bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Energy Absorption of Combined Foam-Honeycomb Layered Structures
Authors: Karagiozova Dora , Alves Marcilio 
Published: October 2016

Analytical and numerical analyses are carried in order to reveal the importance of the topology of the cellular materials for their dynamic compaction. The aim is to distinguish between the deformation mechanisms and energy absorption of materials, which exhibit structural softening, such as out-of-plane loaded honeycomb, and structural hardening (foam). It is shown that the dynamic compaction of honeycombs does not obey the law of shock wave propagation and a new phenomenological model of the velocity attenuation in out-of plane loaded honeycomb is proposed. Comparisons with some currently available theoretical models of the dynamic compaction of cellular materials are discussed when paying attention to the effect of the material homogenization of the honeycomb on their response to impact loading.
A numerical analysis of a bi-layer cellular structure comprising layers with dissimilar constitutive properties is carried out to reveal the possibility for the peak load reduction in cellular structures when subjected to impact loading. In the reported examples, a foam material (Alporas with density of 245 kg/m3) and hexagonal honeycomb made of aluminium alloy AA5056 and having densities of 60.46 kg/m3 and 96 kg/m3 are used.
Numerical Simulation of Icebreaking Process and Parameters Sensitivity Analysis
Authors: Qiao Yue , Han Duanfeng , Teng Mange , Wang Guoliang , Liu Feng 
Published: October 2016

The interdependence exists between ship response and ice load during the ship-ice interaction process. According to the ice properties and the velocity between a ship and ice can make influences on ice load, taking a Russian icebreaker as model, a series of numerical simulations were performed to research the ice load variation tendency rules in 3 axial directions and the total force direction. On the basis of regarding ice elements as elastic materials, the theory of a semi-infinite elastic plate resting on an elastic foundation was used to simulate ice sheet.
By means of finite element model, stress and strain contours of typical moment and ice load history curve in four directions were obtained. Furthermore, the effect of important parameters such as elasticity modulus of ice, ice thickness and ship speed on the impact force were also analyzed.
The results indicate that ice sheet will crack in the form of a circle centered on the collision point which accord with actual circumstance, and there are some certain variation relationships between each calculation parameters and ice load values. At the same time, the study can also provide technological support for ice load research.
Experimental Study of Flow Field Characteristics in Tidal Stream Turbine Arrays
Authors: Nuernberg Martin , Tao Longbin 
Published: October 2016

Tidal currents at many locations around the world have great potential to be used as a large scale renewable energy resource in the future. For large tidal turbine arrays to be commercially viable, the interactions of large devices operating in a confined operating environment need to be understood to optimise the layout of arrays to maximise electricity generation.
This study presents results from a comprehensive experimental investigation of the flow field characteristics within tidal turbine arrays across a number of array layout configurations and current velocities. Up to four small scale turbines were placed in a circulating water channel to investigate the effects of changing array configuration and wake interaction on the flow velocity and turbulence characteristics in small array layouts. Detailed account of the resulting flow field characteristics has been taken by particle image velocimetry measurements at a number of locations within the wake of the array thus providing a large set of instantaneous flow recordings for further analysis of flow features and wake characteristics.
Results are shown for experimental studies of single, three and four turbine arrays and some preliminary comparison between experimental measurements and numerical results are made.
Alternative Stress Models With Focus on Full FE Model for Flexible Risers
Authors: Wang Lidong , Sævik Svein , Ye Naiquan , Yue Qianjin , Yang Zhixun , Chen Jinlong 
Published: October 2016

Flexible risers are exposed to complicated loading conditions including internal/external pressure, wave and current loads, as well as floater movements. The combination of these three loads may lead to instability of the tensile armor wire in both longitudinal and transverse directions, which may result in different stress state based on different numerical models in BFLEX software. Simplified models have been implemented to calculate the stress in tensile armor wires with moderate accuracy, with only considering the longitudinal slip of wires.
In order to investigate how the transverse slip will influence the stress state, a full finite element (FullFE) modeling option has been implemented recently to capture the interaction between different layers more precisely thus giving more accurate stress prediction. Different stress components will be compared with already existing simplified approaches. In addition, geodesic and loxodromic slip assumptions will be applied to study the slip behavior of the tensile armor layers.
Prediction of the Damage Extents of Ship’s Double Hull Side Structures Subjected to Lateral Collisions
Authors: Cho Sang-Rai , Kim Kyeong-Ryun , Song Seung-Uck , Park Sang-Hyun , Lee Joo Sung , Lee Jin Tae 
Published: October 2016

Lateral collision tests were conducted on two steel double-hull side structure models, models DH-3 and DH-4. The models were approximately one-seventh scale of a VLCC (Very Large Crude Carrier), and the small longitudinal stiffeners of a VLCC were smeared into the shell plates. The collision tests were performed using a car crash testing facility. The striker had a knife-edge type header and its mass was 1,350 kg. The collision velocities were 7.224 m/s and 10.0 m/s for models DH-3 and DH-4, respectively. The collision test results are briefly reported in this paper.
Using a commercial FEA package, numerical collision analyses were then conducted for the two new models together with another two models of one-tenth scale, which were reported elsewhere. In the numerical analyses the strain and strain-rate hardenings were considered. The convergence test was also performed to obtain an optimal mesh size. The numerical predicted damage extents were compared with those of the experiments. The prediction errors were in the range of −5.7% to +6.8%.
An analytical approach was also attempted to predict the damage extents of double-hull structures subjected to lateral collisions. Compared with the experimental and numerical predictions the analytical predictions provide acceptable accuracies for the initial design stage. For a more rational ship structural design against collision, future studies are proposed to improve the prediction accuracy and reliability.
Experimental and Numerical Study on Flow Past Four Rectangular Columns in Diamond Configuration
Authors: Liang Yibo , Tao Longbin , Xiao Longfei , Liu Mingyue 
Published: October 2016

Vortex-Induced-Motions (VIM) is a cyclic rigid body motion that is induced by vortex shedding of a large sized floating structure (Spar, Semi-Submersible and Tension-Leg Platform) in deep water. Since the potential impact of VIM on fatigue life of mooring and riser systems can be critical, the study of the VIM phenomenon has drawn considerable attention among offshore engineering community. Despite the effort, there is still lack of understanding the complex fluid-structure interaction phenomenon. To date, it is very much relying on the simplified empirical approach in practical design.
Most of the Semi-Submersibles consist of four rounded-cornered rectangular columns. To investigate the flow interaction between each columns can reveal some physics behind the VIM. In this study, flow past four stationary rounded-corner rectangular columns are tested in the circulating channel and numerically simulated by the Star-CCM+ CFD package. Forces on the columns and the flow characteristics behind the structures are present in this study. A 2-D particle imaging velocimetry (PIV) technic has been adopted in present study to obtain the flow characteristics. The aim of this study is to investigate the interactions between four square columns.
Fatigue Life Analysis Method of Upper-Hinge Joints of FPSO SYMS Based on Real-Time Proto-Type Monitoring Technique
Authors: Wu Wenhua , Lv Baicheng , Li Wenyuan , Wang Yanlin , Yue Qianjin , Zhang Yantao 
Published: October 2016

At present, the complexities of distributive characteristics in temporal and spatial domain of ocean environmental loading contribute to the difficulties of the fatigue life estimations of marine structures.
In shallow water, soft yoke mooring system (SYMS) is considered to be the best mooring system, and has been widely used in oil development in the Bohai Bay and the Gulf of Mexico. Soft yoke mooring system establishes the mooring functions via the multi-dynamic mechanism of thirteen hinge joints. The accuracy of fatigue life of the hinge joints is important to ensure the safety of mooring system. The damage failure of hinge joints would cause great financial loss.
In 2012, Dalian University of Technology set up a full coupled proto-type monitoring system which consisted of the four sub-monitoring systems, that is, ocean environmental parameters sub-system including wind, current and wave factor, motions and attitudes of the FPSO including six degree freedom of vessel motions, motions and the mooring force monitoring system of the mooring leg. The massive monitoring information is obtained by the integrated software with continuous. The present paper proposes a real-time fatigue life prediction method of upper hinge joint of SYMS based on the prototype monitoring technique.
The friction parameter of hinge joints contact surface is increased in long-term service and reduced by adding lubricant. In the SYMS design phase, there is no effective analysis of the repeated friction parameter changes. The variations of friction coefficients caused by long-term cycle stress and maintenance are considered in the fatigue calculation. The stress distribution of hinge joints under design parameter is carried out by using ABAQUS. Through calculation and comparison, the equivalent stress and fatigue damage variable of KPA (Key Process Area, large deformation units and easy wear area) units in the condition of the friction coefficient is 0.15 (design parameter) and 0.95. We found that the friction coefficient change due to long-term service will speed up the fatigue failure of the hinge joints.
The relationship between friction coefficients and KPA regional stress of mooring legs swinging angle are established through the finite element simulation. Through prototype monitoring software analysis the marine environment loading, structural response and KPA regional stress information, the abrasion of the hinge node and fatigue damage variable Dθμ can be real-time predicted.
The present fatigue life analysis method based on monitoring technique exhibits good advantages and research value for the fatigue life estimation of offshore structure subject to wave induced motions.
Motion Analysis of TAD and TLP Platforms Operating Side by Side
Authors: Hannan Mohammed Abdul , Wei Bai , Magee Allan Ross , Choudhary Ankit , Jain Amit , Adaikalaraj Peter Francis Bernad , Hussain Anis 
Published: October 2016

A Tender Assisted Drilling (TAD) is typically a support vessel that serves support of a drilling rig. The TAD acts as a platform for supplies and is stationed alongside the drilling rig from which the rig will work off to reduce the loads on the actual rig. While operating, the TAD needs to be structurally coupled with the floating production platform. The coupling makes sure that the Tender does not drift away from the platform and provides stiffness to the relative motions between the TAD and the production platform. Current practice is to couple the TAD and the platform by using nylon hawser ropes. The hawsers provide adequate elasticity to accommodate the low frequency motions and do not allow the TAD to drift away from the production platform. In this study the individual free floating TAD and Tension Leg Platform (TLP) system is model first using the commercial software Hydrostar. After that the technique of developing equivalent stiffness matrix to represent the TLP tendons are applied in order to simulate the influence of the tendons on TLP motions. The response of these individual models are then calculated numerically and validated against existing data. After validation is performed, coupled interactions of this two body is simulated while both the bodies are freely floating side by side. Several possible side by side orientations of the TAD and TLP are tested and the results are compared for this first phase of the study. Later, the freely floating bodies are connected to each other by means of springs. The connection between the two floating bodies is modeled using equivalent stiffness matrix for connections.
The results obtained from this first phase frequency domain analysis will help to clearly understand the coupled behavior of such system under various orientations. In later phases, this model will be further developed in order to perform the time domain analysis and several innovative types of connections other than simple hawsers will be tested in order to couple this TAD and TLP system.
Combined Experimental and Numerical Studies of Ocean Basin Inlet Design
Authors: Magee Allan R. , Dao My Ha , Zheng Yingying , Jaiman Rajeev Kumar , Lim Kian Yew 
Published: October 2016

Current generation systems consisting of pumps or impellers are conventionally used in deepwater model test facilities for producing realistic full-depth steady current flows. A typical current inlet design involves the diversion of current into a mixing chamber which is then channeled into the basin through an array of flow-conditioning filters (screens) installed along the width of the basin. The screens are used to reduce turbulence and create an overburden pressure within the mixing chamber to enhance inflow uniformity. However, one undesirable consequence of this setup is that it increases energy loss to the system which leads to a higher operating cost.
In order to address this problem, the present work is aimed at establishing an effective and energy-efficient inlet design and screen configuration to improve spatial uniformity of inflow with minimal energy loss to the system. A wind tunnel study is carried out to determine an optimal tapered culvert angle and honeycomb screen configuration to achieve the aforementioned objectives. Uniformly-distributed wind flow of up to 20 m/s is channeled into a Perspex chamber and allowed to escape sideways through plastic honeycomb screens. Pressure drops are measured with an array of transducers at locations upstream and downstream from the honeycomb screen, while streamwise velocity distribution across the width of the chamber is captured with a pitot-static tube mounted on a traversing mechanism. Three cases of flow resistance are investigated, i.e. no screen, thin honeycomb screen (thickness = 12mm), and thick honeycomb screen (thickness = 50mm). For each case, the culvert angle is varied between 7°, 13° and 21°. A CFD model is developed with OpenFoam and compared with the present experimental data. The validated model is expected to be used to investigate more complex inlet configurations and assess the performance of realistic ocean basin geometry.
TRM Versus FRP as Strengthening Material for Improving Impact Resistance of RC Slabs
Authors: Abbas Husain , Almusallam Tarek , Al-Salloum Yousef , Siddiqui Nadeem , Abadel Aref 
Published: October 2016

This study experimentally investigates the effectiveness of textile reinforced mortar (TRM) in controlling the local damage in reinforced concrete (RC) slabs subjected to impact loads. The results are then compared with that of conventional FRP strengthening of RC slabs. The impact tests were conducted using the strike of hemispherical nosed steel projectile on TRM- and FRP-strengthened RC slabs. The unstrengthened specimens considered as control were 600 mm square, 90 mm thick RC slabs. The slabs were reinforced with 8 mm diameter steel rebars at 100 mm c/c spacing both-ways. The slabs were strengthened by externally bonding single layer of Carbon FRP (CFRP) and two layers of TRM on the rear face of the slabs. In TRM strengthening, the textile contained equal quantity of high strength carbon fiber roved in two orthogonal directions. They were simply placed on the top of each other and bonded on a secondary polypropylene line. A commercial polymer modified cement mix was used as mortar in TRM strengthening. The velocity of 40 mm diameter steel projectile was varied within sub-ordinance range and the projectile was made to strike normal to the slab using a gas gun.
Based on the experimental testing conducted in this study, it was observed that CFRP and TRM strengthening of RC slabs are effective in reducing the local damage in RC slabs from front and rear faces for the same impact velocity. Both TRM and CFRP strengthening cause increase in the ballistic limit velocity and the perforation energy of RC slabs. Moreover, the CFRP sheet and TRM layer considerably reduce the generation of secondary projectiles which are in the form of flying debris in un-strengthened RC slabs. Overall, among the two strengthening methods studied, the TRM strengthening of RC slabs is found to be either equally good or better than the CFRP strengthening in resisting impact loads.
Experimental Study on a 3-Dimensional Hydro-Elastic Deformation of “Underwater Platform” With Multi-Towers in Waves
Authors: Haneda Ken , Murai Motohiko , Yamanoi Jun 
Published: October 2016

Underwater platform was proposed in OMAE 2015 for the purpose of enhancing productivity of various types of renewable energy converter on the sea and its feasibility study was carried out through 2 types of tank experiment [1]. The underwater platform which is a very large frame shape structure connects several floaters under the sea to share power cables and mooring lines and to keep relative distances between the floaters. In the experiment, 1/200 scale elastic model with three spar buoys was used. The buoys imitated spar type floating offshore wind turbines (FOWTs). From the experiment, it was shown that the platform with large draft can reduce its response in waves.
In this paper, we report new result and knowledge obtained by additional model experiments use the 1/200 model. In the experiment, we changed the arrangement and draft of the model and measured hydro-elastic deformation of the underwater platform in waves. From the last experiment, relationship between draft settings and response was shown. In the experiment, relationship between wave angles and response was surveyed.
From the experiment, we have confirmed followings: 1. Rigid-body motion is remarkable in beam waves, 2. Elastic response is remarkable in head waves, and 3. Remarkable torsional motion is occurred in 45 degrees’ waves. The more important thing, however, is that the experimental result indicated that the platform of large draft decreases its motion in the all the wave angles.
Human Factor Study for Maritime Simulator-Based Assessment of Cadets
Authors: Liu Yisi , Hou Xiyuan , Sourina Olga , Konovessis Dimitrios , Krishnan Gopala 
Published: October 2016

Maritime accident statistics show that the majority of accidents/incidents are attributed to human errors as the initiating cause. Some studies put this as high as 95% of all accidents (collision, grounding, fire, occupational accidents, etc). The traditional way to investigate human factors in maritime industry is the statistical analysis of accident data. Although this analysis can provide key findings, it cannot capture the causal relationship between performance shaping factors and human performance in the everyday routine work, and is not suitable to be used in the individual assessment of cadets.
To reveal the effects of human factors in maritime and assess the performance of cadets, a full-mission simulator is widely used. Different scenarios such as bad weather, day and night environment, different traffic load, etc. can be simulated. The fine details of the cadet performance can be recorded in the simulator during the assessment. As a result, other than performance failure, the near misses can also be detected. Additionally, a number of cadets can go through the same scenarios at the same time and between-subjects comparison is enabled.
Besides the operations recording provided by the simulator, biosignal-based tools can additionally help in the human factors study in maritime. The existing methods include palmer perspiration, electrocardiography, etc. However, the psychophysiological states that can be recognized by these methods are limited. Electroencephalogram (EEG) biosignals can be used to directly assess the “inner” mental states of subjects. Nowadays, since the EEG devices become portable, easy to setup, and affordable in price, EEG-based tools can be used to assess psychophysiological state of subjects. Using the sensors during performing the task we can recognize the cadet/captain’s emotions, attentiveness/concentration, mental workload, and stress level in real time. In this work, we propose a real-time brain state recognition system using EEG biosignals to monitor mental workload and stress of cadets during simulator-based assessment. Currently, the proposed and implemented system includes stress and mental workload recognition algorithms. The EEG-based mental state monitoring can reflect the true “inner” feelings, stress level and workload of the cadets during the simulator-aided assessment. The time resolution is up to 0.03 second. As a result, we can analyze the recognized brain states and the corresponding performance and behavior recorded by the simulator to study how human factors affect the subject’s performance. For example, we can check is there any correlation of the cadet’s stress level and performance results. Finally, the proposed EEG-based system allows us to assess whether a cadet is ready to perform tasks on the bridge or needs more training in the simulator even if he/she navigated with few errors during the assessment.
A Ballast System for Automated Deep-Sea Ascents
Authors: Golz Matthias , Boeck Florin , Ritz Sebastian , Holbach Gerd 
Published: October 2016

The efforts to discover the world’s oceans — even in extremely deep-sea environments — have grown more and more in the past years. In this context, unmanned underwater vehicles play a central role. Underwater systems that are not tethered need to provide an apparatus to ensure a safe return to the surface. Therefore, positive buoyancy is required and can be achieved by either losing weight or expanding volume. A conservative method is the dropping of ballast weight. However, nowadays this method is not appropriate due to the environmental impact.
This paper presents a ballast system for an automated ascent of a deep-sea seabed station in up to 6000 m depth. The ballast system uses a DC motor driven modified hydraulic pump and a compressed air auxiliary system inside a pressure vessel. With regard to the environmental contamination in case of a leakage, only water is used as ballast fluid. The modification of an ordinary oil-hydraulic radial piston pump and the set-up of the ballast system is introduced.
Results from sea trials in the Atlantic Ocean are presented to verify the functionality of the ballast system.