mathematical model formulation consideration kinetic energy coefficient dissipation function taranukha lagrange equation displacement...
Abstract

ABSTRACT The article is devoted to research of fluctuations (vibration) of complex real shells. An example of such shell can be the ship hull. Part of the ship hull interacts with adjoining fluid. The forced harmonic fluctuations are considered. The purpose of this study is derivation of mathematical model for fluctuations of a shell using the module-element method (MEM). The module-element method is the modification of the finite element method. The important feature of the proposed mathematical model is the consideration of the fluctuation of the shell together with an adjoining fluid. The coupled system "structure- liquid" is considered. The problem is solved using theory of hydroelasticity. The theoretical problem is solved using combination of two numerical methods: a module-element method and a boundary element method. The mathematical model also accounts for the effect of damping on fluctuations of coupled system "structure- liquid". INTRODUCTION The theoretical solution of the problem of vibration of the complex real shells is challenging due to following reasons: the complex geometry of real shell; the internal damping or damping of shell material. This damping can be related to the properties of the material, the energy loss in welds and other energy loss; the damping of the external environment, for example, damping due to viscousity of the adjacent liquid; inertial interaction of the fluctuating shell with the liquid involved in the joint movement; complicated external impacts on a real shell. The vibrations of complex real shells can lead to unexpected events of resonant oscillations which reduces reliability and operability of complex real shells. INITIAL EQUATIONS FOR THE CONSIDERED CASE Input equations. We will consider a case of the forced fluctuations of complex system taking into account external and internal damping using theory of hydroelasticity. Only small fluctuations (vibrations) are considered. The problem will be solved using Module Element Method or MEM (Postnov and Taranukha, 1990; Taranukha and Leizerovich, 2005).

Proceedings Papers

Paper presented at the The 28th International Ocean and Polar Engineering Conference, June 10–15, 2018

Paper Number: ISOPE-I-18-701

... has been studied numerically by Chung and Cheng. (1996). internal flow wavelength coriolis viv equation simulation critical wavelength

**expression**internal density wave upstream oil & gas frequency amplitude mining riser vibration riser displacement internal mass cross-flow...
Abstract

ABSTRACT Risers used for deep sea mining will be subjected to vortex-induced vibrations (VIV) caused by ocean currents. The internal flow, consisting of e.g. mineral ore and water, will have a non-uniform density. This traveling density wave may influence the dynamic response of the riser. In this paper, a simplified analytical approach is adopted to estimate the disturbance caused by the internal flow. The analytical model predicts a large disturbance (resonance) at a certain critical wavelength, which is verified by numerical simulations. INTRODUCTION The global demand for minerals is continuously increasing. Higher living standard in developing countries is one important factor. In addition, various minerals are needed for the continued implementation of environmentally friendly technologies in developed countries. With this in mind, there is a growing concern about the scarcity of metals, as traditional land-based mines may be unable to meet future demands (Ali et al. 2017). As mineral resources on land are not evenly distributed, there may also be strategic reasons to why some nations want to find alternative sources. Mineral deposits in the deep ocean include sea-floor massive sulfides (SMS) and manganese nodules. SMS deposits, found around the black smokers along the ridges of tectonic plates, are characterized by high grades of metals such as copper, zinc, silver and gold (Petersen et al. 2016). Manganese nodules are found on abyssal plains at great water depths, and contain manganese, nickel, cobalt and copper. Much research into deep sea mining was conducted in the 1970s (see e.g. Mustafa and Amann, 1980), but interest declined because of sufficient supply from mines on land. Recently, this interest has been renewed. Commercial deep sea mining is planned to commence outside the coast of Papua New Guinea in 2019 (Nautilus Minerals, 2016), and a mining pilot test was recently conducted close to Okinawa, Japan (METI, 2017). Despite of large research efforts, many uncertainties remain. These are particularly related to environmental (Durden et al. 2017), but also economical and technical issues. As less than 0.5 % of the world's ocean area has been mapped (Beaulieu et al. 2017), much exploration is necessary before it is possible to quantify the amount of valuable minerals with certainty. Among the technical challenges are energy supply, extraction, vertical transportation and processing. When it comes to the transportation of mineral ore from seabed to surface, different methods have been suggested, such as mechanical lifting by a continuous bucket system, hydraulic lifting using slurry pumps and airlift methods (Schulte, 2013). In the case of slurry pumping or airlift, a vertical pipe, i.e. a riser , must be used to convey the ore/water mixture. As the riser represents a critical component of an ocean mining system, the integrity of this structure needs to be verified. The dynamic response of very long ocean mining pipes subjected to waves and top-end motion has been studied numerically by Chung and Cheng. (1996).

Proceedings Papers

Paper Number: ISOPE-I-18-706

... 1981; O'Brien et al . 1988; Kordkheili et al . 2011). submerged length offshore structure variation equation dynamic analysis position vector free surface relative velocity submerged part vector angelide corotational beam element

**expression**tsolaridou hydrodynamic force element...
Abstract

ABSTRACT This paper deals with the derivation of a mathematical model for the dynamic analysis of flexible offshore structures using the finite element method. This model was developed recently by the authors and refers to a three dimensional corotational beam element that can undergo large rotations and translations, but small strains. The applicability of the model has been tested in the past only for pure structural systems and for submerged systems subjected to currents. In the present paper, the mathematical model is extended to include also the influence of the free surface on flexible structures. For the part of the structure close to the free surface, the model evaluates the instantaneous wave profile in the vicinity of the element's nodes. By this way it is deduced whether the element is completely, partially or not at all submerged and then the submerged length is evaluated. Regarding the hydrostatic forces, they are evaluated from the potential energy for the submerged part of the element. Further on, the equivalent hydrodynamic force is evaluated using a modified Morison equation. For completely submerged elements, the applied force is formed using the nodal fluid accelerations and relative velocities normal to the beam axis. In case of a partially submerged element, the evaluation of the hydrodynamic force is based on the fluid accelerations and relative velocities at the submerged node and at the point that the element pierces the free surface. Finally, the consistent stiffness matrix due to the hydrodynamic and hydrostatic forces is meticulously evaluated considering both the cases of a completely submerged element and of a piercing beam. INTRODUCTION Commonly, for the analysis of offshore and space structures, three dimensional beam elements that undertake finite displacements may be applied. Currently, there are several models in the literature for the structural dynamic analysis of flexible beams (e.g. Le et al., 2014; Hsiao et al., 1999; Crisfield et al., 1997; Ibrahimbegovic and Mikdad, 1998; Cardona and Geradin, 1988; Simo and Vu-Quoc, 1986). Especially, the papers of Le et al. (2014), Hsiao et al., (1999) and Crisfield et al., (1997) refer to corotational formulations of spatial beams for pure structural applications. However, it seems that only the investigation of Crisfield et al., (1997) was extended to consider the existence of the fluid. The extended model was presented in Yazdchi and Crisfield (2002) with application to marine pipes and risers. Of course there are other dynamic formulations that use other methods than the corotational one for the analysis of flexible structures considering the fluid environment (e.g. for risers: Felippa and Chung 1981; O'Brien et al . 1988; Kordkheili et al . 2011).

Proceedings Papers

Paper Number: ISOPE-I-18-679

... and laboratory test data shows good agreement. KEYWORDS: Free fall penetrometer (FFP); Ball penetrometer; Numerical analysis; Finite element; Large deformation; coupled Eulerian Lagrangian (CEL). NOMENCLATURE A Projected area of the ball B1, B2 Exponent of the power law

**expression**C1, C2 Constant of...
Abstract

ABSTRACT Coupled Eulerian Lagrangian technique is employed in finite element analysis (FEA) of free fall penetration of a ball penetrometer in clay. An energy-based methodology is proposed to estimate final depth of penetration d p of the penetrometer. FEA results are analyzed using the proposed methodology and d p values are derived for a range of values of relevant parameters (i.e., mass, diameter and impact velocity of the penetrometer and shear strength of soil). This methodology can be used to select optimal values of test parameters for achieving a desired depth of penetration. Comparison of numerical predictions with published field and laboratory test data shows good agreement. INTRODUCTION Strength characterization of seabed soil is essential for safe design, installation and operation of offshore hydrocarbon extraction facilities. However, extraction of undisturbed soil samples from deep water seabed is extremely difficult due to the presence of very soft soil deposits. Hence, in situ soil strength characterization has long been preferred by the offshore geotechnical community. Conventional in situ soil strength characterization techniques used in the harsh offshore conditions are not simple either. Moreover, such exploration techniques require specialized driving machinery that makes the testing program time consuming and expensive. Owing to the simplicity of use and time- and cost-efficiency of the test procedure, free fall penetrometers (FFP) may offer pragmatic solution to problems associated with conventional in situ offshore site exploration techniques. FFPs are first lowered into the water from a moving or stationary vessel and then released (with zero initial velocity) from a certain height above the seabed to fall under gravity. FFP accumulates velocity, due to gravitational acceleration, during its ‘free’ fall through water and hits the seabed with a certain impact velocity. Apart from hydrodynamic factors, the impact velocity depends on the height (above the seabed) of fall, mass and shape of the FFP tool. After the impact, the FFP tool penetrates through the seabed and starts decelerating due to the resistance offered by the soil. The penetration process continues until the tool comes to a complete halt, i.e., when FFP velocity becomes equal to zero. FFPs are generally used for soil characterization of a few meters below the mudline. This shallow seabed characterization aids in the design of several subsea infrastructure facilities such as oil well heads and pipeline end terminals, which are embedded to very shallow depths, and pipelines that run through several kilometers on the seabed. The major potential application of FFPs is thus in characterization, down to shallow depths, of a very large area of deep water seabed. FFPs of different shapes and sizes have been developed and tested in the field. Some of the commonly adopted geometries are ball without shaft - e.g. Instrumented Free Fall Sphere or IFFS (Morton et al., 2016), cylindrical shaft with conical tip - e.g. Free Fall Cone Penetrometer or FFCPT (Stegmann et al., 2006), Nimrod (Stark et al., 2017), and thin cylindrical shaft with plate tip - e.g. Seabed Terminal Impact Naval Gauge or STING (Mulhearn, 2003). Attached sensors (e.g., accelerometer, load cell) continuously record data during FFP penetration. Recorded data are used to derive soil shear strength profile using force equilibrium method (Jeanjean, 2012; Morton et al., 2016; Chow et al., 2017) or energy balance method (Mana et al., 2018). The final depth of FFP penetration can also be derived from recorded accelerometer data.

Proceedings Papers

Paper Number: ISOPE-I-18-168

... al (2013), Ma et al (2017), Ma et al (2018). The Froude number F is defined as F V/ gL (1) where g denotes the acceleration of gravity. Within the framework of linear potential flow theory considered here, the flow created by the ship can be formally

**expressed**as the sum of a non-oscillatory local...
Abstract

ABSTRACT The important basic practical problem of filtering inconsequential short waves that have no significant influence upon the wave drag of a ship that travels at a constant speed in calm water of large depth is considered. This problem is an essential and nontrivial element of the prediction of ship waves within the Neumann-Michell theory, a practical theory useful for routine applications to ship design. A simple analytical relation that explicitly determines the wavenumber of insignificant short waves in terms of the Froude number and three main parameters that characterize the ship hull shape is given. This relation is obtained via a parametric numerical analysis, based on the classical Hogner potential flow model, for a wide range of Froude numbers and thirty hull forms associated with a broad range of nondimensional hull-shape parameters. The relation provides a reliable and particularly simple way of filtering inconsequential short waves that have no appreciable influence upon a ship drag. INTRODUCTION The flow around a ship of length L that travels at a constant speed V along a straight path, in calm water of large depth and horizontal extent, is considered within the classical framework of linear potential flow theory, which is realistic and useful for most practical purposes as is well documented; e.g. Noblesse et al (2013a), Huang et al (2013), Yang et al (2013), Ma et al (2017), Ma et al (2018). The Froude number F is defined as (equation) where g denotes the acceleration of gravity. Within the framework of linear potential flow theory considered here, the flow created by the ship can be formally expressed as the sum of a non-oscillatory local flow component that vanishes rapidly away from the ship and a wave component, dominant in the far field as well as in the nearfield. The local flow component can be evaluated in a straightforward manner, as is shown in Noblesse et al (2011), Wu et al (2016), and is not considered here. The ship waves can be expressed as a linear Fourier superposition of elementary waves, and can also be evaluated very simply via the classical Fourier-Kochin approach; e.g. Noblesse et al (2013a), Huang et al (2013), Zhu et al (2017).

Proceedings Papers

Paper presented at the The 27th International Ocean and Polar Engineering Conference, June 25–30, 2017

Paper Number: ISOPE-I-17-480

... based on modified

**expressions**of the semi-empirical Morison s equation (Morison et al. 1950). The pure Morison s equation evaluates the hydrodynamic force for vertical cylinders that are stationary. Modifications can be applied to overcome those limitations. Specifically, for the case of a randomly...
Abstract

ABSTRACT The present paper aims mainly at developing a finite beam element that could be applied for the analysis of flexible offshore structures, such as deep water ones of frame type, and the mooring lines of floating structures. The first goal of the paper, is to form the dynamic matrices, i.e. inertia force vector and mass matrix for a corotational beam element. This element can undergo large rotations and translations, but small strains. The second goal of this work, is to extend the proposed structural model in order to consider a fluid surrounding the system studied. Specifically, an equation of the applied hydrodynamic force is used applicable to a beam element arbitrarily oriented. Furthermore, for the beam element, the added mass of the fluid is considered within the element's mass matrix, which is formed through the usage of the element's shape functions. A numerical example is presented that illustrates the efficiency of the pure structural model within the field of large displacements. Finally, a second problem concerning fluid-structure effects is also studied numerically. INTRODUCTION Three dimensional beam elements that undertake displacements unrestricted in size may be applied for the modeling of members of offshore and space structures. Currently, several models exist in the literature regarding the structural dynamic analysis of flexible beams (e.g. Crisfield et al., 1997; Ibrahimbegovic and Mikdad, 1998; Cardona and Geradin, 1988). However, those works, have not been extended to consider the existence of the fluid. On the other hand, there are also dynamic formulations for the analysis of flexible structures considering the fluid environment (e.g. for risers: Felippa and Chung 1981; O'Brien et al. 1988; Kordkheili et al. 2011). The present paper extends a pure structural model of a static beam element to the dynamic regime. Then, the structural model is extended to consider the motion of the beam within a moving fluid. The model for the pure structural analysis is based on the corotational theory. The term corotational is consistent with the idea that a local frame is applied which is able to translate and corotate with the element in order to track its deformation; this allows the decomposition of the total motion of the element into a rigid body motion and a deformational one. This is a great advantage, as the geometric nonlinearity, imposed by the large motion of the element, takes place only during the rigid body motion. The static terms of the model are evaluated based mainly on the work of Nour-Omid and Rankin (1991). The first goal of this paper is to derive the dynamic terms where special care was taken to end up to concise mathematical equations. Only the dynamic terms of the formulation have integrals and they were appropriately handled to confine the pure integrable quantities and then to evaluate them analytically. The previous actions enhance the computational efficiently of the proposed model. The set of equations are highly nonlinear and for this reason they are solved using the Newton-Raphson iterative procedure, while through the linear approximation of the set of equations the effective stiffness matrix for the corotational beam element was evaluated. In the analysis of offshore structures it is important to use formulations which account for torsional-bending coupling (e.g. Felippa and Chung 1981). The present structural model accounts for this coupling and this is validated through a relevant numerical example. It should be noted that the proposed structural model is applicable to beam elements with geometric nonlinearity but without surrounding fluid. The second goal of the paper is the extension of the structural model to consider fluid motion around the beam and also the motion of the beam within the fluid.

Proceedings Papers

Paper presented at the The 27th International Ocean and Polar Engineering Conference, June 25–30, 2017

Paper Number: ISOPE-I-17-159

... loading duration for the maximum deflection approximately equals the reciprocal of the square root of the ratio of their yield stresses. The

**expression**forms of the dimensionless saturated permanent deflection and the dimensionless saturated impulse for the maximum deflection of a square plate are...
Abstract

ABSTRACT This paper studies the relationship of the saturated impulse between square plates made of steels with various yield stresses. Material of square plates is assumed to be elastic, perfectly plastic. Finite element (FE) code ABAQUS is employed to simulate the elastoplastic response of plates under uniform rectangular pressure pulse. The quantitative relationships of the saturated permanent deflection and the saturated loading duration for the maximum deflection between various yield stress-steel plates are obtained, in which the plates have the same size and are under the same magnitude of loading. For different steel square plates with various yield stresses under a pressure amplitude, provided a rupture failure does not occur the ratio of their saturated permanent deflection approximately equals the reciprocal of the ratio of their yield stresses; the ratio of their saturated loading duration for the maximum deflection approximately equals the reciprocal of the square root of the ratio of their yield stresses. The expression forms of the dimensionless saturated permanent deflection and the dimensionless saturated impulse for the maximum deflection of a square plate are proposed. The dimensionless saturated permanent deflection is a power function of the dimensionless pressure amplitude. The dimensionless saturated impulse for the maximum deflection is linearly related to the dimensionless pressure amplitude. Some fitting formulae for the deflection and saturated impulse are proposed. Finally, an estimation of the dimensionless pressure amplitude for the onset of failure Mode 2 indentified by Menkes and Opat (1973) for a square plate by using a rigid-plastic procedure is made and its comparison with prediction from elastoplastic finite element model (FEM) is satisfactory. INTRODUCTION The design process for structures often requires an estimate of the response for large dynamic loadings arising from impact and/or explosive events so that many efforts have been focused on the analysis of dynamically loaded structural elements. Saturated impulse phenomenon is a characteristic of the response of plates subjected to a pulse loading when large inelastic deformation occurs. The concept is that if a plate is subjected to a rectangular pressure pulse with a sufficiently long duration, then only an early part of the pulse contributes to the maximum and permanent deflections of the plate, and the rest of the loading pulse will cause no further increase of these deflections.

Proceedings Papers

Paper presented at the The 27th International Ocean and Polar Engineering Conference, June 25–30, 2017

Paper Number: ISOPE-I-17-149

... (see «Ice conditions For calculating of ice load on an isolated support of cylindrical (in plan) configuration the extra factors of shape are introduced which results in 1.5 increase of load. Defined Ice load obtained by the given

**expressions**(1) must not be greater than the Ice load defined by the...
Abstract

ABSTRACT Effect of ice load on shell structures with infill on compressible soil is considered in this article. These structures are used as support in the construction of various coastal infrastructure projects. Local soil conditions may require the construction of these shell gravity structures on compressible foundation soils. Also such structures may be exposed to severe climatic conditions, e.g., coastal infrastructure facilities of oil and gas exploration on the shelf of the Arctic and subarctic seas. The numerical model is proposed, which takes into account the interaction between soil environment, effect of ice load and thin shell with infill, to predict the stability and durability of shell structures under ice load. As the result of calculation analysis the necessity of cyclic loads accounting when evaluating stresses and strains in the components of "shell with infill - compressible soil" system has been shown. INTRODUCTION Thin shell structures with infill are very rational composite hydraulic engineering structures commonly used in waterfronts and offshore as retaining walls, breakwaters, and berth foundations. They effectively combine the benefits of low-cost infill with shell material which restrains the infill, forming a massive gravity structure. The shell component can be made up of either one large circular piece (Tsimbelman et al., 2015) or of individual sheet piles installed to form the shell, i.e. cellular cofferdam (Iqbal, 2009). In addition, the circular shell structures have been used in wide variety of applications by various industries. For instance, in mechanical and energy industry they are used for storage and transportation of various liquids, such as fuel (in the form of tank, rocket body, pipeline, and solid-propellant motor). In civil engineering, they are mainly used as massive earth retaining or bearing structures, where infill occupies considerable volume of the whole structures. The infill material can be different types of soil and/or concrete. The shell is made of a more durable material, such as concrete, steel sheet piles, steel sheet, or plastic materials.

Proceedings Papers

Paper Number: ISOPE-I-17-383

... defined for variables in the datasets when the

**expression**of model is unknown. The approach can be straightforwardly applied to datasets. At the underwater vehicle system discovery for model parameters and model structure, there is a set of possible functions that could be created. The model of underwater...
Abstract

ABSTRACT Models for underwater vehicles explaining its relationship between movement and the force exerting on the robot permit a wide range of development to be used in control and navigation. On the premise of previous evidence, system identification is usually utilized to explore the empirical data by determining coefficients in the equation. However, no general method arrives a better model with structure and parameters for vehicles automatically when laws underlying vehicle models and laws reflecting the underwater environment are unknown. In this work, symbolic regression based on genetic programming is adopted to discover the representation and parameters of vehicle model via mining dataset. The solution for the six degree of freedom of underwater vehicle model can be obtained via evolution after function set and terminals set are chosen. Results show that it achieves an more general, accurate model and less optimization time than parameter identification methods like Levenberg-Marquardt algorithm. INTRODUCTION The concept of models has been used to represent an observable state of a system in many scientific domains, where the models are usually seen as the generative process(Menezes and Roth, 2014). The generative processes consist of an approximated model that appears to describe the relationships between states, forces, moments and environments when systems are not understood clearly. Although current technological advances have been making it much easier to collect datasets for underwater vehicles system, it is difficult to extract models from this data without knowing the specific mathematical structure of model. This difficulty can be attributed both to the quality of massive data and to the non-linear dynamics of many of these complex systems, which cannot be defined as the object function. Another difficulty is brought by the mapping between the models and data since there is a generative process in environments vehicle operates. To address this the novel symbolic regression machine learning method are introduced in this article. An obscure relationship are defined for variables in the datasets when the expression of model is unknown. The approach can be straightforwardly applied to datasets. At the underwater vehicle system discovery for model parameters and model structure, there is a set of possible functions that could be created. The model of underwater vehicle becomes fully defined if it provides a way to prefer some better equations over the others. In addition to the precise model obtained by identifying key parameters in equation of underwater vehicle, a very simple one only laying some variables of the datasets can also be created without knowing the mapping between. Besides, the simple equation can be treated as simplification of complicated system model for control scheme.

Proceedings Papers

Paper Number: ISOPE-I-17-533

..., because of existence of the flare, an accurate and stable free surface updating scheme is required in nonlinear time-domain simulation.

**expression**geometry upstream oil & gas nonlinear wave diffraction computational domain reservoir simulation waterline wave elevation time history...
Abstract

ABSTRACT Interactions between water waves and non-wall-sided structures are analyzed based on fully nonlinear potential theory. Arbitrary Lagrangian Eulerian (ALE) formulation is used for tracing markers on free surface as well as wave-body intersections. The feature of ALE is that complex mesh is generated only once at the beginning and fluid marker is moved along prescribed path at all other time steps. Since the prescribed path for each marker is equidistantly arranged, at any instant, the relative positions of adjacent markers are well maintained, and thus good mesh quality can be guaranteed throughout the computation. In order to trace the exact wave-body intersections i.e. waterline, the marker (intersection) is enforced to move along cross section line of body surface, which can take into account complex body geometry above still waterline. In the computation, HOBEM and 4th-order Runge-Kutta method are adopted as initial boundary value problem (IBVP) solver. For improving computational efficiency, the total velocity potential is split into incident wave component and disturbed one. In this paper, we focus on diffraction of nonlinear waves by non-wall-sided structures. As a validation, we firstly study the diffracted waves by a circular cylinder. And then, the cases that circular cylinders with different flares are studied. To prove capacity of current scheme, nonlinear wave diffraction by ship geometry is also studied and by comparison with our experiment, pronounced agreement is achieved. INTRODUCTION In industry of ocean engineering, flared geometry may arise in design of fixed offshore structures and/or moving ships. An example is the Draugen oil production platform which was installed in the Haltenbanken area of the Norwegian Sea in 1993 (Wang, Wu and Drake, 2007). The platform has a prestressed concrete monotower substructure with a flare above the mean sea level to provide efficient support for the integrated topside facilities. Simulations that take into account the geometry of non-wall-sided bodies in steep waves are important in these cases. However, because of existence of the flare, an accurate and stable free surface updating scheme is required in nonlinear time-domain simulation.

Proceedings Papers

Paper presented at the The 26th International Ocean and Polar Engineering Conference, June 26–July 2, 2016

Paper Number: ISOPE-I-16-674

... effective, fracture assessments of girth welds in lined pipes become more complex due to the dissimilar nature of these materials. piping design growth resistance curve configuration procedure upstream oil & gas

**expression**thickness fracture mechanics evaluation hydraulic fracturing...
Abstract

Abstract This work presents an exploratory experimental investigation of the ductile tearing properties for the girth weld of a typical CMn pipe internally clad with a nickel-chromium corrosion resistant alloy (CRA) using crack growth resistance curves (J -Δ a curves). Here, the material of the external pipe is an API 5L Grade X65 pipeline steel whereas the inner clad layer is made of ASTM UNS N06625 Alloy 625. Unloading compliance (UC) testing of the pipeline girth welds employed side-grooved, clamped SE(T) specimens with a weld centerline notch to determine the crack growth resistance curves. This exploratory experimental characterization provides additional toughness data which serve to evaluate the effectiveness of current procedures in determining experimentally measured R -curves for this class of material. INTRODUCTION The increasing demand for energy and natural resources has spurred a flurry of exploration and production of oil and natural gas in more hostile environments, including very deep water offshore hydrocarbon reservoirs. One of the key challenges facing the oil and gas industry is the assurance of more reliable and fail-safe operations of the infrastructure for production and transportation. Currently, structural integrity of submarine risers and flowlines conducting corrosive and aggressive hydrocarbons represents a key factor in operational safety of subsea pipelines. Advances in existing technologies favor the use of CMn steel pipelines either clad or mechanically lined with corrosion resistant alloys (CRA), such as ASTM UNS N06625 Alloy 625 (American Society for Testing and Materials, 2009, 2011a), for the transport of corrosive fluids. Accurate measurements of fracture resistance properties, including crack growth resistance curves of the girth weld material, become essential in defect assessment procedures of the weldment region and the heat affected zone, where undetected crack-like defects (such as lack of penetration, deep undercuts, root cracks, etc.) may further extend due to to the high tension stresses and strains. However, while cost effective, fracture assessments of girth welds in lined pipes become more complex due to the dissimilar nature of these materials.

Proceedings Papers

Paper presented at the The Twenty-fifth International Ocean and Polar Engineering Conference, June 21–26, 2015

Paper Number: ISOPE-I-15-626

... also on loading cycles based on the observation of experiments. Unlike the classical formulation involving only the mean load, a new empirical

**expression**which takes into account of all three parameters including mean load, strain amplitude and loading cycles is employed into the mooring analysis model...
Abstract

Abstract Synthetic fiber ropes e.g. polyester, aramid and HMPE ropes, as the main component of the taut mooring systems, have totally different mechanical properties i.e. tension-elongation relationship compared with the steel mooring chain and wire ropes especially under cyclic loading conditions induced by the combined effects of wind, wave and current. Dynamic stiffness has to be modelled to represent the dynamic effect of the tension-elongation properties of the fiber ropes. Indeed, the dynamic stiffness is dependent not only on the mean load, strain amplitude or load amplitude, but also on loading cycles based on the observation of experiments. Unlike the classical formulation involving only the mean load, a new empirical expression which takes into account of all three parameters including mean load, strain amplitude and loading cycles is employed into the mooring analysis model. The iteration process is performed based on the update of the mean load for the calculation of the stiffness until it is converged. The mooring lines utilizing the three materials including polyester, aramid and HMPE fiber ropes are analyzed by the mooring analysis method. The effects of all the parameters especially the loading cycles are investigated and compared with other traditional empirical expressions of the dynamic stiffness. It is demonstrated that the loading cycles have obvious influence on the axial tension response at the fairlead due to the increase of more than 10% brought to the dynamic stiffness with the loading process.

Proceedings Papers

Paper presented at the The Twenty-fifth International Ocean and Polar Engineering Conference, June 21–26, 2015

Paper Number: ISOPE-I-15-424

... model and various parametric effects analysis, the explicit

**expression**of weld toe magnification factor (MK) is acquired by surface fitting. So, the simple method to calculate SIF at the deepest point enable to be realized when the MCOD is known. And then, this method is demonstrated to be suitable for...
Abstract

Abstract This paper presents a new method to evaluate the stress intensity factor at the deepest position for welded plate joints with semi-elliptical surface crack in tension, based on maximum crack opening displacement (MCOD) of surface crack. T-butt plate joints are chosen as research objects, and series of values of MCOD and stress intensity factor (SIF) at the deepest point are obtained by finite element method. Subsequently, by the proposed method to calculate SIF by MCOD for the surface cracked finite plate model and various parametric effects analysis, the explicit expression of weld toe magnification factor (MK) is acquired by surface fitting. So, the simple method to calculate SIF at the deepest point enable to be realized when the MCOD is known. And then, this method is demonstrated to be suitable for any form of plate joints.

Proceedings Papers

Paper presented at the The Twenty-fifth International Ocean and Polar Engineering Conference, June 21–26, 2015

Paper Number: ISOPE-I-15-273

.... breakwater

**expression**geometry equation safety factor rubble mound foundation losada caisson breakwater interaction reservoir simulation stability goda foundation hs 0 variability displacement water level prediction realization engineering The Role of Uncertainty in the Wave-Caisson...
Abstract

Abstract Knowledge of the magnitude and behaviour of sea waves at the project site is an essential for design of coastal protection structures, however, naturally the waves are complicated by be irregular and random. Hence, in order to assess the uncertainty in the displacements failures predictions, Monte Carlo simulations are employed to conduct fortyfive realizations, corresponding to the same energy density spectra (JONSWAP) but employing different random phases. Finally, new parameterization for sliding, that include the uncertainty bounds in their prediction, are presented.

Proceedings Papers

Paper presented at the The Twenty-fourth International Ocean and Polar Engineering Conference, June 15–20, 2014

Paper Number: ISOPE-I-14-301

... electrical resistivity survey drilling fluid management & disposal water content shinichi ito 1 estimation upstream oil & gas drilling fluids and materials reservoir characterization specific resistance specific resistivity underground temperature kazuhiro oda 1 log analysis

**expression**...
Abstract

Abstract In recent times, shallow landslides have occurred at many locations in Japan. One cause of shallow landslides is a drop in effective stress due to rainwater penetration into the ground. It is therefore important to understand the behavior of water in the ground. In this study, the estimation of volume water content was carried out using a resistivity survey based on the results of a field survey. These results indicate that the relationships between ground temperature and specific resistivity are different in each range in volume water content. It is necessary to correct the specific resistivity using underground temperature. As a result of the correction, this study shows that it is possible to estimate volume water content from resistivity.

Proceedings Papers

Paper presented at the The Twenty-third International Offshore and Polar Engineering Conference, June 30–July 5, 2013

Paper Number: ISOPE-I-13-245

... previous results and theory. subsea system

**expression**artificial intelligence logarithmic function loading cycle renewable energy cyclic test displacement rotation relative density one-way loading deformation correlation coefficient roesen leblanc setup loading wind energy load...
Abstract

ABSTRACT Offshore wind turbines are normally founded with large diameter monopiles and placed in rough environments subjected to variable lateral loads from wind and waves. A long-term lateral loading may create rotation (tilt) of the pile by change in the pile-soil system which is critical in the serviceability limit state. In this paper small-scale testing of a pile subjected to cyclic, lateral loading is treated in order to investigate the effect of cyclic loading. The test setup, which is an improvement of a previous setup, is described and the first results of testing are compared with previous results and theory.