bluuebunny/crossref_metadata_2025 huggingface dataset:
Geometric Complexity Estimation of Continuous Surfaces for Fitting Processes
Authors: Bahabadi Hossein Gohari , Barari Ahmad
Published: November 2019

The advances in manufacturing methods such as Additive manufacturing provide more flexibility in fabrication of complex geometries. Meanwhile, design tools such as aesthetic design and topology optimization algorithms have been implemented in industrial applications mostly due to the provided flexibility to manufacture freeform surfaces. Computational time and efficiency of the developed algorithms for design, manufacturing and inspection are heavily dependent on the geometric complexity of surfaces. In this paper a measure to estimate the geometric complexity is introduced based on the inherent property of a surface which is curvature. A quantitative value for the geometric complexity is defined through normalization and integration of the mean curvatures. Case studies of the implementation of the proposed measure of complexity verifies the ability of the method to predict the convergence of a surface fitting algorithm based on the geometric complexity of the input model.
Enabling Performance Qualification of Additively Manufactured Parts Under Multiaxial Loading Emulating In-Service Conditions
Authors: Michopoulos John G. , Iliopoulos Athanasios P. , Steuben John C. , Nguyen Trung , Phan Nam
Published: November 2019

The material imperfections generated by Additive Manufacturing (AM) processes across multiple scales can differ significantly from those arising by conventional manufacturing (CM) methods. To qualify these parts in a manner that accounts for all these imperfections without accounting explicitly for each of them, an outline of a rapid functional qualification methodology based on the concept of Performance Signature (PerSig) is presented first. The PerSigs are defined for both the prequalified CM parts and the AM-produced ones. Comparison measures are defined and enable the construction of differential PerSigs (dPerSig) in a manner that captures the differential performance of the AM part vs. the prequalified CM one. This approach is extended in this paper for the case of multiaxial loading conditions reflecting actual in-service loading. Application of the methodology is presented for a fitting bracket in the P-3C Orion aircraft platform and is based on synthetic data. The application of multiaxial loading emulating in-service loading conditions is proposed by the utilization of a custom-designed 6-DoF robotic testing system that will generate physical data.
Flexion and Extension Capable Motor Tendon Actuated Exosuit Glove With Open Palm
Authors: Patterson Georgia S. , Zell Tyler D. , Parker David E. , Grieve John , Watson Samuel C. , Vikas Vishesh
Published: November 2019

Patients suffering from medical conditions resulting in hand impairment experience difficulty in performing simple daily tasks, like getting dressed or using a pencil, resulting in a poorer quality of life. Rehabilitation attempts to help such individuals regain a sense of control and normalcy. In this context, recent advances in robotics have manifested in multiple designs of hand exoskeletons and exosuit gloves for assistance and rehabilitation. These designs are typically actuated using pneumatic, shape memory alloys and motor-tendon actuators. The proposed Motor Tendon Actuated Exosuit Glove (MTAEG) with an open palm is a soft material glove capable of both flexion and extension of all four fingers of the human hand. Its minimally invasive design maintains an open palm to facilitate haptic and tactile interaction with the environment. The MTAEG achieves flexion-extension motion with joint angles of 45° at the metacarpal joint which is 57% of the desired motion; 90° at the proximal interphalangeal joint which is 100% of the desired motion; and 50° at the distal interphalangeal joint which is 96% of the desired motion. The paper discusses the challenges in achieving the desired motion without the ability to directly model human tendons, and the inability to actuate joints individually.
Prediction of Nitrogen Concentration in Fuel Cells Using Data-Driven Modeling
Authors: Lin Tong , Hu Leiming , Litster Shawn , Kara Levent Burak
Published: November 2019

This paper presents a set of data-driven methods for predicting nitrogen concentration in proton exchange membrane fuel cells (PEMFCs). The nitrogen that accumulates in the anode channel is a critical factor giving rise to significant inefficiency in fuel cells. While periodically purging the gases in the anode channel is a common strategy to combat nitrogen accumulation, such open-loop strategies also create sub-optimal purging decisions. Instead, an accurate prediction of nitrogen concentration can help devise optimal purging strategies. However, model based approaches such as CFD simulations for nitrogen prediction are often unavailable for long-stack fuel cells due to the complexity of the chemical environment, or are inherently slow preventing them from being used for real-time nitrogen prediction on deployed fuel cells. As one step toward addressing this challenge, we explore a set of data-driven techniques for learning a regression model from the input parameters to the nitrogen build-up using a model-based fuel cell simulator as an offline data generator. This allows the trained machine learning system to make fast decisions about nitrogen concentration during deployment based on other parameters that can be obtained through sensors. We describe the various methods we explore, compare the outcomes, and provide future directions in utilizing machine learning for fuel cell physics modeling in general.
A Load Distribution Model for Double-Planet Planetary Gear Sets
Authors: Hu Yong , Talbot David , Kahraman Ahmet
Published: November 2019

In this paper, a load distribution model for a double-planet planetary gear set is developed by modifying an existing single-planet planetary gear set model [1] to account for an additional planet to planet gear mesh and their impact on phasing relationship among different sun-planet, planet-planet and planet-ring gear meshes. Similar to the single-planet planetary gear set model, the double-planet planetary gear set model accounts for effects of various component and system level variations such as supporting conditions, gear tooth modifications, manufacturing errors and kinematic configurations. The double-planet planetary gear load distribution model is derived for both rigid and flexible ring gear rim, while only parametric studies for a rigid ring gear rim is presented in this paper to demonstrate load distribution characteristics of double-planet planetary gear sets with different planet bearing stiffness and combination of various types of manufacturing errors, including pin hole position error and runout errors.
ContaBat: Designing and Prototyping an Attachable Sports Analytics Device That Provides Ball-Bat Impact Location for Performance Enhancement
Authors: Sarwar Umair , Cheema Kamran , Reid Tahira
Published: November 2019

This paper introduces ContaBat, an attachable device for a cricket bat that provides important performance metrics like ball-bat impact location, rotation due to impact, and impact force which could be used by players, coaches and fans to gain insights about their performance. Of the metrics mentioned, obtaining the impact location is the most novel feature and is the focus of this paper. Piezo-electric sensors placed at the back of the bat are used to record pressure measurements due to impact and utilize time difference of arrival techniques (TDOA) to pinpoint the impact location. For further product realization and development, it was essential to create a prototype. The prototype was instrumental in providing testing conditions that could simulate a real-world environment, identifying the limitations of the data acquisition methods used, evaluating the usability of the product, and helping future researchers envision the final form of the product and the impact it could create before commercializing the product. The results of the algorithms showed that the accuracy of the methods used resulted in the impact location being within 0.002 m of the hit spot, with the percentage error being higher towards the edges of the bat than the middle. This paper will discuss in detail the data acquisition and data analysis methods used to measure impact location on a cricket bat, the design considerations while creating the prototype, and the insights gained from prototyping.
Investigation on the Vibration of High Speed Cable Robot Manipulation due to Tension Around Drum
Authors: Jung Jinwoo , Piao Jinlong , Choi Eunpyo , Park Jong-Oh , Kim Chang-Sei
Published: November 2019

A cable-driven parallel robot (CDPR) consists of an end-effector, flexible lightweight cables, pulleys, winches, and a rigid base frame. As opposed to the rigid links of the traditional serial robots and parallel robots, the flexible lightweight cables allow the CDPR to easily achieve the high speed, heavy payload manipulation, and scalable workspace. Especially, the conventional high-speed pick and place operation can be realized due to the lightweight of its flexible cables. However, the flexibility of the lightweight cables can introduce a considerable vibration problem to the high speed cable robot system. One of main causes can be a cable tension difference between initial pre-tension and winding tension around a drum of the winch-motor actuator. To effectively investigate the effect of the tension around the drum on the high speed manipulation of the cable robot system, the spatial eight-cable high speed cable robot was reduced to the horizontal two cable system. The reduction of the number of the cable enables us to minimize the influences from the other factors such as the cable sagging and the geometric errors. A series of experiments was conducted using the combinations of the low and high initial pre-tensions and low and high tensions around the drum. The experimental results clearly show that the low tension around the drum can cause the vibration problem during the high speed pick and place operation. Also, it demonstrates that securing the drum tension similar to the initial pre-tension can effectively reduce the magnitude of the vibration.
A Real-Time Human Recognition and Tracking System With a Dual-Camera Setup
Authors: Wu Haoyu , Xiong Shaomin , Hirano Toshiki
Published: November 2019

Most surveillance camera systems are still controlled and monitored by humans. Smart surveillance camera systems are proposed to automatically understand the scene captured, identify the objects of interest, detect the abnormality, etc. However, most surveillance cameras are either wide-angle or pan-tilt-zoom (PTZ). When the cameras are in the wide-view mode, small objects can be hard to be recognized. On the other hand, when the cameras are zoomed-in to the object of interest, the global view cannot be covered and important events outside the zoomed view will be missed.

In this paper, we proposed a system composed of a wide-angle camera and a PTZ camera. The system is able to capture the wide-view and the zoomed-view at the same time, taking the advantages from both views. A real-time human detection and identification algorithm based on a neural network is developed. The system can efficiently and effectively recognize humans, distinguish different identities, and follow the person of interest using the PTZ camera. A multi-target multi-camera (MTMC) system is developed based on the original system. In the MTMC system, multiple cameras are placed at different places to look at different views. The same person shown in any camera can be recognized as the same person while different persons can be distinguished among all the cameras.
Optical Simulation for Designing a PPG Signal Patch
Authors: Pribadi Eka Fitrah , Chao Paul C.-P.
Published: November 2019

Designing an optical patch for photoplethysmogram (PPG) signal considers the optical simulation of the patch on the skin. The skin model for the optical simulation consists of epidermis, a dermis, a subcutaneous fat, and a blood vessel, while the model of the patch includes an organic light emitting diode (OLED) and an organic photodiode (OPD). Each model of skin layers is implemented using bulk and scattering of the optical parameter. In order to model the AC/DC of PPG signal, the blood vessel of the optical model uses the diameter of 2 mm and 2.2 mm. The simulation conducted by sweeping the distance of OPD model apart of OLED in knowing the optimal distance between OLED and OPD. The simulation of the different shape of patches is conducted to know the optimum shape of the patch. The 8-shaped patch has the optimum value of the AC/DC signal which is 0.0045.
Sound-Induced Vibration to Hard Disk Drive in a Data Storage Enclosure
Authors: Xiong Shaomin , Hirano Toshiki
Published: November 2019

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Effect of Stress History and Shallow Embedment on Centrifuge Cone Penetration Tests in Sand
Authors: Roy Anamitra , Chow Shiaohuey , O’Loughlin Conleth , Randolph Mark
Published: November 2019

The paper investigates the effect of stress history and shallow embedment on centrifuge cone penetration tests in sand. A series of centrifuge cone penetration tests were performed in loose and dense silica sand at g-levels ranging between 20 and 100 with corresponding overconsolidation ratio (OCR) between 1 and 5. Based on the measured cone tip resistance (qc) profiles, improved empirical correlations have been proposed with depth factors (fD) to impart additional flexibility in accurately back predicting sand relative density (RD) at shallow embedment in normally consolidated (NC) sands. The qc - RD correlations are then extended to capture overconsolidation effects in cone tip resistance, which is broadly consistent with the changes in compressibility and in-situ lateral stresses taking place in sands with increasing OCR levels. The proposed expressions allow accurate quantification of depth corrected CPT profiles in soils of varying overconsolidation ratio, for application in the interpretation of model tests on shallow foundations and anchors and in shallowly buried structures such as pipelines. The expressions also have application for interpretation of field CPT profiles where the thickness of interbedded layers is of similar order of magnitude to the cone diameter.
Effect of Seabed Imperfection on the Buckling of Buried Pipelines Subjected to Wave-Induced Loads
Authors: Suresh Kumar D. , Sunny M. R. , Sahoo T.
Published: November 2019

Subsea pipelines operating under high pressures and temperatures are typically buried to protect from the environmental impacts and to prevent the instigation of global buckling. As the seabed profile is generally uneven, certain initial imperfections generally exist along the pipeline. As the pipe traverses in shallow waters, the seabed can be subjected to hydrodynamic loads caused by surface gravity waves. The hydrodynamic pressure, which typically depends on the wave height and water depth, leads to the development of pore pressures within the soil medium. This gradient of the pore pressures can cause significant uplift forces on the pipe, which may initiate the buckling in the vicinity of the imperfection. This study focuses on understanding the influence of these wave induced uplift forces on the buckling of the initial imperfect pipelines. Four typical imperfection profiles are considered in the study. The influence of imperfection shape on the buckling behavior is compared for surface laid and buried pipelines. Thereafter buckling behavior of the considered imperfect pipelines is studied with and without consideration of wave loads for a range of wave particulars and burial depths. The wave forces on the pipeline are estimated by solving Biot’s consolidation equations using finite element software COMSOL and the buckling studies are carried out using ABAQUS.
A Multipurpose Framework for Modelling and Simulation of Marine Aquaculture Systems
Authors: Su Biao , Reite Karl-Johan , Føre Martin , Aarsæther Karl Gunnar , Alver Morten Omholt , Endresen Per Christian , Kristiansen David , Haugen Joakim , Caharija Walter , Tsarau Andrei
Published: November 2019

Research within marine aquaculture has either focused on technology (e.g. farming structures, autonomous systems, harvesting and transport technologies) or biology (e.g. biomass control, feeding process, fish behavior and welfare). Here, we present a computational framework allowing the integrated analysis of these two aspects in a flexible and evolutive way. This framework is called FhSim which was originally developed for the modelling and simulation of fisheries operations and aquaculture structures, but its application domain has been continuously extended through different research projects.

In this paper, we present the basic design principles and functionality of the FhSim framework with the focus on modelling and simulation of marine aquaculture systems. The basic theories and methods used for the modelling of open net cages, closed cages, fish behavior, feeding processes, and ROV operations in net cages are introduced, respectively. It is also shown how the technological and biological aspects of fish farming can be considered in a specialized or integrated analysis. Furthermore, approaches for combining numerical models with monitoring sensor data, techniques for real-time simulation of fish farming operations and the coupling of FhSim with other simulation programs are discussed.
Influence of Mixed Flows on Ship Hydrodynamics in Dredged Channels
Authors: Terziev Momchil , Tezdogan Tahsin , Incecik Atilla
Published: November 2019

Although there is a significant body of research devoted to the shallow water hydrodynamic aspects of ships, several unexamined topics remain. Among these is that of critical outer flow in a dredged channel and its influence on parameters of interest. While empirical methods can be used with ease to resolve this, they can provide results with reliability sufficient only for an early design stage. On the other hand, more sophisticated potential flow theories are either inapplicable or do not perform well at the critical limit. However, RANS (Reynolds Averaged Navier-Stokes) – based tools can accurately capture all underlying phenomena without relying on limiting assumptions. This paper presents an attempt at comparing some results obtained via a CFD-based RANS solver and the slender body theory for critical outer flow in a dredged channel.
Study of Grouted Connections in Offshore Monopile Structures
Authors: Theotokoglou Efstathios E. , Papaefthimiou Georgia
Published: November 2019

In this paper the grouted connection (GC) of an offshore wind turbine is studied. The study is performed numerically by the finite element method (FEM). Initially, a description of the connection, its geometrical variations and its materials are presented. Moreover, analytical types about the deformation of the connection are presented. Subsequently, the analysis of the three dimensioned problem is performed numerically and the procedure as well as the parameters used, are given step by step. The case of the contact analysis problem is also studied. Practical issues such as mesh density and materials interaction are confronted. Finally, the stress state (SS) will be given in the analysis results, in order to specify the behavior of the connection under static loading.
Fatigue Life Assessment for Pipeline Dents Under Highway Crossings
Authors: Liu M. , Cross Colin , Brown Jason
Published: November 2019

A routine inline inspection pigging operation revealed a number of dent anomalies in an onshore pipeline transporting refined products. A detailed fitness for service assessment was subsequently performed by a leading engineering consultant company using the best industry practices, concluding that the dent defects with varying level of ovality in the order of 5% presented no immediate threat to the normal service under projected pressure cycles. The plain dent defect features were classified into a non-urgent category well down the scheduled repair list, requiring no priority intervention or replacement programme except further monitoring inspections and operating pressure control before a repair was planned. However, the dent defects in the proximity of highway crossings predicted to have longer remnant fatigue life failed unexpectedly within a much shorter time span, leading to costly emergency replacement and disruptive system downtime. This disparity has raised a question about the likely failure cause, uncertainty and reliability of the defect assessment. To this end, one anomaly was re-examined and its study is presented in this paper on how a fitness for service assessment for such dent anomalies can be improved using FEA modelling and consideration of some of the lessons learnt from similar failures and assessment experiences. It demonstrates that certain dynamic loading and additional fatigue promoting factors commonly ignored are of importance for fatigue life assessment.
Fatigue Crack Growth Rate Testing for Clad and Lined Pipe Girth Weld
Authors: Yang Zhengmao , Wu Youyou , Tronskar Jens P. , Xu Daqin
Published: November 2019

The Direct Current Potential Drop (DCPD) method is a common method used to detect the initiation of cracks, measure crack growth rates and monitor crack propagation. The method records total measurement of crack propagation, and can be used without visual accessibility, being suitable for special environments like high temperature, high pressure and sour service. Due to the discontinuity represented by the presence of a crack, when electric current flows through the component the crack size can be measured indirectly by the change of the electrical field. The potential difference can be related to crack size through experimental, analytical or numerical calibration curves. Analytical solutions are only limited to a small number of simpler geometries and homogeneous material. For clad and lined pipe, the clad/liner is stainless steel or nickel base alloys but the base pipe is carbon steel. The conductivities of the different materials are different. For lined pipe a small gap exists between liner and base pipe, this may change the electrical field around the root of girth weld. In this paper, finite element analyses are performed to generate the numerical calibration curves for the fatigue crack growth rate testing in sour service environment for clad and lined pipe girth welds. The method developed and described in this paper measures the fatigue crack growth rate for the crack located at the weld root which is in direct contact with the operating environment.
Experimental Investigation of Over-Trawlability of an Innovative Arctic Subsea Production Unit (SPU)
Authors: Wu Jie , Muthanna Chittiappa , Alsos Hagbart , Juhlin Rasmus , Karunakaran Daniel
Published: November 2019

Model tests have been performed to examine the overtrawlability of Subsea7’s Subsea Production Unit (SPU) in SINTEF Ocean’s Ocean Laboratory in November/December 2017. In this test campaign, 50 tests with different SPU orientations and trawling equipment were carried out. Two trawling water depth (100 m and 500 m) were simulated in the model test. Two types of trawl door, i.e. Thyborøn (5.5t) and Poly Ice (3.8t), with Selstad No. 620 type fishing net were used in present test. Overtrawling with a roller clump (7.6t) was also tested. Two trawling speeds of 1.6 m/s and 2.6 m/s and 5 SPU orientations were examined. Force measurements both on the fishing lines, and directly measured on the SPU were used to determine overtrawlability of the SPU. The dynamometer used in present test to measure the forces directly on the SPU is the first time that this type of measurement has been undertaken at SINTEF Ocean at the Ocean Basin facility with fully modelled trawling gear.