bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimum Design and Control of Anchored Wave Energy Generators
Authors: Abuelnaga A. , Seireg A.
Published: November 2009

The study reported in this paper deals with the development of design data and strategies for optimizing the performance of wave energy generators. Rectangular buoys are considered for illustration. The buoy dimensions necessary for maximizing the conversion efficiency while minimizing its size for a particular ocean condition are evaluated. A control scheme based on changing the load damping coefficient provides an effective means for maximizing the conversion efficiency at different wave frequencies.
Optimum Design of Spread Mooring Systems
Authors: Jones H. L. , Nelson J. K.
Published: November 2009

The design of a spread mooring system of given pattern with single segment lines on a flat seafloor is formulated as a mathematical programming (optimization) problem. Design variables are the outboard length and initial tension in each line. Constraints limit maximum tension, anchor pull and anchor uplift for each line under each loading condition. Maximum vessel excursion is limited to a circle of specified radius. The optimal design is that which minimizes total weight of outboard line and is obtained by computer solution of the optimization problem. Three examples are presented to demonstrate the method.
An Investigation of Stresses in Bolted Connectors for Marine Risers
Authors: Moyer M. C. , Marshek K. M.
Published: November 2009

This paper presents a procedure on the finite element method for analyzing a bolted flange connector and compares this method with three traditional approaches. The finite element method considers such effects as flange interface separation, nonlinear and nonconstant flange stiffness, and bolt bending. A comparison of the finite element model with the three traditional methods (each employs a formula for flange stiffness) shows a fairly close correlation for total bolt force versus applied load, but a wide discrepancy for maximum bolt stress versus applied load. The discrepancy between the finite element model analysis and the three other methods (empirical by Weiss and Wallner, truncated conical area by Roetscher, and the classical hollow cylinder approach) can be attributed to the change in flange stiffness during separation and the occurrence of bolt bending. The selected method of analysis was shown to significantly affect the results of a bolt fatigue analysis, but was shown to have little effect on a static analysis. In offshore applications, the environment creates dynamic stresses which make a fatigue analysis essential for long-term safety.
On Dynamic Fracture of Rock Under Bit Impact Loads
Authors: Eronini I. E.
Published: November 2009

A characterization of the dynamic interaction between an impacting tool and rock is presented. The analysis is based on the concept of rock fracture energy and on simple representations of the amount of fracturing and energy storage in the rock during fracture propagation. The governing equations are not complicated. They contain a small number of parameters and impose minimum restrictions on the form or sophistication of the model of the impacting tool. Simulation results are shown for bit-tooth drop tests on Indiana limestone under different values of the differential pressure across the rock face and for various heights of drop. The predicted dynamic force-penetration curves, force-time, displacement-time and velocity-time histories agree well with reported Laboratory data and demonstrate that the essential elements of tooth drop loading are adequately represented by the model.
A Dynamic Model for Rotary Rock Drilling
Authors: Eronini I. E. , Somerton W. H. , Auslander D. M.
Published: November 2009

A rock drilling model is developed as a set of ordinary differential equations describing discrete segments of the drilling rig, including the bit and the rock. The end segment consists of a description of the bit as a “nonideal” transformer and a characterization of the rock behavior. The effects on rock drilling of bottom hole cleaning, drill string-borehole interaction, and tooth wear are represented in the model. Simulated drilling under various conditions, using this model, gave results which are similar to those found in field and laboratory drilling performance data. In particular, the model predicts the expected relationships between drilling rate and the quantities, weight on bit, differential mud pressure, and rotary speed. The results also suggest that the damping of the longitudinal vibrations of the drill string could be predominantly hydrodynamic as opposed to viscous. Pulsations in the mud flow are found to introduce “percussive” effects in the bit forces which seem to improve the penetration rate. However, it is known from field observations that drill pipe movements, if strong enough, may induce mud pressure surges which can cause borehole and circulation problems. Bit forces and torques are shown to be substantially coupled and the influence of certain rock parameters on variables which are measurable either at the bit or on the surface support the expectation that these signals can furnish useful data on the formation being drilled. Other results, though preliminary, show that the effects of the lateral deflections of the drill string may be large for the axial bit forces and significant for the torsional vibrations. For the latter, the unsteady nature of the rotation above the bit increases and the resistance to rotation due to rubbing contact between the drill string and the wellbore accounts for very large power losses between the surface and the bit.
An Analytical Examination of the Behavior of Oil Sand Fragments in Heated Streams
Authors: Hanafi A. , Karim G. A.
Published: November 2009

The physical and chemical processes that occur typically within and around an oil sand fragment are considered when the fragment is suddenly introduced into a hot, low-uniform velocity, gaseous oxidizing stream. In this analytical study, the extent of bitumen volatilization was obtained from a consideration of the simultaneous heat and mass transfer within spherical oil sand fragments combined with a simplified cracking scheme of the heavy oil and asphaltene into coke and distillate. The resulting system of equations together with the boundary conditions arising from subjecting the fragments to hot convective streams were solved using Laplace transformation. The transient concentrations of bitumen and temperature within the fragments were then obtained under a wide range of operating conditions. The similarity of the expression obtained for the extent of bitumen volatilization to the expression derived from simplified analysis, based on a dropletlike model, was demonstrated for cases where the transient effects within the fragments were considered to be negligible. The results of the theoretical analysis show relatively good agreement with their corresponding experimental values at high stream temperatures, while they showed relatively inferior agreement at low temperatures.
Specifying Linepipe Suitable for Safe Operation in Sour, Wet Service
Authors: Moore E. M. , Hansen D. A.
Published: November 2009

This paper describes the specifications recommended by the authors for buying linepipe in grades up to X-70 for wet, sour service. The linepipe is tested to verify that it is resistant to hydrogen-induced cracking (HIC). In addition, fracture control requirements are imposed so that if a failure does occur for any reason, the crack is guaranteed to self arrest, thus minimizing the consequences of the failure. Pipe meeting the specifications described in this paper is readily available from numerous European and Japanese mills.
Well Test Analysis for Enhanced Oil Recovery Projects
Authors: Ikoku Chi U.
Published: November 2009

Recent studies on the transient flow of non-Newtonian fluid in porous media have proposed new well test analysis techniques for non-Newtonian injection wells. This paper extends these new techniques to non-Newtonian injection well falloff testing. The practical use of this well test analysis method is demonstrated. The limitations of the techniques are also addressed. Exmaples of field data are used to demonstrate how this analysis can aid in well test interpretation and provide data and insight for the design and operation of enhanced oil recovery projects.
Industrial Application of a Direct Refrigeration System for Energy Conservation
Authors: Shea D. P. , Shelton J. E. , White T. L.
Published: November 2009

A large direct industrial refrigeration system was installed to reduce energy consumption in a chemical process plant. Electrical energy was saved by eliminating an intermediate cooling circuit including chilled liquid heat exchangers and glycol circulating pumps. A benefit of the system was increased production capacity by improving evaporator heat transfer, which reduced batch cycle time. This paper discusses system design, start-up and operating experience, and energy savings.
Effects of Synthetic Industrial Fluids on Ball Bearing Performance
Authors: Morrison F. R. , Zielinski J. , James R.
Published: November 2009

A series of laboratory tests was conducted using rolling contact bearings to compare the lubricating properties of a specially formulated synthetic lubricant based on diester to those of a specific mineral oil currently in service in petrochemical plant equipment. Two synthetic lubricants and two mineral oils of varying viscosities were experimentally compared. The test results indicated that the synthetic lubricant, having a viscosity of 32 m2 / s (32 cSt) at a temperature of 313K, offered longterm contact surface protection equivalent to that of the base line mineral oil which has a viscosity of 68 m2 / s, without reducing bearing service life below the theoretically predicted levels. The same good wear protection could not be achieved with a reduced viscosity mineral oil. The use of the lower viscosity synthetic lubricating fluid could provide projected energy savings of $75,000 per year when elements of a total petrochemical complex are considered.
Stability of a Penny-Shaped Geothermal Reservoir in the Earth’s Crust
Authors: Abe´ H. , Sekine H. , Kitada S.
Published: November 2009

The theoretical analysis of a penny-shaped geothermal reservoir in the earth’s crust subject to linear tectonic stress gradients has been made on the basis of the three-dimensional theory of elasticity. The condition for stability of a reservoir requires K1 < Kc, where K1 and Kc are, respectively, the stress intensity factor for the opening mode and the fracture toughness of the surrounding rock. From this condition the upper critical pressure being necessary for the reservoir stability is obtained and is shown graphically.
Stress Analysis of Submerged Cylindrical Structures by Elasticity and Shell Theories
Authors: Amirgholizadeh E. , Bert C. W.
Published: November 2009

A thick-walled circular cylinder, made of either isotropic or composite material, is analyzed using closed-form solutions to two different theories. The cylinder is submerged, so that the loading includes gravity body forces, external hydrostatic pressure at the outer boundary, and a physically realistic distribution of counterbuoyancy force at the inner boundary. The elasticity theory is formulated as one in plane strain using the Airy stress function. The shell theory used is a refined thick shell theory formulated in terms of generalized displacements.
The Impact Energy of a Moored Tanker Under the Action of Regular Waves
Authors: Li Yu-Cheng
Published: November 2009

The influence that factors such as mooring line conditions, fender arrangements, dolphin arrangements, degree of ship loading, waves of long period, wave direction, and wind on the impact energy of a moored tanker were studied. Based on systematic test data, a semi-empirical formula was developed to calculate the impact energy of the moored ship on the berthing facilities under the action of regular waves. It was shown by experiment that this method is suitable for calculating the impact energy of moored ships of capacities as great as 200 × 103 t.
An Experimental Study of Rotor-Filter Pump Performance
Authors: Marshek K. M. , Naji M. R. , Andries G. C.
Published: November 2009

The performance of a rotor-filter pump has been studied experimentally. To develop an understanding of pump performance, and in particular to discern the mechanism of hydraulic pulsing, flow visualization in the rotor, vibration analyses of the pump, frequency analysis of the pump hydraulic pressure pulsation, and analyses of flow characteristics for different pick-up tubes in combination with different impellers and cover plates were conducted. The frequencies of the pump’s hydraulic pulsation is shown to be a function of the number of pick-up arms and the motor speed. The pump vibration and its pulsation amplitude were reduced by increasing the number of pick-up arms or by adding a radial impeller. These actions increased the lowest frequency of pulsation and decreased the chance of excitation of the pump system parts.
Radial Inflow Expansion Turbines for Power Recovery
Authors: Bergmann D. A.
Published: November 2009

Performance data for single-stage, radial inflow, expansion turbines is presented in a manner to enable the process designer to quickly estimate the amount of power available from a process stream, the maximum effective pressure ratio and the temperature drop. All data presented is based on the current state of the art and recognizes the different levels of technology which may be applied.
Optimization of Stinger Geometry for Deepsea Pipelaying
Authors: Maier G. , Corradi L. , Mazzoli A. , Michelini R.
Published: November 2009

The configuration of the stinger and ramps of a laying barge can be adjusted by varying the angles between adjacent segments and the arm of each support. On the basis of suitable idealizations and discretizations, a method is developed apt to optimize, for a given laying situation, the choice of the foregoing geometric parameters, alone at given tension or in association with the tensioner thrust. In the former case the function to minimize is the maximum absolute value of the bending moment in the overbend. In the latter case the thrust at the tensioner is minimized for given upper bound on the maximum stress in the overbend. The optimization procedure proposed consists of three phases and allows for unilateral contact between pipe and supports.
Dynamics of the Water-Pipeline-Soil Interaction
Authors: Karal K. , Halvorsen S. A.
Published: November 2009

A design engineer-oriented approach to determining the pipeline dynamic response to ocean forces accounting for complex environmental and pipeline conditions is presented. The described analysis yields time histories of pipeline motion and steel pipe stresses induced by water motion. Sinusoidal variation of normal water particle motion in time and along the pipeline, waves, flexural rigidity of pipe, damaged concrete coating, among other effects, are accounted for in the mathematical model.
Improved Strip Theory for Wave-Induced Loads on Twin Hull Semisubmersibles
Authors: Mathisen J. , Borresen R. , Lindberg K.
Published: November 2009

Wave-induced loads on semisubmersible platforms in operational and survival conditions are usually evaluated from the Morison equation. If the pontoons are unusually large, closely spaced, or near the sea surface, then interaction effects that are not included in the Morison equation approach become significant. In the transit condition, when the pontoons are floating in the sea surface, the wave loads must be calculated by other methods. An improved strip theory approach is presented utilizing “opposed motion potentials.” Interaction effects between the pontoons are included. The present improvement provides additional information about the spatial distribution of the diffraction forces, enabling the determination of the internal forces between the pontoons. Comparisons are shown between results from the Morison equation approach, the improved strip theory, and model tests for a recent semisubmersible design at operational draught. The improved strip theory is also compared to 3-D sink-source calculations for the same rig at transit draught.
The Effect of a Vertical Wall on the Sway-Added Mass of a Lewis-Form Section in Shallow Water
Authors: Kim C. H. , Chen N.
Published: November 2009

A method is presented for evaluating sway-added mass due to lateral translation of a shiplike Lewis-form cylinder in the presence of a vertical wall in shallow water. This is an extension of a previous paper on sway-added mass of a cylinder at zero frequency in a horizontally unbounded shallow water domain. Formulations are given and numerical results are presented in figures.
The Significance of Dynamic Response in the Estimation of Fatigue Life
Authors: Vandiver J. K.
Published: November 2009

The fatigue life of offshore structures is investigated under the conditions that dynamic response to waves is assumed to play a significant role. Under these conditions, the study emphasizes the significance of the placement of natural frequencies and the amount of modal damping. The results may be used to assess the confidence bounds on fatigue life estimates that result from uncertainties in design stage estimates of structural natural frequencies, and damping.
Performance Evaluation of Buoy Shapes for Deep Ocean Systems
Authors: Petrie G. L. , Hartman P. J.
Published: November 2009

The dynamic motion responses of buoy hulls employed in deep ocean systems are often a critical factor affecting the operability of data links, sensors, or other components. The degree of coupling between the buoy and the wave surface, and consequently the expected motion characteristics are commonly described in terms of “surface following” and “surface piercing” behavior. However, as a basis for buoy hull selection and design, it is necessary to fully evaluate the expected performance of the buoy, based on static and dynamic motion responses in a realistic seaway, in the context of the mission constraints as well as the wave properties at the deployment site. A comparison of several different buoy shapes is described, and it is shown that mission requirements, operational constraints, and location can significantly alter the selection of the best hull shape for each set of conditions.
Rock Properties and Their Effect on Thermally Induced Displacements and Stresses
Authors: Chan T. , Hood M. , Board M.
Published: November 2009

A discussion is given of the importance of material properties in the finite-element calculations for thermally induced displacements and stresses resulting from a heating experiment in an in-situ granitic rock, at Stripa, Sweden. Comparisons are made between field measurements and finite element method calculations using (i) temperature independent, (ii) temperature dependent thermal and thermomechanical properties, and (iii) in-situ and laboratory measurements for Young’s modulus. The calculations of rock displacements are influenced predominantly by the temperature dependence of the thermal expansion coefficient, whereas the dominant factor affecting predictions or rock stresses is the in-situ modulus.
Wave Propagation at the Interface in a Hot Water Store
Authors: Rehbinder G.
Published: November 2009

Solar heat or surplus heat can be stored in large steel tanks or even better in unlined rock caverns. If the loading and unloading is done with a heat exchanger it is important that the stratification in the store can be maintained. The risk of destabilization of the interface between hot and cold water due to Helmholz-Kelvin instability of interfacial waves is discussed. The discussion indicates that the risk is negligible.
Nonlinear Transient Motion of Deep Ocean Mining Pipe
Authors: Chung J. S. , Whitney A. K. , Loden W. A.
Published: November 2009

For accurate and economic time-domain analysis of deep ocean pipes, a realistic representation of hydrodynamic forces along the pipe and an efficient numerical method are required. A transient analysis procedure is formulated and implemented for the numerical determination of nonlinear transient motion of pipes using, as an initial condition, the nonlinear static configuration. The pipe is modeled by three-dimensional beam finite elements which account for coupled axial, bending and torsional deformations. We used 1) vertical variation of seawater properties and hydrodynamic force in the stratified ocean, 2) relative pipe velocity and response for each state in the force computation, and 3) an implicit time-integration method. Several cases are presented for accelerating, turning, and oscillatory motions of the ship and an 18,000-ft pipe, bottom end free. The subsurface environment and force coefficient selection greatly affects the results. The method can be directly applied to the analysis of deepsea risers and OTEC pipes.
Analysis for an Embedded Ice Pressure Sensor
Authors: Templeton J. S.
Published: November 2009

A plane elastostatic analysis is presented for the problem of a rectangular, orthotropic, elastic inclusion in an isotropic elastic host, with differential thermal expansion between the inclusion and the host. The analysis assumes that bending as well as shear deflection of the inclusion boundaries can be neglected. The product of this analysis is a closed form solution applicable to an embedded ice pressure sensor of rectangular cross section having relatively rigid sensing face cover plates. The form of the solution displays several significant results concerning inclusion effects for both in-line and transverse ice stresses, Poisson’s ratio effects, and thermal expansion effects. The most striking result is that the magnitude of the error induced in ice pressure measurements by neglecting differential thermal expansion is not a function of the sensor’s stiffness in the sensing direction.
Permeability Enhancement Using Explosive Techniques
Authors: Adams T. F. , Schmidt S. C. , Carter W. J.
Published: November 2009

In-situ recovery methods for many of our hydrocarbon and mineral resources depend on the ability to create or enhance permeability in the resource bed to allow uniform and predictable flow. To meet this need, a new branch of geomechanics devoted to computer prediction of explosive rock breakage and permeability enhancement has developed. The computer is used to solve the nonlinear equations of compressible flow, with the explosive behavior and constitutive properties of the medium providing the initial/boundary conditions and material response. Once the resulting computational tool has been verified and calibrated with appropriate large-scale field tests, it can be used to develop and optimize commercially used explosive techniques for in-situ resource recovery.
Modeling of Hydraulically Fractured Gas Wells Completed in Noncontinuous Lenticular Formations
Authors: Evans R. D. , Carroll H. B.
Published: November 2009

A mathematical model is presented which forms the basis for a reservoir simulator that can be used to assist in the interpretation and prediction of the performance of hydraulically fractured gas wells completed in noncontinuous sand lense formations. Equations are derived to simulate both reservoir and well performance. They are general in that the following effects are considered: 1) noncontinuous sand lenses, 2) three-dimensional flow in the reservoir and one-dimensional flow in the fracture, 3) non-Darcy flow in the reservoir and fracture, 4) wellbore and fracture storage, 5) formation damage on the fracture face, 6) frictional pressure drop in the production string, and 7) Klinkenberg effect. An operational two-dimensional gas reservoir simulator has been developed which includes these effects.
Drill Stem Steels for Use in Geothermal Environments
Authors: Salzbrenner R.
Published: November 2009

Steels which are used in drill stem for conventional drilling have been selected primarily to satisfy certain static strength requirements and cost considerations. As the environments in which drilling is performed become more severe (e.g., in geothermal fluids) additional considerations must be given to the design of alloys which are resistant to general corrosion, stress corrosion, and corrosion fatigue. General design considerations for steel alloys which should provide an enhanced resistance to geothermal drilling operations are presented. These considerations include discussion of the chemistry and metallurgical substructure, and how their variation affects the mechanical and corrosion properties of steel used for drill stem applications. A duplex ferritic-martensitic steel has an advantageous combination of compositional and microstructural features which should lead to improved chemical resistance (particularly to hydrogen sulfide) as well as provide a good combination of strength and toughness properties. This duplex steel is based on the iron-2.0 weight percent silicon-0.1 weight percent carbon system, and offers the potential of enhanced performance in geothermal drilling as well as low alloy cost.
An OTEC Pilot Plant Heat Engine
Authors: Richards D. , Perini L. L.
Published: November 2009

This paper summarizes the heat-engine system design for an ocean thermal energy conversion (OTEC) plant and its integration in the platform, and describes system components and their performance and construction requirements together with the computed overall cycle performance and operation. Ancillary equipment and platform arrangement and support requirements are discussed as to their effect on the platform design. The heat engine and platform design is based upon the JHU/Applied Physics Laboratory (APL) folded-tube, shell-less heat exchanger module concept as developed from analytical and experimental work previously reported. The heat engine design discussed is among the candidates for the construction of large commercial OTEC plantships. In the APL concept, the plantship will cruise (graze) the tropical oceans to utilize the maximum available ocean temperature difference. They will produce energy-intensive products such as ammonia, which can be synthesized from sea water and air and shipped to U.S. or foreign ports for use as fertilizer or as a hydrogen fuel carrier. The pilot plant design presented is for a 10–20-MW net output plant made up of 2.5-MWe net heat exchanger modules manifolded to 5 MWe net turbine-generator sets. In this approach, it is anticipated that all construction requirements, manifolding, cycle control, and installation and operational requirements can be determined and evaluated for the detailed design of large commercial vessels.
Phase Change Around Insulated Buried Pipes: Quasi-Steady Method
Authors: Lunardini V. J.
Published: November 2009

The heat transfer problem for cylinders embedded in a medium with variable thermal properties cannot be solved exactly if phase change occurs. Approximate solutions have been found using the quasi-steady method. The temperature field, phase change location, and pipe surface heat transfer can be estimated using graphs presented for parametric ranges of temperature, thermal properties, burial depth, and insulation thickness. The accuracy of the graphs increases as the Stefan number decreases and they should be of particular value for insulated hot pipes or refrigerated gas lines.
Analysis of Motions of a Catamaran in Arbitrary Heading Waves
Authors: Sun F.
Published: November 2009

This paper analyzes the motions of a catamaran advancing at a constant speed in arbitrary heading waves. The mathematical expressions of the hydrodynamic coefficients and exciting forces are derived. These mathematical expressions apply not only to catamaran, but also to monohull, and can be extended to multihull. In analyzing the hydrodynamic and exciting forces, the hydrodynamic interactions between the two hulls are considered in addition to the effect of forward speed and aftermost section. These hydrodynamic interactions should not be neglected for the motions of catamaran.
A Technical Evaluation of Modular Incinerators With Heat Recovery
Authors: Frounfelker R. E. , Kleinhenz N. J.
Published: November 2009

The use of small modular incinerator systems for solid waste disposal and energy recovery in municipal and industrial applications is studied. The technical evaluation presented herein is based on the results of three 1-wk field tests at each of two sites. Test data were used to calculate the following for each system: a mass balance, an energy balance, the heat recovery efficiency, the environmental effects, and the overall effectiveness of the system as a solid waste disposal facility. As a result of a nationwide survey, two facilities which best satisfied selection criteria were chosen. These selection criteria included that the sites consist of modular incinerators with heat recovery having a capacity of 50 tons (45 t) or less per day and that the systems be representative of current technology, designs, and operational procedures. The two facilities selected for this study included a municipal incinerator plant with a Consumat system in North Little Rock, Arkansas, and an industrial incinerator facility with a Kelley system in the plant of the Truck Axle Division of the Rockwell International Corporation in Marysville, Ohio. Since the two systems differ in many respects and operate on dissimilar waste streams, direct comparisons of the two systems are not included.
State-of-the-Art of Models for Geothermal Recovery Processes
Authors: Tsang C. F. , Wang J. S. Y.
Published: November 2009

Recent interest in geothermal energy development has contributed to the advance in the modeling of nonisothermal flows, especially of the two-phase, steam-water phenomena. In this paper, the key processes associated with a geothermal energy reservoir are described and the current approaches are pointed out. The state-of-the-art of geothermal modeling is reviewed by comparing the governing equations, numerical methods, code availability, validations, and applications of several selected major existing models. The needs for further studies are discussed.
State-of-the-Art of Thermal Recovery Models
Authors: Farouq Ali S. M. , Ferrer J.
Published: November 2009

Thermal recovery models for oil recovery consist of steam injection and in-situ combustion simulators. At the present time, steam injection simulators have been developed to a point where it is possible to reliably simulate portions of a fieldwide flood. Cyclic steam stimulation simulation still entails a number of questionable assumptions. Formation parting cannot be simulated in either case. In-situ combustion simulators lack the capability for front tracking. Even though the models are rather sophisticated, process mechanism description and input data are inadequate.
Long-Distance, High-Volume Transport of Coal by Slurry Pipeline
Authors: Stripling T. E. , Holter R. G.
Published: November 2009

Several long-distance, high-volume coal slurry transportation systems are planned or proposed for the United States. These new systems offer a method of transport that is both economical and environmentally attractive. The design of these systems will be a challenge to the pipeline engineer since an integrated, system design of several components is necessary to achieve an optimum overall effect. The pipeline, pump stations, instrumentation and controls, slurry preparation, and utilization facilities must all be considered in the design. The purpose of this paper is to describe the system components of a large coal slurry transportation system in detail and to show the special design considerations required for the overall system design considering the interrelationships of the various components.
A Rate-Dependent Stress-Strain Relationship for Sea Ice
Authors: Wang Y. S.
Published: November 2009

A one-dimensional rate-sensitive stress-strain relationship is developed to describe the uniaxial mechanical behavior in compression for sea ice. It is a one-term, nonlinear model and is simpler in form than the nonlinear models proposed by other investigators. It contains four independent constants that are determined by experimental data. This model can describe the behavior of sea ice very well under constant strain rate loading, constant stress rate loading and creep loading conditions. In particular, it describes the following features of sea behavior: 1 the increase in ice strength with strain rate and with stress rate; 2 the increase in strain-softening effects with strain rate; 3 the relative difference between the strengths obtained by constant stress rate and constant strain rate tests; 4 the rate dependence of ice stiffness; 5 primary, secondary, and tertiary creep, where the duration and rate depend on the applied stress level. This paper presents the proposed rate-sensitive stress-strain relationship and discusses its behavior under various loading conditions. A set of coefficients has been selected to compare with test results under constant strain rates. Agreement between predicted and observed stress-strain behaviors is very good. Predicted behavior under constant stress rate and creep are also presented.
Application of Dual-Energy Gamma-Ray Technique for Nondestructive Soil Moisture and Density Measurement During Freezing
Authors: Ayorinde O. A.
Published: November 2009

Frost heave is a phenomenon unique to freezing soils. To study frost heave, a dual-energy gamma-ray technique has been adapted to determine nondestructively the soil bulk density variation and moisture migration that occur as the soil freezes and heaves. The technique uses two radioactive sources for simultaneous measurement of density and moisture content. Test results show good agreement between measured and calculated data for density and moisture content. The test data indicate that the dual-energy gamma-ray technique can accurately and reliably provide continuous nondestructive monitoring of both density and moisture content variations along a freezing soil column. Freeze front location can also be determined.
Properties of Air Leaving a Hydraulic Air Compressor (HAC)
Authors: Chen Li-Ting , Rice W.
Published: November 2009

An analysis is made of the diffusion-rate-controlled absorption of air into the water in the two-phase flow processes occurring in a hydraulic air compressor (HAC). The analysis enables calculation of the fraction of air absorbed, when implemented as an addition to an earlier computerized model for the flow in an HAC, which did not account for air absorption. Furthermore, the calculations account for oxygen and nitrogen absorption separately, and thus allow determination of the mole fraction of oxygen in the compressed air. Excellent agreement was found for the calculated results when compared with a single point of experimental data from a large, old HAC. It was found that the efficiency of low-head HAC is greatly decreased by the air absorption phenomena, while the efficiency of higher-head HAC is much less affected.
Behavior and Wear of Check Valves
Authors: Collier S. L. , Hoerner C. C. , Davila C. E.
Published: November 2009

Since check valves are often installed and forgotten, some guidance is needed for their installation so that maintenance can be minimized and scheduled. A study of their behavior over a wide range of flows when installed at various spacing from disturbances (elbow, swedges, pump discharge) was undertaken. Film taken through transparent pipes showed the action to be erratic. In order to obtain relative quantitative data, a large number of tests were run in which the wear was accelerated greatly by the use of very soft parts. These results are presented in a number of graphs. Operating behavior is compared to certain of the accelerated tests for comparison purposes, showing that the results offer reasonable guidance for planning and installing valves of this general type to minimize maintenance by good installation practices.
Estimation of the Mean Velocity of Acoustic Signal Propagation for Sea Operations
Authors: Menck H. C.
Published: November 2009

A representative velocity profile and a priori bathymetric information about possible undersea device depths are the only data required to generate coefficients for a three-dimensional quadric polynomial surface which then expresses an accurate estimate of the mean velocity of acoustic signal propagation as a function of measured travel time and receiver depth. The resultant polynomial estimator is easily implemented in real-time navigating, station keeping, and undersea device tracking software to account for the variable refraction effects on mean velocities encountered in raypath trajectories that extend from the vertical out to and including the limiting direct raypaths.
Field In-Ice Pressure Sensor Response Tests
Authors: Chen A. C. T. , Templeton J. S.
Published: November 2009

An ice pressure sensor has been designed and built at Exxon Production Research Company (EPR) to measure the pressure in an ice sheet. Laboratory and analytical studies were performed to establish a data reduction procedure to relate the pressure sensor output to the pressure in the ice sheet. However, because of the complex mechanical behavior of sea ice, the present experiment was conducted to validate this data reduction procedure. The validated procedure is considered applicable to a broad class of embedded ice pressure sensors. Field in-ice pressure sensor response tests were conducted near Prudhoe Bay, Alaska, between February and April of 1978. Twenty-two tests were conducted on three test blocks of ice to investigate the in-ice response of three ice pressure sensors. An ice block measuring 10 ft by 20 ft and of full thickness of the natural annual ice was cut free from the surrounding ice sheet after the pressure sensor was installed at the center of the block. This ice block was loaded by an in-situ hydraulic ice loading device capable of delivering approximately two million lb of load. The pressure sensor output and the test load were monitored continuously during each test so that the pressure sensor output could be compared directly to the corresponding applied pressure. The test results indicated ratios of applied ice pressure to measured sensor pressure within the range hindcast by theoretical analysis.
Sway-Added Mass and Impact Load of a Large Tanker to a Jetty in Shallow Water
Authors: Kim C. H.
Published: November 2009

This paper presents a new simple technique for evaluating sway-added mass and the impact energy absorbed by fenders and dolphins when maneuvering a tanker to a jetty in a shallow water environment. The technique is based on the law of energy conservation, i.e., that the kinetic energy of the berthing ship is totally absorbed by the fenders during the compression phase. A time-averaged zero-frequency sway-added mass in shallow water is used in the evaluation of the kinetic energy. The theoretically calculated values of maximum deflection and fender loads are presented and compared with available experimental and analytical data. Discussion of the present method with respect to its degree of practical usefulness is given, while indicating problem areas.
Flow-Induced Motions of Multiple Risers
Authors: Overvik T. , Moe G. , Hjort-Hansen E.
Published: November 2009

Vortex-induced and galloping vibrations of flexible risers in steady, uniform currents have been investigated. The cross sections consisted of a bundle of pipes tied together to form a so-called multiple production riser, see Fig. 3(b). The tests have been carried out in a wind tunnel at subcritical Reynolds numbers, using spring-mounted sectional models. The tests used the single tube case as a reference case, and the results indicated increased motions for all of the multiple configurations compared to the reference case. For some cases, vortex-induced motions gave the largest excursions, for others galloping. Crude calculations indicate that a typical 400-m depth riser configuration would experience significant galloping motions as well as vortex-induced motions in steady, uniform currents at 0.5 m/s or less.
Nonlinear Response of Reinforced Concrete Slabs Represented by Beam Grids
Authors: Morrison D. G.
Published: November 2009

The objective of this paper is to present a grid model for the nonlinear analysis of plates. The model, composed of a grid of beam elements responding in flexure and torsion, is described in the following sections. To verify the modeling approach, calculated and measured response to two plate-column connections are compared. This comparison follows a description of the grid model, and an explanation of the tested connections. The connections are of reinforced concrete, differing in slab reinforcement ratio, and the modeling accounts for a number of nonlinearities. By modeling the plate as a grid of beam elements, relatively simple stress-analysis programs may be used to approach the nonlinear behavior in a series of linear steps. Reinforced concrete slabs have been proposed in various offshore structures, such as floating concrete platforms [1] and LNG offshore structures [2], and the response into the nonlinear range is of importance.
Experimental Study of Hydraulic Fracturing in an Impermeable Material
Authors: Rubin M. B.
Published: November 2009

A laboratory experiment was conducted to study hydraulic fracturing in an impermeable material (PMMA). Quantitative experimental data were obtained to compare with numerical predictions for a simple hydraulic fracture treatment that is not complicated by the effects of fluid leak-off and proppant transport. The borehole pressure, the pressure in the fracture at three locations, the fracture width at one location, and the fracture length were measured as functions of time during propagation of a vertically contained hydraulic fracture. The experimental data are compared with the predictions of simple solutions and the results indicate that when the finite width of the laboratory model is included in the analysis, the comparison between theory and experiment is quite good. The results also indicate that the assumption of a uniform pressure distribution in the fracture is adequate to accurately predict the critical parameters (fracture width and length) even when the fracturing fluid is very viscous.
Rock Bit Cutter Tooth Design and Analysis
Authors: Feng G. C. , Schumacher P. W.
Published: November 2009

The finite element method was used to analyze the stresses in a rock bit cutter tooth under applied loads. Detailed finite element models were constructed to allow accurate descriptions of the structural material properties of a tooth design which includes carburization and hardmetal application. Numerical solutions were obtained for investigating stress concentrations and plastic region growths in a cutter tooth when loaded beyond its yield point. It was found that the finite element method can be a powerful tool for improving the performance of a cutter tooth. Design objectives can be achieved through parameteric studies of stress level variations against geometry and material property changes on a computer system.
A Side Wall Burn Model for Cavity Growth in Underground Coal Gasification
Authors: Eddy T. L. , Schwartz S. H.
Published: November 2009

A mechanistic computer model is presented which predicts the 3-D cavity growth during the gasification phase of underground coal gasification. Developed for swelling bituminous coals, the model also obtains reasonable cavity width and length values for shrinking sub-bituminous coals. The model predicts cavity shape and burn-through times based on the coal properties, seam thickness, water reacting and the interwell distance. Employing a 2-D boundary layer model to determine the convective diffusion rate of oxygen to the reacting walls, it is found that natural convection diffusion must be included. The model includes flow in the injection region, the swirling, mixing effect in the cavity, and transitions from thick to thin seam geometry. Simulations of the Hanna II, Phase 2 and Pricetown I field tests, as well as a parametric study on Pittsburgh seam coal, are presented.
Shallow Magnetic Induction Measurements for Delineating Near-Surface Hot Groundwater Sources in Alaskan Geothermal Areas
Authors: Osterkamp T. E. , Kawasaki K. , Gosink J. P.
Published: November 2009

Variations in the electrical conductivity of a soil and water system with temperature and salt concentration suggest that a soil containing hot and/or saline groundwater may be expected to have a higher conductivity compared to a cooler and/or less saline system. Temperature and conductivity surveys were carried out at Pilgrim Springs, on the Seward Peninsula, and at Chena Hot Springs, near Fairbanks, to test the use of a magnetic induction method (which measures electrical conductivity) for delineating near-surface hot groundwater sources in geothermal areas surrounded by permafrost. Comparison of the temperature data and conductivity data from these surveys demonstrates that the conductivity anomalies, as measured by the magnetic induction method, can be used to define the precise location of hot groundwater sources in these geothermal areas with the higher temperatures correlating with higher values of conductivity. Magnetic induction measurements of conductivity can also be used to define the lateral extent of the thawed geothermal areas (used for calculating the stored energy) in permafrost terrain. The utility of these magnetic induction measurements of conductivity for reconnaissance geophysical surveys of geothermal areas is that a much greater density of data can be obtained in a shorter time in comparison with shallow temperature measurements. In addition, it is simpler, cheaper and easier (physically) to obtain the data. While conductivity anomalies can result from other than hot and/or saline groundwater, these conductivity data, when coupled with a few measured temperature profiles and groundwater samples, should result in reliable reconnaissance level geophysical surveys in Alaskan geothermal areas.
Underground Coal Gasification Research
Authors: Harloff G. J.
Published: November 2009

Recent successful field tests of underground coal gasification, UCG, have demonstrated the potential for UCG commercialization. This paper presents results of mathematical modeling and laboratory research studies which have been conducted to improve our understanding of the complex processes involved. These studies include: cavity growth including resource recovery, gas composition, and subsidence. Both single and multi-module results are presented.
Stresses in Stiffened Tubular T Joint of an Offshore Structure
Authors: Shiyekar M. R. , Kalani M. , Belkune R. M.
Published: November 2009

The effect of internal ring stiffeners has been studied theoretically and experimentally for the welded tubular T joints occurring in conventional jacket-type offshore structures. Four welded tubular joint models of T shape, with different diameter ratios, have been tested under axial loading in the branch. The analytical results have been obtained by finite element technique. The results indicate a significant reduction in the stress concentration factor and a fairly uniform transfer of load from branch to the chord. A simplified analysis of stiffener rings have been proposed. The stress results of joints strengthened by ring stiffeners and joint can are compared.
Fatigue Strength of Welded Tubular T Joints Under Variable Amplitude Loading
Authors: Kawahara M. , Katoh A. , Iwasaki T.
Published: November 2009

This paper describes an experimental study on fatigue strength of welded tubular T joints, performed in small and large-scale models fabricated from mild steel tubes. Fatigue tests were conducted under three kinds of loading patterns: constant amplitude loading, block programmed loading and random loading. In block programmed loading tests, the period of load sequence was varied, while the load spectrum was the same. Thus, the effects of the difference in load sequences upon fatigue lives were examined independently from the effect of load spectrum. Crack initiation life was hardly affected by the load sequence patterns. However, the crack penetration life or failure life were largely affected by types and periods of load sequences. The limit of validity of the Miner’s rule are discussed together with possible interpretations on the effects of the difference in load sequence patterns.