bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.