bluuebunny/crossref_metadata_2025 huggingface dataset:
A Method for Ultimate Strength Assessment of Plates in Combined Stresses
Authors: Zhang Shengming , Jiang Lei
Published: October 2015

It is becoming a normal practice in structural engineering, including ships and offshore industry, to perform non-linear finite element analysis to assess the structure’s capacity for design or evaluation purposes. However, experience has shown that the quality and accuracy of the non-linear FE analysis results are highly dependent on the person’s skills and analysis procedures used. In some cases, the results could lead to a wrong conclusion. Simplified method with good accuracy is still a preferred approach in design by the industry because it is simple and easy to use. However, even the method for the simple model, a plate under combined loads, has not been addressed completely because of its complexity. This paper has thus developed a simple method for the ultimate strength analysis of square plates under combined longitudinal and transverse compressive stresses. The method is fully validated with a systematic non-linear FE analysis results. The paper has also compared the methods from the industry standards BS5400 and DIN18800. Analysis examples are also provided in the paper for reference and discussions.
Test Facilities for Safety Studies of Ships and Offshore Structures Associated With Extreme and Accidental Conditions
Authors: Paik Jeom Kee , Ha Yeon Chul , Kim Bong Ju , Seo Jung Kwan
Published: October 2015

Ships and offshore structures can face extreme and accidental events that can result in catastrophic consequences in association with casualties, property damages and pollution. Because the mechanism and its responses of structures in extreme and accidental events are highly nonlinear, it is essential to take advantage of experimental approaches as well as computational approaches in terms of identifying such nonlinear responses. Relevant test facilities are then required to meet the needs where full scale or at least large scale models should be dealt with. The objective of this article is to introduce test facilities recently built in the Korea Ship and Offshore Research Institute (KOSORI) at Pusan National University in Korea in terms of specifications and capabilities of various test facilities. Those facilities include test infrastructures in association with ultra-high subsea pressure, fires, explosions, structural failure and dropped object as well as high speed material test.
A Vertical Axis Wave Turbine With Cup Blades
Authors: Yang Yingchen , Diaz Isaiah , Morales Misael , Obregon Pablo
Published: October 2015

A new wave energy converter (WEC) design and some test results are discussed in this work. Among a variety of WEC technologies being explored to date, a huge majority employs wave-driven reciprocating motion (e.g., heave, pitch, sway, reciprocating bending or curving, etc.) to harness energy. It is well known that reciprocating WECs only work well at or near a predefined wave frequency, in a preferred alignment angle with the wave direction (except for the heave type), and in organized waves. But real ocean waves are chaotic and have daily changing frequencies and propagation directions. To circumvent those issues of the reciprocating WECs, a new unidirectional WEC concept — a vertical axis wave turbine — is explored in this research. The key component of the wave turbine is a rotor, which has a number of uniquely arranged hemispherical shells as blades. When the rotor is exposed in waves with its shaft vertically oriented, local water motion in any spatial directions (due to waves) can always drive the rotor for unidirectional rotation regardless of the wave type and propagation direction. In other words, the rotor can rely on omnidirectional water motion to realize its unidirectional rotation. A model wave turbine employing this rotor design has been tested in a wave flume. Upon a successful demonstration in simulated irregular waves, the rotor’s unidirectional performance was systematically characterized under various experimental conditions in simple waves.
Two-Phase Flow Modeling in Oil and Gas Applications
Authors: Awad M. M. , Butt S. D.
Published: October 2015

In the current study, two-phase flow modeling in oil and gas applications using asymptotic analysis is presented. Examples of two-phase liquid-liquid flow in pipes, two-phase gas-liquid flow in fractures, and two-phase gas-liquid flow in porous media are presented. In the present study, a simple semi-theoretical method for calculating the two-phase frictional pressure gradient in oil and gas applications using asymptotic analysis is presented. The proposed model can be transformed into two-phase frictional multiplier as a function of the Lockhart-Martinelli parameter, X. The advantage of the new model is that it has only one fitting parameter (p). Therefore, calibration of the new model to experimental data is greatly simplified. The new model is able to model the existing multi parameters correlations by fitting the single parameter p. Comparison with experimental data for two-phase frictional multiplier versus the Lockhart-Martinelli parameter (X) is presented.
Risk Based Inspection Planning for Fatigue Damage in Offshore Steel Structures
Authors: Lassen Tom , Recho Naman
Published: October 2015

High fatigue reliability is one of the most important design criteria for welded offshore steel structures. Due to repeated wave loading fatigue cracks may initiate and grow in welded joints that are important for the integrity of these structures.

The present paper presents the methodology and the practical calculations for risk based inspection planning for fatigue cracks in welded details. Due to the uncertainty in the variables involved in the problem the planning has to be carried out by stochastic modeling and risk based assessments. Scatter in potential crack growth has to be analyzed by applied probabilistic facture mechanics and the uncertainty in the performance of the actual inspection technique has to be determined. With given risk acceptance criteria the practical outcome of the analyses is recommended inspection techniques and associated planned inspection time intervals. The classical theory is outlined and the latest recommendations from a Joint Industry Project recently completed by Det Norske Veritas in Norway are discussed. Discussion on how to model the fatigue process correctly is emphasized, particularly the role of time to crack initiation versus the subsequent crack propagation phase. Proper modeling of these two phases is crucial to get the potential crack path correct and thus obtain a reliable estimate of the probability of crack detection. For the crack propagation phase the selection of geometry functions is addressed.

A practical case study for life extension of an offshore oil loading system is finally presented. A structural significant item in the system is the steel gooseneck connection for the sub-sea flexible loading hoses. The case is an interesting one in the way that two similar systems were analyzed independently, one analysis based on the tradition S-N approach and one where the decisions were reliability based by applying the Risk Based Inspection approach.
Integrity Assurance of an Oil Transportation Pipeline in a Transformed Design Environment
Authors: Kumar Amitabh , McShane Brian , McQueen Mark
Published: October 2015

A large Oil and Gas pipeline gathering system is commonly used to transport processed oil and gas from an offshore platform to an onshore receiving facility. High reliability and integrity for continuous operation of these systems is crucial to ensure constant supply of hydrocarbon to the onshore processing facility and eventually to market. When such a system is exposed to a series of complex environmental loadings, it is often difficult to predict the response path, in-situ condition and therefore the system’s ability to withstand subsequent future loading scenarios.

In order to continue to operate the pipeline after a significant environmental event, an overall approach needs to be developed to — (a) Understand the system loading and the associated integrity, (b) Develop a series of criteria staging the sequence of actions following an event that will verify the pipeline integrity and (c) Ensure that the integrity management solution is simple and easy to understand so that it can be implemented consistently.

For a complex loading scenario, one of the main challenges is the ability to predict the controlling parameter(s) that drives the global integrity of these systems. In such scenarios, the presence of numerous parameters makes the technical modeling and prediction tasks arduous. To address such scenarios, first and foremost, it is crucial to understand the baseline environment data and other associated critical design input elements. If the “design environmental baseline” has transformed (due to large events e.g. storms etc.) from its original condition; it modifies the dynamics of the system. To address this problem, a thorough modeling and assessment of the in-situ condition is essential. Further, a robust calibration method is required to predict the future response path and therefore expected pipeline condition.

The study further compares the planned integrity management solutions to the field data to validate the efficiency of the predicted scenarios. By the inclusion of real field-data feedback to the modeling method, balanced integrity solutions can be achieved and the ability to quantify the risks is made more practical and actionable.
Modeling of Two-Phase Frictional Pressure Gradient in Circular Pipes
Authors: Awad M. M. , Muzychka Y. S.
Published: October 2015

In this article, three different methods for modeling of twophase frictional pressure gradient in circular pipes are presented. They are effective property models for homogeneous two-phase flows, an asymptotic modeling approach for separated two-phase flow, and bounds on two-phase frictional pressure gradient. In the first method, new definitions for two-phase viscosity are proposed using a one-dimensional transport analogy between thermal conductivity of porous media and viscosity in two-phase flow. These new definitions can be used to compute the two-phase frictional pressure gradient using the homogeneous modeling approach. In the second method, a simple semi-theoretical method for calculating two-phase frictional pressure gradient using asymptotic analysis is presented. Two-phase frictional pressure gradient is expressed in terms of the asymptotic single-phase frictional pressure gradients for liquid and gas flowing alone. In the final method, simple rules are developed for obtaining rational bounds for two-phase frictional pressure gradient in circular pipes. In all cases, the proposed modeling approaches are validated using the published experimental data.
Global Benefits and Operational Challenges of Vessel Relocation
Authors: Zhao ‘Claire’ Yue , Haveman Curt E. , Cribbs Allison R. , Miller Jonathon D.
Published: October 2015

Movement of moored floating production vessels, such as Spars, Semi-submersibles, Deep Draft Floaters and Floating Production Units, due to environmental loading is often considered a design challenge to be addressed during the design phase of a structure. Proactive vessel relocation through mooring line adjustment can be integrated as part of an operational method to improve and extend component lives. This method may be implemented during the initially planned life of the structure to overcome riser fatigue life challenges, or as one of the methods to extend service life. The benefits are particularly noteworthy for steel catenary risers and mooring systems and have been discussed in previous works. However, vessels often deviate from the original relocation plan in practice. This paper assesses the benefits of a vessel relocation program with conscientious focus on the associated operational challenges. Risks associated with vessel relocation are also investigated. Suggestions are made to optimize such a program and to minimize interruption to production.
Development and Validation of a Highly Nonlinear Model for Wave Propagation Over a Variable Bathymetry
Authors: Gouin Maïté , Ducrozet Guillaume , Ferrant Pierre
Published: October 2015

Liu and Yue [1] developed a numerical scheme for propagating waves over a variable bathymetry with a High-Order Spectral (HOS) Method. The development of this nonlinear model is detailed and validated on three different test cases. They intend to demonstrate that such a model may be applied to small bottom variations as considered in [1] but also on cases where the bottom variation may be important. In this concern, the very well documented test case of a 2D underwater bar is studied in details. Comparisons are provided with both experimental and numerical results.
The Encountered Extreme Events and Predicted Maximum Ice-Induced Loads on the Ship Hull in the Southern Ocean
Authors: Suominen Mikko , Kujala Pentti , Kotilainen Mikko
Published: October 2015

This paper studies the causes (ship operations and ice conditions) for the maximum ice-induced loads on the ship hull. Furthermore, the extreme loads are predicted with the Gumbel I asymptotic distribution. The study utilizes the full-scale measurement data collected in the Antarctic waters onboard S.A. Agulhas II between Dec 2013 and Feb 2014. The iceinduced loads were measured at the bow, bow shoulder and stern shoulder. The ice conditions were observed visually and the machinery control and navigational data were recorded continuously.

The study showed that the turning of the ship has a major effect on the loading at the stern shoulder. The maximum loads also showed an increasing trend as a function of the observed ice concentration and maximum ice thickness in all three areas of the hull. In addition, the maximum loads at the bow showed a decreasing trend as a function of an increasing ice floe diameter. Furthermore, the study with the return period of the ice-induced loads showed that the return period of the loads was at the same level at the bow and stern shoulder. However, the extreme values exceeded with a probability of 1 % or 0.1 % are clearly higher for the bow.
Prediction of Response of a SCR Using the Multi-Gaussian Maximum Entropy Method
Authors: Alibrandi Umberto , Ma Chenyin , Low Ying Min , Koh Chan Ghee
Published: October 2015

The dynamic analysis of deepwater floating production systems has many complexities, such as the dynamic coupling between the vessel and the lines, the coupling between the first-order and second-order wave forces, several sources of nonlinearities. These complexities can be captured by fully coupled time domain analyses. However they require an enormous computational cost, especially for the evaluation of tails of the distributions of the extreme responses, which are of great interest for practical reliability design purposes. In this paper the non-Gaussian probability density functions of the responses are evaluated through a novel moment-based approach, based on the Maximum Entropy principle, called Multi-Gaussian Maximum Entropy Method (MGMEM). The application to a Steel Catenary Riser (SCR) shows the accuracy and effectiveness of the presented procedure.
Fatigue Life Calculation of Deep Water Composite Production Risers by Rain Flow Cycle Counting Method
Authors: Singh Manander , Ahmad Suhail
Published: October 2015

Composite production risers in deep sea condition operate in harsh environment induced by wind and waves together with large axial tension fluctuations. Therefore, a suitable fatigue analysis of the riser stress joints must be undertaken at the structural design stage to ensure their adequate lifespan of 25–30 years. The composite riser, under study, is considered to be a part of Tension Leg Platform (TLP) to be installed at a depth of 2000 m. The probabilistic records of twelve sea states are used to simulate the expected loads for its entire service life. The response time histories are obtained by implicit time domain analysis of the composite riser for each sea state of random nature, duly considering the nonlinearities involved. Each stress time history is decomposed into equivalent stress blocks. A stress range histogram is generated in terms of the number of cycles in each block. The rain flow cycle counting method is hence used to estimate the cumulative fatigue damage. Palmgren-Miner rule is used to calculate the damage caused by stress signals of variable amplitudes. The damage fractions are then summed linearly to give an estimate of the total fatigue life for a particular stress history. The cumulative estimate for its entire service life is hence estimated considering all expected sea states.
Engagement in the Arctic: The ‘Modular Arctic Hub (MODARC)’ Facilitates the ‘Kick-Off’
Authors: Hoog Sven , Longrée Mark , Menze Andreas
Published: October 2015

It seems to be certain that a huge variety of activities will be established in the Arctic in turn of global warming in the coming decades. These activities comprise fishery, tourism, cargo shipping and resource extraction mainly taking place in Arctic waters, at coastal areas and at shore. As history shows, these activities often suffer from a complicate supply of skilled personnel, insufficient infrastructure and not suitable tools for use in harsh environment, which are significant obstacles towards a cost efficient setup of required hubs supporting the ‘conquering of the Arctic’.

IMPaC has taken the chance of participating in the European funded joint research project ACCESS (Ref. [3]) to develop a concept for the modular establishment of stations in the Arctic: MODARC (MODular ARCtic Hub). The basic module of MODARC shall act as initial hub providing fundamentals like accommodation, energy, communication in a safe and secure way. The hubs shall be self-sufficient for an extended kick-off period and operable conforming to a zero-emission policy, which IMPaC has already met during projects for the Caspian Sea (Ref. [2]).

The basic modules are operable right after installation allowing supporting the establishment of further specialized activities serving the various means of activities mentioned above. Thus, the character of each settlement will be case (project) dependent but comparable in its basic concept. Paramount advantage of the MODARC concept is the idea of producing the floating modules in worldwide benign conditions like harbors or wharfs allowing testing and certifying each module prior to send out and installation at location. Even personnel can be trained before or during the shipment to the operation location — just like it is usual e.g. in Aerospace technology.
Prediction and Qualification of Radial Birdcage and Lateral Buckling of Flexible Pipes in Deepwater Applications
Authors: Zhu Linfa , Tan Zhimin , Nogueira Victor Pinheiro Pupo , Liu Jian , Clevelario Judimar
Published: October 2015

Increasing oil exploitation in deepwater regions is driving the R&D of flexible pipes which are subjected to high external pressure loads from the hydrostatic head during their installation and operation. One of the challenges of flexible pipe design for such applications is to overcome the local buckling failure modes of tensile armor layers due to the combination of high external pressure, compressive loads and pipe curvature. This paper presents the latest progress in local buckling behavior prediction theory and the qualification process of flexible pipes. First, the mechanisms of two types of buckling behaviors, radial birdcage buckling and lateral buckling, are described. For each failure mode, the analytical buckling prediction theory is presented and the driving parameters are discussed. As part of the qualification process, the ability to resist radial birdcage and lateral buckling must be demonstrated. Suitable test protocols are required to represent the installation and operation conditions for the intended applications by deep immersion performance (DIP) tests. Several flexible pipes were designed based on radial birdcage and lateral buckling prediction theory, and pipe samples were manufactured using industrial production facilities for DIP tests. The results clearly show that flexible pipes following current design guidelines are suitable for deepwater applications. An alternative in-air rig was developed to simulate the DIP tests in a controlled laboratory environment to further validate the model prediction as a continuous development.
Sliding-Mode Control System Design for an Experimental Model With Resonance-Free SWATH
Authors: Kajiwara Hiroyuki , Kanda Masamitsu , Yoshida Motoki
Published: October 2015

Given an experimental model with a resonance-free SWATH, the paper represents successful experimental results of sliding-mode control applied to the pitch control loop, which indicate its effectiveness in regular-wave disturbance rejection compared with the case of using PD control only.
Uncertainty Analysis in Ship-Model Resistance Test
Authors: Steen Sverre , Ankit  , Gavrilin Sergey
Published: October 2015

In a ship model resistance test, the towing force measurements usually contain high amplitude and low frequency noise. The length of the towing tank is finite, which induces an uncertainty in the estimated mean value of the towing force. In practical work, a time-window is manually selected from the complete measurement time history to compute the mean value to be used in the further analysis. Due to the combination of high-amplitude, low frequency noise and limited length of time series, the selection of the time window is found to matter for the resulting mean value. The idea pursued in this paper is that the uncertainty in the estimated mean value of resistance can be improved by considering multiple time windows rather than just one.

First, the paper deals with the estimation of mean value of resistance from the given towing force data using 1) Single Time Window (STW) technique 2) Multiple Time Windows (MTW) technique. By applying these techniques to a given time series with a known mean, we can compare reliability of these estimators. Finally, the carriage and ship model are mathematically modeled as moving spring-mass-damper system. Comparison of the simulated towing force data with the experimental data allows us to understand the major sources of noise in towing force data.
Flexible Pipe Anchoring System: Resin Ratio Effects on Mechanical Properties
Authors: Torres Rafael N. , Tanaka Rafael L. , Morini Rafael G. , Otte Filho Olaf O. , Vilela Thamise
Published: October 2015

At the end of flexible pipe manufacturing, the assembly of end fittings ancillaries is necessary to provide the connection with the platform and the subsea systems. The assembly process uses epoxy resin to ensure the holding of the tensile armor layers inside the end fitting. The anchoring system has great importance in the integrity of the flexible pipes system, since their failure causes the separation between the flexible pipe and ancillaries, what can put on risk the production and the environment. During the qualification tests of new structures were observed that some variables of the process could be determinant on the mechanical strength resistance required for the product. One of these known variables is the ratio resin/hardener. Resin supplier specifies at the datasheet the proper ratio to obtain the full cure, but it was observed that small variations in the concentration alters the maximum tensile anchoring strength supported by the structure, as well the minimum curing time that should be obeyed, so it can be better used regarding their mechanical properties. In this way, laboratorial tests were conducted to enhance the performance of this resin in the tensile anchoring system, according to Prysmian Surflex products’ necessity. Compression tests varying the resin/hardener ratio were done to evaluate the resistance as a function of curing time. Besides this, tensile tests (tensile wire pulls over from resin) were conducted to establish a relation between maximum tensile load and the resin ratio, and so provide enough data to control the best proportion of resin during the end fitting assembly phase.
A Method for Estimating Quasi-Static Riser Deformation and Applied Forces From Sparse Riser Inclination Measurements
Authors: McNeill Scot , Saruhashi Tomokazu , Sawada Ikuo , Kyo Masanori , Miyazaki Eigo , Yamazaki Yasuyuki
Published: October 2015

A method was recently presented for determining quasi-static and dynamic riser angles using measured data typically found in a riser fatigue monitoring system, specifically acceleration and angular rate data. The riser angles were determined at sensor locations. In this paper quasi-static riser displacement, inclination angle, curvature, and stress are estimated along the entire length of the riser, using only the quasi-static inclinations angles at sparse sensor locations. In addition the distribution of applied forces along the entire riser length is also estimated. A rough representation of the current profile can be calculated using the drag coefficients of riser joints.

The riser deformation (displacement, inclination, curvature) and applied forces are estimated by solving the matrix equation f = K*x, where f is the vector of forces and moments, K is the stiffness matrix and x is the vector of displacements and inclination angles. In the equation, force and displacement vectors are unknown and the stiffness matrix is determined using Finite Element (FE) modeling. Constraints are applied, setting the inclination angle at the sensor locations to the values derived from measured data. The remaining highly-underdetermined problem cannot be solved in a classical sense, as it admits infinite solutions. To get a solution that is consistent with the physics of riser deformation, smoothness of the solution is enforced as a constraint. The smoothest solution is solved using quadratic programming methods.

Following implementation of the method in Matlab®, the procedure was validated using numerical simulations of a riser in applied current. Both connected (to the wellhead) and disconnected cases were simulated. Estimated riser displacements, slopes, curvatures and applied forces are found to match the simulation results closely.

The algorithm was then run using measured data from an emergency disconnect event that occurred on the Chikyu drill ship in November, 2012. The riser displacement, inclination and curvature were determined and found to agree well with results determined using another method.

The additional capabilities presented herein further expand the utility of a riser monitoring system. Quasi-static and dynamic riser angles are derived from acceleration and angular rate sensors using previously published methods. Using the method developed herein, the quasi-static inclination angles at the sensor locations can be used to determine the displacement, inclination, curvature (stress) and even applied force along the entire riser. These results are particularly useful in strength assessment, model verification, clashing and emergency event reconstruction analyses.
Numerical Investigation on Interaction Between a Semi-Submersible Platform and its Mooring System
Authors: Liu Yuanchuan , Peng Yao , Wan Decheng
Published: October 2015

With the increasing demand of floating structures in offshore, coastal and marine renewable energy engineering, the interaction between the mooring system and floating structure becomes more and more important. In this paper, motion responses of a semi-submersible platform with mooring system under regular wave conditions are investigated numerically by a viscous flow solver naoe-FOAM-SJTU based on the open source toolbox OpenFOAM. Influence of the mooring system on the platform motion responses is evaluated in two different ways. Investigations are covered for analysis methods adopted for solving mooring lines and the length of each part of a multi-component mooring line. Several important conclusions are drawn.
Nonlinear Computation of Ship Motions in the Time-Domain Using 2D+t Theory
Authors: Meng Wei , Qiu Wei
Published: October 2015

Motions of high-speed displacement ships in waves have been predicted based on a body-exact strip-theory method in the time domain (2D+t). Nonlinear body boundary conditions were applied on instantaneous wetted surfaces. Linear boundary conditions were used on the free surface so that the 2D transient free surface Green function can be employed. Interactions among the strips of the ship hull were considered. A far field method was adopted to compute the hydrodynamic forces. Validation studies have been carried out for two Wigley hull ships in regular waves. Numerical results were compared with experimental data and those by other numerical methods.
Thermal Effects on the Anchoring of Flexible Pipe Tensile Armors
Authors: Otte Filho Olaf O. , Tanaka Rafael L. , Morini Rafael G. , Torres Rafael N. , Vilela Thamise S. V.
Published: October 2015

In the design of flexible pipes, predict the anchoring behavior on end fittings is always challenging. In this sense, Prysmian Surflex has developed a finite element model, which should help the end fitting design as well the prediction of the structural behavior and the acceptable maximum loads. The current model considers that the contact between armor-resin is purely cohesive and has been suitable for the design of end fittings [1] and [2]. But tests and new studies [3] and [4] indicate that only cohesive assumption would not be the best approach. Experimental data from prototype tests also show that the current model would not predict acceptable results for loads higher than those used in previous projects.

This document will describe a study developed considering the friction and thermal contraction, instead of the cohesive phenomenon in the anchoring behavior analysis. Small scale tests were conducted in order to understand the anchoring relation between the resin and the wire used in the tensile armor. For this purpose, a special test device was developed to simulate an enclosure system. A parametric study was also performed to identify the cooling temperatures, coefficients of friction and contact properties parameters taken from small scale tests. The finite element model considers the thermal effects during exothermic curing.

Using the new parameters obtained, a second model was developed. This model consists of only one real shaped bended wire inside an end fitting cavity. To validate the model, samples were tested on laboratory according anchoring design. The results of this round of tests were studied and corroborate the argument that use friction and thermal effects is better than use only the cohesive condition.
Structural Health Monitoring of Subsea Pipelines by Genetic Algorithms
Authors: Wang X. M.
Published: October 2015

The measured dynamic response can be used to calibrate and update the numerical model used in the design so as to better predict the structural response and assess the structural safety, by means of a suitable system identification strategy, which can be further applied to monitor the “health” of the structures continuously. Recently, structural health monitoring (SHM) of offshore structures has increasingly gained more and more attention as it can provide useful information to predict potential damages or accidents. This paper presents a numerical study on subsea pipeline bedding condition assessment, focusing on pipe integrity and free span identification. Since subsea pipelines are usually very long without clear boundaries, only a span of pipelines is modeled to study. Improved Genetic algorithms (GA) method is adopted to identify the key parameters, due to its advantages of robustness and ease of implementation. Output-only substructural identification is formulated and applied. Numerical study is conducted by Fortran programming, and it is shown that the proposed identification strategy is effective for global system identification of subsea pipelines.
Ice Resistance Calculation Methods and Their Economic Impact on Ship Design
Authors: von Bock und Polach Rüdiger U. Franz , Tõns Tõnis , Erceg Sandro
Published: October 2015

A ship is an investment and built to create revenue. The decision whether the design of a ship is realized or not is therefore strongly affected by the natural obstacles of mission and route. The occurrence of ice along arctic routes is such an obstacle and affects significantly the resistance and the required propulsion power. Advanced simulation environments, such as panel methods or CFD do not exist yet for ice resistance calculations and hence semi-empirical formulations or model tests need to be employed to assess or validate a design. Ice model tests impose great expenses in terms of time and money, which often does not allow testing design variations. On the other hand, the results of semi-empirical formulas might be accompanied by significant uncertainties. The academic study presented in this paper is a transit simulation on the Northern Sea Route (NSR) for the ice-capable tanker MT Varzuga (formerly MT Uikku). The study evaluates the ice conditions along several NSR alterations and the ice resistance-related performance with available semi-empirical methods and ice model tests. Finally, the economic impact of the applied ice resistance prediction methods is evaluated and the differences are quantified.
Experimental and Numerical Studies of Axisymmetric Tuned Liquid Dampers
Authors: Molin Bernard , Remy Fabien , Bonnici Julien
Published: October 2015

Tuned Liquid Dampers (TLDs) have proved their efficiency to mitigate the vibratory response of slender buildings under wind or earthquake excitation. Simple semi-analytical models are proposed here to derive the hydrodynamic coefficients (added mass and damping) of axisymmetric TLDs fitted with circular or radial perforated screens. Comparisons are made with experimental values obtained with an Hexapode test bench. Good agreement is observed.
Preliminary Analysis About Coupled Response of Offshore Floating Wind Turbine System in Time Domain
Authors: Liu Geliang , Hu Zhiqiang , Duan Fei
Published: October 2015

This paper presents a preliminary analysis of Offshore Floating Wind Turbine system subjected to coupled wind and wave loads in time domain. Floating Wind Turbine system in deep water has the great potential in exploiting renewable wind energy in the near future due to the energy and environmental issues. Distinct structural arrangements determine the complexity of motion behaviors and loading characteristics of OFWTs. The aerodynamic loads play a dominant part in the loading pattern, which is distinguished from traditional floating offshore oil and gas structures. To simulate the response induced by wind and wave, a calculation scheme is proposed containing the coupling between aerodynamics and hydrodynamics. Accordingly, a set of time-domain numerical codes is developed and presented. With the integrated aero and hydro dynamic analysis codes, simulations are conducted to obtain performance of Hywind system. Cases for decay, white noise, wind only and the coexistence of wind and wave are investigated. The results are compared to the test statistics collected from a model test, which was carried out in Deepwater Offshore Basin in Shanghai Jiao Tong University.
Model Tests of a Spar-Type Floating Wind Turbine Under Wind/Wave Loads
Authors: Duan Fei , Hu Zhiqiang , Wang Jin
Published: October 2015

Wind power has great potential because of its clean and renewable production compared to the traditional power. Most of the present researches for floating wind turbine rely on the hydro-aero-elastic-servo simulation codes and have not been exhaustively validated yet. Thus, model tests are needed and make sense for its high credibility to master the kinetic characters of floating offshore structures.

The characters of kinetic responses of the spar-type wind turbine are investigated through model test research technique. This paper describes the methodology for wind/wave model test that carried out at Deepwater Offshore Basin in Shanghai Jiao Tong University at a scale of 1:50. A Spar-type floater was selected to support the wind turbine in this test and the model blade was geometrically scaled down from the original NREL 5 MW reference wind turbine blade. The detail of the scaled model of wind turbine and the floating supporter, the test set-up configuration, the mooring system, the high-quality wind generator that can create required homogeneous and low turbulence wind, and the instrumentations to capture loads, accelerations and 6 DOF motions are described in detail, respectively. The isolated wind/wave effects and the integrated wind-wave effects on the floating wind turbine are analyzed, according to the test results.
Analysis of Uncertainty Attributed to Measurement Error in Directional Surveying With Different Models
Authors: Mittal Manish , Samuel Robello , Kumar Aniket
Published: October 2015

The current interest in directional survey calculations is related to the increased number of highly deviated holes drilled from offshore platforms. Positional accuracy is important because, when two wellbores closely approach one another, it is essential to avoid intersection. Also, when a relief well is drilled, it is important to achieve intersection with the wild cat well. Unfortunately, there is no set of calculations that can be used to analytically determine exact bottomhole position relative to the top hole. Therefore, uncertainty with respect to estimating the wellbore position should be determined using directional surveys and the different models being used.

Errors in estimating the target primarily derive from two sources — model errors and measurement errors. Model errors occur in the calculations used to estimate borehole position because of a lack of complete information, which can only be tackled by having an infinite number of survey stations throughout the well path. On the contrary, measurement errors occur in the readings of inclination angle (I), azimuthal angle (A), and the distance between two stations (L). This paper focuses on estimation of measurement error, which is an inherent property of measuring instruments being used for the survey and can be evaluated numerically after making some assumptions necessary for such an analysis. The said analysis would ultimately provide ellipses of uncertainty for the target point based on different survey models.

The study is based on a paper by Walstrom et al. [1], which uses the angle averaging (AA) method for survey calculations. The study is extended for calculating measurement errors in the following models: the radius of curvature (ROC), minimum curvature (MC), and natural curve (NC) methods.
Uptake Riser for P-25 Platform in Albacora Field in Campos Basin
Authors: Franciss Ricardo , Custódio Anderson Barata
Published: October 2015

The P-25 platform is located at 575 m water depth in Campos Basin, offshore Brazil. In the time of its conversion (1996), its process plant was designed to use cold water streaming from the Antartic continent to cool its equipment, accessories and compressing gas plant for exportation.

The uptake riser installed in 1997 is 330 m long, 24″ OD pipe, hanging from the pontoon and the cold water flowing through it enters a sea chest located next to the support.

This fully rigid riser was recently asked to be replaced. This paper presents the stages of the reanalysis of this compliant structure under conditions of low cost, so that the platform continues to suck cold water. Because of the presence of the uptake riser, the platform does not have a cooling plant that would else request area and weight, two important items in an arrangement, besides the high cost involved.

Within the scope of the analyses, the replacement of the material (originally steel) with offloading hoses is tried out, in search for weight savings and lower cost. These hoses were reinforced with steel cables and their behavior was checked. Some tests were performed to verify the mechanical strength of this material and vibrations by VIV that occur in this structure.

Monitoring systems were designed to check all forces and displacements during the referred installation.

These actions will consolidate the technology for Petrobras leading to another riser system option for production in ultra deep waters.
Modelling Shallow-Water Waves: Truncated Hermite Models and the ShallowWave Routine
Authors: Winterstein Steven R. , Haver Sverre
Published: October 2015

Statistical modelling of ocean waves is complicated by their nonlinearity, which leads in turn to non-Gaussian statistical behavior. While non-Gaussianity is present even in deep-water applications, its effects are especially pronounced as water depths decrease. We apply two types of wave models here: (1) local models of extreme wave heights/periods and breaking limits, and (2) random process models of the entire non-Gaussian wave surface. For the random process approach, we derive a new “truncated” Hermite model, which can reflect four moments and both upper- and lower-bound limiting values due to breaking and finite-depth effects. Results are calibrated and compared with an extensive model test series, comprising up to 23 hrs of histories across 19 seastates, at depths from 15–67m (full scale).
Dynamic Response Analysis of a Triangular Tension Leg Platform
Authors: Guo Qiang , Ma Gang , Sun Liping , Wang Hongwei , Cui Na
Published: October 2015

The tension leg platform is widely used in the world. In this paper, a newly developed tension leg platform is evaluated under the environment loads of the South China Sea. The focus is on the coupling response of the platform hull and tendons. The three dimensional potential theory is used to analyze the new developed tension leg platform and its mooring system in the time domain. The new developed TLP is in a triangular-shape with three group tension legs. Every group consists of five tendons; the mooring system has been optimized after preliminary design. Coupling analysis in time domain has been conducted to evaluate its motion and tendon tension under different environmental loads. The results demonstrate the great improvement in the motion responses of this new developed TLP. The coupled motion responses of this platform with tendon lines system in extreme environmental conditions have also been evaluated in order to evaluate the safety in operation conditions.
An Assessment of Iceberg Loads for Operations in the North Barents Sea
Authors: Raghuvanshi Ujjwal , Ehlers Sören
Published: October 2015

With increasing demand for oil, drilling operations are soon going to start in the North Barents Sea. This area experiences iceberg occurrences. A systematic mapping of iceberg needs to be done to keep a tab on the iceberg location. Also, a study is required to assess the loads that come on to the mooring system in case of an iceberg – floater interaction. Therefore, this paper seeks to create a systematic mapping procedure for the occurrence of icebergs in the North Barents Sea using MATLAB. Further, from information on iceberg attributes and drift speed, the paper computes the iceberg mass and energy to define a probability density function of encountering an iceberg of a particular size. A scenario of an iceberg-floater interaction has been studied for different contact area geometries based on the kinetic energy model. Forces that develop on the mooring lines of a floater have been computed to aid in the designing of the mooring system of structures operating in the region fraught with the dangers of floating icebergs like the North Barents Sea.
Numerical Method Research on Nonlinear Roll System of Large Container Ship
Authors: Liu Yachong , Hu Ankang , Han Fenglei , Lu Yu
Published: October 2015

When dealing with the ship-roll problem, the roll motion is mainly regarded as a single degree-of-freedom dynamical system, and the nonlinear properties are reflected in the nonlinear damping term and restoring moment term. Previous studies have shown that transverse chaotic phenomenon means the damage of ship-roll stability which will lead to ship capsizing, and for ultra large container ships, the wind area above water surface can not be neglected, which turns the ship-roll system into asymmetric dynamical system.

The concept of safe basin is usually used to express the boundedness of motion. It is defined as the set of bounded solution to dynamical system, and the erosion phenomenon of safe basin is normally explained as the global instability. This concept was firstly brought out by Thompson [1] when he studied the problem of ship capsizing and then was applied to different fields of engineering.

Based on this background, the following three tasks are completed in this paper. a) For the calculation of chaos threshold, two numerical methods, namely, Pade approximation and Gauss-Legendre integration are adopted, analyzed and compared. b) One 9200TEU container ship is selected and the chaos threshold is calculated by virtue of Gauss-Legendre method. As numerical verification, the gradually erosion phenomenon of ship’s safe basin is observed and phase trajectories of points located in broken domain are traced; c) When encountered with crosswind (When winds are not parallel to or directly against the line of travel, the wind is said to have a crosswind component; that is, the force can be separated into two vector components, a crosswind component and a headwind or tailwind component.), the symmetry of ship-roll system begin to break. In the last part of this paper, the effect of crosswind on safe basin, asymmetry, and stability are studied.
Simulation Environment for Risk Assessment of E-Navigation Systems
Authors: Hahn Axel
Published: October 2015

“Safe voyage from berth to berth”: This is the goal of all e-Navigation strains, driven by new technologies, new infrastructures and new organizational structures on bridge, on shore as well as in the cloud. To facilitate these efforts suitable engineering and safety/risk assessment methods are required. Understanding maritime transportation as a sociotechnical system allows the usage of system-engineering methods. Simulation based test beds for verification and validation of e-Navigation technologies are important methods to obtain functional safety and reliability [1]. The modelling and simulation toolset HAGGIS is a co-simulation system for evaluation of e-Navigation concepts and systems. It provides a maritime traffic simulator and a physical world (n-body) simulator and services for finding rare events of failures. HAGGIS is accompanied by the physical test bed LABSKAUS which implements a reference port and waterways. This paper describes an integrated and seamless approach for developing new e-Navigation technologies starting with virtual simulation based safety assessment and ending in physical real world demonstrations. It gives an overview of the actual test bed and introduces requirements, concepts and elements of HAGGIS and LABSKAUS, which are joined in the eMIR test bed.