bluuebunny/crossref_metadata_2025 huggingface dataset:
Potential Advantages to Water Jet Drilling for Use in In-Situ Coal Gasification Processes
Authors: Summers D. A. , Barker C. R.
Published: November 2009

Current methods of in-situ gasification require that inter-well connection be by means of either reverse combustion burning or by directional drilling. High-pressure water jet drills concentrate the energy of cutting in a small area and the total thrust required to advance this system is thus minimized. This has been used advantageously to develop a drill for coal seams which can be lowered down a vertical well turned through a 90-deg angle and then advanced horizontally through the coal. A test unit operating at a pressure of 70 MPa and a flow rate of 90 L/min has been used to demonstrate, in a surface trial, the practicality of this concept for interconnecting two in-situ gasification wells located 20 m apart.
System Thermodynamics of Energy Conversion Plants for Geopressured Resources
Authors: Lamb J. P. , Polansky G. F.
Published: November 2009

Performance of conversion plants for geopressured fluids has been predicted using realistic wellhead conditions and idealized thermodynamics. A method is developed for estimating the maximum output of a combined hydraulic-thermal recovery system. Performance of both flash and organic Rankine cycle schemes for thermal recovery is considered and the importance of hydraulic recovery is illustrated. Rankine cycle performance results for propane and isobutane are presented. Results are also given which illustrate the extreme importance of recovering dissolved methane due to its effect on both energy production and related economic viability.
Biogasification of Municipal Solid Wastes
Authors: Diaz L. F. , Savage G. M. , Trezek G. J. , Golueke C. G.
Published: November 2009

A series of experiments on the anaerobic digestion of the organic fraction of municipal refuse was performed. The refuse fraction used in the study was one of the portions segregated in a resource recovery system developed at the University of California, Berkeley. The scale of experiments includes 4, 9, and 1600-L digesters. The refuse used as feed was enriched by the addition of raw sewage sludge in various ratios, i.e., from 0–100 percent of the total volatile solids. No other sources of nutrients or chemicals for pH control were introduced into the reactors. Organic loading rates ranging from 1.1–6.4 g of volatile solids/L•d. Typical hydraulic detention times were 15 to 30 days. Temperatures were kept within the range of 72–104 F (22–40 C). Digestion efficiency was based on energy conversion and gas production.
Development of Affinity Relations for Modeling Characteristics of Check Valves
Authors: Collier S. L. , Hoerner C. C.
Published: November 2009

The moving element in a check valve assumes positions depending on flow which makes modeling more complicated than that of fixed geometry devices. Thus, it is necessary to determine the force on the plate to predict the equivalent in larger valves which may be inconvenient to build and test at full scale. Test data is obtained and affinity relations developed for scaling the resistance to flow, torque, and position. An example of the complete procedure for a geometrically similar valve is provided showing the test torque at several fixed angles and the prediction of the pressure loss and plate angles in a much larger valve, together with field data confirming the results.
A Simple Model of Seasonal Sea Ice Growth
Authors: Miller J. D.
Published: November 2009

An energy conservation approach is applied to the problem of sea ice growth. A simulation model which establishes an explicit relationship between the surface temperature and each component of the energy balance is presented. Included are the effects of a snowpack and variable thermal properties for snow and ice. The sea ice growth is treated as a response of the thermodynamic interaction of the atmosphere, snow, ice and ocean. Daily estimates of the radiative, turbulent, conductive and melt-induced energy fluxes, the surface and snow-ice-interface temperatures, the average ice salinity and the ice thickness are provided by the model. A comparison of sea ice growth observations at three Arctic locations with model predictions indicates a good reproduction of real world conditions by the computer simulation.
Vibrations of Long Marine Pipes due to Vortex Shedding
Authors: Whitney A. K. , Chung J. S. , Yu B. K.
Published: November 2009

Lateral vibrational displacements and accelerations due to vortex shedding are analyzed for very long marine pipes with a bottom end mass for application to deep ocean-mining lift pipes. Estimates of maximum RMS values of displacement and acceleration are presented for a range of tow speeds, pipe lengths, pipe diameters and wall thicknesses, and for various values of the pipe end mass. In contrast to the case of short pipes, higher modes of pipe vibration can be excited even at low towing speeds. In addition, the critical tow speeds, at which the vortex-shedding frequency equals a pipe natural frequency, are closely spaced, and there are no speeds where the vibrations vanish.
The Natural Frequencies and Mode Shapes of Cables With Attached Masses
Authors: Sergev S. S. , Iwan W. D.
Published: November 2009

An algorithm has been developed to calculate mode shapes and natural frequencies of taut cables with attached masses. The transcendental equations of motion are solved by an iterative technique allowing accurate calculation of extremely high mode numbers. The algorithm has been implemented as a FORTRAN program primarily as a tool in determining drag coefficients of strumming cables. To assess the accuracy of the program a simple experiment was conducted to determine the natural frequencies and mode shapes of a wire with attached masses driven sinusoidally by a shaker. The algorithm shows close agreement with the experimental data.
Linear Prediction Theory for Digital Simulation of Sea Waves
Authors: Spanos P.-T. D. , Hansen J. E.
Published: November 2009

Most of the currently used algorithms for numerical generation of sea wave records which are compatible with a specified power spectrum are based on the super-position of several harmonic waves. This article presents an alternative method of simulation. The basis of the method is the Linear Prediction Theory (LPT) which has been extensively used in processing digital data in other technical fields. Specifically, records of sea waves which are compatible with the target spectrum are obtained as the output of a recursive digital filter to a white noise input. A procedure for determining the filter parameters is discussed. Several numerical examples are presented.
Model Studies on Immediate Settlement Behavior of Submarine Pipelines
Authors: Gulhati S. K. , Rao G. V. , Gupta S. K. , Rammurthy Y. N.
Published: November 2009

Currently immediate settlement of submarine pipelines can be assessed by using a method proposed by Small, et al. [3]. Concepts advanced by Reid [2] and Ghazzaly and Lim [4] have been extended herein to enable evaluation of immediate settlement. The immediate settlements of model pipelines measured in an apparatus devised for this purpose, in two cohesive soils at water contents in excess of liquid limits, have been used to assess the validity of the three methods. For immediate settlement to diameter ratio (Df/D) ≤ 0.4, experimentally observed values agree with prediction based on concepts of Ghazzaly and Lim as extended herein. For Df/D ≥ 0.5, Small, et al.’s theory compares well with observed data.
Enhanced Oil Recovery by Flooding With Dilute Aqueous Chemical Solutions
Authors: Kamath K. I. , Yan S. J.
Published: November 2009

The theory of enhanced oil recovery by surfactant flooding (micellarpolymer and “low-tension” floods) is based on three premises: that the chemical slug is 1) less mobile than the crude oil, 2) miscible with the reservoir fluids (oil and brine), and 3) stable over long periods of time (years) in the reservoir environment. We report here a rather simple process in which none of these expensive and exacting requirements have to be met. In this process, relatively small amounts of “EOR-active” substances present in certain petroleum-based sulfonates are found to recover 15–20 percent of the residual oil from waterflooded Berea sandstone cores. The chemicals are injected in the form of slugs of their aqueous solutions. If the chemical slugs are followed with similar slugs of additives such as partially hydrolyzed polyacrylamide, acrylamide monomer, urea, EDTA, or anions such as P2O7‴‴‴‴ and PO4‴‴‴, the oil recovery is increased 30–40 percent of the in-place residual oil. The concentrations of the “active” sulfonate and additive in their respective slugs appear to be of the order of 500 ppm or less. Extrapolation of the laboratory data to field conditions indicate that chemical requirements for the recovery of a barrel of tertiary oil are about 0.5–2 lb of sulfonate and a like amount of additive. The main features of the displacement process are: 1) Oil recovery is independent of oil viscosity in the tested range of 0.4–100 cps. 2) The process is essentially an immiscible displacement in which oil recovery depends on the amount of active chemical in the slug and not its concentration. 3) Tertiary oil is produced in the form of a clean “oil bank” and the buildup of a residual oil saturation at the producing end of linear cores occurs during the flood. From the data on hand, it is apparent that the oil recovery mechanism differs basically in character from the conventional Buckley-Leverett-type immiscible displacement. The low level concentrations of sulfonate and additive involved, and the independence of oil recovery with respect to oil viscosity suggest that the recovery mechanism is possibly actuated by certain specific functional groups in the structure of the EOR-active molecule or its anion, and of the additive. The results hold great potential for developing a simple and economical tertiary oil recovery process that can recover, very substantially, more oil (light as well as moderately viscous) than is now considered possible by conventional chemical floods.
Modeling Requirements for Geopressured-Geothermal Reservoir Production
Authors: MacDonald R. C. , Ohkuma H. , Sepehrnoori K.
Published: November 2009

The modeling requirements for geopressured-geothermal reservoir analysis are discussed and demonstrated in this paper. Compaction effects, reservoir hetereogeneities, localized gas evolution, and shale dewatering mechanisms are implemented into a specific model. Applications which demonstrate the potential sensitivity of reservoir pressure-production behavior to these mechanisms are illustrated.
Laminar-Turbulent Transition in Pipeflow of Casson Model Fluids
Authors: Hanks R. W.
Published: November 2009

Methanol-coal slurries are known to behave as homogeneous non-Newtonian suspensions. Darby has shown that the Casson and Bingham models reasonably describe the rheology of methanol-lignite slurries. Theoretical methods are available for predicting critical velocities for Bingham model slurries, but none exist for Casson model slurries. Theoretical equations and design curves are derived and presented for Casson model slurries. These are based upon a proven general theory for transition critical velocities. These results are the essential first phase of a coordinated theory-based design method for transitional and turbulent flow of methanol-coal slurries and any other slurries having Casson-model rheology.
Engine Fuels From Biomass
Authors: Parker H. W.
Published: November 2009

Sources of biomass fuels for engines are compared to other synfuels. Biomass can be converted to gaseous and liquid engine fuels by the same processes utilized for coal conversion such as gasification, direct liquefaction, and indirect liquefaction. Alternatively, biomass can be converted into liquid fuels by fermentation to methane or ethanol. The quantities of biomass-derived engine fuels potentially available in the next decade are relatively small, and the anticipated costs are significantly greater than for liquid engine fuels made from coal or oil shale.
Parameters on Fracture Strength of Sea Ice
Authors: Urabe N. , Yoshitake A. , Iwasaki T. , Kawahara M.
Published: November 2009

Compressive crushing strength on brackish ice and sea ice and fracture toughness value on sea ice were measured as parameters associated with fracture strength of ice. The compressive crushing strength depends on salinity, temperature and strain rate. At constant salinity and temperature, the strength increased with increase in strain rate and reached maximum value at about a strain rate of 10−3 s−1, then decreased with increase in strain rate. An empirical equation to estimate the compressive crushing strength was derived as a function of brine volume, temperature and strain rate. As far as fracture toughness is concerned, a simplified test procedure on notched cantilever beam specimen was developed in order to avoid complicated manipulation in field conditions. The fracture toughness value (KIC) coincided well with the value obtained from fracture toughness tests conducted in conformity with the standard test method.
Floating Ice Road Construction
Authors: Finucane R. G. , Scher R. L.
Published: November 2009

During the winter of 1980–81, Exxon built about 16 km of floating ice roads in the Beaufort Sea off the north slope of Alaska. These roads were used to haul gravel and other materials for the construction of four offshore drillsites and to provide logistical support to subsequent exploration drilling operations. Ice roads over tundra and grounded lake or sea ice have been used for many years in the Arctic. Over the past three years, exploration activities have progressed offshore to water depths where the sea ice is floating. This paper summarizes the procedures, equipment, and production rates achieved during the construction of our 1980–81 winter floating ice roads. Also presented are the results of performance tests on some of the various auger pumping systems presently available.
Freezing and Thawing: Heat Balance Integral Approximations
Authors: Lunardini V. J.
Published: November 2009

The study of conductive heat transfer with phase change — often called the Stefan problem — includes some of the most intractable mathematical areas of heat transfer. Exact solutions are extremely limited and approximate methods are widely used. This paper discusses the heat balance integral approximation using the collocation method. The method is applied to some standard problems of phase change — Neumann’s problem — and a new solution is presented for the case of a semi-infinite body with surface convection. Numerical results are given for soil systems and also for materials of interest in latent heat thermal storage.
Experiments With a Diffuser-Augmented Model Wind Turbine
Authors: Gilbert B. L. , Foreman K. M.
Published: November 2009

The initial stages of the experimental development of the diffuser-augmented wind turbine (DAWT) employed various screen meshes to simulate the energy extraction mechanisms of a wind turbine. In this investigation in a 2 × 3 m wind tunnel, a three-bladed constant chord, untwisted turbine model was incorporated into a DAWT model. The objectives were to add real turbine characteristics such as swirl, and centerbodies effects, to the flow. Although this turbine model was not well matched to the diffuser, the model DAWT system increased the power output by more than four times that of the model turbine operating as a conventional wind energy conversion system; more than 3.4 times the power potential of an ideal wind turbine was measured.
A Facility and Approach to Performance Test of Check Valves
Authors: Collier S. L. , Hoerner C. C.
Published: November 2009

The important time for a check valve is the short period during which flow decelerates. The characteristics of this period are not well defined. The investigation suggests the use of deceleration (g) as a parameter, describes a test facility that provides a range of deceleration rates and presents results of tests at various g’s. This method couples the estimation of a system’s deceleration with the performance of the valve so that provisions can be made for the expected behavior and surge in a new installation or an improvement can be predicted for an existing problem situation.
Spun Steel Pipes for the Offshore Industry
Authors: Royer A. , Dumas B. , Gantois M.
Published: November 2009

Many parts either for sea-line pipes as “buckle” or “crack arrestor,” or for structures may require the use of wall tubular products with high mechanical properties. Such heavy-wall pipes may be produced by centrifugal casting. Two Mn-Mo steels have been developed for medium-wall pipes (e≤35 mm) to be used under very severe climatic conditions: an acicular ferritic steel, a pearlite reduced steel produced by controlled rolling techniques [1, 2, 3]. More alloyed chemical composition and heat-treatments are needed to produce heavy-wall pipes. Then, production of such pipes is more difficult and sometimes impossible. Observations made on controlled-rolled Mn-Mo steel led to a better understanding of the influence of metallurgical structures and chemical composition on steel characteristics. Similar metallurgical structures can only be reached via other routes, for example centrifugal-casting of steel associated with heat-treatment, lead to the production of heavy-wall pipes with high strength and suitable transition temperature. After a brief description of the centrifugal casting technique, we introduce the grades developed for heavy-wall pipes with yield strength up to 100,000 psi. The mechanical properties, Battelle, fatigue, static bending, C.O.D., weldability, etc., of Centrishore II are given and compared to other materials. Possible offshore applications and other potential applications of parts produced by centrifugal casting are described.
Identification and Rock Failure Characterization in Bit-Tooth Penetration
Authors: Umez-Eronini E. I.
Published: November 2009

Parameter values required in a previous rock model are estimated using the invariant imbedding identification technique applied to a bit-tooth drop test. Sequential data generated during the identification is relevant to the adequacy of the model and may suggest possible enhancement of the rock description.
The Fatigue Behavior of Large-Scale As-Welded and Stress-Relieved Tubular T Joints
Authors: Shinners C. D. , Abel A.
Published: November 2009

The changing strain distribution within large-scale tubular T joints, subjected to fully reversed axial brace fatigue loading, were measured in as-welded and stress-relieved conditions. Initial static loading enabled estimation of stress concentration factors and comparisons with the predictions of available published formulas. Dynamic load amplitudes were selected to give approximately equal hot-spot strains in all joints, thus facilitating direct comparison between specimens with different dimensions. Post-weld heat treatment increased the cycles needed for crack initiation and also reduced the crack propagation rates.
Fatigue Tests and Design of Offshore Tubular Joints
Authors: Dutta D. , Mang F.
Published: November 2009

The AWS-X “hotspot stress-load cycle” curve used at present for designing tubular joints is based mainly on the fillet-welded plate test data and some more data from small-scale tests on tubular joints, which were available in the early 1970s. A review of further tests carried out in the recent years, including those by the authors, leads to the conclusion that the influence of the diameter and thickness of the tubes plays a significant role in the joint fatigue behavior. Hence, they must be taken into consideration while designing tubular joints accurately and more economically. A modified design method is proposed here with design curves for four diameter values. Further, the results of fatigue tests on K-type joints investigating the effect of stress ratio R and of post-weld heat treatment on the joint fatigue strength are described in this paper.
Rig Jacking on Soft Soil Foundations: Improvements in Safety and Speed by Monitoring Leg Loads
Authors: Ansquer P. F. , Antalovsky S. A.
Published: November 2009

The stability of jack-up rigs with spud-cans, particularly during the jacking-up and preloading operations, has always been critical in soft soil conditions. In the offshore areas opened to prospection in Cameroon, unconsolidated clays and silts are frequent, and therefore the need to conduct these critical operations with maximum safety is of utmost importance. The monitoring of soil reactions at the spud-cans and of structural loads at the jack-houses enabled jacking operations to be conducted safely, in an area where other rigs previously encountered severe difficulties (capsizing). Data recorded by instrumentation have shown that leg maneuvering with soil penetrations of up 40 m (131 ft) may induce dangerous overloads to the structure. The continuous monitoring and control of soil reaction forces and structural loads during drilling ensured the safety of the rig. For jacking-down, the monitoring of the loads was necesary to control the structural stresses induced by the legs pulling out. To the authors’ knowledge, no similar measurements have been reported in the past.
Nonlinear Dynamic Analysis of Guyed Tower Platforms
Authors: Hanna S. Y. , Mangiavacchi A. , Suhendra R.
Published: November 2009

A method of analysis is presented to predict the nonlinear dynamic behavior of compliant offshore structures, in particular guyed tower platforms. The structural model is analyzed in time domain using the normal mode superposition approach. Nonlinearities due to fluid-structure interaction are considered. The nonlinear stiffness of the mooring system is included by suitable modification of the forcing function. Secondary overturning effects due to large deflection are introduced by equivalent lateral forces at each mass point. In analogy to the treatment of the nonlinear mooring stiffness, the nonlinearity of the soil-pile foundation can be accounted for by applying external forces and moments. By way of example, the results of dynamic analyses performed on a guyed tower designed for the North Sea are included.
Reliability Analysis of Total Systems Using Component Failure Data
Authors: Hartman P. J. , Luetjen P. , Mandel D.
Published: November 2009

Assessment of total system reliability has been accomplished using component failure data in conjunction with system operating rules and sparing policies. This paper describes the computer simulation used by the Naval Sea Systems Command (NAVSEA) to predict the reliability and availability of each new Naval ship design. The computer program utilizes stochastic simulation to predict reliability, availability, and ordered lists of critical system components. This simulation is unique in that reliability block diagrams for the total system of 500 equipment can be readily translated into compact input coding. Assessment of total ship performance presently takes less than one minute using a vector super computer. This paper describes the methods used to predict long and short-term failures in such equipment as hydrofoil struts and highly complex electronic systems. Long and short-term failure data have been modeled using a Restricted Erlang Distribution for use in the simulation.
Thermal Performance Evaluation of MSW-Fired Steam Generators—A New Approach
Authors: Hecklinger R. S. , Grillo L. M.
Published: November 2009

Determination of thermal performance or efficiency of steam generators by traditional ASME procedures is a complex and difficult undertaking. When the fuel is municipal solid waste, additional variables are introduced to confound the procedures further. A new approach is proposed as a basis for discussion. The intent of the new approach is to reduce the time and effort required to achieve agreement that a municipal-solid-waste-fired steam generator has performed as specified and/or guaranteed.
A Design Basis for the J-Tube Method of Riser Installation
Authors: Walker A. C. , Davies P.
Published: November 2009

Economic and technical factors have lead to the use of J-tubes for the connection of subsea pipelines to fixed offshore production platforms. This paper describes some of the technical aspects of this method of installation. The design analysis presented provides basic information for the prediction of pull-in loads and associated support loadings for practical installations. The analysis is based on the results of, and observations made during, a series of tests on small-scale pipelines and J-tubes. Using the knowledge of the geometrical arrangement of the contact points between the riser and J-tube, the pull-in loads and riser strains can be estimated using simple mechanics. Use of the analysis is demonstrated by means of an example of its application to a typical J-tube design.
Longitudinal Resonant Behavior of Very Deep Water Risers
Authors: Sparks C. P. , Cabillic J. P. , Schawann J.-C.
Published: November 2009

This paper is concerned with the problem of longitudinal resonant vibration of a 3000-m-long disconnected riser. Theoretical investigations of natural frequencies and induced displacements and dynamic tensions are presented, as well as practical investigations of riser longitudinal hydrodynamic damping and of short period heave excitation, likely to be communicated to such a riser, by a typical drillship. Analytical expressions, useful for describing and understanding resonant behavior, are developed in the Appendix.
Dynamic Interaction of a Guyed Tower With Its Guying System
Authors: Brinkmann C. R.
Published: November 2009

A guyed tower offshore platform differs from conventional fixed-base platforms in the way environmental loads are resisted. Horizontal wave, wind and current loads on a guyed tower are resisted by an array of guylines attached to the upper end of the structure rather than by a conventional fixed-base foundation. One of the key aspects of designing a guyed tower is the selection of a guying system that can adequately resist the anticipated environmental forces. Inclusion of guyline dynamics in an analysis of guyed tower motions is necessary to accurately predict maximum tower tilt and maximum guyline tensions in the design storm conditions when the clump weights are lifted completely off the sea bottom. The inclusion of dynamic loads on the guylines will increase the maximum tension in the guylines and reduce the maximum tower tilt induced in the platform by environmental forces. Because the dynamic motions of the tower and guylines interact, it is necessary to couple these two systems to predict the response of both systems accurately under storm conditions.
Statistical Analysis of Slow-Drift Responses
Authors: Stansberg C. T.
Published: November 2009

The statistical properties of second-order wave-induced response processes are investigated theoretically. Emphasis is placed on the slow-drift components. The assumed forcing waves are irregular with continuous frequency spectra. A spectral analysis of the response of a general system is made. It is shown that the slow-drift components are closely connected to the complex analytical signal and the Hilbert envelope of the wave elevation. A simple mathematical expression exists for the slow-drift components, based on the complex wave signal and the second-order impulse response of the system. By use of this explicit formula, the theoretical probability functions of slow-drift responses are investigated. The analysis is based on the Kac-Siegert method. A similar approach has earlier been applied to study the sum of both the low-frequency and the high-frequency second-order responses. Final calculations of the probability density functions are in general very complicated, but it can be simplified by the use of a simple idealized model for the second-order transfer function. Probability density curves for a few simple cases are presented.
Energy Losses Related to Automatic Steering of Ships in Waves—Part I: Losses Under Conventional Autopilot Control
Authors: Reid R. E. , Mears B. C. , Griffin D. E.
Published: November 2009

Results are presented relating to energy losses due to ship steering in waves. Propulsion losses related to yawing and rudder activity of ships during open-seas course-keeping are evaluated. Two representative tankers of 250,000 and 400,000 dwt, and an 880 ft (268 m) long containership are examined, using hydrodynamic data resulting from captive model tests. The approach presented involves time-domain computer simulation studies of the yaw-sway-surge-rudder coupled motions of the ships. Evaluation of losses due to both yawing of the uncontrolled ship and those resulting from yawing and rudder effects in the automatically steered case are made. On the basis of the results presented it is shown that under the action of waves yawing of a ship results in significant energy losses. It is also shown that a substantial increase in energy losses occurs under automatic steering control with commonly accepted autopilot specifications.
Nonlinear and Hysteretic Twisting Effects in Ocean Cable Laying
Authors: Shashaty A. J.
Published: November 2009

Armored ocean cable unlays under the action of installation tensions and restraining moments applied by the ocean bottom and the ship’s bow sheave. The process of elongation and twist is nonlinear and hysteretic. This process has often been assumed linear and reversible. The equations describing the moment which is developed in laying cable on the ocean bottom are worked out, without assuming linearity and reversibility. These equations are applied to some cases likely to arise. For a typical armored coaxial cable laid in 3700-m (2000-fathoms) depth without bottom tension, a steady-state laying-up moment of 134 Nm (99 lbf. ft) is developed. For the reversible case, no moment is developed. If the bottom tension is increased from zero to 33,375N (7500 lbf) and then returned to zero, a peak moment of 198Nm (146 lbf. ft) is developed.
A Comparison of Two Sea Ice Trajectory Models With AIDJEX Observations
Authors: Kolle´ J. J. , Pritchard R. S.
Published: November 2009

Two mathematical models (free drift and complete ice dynamics) that simulate sea ice motions driven by winds and currents are described. Accurate wind and current observations and motion data obtained from data buoys and camps located in the Beaufort Sea during the AIDJEX main field experiment 1975–76 are used as input to these two models for evaluating model performance. Comparison of modeled and observed ice displacements shows that the free-drift model accurately predicts ice motions in the summer only whereas the complete ice dynamics model simulates year-round ice motions with a good degree of accuracy.
Limit Analysis of Ice Sheet Indentation
Authors: Karr D. G. , Das S. C.
Published: November 2009

The methods of plastic limit analysis are used to determine the indentation pressures of a flat rectangular punch on an ice sheet. The ice sheet is idealized as a semi-infinite layer of elastic-perfectly plastic material. Lower bounds are computed by application of the lower bound limit theorem. The suitability of basic yield functions are assessed based on their ability to predict failure at demonstrated ice failure stress ratios. The particular yield functions that are employed include the generalized Mohr-Coulomb (or Drucker-Prager) criterion, a modified Drucker-Prager criterion, as well as a parabolic yield criterion used previously in literature on this topic. A study of the effects on indentation pressure of varying ice strength parameters is presented. Limit analysis solutions are obtained for plane stress conditions, and thus the applicability of a particular yield function can be evaluated for a range of ice strengths for indentation problems involving high aspect ratios.
Rheology of Foam and Its Implications in Drilling and Cleanout Operations
Authors: Sanghani V. , Ikoku C. U.
Published: November 2009

Experimental analysis was carried out to study the rheological properties of foam. Foam was generated by simultaneously injecting air and an aqueous solution of the foaming agent through a coiled tubing foam generator. Foam was injected at the bottom of an annulus with 4.0-in. (i.d.) casing diameter and 1.5-in. (o.d.) tubing diameter. Qualities ranged from 0.65 to 0.95. Shear rates ranged from 150 to 1000 sec−1. Effective viscosities were calculated and were found to range from 60 to 500 cps. Results showed that flowing foam behaved as a pseudo-plastic fluid with no yield value; effective foam viscosity decreased with an increase in shear rate for a fixed quality. For shear rates in the range 500 sec−1 to 1000 sec−1, the effective foam viscosity was independent of foam quality. This is useful since most field applications fall in this range.
Combined Cycles—Alternative for Process Steam Systems
Authors: Harkins H. L.
Published: November 2009

The state-of-the-art combined cycle system consisting of combustion turbines, heat recovery steam generators, and steam turbine-generator units, offers a high-efficiency method for the production of electrical and heat energy at relatively low installed and operating costs. Regional fuel usage projections for major petrochemical areas of the country indicate a substantial continued usage of lighter fuels for the next 15 to 20 yr by electric utilities and industrials. Only the highest efficiency utilization of these premium fuels should be considered, and this paper discusses systems for this higher utilization. Typical plant systems are compared to more efficient systems, the relative economic incentives are considered, applications for specific requirements representative of industry practice are developed, and alternative fuel considerations for combined cycle systems are included.
Startup and Shakedown of Albany New York Solid Waste Energy Recovery System
Authors: Nollet A. R. , Greeley R. H.
Published: November 2009

This paper describes the Albany New York Solid Waste Energy Recovery System (ANSWERS), which consists of two plants — a City-owned refuse-derived fuel (RDF) plant, and a State-owned boiler plant in which RDF is burned. This paper is chiefly concerned with the City-owned RDF plant, and describes shakedown tests, problems encountered and solutions developed. Operational statistics and operations policies for the City-owned plant are discussed. Laboratory measurements of the heating value of RDF samples are compared with results actually achieved in the State boilers.
Fixed Mesh Finite Element Solution for Cartesian Two-Dimensional Phase Change
Authors: O’Neill K.
Published: November 2009

An algorithm has been developed for two-dimensional freezing and thawing problems, which may also be useful for some other phase change problems. It is designed to be implemented simply in standard finite element heat conduction computer codes which use linear interpolation within elements. Substances with discrete phase change temperatures, such as water, suffer a step change in enthalpy across a phase change isotherm, and hence, feature a theoretically infinite heat capacity there. The algorithm handles this potentially troublesome phenomenon in a natural way through usual finite element procedures, using simple closed form expressions. A program incorporating the algorithm produced stable, accurate, and economical simulations when run for radial and two-dimensional test cases with exact analytical solutions.
The Effect of Stress Application Rate on the Creep Behavior of Polycrystalline Ice
Authors: Cole D. M.
Published: November 2009

This work examines the effect of the rate of stress application on the creep behavior of polycrystalline ice. Stress rates from 10−3 to 1.84 MPa s−1 were used to achieve a creep stress of 3.6 MPa at test temperatures of −5° and −10°C. The treatment emphasizes the effect of stress application rate on primary creep behavior and the accompanying microfracturing activity. Acoustic emission measurements taken in all tests indicate the onset and rate peak of the microfracturing activity. The stress application rate has little effect on the minimum strain rate, the strain at which it occurs, or the characteristics of tertiary creep provided that the loading ramp ends prior to reaching the nominal failure strain of 1.0 percent. Primary creep behavior is significantly affected only at rates below about 10−2 MPa s−1. Results indicate that when the loading ramp continues through the failure strain, no minimum strain rate occurs, but rather the strain rate increases monotonically throughout the entire test.
Interaction of Ice Floes With Columns of a Semi-Submersible Platform
Authors: Noble P. G. , Singh D.
Published: November 2009

A preliminary research project has been carried out to determine the effect of small ice floes on a semi-submersible drilling unit. Physical model tests have been conducted with two main objectives: first, to determine the ability of the columns to prevent ice from passing between them (arching) and thus minimizing the chance of riser damage, and second, to determine the total ice load on the semi-submersible during interaction with ice field concentrations. Three models were used, representing one half of a four, six or eight-legged semi-submersible platform. The dimensions and spacing of the columns were such that the heave and pitch responses were kept constant. The tests were conducted at a model scale of 1:30 using synthetic ice. Test results showed the maximum load measured on a four-legged semi-submersible model, at 100 percent ice floe concentration, was on the order of half of that measured on six or eight-legged semi-submersible models. Also the ice loads on a four-legged semi-submersible model at lower ice floe concentration were substantially less than those for six or eight-legged semi-submersible models. The total ice load on semi-submersible models is found to be a function of ice floe concentration. Up to about 75 percent ice concentration, ice loads varied linearly. Beyond that, the loads increased exponentially for all semi-submersible models.
The Effect of Seabottom Proximity of the Vortex-Induced Vibrations and Fatigue Life of Offshore Pipelines
Authors: Tsahalis D. T.
Published: November 2009

The effect of the seabottom proximity on the vortex-induced vibrations of suspended spans of offshore pipelines is discussed in the light of recent relevant experimental results. It is shown that the effect of the seabottom proximity is to drastically alter the vortex-induced vibrations of supsended spans resulting into longer fatigue lives or equivalently longer safe lengths. A “generalized” fatigue damage is formulated universally applicable to all suspended spans.
Available Ocean Wave Power and Prediction of Power Extracted by a Contouring Raft Conversion System
Authors: Burdette E. L. , Gordon C. K.
Published: November 2009

Techniques are described which have been employed to develop detailed, quantitive estimates of the available ocean wave energy flux. A summary of results for a region of particular interest to potential U.S. developers of wave energy systems — the U.S. Northwest Pacific Coast — is also presented. Comparisons with results of other studies are made. In addition, a method for predicting the amount of mechanical energy captured by a conversion device, based on a frequency domain technique, is presented. Results are predicted for an articulated, contour following raft deployed in deep, open water west of the mouth of the Columbia River.
Thermoelastic Analysis of a Cracklike Reservoir in a Hot Dry Rock During Extraction of Geothermal Energy
Authors: Abe´ H. , Sekine H. , Shibuya Y.
Published: November 2009

The fracture mechanics study of the problem for a fluid-filled cracklike reservoir is made by including the thermoelastic effect. A two-dimensional crack is considered as a model of the vertical cracklike reservoir in the earth’s crust, and the crack is analyzed on the basis of the theory of quasi-static thermoelasticity. The fluid temperature at the outlet and the rock temperature are obtained. The variations of the shape and volume of the reservoir against time are shown in graphs.
The Role of Terzaghi Effective Stress in Linearly Elastic Deformation
Authors: Carroll M. M. , Katsube N.
Published: November 2009

It has been shown that the overall strain of a fluid-filled porous elastic solid is not governed by the Terzaghi effective stress law. We show, in the context of anisotropic linear elasticity, that the overall strain may be resolved into a component which is the average strain of the solid matrix and a component due to change in relative pore geometry, and that the latter is determined by the Terzaghi effective stress. This leads to a simple form of the response laws and, in particular, to effective stress laws for overall strain (obtained previously) and for strain of the pore space.
A Quantitative Evaluation of Two Classical Approximations Used to Predict the Extent of Vertical Hydraulic Fractures
Authors: Rubin M. B.
Published: November 2009

An integral equation was developed to predict the critical parameters (fracture width and length) associated with the propagation of a vertical hydraulic fracture and a numerical solution procedure was developed. The effects of the classical approximations of pressure and fracture width were investigated both separately and together. It was found that the effects associated with the pressure approximation were relatively insignificant, whereas those associated with the fracture width approximation were significant, particularly when the formation was only moderately permeable. Finally, an exact closed-form solution of the integral equation was developed for a special case. It was shown that when the formation is only moderately permeable, this solution provides a better approximation of the exact solution than the classical solution of Carter [2].
Effects of Landfill Cover Design on Methane Recovery Systems
Authors: Massmann J. W. , Moore C. A.
Published: November 2009

A finite difference computer program to aid in optimizing landfill cover design was developed by the authors. The program was used to compare the methane yield from sand-covered and clay-covered landfills equipped with methane recovery systems. The results of this comparison and a brief description of the finite difference program are presented in this paper. These results indicate that a clay cover can restrict air inflow into the landfill system, thus preventing oxygen poisoning of the methane-producing organisms. The practice of monitoring methane to air ratios in the pipelines of the recovery system in order to forewarn of oxygen infiltration into the fill material was shown to be ineffective in some situations. More reliable methods to forewarn of oxygen poisoning were suggested.
The Application of Real Time Flow Modeling to Pipeline Leak Detection
Authors: Thompson W. C. , Skogman K. D.
Published: November 2009

This paper covers the practical and technical aspects of applying transient fluid flow and heat transfer models to a real-time pipeline leak detection system. The system discussed monitors 24 batched products pipelines from a central control facility consisting of dual Data General Eclipse S/250 computers. The 24 pipelines in the system total over 3100 mi in length, ranging in size from a 13-mi, 1-station, 1-terminal, 6-in. line to a 360-mi. 6-station, 7-terminal, 30-in line. The minimum detectable leak size proven in testing is approximately 1/2 of 1 percent of maximum flow rate.
Experimental Determination of Friction Factors for Mist and Foam Drilling and Well Cleanout Operations
Authors: Okpobiri G. A. , Ikoku C. U.
Published: November 2009

This work covers both theoretical and experimental analysis of frictional losses due to the presence of solids in vertical flow of solids-foam slurries. Rabinowitsh-Mooney generalized flow equations for time-independent fluids from the theoretical basis for the rheological analysis. Experimental work was done with an apparatus designed to simulate actual field conditions as closely as possible. The test section consists of an annulus with 4.0-in. casing and 1.5-in. tubing. The surface active agent used is an aniomic biodegradable foamer (ADOFOAM BF-1) and constitutes 1 percent of the liquid volume. Foam qualities and wall shear rates ranged from 0.64 to 0.99, and 100 to 1000 sec−1, respectively. Semi-empirical equations for predicting friction factors due to solids are presented. Sandstone and limestone particles were used. Average particle size ranged from 0.025 to 0.11 in. and a total of 337 data points were used in the correlations. Data collection was carried out above solid saltation velocities under fully developed steady-state flow conditions. Results show that the friction factor of suspension can be treated as the sum of the friction factor due to the fluid and that due to the solids. For a constant foam Reynold’s number, the frictional losses due to the presence of solids increase as the solids mass flow rate (or solids content) increases. Solids friction factor was found to increase with increasing particles Froude number (gds/VF2), density ratio (ρs/ρF), solids concentration, but decreases with increasing fluid Reynolds’ number.
Post-Yield Strain Tests of 20-in. Casing With Weld-on Connectors
Authors: Blackstone W. R. , Blose T. L. , Galate J. W.
Published: November 2009

Soils in permafrost regions may undergo significant subsidence due to thawing. Oil well surface casing embedded in such soils may be subjected to strains well beyond yield, whatever the casing properties might be. To deal with this, the State of Alaska has issued a specification defining the amount of axial strain that the casing, together with its connectors, must be able to withstand without parting. This paper presents full-scale tension and compression test data demonstrating that a particular weight and grade of 20-in. casing with premium weld-on connectors is a system exceeding those requirements. It is shown that, in tension, the material ultimate strength is reached first in the casing. Similarly, it is shown that, in compression, the casing buckles plastically before the connector fails.
Analysis and Testing of Factors Affecting Collapse Performance of Casing
Authors: Fowler J. R. , Klementich E. F. , Chappell J. F.
Published: November 2009

This paper describes testing and analysis which demonstrates that collapse specimens tested in short testers with rigid end seals give artificially high collapse values. It also compares the API collapse formulas with conventional strength of materials collapse criteria which incorporate ovality and finds the two approaches give very similar results. A statistical analysis indicates that ovality, while not nearly as important as yield strength and D/t, is important to collapse. Finally, it shows that pipe with lower ovality exhibits better collapse resistance.
Freezing of a Semi-Infinite Medium With Initial Temperature Gradient
Authors: Lunardini V. J.
Published: November 2009

Exact solutions to problems of conductive heat transfer with solidification are rare due to the nonlinearity of the equations. The heat balance integral technique is used to obtain an approximate solution to the freezing of a semi-infinite region with a linear, initial temperature distribution. The results indicate that the constant temperature Neumann solution is acceptable for soil systems with a geothermal gradient unless extremely long freezing times are considered. The heat balance integral will yield good solutions, with simple numerical work, even for non-constant initial temperatures.
Structural Response Analysis of Tension Leg Platforms
Authors: Yoshida K. , Ozaki M. , Oka N.
Published: November 2009

A linear response analysis method of the tension leg platform (TLP) subjected to regular waves is proposed. In this analysis method, flexibility of the superstructure can be taken into account in the equations of motion; response motions, tension variations of tendons and structural member forces are solved simultaneously. The applicability of this method is confirmed by comparison with the test results on two kinds of small-scale TLP models. The structural responses obtained from these calculations and their effects on tension variation of tendons are studied. Finally, several kinds of structural response characteristics are conclusively discussed.