bluuebunny/crossref_metadata_2025 huggingface dataset:
Plastic Effects on High Cycle Fatigue at the Edge of Contact of Turbine Blade Fixtures
Authors: Richter C. H. , Krupp U. , Zeißig M. , Telljohann G.
Published: October 2017

Slender turbine blades are susceptible to excitation. Resulting vibrations stress the blade's fixture to the rotor or stator. In this paper, high cycle fatigue at the edge of contact (EOC) between blade and rotor/stator of such fixtures is investigated both experimentally and numerically. Plasticity in the contact zone and its effects on, e.g., contact tractions, fatigue determinative quantities, and fatigue itself are shown to be of considerable relevance. The accuracy of the finite element analysis (FEA) is demonstrated by comparing the predicted utilizations and slip region widths with data gained from tests. For the evaluation of EOC fatigue, tests on simple notched specimens provide the limit data. Predictions on the utilization are made for the EOC of a dovetail setup. Tests with this setup provide the experimental fatigue limit to be compared to. The comparisons carried out show a good agreement between the experimental results and the plasticity-based calculations of the demonstrated approach.
Quantification of Gas and Water Transfer Between Coal Matrix and Cleat Network During Drainage Process
Authors: Zou Mingjun , Wei Chongtao , Zhang Miao , Lv Xiaochun
Published: October 2017

Mathematical models were developed in this study to quantify the gas and water transfer between coal matrix and cleat network during coalbed methane (CBM) drainage, which can be helpful to achieve some useful findings on features of fluid migration within coal reservoirs during drainage process. A typical CBM well located at southern Qinshui basin of China was selected as the case study. The ineffective critical porosity was defined and was used to acquire fluid transfer as a key parameter of the established model. Results showed that both the gas and water transfer controlled the drainage performances. Water drained from cleat was found to be the main reason for the decrease in the reservoir pressure at the early drainage stage, while the water transfer became significantly more important with the continuation of the drainage process. The first peak of gas production was controlled by gas desorption, and the subsequent peaks were influenced by the gas transfer.
Application of the Blade Element Momentum Theory to Design Horizontal Axis Wind Turbine Blades
Authors: Dehouck Vincent , Lateb Mohamed , Sacheau Jonathan , Fellouah Hachimi
Published: October 2017

Small horizontal axis wind turbines (HAWTs) are increasingly used as source of energy production. Based on this observation, the blade element momentum theory (BEMT) is applied all along the blade span to calculate the optimal turbine aerodynamic performances. The main objective is to optimize the HAWT blade profile for specific initial conditions. The effects of three geometric parameters (the blade tip radius, the number of blades, and curvature) and one dynamic parameter (the tip speed ratio (TSR)) are determined for an upstream air speed of 7 m/s. A new empirical relation for the chord distribution over the blade span is presented here; c(r)/R=c0+A[1+r/R]exp(−Br/R), where c0 = 0.04 is the chord offset, A = 1/Z is an amplitude, and B = [(Z/5) + 2] is the decay constant. It takes into account both the effect of blade tip radius and the number of the blades.
Deliberate Salinization of Seawater for Desalination of Seawater
Authors: Arias Francisco J.
Published: October 2017

The basis of a novel method for seawater desalination is outlined. In this work, pressure-retarded osmosis (PRO) energy is obtained and used posteriorly for the reverse osmosis (RO) process for seawater desalination. Although PRO process coupled with an RO process has been studied in the past, however, in this work, there is a fundamental difference. Instead of bringing river or wastewaters with low salinity to the coast to be mixed with the seawater to run the PRO process, here is the seawater which is deliberately salinized. This technique has one important consequence, namely, that it is no longer required to be in places where rivers or wastewaters flow into the sea. This important difference eliminates this until now somehow paradoxical requirement if one considers that regions needing desalination are generally poor of water resources. On the other hand, it is not a coincidence that regions needing desalination plants are also regions with rich open salt deposits in the neighborhood; high evaporation, high concentration of salt deposits, and the need for freshwater are all of them directly correlated. Therefore, the idea proposed in the paper is consistent with the problem. The high evaporation in the region which is causing the need for desalination also is creating the solution to do this by using the salt deposits created. The economic feasibility of this method is preliminarily assessed in terms of the thermodynamic limits of extractable energy and then with the cost of the salt required to obtain this energy which is compared with the price from electrical grid. It was found that in order to reduce the amount of salt required for the process, and to make the cost of energy competitive, it is necessary to direct the hypersaline draw solution (draw solution) in a cyclic loop and to have the highest possible volume fraction for the nonsalinized solution (feed solution). Additional R&D is required to explore the possibilities of this concept.
Dynamic and Oscillatory Motions of Cable-Driven Parallel Robots Based on a Nonlinear Cable Tension Model
Authors: Baklouti Sana , Courteille Eric , Caro Stéphane , Dkhil Mohamed
Published: October 2017

In this paper, dynamic modeling of cable-driven parallel robots (CDPRs) is addressed where each cable length is subjected to variations during operation. It is focusing on an original formulation of cable tension, which reveals a softening behavior when strains become large. The dynamic modulus of cable elasticity is experimentally identified through dynamic mechanical analysis (DMA). Numerical investigations carried out on suspended CDPRs with different sizes show the effect of the proposed tension formulation on the dynamic response of the end-effector.
Kinematic Analysis of Planetary Gear Trains Based on Topology
Authors: Gao Ming-Fei , Hu Ji-Bin
Published: October 2017

Planetary gear trains (PGTs) are used in automatic transmission to achieve any desired speed ratios. At present, the study on the relationship between speed ratio and topology is not significant. Therefore, this paper focuses on studying the speed ratio based on topology. For this purpose, the graph theory is used to represent PGTs, and a concept of the speed topological graph is introduced. Based on the proposed graph representation, the relationship between the speed ratio and topology is studied. Three types of topological graphs are analyzed, which includes path, tree, and unicyclic graph, and necessary results are presented. The results reveal the relationship between speed ratio and topology, which helps in understanding the PGTs further. The result can help engineers to arrange the clutches and brakes to achieve desired speed ratio during the conceptual design phase, which can greatly improve the design efficiency of PGTs. The presented kinematics analysis method can be extended to analyze multi-input and multi-output planetary transmission.
Experimental Validation of Surrogate Models for Predicting the Draping of Physical Interpolating Surfaces
Authors: Christensen Esben Toke , Lund Erik , Lindgaard Esben
Published: October 2017

This paper concerns the experimental validation of two surrogate models through a benchmark study involving two different variable shape mould prototype systems. The surrogate models in question are different methods based on kriging and proper orthogonal decomposition (POD), which were developed in previous work. Measurement data used in the benchmark study are obtained using digital image correlation (DIC). For determining the variable shape mould configurations used for the training, and test sets used in the study, sampling is carried out using a novel constrained nested orthogonal-maximin Latin hypercube approach. This sampling method allows for generating a space filling and high-quality sample plan that respects mechanical constraints of the variable shape mould systems. Through the benchmark study, it is found that mechanical freeplay in the modeled system is severely detrimental to the performance of the studied surrogate models. By comparing surrogate model performance for the two variable shape mould systems, and through a numerical study involving simple finite element models, the underlying cause of this effect is explained. It is concluded that for a variable shape mould prototype system with a small degree of mechanical freeplay, the benchmarked surrogate models perform very well.
Numerical Investigation on the Leakage and Static Stability Characteristics of Pocket Damper Seals at High Eccentricity Ratios
Authors: Li Zhigang , Li Jun , Feng Zhenping
Published: October 2017

Annular gas seals for compressors and turbines are designed to operate in a nominally centered position in which the rotor and stator are at concentric condition, but due to the rotor–stator misalignment or flexible rotor deflection, many seals usually are suffering from high eccentricity. The centering force (represented by static stiffness) of an annular gas seal at eccentricity plays a pronounced effect on the rotordynamic and static stability behavior of rotating machines. The paper deals with the leakage and static stability behavior of a fully partitioned pocket damper seal (FPDS) at high eccentricity ratios. The present work introduces a novel mesh generation method for the full 360 deg mesh of annular gas seals with eccentric rotor, based on the mesh deformation technique. The leakage flow rates, static fluid-induced response forces, and static stiffness coefficients were solved for the FPDS at high eccentricity ratios, using the steady Reynolds-averaged Navier–Stokes solution approach. The calculations were performed at typical operating conditions including seven rotor eccentricity ratios up to 0.9 for four rotational speeds (0 rpm, 7000 rpm, 11,000 rpm, and 15,000 rpm) including the nonrotating condition, three pressure ratios (0.17, 0.35, and 0.50) including the choked exit flow condition, two inlet preswirl velocities (0 m/s, 60 m/s). The numerical method was validated by comparisons to the experiment data of static stiffness coefficients at choked exit flow conditions. The static direct and cross-coupling stiffness coefficients are in reasonable agreement with the experiment data. An interesting observation stemming from these numerical results is that the FPDS has a positive direct stiffness as long as it operates at subsonic exit flow conditions; no matter the eccentricity ratio and rotational speed are high or low. For the choked exit condition, the FPDS shows negative direct stiffness at low eccentricity ratio and then crosses over to positive value at the crossover eccentricity ratio (0.5–0.7) following a trend indicative of a parabola. Therefore, the negative static direct stiffness is limited to the specific operating conditions: choked exit flow condition and low eccentricity ratio less than the crossover eccentricity ratio, where the pocket damper seal (PDS) would be statically unstable.
Convective Scaling of Intrinsic Thermo-Acoustic Eigenfrequencies of a Premixed Swirl Combustor
Authors: Albayrak Alp , Steinbacher Thomas , Komarek Thomas , Polifke Wolfgang
Published: October 2017

Spectral distributions of the sound pressure level (SPL) observed in a premixed, swirl stabilized combustion test rig are scrutinized. Spectral peaks in the SPL for stable as well as unstable cases are interpreted with the help of a novel criterion for the resonance frequencies of the intrinsic thermo-acoustic (ITA) feedback loop. This criterion takes into the account the flow inertia of the burner and indicates that in the limit of very large flow inertia, ITA resonance should appear at frequencies where the phase of the flame transfer function (FTF) approaches −π/2. Conversely, in the limiting case of vanishing flow inertia, the new criterion agrees with previous results, which state that ITA modes may arise when the phase of the FTF is close to −π. Relying on the novel criterion, peaks in the SPL spectra are identified to correspond to either ITA or acoustic modes. Various combustor configurations are investigated over a range of operating conditions. It is found that in this particular combustor, ITA modes are prevalent and dominate the unstable cases. Remarkably, the ITA frequencies change significantly with the bulk flow velocity and the position of the swirler but are almost insensitive to changes in the length of the combustion chamber (CC). These observations imply that the resonance frequencies of the ITA feedback loop are governed by convective time scales. A scaling rule for ITA frequencies that relies on a model for the overall convective flame time lag shows good consistency for all operating conditions considered in this study.
A Numerical Investigation of the Onset of Flow Separation in Round-Edge Diverging Tees
Authors: Kok Foo , Myose Roy , Hoffmann Klaus A.
Published: October 2017

The onset condition of flow separation in diverging tee junctions was investigated numerically. Flow separation and recirculation at the proximal region of a bypass graft can contribute to early phase graft failure in aortocoronary bypass (ACB) surgery. Rounding the inlet edge of the branch reduces the likelihood of flow separation and recirculation. The recirculating zone at the upstream end of the branch is fully eliminated when a threshold value of mass flow rate ratio is reached. The corresponding flow characteristics obtained from diverging tees with a diameter ratio ≤0.2 and a radius of curvature ≤ 0.25 for a Reynolds number ≤ 1817 indicate that an increasing flow rate ratio induces an exponential decrease in the recirculation length. An increase in the diameter ratio and Reynolds number increases both the onset condition of the flow separation and the recirculation length at the upstream end of the branch. However, a decrease in the diameter ratio reduces the onset condition of separation more effectively than a decrease in the radius of curvature at the junction.
A New Nonsingular Terminal Sliding Mode Control for Rigid Spacecraft Attitude Tracking
Authors: Wang Zeng , Su Yuxin , Zhang Liyin
Published: October 2017

This paper addresses the finite time attitude tracking for rigid spacecraft with inertia uncertainties and external disturbances. First, a new nonsingular terminal sliding mode (NTSM) surface is proposed for singularity elimination. Second, a robust controller based on NTSM is designed to solve the attitude tracking problem. It is proved that the new NTSM can converge to zero within finite time, and the attitude tracking errors converge to an arbitrary small bound centered on equilibrium point within finite time and then go to equilibrium point asymptotically. The appealing features of the proposed control are fast convergence, high precision, strong robustness, and easy implementation. Simulations verify the effectiveness of the proposed approach.
Fabrication of TiO2 Thin Film-Based Fresnel Zone Plates by Nanosecond Laser Direct Writing
Authors: Jwad Tahseen , Deng Sunan , Butt Haider , Dimov Stefan
Published: October 2017

Fresnel zone plates (FZPs) have been gaining a significant attention by industry due to their compact design and light weight. Different fabrication methods have been reported and used for their manufacture but they are relatively expensive. This research proposes a new low-cost one-step fabrication method that utilizes nanosecond laser selective oxidation of titanium coatings on glass substrates and thus to form titanium dioxide (TiO2) nanoscale films with different thicknesses by controlling the laser fluence and the scanning speed. In this way, phase-shifting FZPs were manufactured, where the TiO2 thin-films acted as a phase shifter for the reflected light, while the gain in phase depended on the film thickness. A model was created to analyze the performance of such FZPs based on the scalar theory. Finally, phase-shifting FZPs were fabricated for different operating wavelengths by varying the film thickness and a measurement setup was built to compare experimental and theoretical results. A good agreement between these results was achieved, and an FZP efficiency of 5.5% to 20.9% was obtained when varying the wavelength and the oxide thicknesses of the zones.
Tribological and Vibration Studies on Newly Developed Nanocomposite Greases Under Boundary Lubrication Regime
Authors: Singh Jayant , Kumar Deepak , Tandon N.
Published: October 2017

Greases are widely used in extreme conditions of load, speed, and temperature, altogether with the improvement in the service life of the machinery by reducing the noise and vibration. The present study deals with the development of nanocomposite greases and their tribodynamic evaluation under boundary lubrication (BL), antiwear, extreme pressure (EP), and vibration behavior of nonconformal metallic contacts. The recording of the vibration signals constitutes the indirect approach to evaluate the lubricity of the tribological contacts. The different nano-additives (reduced graphene oxide (rGO) nanosheets, CaCO3, and α-Al2O3 nanoparticles) are dispersed in commercial lithium grease to formulate nanocomposite greases. The microstructural studies of greases are performed on high-resolution transmission electron microscopy (HRTEM). The BL behavior is studied using four ball tester. Further, the functional groups of the greases and the chemistry of the worn surfaces are evaluated through Raman spectroscopy (RS). To explore the involvement of wear mechanism(s), the morphology of worn surfaces is evaluated using scanning electron microscopy (SEM). The results showed that doping of 0.4% rGO and 5% CaCO3 in bare lithium grease can significantly improve the antiwear, EP properties, and vibration behavior, compared to α-Al2O3 dispersed composite grease.
Energy Harvesting From the Vibrations of Rotating Systems
Authors: Cooley Christopher G. , Chai Tan
Published: October 2017

This study investigates the vibration of and power harvested by typical electromagnetic and piezoelectric vibration energy harvesters when applied to vibrating host systems that rotate at constant speed. The governing equations for these electromechanically coupled devices are derived using Newtonian mechanics and Kirchhoff's voltage law. The natural frequency for these devices is speed-dependent due to the centripetal acceleration from their constant rotation. Resonance diagrams are used to identify excitation frequencies and speeds where these energy harvesters have large amplitude vibration and power harvested. Closed-form solutions are derived for the steady-state response and power harvested. These devices have multifrequency dynamic response due to the combined vibration and rotation of the host system. Multiple resonances are possible. The average power harvested over one oscillation cycle is calculated for a wide range of operating conditions. Electromagnetic devices have a local maximum in average harvested power that occurs near a specific excitation frequency and rotation speed. Piezoelectric devices, depending on their mechanical damping, can have two local maxima of average power harvested. Although these maxima are sensitive to small changes in the excitation frequency, they are much less sensitive to small changes in rotation speed.
Digitalization of Seagoing Vessels Under High Dimensional Data Driven Models
Authors: Perera Lokukaluge P. , Mo Brage
Published: October 2017

Modern ships are supported by internet of things (IoT) to collect ship performance and navigation information. That should be utilized towards digitalization of the shipping industry. However, such information collection systems are always associated with large-scale data sets, so called Big Data, where various industrial challenges are encountered during the respective data handling processes. This study proposes a data handling framework with data driven models (i.e. digital models) to cope with the shipping industrial challenges as the main contribution, where conventional mathematical models may fail. The proposed data driven models are developed in a high dimensional space, where the respective ship performance and navigation parameters of a selected vessel are separated as several data clusters. Hence, this study identifies the distribution of the respective data clusters and the structure of each data cluster in relation to ship performance and navigation conditions. An appropriate structure into the data set of ship performance and navigation parameters is assigned by this method as the main contribution. However, the domain knowledge (i.e. vessel operational and navigation conditions) is also included in this situation to derive a meaningful data structure.
Assessment to Iceberg Impact Loads to Fixed Structures in Multi-Planar Space
Authors: Liu Zhenhui , Ming Song , Amdahl Jørgen
Published: October 2017

This paper investigates the iceberg impact force to fixed structures in multi-planar space (3D). The global and local impact mechanics are discussed in details. The global impact energy is calculated by considering the eccentricities of iceberg in multi-planar space considering the tangential impact momentum. Thus, the impact phenomenon in a detailed manner could be assessed, such as the influences of friction and structural inclination to impact loads et.al.. It is found that the dissipated energy during an impact does not depend on the local stiffness within the contact area. Meanwhile, the impact force and duration are linked to the local stiffness. A semi-integrated analysis has been demonstrated to approach the local deformations of structure and iceberg. The structure and ice deformation could be simplified as linear/nonlinear springs. The ice pressure-area relationship and the force-deformation curve are used respectively to approach the local deformation. The methodology proposed here shows excellent agreement with previous work in planar case (2D). Sensitivity studies have been performed both to global and local mechanics. Conclusions and summaries have been included.
Reproduction of Monopile Ringing Events in Reduced-Duration Model Tests
Authors: Bachynski Erin E. , Kristiansen Trygve
Published: October 2017

Monopile support structures for offshore wind turbines may experience ringing-type responses in steep wave conditions. In order to experimentally capture the statistical distribution of the hydrodynamic loads and structural responses, traditional practice is to generate many 3-hour (full scale) realizations of the relevant sea states. An experimental campaign at 1:48 scale was carried out in the Lilletanken wave tank at NTNU/MARINTEK in order to examine the possibility of using shorter time windows to recreate irregular wave ringing events. Wave elevations and hydrodynamic loads on a rigid vertical circular cylinder in 27 m water depth were measured for a variety of 3-hour, 450 s (7.5-minute), 800 s (13.3-minute), 1150 s (19.2-minute), and 1500 s (25-minute) wave realizations, where all durations are listed in full scale. Wavelet transformations and a single degree-of-freedom oscillator were used to investigate the magnitude and repeatability of the high-frequency content of the wave loads. Large variations in the repeatability were seen among events. On average, the repeatability in the ringing response was 4.2 % for 3-hour tests, while 13.3-minute tests reproduced the same events within 9.1 %. The maximum deviation was, nonetheless, much higher when only 13.3 minutes were used.
Viscous Damping Modelling of Floating Bridge Pontoons With Heaving Skirt and its Impact on Bridge Girder Bending Moments
Authors: Xiang Xu , Svangstu Erik , Nedrebø Øyvind , Jakobsen Bernt , Eidem Mathias Egeland , Larsen Per Norum , Sørby Bernt
Published: October 2017

The current floating bridge concepts of Norwegian Public Roads Administration (Statens vegvesen, NPRA) use a flange shape part at the bottom part of the pontoons. The flange is in principle similar to the damping plates used in the offshore industry for SPAR type of structures. The project group initiated the flange part based on the requirement of extra added mass for tuning the bridge system Eigen-modes. Thus, the important modes can be shifted out of the main wave energy zone. The current study will focus on the damping effects of such structure. The damping effects on weak axis bending moment prediction is studied. The modelling of such damping is first proposed according to relevant literature based on both numerical and experimental studies. Since the reference studies were mainly focused on cylindrical structures, it is difficult to obtain an accurate estimation of the damping coefficient for the current bridge pontoon design, which contains a rectangular part between two half-cylindrical parts. In addition, the estimation of pontoon motions needs the input of damping coefficient, which means that the evaluation of damping coefficient is an iteration process. In order to include the uncertainties, a conservative value was adopted to represent the damping effect. The comparison of accounting for the damping effects or not has been given for all the bridge pontoons. The results show that the damping effects are important at the peaks of the responses; in addition, the reduction of the predicted maximum bending moments can be expected around 10–15 percent along different positions of the bridge. However, a further investigation also shows that viscous excitation would increase the bending moments slightly. The comparison also indicates the value of further investigating the effects by CFD or model test methods.
Real-Time Hybrid Model (ReaTHM®) Testing of the Hybrid Power Plant: Concept and Feasibility Test
Authors: Yum Kevin Koosup
Published: October 2017

Concept of the real-time hybrid model (ReaTHM® 2) testing framework for marine hybrid power plant is presented. The benefits and challenges with regard to using the model-scale power plant for the testing are explained. As a feasibility study of the methodology, tests are performed at the Hybrid Power Laboratory with a model-scale physical diesel-electric power plant. In this test, a load profile from onboard measurements from a ship is used as a numerical part of the system. In the model-scale power plant, the electrical part of the plant is used as an actuator to generate the load for the diesel engine. The traceability of the components and the total system to the given load profile is quantified in terms of time delay and tracking errors. For conclusion, the limitation of the test is analyzed and suggestions for improving the results are provided.
Extending the Limits for Thick Walled Pipe (D/t<20) for External Pressure and Combined Loading
Authors: Smienk Henk , Karjadi Erwan , Huiskes Steven
Published: October 2017

During the operational and installation phase of submarine pipelines, the collapse and local buckling behaviour is of interest. Existing research [1] shows conservatism in the pure collapse DNV formula for thick walled pipe. The first part of the paper will focus on the collapse behaviour of empty thick walled pipe under external pressure. Using 2D and 3D FE Analysis an investigation into the collapse behaviour of pipe with a D/t < 20 is conducted. The analysis also covers an extensive sensitivity analysis with regard to geometrical imperfections and different material models.

The local buckling behaviour during the combined external pressure, bending moment and effective axial force loading encountered in the sagbend is also investigated. To obtain a realistic load path for the sagbend loading, static Flexcom analyses are performed. If the load case is not sufficient to initiate collapse because of the stiffness of the catenary due to the low D/t, the pipe will be bent to the limit state while setting the effective tension to zero.

The effect of each sensitivity on the collapse and local buckle behaviour of thick walled pipe in the sagbend including effective axial tension is discussed.
Study of Self-Propelled Pufferfish Driven by Multiple Fins: A Comparison Between Rigid and Deformable Fins
Authors: Li Ruoxin , Xiao Qing , Li Lijun , Liu Hao
Published: October 2017

In this work, we numerically studied the steady swimming of a pufferfish driven by the undulating motion of its dorsal, anal and caudal fins. The simulations are based on experimentally measured kinematics. To model the self-propelled fish swimming, a Computational Fluid Dynamics (CFD) tool was coupled with a Multi-Body-Dynamics (MBD) technique.

It is widely accepted that deformable/flexible or undulating fins are better than rigid fins in terms of propulsion efficiency. To elucidate the underlying mechanism, we established an undulating fins model based on the kinematics of live fish, and conducted a simulation under the same operating conditions as rigid fins. The results presented here agree with this view by showing that the contribution of undulating fins to propulsion efficiency is significantly larger than that of rigid fins.
Comparing Wave Force and Wave-Induced Overturning Moment of Three Offshore Support Structures
Authors: Jeong Youn-Ju , Park Min-Su , Kim Jeongsoo
Published: October 2017

In this study, in order to investigate wave force and wave-induced overturning moment according to the support structure types and sea levels, wave force tests were carried out for the three offshore support structures of Monopile, GBS, and Hybrid under three sea levels of HSWL, MSL, and LSWL. As the results of this study, it was found that, as the wave height increased at the shallow water (LSWL), wave force increased significantly because of the wave nonlinearity, named wave shoaling. Also, as the structural member size became larger, wave nonlinearity effects on wave force at the shallow water (LSWL) were reduced because of the wave diffraction effect of the large-sized member. Accordingly, variations of wave force and wave-induced overturning moment according to the wave heights and sea levels were larger in the slender member and smaller in the large-sized member. Therefore, it was concluded that wave force and wave-induced overturning moment of the large-sized support structure were little sensitive to the wave height and sea level than the slender support structure. Maximum overturning moments occurred at the HSWL in the Monopile, at the MSL in the GBS, and at the LSWL in the Hybrid, respectively.
Investigation on High-Order Coupled Rigid-Flexible Multi-Body Dynamic Code for Offshore Floating Wind Turbines
Authors: Hu Zhiqiang , Chen Jiahao , Liu Geliang
Published: October 2017

This paper presents a preliminary development and validation of a high-order coupled time-domain simulation code DARwind for floating offshore wind turbine systems. In the code, unsteady Blade-Element-Momentum method with some corrections has been utilized to calculate aerodynamic loads. Combination of potential-flow theory and Morison“s equation are applied to calculate hydrodynamic loads. A quasi-static catenary mooring model is used to consider restoring forces from mooring lines. Kane“s dynamic equations and a high-order coupled model with mode superposition are proposed to model kinematics and structural dynamics of floating offshore wind turbine systems. Subsequently, the effectiveness of the code and its unique high-order coupled dynamic characteristics have been verified by code-to-code tests.
Roll Damping Analysis of In-Field FPSO Roll Response
Authors: Voogt Arjan , Pillai Harish , Seah Robert
Published: October 2017

Due to the resonance behavior of roll motions, roll damping is an important consideration for vessel motions and associated extreme and fatigue loading on the hull, topsides and risers of an FPSO. In many cases radiation damping is limited and passive damping devices such as bilge keels are installed to spur viscous eddies and hence limit the roll motions. This contributes nonlinear damping to an already complex problem. Designers often rely on model tests to assess this damping. Based on test results, empirical and semi-empirical estimation models have been developed for different ship types and are available in current literature, but examples of benchmark validation with real world data are limited. These benchmarks are often hindered by uncertainty in the observed weather conditions, vessel loading conditions and vessel heading with respect to the waves. This paper discusses these challenges and introduces a novel approach used to characterize the actual roll damping for an FPSO under real world conditions. The assumptions, methodology and results will be discussed in this paper. In this study, 5 years of hindcast weather data is examined along with FPSO heading and roll motion measurements. The roll damping characteristics of this FPSO was expected to change over the course of the measurements and the study documents the actual variation of roll damping under various conditions over this period.
Optimal Routing of Short-Distance Ferry From the Evaluation of Mooring Criteria
Authors: Sasa Kenji
Published: October 2017

In optimal ship routing, the ship behavior in the ocean is the main concern. However, there is also different type of ship service, namely the short-distance ferry. It is evident that a novel optimal ship routing must be proposed. A ferry service in southern Japan is the focus of this study. This service takes into account the typhoons or atmospheric depressions that influence the ferry ports. The ferry service is sometimes suspended because of the considerable motion of the ships moored in harbors. A wave monitoring system has been operational since 2015; however, the methodology has not been established from the viewpoint of optimal operation. The current situation regarding the ferry service is summarized in detail in this study, and patterns of typhoons and atmospheric depressions are revealed. In particular, it is difficult for ferry users to understand the reason for suspension of the ferry service when typhoons pass several hundred kilometers away with offshore wave heights of less than 2 m. Firstly, the relation between long period waves and the actual operation is clarified. Secondly, moored ship motions are numerically simulated using measured wave data to evaluate mooring criteria. The estimation formula of the mooring criteria is modeled, and the novel concept of optimal routing for the short-distance ferry is proposed.
Numerical Modeling Using CFD and Potential Wave Theory for Three-Hour Nonlinear Irregular Wave Simulations
Authors: Baquet Aldric , Kim Jang , Huang Zhenjia (Jerry)
Published: October 2017

In this paper, we focus on the modeling of a fully-nonlinear, steep, irregular wave field of three-hour duration without structures in it. The fully-nonlinear effects are considered in the wave simulations using computational fluid dynamics (CFD), as well as potential theory. The overall approach for the numerical modeling is described in the paper. The Euler Overlay Method (EOM) is used to incorporate incoming waves, nonlinear effects, and CFD simulations in the numerical modeling. For computational efficiency, we also use potential theory to model the fully-nonlinear waves. Numerical damping was applied locally around the breaking region to enable simulations for large breaking waves. To compensate for energy loss in the numerical simulations, energy compensation factors of wave spectral frequency components are applied to the input wave spectrum. Results of convergence study, validation against high-order Stokes waves and fully-nonlinear irregular wave with prescribed target spectrum, as well as comparison between numerical wave crest distributions and those from multiple realizations of wave calibration tests are presented.
Large-Scale Tests for Identifying the Nonlinear, Temperature-Sensitive, and Frequency-Sensitive Bending Stiffness of the NordLink Cable
Authors: Komperød Magnus , Juvik Jon Ivar , Evenset Gunnar , Slora Roger , Jordal Lars
Published: October 2017

The NordLink project is a cooperation between Statnett, TenneT, and KfW to build a subsea High Voltage Direct Current (HVDC) system between Norway and Germany. The cables are produced by Nexans Norway and ABB. This paper presents the main results of 30 bending stiffness tests run on the NordLink cable using a novel, dynamic bending stiffness test rig developed by Nexans. It is concluded that there is a highly nonlinear bending moment vs. bending curvature relationship. Also, this relationship is most sensitive to the temperature and somewhat sensitive to the frequency of the cable oscillations. Within a realistic range of curvature amplitudes, temperatures, and frequencies, the bending stiffness varies from 12 to 124 kNm2. These observations strongly suggest that the common industry practice of using a constant bending stiffness should be abandoned.
Electric Impulse Drilling: The Future of Drilling Technology Begins Now
Authors: Anders Erik , Voigt Matthias , Lehmann Franziska , Mezzetti Margarita
Published: October 2017

The Electric Impulse Drilling (EID) uses high voltage impulses to destroy the rock. Without any mechanical interaction between a bit and the rock, it works with almost no wear. Because of that, there is a big potential for reducing roundtrips and non-productive time. In a current R&D project, an EID system is built up and will be tested in a shallow well. A very difficult task during the development is the adjustment of the process to high-pressure conditions.
Visual Analytics in Ship Performance and Navigation Information for Sensor Specific Fault Detection
Authors: Perera Lokukaluge P. , Mo Brage
Published: October 2017

Ocean internet of things (IoT - onboard and onshore) collects big data sets of ship performance and navigation information under various data handling processes. That extract vessel performance and navigation information that are used for ship energy efficiency and emission control applications. However, the quality of ship performance and navigation data can play an important role in such applications, where sensor faults may introduce various erroneous data regions and that may degrade to the outcome. This study proposes visual analytics, where hidden data patterns, clusters, correlations and other useful information are visually from the respective data set extracted, to identify such erroneous data regions. The domain knowledge (i.e. ship performance and navigation conditions) has also been used to interpret such erroneous data regions and identify the respective sensors that relate to the same situations. Finally, a ship performance and navigation data set of a selected vessel is analyzed to identify erroneous data regions for three selected sensor fault situations (i.e. wind, log speed and draft sensors) under the proposed visual analytics. Hence, this approach can be categorized as a sensor specific fault detection methodology by considering the same results.
Movement of a Sphere on a Flat Wall in Non-Newtonian Shear Flow
Authors: Ignatenko Yaroslav , Bocharov Oleg , May Roland
Published: October 2017

For a particle on a wall or cuttings bed in a multiphase flow in confined geometries a condition for onset and lift-off is very important. In this case, a fundamental problem of hydrodynamic forces and torque acting on a particle moving near and on the wall in a viscous fluid needs to be solved.

In this paper, systematical simulation of a flow was performed around a perfect rolling or sliding spherical particle near the wall. A shear flow of Newtonian and Herschel-Bulkley fluids was investigated. The simulation was conducted for Reynolds numbers up to 200 and the dimensionless positive particle velocity Vp < 1.4. The relative particle velocity was made dimensionless by dividing it by the incoming flow velocity in front of the particle. The simulation was performed using the open-source CFD package OpenFOAM. The simulation results for Newtonian fluid agree with data presented in the literature.

For the particle’s low translational velocity the drag force coefficient in the non-Newtonian fluid is lower than in Newtonian fluid, but for increasing translational velocity the drag force coefficient increases.

The lift force coefficient behavior is non-monotonic versus rheology parameters. Lift and drag force show a sudden drop for very small translational velocities.

Our simulation shows that in the case of large Bingham numbers the particle’s lift force can be negative for steady perfect particle rolling. Thus, friction between particle and surface prevents particle’s take-off in some cases.

Knowing the dependence of the lift force on Reynolds number and rheological parameters allows one to determine incipient motion and take-off conditions for a spherical particle.
Torsion Instability of Offshore Cables During Installation
Authors: Sævik Svein , Koloshkin Evgenii
Published: October 2017

The present paper addresses torsion instability at the touch down point during installation of offshore cables and flexible pipes. A model for installation instability analysis is established on the basis of standard co-rotated beam elements. The model is validated with respect to the Greenhill analytical solution as well as results obtained for the linear elastic case reported in literature. A case study is then carried out to investigate the effects of cross-section friction moment, inherent torque and vessel motion. This is then used as basis for a proposed design criteria and recommended analysis procedures for evaluating kink formation of offshore flexibles during installation.
Improving the Panel-Free Method for the Prediction of Ship Motions and Wave Induced Loads
Authors: Qiu Wei , Peng Heather , Wang Junshi , Nizam Shahriar
Published: October 2017

Frequency-domain methods are proven efficient and reliable, especially for zero forward speed, in early design stage for the prediction of ship motions and wave-induced wave loads. There are still challenges for ships with forward-speed due to the inaccuracy in the computation of m-terms. In this paper, the panel-free method is further improved to predict motions and wave-induced loads on real ships with forward speeds. A simple algorithm has been developed to re-arrange the control points for Non-Uniform Rational B-Splines (NURBS) surfaces. This method led to reliable and accurate m-term computations and therefore improved ship motion and load predictions. Validation studies have been carried out for a hydroelastic model of a frigate. Computed motions and loads were compared with experimental data.
Assessment of Fatigue Strength of Welded Connections in Thick Plates
Authors: Toor Kashif Kamran , Lotsberg Inge
Published: October 2017

Fatigue is a governing limit state for design of wind turbine structures. This implies use of thicker plates in these structures than that used as basis for derivation of standard design S-N curves. Due to a significant number of wind turbine support structures designed in a similar way it is important to use a reliable design procedure that does not require use of unnecessary steel costs or fabrication costs. There are also questions related to calculation of structural stresses to be entered the different S-N curves for calculation of fatigue lives. Therefore an alternative assessment method based on notch stress and very fine element meshes has been used to assess target hot spot stress values for calculation of best estimates of fatigue lives.
Prediction of Propeller Tip Vortex Using OpenFOAM
Authors: Ali Md Ashim , Peng Heather , Qiu Wei , Bensow Rickard
Published: October 2017

It is important to predict the propeller tip vortex flow and its effect on hull vibration and noise. In our previous work, the tip vortex flow of the David Taylor Model Basin (DTMB) 5168 propeller model has been studied based on the Reynolds Averaged Navier-Stokes equation (RANS) solution using various eddy viscosity and Reynolds Stress turbulence models. A set of structural grids were used, however, large Jacobian values of the structural grids around the propeller tip region led to the convergence problem and inaccurate solutions. In the present work, the numerical prediction of the same propeller model was improved by using a steady-state RANS solver simpleFoam in OpenFOAM with locally refined unstructured grid along the tip vortex trajectory. The computed thrust and torque coefficients and the velocity components across the vortex core are compared with experimental data and results in the previous studies. Improvement in the prediction of velocity components across the tip vortex core were achieved.
A Numerical Study of the Descent and Ascent Motion of a Full Ocean Depth Human Occupied Vehicle
Authors: Jiang Zhe , Shen Xiaochan , Hu Yong , Cui Weicheng
Published: October 2017

To meet the needs of scientific discoveries in hadal zones, the hadal science and technology center (HAST) of Shanghai Ocean University has made a significant commitment to construct a movable laboratory for hadal trenches in 2013, which includes a mothership, an full ocean depth (FOD) human occupied vehicle (HOV), an FOD Autonomous and Remotely-operated Vehicle (ARV) and several FOD landers. Presently, the HOV is in concept design phase.

Current HOVs in service could only work below 7,000m. To increase the submergence depth from 7,000m to 11,000m for a FOD HOV, the time spending in descent and accent will take a majority part of power endurance and leave little time in scientific studies. Hence, the descent/ascent motion analysis and optimization will play a bigger role in FOD HOV designs contrasting to current HOVs.

In this paper, in order to investigate resistance characteristics and drag coefficients in decent and ascent directions of the FOD HOV, the Reynolds Averaged Navier-Stokes (RANS) equations were solved using computational fluid dynamics. To achieve a faster descent and ascent process, diving and floating with various attacking angles were tried. The numerical analysis for each scenario has been conducted and results were discussed. The method and theory presented in the paper will be applied to the design of a practical deep manned submersible.
Regular Wave Experiments for Twin Circular Submerged Floating Tunnel Tethered to Sea Bottom
Authors: Oh Sang-Ho , Park Woo Sun
Published: October 2017

Assessment of hydrodynamic performance of submerged floating tunnel (SFT) under wave loading is one of important factor in the design of the structure. In this study, physical experiments were conducted in a two-dimensional wave flume to investigate hydrodynamic characteristics of a twin circular SFT model under the action of regular waves having different heights and periods. Five different configurations of the twin SFT model was tested in the experiment. The experimental results showed that the three-degree motions of the twin SFT and the associated tensile forces on the tension legs greatly vary with the configurations of the model. It was found that the CD0 configurations are most adequate for satisfactorily restricting the horizontal and vertical motions of the SFT model.