bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sound-Induced Vibration to Hard Disk Drive in a Data Storage Enclosure
Authors: Xiong Shaomin , Hirano Toshiki 
Published: November 2019

Abstract
The data read and write operation in a hard disk drive (HDD) relies on precision mechanical components, such as air bearing sliders, suspension, and piezo actuators. Many of those mechanical components are sensitive to mechanical disturbances. It is found that sound a disturbance (or airborne disturbance) increases the position error signal (PES), such that the tracking, following and seeking performance is compromised. For a data storage enclosure and server in a data center, cooling fans generate strong sound noise, resulting in degradation of the performance of HDDs. In this study, we showed that the PES degrades when placing a sound source next to the HDD, indicating that the sound-induced vibration links to the mechanical components inside the HDD. It is also found that the PES is very sensitive to the location of the sound source. A vibration model was built by finite element method (FEM). The simulation results were compared to experiments on a thin plate structure to explain this dependency on the location of sound source.
Towards the Development of an Ocean Engineering Library for OpenModelica
Authors: Viswanathan Savin , Holden Christian 
Published: November 2019

Abstract
The development of component models to populate a proposed OpenModelica standard library for the ocean engineering domain is described through the process of modelling the response of catenary-moored wave-energy converters in the ‘free-to-use’ OpenModelica simulation environment and its associated OMEdit graphical user interface. A wave energy conversion concept is presented, followed by the implementation of Modelica component models and functions to simulate wave, current, and mooring loads on a cylindrical floating object. The irregular sea surface is specified using the Pierson-Moskowitz spectrum and the heave force on the buoy is determined based on the Froude-Krylov formulation. Mooring load formulation is based on the catenary theory. Combined wave and current loads on the buoy and on the mooring chain are arrived at using the Morison equation. The results are verified with the commercial software Orcaflex, and the preliminary OceanEngineering library is made available for download. The integrated simulation of the multiphysical wave energy buoy system is then carried out to determine the energy harvest potential, and results discussed. An alternative design is then suggested and simulated to demonstrate the advantages of using the component-based approach.
Inner Bend Cracks in Mooring Chain: Investigation of Cracks Observed on Chains Taken Out of Service
Authors: Gabrielsen Øystein , Kulbotten Inge Morten , Martinez Perez Imanol , Håskoll Lars 
Published: November 2019

Abstract
The last decade Equinor has taken a significant amount of mooring chains out of service. Typically, one mooring line for an offshore installation has been replaced. Purpose has been to assess whether current chain condition (corrosion and wear), make the remaining chains fit for further use. The chains have been subject to thorough inspection, break load testing and fatigue testing. Depending on results of the inspection and tests, the remaining mooring chains have either been replaced or found fit for further use.
From one installation, smaller cracks on the inside of the crown of chain links have been observed. These cracks do not coincide with known fatigue hot spots or fatigue breakages from fatigue testing of chains. Many cracks are visible with the bare eye, and NDT techniques are not necessary for detection. Chains with such cracks have been subject to both break load testing and fatigue testing. Overload breakage and fatigue cracks have not occurred or developed from the cracks. Chain links with cracks have been dissected to investigate crack depth. Dissection has also aimed to assess the age of the cracks. Both chain links that have and have not been subject to full scale fatigue testing have been dissected. This paper presents example of the observed cracks, including details on link location in the mooring line, crack positions in links, and measured depth and length of cracks. The paper also discusses the different possible causes of the cracks, and whether the cracks are critical for the endurance of the chains.
Dynamic Responses Prediction for a Spar-Type Offshore Floating Wind Turbine Under Ship Collision Scenarios
Authors: Zhang Yichi , Hu Zhiqiang 
Published: November 2019

Abstract
A potential collision hazard between offshore floating wind turbines (OFWT) and ships passing-by needs to be paid further attention as more OFWT fields have been designed and will be built in the coming years. In this paper, a theoretical model is proposed to analyze the dynamic responses of a spar-type offshore floating wind turbine under the scenario of ship impact. Firstly, the collision duration is assumed to be quite short and the impact force is assumed to be large enough to assure all other external forces can be ignored temporarily. The hydrodynamic effects are considered by introducing the added mass matrix during the collision process and then on basis of the rigid body impact principle, and the expressions of energy dissipation and some other kinetic characters are derived. Secondly, the dynamic responses of the OFWT after collision are investigated. In this process, external forces which play significant roles will be taken into account. The hydrodynamic forces are estimated using Morison’s Equation with linear wave theory while the wind thrust force is calculated using BEM methods. The mooring system is considered by the simplification to be a linear elastic spring. Finally, based on the theoretical model derived above, a time-domain analytical program is developed, which can be used to evaluate the dynamic responses for the scenario of spar-type OFWT under ship impact scenario. With the newly proposed program, a series of parametric case studies are conducted and by comparing the results, some characters sensitive to them are further discussed.
Exchange Flows in Well Abandonment Operations
Authors: Naccache Mônica F. , Varges Priscilla R. , de Souza Mendes Paulo R. , Fonseca Bruno , Cavalcante Gabriella , Miranda Cristiane 
Published: November 2019

Abstract
In this work we perform an experimental study of the buoyancy-driven exchange flow of the cement plug placement in oil wells, most commonly for abandonment and sidetracking. In this process, a denser fluid is placed above a less dense one, generating a highly unstable situation that can lead to unsuccessful operations when their positions invert before the cement curing. To analyze the exchange flow we perform visualization experiments with real drilling fluids positioned above a lower-density liquid in a Plexiglas vertical tube. The use of a drilling fluid, instead of a real cement plug at the top, was chosen in order to eliminate the curing influence on the preliminary tests. Thus, the same density difference between cement and other well fluid can be evaluated. A sliding gate ensures an initially flat interface that evolves with time immediately after the gate opening. The interface shape and front speed is recorded with the aid of a digital camera, and measured through image processing and analysis. Since in the real situations the well diameters are larger than the ones used in the laboratory, the interfacial tension effects are naturally negligible. Hence, surfactants are used to reduce the influence of interfacial tension on the experiments. The effects of the governing parameters on the inversion velocity and flow regime are analyzed for different combinations of fluids. Drilling fluids and cement plugs have non-Newtonian viscoplastic behavior, and careful rheological tests are performed to obtain the rheological parameters. Therefore, yield stress, viscosity levels, geometric parameters and density ratios between the fluids can lead to different flow patterns that will contribute to a successful or unsuccessful operation. The analysis of the experimental results will allow one to identify, for a given pair of fluids, the operational window in the governing parameter space within which the inversion velocity is sufficiently low (or zero) to ensure the heavier fluid placement success.
Influence of Suction Dredging on the Failure Mechanism of Sandy Submarine Slopes: Revisited With a Coupled Numerical Approach
Authors: Kanitz Manuela , Grabe Juergen 
Published: November 2019

Abstract
The installation of shallow foundation systems for offshore wind turbines like gravity foundations requires the excavation of the weak top soil of the seabed to place the structure on more stable ground. This excavation can be done through suction dredging resulting in a pit. Different slope angles of this pit can be realized using this technique. As the failure mechanisms of artificial submarine slopes using suction dredging are barely investigated, relatively small final slope angles of max. 10 degree are reached to guarantee stability. Nevertheless, small-scale experiments show that submarine slopes with overcritical slope inclinations can be stable for a while when prepared with suction dredging. Steeper inclinations would significantly reduce the disturbance of the marine fauna and the amount of sand to be removed and therefore meet both economic and ecological interests. The investigations of the failure mechanism in the submarine slope during suction dredging are carried out with a coupled Euler-Lagrange approach, namely the combination of the Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM). This method enables the computation of particle-particle as well as the fluid-particle interaction forces and hence their influence on the investigated submarine slope behavior. The calculations are carried out with the open source software package CFDEM® coupling, which combines the discrete element code LIGGGHTS® with CFD solvers based on OpenFOAM®. Additionally, small scale model tests of suction dredging of sandy submarine slopes are carried out. The displacement of the soil grains is monitored with a high-speed camera. To take into account effects of contractancy and dilatancy, a loosely and a densely packed sand are investigated and the influence of the packing density on the failure mechanism is evaluated. The experimentally gained results will be compared to the numerical ones to evaluate the capability of the coupled CFD-DEM method to depict the failure behavior of submarine slopes during suction dredging.
Developments in Metocean HF Radar Technology, Applications and Accuracy
Authors: Wyatt Lucy R. , Moorhead Mike D. , Fairley Iain A. 
Published: November 2019

Abstract
HF radar surface current measurement is now a well-accepted technology and part of many operational oceanography systems. Although the UK was involved from the early stages in this technology there has not been the take-up seen elsewhere in the world most notably in the US and, more recently, in the Far East where such data are being routinely used for model evaluation and other applications. In addition to surface currents, simultaneous measurement of waves and winds has also been demonstrated although these are still often regarded as experimental and unreliable. This is in part because good quality wave measurement requires much higher quality radar data which is not always available so some published results are rather noisy. This paper will review the current state of the art in all these measurements and highlight some new developments which have the potential to increase their availability, accuracy and scope. The original wave measurement work in the UK was carried out using the Pisces HF radar system which was designed specifically for this application. New measurements using a modification of this radar, which exploits the fact that different radar operating frequencies have different responses to wave conditions, will be presented. Software developments to increase the robustness of HF radar metocean measurements will be discussed.
Nonlinear Wave Surface Elevation Characteristics Analysis Around a Multi-Body Offshore Platforms System
Authors: Ren Xiudi , Liang Yibo , Tao Longbin 
Published: November 2019

Abstract
Along with the development in offshore technology, the offshore platforms are gradually becoming larger and more complex. Recent development of oil and gas field in the deepwater region often involves multiple floating platforms adjacent to each other. Wave free surface associated with the air-gap design is one of the most important issues as the interaction between the platforms can complicate the hydrodynamics further. In this paper, the nonlinearity of incident wave and scattered wave are considered in diffraction analysis based on the potential theory. In addition, the nonlinear incident wave is considered to capture the nonlinear features of free surface due to wave diffraction and radiation. The wave surface amplitude around a multi-body platforms system is numerically analyzed in the frequency domain and compared with the numerical results of a single platform. The distribution of wave surface amplitude with different scatter parameter at different wave steepness is investigated to examine the relationship between the two parameters critical to the nonlinear wave surface elevation.
Larger MW-Class Floater Designs Without Upscaling?: A Direct Optimization Approach
Authors: Leimeister Mareike , Kolios Athanasios , Collu Maurizio , Thomas Philipp 
Published: November 2019

Abstract
The trend towards larger offshore wind turbines (WTs) implies the need for bigger support structures. These are commonly derived from existing structures through upscaling and subsequent optimization. To reduce the number of design steps, this work proposes a direct optimization approach, by which means a support structure for a larger WT is obtained through an automated optimization procedure based on a smaller existing system. Due to the suitability of floating platforms for large MW-class WTs, this study is based on the OC3 spar-buoy designed for the NREL 5 MW WT. Using a Python-Modelica framework, developed at Fraunhofer IWES, the spar-buoy geometry is adjusted through iterative optimization steps to finally support a 7.5 MW WT. The optimization procedure focuses on the global system performance in a design-relevant load case. This study shows that larger support structures, appropriate to meet the objective of the hydrodynamic system behavior, can be obtained through automated optimization of existing designs without the intermediate step of upscaling.
Case Study: Non-Conventional Remaining Life Assessment of a Significant Dent in a Subsea Pipeline Scheduled for Decommissioning
Authors: Brett A. , Russell A. 
Published: November 2019

Abstract
An inline inspection of a subsea oil pipeline located in the North Sea identified a large top of line dent.
The pipeline was scheduled for decommissioning within 3 years, however conventional fatigue assessment of the dent indicated that the pipeline could become unsafe before the scheduled decommissioning date.
As the required remaining life could not be justified by conventional assessment, a review was completed to determine whether a case-specific assessment methodology could be developed to reduce the conservatism, while reliably demonstrating that the pipeline could be safely operated up until the planned decommissioning date.
This review identified that the pipeline had a unique pressure history, which included a large one-off pressure spike that had occurred following detection of the dent. This raised the possibility of a pseudo-hydrotest type assessment to justify the required remaining life.
This paper describes the non-conventional pseudo-hydrotest assessment that was undertaken for the dent to demonstrate acceptability, which used a combination of state of the art finite element analysis and fatigue crack growth assessment.
A Numerical Investigation on the Effect of Heave Motion Frequency in the Deep Sea Mining System
Authors: Wu Qi , Yang Jianmin , Lv Haining , Lu Wenyue , Peng Tao , Li Jun 
Published: November 2019

Abstract
In this paper, the effect of top heave motion frequency on the global dynamic responses of a deep sea mining system is presented. The excitation of different frequencies is induced by time-varying heave motion of the surface vessel. First the numerical model of the system is established which can be solved by the lump mass method. Then three different scenarios caused by harmonic heave motion corresponding to different heave motion frequencies are introduced. On these basis, the pipe tension at bottom, deflection and bending force of the system are presented and discussed. Amplitude spectrum through FFT and the phase plots for the time histories of pipe bottom motion are made to analysis the possible different motion modes.
Risk Assessment of Ship Systems Based on Forward FTF Method
Authors: Mai Songyan , Zeng Ji , Feng Qi , Liu Renan , Chen Yan 
Published: November 2019

Abstract
Ocean-going vessels sailing alone in the boundless sea often encounter various problems and pose a serious threat to the safety of the ship. According to statistic, many of these accidents are caused by problems such as aging equipment and lack of maintenance. After IMO issued mandatory regulations, China Classification Society (CCS) released Failure Mode and Impact Analysis Guide in 2017 (Guidance Notes GD16-2017), in connection with failure mode and impact analysis for ship equipment and systems. In this paper, based on a multi-purpose offshore carrier, the forward FTF (FMECA & FTA) method is adopted. The failure mode, effects and criticality analysis (FMECA) is conducted for the study on failure mode of ship system, including failure rate, cause and effect (probability and severity). Fault tree analysis (FTA) is to calculate and assess the risk of the ship system. Based on the forward FTF principle, Smart Captain, an operation and maintenance management system was developed for this ship. The system can identify the faults of the ship system and carry out different levels of alarms automatically, then a corresponding maintenance and operation instructions according to the equipment manual is given. By using Smart Captain, the crew member can carry out ship operation and maintenance efficiently safely.
The Increase in Wave Wake Characteristics of Marine Vessels When Accelerating
Authors: Macfarlane Gregor , Graham-Parker Keegan , Connellan Michael 
Published: November 2019

Abstract
The waves generated by ships and boats (often referred to as wake wash, wave wake or simply wash) have been known to result in the erosion of riverbanks, damage to maritime structures, or be hazardous to other users of the waterway. The vast majority of research in this field to date has focused on the characteristics of these waves when the vessel is travelling at constant forward speed. Recent work by the authors has identified significant transient effects that occur while a vessel accelerates up to the desired operational speed, where both the height and period of the maximum wave generated are significantly greater than those generated at the corresponding steady-state speed. This notable increase in wave energy can be important, particularly where vessels are required to accelerate on a regular basis when operating in sheltered waterways with limited water depth. Common examples are commuter ferries that make regular passages between passenger terminals and hence pass through the transcritical speed zone to operate at supercritical speeds (in terms of depth Froude number).
In this paper, a study into these transient effects through physical scale-model experimentation is expanded to include different hull forms, including a typical “low wash” catamaran river ferry and a prismatic monohull. Results indicate that the increase in height of the maximum wave can exceed 80% and the period of this wave increase by more than 30% as a result of the acceleration phase compared to the steady-state speed. This poses the question whether these transient effects should form part of the assessment process when considering whether a vessel meets criteria imposed to regulate wash impacts.
The same model scale data is also used to advise the model test community the required distance for a ship model to achieve a steady-state following the acceleration phase during model scale tests in facilities such as towing tanks or basins.
Walking Anchors: When to Fix One or Both Ways?
Authors: Carneiro Daniel , Franco Luciano 
Published: November 2019

Abstract
Anchors to mitigate pipeline walking often involve very large piles, requiring large crane installation vessels, which bring cost, schedule and HSE risk implications. Optimizing such piles traditionally require substantial FEA effort, and frequently, project decisions are made, and purchase orders are placed based on conservative assumptions.
The choice of anchor-to-pipeline connection can significantly influence the anchor sizing. In some cases, allowing some free slide-back displacement when the anchor is being unloaded can substantially reduce the maximum load levels.
This paper presents simple analytical calculations that can be used to determine whether this artifice is effective or not for any given condition; how much load reduction can be achieved; and how much slide-back length is required for that. Results for typical, hypothetical pipeline properties are presented. These show that while some cases will see no benefit, in others cases the load can be reduced by over 1 MN by allowing no more than a few centimeters slide-back tolerance.
Having the ability to assess multiple options with minimum effort, then use FEA for detailed confirmation (rather than using expensive FEA on a trial and error basis) will allow certain projects to realize significant savings.
Efficient Fluid-Fluid Displacement of Yield Stress Fluids in Axially Rotating Pipes
Authors: Lyu Shan , Taghavi Seyed Mohammad 
Published: November 2019

Abstract
Oil and gas well primary cementing operations involve pumping a sequence of fluids into the well, for example, cement along a circular pipe (casing) to remove (displace) in situ drilling mud. Cementing is vital to the implementation of zonal isolation and well integrity in the completion of oil and gas wells. The success of a cementing operation is largely determined by the displacement efficiency. There are several factors, such as rheological properties of fluids, geometrical specifications of the annulus, flow rate, and pipe movement, which can considerably affect the displacement efficiency. A casing rotation is generally believed to improve the displacement process, but without solid laboratory experiments to prove that such rotation is indeed effective. In this work, the influence of a pipe rotation on a displacement flow which consists of a yield stress displaced fluid is analyzed via experimental methods. A heavy Newtonian fluid (salt water) displaces a light viscoplastic fluid (Carbopol gel) in a long, inclined pipe. Our results show that the pipe rotation helps break up the Carbopol gel remained on the surface of the flow geometry, and eventually leads to an efficient removal of the displaced fluid above a critical rotation speed. The analysis includes measuring the propagation velocity of the leading front (V̂f) for different parameters, such as the pipe inclination angle, the imposed flow velocity (V̂0) and the rotation speed. The leading front velocity decreases as the rotation speed increases and it is found V̂f ≈ 1.6V̂0. Three flow regimes are observed: slumping type, ripped type and effective-removal type.