bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Analysis of Impact Loads on Subsea Structures During Water Entry in Presence of Waves
Authors: Momm Gustavo Garcia , Mota de Menezes Ivan Fábio
Published: December 2020

Subsea structures employed on offshore oil and gas production systems are likely to be subject to severe loads during deployment. Lowering these structures through the wave zone is a critical operation and the prediction of the loads associated is complex as it involves accelerations of these bodies induced by the vessel motion and the sea surface displacements. This work presents a numerical approach to assessment of the effect of waves on the impact loads that subsea structures are subject to during water entry. A 2D one degree of freedom model using the SPH method was developed to estimate slamming loads on rigid bodies during water entry considering both calm and wavy surfaces. Initially the model was employed to simulate the water entry of wedge considering both free fall and constant velocity cases, obtaining loads profile similar to experiments and numerical simulations from the literature. Later, the constant velocity model was configured to a flat bottom surface rigid body in order to represent a subsea manifold. A regular waves generator provided different wavelength, height and phase enabling slamming load assessment in various situations.
Design and Testing of AUV Docking Modules for a Renewably Powered Offshore AUV Servicing Platform
Authors: Haji Maha N. , Tran Jimmy , Norheim Johannes , de Weck Olivier L.
Published: December 2020

Autonomous Underwater Vehicle (AUV) missions are limited in range and duration by the vehicle’s battery capacity, and sensor payloads are limited by the processing power onboard which is also restricted by the vehicle’s battery capacity. Furthermore, the power consumption of a vehicle’s acoustic system limits the possibility of substantial data transmission, requiring the AUV be retrieved to download most data. The Platform for Expanding AUV exploRation to Longer ranges (PEARL), described in this paper, aims to extend the range and endurance of AUVs while reducing data latency and operating costs. PEARL is an integrated autonomous floating servicing station that utilizes renewable energy to simultaneously provide AUV battery recharging and data uplink via new generation high-bandwidth low-Earth orbit satellite constellations. This paper details the design and testing of two potential AUV docking modules of the PEARL system. The modules are uniquely located near the ocean surface, an energetic environment that presents a particular set of challenges for AUV docking. The results will be used to inform the design of a prototype system to be tested in an ocean setting.
Development of Accidental Scenarios Involving Human Errors for Risk Assessment in Restricted Waters
Authors: Abreu Danilo Taverna Martins Pereira de , Coelho Maturana Marcos , Martins Marcelo Ramos
Published: December 2020

The navigation in restricted waters imposes several challenges when compared to open sea navigation. Smaller dimensions, higher traffic density and the dynamics of obstacles such as sandbanks are examples of contributors to the difficulty. Due to these aspects, local experienced maritime pilots go onboard in order to support the ship’s crew with their skills and specific regional knowledge. Despite these efforts, several accidents still occur around the world. In order to contribute to a better understanding of the events composing accidental sequences, this paper presents a hybrid modelling specific for restricted waters. The main techniques used are the fault tree analysis and event tree analysis. The former provides a framework to investigate the causes, while the latter allows modelling the sequence of actions necessary to avoid an accident. The models are quantified using statistical data available in the literature and a prospective human performance model developed by the Technique for Early Consideration of Human Reliability (TECHR). The results include combined estimates of human error probabilities and technical failure probabilities, which can be used to inform the causation factor for a waterway risk analysis model. In other words, given that the ship encounters a potential accidental scenario while navigating, the proposed models allow computing the failure probability that of the evasive actions sequence. The novelty of this work resides on the possibility of explicitly considering dynamicity and recovery actions when computing the causation factor, what is not a typical feature of similar works. The results obtained were compared with several results available in the literature and have been shown to be compatible.
Characteristics of OWC Type WEC Dampers Installed on a Very Large Floating Structure
Authors: Ikoma Tomoki , Furuya Shoichiro , Aida Yasuhiro , Masuda Koichi , Eto Hiroaki
Published: December 2020

Oscillating water column (OWC) type wave energy converters (WECs) have been researched and developed. OWC WECs are relatively friendly to maintain them in operation because all of mechanical units are set above a sea water surface. In addition, a feature of an OWC device is similar to an air dumper system. Thus, it should be possible not only to harvest wave energy but also to reduce motion of a floating system at the same time. As well as WEC system should be used with other ocean renewable energies as a combined system.

This paper describes hydrodynamic characteristics of OWC devices and wave fields around them of multi-OWC devices equipped large floating structures. For this research, the linear potential theory based in-house programme code was applied to calculate hydrodynamic performance of OWC regions and elastic motion behaviours of the structures. Besides, calculation results were compared with some experimental results of characteristics of OWC devices on reference papers published. Then we proved validity of the calculation method. We have quantitatively summarized how much the reduction effect can be seen according to the aircushion placement and the number of aircushions on the floating body. the paper investigated arrangement of OWC devices on the floating structure with several variations.

Using the prediction method, effects of arrangement of OWC devices on the performances are investigated.
Monitoring-System Development of Gillnet Using Artificial Neural Network
Authors: Jin Chungkuk , Kim HanSung , Park JeongYong , Kim MooHyun , Kim Kiseon
Published: December 2020

This paper presents a method for detecting damage to a gillnet based on sensor fusion and the Artificial Neural Network (ANN) model. Time-domain numerical simulations of a slender gillnet were performed under various wave conditions and failure and non-failure scenarios to collect big data used in the ANN model. In training, based on the results of global performance analyses, sea states, accelerations of the net assembly, and displacements of the location buoy were selected as the input variables. The backpropagation learning algorithm was employed in training to maximize damage-detection performance. The output of the ANN model was the identification of the particular location of the damaged net. In testing, big data, which were not used in training, were utilized. Well-trained ANN models detected damage to the net even at sea states that were not included in training with high accuracy.
An Investigation Into KCS Parametric Rolling Through Coupling Different DOFs
Authors: Wang Shuang
Published: December 2020

The research of parametric rolling has encountered many challenging problems due to its nonlinearity. In this paper, an in-house CFD code HUST-Ship based on fully structured overset grids is used for the investigation of KCS parametric rolling, which can overcome the shortcomings of potential flow method. Modeling errors and numerical errors are presented to improve the credibility of CFD simulation. The grid and time step are studied for the quantification of numerical errors. The phenomenon of parametric rolling is successfully captured in the paper and motion responses of KCS have a good agreement with experimental data. The characteristics of motions, forces and moments under parametric rolling are investigated by using fast Fourier transform. The relationship between wave characteristics and motion responses of ship is revealed in this paper. Following, a simulation model with three DOFs’ model (heave-roll-pitch model) is used to investigate the influence of surge motion on parametric rolling. Result shows that the excluding of surge motion has no qualitative influence on the prediction of parametric rolling. In general, the simulation limited to heave-roll-pitch coupling is adequate for its capture.
Data Mining Well Logs for Optimum Well Placement
Authors: Pandey Anuroop , Al Dushaishi Mohammed F. , Hoel Espen , Hellvik Svein , Nygaard Runar
Published: December 2020

Well placement with geosteering can get very complex in reservoirs with formation change not simply addressed by changes in the gamma ray log response. This paper uses data mining to characterize complex reservoirs for optimum well placement. The objective of this paper is to develop a data mining process to evaluate non-trivial geologic settings for geosteering reservoir well placement. The well logs’ data was collected from multiple wells in a Norwegian North Sea field, where the reservoir rocks are characterized with high heterogeneities. Principal component analysis was used to recognize data pattern and extract underlying features. The extracted features are then into distinct groups using Hierarchical clustering (HC) analysis. A classification model, that is based on the deviance analysis, was constructed to build a criterion to identify each cluster within a set of well log data. The results show that the data mining approach sufficiently identified highly heterogeneous formations and can be used for geosteering applications. Classification trees defined quantitative decision criterion for the identified clusters. The approach is capable of distinguishing between potential and non-potential steering clusters, as the identified clusters have distinct decision criteria and effectively explain the variations within a section, as verified with the lithology described from core analysis.
On GIS Based Selection of Suitable Site Including Cooperation With Surrounding Medical Facilities by Mesh Analysis of Floating Medical Support System on Big Disaster
Authors: Eto Hiroaki , Shimomoto Sena , Togawa Sachio , Yamamoto Morikazu , Miyasawa Shintaro , Yamaguchi Junko , Ikoma Tomoki , Aida Yasuhiro , Masuda Koichi , Udagawa Hiroki
Published: December 2020

The Great East Japan Earthquake that occurred in Japan in 2011, an innumerable number of buildings in the coastal part of the east side of Japan suffered catastrophic damage, and medical facilities in coastal areas have become dysfunctional because of the significant damage incurred due to the tsunami. And land routes are not passable, but there are records of support activities utilizing water areas such as sea and river networks being extremely effective in such disaster conditions. Therefore, as one of the effective methods of medical support in the affected area immediately after the disaster, a Floating Medical Support System (hereafter Medi-float) on big disaster that can be accessed from the water area was proposed. In the near future, the area along the Arakawa River is expected to be seriously damaged by the earthquake directly under the Tokyo metropolitan area. Therefore, by installing a Medi-float that can perform medical support activities from the water area to the land without being damaged by an earthquake, since Medi-float performs medical support activities in cooperation with medical facilities on land area, preventable death is reduced. In previous studies, a procedure to estimate the facilities scale and select a suitable site for Medi-float practically based on GIS data such as the number of collapsed buildings in the target area, distribution of injured people due to the earthquake were presented. However, even if Medi-float is installed in the target area, it cannot be denied that there is a shortage of medical facilities. In consideration of smooth transportation outside the region and cooperation with surrounding medical facilities, it is hoped that a concrete and realistic medical support system by Medi-float will be established. Therefore, in this study, in order to grasp the time it takes for the injured to be transported to the medical facility and the congestion status of the medical facility, the target area was divided into 250m meshes and a time-series simulation was performed. Specifically, the distribution of injured people during a disaster was calculated on a mesh basis from the number of buildings collapsed and the number of fires. And the transport time of the injured people is calculated from the distance between each mesh and the medical facility, the movement of the injured people in consideration of the congestion status of the medical facility was simulated, necessity of cooperation between medical facilities and wide area transportation was clarified, the effect of Medi-float, which is active in the disaster area, was also evaluated.
Irregular Wave Simulation and its Impact on Riser Extreme Response for a Production Semi
Authors: Zhang Shaosong , Cheng Yongming , Cai Yuanlang , He Ning , Yang Xiaolong , Cao Zhi
Published: December 2020

Steel Catenary Risers (SCRs) are widely used in deepwater and ultra-deepwater field developments. The dynamic strength of SCRs is a concern in terms of the global performance. The analysis results are quite scattered in many cases due to the nature of the irregular wave stochastic properties. The widely accepted approach to predict the riser dynamic response in the irregular seas is to run the multiple time domain simulations based on different random seeds. This paper will address the impacts on the predicted riser dynamic response due to the random seeds selection. The discussion is based on the independent engineering verification work for a production Semi project in South China Sea.

The site specific irregular waves are usually defined by not only the wave spectrum, but also the properties of individual waves, such as maximum wave height and minimum wave trough, which have big impacts on the riser extreme response. The code recommended approach for irregular wave simulation is based on the linear wave theory, which can ensure the match of the target wave spectrum, for example, Hs, Tp (or Tz), wave peakness for JONSWAP spectrum. But the variation of simulated individual wave properties to the specified value can be significant or there is no specified value to match. The simulated irregular waves based on linear theory is also a distortion to the real wave elevation time trace, such as the asymmetry of the wave crest and trough, especially for the tropical cyclone sea states. Some riser response, such as the compression load at riser touch down zone, can be significantly impacted by the nonlinear nature of the waves and the variation to the target individual wave properties.

This paper will discuss the random wave simulation and its impacts on riser dynamic response. A SCR strength design case is presented for illustration in this paper. Key parameters are identified to show the correlation with the SCR dynamic response. The conclusion is finally drawn from the work presented in this paper.
Impact of Accelerometer Placement on Modal Extraction of Offshore Wind Structures
Authors: Richmond M. , Siedler S. , Häckell M. , Smolka U. , Kolios A.
Published: December 2020

The modal parameters extracted from a structure by accelerometers can be used for damage assessment as well as model updating. To extract modal parameters from a structure, it is important to place accelerometers at locations with high modal displacements. Sensor placement can be restricted by practical considerations, and installation might be conducted more based on engineering judgement rather than analysis. This leads to the question of how important the optimal sensor placement is, and if fewer sensors suffice to extract the modal parameters.

In this work, an offshore wind substation (OSS) from the Wikinger offshore wind farm (owned by Iberdrola) is instrumented with 12, 3-axis accelerometers. This sensor setup consists of 6 sensors in a permanent campaign where sensors were placed based purely on engineering judgement, as well as 6 sensors in a temporary campaign, placed based on a placement analysis. An optimal sensor placement study was conducted using a finite element model of the structure in the software package FEMtools, resulting in optimal layouts. The temporary campaign sensors were placed such that they, in combination with the permanent campaign, can be used to complete the proposed layouts.

Samples for each setup are processed using the software ARTeMIS modal to extract the mode shapes and natural frequencies through the Stochastic Subspace Identification (SSI) technique. The frequencies found by this approach are then clustered together using a k-means algorithm for a comparison within clusters.

The modal assurance criterion (MAC) values are calculated for each result and compared to the finite element model from which the optimal sensor placement study was conducted. This is to match mode shapes between the two and thus determine the importance of off diagonal MAC elements in the sensor optimization process. MAC values are also calculated relative to a cluster-averaged set of eigenvectors to determine how they vary over the 1.5 months.

The results show that for all sensor layouts, the three lower frequency modes are consistently identified. The most optimized sensor layout, consisting of only 3 sensors, was able to distinguish an additional, higher frequency mode which was never identified in the 6-sensor permanent layout. However, the reduced sensor layout shows slightly more scatter in the results than the 6-sensor layout. There is a higher signal to noise ratio in the temporary campaign which results in scatter. We conclude that with an optimized placement of accelerometers, more modes can be identified and distinguished. However, off diagonal elements in the original MAC matrix, as well as loss of sensor degrees of freedom, can result in additional scatter in the measurements. Some of these findings can be extended to other offshore jacket structures, such as those of wind turbines, in that it gives a better understanding of the consequence of an optimal sensor placement study.
The Course Control of Air Cushion Vehicle With Uncertainties and Input Saturation
Authors: Wang Yuanhui , Jiang Xiyun , Fu Mingyu
Published: December 2020

In the presence of input saturation and unknown the internal uncertainties, external disturbances, including sea wind, waves and currents, this paper develops a course control law for the system of air cushion vehicle (ACV) using neural network and auxiliary dynamic system to improve the maneuverability and safety. In the design process of the course control law of air cushion vehicle, the two problems of input saturation and uncertainties are considered. On one hand, an effective auxiliary dynamic system is introduced to solve the input saturation problem and reduce its impact on the system. On the other hand, in order to deal with the internal and external disturbances of the system, the fully turned radial basis function network (FTRBFNN) is combined with the control law, and its adaptive ability makes the system compensate better for unknown uncertainties better than RBFNN. The stability of closed-loop system is proved by Lyapunov analysis. It is proved that the designed course control law can maintain ACV’s heading at desired value, while guaranteeing the uniform ultimate boundedness of all signals in the ACV closed-loop control system. Finally, simulations on ACV are carried out to demonstrate the effectiveness of the developed ACV course control law.
Real-Time Natural Gas Leak Detection of Offshore Platforms Using Optical Gas Imaging and Faster R-CNN Approach
Authors: Shi Jihao , Chen Guoming , Zhu Yuan
Published: December 2020

This study aims to introduce the integrated approach, namely the integration of the Faster R-CNN technique and Optical gas imaging (OGI) for real-time natural gas leak detection of offshore platforms. OGI is used to record large number of leak videos which are essential to develop the desirable Faster R-CNN model. Due to the fact that the natural gas leak incidents are rare on the offshore platforms, it is difficult to record large number of the real-world leak videos by using the OGI. This study firstly proposes the strategy to simulate the OGI by the CFD tool. The proposed strategy could generate large number of virtual infrared images. Based on the infrared images, the Faster R-CNN approach is trained and its performance is tested. A case study of deep-water drilling platform is conducted. The results demonstrate the feasibility of the proposed strategy as well as the competing performance of the Faster R-CNN approach for the real-time automatic natural gas leak detection of offshore platforms.
Finite Element Analysis of Structure Strength on Engine Room of a Submerged Waterjet Propelled Ship
Authors: Wang Hanqi , Ding Jiangming
Published: December 2020

The submerged waterjet offers further benefits with respect to excellent stealth performance, low inflow energy loss, high propulsive efficiency at low and medium speeds, and excellent underwater acoustic performance. It also offers potential for space savings as a result of the high integration with the hull bottom. A parameterized stern line layout method for DTMB 5415 is proposed to design a new ship type fitted with submerged waterjet propeller. Based on the finite element method, the strength analysis and modal analysis of the new hull-form are carried out. The transom equipped with submerged waterjets is constructed by three main parameters which includes tunnel lengths, tunnel transverse positions and shaft angles. CFD calculation of hull flow field and resistance was carried out based on the designed new ship type to evaluate hydrodynamic load. Based on the finite element method, MSC.Patran/Nastran and Abaqus CAE was used to analysis the stress and deformation of the engine room under the static load, and the modal analysis of the engine room was carried out to calculate the vibration frequency and mode of the engine room. Numerical results show that the stress and deformation of the section are agree with the design and the section will not be broken. The different order total modal deformation and natural frequency are given, which lays a foundation for the research of vibration noise prediction and noise reduction technology of ship engine room.
Scaling Up of Local Ice Pressures for a Fixed Offshore Platform Based on Ice Basin Model Data
Authors: Aleksandrov Anatolii V. , Platonov Viktor V. , Shaposhnikov Valery M.
Published: December 2020

Fundamentals of the similarity theory in the ice deformation mechanics, as well as problems related to scaling up of local ice pressures measured during tests in an ice basin to full scale values are considered. A new scaling principle based on a hypothesis of ice deformation limiting surface isomorphism and direct computer simulation is proposed.

An ice-resistant platform, for which local pressures were measured in ice tests and ice pressures were recalculated to full scale values using generated ice deformation limiting surfaces, was considered as an example.
Effect of Large Deformation Analysis for Site Investigation Tool - CPT in Layered Soils
Authors: Xie Qiang , Hu Yuxia , Cassidy Mark J.
Published: December 2020

Cone penetration test (CPT) is regularly used during offshore site investigations to interpret soil stratification and soil characteristics due to its continuous penetration resistance profile. However, its use could be improved if better numerical methods to simulate its penetration could be developed. Finite element (FE) analysis, for instance, has the potential to provide insightful information on soil response and soil flow mechanisms. However, it is challenging to simulate CPT in layered soils, as the soil experiences extremely large strains around the cone and the simulation costs are high. In this study, the efficiency of using a partial large deformation FE (LDFE) approach was explored to examine the pre-embedment depth allowed for saving LDFE analysis cost. The LDFE analysis was conducted using the remeshing and interpolation technical with small strain (RITSS) method to model the large strain problem. Both soft-stiff-soft clays and clay-sand-clay soil were considered to study the thin stiff layer effect when it was sandwiched in soft clay. The LDFE/RITSS analysis compared a CPT penetrating from the soil surface with penetrations from a pre-embedded depth above the stiff layer. Pre-embedded small strain analysis was also conducted for comparison.

The results show that the small strain analysis underestimated the resistance in both clay and sand. For the partial LDFE analysis with pre-embedment in the top clay layer, the CPT response in the middle stiff clay layer could be well captured regardless of the initial pre-embedment depth. However, for the middle medium dense sand layer (ID = 60%), the pre-embedment depth needs to have sufficient distance above it (10D, D is cone diameter) to capture the soil response in the sand layer correctly.
Combined Wave-Current-Turbulent Flow Environments Generation for Tidal Turbine Design
Authors: Li Qian , Vengatesan Venugopal , Barltrop Nigel
Published: December 2020

In this paper, a methodology to generate combined wave, tidal current and turbulent flow environment for application to determining hydrodynamic loading on a horizontal axis Tidal Stream Turbine (TST) is proposed. A systematic investigation has been conducted within the framework of OpenFAST software suite. Necessary modifications in OpenFAST tool is made to simulate the hydrodynamics of the TST under combined wave-current-turbulence conditions. The modified software will be able to generate the inflow conditions for the TST accounting for the regular and irregular wave and current interactions, and, involve the impact of ambient turbulence on the loadings of TST. The modified algorithm is validated by comparing the numerical results with experimental test data and other numerical simulation results. Good agreements are achieved for both regular and irregular wave kinematics in time-domain and flow velocity/elevation spectra in the frequency domain. Also, each of the wave-current configuration has been tested with different turbulence intensities. The results suggests that the wave kinematics is greatly altered when waves propagating on currents and wave travelling on the following and opposing directions current shows remarkably different characteristics in relation to wave amplitude and frequency. It is also found that combined wave-current flow with different turbulence levels have strong correlations with the flow properties which is important for TST fatigue prediction. All the conclusions emphasis the fact that proper wave-current-turbulence interactions should be included in TST modelling.
Evaluation of Metal Seals With for Interval Control Valve With Roundness Error Intelligent Well Considering Roundness Error
Authors: Yang Yiwei , Zhu Hongwu , Yang Yiwei , He Dongsheng , Zheng Yan , Li Chuan , Xu Liangbin , He Yufa
Published: December 2020

Intelligent wells armed with the interval control valve (ICV) are more and more widely applied in the oilfields. In an ICV, the metal seal pair composed of the metal seal ring and the sliding sleeve is designed to isolate the produced fluid flow between the casing annulus and the tubing. The evaluation of the metal seals for ICVs is necessary to enhance the reliability. In this paper, the influences of medium pressure and initial interference on the contact mechanical behaviors of the metal seal for the ICV are studied by using finite element analysis (FEA) when both of the metal seal pair elements have roundness errors. The results indicate that when the both long axes of the metal seal pair’s elliptical sections coincide or are orthogonal, the contact stresses on the core area for the seal face present cosine or sine curve distributions. Each distribution curve becomes smoother with the increase of medium pressure, initial interference or the reduction of sliding sleeve roundness error. And for the contact stress distribution curves, the maximum at the peaks and troughs and the average increase with the increase of the medium pressure, the initial interference and the roundness error of the sliding sleeve. Moreover, when the angle between the metal seal pair elliptical sections’ long axes increases from 0 ° to 90 °, the contact stress distribution curves on the core area for the seal face change from cosine to sine type, and the maximum at the peaks and troughs and the average first decrease and then increase. The relationship curves between the maximum or average contact stress and the angle of two long axes are approximately symmetrical about the line θ = 45° . This paper provides a simulation evaluation for the ICV metal seal pair with roundness error.
Spatial Features of Extreme Waves in Gulf of Mexico
Authors: Wada Ryota , Jonathan Philip , Waseda Takuji
Published: December 2020

Extreme value analysis of significant wave height using data from a single location often incurs large uncertainty due to small sample size. Including wave data from nearby locations increases sample size at the risk of introducing dependency between extreme events and hence violating modelling assumptions. In this work, we consider extreme value analysis of spatial wave data from the 109-year GOMOS wave hindcast for the Gulf of Mexico, seeking to incorporate the effects of spatial dependence in a simple but effective manner. We demonstrate that, for estimation of return values at a given location, incorporation of data from a circular disk region with radius of approximately 5° (long.-lat.), centred at the location of interest, provides an appropriate basis for extreme value analysis using the STM-E approach of Wada et al. (2018).
Consistent State Space Modelling of Hydrodynamic Memory
Authors: Kaasen Karl E.
Published: December 2020

The conventional way to model hydrodynamic memory or radiation force is to use retardation functions. These functions are usually derived from frequency-dependent damping functions that are calculated by a diffraction-radiation code using potential theory. Calculating the retardation functions can be challenging due to lack of information at high frequency. In simulation of wave-driven vessel motion the retardation function is convolved with the velocity to give the wave radiation force, which is time-consuming. The paper describes how the memory effects can be modelled consistently by linear differential equations, such that coupled modes of motion share one set of poles.

The coefficients of the differential equations are found by least squares fitting of a certain rational function to the numerical damping function. One advantage of this is that no assumption need to be made about the added mass at infinite frequency. Nor is any conditioning of the given data necessary.

Using the fitted model in time-domain simulation is much quicker than using retardation functions. The method is applied to data representing the sway, roll and yaw motions of an FPSO of 238 m length. It was found that a sixth-order differential equation model fitted the given numeric radiation function well.

It is shown how the high frequency asymptote for added mass can be estimated with high accuracy, which is valuable when it is not known in advance.
Study of Hot Cracking on Automatic Tandem Butt Welding
Authors: Maeda Shintaro , Shibahara Masakazu , Nishihara Kensaku , Takeda Hiroyuki , Miwa Tsuyoshi , Yamazaki Kei , Morimoto Tomokazu , Ma Ninshu
Published: December 2020

In recent years, ship hulls have become larger. And the welding has become more important technology in ship building. In other word, welding has become more important technology in shipbuilding. In Japanese shipbuilding, multiple electrode butt welding has been performed with large current and high speed to increase construction efficiency. However, the multiple electrode welding method may cause a hot cracking. X-ray or ultra sonic wave inspection and repair welding are necessary due to the generation of hot cracking. These will increase the production cost. Therefore, it is important to prevent hot cracking. It is known that hot cracking is generated by both metallurgical and mechanical factors. The authors propose a new evaluation method of hot cracking based on the modeling of both mechanical and metallurgical behaviors. In the developed method, from the metallurgical point of view, solidification growth direction is determined from the temperature gradient obtained by the heat conduction analysis to predict the position of hot cracking. Moreover, from the mechanical point of view, the possibility of the generation of hot cracking is assessed using plastic strain increment in Brittleness Temperature Range (BTR). In order to show the validity of the developed method, the developed method is applied to the analysis of hot cracking on automatic tandem butt welding through the comparison with experimental results. As a result, it is demonstrated that the hot cracking can be evaluated by using the developed method.
Evaluation of Singular Value Decomposition (SVD) Enhanced Upscaling in Reservoir Simulation
Authors: Zhou Xu , Tyagi Mayank
Published: December 2020

Reservoir upscaling is an important step in reservoir modeling for converting highly detailed geological models to simulation grids. It substitutes a heterogeneous model that consists of high-resolution fine grid cells with a lower resolution reduced-dimension homogeneous model using averaging schemes. Its objective is to use a coarse grid model to represent a fine grid model, thus to reduce simulation time. The benefit of upscaling in reservoir simulation is that it efficiently saves simulation time, and effectively preserves key features of data for flow simulation.

Singular Vector Decomposition (SVD) is a matrix decomposition method. It has been used for image processing and compressing. It has been proved to be capable of providing a good compression ratio, and effectively saves digital image storage space. SVD also has been used in noise suppression and signal enhancement. It has been shown to be effective in reducing noise components arising from both the sound sampling and delivery system.

This study evaluates the effect of SVD in parameterization and upscaling for reservoir simulation. A two-phase flow reservoir model was created using data from the SPE tenth comparative solution project [1].

Simulation results show that SVD is valid in the parameterization of permeability values. The reconstructed permeability matrices using certain amount of singular values are good approximations of the original permeability values. Simulation results from SVD processed permeability values are similar to that using the original values.

SVD is then applied on the upscaled permeability value to evaluate the effectiveness on upscaling. Simulation results were compared between the base case, upscaled case, and SVD upscaled case. The simulation results did not show a significant improvement in the accuracy of predicting oil production by applying SVD on the upscaled permeability values. It could be because the reconstructed permeability matrix has the same dimension before and after the SVD processing, thus the model accuracy and efficiency are not significantly improved.

Future work includes adding more cases to further explore the effect of SVD on upscaling. The number of grid blocks may be increased, and more layers can be added to investigate whether SVD enhance upscaling for larger scale reservoir simulation models.
Comparative Study on Stress Intensity Factors for Surface Cracks in Welded Joint and Flat Plate by Using the Influence Function Method
Authors: Kyaw Phyo Myat , Naoki Osawa , Ramy Gadallah , Satoyuki Tanaka
Published: December 2020

Welding is an effective method for joining metallic structures which are very common in the construction of ships and offshore platforms. However, welded joints are prone to fatigue failure under cyclic loading due to the associated high residual stresses. In order to assess the fatigue crack propagation (FCP) accurately, precise evaluation of stress intensity factors (SIFs) is a key parameter. The residual stress distribution on the crack face of welded joints is usually non-uniform and also depends on boundary conditions. Therefore, an efficient technique is required to calculate SIFs for welded joints under non-uniform stress distribution.

In this study, SIFs of semi-circular surface cracked welded joints are calculated by using the influence function method (IFM). The IFM has been introduced as an efficient method to evaluate SIFs under arbitrary stress distribution. The influence coefficient databases (ICDB) are developed for welded joints and flat plate models using IFM in this study. As the crack face traction (CFT) integral is employed in this developed influence coefficients (IC), the SIFs given by IFM are more accurate compared to the previously established solutions without CFT-integral. The ICDB and SIFs evaluated by using welded joint and flat plate models are compared and discussed. This study reveals the difference between ICDB of flat plates and welded joints, and estimation error of calculated SIFs for welded joints by using flat plate ICDB.
A Novel Bi-Modal Wave Analysis Approach to Pipelay Installation Analysis
Authors: Lee Dan , Niesluchowski Piotr
Published: December 2020

The single wave or uni-modal wave analysis approach to define the installation seastates, based on a single wave with varying directions, wave heights and periods, is a standard approach among the installation contractors. However, in many of the offshore projects, e.g. offshore Trinidad, and Senegal and Mauritania, bi-modal seatates or waves are a common occurrence, but they are not considered in the installation analysis due to the complexity of the analysis and the computation time required to capture two waves, i.e. wind-sea and swell concurrently from different directions.

A novel bi-modal wave analysis approach is developed to assess the risk to pipelay installation operations due to the impact of bi-modal waves on the installation vessel, characterised by two peak frequencies of varying directions, wave heights and periods. The approach requires the use of clustered data, based on hindcast wave data over a period of time which can be provided by the Metocean Specialist. A combination of statistical evaluation of the clustered data and vessel response screening is used to identify critical clustered pairs for further installation analysis, and to complement the established single wave analysis and the associated installation seastates.

An example is provided in this paper to illustrate the benefits of bi-modal waves consideration, and to demonstrate the use of this novel approach in order to ensure any potential risk is captured so that the pipelay installation operations can be carried out in a safe offshore environment.
HSE Consequences of FPSO Mooring Lines Pretension Uncertainty in Deep Waters Applications
Authors: Araújo Jairo B. , Sales Joel S. , Fernandes Antonio C. , Thurler Ana C. S.
Published: December 2020

The purpose of FPSO (Floating Production Storage and Offloading) mooring system is to keep the unit operating in site in order to attend the Health, Safety and Environment (HSE) requirements and to meet the production risers design requirements. The pretension specification is a design task and it is a key activity due to its influence on extreme loads and fatigue life for both the mooring lines and risers. It is surprising that the project pretension specifications are not always actually implemented in practice and followed during all the unit life. Some inaccurate methods are used to get the actual pretension and may cause significant errors, and this may cause pretensions values outside design allowable tolerances.

A contemporary uncertainty analysis method that uses numerical simulations to estimate the consequences and propagation of the uncertainties in pretensions is applied. A case study is presented for the case of an operating FPSO moored by a spread system, offshore Brazil. A second investigation compares the uncertainty of pretensions measured by means of sensors with the uncertainties that arise from indirect measurements by top angles and as built data for mooring segments and anchor points.

The paper finally shows the need of a Mooring Integrity Management (MIM) implementation of at least annual pretension measurements with a robust and higher precision system.
Adjusting Environmental Contours for Specified Expected Number of Unwanted Events
Authors: Vanem Erik
Published: December 2020

Environmental contours are applied in probabilistic structural reliability analysis to identify extreme environmental conditions that may give rise to extreme loads and responses. Typically, they are constructed to correspond to a certain return period and a probability of exceedance with regards to the environmental conditions that can again be related to the probability of failure of a structure. Thus, they describe events with a certain probability of being exceeded one or more times during a certain time period, which can be found from a certain percentile of the underlying distribution. In this paper, various ways of adjusting such environmental contours to account for the expected number of exceedances within a certain time period are discussed. Depending on how such criteria are defined, one may get more lenient or more stringent criteria compared to the classical return period.
Ship Resistance When Operating in Floating Ice Floes: A Derivation of Empirical Equations
Authors: Huang Luofeng , Ryan Christopher , Igrec Bojan , Grech La Rosa Andrea , Stagonas Dimitris , Thomas Giles , Li Zhiyuan , Li Minghao , Ringsberg Jonas W.
Published: December 2020

With the effects of global warming, the Arctic is presenting a new environment where numerous ice floes are floating on the open sea surface. Whilst this has unprecedentedly improved Arctic shipping navigability and brought about significant opportunities, the interaction of such floes with ships has yet to be understood, thus hindering appropriate assessment of corresponding ship performance. This paper presents work on developing empirical equations to estimate the effects of such floes on ship resistance. Based on extensive data from validated computational simulations, the ice-floe resistance has been shown to correlate with ship beam, ship speed, ice concentration, ice thickness and floe diameter, and the regression powers of each the parameter on resistance are ascertained for a container ship. This leads to an empirical equation that can immediately predict ice-floe resistance in a given condition. The proposed approach has the potential to facilitate propulsion power estimates for Arctic shipping, as well as providing valuable insights into ship design for these environmental conditions.
Efficient Nonlinear Response Determination of an Array of OWC Energy Harvesters
Authors: Malara Giovanni , Spanos Pol D.
Published: December 2020

Oscillating Water Columns (OWC) are utilized for producing electrical energy from sea waves by exploiting the oscillation of a water column located under an air chamber for producing an air flow driving an air turbine connected to an electrical generator. The array configuration is considered in several engineering applications, where the OWCs are embedded in coastal infrastructures, such as vertical breakwaters. In this context, the water columns are likely to be placed nearby. Thus, interactions among chambers occur because of wave radiation phenomena.

This article describes a nonlinear model governing the dynamics of an OWC array embedded in a vertical breakwater. The differential equations include effects associated with hydrodynamic memory and isentropic thermodynamics, which prohibit the derivation of an exact solution giving the OWC array response. Thus, the article develops approximate solutions determined by relying on the concept of equivalent linearization, which is applied under the assumption of both deterministic, and stochastic excitations. Juxtaposition of the approximate approach results with relevant direct numerical integration data confirm its reliability and efficiency.
Collapse Pressure Enhancement of Offshore Pipeline Considering ERW Pipe Manufacturing Process
Authors: Han Seong-Wook , Park Yeun Chul , Kang Soo-Chang , Kim Ho-Kyung , Yi Jiwoon
Published: December 2020

As the application of electric resistance welded (ERW) pipes in deep-water increases, accurate structural performance assessment satisfying the limit state, which is collapse performance, is necessary. Advantages of ERW pipes are effective productivity coming from continuous manufacturing process, but it is hard to track change in mechanical properties during manufacturing. In this study, the ERW pipe manufacturing process was simulated as a three-dimensional finite element method, and the collapse analysis was performed by reflecting the results of the ERW pipe manufacturing process. The results showed that adjustment of ERW pipe manufacturing process had a significant effect on enhancement of collapse performance.
Development of Data-Driven Models for Prediction of Mooring Line Tensions
Authors: Kumar Nitesh , Liong Ching Theng , Chen Wei Kean , Magee Allan Ross , Chua Kie Hian , Choo Yoo Sang
Published: December 2020

This paper describes the development of data-driven models for the prediction of mooring line tensions by separating the low- and wave-frequency components of the tensions, such that the former is approximated as quasi-static tensions while the latter is predicted using ANN models.

A bilinear model is used to interpolate the low-frequency quasi-static tensions between known values in a look-up table while a feed forward neural network model that utilizes the fairlead motions as input is used to predict the tension dynamics at the fairlead. The ANN models are trained using the results from numerical simulations, such as those generated during the engineering design and construction stages of the floating structure.

The predicted line tensions are compared with those obtained using coupled numerical simulations, including test cases for different wave realizations that are not included in the training dataset. Models trained for single and multiple directions of the environment are also assessed for prediction accuracy.

Initial comparisons show that good predictions of line tensions can be obtained for certain environments using the proposed approach, thus demonstrating the potential for use in applications where real-time predictions are required to enhance the safety and / or reliability of mooring systems.