bluuebunny/crossref_metadata_2025 huggingface dataset:
Hematopoietic stem cell transplantation from non‐sibling matched family donors for patients with thalassemia major in Jordan
Authors: Hussein Ayad Ahmed , Al‐Zaben Abdulhadi , Khattab Eman , Haroun Anas , Frangoul Haydar
Published: October 2015

There are limited data on the outcome of patients with thalassemia receiving HSCT from non‐sibling matched family donors. Of the 341 patients with thalassemia major that underwent donor search at our center from January 2003 to December 2011, 236 (69.2%) had fully matched family donor of which 28 patients (8.2%) had non‐sibling matched family donors identified. We report on seven patients with a median age of eight yr (4–21) who underwent myeloablative (n = 4) or RIC (n = 3) HSCT. The median age of the donors was 33 yr (4–47), three were parents, two first cousins, one paternal uncle, and one paternal aunt. All patients achieved primary neutrophil and platelet engraftment at a median of 18 (13–20) and 16 days (11–20), respectively. One patient developed grade II acute GVHD, and two patients developed limited chronic GVHD. One patient experienced secondary GF requiring a second transplant. At a median follow‐up of 69 months (7–110), all patients are alive and thalassemia free. Our data emphasize the need for extended family HLA typing for patients with thalassemia major in regions where there is high rate of consanguinity. Transplant from non‐sibling matched family donor can result in excellent outcome.
The Dialogue Continues: The Future of Public Health Nursing
Authors: Meighoo Padi
Published: October 2015

This editorial reflects upon the current discussion among nursing academics and educators about the division between individual level care and population health and its implications for the subdiscipline of public health nursing, from the perspective of a current practitioner in the field.
Striped Pants versus Fat Cats: Ambassadorial Performance of Career Diplomats and Political Appointees
Authors: Haglund Evan T.
Published: October 2015

The growing bureaucratic performance literature focuses on differences in programs or agencies led by either careerists or political appointees; yet this literature still struggles to measure and then compare performance across agencies. This article examines ambassadorial performance to provide new measures of individual‐ and organization‐level performance. Using a new data set of embassy inspection reports by the State Department's inspector general, I find that the traditional dichotomy of careerists versus appointees explains some performance differences even as some key individual‐level characteristics that are expected to affect performance are not influential. These findings have important implications for presidents and agencies in their approaches to leadership selection and performance evaluation.
Presidential Particularism in Disaster Declarations and Military Base Closures
Authors: Kriner Douglas L. , Reeves Andrew
Published: October 2015

In The Particularistic President we challenge the dominant paradigm asserting presidential universalism. Instead, we argue that presidents possess strong electoral and partisan incentives to pursue policies that prioritize the needs of some Americans over those of others. In this article, we review our larger argument and expand upon our analyses of two policy areas where presidents have unilateral authority over distributive outcomes: natural disaster declarations and military base closures. In the former, we find strong evidence that President Barack Obama favored both swing and core states in the 2012 election year. In the latter, we find evidence of both electoral and partisan particularism.
Reagan Reorders the Political Regime: A Historical–Institutional Approach to Analysis of Change
Authors: Nichols Curt
Published: October 2015

The future of reconstructive presidential leadership is in question. It is increasingly difficult to tear out and replace institutions in today's constraining environment. However, historical–institutional theory suggests that alternative leadership possibilities exist. A reconstructive president may be able to reorder the political regime through application of a multiple modalities of change strategy. This project explores this prospect through study of Ronald Reagan's accomplishments in the budget battles of 1981. It applies a new analytic approach to determine if his well‐known successes can be translated into the historical–institutional conceptual framework. It confirms that previously hypothesized leadership possibilities exist and demonstrates the utility of the new analytic approach to the study of institutional change. Pros and cons of modern reconstructive leadership are illuminated and the new change‐framework is recommended for broader application in presidential studies.
Public Opinion Toward Presidential Power
Authors: Reeves Andrew , Rogowski Jon C.
Published: October 2015

According to more than a half‐century of scholarship, a president's prestige is one of his primary sources of power. In this article, we examine the public's attitudes toward the levers of presidential power. Using data from a nationally representative survey, we show that respondents who provided higher approval ratings of the president were significantly more supportive of presidential powers. These findings provide striking evidence that views toward executive power are shaped by presidential approval and suggest that popular presidents can use their prestige to expand the scope of powers available to the presidency.
The Law Barack Obama and the Clemency Power: Real Reform on the Way?
Authors: Crouch Jeffrey
Published: October 2015

On February 9, 2014, the New York Times editorial board described the Obama administration as “one of the least merciful … in modern history.” Over the past year and a half, President Barack Obama has shown renewed interest in clemency. However, as of July 13, 2015, real reform remains elusive: Obama has granted less than 1% of pardon and commutation requests. Is anything likely to change in the remaining months of the Obama administration? In this article, I look for hints of Obama's plans by considering his clemency record in detail, paying particular attention to the types of offenses that have been deemed worthy of clemency and those that have not.
The Historical PresidencyPresidential Incentives, Bureaucratic Control, and Party Building in the Republican Era
Authors: Rogowski Jon C.
Published: October 2015

Though scholars have developed theoretically rich and empirically sophisticated accounts of presidential behavior within the modern era, it is less clear whether these insights shed light on presidents who served in earlier periods of history. In this paper, I sketch an outline of the incentive structures faced by late‐ nineteenth‐century presidents that focuses on their contributions to party building and use county‐level data from 1876 to 1896 to show that presidents’ core partisan constituencies were disproportionate recipients of federal post offices. While presidential incentives may have differed across history, presidents appeared to be well positioned to act upon them.
Overcoming Learning Aversion in Evaluating and Managing Uncertain Risks
Authors: Cox Louis Anthony (Tony)
Published: October 2015

Decision biases can distort cost‐benefit evaluations of uncertain risks, leading to risk management policy decisions with predictably high retrospective regret. We argue that well‐documented decision biases encourage learning aversion, or predictably suboptimal learning and premature decision making in the face of high uncertainty about the costs, risks, and benefits of proposed changes. Biases such as narrow framing, overconfidence, confirmation bias, optimism bias, ambiguity aversion, and hyperbolic discounting of the immediate costs and delayed benefits of learning, contribute to deficient individual and group learning, avoidance of information seeking, underestimation of the value of further information, and hence needlessly inaccurate risk‐cost‐benefit estimates and suboptimal risk management decisions. In practice, such biases can create predictable regret in selection of potential risk‐reducing regulations. Low‐regret learning strategies based on computational reinforcement learning models can potentially overcome some of these suboptimal decision processes by replacing aversion to uncertain probabilities with actions calculated to balance exploration (deliberate experimentation and uncertainty reduction) and exploitation (taking actions to maximize the sum of expected immediate reward, expected discounted future reward, and value of information). We discuss the proposed framework for understanding and overcoming learning aversion and for implementing low‐regret learning strategies using regulation of air pollutants with uncertain health effects as an example.
Pilot study of oral metformin in cancer‐bearing cats
Authors: Wypij J. M.
Published: October 2015

A prospective dose escalation pilot study was performed in cancer‐bearing cats to assess toxicity and surrogate biomarkers of pharmacologic activity of oral metformin hydrochloride. Nine cats with measurable spontaneous cancer were treated with oral metformin for 14 days. Monitoring included complete blood count (CBC), serum biochemistry, lactate,pH, insulin‐like growth factor‐1, and vascular endothelial growth factor serially until study completion. At the maximum tolerated dose of 10 mg kg−1q12 h side effects were primarily mild to moderate gastrointestinal upset (anorexia, vomiting, and/or weight loss). All cats developed a reduction in haematocrit. Six of nine cats developed new or progressive hyperlactatemia and one cat developed asymptomatic lactic acidosis. There were no clinical responders and two cats had modest measurable reduction in tumour size. In conclusion, we demonstrate potential pharmacologic activity of metformin at a clinically relevant dose and identify parameters for clinical monitoring and supportive care. Further investigation of metformin in cancer‐bearing cats is warranted.
Response of Pore Pressure and Effective Stress in Seabed to Waves Around a Permeable Submerged Breakwater
Authors: Chen Hao , Zheng Jinhai , Li Qianzhen , Zhang Naiyu , Chen Hanyi , Zhang Jisheng
Published: October 2015

As the unexpected wave-induced seabed instability may cause foundation failure, the evaluation of wave-induced pore pressure and effective stress in seabed plays an important role in the design of the foundation of marine structures. In this study, a two-dimensional integrated mathematical model, based on COBRAS wave model and SWANDYNE seabed model is developed to numerically investigate the mechanism of wave-induced seabed response in the vicinity of a permeable submerged breakwaters. Numerical results indicate that this model has a great ability in predicting the dynamic response of the pore pressure and effective stress around the breakwater. Both the pore fluid pressure and effective stress in seabed largely changes with an increasing water depth. It is also found that the responses of the pore pressure and effective stress of different locations to the dynamic wave loading are significantly different in the cases with variable top width of the breakwater.
An Investigation on Turbulence Assessment Methods for the Offshore Helideck Availability Study
Authors: Park Sung-In , Kim Min-Ho , Kwon Seungmin , Chi Hye-Ryoun , Lee Jae-Bong , Hwang Yoon-Sik
Published: October 2015

The aim of this study is to investigate methods of assessing the turbulence effect for the helideck availability study. Due to the limited space on offshore platforms, a helideck is normally positioned on cramped areas and this makes turbulence flows around the helideck. CAP 437, the representative standard for the offshore helideck design suggests various criteria for the helideck availability assessment and recommends a Standard Deviation of Vertical airflow Velocity (SDVV) value to be used for the turbulence effect assessment. Although there is a specific value of SDVV recommended in CAP 437, different interpretations are possible in the calculation of the value resulting in totally different assessment outcomes even under the same analysis condition. In this study, two different approaches are investigated and their results are compared. One approach is based on the spatial variation of the mean vertical velocity while the other utilizes the Turbulence Kinetic Energy (TKE) value from the Computational Fluid Dynamics (CFD) simulation. With a CFD tool, Kamelon FireEX (KFX), a couple of 3-dimensional simulations is performed and turbulence flows around an offshore semi-rig are obtained. SDVV values are calculated using both approaches and compared each other as well as with criteria recommended in CAP 437. It is hoped that the result of this study is helpful to engineers for understanding evaluation methods of turbulence effects in the helideck availability assessment.
The Added Mass and Viscous Damping of a Spar Platform With Semi-Closed Moon Pool
Authors: Liu Li-qin , Man Jin-shuang , Qiu Yu
Published: October 2015

The CFD (Computational Fluent Dynamics) method was used to calculate the added mass and the viscous damping of the Spar platform considering the semi-closed moon pool in this paper. The three-dimensional models of the platform with water inside the semi-closed moon pool were established by the VOF (Volume of Fluid) method. The UDF (User Defined Function) was adopted to oscillate the platform. The added mass and the damping coefficients were calculated under different KC (Keulegan-Carpenter) number and flow velocity for different opening ratio of the moon pool. The viscous damping and natural period of the platform heaving were obtained by calculating the platform motion in the static water. The influences of water inside the moon pool on the Spar platform motion were analyzed.
Combined FIV and VIV Effects on a Cantilevered Pipe Discharging Fluid in Deep Waters
Authors: Meng Shuai , Kajiwara Hiroyuki , Srinil Narakorn
Published: October 2015

To avoid or mitigate global warming, several ocean carbon capture and storage concepts have been proposed. One of the recent approaches is to dispose carbon dioxide via a fixed vertical cantilevered pipe onto the seabed in deep waters. Due to a high aspect ratio and flexibility of such long pipe conveying fluid with fixed-free end conditions and external hydrodynamic loading caused by currents, the pipe may experience large-amplitude 3-D vibrations leading to structural failure. Hence, it is essential to understand and investigate the pipe nonlinear dynamic behaviors subject to combined flow-induced vibration (FIV) and vortex-induced vibration (VIV).

In this study, the 3-D nonlinear equations of a cantilevered pipe discharging fluid in the sea are analyzed using a Galerkin-based multi modal approach combined with a finite difference Houbolt’s integration scheme. Particular attention is paid to the combined effects of FIV and VIV on the dynamic response of the cantilevered pipe in water. To model the fluctuating lift and drag forces associated with VIV, the two dimensional wake oscillators distributed along the pipe are adopted. Numerical simulations in the FIV case of a pipe discharging fluid in the air are first validated with experimental results in the literature to justify the mathematical models and numerical approaches. Modal convergence analysis is also performed. Results in the combined FIV and VIV cases are then highlighted in order to show the effects of cross-flow and in-line VIV when compared with the pure FIV case. The effects of geometric nonlinearities, the coupling/interaction of multi modes and the space-time modifications of pipe responses and trajectories are highlighted. It is hoped that the numerical observations and findings obtained from this study could be verified by experimental studies which are presently lacking in the literature.
Long Term Analysis for Estimation of Wave Slamming Pressures for Spar Design
Authors: Lim Ho-Joon , Lian Gunnar , Haver Sverre , Dalane Oddgeir , Koo Bonjun , Sablok Anil , Lambrakos Kostas
Published: October 2015

A long term analysis was performed to determine extreme wave slamming loads on the Aasta Hansteen Spar, the first production and storage Spar to be installed in the Norwegian Sea. The Spar will experience high slamming pressures on the hull due to harsh environments in the field. Extensive model tests were performed to measure the wave slamming pressure which is one of challenging design parameters.

The slamming loads were measured with a 3×3 array of force transducer panels attached to the Spar hull. The extreme slamming loads were estimated from 3-hour simulations of the 100-yr and 10000-yr wave environments at the Aasta Hansteen field in the Norwegian Sea. The wave simulations included fourteen sea states, and each sea state was represented by as many as 20 realizations.

Based on model test data, short term analysis of 3-hour extreme pressure at each tested sea state was performed using the Gumbel distribution. Due to high variability of 3-hour maximum pressures, a long term analysis was required to investigate the proper percentile level to be used in the design.

The paper presents a long term statistical methodology for extreme wave slamming loads that is used to calculate long term slamming pressures corresponding to a specified annual exceedance probability of q (e.g., q = 10−2 and q = 10−4). The paper also derives the appropriate non-exceedance probability for a short term wave environment that reproduces the long term pressures of a specified annual exceedance probability, q.

Various sensitivity analyses (e.g., on the two Gumbel parameters, number of realizations, etc.) were performed to validate the short term target percentiles and associated extreme pressures derived from this approach.

Details of the model tests and methodology to define the design pressure profile above mean water level (MWL) are presented in a companion paper of this Conference.
Practical Design Considerations for Managing Marine Growth on VIV Suppression Devices
Authors: Allen Don W. , Lee Li , Henning Dean , Liapis Stergios
Published: October 2015

Most deepwater tubulars experiencing high currents frequently require vortex-induced vibration (VIV) suppression to maintain an acceptable fatigue life. Helical strakes and fairings are the most popular VIV suppression devices in use today.

Marine growth can significantly affect the VIV of a bare riser, often within just a few weeks or months after riser installation. Marine growth can have a strong influence on the performance of helical strakes and fairings on deepwater tubulars. This influence affects both suppression effectiveness as well as the drag forces on the helical strakes and fairings. Unfortunately, many VIV analyses and suppression designs fail to account for the effects of marine growth at all, even on a bare riser.

This paper utilizes results from both high and low Reynolds number VIV test programs to provide some design considerations for managing marine growth for VIV suppression devices.
Simulation of Fluttering and Autorotation Motion of Vertically Hinged Flat Plate
Authors: Rostami Ali Bakhshandeh , Fernandes Antonio Carlos
Published: October 2015

This paper is dedicated to the simulation of fluttering (oscillatory) and tumbling (rotational) phenomenon that may occur during the flow induced rotation in the water or air current. Fluttering is the oscillation of body about an axis and the tumbling, better called here as autorotation, is a name given to the case when the body turns continuously around the axis. This work describes the simulation of these phenomena by a nonlinear time domain code on freely rotating plate about a fixed vertical axis. The dimensional analysis proves that the rotational motion induced by flow is governed essentially by the dimensionless moment of inertia (I*) and Reynolds number. For Reynolds number less than 15000, plate experiences small amplitude fluttering motion that is independent of I*. It is shown that by increasing I* the fluttering bifurcates to autorotation, with a transition point that is approximately independent of Reynolds number and is such that I*=0.083.
Estimation of the Damping Parameter Governing the VIV of Long Flexible Cylinders
Authors: Rao Zhibiao , Vandiver J. Kim
Published: October 2015

Much effort in the past half century has been made to explain the role of damping in the prediction of VIV. Scruton (1965), Griffin et al. (1975), Klamo, et al. (2005) and Govardhan & Williamson (2006) all made significant contributions. None fully characterized the role of damping in governing the response over the full range reduced velocities, which encompass the wake synchronized region. In 2012 Vandiver devised a way to do that with a new damping parameter c*. His results were verified using 2D spring-mounted cylinders in uniform flow.

The primary objective of the research described in this paper is to find a c* -like quantity for flexible cylinders, which is capable of organizing response data for flexible cylinders, which may have many modes, be exposed to sheared flows and possess spatially varying properties, such as the coverage of strakes and fairings. Data from a recent high mode VIV model test campaign conducted by SHELL Exploration and Production Company are used to illustrate the application of c* to flexible cylinders. It is shown that, if one accounts for Reynolds number, the response of flexible cylinders with varying strake coverage in the SHELL Tests collapse onto a single curve.
Efficient Simulation Method to Predict Green Water Loads on Superstructures
Authors: Theilen Lasse , Detlefsen Ole , Abdel-Maksoud Moustafa , Bohm Michael
Published: October 2015

The numerical prediction of green water loads on super-structures is challenging due to the high number of required calculations to identify the critical operational conditions in the seaway which lead to overcoming seawater on deck. Further, the simulation of the non-linear behaviour of water on the deck and the prediction of impact loads require high computational effort. This paper presents an efficient three-step approach to simulate green water loads. The application of the developed procedure will be demonstrated on a mega yacht geometry.
Response Surface Models for Analyzing Sinkage and Trim Effects on Planing Hull Motions in a Vertical Plane
Authors: Sayeed Tanvir Mehedi , Lye Leonard M. , Peng Heather
Published: October 2015

Further to the studies presented by Sayeed et al. (OMAE2014-23489), response surface models have been improved by including the effects of sinkage and trim to the vertical plane motions of planing hull in head sea. This was achieved by including longitudinal center of gravity (LCG) as an additional factor to the existing model and change in LCG eventually incorporated the effects of sinkage and trim. The validated non-linear mathematical model, Planing Hull Motion Program (PHMP) can predict the heave and pitch motions and bow and center of gravity accelerations with reasonable accuracy at planing and semi-planing speeds. This paper again illustrates an application of modern statistical design of experiment (DOE) methodology to develop response surface models to assess planing hull motions in a vertical plane in head seas. Responses were obtained from PHMP based on a multifactor uniform design scheme. Results showed that the simple one line regression models provided adequate fit to the generated responses and provided valuable insights into the behaviour of planing hull motions in a vertical plane. The new response surface models includes all possible influential factors that affect the vertical plane motions of planing hull in head sea. The simple surrogate models can be a quick and useful tool for the designers during the preliminary design stages.
Three-Dimensional Mechanical Analysis of Flexible Jumper Installation
Authors: Ruan Weidong , Liu Ting , Bai Yong , Shi You , Fu Jianbo , Su Feng
Published: October 2015

This paper presents a simple method to study the installation process of a flexible jumper lowered into deep water by use of cables in a 3D space. Based on the catenary theory, the initial configuration of the installation system can be obtained easily. Then an iterative procedure, which uses force equilibrium and compatibility requirements as convergence criteria, is adopted to establish the final configuration considering the environmental loads. The internal force, bend radius and displacement of the flexible jumper are also obtained by finite-element discretization. The acquired results are compared with those derived from OrcaFlex finite-element model, in order to verify the accuracy and reliability of the proposed method. The influence on the minimum bend radius and maximum axial tension of the flexible jumper due to the difference between the lowering cable lengths, is also studied. The approach presented throughout this paper can offer some suggestions in regards to the installation of a flexible jumper in practical engineering.
An Accident Model for Arctic Shipping
Authors: Smith Doug , Veitch Brian , Khan Faisal , Taylor Rocky
Published: October 2015

This paper examines historical Arctic marine accidents from 1995–2004. It was seen during this time period that sinking and grounding of (fishing) vessels was the most common type of Arctic marine accident. A comprehensive accident model is presented to describe Arctic shipping accidents and their causation factors. The accident model is based on epidemiological concepts which explain how non-sequential factors result in an unwanted outcome, analogous to disease spreading through a human body. The causation factors are non-sequential and non-linearly dependent. The applicability of the model is demonstrated through examination of two past accidents: the Kolskaya and the Kulluk. Detailed description of how the accident model could be used for predictive accident modelling and risk analysis of Arctic shipping scenarios is also presented.
Assessing Evacuation Operation Performance in Harsh Environments
Authors: Norazahar Norafneeza , Khan Faisal , Veitch Brian , MacKinnon Scott
Published: October 2015

This paper addresses the severity of consequences of ineffectively performing evacuation operations of offshore installations in harsh environments. Hazards, particularly fire, smoke, heat, and extreme weather conditions, can harm personnel both directly and indirectly and prevent personnel from performing an evacuation operation successfully. To demonstrate the dependence of consequences on the hazards, this paper uses an event tree (ET) analysis. The event tree analysis maps all possible sequences of events leading to an accident and thus, reflects the level of knowledge about the evacuation operation. The paper uses ET analysis to develop a logical approach to hazards and consequences with the presence of safety functions. Applications of an ET analysis are discussed for two emergency response actions: a) detecting the emergency alarm, and b) moving along the escape route. In a situation where the offshore installation manager (OIM) delays activating the emergency alarm or the alarm system is damaged, personnel may not receive or hear the message. Availability of both primary and alternative escape routes enable personnel to move to a safe area in an escalating event, such as a series of fires and explosions. The paper discusses the ET analysis of hazards and consequences in specifically a qualitative manner. Information from the analysis can be used in a risk assessment of evacuation operations.
A New Quantitative Assessment of Current Profile Clustering Methods for Riser Engineering
Authors: Jeans Gus , Gibson Richard , Jones Oliver
Published: October 2015

This paper presents a new quantitative approach of defining current profiles for application to riser fatigue assessment using profile clustering methods.

The analysis presented here was undertaken using a one year long deepwater current profile dataset from the Gulf of Mexico. The data included near full water column measurements in 3250m water depth at one hour intervals, providing nearly 9000 individual profiles. Riser fatigue damage for each profile had been previously computed as part of the Worldwide Approximation of Current Profiles (WACUP) joint industry project.

The new assessment described in this paper applies clustering methods not considered in WACUP, including the K-Means Algorithm (KMA) and Maximum Dissimilarity Algorithm (MDA). These both demonstrate superior performance compared to a much simpler direct method of characterisation. Features of the KMA and MDA methods are contrasted, within the context of previously published application to ocean wave data.
Evaluation of Spar In-Field Performances for Topsides Payload Increase and Operational Changes
Authors: Baquet Aldric , Zhou Joe , Xu Lixin , Chen Yong
Published: October 2015

In the initial design stage of an offshore platform, some conservative assumptions might be used for the platform hull and Topsides weights, wind area and Metocean criteria of environments. After the platform is installed, actual results from weight surveys and real-time snapshots of the as-built operating platform typically provide more accurate information for the purpose of assessing real operational conditions and future changes of these conditions. For example, in field operations, it is particularly useful to quantify how much weight can be added to the as-built operating facility, while assuring that the platform still meets the overall design criteria and regulatory requirements.

This paper presents an effective method for evaluation of an in-field operating Spar platform, to determine the maximum allowable envelops for topsides weight change verse the topsides VCG, based on the Spar global performances and riser operating limits. The case study is performed for a Spar in the Gulf of Mexico (GOM), based on the Spar as-built data and actual in-field configurations of hull/mooring and risers, and using the updated Metocean criteria (after the Hurricane Katrina in the GOM).

The analysis results of the allowable topsides weight change and topsides VCG limits, accounting for the Spar in operating, extreme and survival conditions, are based on three governing factors: (1) the Spar motions meet the original design criteria for global performances, and are within the safety range of riser operations; (2) the maximum loads at critical connections between the Spar hard tank and the topsides structures are within the design loads; and (3) the reserve variable ballast is sufficient to balance the Spar at an even keel position at the design draft for all required operating conditions.
A Comparative Study Between DNS, LES and PIV for a Marine Riser With Fairings
Authors: Strandenes Håkon , Canabes José Patricio Gallardo , Visscher Jan , Pettersen Bjørnar , Andersson Helge I. , Lie Halvor , Baarholm Rolf
Published: October 2015

This paper present results from numerical simulations and laboratory experiments investigating the flow around a riser with fairings at Reynolds number of 5000. We present fully resolved direct numerical simulations (DNS), large eddy simulations (LES) and compare the results with flowfields obtained from particle image velocimetry (PIV) experiments in a circulating water tunnel. The DNS and LES results do agree very well on surface integral quantities such as drag and lift force, but there are discrepancies in first order statistical flow parameters such as recirculation length. This indicate that a comparison of force coefficients is not sufficient to validate this type of bluff body wake flows. Comparing the simulation data with the experimental PIV data, also reveals significant discrepancies in the mean flow field, although the Strouhal number agrees between DNS and PIV results.
The Pros and Cons of Wall Functions
Authors: Eça Luís , Saraiva Gonçalo , Vaz Guilherme , Abreu Hugo
Published: October 2015

Simulations of viscous flows based on the Reynolds-Averaged Navier-Stokes (RANS) equations have become an engineering tool used on a daily basis. One of the main goals of such calculations is to determine friction forces, which are a consequence of the shear-stress at solid walls.

In RANS (and other more sophisticated mathematical models), there are two main approaches for the determination of the shear-stress at a wall: direct application of the no-slip condition, i.e. the velocity gradient is determined directly at the surface; wall functions which determine the shear-stress at the wall from semi-empirical equations applicable up to the outer edge of the so-called “wall layer/log layer”. Although the first option is physically preferable, its numerical requirements may lead to iterative convergence problems and/or excessive calculation times. Therefore, especially at high Reynolds numbers, it is not unusual to use the latter approach.

In this paper we discuss the advantages and disadvantages of wall-function boundary conditions. To this end we have calculated the flow around a flat plate, conventional and laminar airfoils and a circular cylinder. The influence of the location where wall functions are applied (distance to the wall) and the effect of the Reynolds number (ranging from model to full scale applications) are discussed. Griding requirements for wall-function boundary conditions are also addressed. The results obtained with wall functions are compared with those obtained from the direct application of the no slip at the wall.

The results obtained in this study show that the use of wall functions in viscous flow calculations may be justifiable or completely unacceptable depending on the flow conditions. Furthermore, it is also shown that wall-function boundary conditions also require clustering of grid nodes close to the wall, but obviously less demanding than the direct application of no slip condition.
Geotechnical Investigation of Pore Pressure Behavior of Muddy Seafloor Sediments in an Arctic Permafrost Environment
Authors: Stark Nina , Quinn Brandon , Ziotopoulou Katerina , Lantuit Hugues
Published: October 2015

Herschel Island, Yukon, Canada, is made of ice-rich permafrost and is affected by high rates of coastal erosion, likely to increase with decreasing summer sea ice extent. During an interdisciplinary expedition to Herschel Island in July 2014, geotechnical investigations were carried out in shallow water environments of up to 20 m water depth and at different beaches. The free-fall penetrometer BlueDrop was deployed at 299 positions. Apart from obtaining vertical profiles of sediment strength and the pore pressure response upon impact, the pore pressure evolution over a period of one hour after deployment was investigated. The focus area for these tests was Pauline Cove, located at the south-eastern side of the island, being sheltered by a spit from the open Beaufort Sea and affected by a number of old and young retrogressive thaw slumps, delivering large amounts of mud. The sediment resistance profiles revealed up to three distinct layers of sediment strength, expressing different consolidation states, or possibly changes in sediment composition. This stratification was supported by the pore pressure results, including pore pressure evolution “on-the-flight” during penetrometer penetration as well as pore pressure evolution at maximum penetration depth with the penetrometer being at rest. The sediment surface layer 1 was characterized by a thickness of 5–20 cm depending on the respective location, low sediment resistance and predominantly hydrostatic pressure. It most likely has frequently been reworked by wave action, and exhibited similar geotechnical signatures as fluid mud. Layer 2 reached sediment depths of 30–60 cm, showed an increase in sediment resistance and distinct subhydrostatic pore pressures during penetration, while pore pressures increased in an asymptotic manner to suprahydrostatic (160–180% of hydrostatic pressure) over an observation period of 30–50 minutes. Based on comparison to other examples from the literature, it was hypothesized that layer 2 was composed of overconsolidated mud. Layer 3 featured a significant increase in sediment resistance as well as pore pressure during penetration. As soon as the probe came to rest, the pressure decreased significantly to subhydrostatic conditions, before swinging back to being suprahydrostatic and then slowly dissipating. A similar behavior has been associated to silty sands and high bulk densities. Here, it may suggest a change in sediment composition, likely influenced by coarser nearshore and beach sediments, representing also a denser sediment matrix. The pore pressure results will complement the geological and geotechnical characterization of the coastal zone of Hershel Island, and contribute to the investigation of erosion and deposition processes.
Coupled Axial/Lateral VIV of Marine Risers in Sheared Currents
Authors: Zanganeh Hossein , Srinil Narakorn
Published: October 2015

Modelling and prediction of vortex-induced vibrations (VIV) of marine risers is a challenging task due to the associated multi degrees of freedom in both cross-flow/in-line directions and the multi-mode fluid-structure interactions. In addition, the axial motion and its geometrically nonlinear coupling with lateral responses can be significant, especially at higher-order modes. Nevertheless, several papers in the literature dealing with VIV predictions have often overlooked such aspects. Therefore, this study aims to investigate and understand the effect of axial or longitudinal motion through a theoretical model and numerical approach in time domain.

Attention is paid to VIV of vertical risers subjected to linearly sheared currents. To capture a three-dimensional aspect of the flexible cylinder experiencing VIV, a semi-empirical model is developed consisting of nonlinear equations of cross-flow, in-line and axial structural oscillations which are coupled with the distributed van der Pol-type wake-oscillators modelling the fluctuating fluid lift/drag forces. The mean drag force is also taken into account. These model equations are numerically solved via a space-time finite difference scheme, and the obtained numerical results highlight several aspects of VIV of elastic cylinders along with the axial motion effects.

Apart from the validation of the numerical model with published experimental results, this study reveals how the effect of axial motion and its nonlinear coupling with the two lateral cross-flow/in-line motions can be very important. These depend on the flow velocity, the fluid-structure parameters, the single or multi-mode lock-in condition, and the standing-wave or travelling-wave feature. We recommend that the axial response should be accounted for in VIV analysis and prediction model.
A Multi-Body Dynamic Model Based on Bond Graph for Maritime Hydraulic Crane Operations
Authors: Chu Yingguang , Æsøy Vilmar
Published: October 2015

This paper presents a bond graph model of a maritime crane lifting system comprised of a 3DOFs crane with three revolute joints, a winch, a segment of wire, and a pendulum load. The multi-body model contains the dynamic properties of the system and 3D animation of the operational behaviors. Lagrange’s method was used to derive the dynamic equations of the multi-body crane. Lagrange’s equations provide a clean elegant form for implementation using a special type of bond graph called IC-field. The model based on the bond graph contains interfaces to other domain models, e.g. input devices, control systems, hydraulic actuators, and sensors. Maritime crane operations are challenging due to the impact of heavy lifting, system stiffness and load sway resulted from the unstable working platform. The industry increasingly demands an overall virtual environment for modeling and simulation of maritime operations. The accomplishment will highly increase the efficiency and effectiveness of product and system design, new component and control algorithm testing, and operator training. The multi-body dynamic model is the core building block for modeling and simulation of maritime crane operations.
Simulations for Design and Reconstruction of Breaking Waves in a Wavetank
Authors: Kurnia R. , van den Munckhof T. , Poot C. P. , Naaijen P. , Huijsmans R. H. M. , van Groesen E.
Published: October 2015

To determine forces on fixed and flexible structures such as wind mills and oil platforms, experiments in wave tanks are useful to investigate the impacts in various types of environmental waves. In this paper we show that the use of an efficient simulation code can optimize the experiments by designing the influx such that waves will break at a predefined position of the structure. The consecutive actual measurements agree well with the numerical design of the experiments. Using the measured elevation close by the wave maker as input, the software recovers the experimental data in great detail, even for rather short (up to L/D=1) and very steep breaking waves with steepness parameter (ak) till 0.4.

The experiments were carried out in the TUD-wavetank and the simulation is done by HaWaSSI-AB, a spatial-spectral implementation of a Hamiltonian Boussinesq model with an eddy-viscosity breaking mechanism that is initiated by a kinematic breaking condition.
Numerical Investigation of Flow Interference Effects in Fixed and Vibrating Tandem Square Columns Using Hybrid RANS-LES Models
Authors: Gopalan Harish , Chandar Dominic Denver John , Pillamarri Narasimha Rao , Mengzhao Guan , Jaiman Rajeev K. , Ma Peifeng , Xu Haihua , Choudhary Ankit , Hussain Anis
Published: October 2015

Investigation of flow past tandem and side-by-side circular and square columns is of interest in offshore engineering. Flow past fixed and vibrating circular columns has received a lot of focus in the literature. However, the studies focused on square columns, especially at high Reynolds numbers are very limited due to the computational cost of large eddy simulation (LES). Unsteady Reynolds-averaged Navier-Stokes (URANS) methods are limited by their accuracy, especially for tandem columns in the wake interference regime (spacing to diameter ratio: L=D ∼ 3:0). Hybrid URANS-LES models (URANS near the solid-wall and LES away from the wall) can overcome the drawbacks of the traditional URANS methods and can provide a reasonable prediction of the flow physics at a fraction of the cost of LES without significantly sacrificing numerical accuracy.

Arbitrary Lagrangian-Eulerian (ALE) methods fails when vibrating tandem bodies are in close proximity to each other or vibrate at high reduced velocities. Remeshing the domain can be expensive, especially at high Reynolds numbers (Re). Alternate strategies are necessary to efficiently simulation this problems. This study proposes the use of a non-linear URANS-LES model, coupled with an overset mesh method (for vibrating columns), for studying flow past tandem square columns. Simulations are performed at sub-critical Re to match the experimental Re. The initial results are encouraging for further investigation of fixed and vibrating tandem square column flow interference at high Reynolds numbers.
Numerical Analysis of a Gravity Substructure for 5MW Offshore Wind Turbines due to Soil Conditions
Authors: Park Min-Su , Jeong Youn-Ju , You Young-Jun , Lee Du-Ho , Kim Byeong-Cheol
Published: October 2015

In order to increase the gross generation of wind turbines, the size of a tower and a rotor-nacelle becomes larger. In other words, the substructure for offshore wind turbines is strongly influenced by the effect of wave forces as the size of substructure increases. In addition, since a large offshore wind turbine has a heavy dead load, the reaction forces on the substructure become severe, thus very firm foundations should be required. Therefore, the dynamic soil-structure interaction has to be fully considered and the wave acting on substructure accurately calculated. In the present study ANSYS AQWA is used to evaluate the wave forces. The wave forces and wave run up on the substructure are presented for various wave conditions. Moreover, the substructure method is applied to evaluate the effect of soil-structure interaction. Using the wave forces and stiffness and damping matrices obtained from this study, the structural analysis of the gravity substructure is carried out through ANSYS mechanical. The structural behaviors of the strength and deformation are evaluated to investigate an ultimate structural safety and serviceability of gravity substructure for various soil conditions. Also, the modal analysis is carried out to investigate the resonance between the wind turbine and the gravity substructure.
Extensions and Improvements to the Solutions for Linear Tank Dynamics
Authors: Ludvigsen Arild , Pan Zhi Yuan
Published: October 2015

Linear solvers for the flow exterior to the hull may be used to solve for the fluid dynamics also in the interior of a tank, as discussed in Newman (2005) and Ludvigsen et al. (2013). This introduces extra, erroneous terms in the radiation part of the pressure in the tank, but due to cancellation in restoring and radiation terms, the total representation of the pressure and the global response is correctly obtained.

For some kinds of analysis, specific knowledge is needed of the radiation and restoring parts separately. The cancellation of the extra terms can then not be utilized.

Examples of this are stability analysis and eigenvalue analysis. In stability analysis we need to know the actual real global restoring coefficients. In eigenvalue analysis, we should have the separately correct representations of the added mass and restoring coefficients, respectively, to be able to conveniently use them as input to standard eigenvalue solvers.

Here, we develop the expressions for the corrected, actual terms of the total added mass and restoring coefficients for tanks. This is used in our computer program for performing eigenvalue analysis. Results for peak global response and natural periods of the structure with the influence of tank dynamics are presented. Comparisons are made with results obtained by a quasi-static method for an FPSO and a ship with more largely extensive tanks.

For a completely filled tank, the boundary value problem (BVP) for the velocity potential is reduced to Laplace equation in the fluid domain, subject to a Neuman condition on the fixed boundary and it is not closed. The extra condition of having zero pressure at some point in the tank is then added.

Direct re-use of the BVP solver for the external flow, gives an undetermined set of linear equations for the velocity potential in the tank fluid. A typical solver for sets of linear equations may still return a solution, but this will contain a random undetermined constant. After imposing zero pressure in the top of the tank, this solution is still unstable, contaminated by numerical noise.

An improved method is introduced by imposing algebraically, in the equation system, the constraint of zero pressure in the top of the tank. This gives a non-singular equation system with a stable solution holding zero pressure in some selected point in the tank.
Subsea Oil and Gas Production Assurance Using Artificial Lifts and Nodal Analysis
Authors: Okaro Ikenna A. , Tao Longbin
Published: October 2015

This paper describes how the operation of deep, subsea oil wells can be analyzed and optimized using artificial lift systems. A modest explanation was offered about an enhanced Hubbert model for determining production targets at pre-feed phase of project. In addition, the impact of artificial lifts on the economics of subsea wells facing hyperbolic production decline was illustrated. The principle of Nodal analysis was highlighted and applied to optimize a proposed subsea oil production case. Configurations of a nominally rated rod pump, a multiphase pump and an electrical submersible pump were modelled in a steady-state flow using Pipesim software and the simulated results which were functions of liquid flow rate and pressure distribution across the production system exposed the behavior of the system.

The results showed that over 100% volumetric efficiency was achieved using a combination of electrical submersible pump at the bottom hole and a multiphase pump at riser base. A guide is presented on how to predict, analyze and enhance the recovery curve of subsea oil production using artificial lifts and nodal-system analysis. The benefit of this work is an enabling cost-effective approach for ensuring production assurance in deep water oil and gas production.