bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Natural Convection Heat Loss From a Solar Concentrator Open Cavity Receiver at Varying Angle of Inclination
Authors: Paitoonsurikarn S. , Taumoefolau T. , Lovegrove K.
Published: January 2009

Natural convection inevitably occurs in solar thermal systems, e.g., open cavity receivers in high concentrating solar dishes and solar towers. In most applications, it can contribute a significant fraction of total energy loss, and hence it is an important determining factor in system performance. The present study investigates both experimentally and numerically the natural convection loss from the aperture of open cavity receivers used in paraboloidal dish concentrators. The aim of this study is to quantitatively determine the relationship between convection loss to various pertinent parameters such as ambient temperature, operating temperature, cavity inclination and cavity geometry. The experimental investigation was based on an isothermal electrically heated model receiver, with a test temperature of 450°C. The model receiver is tested at inclinations varying from 0° (cavity facing the side) to 90° (cavity facing straight down). With the numerical work the commercial CFD software package, Fluent 6.0 was used to model cavity convection losses. The range of input parameters used is similar to those of the experimental model. In addition, two cases of full-scaled receivers currently used in ANU dishes are considered. The accuracy concerning grid structure and grid resolution of the numerical model is also discussed. The numerical results obtained are qualitatively in good agreement with those predicted by various previously proposed correlations. The Clausing model [1981] shows the closest prediction to both numerical and experimental results despite its original use for bigger-scale central receivers.
Novel ICPC Solar Collector/Double Effect Absorption Chiller Demonstration Project
Authors: Duff William S. , Winston Roland , O’Gallagher Joseph J. , Bergquam James , Henkel Thomas
Published: January 2009

In 1998 two new technologies were demonstrated for the first time in a commercial building: a new ICPC solar collector and the solar operation of a double effect (2E) chiller. The demonstration project in Sacramento has now been in operation for almost five years. Daily collection efficiencies of over 50 percent, instantaneous collection efficiencies of over 60 percent and daily chiller COPs of about 1.1 have been achieved.
Managing Anthrax Contaminated Waste
Authors: McManus Thea
Published: January 2009

The purpose of the presentation is to describe what the Federal Government’s guidance is on the many issues regarding the disposal of contaminated and/or previously contaminated anthrax wastes. The presentation will describe various disposal options and scenarios.
Mercury Emissions From High-Temperature Sources in the NY/NJ Hudson-Raritan Basin
Authors: Themelis N. J. , Gregory A. F.
Published: January 2009

This report presents some of the results of a study conducted for the New York Academy of Sciences on the sources of past and current emissions of mercury in the Hudson-Raritan basin (HRB), an area of 42,000 square kilometers with a population of fifteen million. Mercury emissions to the atmosphere are reported from all high temperature processes, such as utility, commercial and residential boilers, secondary iron and steel smelters, Waste-to-Energy (WTE) plants, and sewage sludge incinerators. At present, the primary sources of atmospheric emissions in HRB are utility and industrial boilers (873 kilograms of mercury/year), secondary iron and steel plants (595 kg), Waste-to-Energy plants (147 kg), and sewage sludge incinerators (90 kg). The total deposition of mercury from the atmosphere on the surface of HRB was estimated at about 1,100 kilograms per year. The study examined in detail the decrease in mercury emissions from WTE plants. A metric was developed that expresses emissions from WTE plants as kilograms of mercury per million tons of MSW combusted. It was shown that reported annual emissions of mercury from the U.S. WTE plants have decreased from a high of 81,800 kilograms in 1989 to an estimated 2,200 kilograms at the present time.
Characteristics and Environmental Fate of Mercury in Municipal Waste Combustor Ash Before and After Implementation of the “Maximum Achievable Control Technology” Air Standards
Authors: Hahn Jeffrey L.
Published: January 2009

Mercury emissions from waste-to-energy facilities have been a source of public concern for more than ten years following release in the early 1990s of the EPA’s inventory of anthropogenic sources of mercury that listed MWCs as a significant source of mercury air emissions. Since 1990, source reduction, product reformulation, and increasingly effective battery recycling programs reduced mercury in trash by about 90%, according to the EPA. Pollution control equipment on waste-to-energy plants thereafter remove greater than 90% of the remaining mercury in the waste stream that is used as a fuel to generate power. The use of mercury by U.S. manufacturers will decline even further due to the virtual elimination of mercury from alkaline batteries and aggressive recycling and product substitution at hospitals, homes, and businesses. The Clean Air Act regulations promulgated in 1995 under the Maximum Available Control Technology standards have ensured that mercury emissions from waste-to-energy plants nationwide represent less than 3% of the U.S. inventory of man-made mercury sources, according to EPA, (or less than 1% of mercury emissions from all sources). Furthermore, health risk assessments completed over the past several years for new and existing waste-to-energy plants consistently reveal that the levels of mercury emissions result in exposures which are 100 times less than the threshold health effects standard established by federal and state regulatory agencies. Nonetheless, certain environmentalists and critics claim that the significant reduction in mercury air emissions has resulted in a transformation of the metal into the ash. In other words, the questions posed is whether what is not now going up the stack is instead finding its way into the ash. This paper answers that question with a resounding “no.” Based on an analysis of test data, mercury in MWC ash has not increased despite a greater than 90% reduction in mercury emissions.
Numerical Simulation of Biological Impact in Direct Injection of Carbon Dioxide in the Ocean
Authors: Sato Toru
Published: January 2009

Direct injection of carbon dioxide (CO2) in the deep ocean is one of the promising ways to mitigate the global warming. One of uncertainties in this method is, however, its impact on marine organisms in the near field before CO2 is diluted widely in the ocean. Since field experiments cost enormously, computational simulations are alternatively expected to show detailed information on the dilution process near injection points and its impact on marine organisms. In general, for testing acute impact of some toxicity on organisms, the LC50 concept is widely used. As a biological impact model, we, therefore, consider mortality that reflects the recent laboratory experiment of fish and zooplankton for various concentration of CO2. Here we regard the sigmoid-transferred mortality as a linear function of time in the logarithmic scale, not alone of the concentration of CO2 in the logarithmic scale. This model can easily be applied to unsteady CO2 experience for marine organisms. The model was installed in a computational simulation code for the reconstruction of small-scale ocean turbulence. Its results suggested that the effect is not nontrivial when CO2 of 0.1ton/sec is injected in the form of spray by 100 nozzles provided vertically on a pipe with 10m interval. This is because of the initial high concentration of CO2 near the injection points. It is, therefore, necessary to develop effective engineering measures for the initial dilution.
Float Over Installation Method: Numerical and Model Test Data
Authors: Tahar Arcandra , Halkyard John , Steen Atle , Finn Lyle
Published: January 2009

Installing a large deck onto a platform, such as a spar, using the floatover method is gaining popularity. This is because the operational cost is much lower than other methods of installation, such as modular lifts or a single piece installation by a heavy lift barge. Deck integration can be performed on land, at quay side and will not depend on a heavy lift barge. A new concept for a floatover vessel has been developed for operations in the Gulf of Mexico and West Africa. In this application sea state conditions are essential factors that must be considered in the Gulf of Mexico, especially for transportation. In West Africa, swell conditions will govern floatover deck (FOD) installation. Based on these two different environmental conditions, Technip Offshore Engineering developed the FOD installation concept using semi-submersible barge type vessels. A significant amount of development work and model testing has been done on this method in recent years on spar floatover. These tests have validated our numerical methods. Another test was conducted to investigate the feasibility of a deck float-over operation onto a compliant tower for the Benguela Belize (BBT) project. The BBT project consists of a compliant tower supporting a 25,401 metric ton (28,000 s. ton) integrated deck. This paper will describe comparisons between model test data and numerical predictions of the compliant tower floatover operation.
Flexible Pipe Sensitivity to Birdcaging and Armor Wire Lateral Buckling
Authors: Braga Mauro Pastor , Kaleff Peter
Published: January 2009

Petrobras has been successfully dealing with deep water floating production systems using flexible pipes since 1977. During the completion of Marlim South 3 well in 1977, Petrobras was surprised by the occurrence of two birdcage type failures. At that time, Marlim South 3, in a water depth of 1709 m was the deepest offshore production well in operation. Since then, Petrobras has been testing flexible pipes using a field test known as DIP test. In a DIP test, an empty end capped sample of a flexible pipe, about 150m long, is partially supported by the sea bottom and connected to a lay vessel by a pipe follower or a wire rope. The flexible pipe has to withstand a 4 hour period of cyclic bending due to the motions of the lay vessel. The DIP test has provided Petrobras with information on a new failure mode: lateral buckling in the armor wire. Although a birdcage failure is equally undesirable, lateral buckling of the armor wires implies more danger because it can go unnoticed. In 2001, a research project was set up by the Research and Development Center of Petrobras that was aimed at reproducing the flexible pipe failure modes under laboratory conditions. The purpose was to obtain a better understanding of the failure process, as well as to develop testing alternatives to avoid the significant costs related to DIP tests. In order to assess the effect of cyclic bending as a major factor in degrading the longitudinal compressive strength of flexible pipes 15 destructive tests were performed on 4 inch diameter flexible pipe samples. Two test rigs that accommodated three types of test and a number of test procedures were developed in the project. The number of bending cycles to failure for each sample was determined when subjected to compressive action corresponding to its operational depth. Tests to evaluate the effect of pre-existing damage were also conducted. Special attention was devoted to the effect of layer arrangement on compressive failure. The test results clearly identified the basic failure modes under investigation (i. e. birdcaging and lateral buckling of the armor wires). Suggestions regarding simplified testing procedures and corresponding performance criteria are also presented.
Crack Identification on a Cross-Stiffened Plate Panel
Authors: Budipriyanto Agung , Swamidas A. S. J. , Haddara M. R.
Published: January 2009

Early identification of cracks in complex structures is desirable for the safety of operation and economy of maintenance of the structure. Monitoring of the vibration response of structures is a well-known technique for crack identification. As the complexity of the structure increases manual inspection becomes difficult and the use of on-line monitoring techniques for crack detection becomes more desirable. This paper discusses the use of a structure’s vibration response in the early detection of cracks. Analytical and experimental studies of the effect of cracks on the vibration response of an 1/20 scale aluminum model of the stiffened side shell panel of a tanker were carried out. The model was carefully designed to obtain natural frequencies and mode shapes similar to those of the prototype structure. The results of the analytical study were used to determine the best locations to place the sensors on the experimental model. Results of the experimental and analytical studies are reported.
Downtime Analysis Techniques for Complex Offshore and Dredging Operations
Authors: van der Wal Remmelt J. , de Boer Gerrit
Published: January 2009

Offshore operations in open seas may be seriously affected by the weather. This can lead to a downtime during these operations. The question whether an offshore structure or dredger is able to operate in wind, waves and current is defined as “workability”. In recent decades improvements have been made in the hydrodynamic modelling of offshore structures and dredgers. However, the coupling of these hydrodynamic models with methods to analyse the actual workability for a given offshore operation is less developed. The present paper focuses on techniques to determine the workability (or downtime) in an accurate manner. Two different methods of determining the downtime are described in the paper. The first method is widely used in the industry: prediction of downtime on basis of wave scatter diagrams. The second method is less common but results in a much more reliable downtime estimate: determination of the ‘job duration’ on basis of scenario simulations. The analysis using wave scatter diagrams is simple: the downtime is expressed as a percentage of the time (occurrences) that a certain operation can not be carried out. This method can also be used for a combination of operations however using this approach does not take into account critical events. This can lead to a significant underprediction of the downtime. For the determination of the downtime on basis of scenario simulations long term seastate time records are used. By checking for each subsequent time step which operational mode is applicable and if this mode can be carried out the workability is determined. Past events and weather forecast are taken into account. The two different methods are compared and discussed for a simplified offloading operation from a Catenary Anchor Leg Mooring (CALM) buoy. The differences between the methods will be presented and recommendations for further applications are given.
Coupled Nonlinear Barge Motions: Part I — Deterministic Models Development, Identification and Calibration
Authors: Yim Solomon C. , Nakhata Tongchate , Bartel Warren A. , Huang Erick T.
Published: January 2009

This paper focuses on the development of optimal deterministic, nonlinearly coupled barge motion models, identification of their system parameters and calibration of their prediction capability using experimental results. The ultimate objective is to develop accurate yet sufficiently low degree-of-freedom stochastic models suitable for efficient probabilistic stability and reliability analyses of US Naval barges for preliminary design and operation guideline development (see Part II). First a three-degree-of-freedom (3DOF) fully coupled Roll-Heave-Sway model, which features realistic and practical high-degree polynomial approximations of rigid body motion relations, hydrostatic and hydrodynamic force-moment specifically suitable for barges, is examined. The hydrostatic force-moment relationship includes effects of the barge’s sharp edge and combined roll-heave states, and the hydrodynamic force-moment specifically suitable for barges, is examined. The hydrostatic force-moment relationship includes effects of the barge’s sharp edge and combined roll-heave state, and the hydrodynamic terms are in a “Morison” type quadratic form. System parameters of the 3DOF model are identified using physical model test results from several regular wave cases. The predictive capability of the model is then calibrated using results from a random wave test case. Recognizing the negligible sway influence on coupled roll and heave motions and overall barge stability, and in an attempt to reduce anticipated stochastic computational efforts in stability analysis, a 2DOF Roll-Heave model is derived by uncoupling sway from the roll-heave governing equations of motion. Time domain simulations are conducted using the (3DOF) Roll-Heave-Sway and the (2DOF) Roll-Heave models for regular and random wave cases to validate the model assumptions and to assess their (numerical) prediction capabilities.
Experimental Study of Dissolution Rate of a CO2 Droplet and CO2 Solubility in High Pressure and Low Temperature Seawater With Hydrate Free
Authors: Song Yongchen , Chen Baixin , Nishio Masahiro , Akai Makato
Published: January 2009

Against the background of carbon dioxide (CO2) ocean sequestration technology, we investigated the solubility of CO2 in seawater at a thermodynamic state similar to that at an ocean depth of 1000 m. The experiment was performed in two steps. In the first step, we reexamined and modified the fundamental relationship between Sherwood (Sh) number and Rayleigh (Ra) number in a natural convective flow over an up-down CO2 droplet. We derived a new expression of the Grashof number for CO2 dissolution in water and seawater with the aid of the relation between the density of CO2 solution and CO2 concentration. In the second step, this new expression was applied to the estimation of solubility of CO2 from experiments examining the dissolution of an individual CO2 droplet in seawater at hydrate-formable pressure and temperature states. We found from our experiments: that (1) at hydrate-formable conditions (step two), no hydrate appeared at interface between liquid CO2 and seawater throughout the experiments within 5 hours, which suggested that a thermodynamic state (pressure and temperature) is indispensable but not a complete condition for hydrate formation; and (2) associated with this dual nature, the data of CO2 solubility estimated from this experiment are much larger than those obtained by Kimuro et al [1] from experiments of hydrate coexistence. Our data ranged from 0.052 to 0.062 in mass fraction.
Hydroelastic Response of a Mat-Like Floating Circular Plate Advancing in Waves: Analytical Solution
Authors: Matsui Tetsuya
Published: January 2009

The boundary-value problem is formulated to predict the hydroelastic response of a mat-like floating circular plate advancing slowly in waves. The potential flow theory is employed with low forward-speed assumption. The plate is modeled as an elastic plate with zero draught. This assumption allows the steady disturbance potential due to forward speed be neglected, simplifying considerably the problem. By applying the eigenfunction-expansion domain-matching method analytical solutions are derived for the scattering and radiation potentials up to the leading-order terms of the speed-dependent parts. Numerical results are presented for the typical plate geometry. It is shown that the forward-speed effect on the hydroelastic response, especially on the bending strain response, of the plate is significant.
Added Mass Depending on Vibration Modal Shape in Floating Artificial Base
Authors: Maruyoshi Koichi , Saijo Osamu
Published: January 2009

The floating structure of pontoon type, for example Mega-Float, can be expected to use as a supporting structure, it is called “floating artificial base”. A building can be built on the surface of that base. Many studies with regard to the floating artificial base have been carried out. Consequently, it was concluded that the large floating artificial base had to be analyzed by elastic behavior problem. It is essential for dynamic analysis of floating structure to estimate fluid influence. Therefore, we have been studying the added mass evaluation relating as coupled vibration analysis between fluid and structure. It was assumed that this floating artificial base was a plate structural system. In order to propose added mass depending on vibration modal shape for natural frequency analysis and for wave response analysis, the study has been approached by way of experiment and theoretical approach. A simple equation for calculation of the added mass could be proposed through the study of the characteristics of added mass distribution. This simple equation was introduced in the last OMAE conference. That equation showed well in agreement with the experimental result and the other published data. We have been continuing to examine its validity by comparison with data obtained through the systematic experiments using different testing plate models, and also the comparison was done with the measured data from the existing floating structures. This paper reports the evaluation of present simple equation from a serious of research work.
A Model of Fatigue Crack Growth Based on Damage Accumulation
Authors: Chand Satish , Pandey K. N.
Published: January 2009

A fatigue crack growth model based on cumulative damage is presented, when a material element ahead of the crack tip, is approached by the tip of the crack. The cyclic plastic zone and process zone ahead of the crack tip are taken as the area where damage accumulation takes place when the material element, first, enters into the cyclic plastic zone and then into the process zone. During this period, the Coffin-Manson damage law in conjunction with Miner’s linear damage accumulation is used to determine the damage in the material element. A constant strain gradient was assumed along the process zone ahead of the crack tip and the size of process zone was taken to be variable and dependent on the range of stress intensity factor. For a cyclic loading, the effective crack driving force takes into consideration the crack tip blunting process. The model results are in good agreement with experimental data available in literature for a number of materials.
Ice Loads on Azimuthing Podded Propulsors
Authors: Akinturk Ayhan , Jones Stephen J. , Duffy Dale , Rowell Barbara
Published: January 2009

The paper describes the experimental setup and presents some of the results obtained. The experimental system is designed and built to measure the loads on the blade, on the propeller shaft bearings, on the shaft, and on the whole propulsion unit (global loads). Experiments have been conducted at various headings form 0° to 180°, thrust directions (aft or forward), and advance coefficients. In the experiments, ice sheets of 60 mm thickness were used. Target flexural strength of the ice sheets was 60 kPa at the start of the experiments. During the course of the experiments, thickness, flexural, compressive and shear strength values of the ice sheets were sampled at certain time intervals in order to record the variations in the ice properties. Initial results suggest that there was an increase of the loads exerted on the podded system due to ice. The increase varies at different azimuth angles and advance velocities.
CFD Analysis of Large Caisson Interaction With Current at Supercritical Reynolds Number
Authors: Chakrabarti Subrata K. , Debus Kristian K. , Berkoe Jonathan , Rosendall Brigette
Published: January 2009

The newly constructed Tacoma Narrows Bridge Piers represent large concrete floating caissons during their construction. For designing their mooring system the current force applied on the caissons in the Narrows must be known. The flow field around the caisson is highly complex and the calculation of the current load on the caisson by analytical means is difficult. On the other hand, model tests suffer from the distortion in the Reynolds number. Therefore, a two-prong approach was undertaken. Besides the fixed model test of the caissons for current forces, a CFD analysis of the flow around the caisson is chosen. A 3-D CFD approach is considered more appropriate than a 2-D one, since the bottom contour at the site is irregular and water depth is rather shallow. This paper discusses the CFD method and the results obtained from such analysis. The numerical analysis was carried out in both ebb and flood flow of the tidal current in the basin. One of the difficulties of the computational method is very high Reynolds number encountered by the large current and large size of the caisson. The analysis was performed in both model and full scales so that the difference in the results may be investigated. Also, since the model test data was available, comparisons could be made between the CFD and model test results on the drag and lift forces on the caisson.
Instability of a Simplified Model of a Free Hanging Riser Conveying Fluid
Authors: Kuiper Guido , Metrikine Adrei , Efthymiou Mike
Published: January 2009

Studying stability of a vertically suspended, fully submerged pipe conveying water (free-hanging water intake riser), researchers have found that if a critical flow velocity is reached, these pipes may flutter. However, there are different predictions for the value of this critical velocity. Researchers have mentioned values changing from infinitely small fluid velocities up to velocities which are unachievable in practice. The nonlinear hydrodynamic damping caused by the surrounding water seems to be crucial for correct description of the stability of the submerged riser aspirating fluid. In this paper, using the Morison’s equation, the nonlinear drag is taken into account as a function of the relative velocity between the current and the velocity of the riser itself. The nonlinear system is studied employing the Galerkin method. Ten-mode discretization turns out to be necessary to obtain an accurate result. It is shown that the current has a strong stabilizing effect. If the internal fluid flow exceeds a critical velocity the riser performs self-sustained oscillations with the amplitude smaller than one diameter.
Structural Integrity Assessment of Critical Components of Converted FPSO Hulls
Authors: Bardanachvili Carlos A. , Pope Alexandre M. , Goulart Roberto O. , Adelson Lena L. , Alves Luiz H. M. , Pereira Marcos
Published: January 2009

Conversion of very (ultra) large crude oil carriers (VLCC,ULCC) into floating production, storage and offloading (FPSO) offshore units has become a common practice in the industry. The conversion planning is complex and demands a careful assessment of the condition of the hull to be converted into a FPSO. The fatigue assessment is especially important at certain components that will experience cyclic loads above the originally allowed in the design of the VLCC (ULCC). A through fatigue assessment of two FPSOs that are now at the final stages of conversion was carried out using current class rules. While for the majority of the hull structure the fatigue design approach used produced satisfactory and conservative results, at the cross tie beam, located at frames in the wing tanks, the fatigue assessment was considered unreliable. This was evident during the conversion stage because a large number of cracks were found in welded joints of the cross tie beams during the hull conversion inspection. A simplified finite element analysis (FEA) showed that the location where the cracks were found was subjected to high cyclic loads during the operation as an oil tanker and that these loads would be also severe during the FPSO operation. Analysis of samples taken from the damaged areas showed that they contained weld toe fatigue cracks. Further FEA was carried out taking into account the displacements from a global structural model, which modelled the hull and the top side structures, in order to estimate the hot spot stresses at the affected welded joints. The additional fatigue assessment demonstrated that the fatigue design approach used needed to be modified to firstly explain the cracks found in the component, secondly to allow for a reliable and conservative estimation of the remaining fatigue life for the cross tie beam after repair work was carried out. The resultant fatigue approach adopted demonstrated that the cross tie beam would not survive the 20 years design requirement of the project unless modifications on the local structural design were undertaken or welded joint fatigue enhancement techniques were applied to the welded joints. To resolve the problem the project decided to adopt a controlled arc welding repair of all cracked joints followed by careful inspection and application of burr machining of weld toes as a fatigue enhancement technique. This paper describes the fatigue assessment undertaken, the suggested modification to the fatigue approach for the assessment of cross tie beams, a description of the repair procedures, non-destructive testing and fatigue enhancement methods adopted by the project.
Comments on Recent Code Developments Related to Pipeline Freespan Analysis
Authors: Ferreira Rony Peterson , Claro Claudia Albergario , Galgoul Nelson Szilard
Published: January 2009

During the last 20 years the Dn V code [1–5] has represented the latest word in design recommendations for pipeline free span evaluations. This is true to the extent that important codes, such as API RP 1111 [6], simply refer to Dn V for further guidelines. During most of these 20 years the majority of the design codes which did have anything to say about vibrations due to vortex shedding, including Dn V, had and in general still have, dissociated axial pipeline forces from the vortex shedding problem. It is well known, however, that the natural period of a compressed element increases as does also the axial compressive force. In March, 2002 Dn V released a new free span recommended practice [5], in which an attempt was made to couple the global free span buckling problem and that of vortex induced vibrations. All those of the pipeline engineering market, who have attempted to use it, will certainly agree that this code has greatly improved the pipeline free span ultimate limit state and fatigue design by introducing more general procedures associated to more sophisticated numerical techniques. Later that same year the authors undertook a large project, in which the use of the aforementioned code was a contractual requirement. If on one hand, however, the owner insisted upon the use of the new Dn V code, on the other he was not willing to accept the very short free span limits, which were resulting from the calculations. This does not necessarily imply that the new code was wrong, because it could be, that previous codes had overestimated the allowable spans, but, in addition to the short spans, it was also found that the new code has some limits of applicability, which, basically, exclude a large range of common pipeline sizes. Because of this the authors were forced to look at the problem in further depth, thus resulting interesting conclusions, which will be presented in this paper. These point out some conservative aspects of the code, and make suggestions as to how these can be overcome in order to use the Dn V safety approach and still produce larger spans, by properly focusing on the frees pan buckling problem.
Acoustic Data Transfer Limits Using an Underwater Vehicle in Very Shallow Water
Authors: Marr William J. , Healey Anthony J.
Published: January 2009

Advances in Autonomous Underwater Vehicles (AUVs) using acoustic communications to transfer relatively high rate downloads of mission information are crucial to future Navy objectives, particularly in Very Shallow Water Mine Countermeasures (VSW MCM). Present understanding is primarily based on fixed node experiments rather than quantified by vehicles working in the real environment. This paper reports on the demonstrated limits of high speed asymmetric acoustic data transfer using an AUV in an adverse very shallow water environment. A comprehensive series of studies in multiple channel geometries was completed using a “state of the art” commercially available modem system installed on the NPS ARIES autonomous underwater vehicle. The maximum operating range for effective high speed data transfer in very shallow water from a dynamic AUV with all integrated systems active was about 300 meters in the horizontal plane with nearly 100% reliability, at bit rates up to a maximum of 800 bits/second.
A Study on Operational Safety in Offshore Drilling and Production Units
Authors: Oliveira V. C. C. , Morooka C. K. , Mendes J. R. P.
Published: January 2009

In the present paper, operational accidents, which occur during offshore drilling and production operations are carefully studied. Data were collected from literature for those operations and each accident was classified according to related operations and carefully analyzed. After that, each accident was classified according to the operation unit where it happened, i.e., drilling, completion, production and workover type unit. Classifying the accidents and analyzing the obtained results has shown that more than half of them are related to offshore petroleum production unit operations, followed by those related to drilling rig operations. The remaining observed cases are related to workover exploration and completion units. The evaluation of operational accidents in offshore petroleum drilling and production units could clarify the behavior of operational safety, particularly variations along the years. It was possible to identify the main factors that contribute to the increase of the number of those accidents in offshore units, as well as, the consequences of each accident. Finally, such procedures provided useful information that can assist engineers in making decisions improving operational safety programs for offshore drilling and production unit operations.
Simplified Method to Assess Dynamic Response of Jacket Type Offshore Platforms Subjected to Wave Loading
Authors: Asgarian B. , Mohebbinejad A. , Soltani R. H.
Published: January 2009

Dynamic response of offshore platforms subjected to wave and current is of fundamental importance in analysis. The first step in dynamic analysis is computing dynamic characteristics of the structure. Because of pile-soil-structure and fluid-structure interactive effects in the dynamic behavior, the model is very complex. In this paper a simplified model for dynamic response of jacket-type offshore structures subjected to wave loading is used. Since wave loads on offshore platforms vary with time, they produce dynamic effects on structures. In the model used in this paper, all of the structural elements are modeled as vertical equivalent cylinders that are in the direction of the wave crest. In the simplified model, the degrees of freedom are considered at the seabed, jacket horizontal elevations and topside center of gravity. The stiffness properties of the model are computed considering the stiffnesses of the vertical bracings, legs and piles. The structural mass is considered as lumped nodal masses at horizontal elevations and topside center of gravity. The hydrodynamic added mass in addition to the structural masses was modeled at jacket horizontal elevations. In the simplified model, for computing wave loading, the projected areas of all members in the direction of the wave crest are considered. For the wave loading calculation, Morison equation is considered. The fluid velocities are calculated for the submerged portions of the structures using a computer program developed for this purpose. In this program both Airy and Stokes wave theories can be used. This model can be used to assess dynamic properties and responses of jacket type offshore structures. The model is used to assess the response of three jacket-type offshore platforms in Persian Gulf subjected to loadings due to several waves. The results in terms of dynamic characteristics and responses were compared with the more accurate analysis results using SACS software. The results are in a good agreement with the SACS analysis outputs, i.e. structural periods, mode shapes and dynamic response.
An Empirical Model of Current Shadow Effect
Authors: Fucatu Carlos H. , Nishimoto Kazuo
Published: January 2009

The ship based Floating Production Storage and Offloading system (FPSO) has been largely used in the recent offshore oil exploration. In most of the cases the oil stored in FPSO is offloaded to a shuttle ship that is connected by a hawser in tandem configuration. Although the tandem mooring is a common procedure in the offshore oil industry, there are few publications related to the theme. Among these, the papers concerned with the current flow interference due to the presence of FPSO on upstream of shuttle ship, here called current shadow effect, are even more uncommon. Neither among the commercial simulators that analyze tandem systems there is none that considers the shadow effect of environmental conditions, providing an analysis different from the real world. In previous studies, the authors presented some experimental results showing that the dynamic behaviors of shuttle ships subject to current were strongly influenced by the presence of a FPSO in an upstream position. This phenomenon was expected since the FPSO disturbs the downstream current field acting on the shuttle ship. Observing this fact, a tentative empirical model based on the disturbed current field was developed. The disturbed current field was obtained through a 3D CFD program and the hydrodynamic forces acting on the shuttle ship were computed using the local cross flow method. At that time, a particular experimental case was analyzed and the proposed model showed to be effective. However, during the model evaluation, it was realized that the proposed model wasn’t able to reproduce some experimental cases. This paper presents the last developments on the shadow effect model and a more comprehensive comparison between experimental and numerical results.
Reliability of Inspection for Root Flaws in Riser Girth Welds
Authors: Rudlin J. R. , Schneider C. R. A. , Razmjoo G. R.
Published: January 2009

The fatigue loading on deep water risers leads to a requirement for the detection of small root flaws during manufacturing inspection. Mechanised welds for offshore pipelines are also subject to extreme loads during laying, leading to a similar requirement. Automated Ultrasonic Testing using zonal methods have been adopted as the inspection method of choice for these inspections, but there is little information in the public domain regarding the expected reliability of the various systems available. Extensive individual inspection qualifications are carried out for each installation. The extent of these could be reduced by the availability of such background information. This paper reviews data from joint industry projects in the area carried out by TWI, and compares results from these with such data as is available in the public domain. An analysis of future requirements and capability of currently available theoretical models for extending the range of qualifications is also given.
Non-Linear Run-Up on a Vertical Surface-Piercing Cylinder
Authors: Retzler C. H. , Rainey R. C. T. , Chaplin J. R.
Published: January 2009

This paper presents and analyses results of experiments in which a vertical surface-piercing cylinder was driven with a horizontal motion a cos ωt in water initially at rest. Using a novel system of 112 water surface elevation gauges that were monitored almost simultaneously at high frequency, measurements were made of the run-up on the cylinder over a wide range of conditions. According to linear theory, the run-up is of the form a cos ωt cos θ. Non-linear components at temporal and spatial frequencies up to the 3rd harmonic were identified in the measurements, and in some of these, the coefficient of the leading term in a polynomial expansion in the amplitude of motion could be computed with reasonable confidence. Very successful comparisons are made with conventional linear potential theory. Some features of the free surface motion that are normally associated with higher order solutions were also computed from the first-order potential, and in some respects they were in good agreement with the measurements.
Improved Spectral Wave Modelling of White-Capping Dissipation in Swell Sea Systems
Authors: Hurdle David P. , van Vledder Gerbrant Ph.
Published: January 2009

An improved method for computing the dissipation by whitecapping in full spectral discrete wind wave models is presented. In this method the rate of dissipation of a certain spectral wave component is determined by the cumulative wave steepness of all spectral components with lower frequencies. This method is known as the cumulative wave steepness method (CSM) and was described by Van Vledder and Hurdle (2002). In this paper some improvements of the CSM are presented which are related to directional and scaling effects. The improved CSM was implemented in the latest release of the SWAN model (version 40.31 of February 2004) and a calibration against a parametric growth curve was performed. Further, the benefits of the CSM in swell-sea systems are illustrated and compared to the method of Komen et al. (1994).
Load Combination for Fatigue Analysis of Ship Structures
Authors: Shin Yung S. , Kim Booki , Fyfe Alexander J.
Published: January 2009

A methodology for calculating the correlation factors to combine the long-term dynamic stress components of ship structure from various loads in seas is presented. The methodology is based on a theory of a stationary ergodic narrow-banded Gaussian process. The total combined stress in short-tem sea states is expressed by linear summation of the component stresses with the corresponding combination factors. This expression is proven to be mathematically exact when applied to a single random sea. The long-term total stress is similarly expressed by linear summation of component stresses with appropriate combination factors. The stress components considered here are due to wave-induced vertical bending moment, wave-induced horizontal bending moment, external wave pressure and internal tank pressure. For application, the stress combination factors are calculated for longitudinal stiffeners in cargo and ballast tanks of a crude oil tanker at midship section. It is found that the combination factors strongly depend on wave heading and period in the short-term sea states. It is also found that the combination factors are not sensitive to the selected probability of exceedance level of the stress in the long-term sense.
Position Control of Floating Structures via Slow-Drift Force Ensemble Simulations
Authors: Nguyen T. D. , Quek S. T.
Published: January 2009

The solution of Riccati equation in conventional linear quadratic optimal control usually neglects effects of forcing function. This will lead to sub-optimization of quadratic cost function as in the case of floating vessels subjected to environment disturbances which are random in nature. The significance of accounting for the forcing function is demonstrated here for the case of dynamic position of moored floating vessels subjected to simulated slow-drift wave forces. For this purpose, the control algorithm developed by [5] is adopted. An ensemble of slow-drift wave forces are simulated in moderate sea and extreme sea state to represent critical environment disturbances acting on floating vessels to arrive at the corresponding set of optimal control parameters. In addition, comparison is made for the control between linear and nonlinear model in moderate sea and extreme sea.
Statistical Analysis of Fatigue Data From an Interlaboratory Testing Program on Weld Improvement Techniques
Authors: Naess A. , Haagensen P. J.
Published: January 2009

A fatigue testing program has been designed to determine the effect on the fatigue strength of several post weld improvement techniques. The program was organized by Commission XIII of the International Institute of Welding (IIW) and twelve testing laboratories in nine countries participated. The main objective of the round-robin test program was to check the reproducibility of the treatments, and secondly to establish design guidance in terms of level of improvement in fatigue strength. Twelve large welded steel plates were distributed and the treatments that included burr grinding, TIG dressing and three types of peening were performed on plate segments in each laboratory. Simple T-joint specimens were fabricated and fatigue testing was carried out following a prescribed procedure. Standard regression analysis was made and the results were reported by each laboratory. The paper briefly reviews the test program and the statistical analyses that were used to evaluate the results.
Numerical Simulation of Vortex Induced Vibration on an Elastically Mounted Cylinder
Authors: Wanderley Juan B. V. , Levi Carlos A.
Published: January 2009

The Vortex-induced vibration on a circular cylinder is investigated by the numerical solution of the unsteady Reynolds Average Navier-Stokes equations and results are compared with experimental measurements obtained by different authors. The Beam and Warming implicit factored scheme is used to solve the governing equations and the Baldwin and Lomax model is used to simulate the turbulent flow in the wake of the cylinder. The cylinder is laterally supported by a spring and a damper and is free to oscillate in the transversal direction in an initially uniform flow for the first flow speed investigated. For the subsequent speeds, the final condition obtained for the previous speed is used as initial condition to reproduce the actual experimental set up. In that case, the measurements are done by progressive increments of the flow speed retaining the fluid memory effect. The complexity and high sensitivity of the flow phenomenon at this configuration requires a very accurate and robust numerical model. Most of the known algorithms failed to duplicate the available experimental measurements. The numerical results for the transversal oscillation amplitude are compared to experimental data showing a fairly precise agreement at the difficult to simulate regime of the lock-in phenomenon.
Mid-Life Structural Assessment of Transit Rail Cars at WMATA
Authors: Taraszkiewicz Marcin N.
Published: January 2009

The Washington Metropolitan Area Transit Authority (WMATA) contracted with Booz Allen Hamilton to conduct a non-destructive structural assessment of the 2000 and 3000 series rapid transit rail cars. The main goals of the assessment were to identify any significant changes that have occurred to key elements of the car body structure since their date of manufacture and to confirm that no significant and obvious structural deterioration or damage exists. The methodology behind selecting a small representative sample of cars is discussed as an introduction to this work. The paper then discusses the process by which several critical areas were selected for non-destructive inspection. One of the biggest challenges in successfully completing this project was not interfering with WMATA’s fleet operating requirements. The use of WMATA facilities had to be coordinated to create minimum interference with WMATA’s daily maintenance activities. Also, the inspection work had to be planned in such a way as to minimize the amount of vehicle component disassembly in order to return the vehicle to revenue service as soon as possible. The inspections produced valuable results regarding the construction and condition of these cars. The structural welds of the car appear to have performed satisfactorily through the operational life of the cars to date without any significant deterioration. Some corrosion was noted in the door opening areas of the cars, particularly at the door thresholds. The findings of this report will be used to target specific areas of the car during the upcoming mid-life rehabilitation project.