bluuebunny/crossref_metadata_2025 huggingface dataset:
Multicriteria Optimization for System Configuration Using Monte Carlo Simulation and RAM Analysis
Authors: Schleder Adriana Miralles , Araujo Paula Cyrineu , Martins Marcelo Ramos
Published: October 2016

Currently, engineers should to deal with conflicting objectives, especially concerning safety and economics constraints. It is necessary to take into account performance indicators like reliability and availability coupled with economic criteria such as the costs of acquisition, maintenance and plant downtime. This paper aims at bringing up a rational process of selecting the optimal configuration of the system in the preliminary design phase considering these conflicting indicators.

Here, it is proposed a coupled approach using Monte Carlo Simulation and Genetic Algorithms to define the system configuration and the time interval between preventive maintenances in order to maximize the availability and the expected profit with the system operation considering possible constraints about the number of maintenance teams.

The approach proposed in this paper has shown to be promising for solving complex system design related to realistic scenarios in which conflicting performance and economic objectives must be taken into account.
Numerical Study of Wave-Driven Impact of a Sea Ice Floe on a Circular Cylinder
Authors: Su Biao , Aarsæther Karl Gunnar , Kristiansen David
Published: October 2016

This paper presents a numerical model for simulating wave-driven ice floe–structure interactions, which is integrated in a software framework (FhSim) for time-domain simulation of marine systems. The FhSim framework has proved to be a valuable tool for research and development within different applications and areas [1]. In this study, the wave-driven impact of a sea ice floe on a circular cylinder is simulated. The simulation setup refers to a recent experimental study [2], and the kinematics of ice floe in wave is compared with the experimental result. As the impact forces were not measured in the experiment, a closed-form analytical solution proposed by ISO/FDIS 19906 (Arctic offshore structures) is used for comparison. These comparisons indicate that the present numerical model is able to reproduce the ice floe kinematics and impact characteristics during floe–structure interaction. Furthermore, a sensitivity analysis is conducted, aimed at investigating how much the simulated impact force is affected by variations in the pressure–area relationship.
Buckling/Ultimate Strength Evaluation for Continuous Stiffened Panel Under Combined Shear and Thrust
Authors: Ogawa Hiroaki , Takami Tomoki , Tatsumi Akira , Tanaka Yoshiteru , Hirakawa Shinichi , Fujikubo Masahiko
Published: October 2016

In this study, FE modeling method for the buckling/ultimate strength analysis of a continuous stiffened panel under combined shear and thrust is proposed. In order to validate the proposed method, shear buckling collapse tests of a stiffened panel and FEM analysis are carried out. As the result of these, it is confirmed that the buckling collapse behavior and the ultimate strength estimated by the proposed method are in good agreement with the test results.
Drilling Riser Model Tests for Software Verification
Authors: Yin Decao , Lie Halvor , Russo Massimiliano , Grytøyr Guttorm
Published: October 2016

Marine drilling riser is subject to complicated environmental loads which include top motions due to Mobile Offshore Drilling Unit (MODU), wave loads and current loads. Cyclic dynamic loads will cause severe fatigue accumulation along the drilling riser system, especially at the subsea well head (WH).

Statoil and BP have carried out a comprehensive model test program on drilling riser in MARINTEK’s Towing Tank in February 2015. The objective is to validate and verify software predictions of drilling riser behaviour under various environmental conditions by use of model test data.

Six drilling riser configurations were tested, including different components such as Upper Flex Joint (UFJ), tensioner, marine riser, Lower Marine Riser Package (LMRP), Blow-Out Preventer (BOP), Lower Flex Joint (LFJ), buoyancy elements and seabed boundary model.

The drilling riser models were tested in different load conditions:

1. Forced top motion tests

2. Regular wave test

3. Combined regular wave and towing test

4. Irregular wave test

5. Combined irregular wave and towing test

6. Towing test (VIV)

Measurements were made of micro bending strains and accelerations along the riser in both In-Line (IL) and Cross-Flow (CF) directions. Video recordings were made both above and under water.

In this paper, the test set-up and test program are presented. Comparisons of results between model test and RIFLEX simulation are presented on selected cases. Preliminary results show that the drilling riser model tests are able to capture the typical dynamic responses observed from field measurement, and the comparison between model test and RIFLEX simulation is promising.
Deformation of the Wave Field Interacting With Offshore Platforms: Comparison Between the Corresponding Results From a Numerical Model and a Wave Tank
Authors: Zaman M. Hasanat , Akinturk Ayhan
Published: October 2016

In the present research, a 3D dispersive numerical model has been developed and utilized to study the modification of the wave field in the presence of offshore structure. The Alternating Direction Implicit (ADI) algorithm has been employed for the solution of the governing equations. Relevant experiments are carried out in the Offshore Engineering Basin (OEB) of National Research Council (NRC) Canada. OEB is a 3D heavy duty 75m × 32m × 2.8m test facility equipped with modern data acquisition and tracking devices to record experimental data. Total 10 wave probes are deployed to measure the data at different locations in the Basin. Later the numerical results are compared with the experimental results. The comparisons of the numerical results show great agreement with the experimental results.
Numerical Study on Added Resistance Computations in Short Waves
Authors: Zhang Xinshu , Tian Kang , You Yunxiang
Published: October 2016

Evaluation of added resistance in short waves is critical to the assessment of the global performance of a ship traveling in a seaway. In this paper, three methods of added resistance evaluation in short waves are briefly reviewed, including those proposed by Fujii & Takahashi [1], Faltinsen et al. [2], and Kuroda et al. [3]. Based on the experimental data collected by Kuroda et al., a new method is developed for the estimation of added resistance in short waves. The proposed method is validated by comparing the obtained numerical results with experimental data and other numerical solutions for different types of hulls, including the Wigley hull I, KVLCC2 hull, Series 60 hull with CB = 0.7, and the S-175 hull. The present study confirms that the developed method can well predict the added resistance in short waves and complement the three-dimensional Rankine panel method developed in a previous study focusing on intermediate and long waves.
Inelastic Analysis of the SENT Specimen of X80 Pipe for Strain Capacity Evaluation
Authors: Cho Woo-Yeon , Kim Ki-Seok , Lee Jae Hyuk , Yoon Young-Cheol
Published: October 2016

Strain capacity of the X80 line pipe with girth weld has been frequently evaluated from the SENT (Single Edge Notch Tension) test for the strain-based design (SBD). Also, it can be predicted from CWPT (Curved Wide Plate Test) and full scale test, which demand much larger scale test environment and higher costs in comparison to SENT test. On this scenario, well-developed numerical scheme can be a very useful tool for the strain capacity evaluation. The numerical scheme should be equipped with appropriate material models and inelastic analysis procedure to simulate the nonlinear behavior of the SENT specimen; in fact, the SENT specimen is expected to properly describe the defect in the girth weld part by using a notch. In this paper, for the validation of tensile strain capacity (TSC) of X80 line pipe, a phenomenological model, which is based on the GTN (Gurson-Tvergaard-Needleman) model, is developed and verified through the comparison with experimental results. The material model is implemented in the commercial finite element program ABAQUS with the aid of the user-defined material module. Calibration of material parameters expressing elastic and plastic behaviors of base and weld metals are done on the basis of the round-bar and full thickness tensile test results, and then the finite element simulations for SENT tests are carried out to predict the TSC. To ensure the reliability of the nonlinear procedure, the predicted strain capacities are compared with the test results as well as those obtained by the conventional design formulae, which are established from statistical analysis of numerous line pipe test data; then application of the nonlinear procedure is extended to the CWPT simulation. In some cases, damping effect was introduced to improve the convergence of iterative nonlinear solution. As a result, the developed nonlinear procedure acquires reliability and accuracy enough to be applied to the strain-based design process. Thus, it is highly expected that the procedure can be used in various numerical evaluations of strain capacity of line pipes with girth welds.
Determining Side-by-Side Current Loads Using CFD and Model Tests
Authors: Koop Arjen
Published: October 2016

When two vessels are positioned close to each other in a current, significant shielding or interaction effects can be observed. In this paper the current loads are determined for a LNG carrier alone, a Shuttle tanker alone and both vessels in side-by-side configuration. The current loads are determined by means of tow tests in a water basin at scale 1:60 and by CFD calculations at model-scale and full-scale Reynolds number.

The objective of the measurements was to obtain reference data including shielding effects. CFD calculations at model-scale Reynolds number are carried out and compared with the model test results to determine the capability of CFD to predict the side-by-side current load coefficients. Furthermore, CFD calculations at full-scale Reynolds number are performed to determine the scale effects on current loads.

We estimate that the experimental uncertainty ranges between 3% and 5% for the force coefficients CY and CMZ and between 3% and 10% for CX. Based on a grid sensitivity study the numerical sensitivity is estimated to be below 5%. Considering the uncertainties mentioned above, we assume that a good agreement between experiments and CFD calculations is obtained when the difference is within 10%.

The best agreement between the model test results and the CFD results for model-scale Reynolds number is obtained for the CY coefficient with differences around 5%. For the CX coefficient the difference can be larger as this coefficient is mainly dominated by the friction component. In the model tests this force is small and therefore difficult to measure. In the CFD calculations the turbulence model used may not be suitable to capture transition from laminar to turbulent flow. A good agreement (around 5% difference) is obtained for the moment coefficient for headings without shielding effects. With shielding effects larger differences can be obtained as for these headings a slight deviation in the wake behind the upstream vessel may result in a large difference for the moment coefficient.

Comparing the CFD results at full-scale Reynolds number with the CFD results at model-scale Reynolds number significant differences are found for friction dominated forces. For the CX coefficient a reduction up to 50% can be observed at full-scale Reynolds number. The differences for pressure dominated forces are smaller. For the CY coefficient 5–10% lower values are obtained at full-scale Reynolds number. The moment coefficient CMZ is also dominated by the pressure force, but up to 30% lower values are found at full-scale Reynolds number. The shielding effects appear to be slightly smaller at full-scale Reynolds number as the wake from the upstream vessel is slightly smaller in size resulting in larger forces on the downstream vessel.
Investigation on the Post-Ultimate Strength Behaviour of Damaged Stiffened Plate of Ship Structure
Authors: Xu Weijun , Yuan Minjie , Wang Xiaotian
Published: October 2016

Post-ultimate strength behaviour of ship structure can directly reflect its changing tendency of load carrying capacity. When the external load exerted on the ship structure exceeds the ultimate strength, sharply reduction of load carrying capacity will occur, especially for the damaged ship structure induced from grounding or collision. This paper focuses on the investigation on the post-ultimate strength behaviour of damaged stiffened plate of ship structure by using FEM, a series of stiffened plate modeling with different kinds of cracks are constructed. The parameters of crack includes length, width, depth, plate thickness and distribution direction. The post-ultimate strength behaviour of stiffened plate with cracks and intact ones are compared. Conclusion can be drawn as follows: (1) crack can induce the reduction of ultimate strength of stiffened plate, meanwhile, the stiffness and its load carrying capacity decrease accordingly. (2) in terms of stiffened thin plate, length of crack has a significant influence on the post-ultimate strength behaviour, the width of the crack has a huge influence on ultimate strength while the depth of crack has little influence; in terms of stiffened thick plate, the influence of crack depth on the post-ultimate strength behaviour becomes obvious. The width of the crack influence the post-ultimate strength behaviour a lot. (3) compare to the transverse crack, the influence of longitudinal crack on the post-ultimate strength behaviour is not obvious.
Springing Responses Analysis and Segmented Model Testing on a 550,000 DWT Ore Carrier
Authors: Li Hui , Wang Di , Zhou Cheng Ming , Zhang Kaihong , Ren Huilong
Published: October 2016

For ultra large ore carriers, springing response should be analyzed in the design stage since springing is the steady-state resonant vibration and has an important effect on the fatigue strength of hull structure. The springing response of a 550,000 DWT ultra large ore carrier has been studied by using experimental and numerical methods. A flexible ship model composed of nine segments was used in the experiment. The model segments were connected by a backbone with varying section, which can satisfy the request of natural frequency and stiffness distribution. The experiments in regular waves were performed and the motions and wave loads of the ship were measured. The experimental results showed that springing could be excited when the wave encounter frequency coincides with half or one-third the flexural natural frequency of the ship. In this paper, the analysis of the hydroelastic responses of the ultra large ore carrier was also carried out using a 3-D hydroelastic method. Comparisons between experimental and numerical results showed that the 3-D hydroelastic method could predict the motions and the vertical bending moments quite well. Based on this numerical method, the fatigue damage was estimated and the contribution of springing was analyzed.
Suction Bucket Foundations for Wind Energy Turbines: A Numerical Study With FEM
Authors: Dutto Paola , Baessler Matthias , Geissler Peter
Published: October 2016

Suction Bucket Jackets (SBJ) are found as a suitable alternative to driven piles for the support of jacket or tripod foundations for offshore wind energy converters. Offshore wind energy turbines are characterized by a small self weight and they can be subjected to different load combinations. The work presented here aims to show the numerical investigation on the behavior of suction bucket foundations under different kind of loads as well as load combinations. In order to do so, a suitable numerical model is much needed. The theoretical basis of the model lies on the Swansea formulation of Biots equations of dynamic poroelasticity combined with a constitutive model that reproduces key aspects of cyclic soil behavior in the frame of the theory of generalized plasticity. An adequate FE formulation, the representation of appropriate soil-structure interfaces and the computational efficiency are key aspects in order to successfully model such complex systems. The 3D numerical simulation allows a special insight into the fundamental behavior of the founding of Suction Bucket Jackets such as the evolution of the pore water pressure or the occurrence of the so called soil liquefaction.
Research on the Trend Toward Public Access to Canals in the Tokyo Waterfront Area
Authors: Sugahara Ryo , Kuroyanagi Akio
Published: October 2016

In recent years, great regard has been given to the participation of various administrative organizations, NPOs and local residents in coastal zone management. Following the formulation of the “Canal Renaissance Project (Tokyo Metropolitan Gov. Bureau of Port and Harbor, 2005)” as a step towards easing restrictions to vitalize canal spaces in the Tokyo waterfront area, local organizations are developing commercial and recreational uses of canal spaces. In this report, we have conducted field research and hearings with managers and business people in five regions of the Tokyo waterfront where the Canal Renaissance Project is being implemented. Through this research, we have observed the usage conditions of the canal spaces and how multiple organizations cooperate with each other, and attempt to identify problems associated with the use of canal spaces by local organizations. The results show that eased regulations on water area usage permissions have created new opportunities for local businesses, store associations and NPOs to utilize canals. By establishing floating restaurants and floating piers, waterfront areas have been developed with consideration for the spatial structure and surrounding area of canals in each region. We have observed a large variety of interactions between organizations and groups, and the establishment of a system centered on a committee made up of local businesses and residents in each region. However, we have also noted that due to the strong individuality of the projects carried out in each region, they have not lead to any inter-regional cooperation, thus not necessarily successfully utilizing the inherent spatial continuity of the canals. There have also been examples of complication of the committees that connect the local residents involved in the projects and the government. This is an issue in the management and operation of canal usage. From the aforementioned results, it is clear that the projects observed in canal usage under the eased regulations are organized such that they are directly carried out by committees, in a so-called “committee-based model.” There is no “local coordinator” present to handle the tasks of reconciling opinions between project leaders, applying for water area usage permission, maintenance of facilities, acceptance of new participants, and the like.
Assessment of Nonlinear Heave Damping Model for Spar With Heave Plate Using Free Decay Tests
Authors: Rao Mahesh J. , Nallayarasu S. , Bhattacharyya S. K.
Published: October 2016

Linear damping models have been used in the past for solving floating body dynamics, especially for simple geometries such as spar. However, due to the addition of heave damping elements to spar such as heave plate, complex flow around these elements may change the relationship between damping and velocity of the body to nonlinear. The damping plays a major role in accurate determination of motion response of spars, especially the heave. Free decay tests have been carried out for spar with and without heave plate in calm water condition. The Computational Fluid Dynamics (CFD) simulation of heave decay is carried out using ANSYS FLUENT and validated by free decay test results using scale models. Mesh convergence study has been conducted to determine the optimum mesh size. The heave motion obtained from CFD are used to derive the damping terms by matching the heave motion obtained using equation of motion by changing the damping term with linear, quadratic and the combination of linear and quadratic. The heave motion obtained from linear damping model matches well with that obtained from measured motion and CFD simulation for spar without heave plate. However, the linear / quadratic damping models alone are not suitable for spar with heave plate. Hence a combination of linear and quadratic damping model is proposed for spar with heave plate. The heave motion computed using a combination of linear and quadratic damping model matches well with that obtained from experimental studies and CFD simulations thus indicating the complexity of flow around heave plate in comparison to the spar alone. Further, the vortices around the spar models obtained from CFD simulations are also presented and discussed with regard to the higher order damping.
Real-Time Hybrid Model Testing of a Braceless Semi-Submersible Wind Turbine: Part I — The Hybrid Approach
Authors: Sauder Thomas , Chabaud Valentin , Thys Maxime , Bachynski Erin E. , Sæther Lars Ove
Published: October 2016

This article presents a method for performing Real-Time Hybrid Model testing (ReaTHM testing) of a floating wind turbine (FWT). The advantage of this method compared to the physical modelling of the wind in an ocean basin, is that it solves the Froude-Reynolds scaling conflict, which is a key issue in FWT testing. ReaTHM testing allows for more accurate testing also in transient conditions, or degraded conditions, which are not feasible yet with physical wind. The originality of the presented method lies in the fact that all aerodynamic load components of importance for the structure were identified and applied on the physical model, while in previous similar projects, only the aerodynamic thrust force was applied on the physical model. The way of applying the loads is also new. The article starts with a short review (mostly references) of ReaTHM testing when applied to other fields than marine technology. It then describes the design of the hybrid setup, its qualification, and discusses possible error sources and their quantification. The second part of the article [1] focuses on the performance of a braceless semi-submersible FWT, tested with the developed method. The third part [2] describes how the experimental data was used to calibrate a numerical model of the FWT.
Modeling and Simulation of the Accumulator During Active Heave Compensation Operations
Authors: Chu Yingguang , Æsøy Vilmar , Bunes Øyvind , Pedersen Eilif
Published: October 2016

The paper presents the modeling and simulation of the thermodynamics of the accumulator system of the heave compensation system. Heave compensators in offshore and subsea applications are used to reduce the relative vertical motion of the load caused by the vessel movement. The accumulator system is an integral part of the power system, which typically can be the hydraulic system of the crane cylinders or the winch motor. The accumulators are mainly used to reduce the power consumption during heave compensation through regenerating power. Hence, the working properties of the accumulator gas become important, and these properties are very dependent upon the temperature and pressure.

Modeling of the dynamics of the accumulator and the hydraulic system is complex due to the nonlinear characteristics of fluid dynamics and thermal processes. The derivation of the constitution formula for the accumulator dynamics is described, and the modeling is presented using the Bond Graph method. The implementation of the modeling and simulation is done in a software tool called 20-sim. The temperature and pressure variations of the accumulator during heave compensation were discussed considering the impacts of the heat transfer process and the pipe flow between the accumulator and the gas bank. Compared to the experimental testing data, the simulation results appear realistic and convincing. The simulation model provides useful information for system design and analysis.
Experimental Validation of a Nonlinear MPC Strategy for a Wave Energy Converter Prototype
Authors: Nguyen Hoai-Nam , Sabiron Guillaume , Tona Paolino , Kramer Morten Mejlhede , Vidal Sanchez Enrique
Published: October 2016

One of the major limitations to the development of advanced wave energy converters (WECs) control strategies are the associated computational costs. For instance, model predictive control (MPC) strategies have the potential to obtain almost optimal performance, provided that the imperfect power conversion in the power take-off (PTO) system is correctly taken into account in the optimization criterion and that the incoming wave force can be estimated and forecast. However, demanding computational requirements as well as the unresolved issue of wave force estimation have so far prevented real-time implementation and validation of such MPC strategies. In this paper, we present the successful experimental results obtained on a scaled-down prototype of the well-known Wavestar machine. Performance comparisons are provided for nonlinear MPC versus a reference PI controller.
Two Methods for the Inverse Estimation of Local Slamming Loads on a Jacket Structure
Authors: Tu Ying , Muskulus Michael , Grindstad Thorvald C.
Published: October 2016

This article illustrates two inverse methods to estimate the local slamming forces on a jacket structure. The experimental data from the hammer test and the wave test are used as the inputs. One method uses two deconvolution techniques: a conjugate gradient technique to solve the impulse response functions and a weighted eigenvector expansion technique to reconstruct the wave impact forces. The other method uses linear regression with the ordinary least square technique to estimate the wave impact forces. The results calculated with these two different methods are highly identical, which enhances the confidence in the result accuracy. The time series of the reconstructed forces are detailed at a millisecond level, which provides decent information on the shape of the forces. This capability enables the methods to be a very useful tool for the further investigations of the local slamming forces.
Calculations of Wave Loads on a Vertical Cylinder Using Potential-Flow and Viscous-Flow Solvers
Authors: Burmester Simon , Guérinel Matthieu
Published: October 2016

In this paper, potential-flow and viscous-flow (CFD) solvers are used to compute wave loads on a suspended surface piercing cylinder, for a Keulegan-Carpenter number of KC ≈ 5. After describing the numerical tools used (Wavec2Wire and Re-FRESCO), and the associated numerical settings, a calibration of the wave height and periods is made with basis on experimental data. On the viscous-flow CFD side, attention is also paid to discretization (space and time) and iterative errors, in order to keep the uncertainty of the calculations the lowest possible. Moreover, both a non-turbulent symmetric domain and a turbulent full domain CFD calculations are performed and compared. On the potential-flow side, calculations with and without considering additional-drag forces of the cylinder are conducted. In general, the comparison between potential and viscous-flow results show small differences, with a slightly better agreement between the viscous-flow results and experiments but with a significant increase on computational costs. For this particular case the consideration of turbulence and of additional-drag forces have negligible influence on the results obtained.
Investigation of Friction Stir Spot Welding Optimal Parameter Combination for Galvanized Trip Steel
Authors: Ratnayake R. M. Chandima , Suleymanov Magomed M. , Skedsmo Lars E. M. , Goa Vegard
Published: October 2016

Friction stir spot welding (FSSW) is performed on transformation-induced plasticity (TRIP) steel (HCT690T) sheets. The influence of parameters: rotational speed, dwell time plunge depth and plunge speed on a mechanical property of lap joints are investigated. An engineering robust design (ERD) approach has been utilized to design the experiment with L9 orthogonal array. In order to minimize the bias, each experiment has been repeated three times, resulting in 27 experiments. For each influence parameter, three levels have been identified (i.e. minimum, average and maximum) based on trial and error experimentation as well as utilizing published research data. The ultimate tensile load capacity (UTLC) of TRIP lap welded joints has been used to assess the joint performance and to calculate the signal-to-noise ratios. Based on the experimental results, optimal parameter levels have been investigated and theoretical joint strength under the optimal parameter settings has been calculated using the additive model proposed in the ERD. A verification experiment has been performed to validate the experimentally investigated optimal settings of FSSW.
Experimental Study on a New Suppressing Floating Device for the Membrane-Type LNG Tank
Authors: Yu Yue-min , Fan She-ming , Ma Ning
Published: October 2016

The membrane-type tank is widely used in LNG storage devices, which include FLNG, FSRU, LNGC, and so on, and sloshing is an internationally important research focus. The run-up along the side wall of the tank and impact will be produced. Many researchers have proposed a variety of suppressing measures to ensure the safety of the tank. Based on the principle of wave eliminating, a new idea is put forward in the vicinity of the liquid surface mounting the floating plate and the original free surface is divided into three sub-surfaces. In the present paper, we make a series of model experiments on the Six-DOF motion platform through changing the frequency of the excitation. As a result, the sloshing mode is separated into the U-tube mode, the separated-tank mode and the diffraction mode. The experiments indicate that the range of the amplitude as for the slamming pressure is much smaller than without the floating plate.
A Basic Study on Ship Speed Loss From the Viewpoint of Geographic Conditions and Ship Performance
Authors: Sasa Kenji , Lu Li-Feng , Chen Chen
Published: October 2016

Currently, for marine transportation, various factors have to be taken account of. Hence, it is necessary to understand the ship performance, especially under heavy sea conditions. In this study, measurement results for a 20,000 DWT class bulk carrier were analyzed, and eight events of remarkable speed loss in heavy seas were observed during the measurement period 20 months from July 2010. The variations in ship performance parameters were statistically analyzed, and a regression analysis was carried out. All cases of remarkable speed loss occurred in seas relatively close to lands (within 200 nautical miles). The magnitude of speed loss was larger in the Southern Hemisphere than in the Northern Hemisphere. This indicates that more accurate weather routing is necessary for the Southern Hemisphere, especially for evaluating ship performance from the viewpoint of intrinsic weather patterns.
Application of the Global Optimization Method to the Preliminary Design of Tension Leg Platforms
Authors: Kim Jeong-Du , Jang Beom-Seon
Published: October 2016

The TLP requires a complicated and time-consuming design process. Principal dimension of hull form and tendons should be carefully determined with the consideration of many design requirements which dominantly affect the safety of the platform. In this paper, a global optimization system for both the hull-form and tendon system is developed. The maximum heave response and total weight of hull and tendons are formulated as an objective function with the several constraints related to the safety of platform. In order to find a technically and economically feasible design, a modelling and assessment processes are fully automated, which enables the algorithm can controls the modelling and analysis process while varying a set of design parameters until it figures out an optimum design. Major design requirements related to the safety of platform is assessed by ultimate limit state (ULS) and fatigue limit state (FLS) approach to ensure the accuracy of analysis. In the ULS approaches, every safety requirement is checked on the basis of the most unfavorable environments. FLS approach is conducted for all tendons since they suffer cyclic deformation for their service life, which results in collapse of mooring system with the relatively small wave loads. In the optimization module, a better set of design parameters is investigated by using a simulated annealing (SA) algorithm. Throughout the optimization system, both the heave responses and total weight of hull and tendons are improved while satisfying the all constraints related to the design requirements.
Axial Load Transfer Characteristics of SCR Pipe-in-Pipe Vibration System With Different Diameter Ratio
Authors: Wang Wenming , Chen Yingchun , Li Haoran , Xiong Minghao
Published: October 2016

Coiled tubing technology can shorten the operating time of offshore oil and gas drilling or repair well, but due to the small stiffness of the coiled tubing, it is easy to cause the buckling in the process of entering the Steel Catenary Riser (SCR). So the research of its axial load transfer characteristics in riser is necessary. In this paper, the external excitation loads of current and ocean waves are analyzed. By building an indoor experiment platform with similarity theory, the influence of axial load transfer characteristics with the same external excitation is studied on different diameter ratio of SCR pipe-in-pipe vibration system. Through the above research, we can reduce the accidents of the riser and coiled tubing, and provide theoretical support and guarantee to the actual operation.
Investigation of the Effect of the Deck Simulator on the Shock Spectrum of Floating Shock Platform
Authors: Xiongliang Yao , Xiongwei Cui , Jun Wang , Wenqi Zhang
Published: October 2016

The investigation of the effect of the deck simulator on the shock spectrum of floating shock platform is conducted in this paper. Generally, the impact assessment tests of large-medium sized shipboard equipment are conducted on the floating shock platform. The structural form of the floating shock platform is similar to the barge’s structural form, with a strong double bottom which can ensure the safety of the bottom structure under the underwater explosion load. The tested equipment is fixed on the inner bottom plating as same as it is fixed on the real ship. It is obvious that there is a huge structural difference between floating shock platform and the real ship. The response of the real ship under explosion load is flexible-body motion, while the main response of the floating shock platform is rigid-body motion[1]. The deck can be regarded as a filter acting on the shock environment which can cause difference between the shock environments of ship and floating shock platform[2]. To decrease the shock environment difference, a special deck which is called deck simulator here is design. Through the numerical simulation and analysis, the FSP with a deck simulator can decrease the shock environment difference and can be used to test equipment with special mounting frequency demand. These conclusions have a certain guiding significance for the assessment of ship equipment in engineering applications.
Numerical Investigation of Fluid-Ice-Structure Interaction During Collision by an Arbitrary Lagrangian Eulerian Method
Authors: Song Ming , Kim Ekaterina , Amdahl Jørgen , Greco Marilena , Souli Mhamed
Published: October 2016

When ice floes collide against marine structures, pronounced hydrodynamic loads are induced by the water-ice-structure interaction. With today’s highly competitive structural design market, it is nearly impossible to ignore the advances that have been made in the computer analysis of fluid-structure interaction (FSI) problems. FSI methods can provide accurate representation of hydrodynamic effects. A number of commercial programs have been developed, and their applications in structural design increases rapidly. For instance, Arbitrary Lagrangian-Eulerian (ALE) formulations have been used to solve underwater explosions problems in ocean engineering, and soil-structure interaction problems in civil engineering. Application to fluid-ice-structure interaction problems is more recent and growing. This paper represents a contribution in assessing the capabilities of the ALE formulation for fluid-ice-structure collision problems. The ALE and coupling algorithms have been successfully validated through the comparison against model tests of an ice-structure collision. The work also examines the numerical convergence and the sensitivity of the results to the theoretical modelling used. From the sensitivity study it is concluded that the effect of viscosity and equation of state for the water model within the ALE formulation are insignificant, whereas the choice of the element size has a noticeable effect on the computed contact forces and the motions of the impacted structure.
Determination of Hydrodynamic Parameters for Remotely Operated Vehicles
Authors: Eidsvik Ole A. , Schjølberg Ingrid
Published: October 2016

In this paper the hydrodynamic parameters that characterize the behavior of a typical unmanned underwater vehicle are evaluated. A complete method for identifying these parameters is described. The method is developed to give a brief and accurate estimate of these parameters in all six degrees of freedom using basic properties of the vehicle such as dimensions, mass and shape. The method is based on both empirical and analytical results for typical reference geometries (ellipsoids, cubes, etc.). The method is developed to be applicable for a wide variety of UUV designs as these typically varies substantially. The method is then applied to a small observation class ROV. The results are first verified using an experimental method in which the full scale ROV is towed using a planar motion mechanism. An additional verification is performed with numerical simulations using Computational Fluid Dynamics and a radiation/diffraction program. The method shows promising results for both damping and added mass for the tested case. The translational degrees of freedom are more accurate than the rotational degrees of freedom which are expected as most empirical and analytical data are for translational degrees of freedom. The case study also reveals that the relative difference between the numerical simulations and the experimental results are similar to the relative difference between the proposed method and the experiment.
Hydrostatic Stability and Global Performance Analysis for Set TLP
Authors: Yuck R. H. , Kim S. J. , Sung S. U. , Kim H. J. , Lee D. Y. , Kim B. K.
Published: October 2016

SET (Samsung Enhanced hull for Tendon) TLP (Tension Leg Platform) has been designed as an innovative TLP hull form with optimized number of tendons compared to conventional TLP design. SHI (Samsung Heavy Industries) designed the SET TLP to have the minimized hull weight with narrow and thin pontoon which results in the less number of tendons without any outboard extension of column or pontoon.

The SET TLP has 8 tendons which are evenly attached along with the octagonal shaped-ring pontoon. The unique shape of octagonal ring pontoon distributes the wave load and concentrated tendon loads in larger areas, which can minimize the structural reinforcement.

To verify the feasibility of the proposed hull concept with regard to the hydrostatic/hydrodynamic characteristics and tendon design, the numerical analyses for the hydrostatic stability and global performance are carried out. Hydrostatic stability is investigated for all the possible loading cases such as float-off, wet transit, tendon installation and operational conditions, and the proper tank compartments are achieved for all the scenarios without using any temporary stability module.

The global performance is validated for all the possible combinations of wave, swell, wind, current and/or squall for a site in Western Africa. Through the frequency-domain analysis and nonlinear time-domain analysis as well, the essential items such as the maximum offset/set-down/top tendon tension, minimum bottom tendon tension are examined and confirms that the certain design criteria of TLP operation are satisfied.
A Study on the Simplified Calculation Method for the Residual Ultimate Strength of Damaged Hull Structures
Authors: Toh Kimihiro , Maeda Shunsuke , Yoshikawa Takao
Published: October 2016

In order to obtain the non-linear average stress-average strain relationships (σ-ε curves) of damaged structural members under both tensile and compressive loads, the systematical calculations are performed using the non-linear FE analysis (FEA) code, LS-DYNA, and the idealized σ-ε curves of damaged structural members are estimated from FEA results.

In addition, by introducing the idealized σ-ε curves of damaged structural members to the simplified calculation program, which is developed by authors and based on the Smith’s method, the residual ultimate strength of damaged hull structures is calculated. The residual ultimate strength of damaged hull structures is also calculated utilizing FEA, the calculation results by the simplified calculation program are compared with the results obtained from FE analyses so as to examine the accuracy of simplified calculation method.
Numerical Analysis of the Effects of Parametric Excitation on Riser VIV
Authors: Lei Song , Zheng Xiang Yuan
Published: October 2016

The design of top-tensioned risers has to face a number of challenges in deepwater. One of the challenges comes from the heave motion of the platform that leads to the fluctuation of the axial tension in the risers, which is called parametric excitation (PE). Vortex-induced vibration (VIV), induced by sea current, is also a notorious challenge, especially for high aspect ratio risers. Usually a marine riser is subjected to parametric excitation and vortex-shedding, simultaneously. However, so far only a limited number of VIV studies has considered axial parametric excitation. Thus, the objective of this paper is to analyze the influence of parametric excitation on the riser VIV. To simulate the fluid-structure interaction, a marine riser is modeled as a Bernoulli-Euler beam with periodical time-varying tension in the axial, while the lifting force generated by vortex-shedding is represented by a distributed wake oscillator model that is coupled with the vibration acceleration of the riser structure. The VIV model is represented by a set of coupled partial differential equations. Such coupling model is solved with a standard centered finite difference method so as to formulate a reduced-order system which is then numerically integrated in the time domain. The dynamic behavior of a TTR system is investigated with several combinations of amplitudes and frequencies in the heave motion. Interesting results are achieved as they are much different from the ones undergoing VIV only. It is revealed that the periodically varying top tension accounts for the artificial transition of vibration modes. In cases where PE frequency is distant away from the vortex shedding frequency, the amplitude of VIV response under dynamic axial tension is smaller than that under static tension, while in the special cases where PE frequency is close to the vortex shedding frequency, the response of VIV is significantly amplified. The sum and difference frequencies of the parametric and vortex-shedding excitation are noticeable in the power spectrum density of riser’s lateral displacement. Under the combined excitations, when the heave motion is mild, vortex shedding dominates riser’s response. However, in a severe sea state with remarkable heave motion amplitudes, the parametric excitation contributes more to the TTR dynamic response, because in this scenario the parametric instability disrupts the generation of vortex-shedding at the spanwise locations of riser.
Availability Estimation of Ship-Based Carbon Capture and Storage (CCS) Chain for Korea CCS Demonstration Project
Authors: Seo Youngkyun , Huh Cheol , Chang Daejun
Published: October 2016

This study estimated the availability of a ship-based carbon capture and storage (CCS) chain to investigate which would be critical components in the chain and to suggest improvement methodology for design and operation. Bo-ryeong coal-fired power plant and Ul-leung basin in South Korea are designated as the target CO2 emission source and the CO2 storage sink, respectively. The CO2 emitted from the power plant was transported by a CO2 carrier to an intermediate storage terminal and then the CO2 is moved to the basin by offshore pipeline. The ship-based CCS chain contained a capture system, a dehydration system, a liquefaction system, temporary storage tanks, a cargo handling system, a CO2 carrier, and a pumping system. The availability was estimated with the commercial code, TARO, based on the Monte-Carlo simulation method. Firstly, a chain configuration was defined for the availability estimation. Factors that might potentially cause production loss during the operation were identified, and those failure frequencies and restoration times were collected from the available literatures. Finally, the availability of the chain was evaluated. The results showed that the most significant factor was the preventive maintenance for the liquefaction system. The minor factor was a ship engine system. The tendencies of several important factors were analyzed through a sensitivity analysis.
Investigation of Synergistic Thermodynamic Inhibition Effect of MEG and Salt Solution on Gas Hydrate
Authors: Seo Yutaek , Kim Hyunho , Park Juwoon
Published: October 2016

This study examined the thermodynamic synergistic inhibition effects of MEG considering in case of produced water breakthrough, which includes high concentration of salts solution mixed with hydrocarbon fluids during natural gas production. First, we proposed the modified model based on Soave-Redlich-Kwong equation of state for expressing the vapor phase and van der Waals and Platteuw theory to predict the hydrate equilibrium conditions in the presence of both MEG and NaCl. The proposed model adopt the change of fugacity of gas component in aqueous MEG and NaCl solution using ENRTL-RK model in Aspen plus v8.6. The activity of water was determined by Margules equation for MEG, Pitzer equation for NaCl and temperature effect. The hydrate equilibrium conditions of solutions containing both MEG and NaCl with high salinity (∼ 20 wt%) was measured as well. The results showed that the hydrate formation condition was shifted toward lower temperature and higher pressure in accordance with the increased NaCl concentration. The proposed model was acceptably correspond with experimental data. For MEG and NaCl mixed solutions, the average deviation of hydrate formation pressures (AADP) of the proposed model had the lowest value of 5.37% compared to 17.52% of CSMGem and 13.77% of Multiflash.