bluuebunny/crossref_metadata_2025 huggingface dataset:
Cross-Flow Vibrations of a Pipe Close to a Rigid Boundary
Authors: Jacobsen V. , Bryndum M. B. , Nielsen R. , Fines S.
Published: November 2009

The paper describes the results of a model test series with the purpose of determining the hydroelastic vibrations of a nearbed pipeline span exposed to flow conditions created by steady current, waves and waves superimposed on steady current. The study has been conducted using a model composed of a spring-mounted rigid pipe segment and a flat plate simulating the sea bed. The hydroelastic cross-flow vibrations of the pipe segment are presented as function of the flow velocity, flow condition (waves and/or steady current) and the relative distance of the pipe to the seabed. A simple approach to analyze the vibrations caused by an irregular wave train is presented.
Vortex-Induced Strumming Vibrations of Marine Cables With Attached Masses
Authors: Griffin O. M. , Vandiver J. K.
Published: November 2009

Twenty full-scale test runs were conducted during the cable strumming experiments reported in this paper. These consisted of ten pairs of equivalent tests conducted in air and in water with a cable fitted with arrays of attached masses. The measured in-air natural frequencies are in good agreement with computed code predictions for the second and higher (up to n = 5) cable modes. The first mode frequency apparently was influenced by the sag of the cable. The measured mode shapes of the cable vibrations in water also are in agreement with the computed mode shapes. For the experiments in water the computed and measured natural frequencies are in good agreement. Drag coefficients in the range CD = 2.4 to 3.2 were commonly observed when the cable-attached mass system was strumming due to the water flow past it.
Time Series Simulations of Wide-Band Spectra for Fatigue Tests of Offshore Structures
Authors: Lin N. K. , Hartt W. H.
Published: November 2009

A time-series simulation method, based on the principle of time series modeling for dynamic systems, is used to reproduce a wide-band stress history from a prescribed stress spectral model for fatigue testing of offshore structures. The optimization procedures and stability of the time series model for the prescribed spectrum are presented and discussed. The optimization procedures are developed on the basis of the Levison-Durbin algorithm, which usually produces a stable time series model if the order of the time series model is even. An example is presented to demonstrate the applicability of the proposed method to long-time, high-cycle fatigue testing.
Comparison of Stress Distributions in a Simple Cast Tubular Joint Using 3-D Finite Element, Photoelastic and Strain Gage Techniques
Authors: Fessler H. , Edwards C. D.
Published: November 2009

Combined strip and rosette gage measurements and results from three-dimensional, finite element calculations are in excellent agreement with frozen stress photoelastic results for an efficient shape of cast-steel node under axial, brace loading. Three different meshes showed that two layers of elements through the thickness are needed.
A Study of Frost-Heave Mechanics of High-Clay Content Soils
Authors: Yong R. N. , Boonsinsuk P. , Tucker A. E.
Published: November 2009

In this study, the problem of frost penetration in high-clay content soils is examined with the view to assessment of cyclic freeze-thaw effects on initial virgin unfrozen natural clays. The requirements for control of the frost-heave problem in many construction projects in the northern regions of Eastern Canada demand that proper prediction be made for both frost-heave pressures and magnitudes of frost heaving in the high-clay content soils. Laboratory cyclic freeze-thaw and frost-heave tests conducted have shown that the mechanical properties of the clay soils, which are virgin unfrozen natural soil samples obtained from Northern Quebec, are sensitive to cyclic freeze-thaw. In the cyclic freeze-thaw tests conducted, scanning electron micrographs taken from samples after various cycles show that the original soil fabric becomes more disturbed after the first few cycles. Particles are re-arranged, and a regrouping of particles into larger stable (or apparently stable) soil fabric units are formed after a certain number of cycles. In essence, this study provides the experimental information concerning the cyclic freeze-thaw effects on mechanical properties for some high-clay content soils, not initially subject to freezing.
Ice Force Prediction Based on Strain-Rate Field
Authors: Bruen F. J. , Vivatrat V.
Published: November 2009

The mechanical behavior of sea ice has been found to be strongly dependent on the deformation rate. Consequently, prediction of ice load on arctic structures must include an adequate consideration of the deformation rate and its effects on the ice behavior. Analytical work for ice load prediction has to date been concentrated on obtaining stress fields around the structure, satisfying an “average” strain-rate dependent strength of ice. In other words, the stress field and the strain-rate field are not directly related. Consequently, there is a gap in understanding the relationship between ice loads and ice deformation. This shortcoming has been recognized, and in the last two years, large-scale field experimental programs have been conducted to measure the deformation pattern and rate around large indenters and an actual offshore island. This paper illustrates a procedure by which the strain-rate dependent mechanical properties of ice can be directly integrated into the force prediction method. This method assumes that the strain-rate field around the structure can be estimated from field measurements and relies on the bound theorems of creep analysis. This paper concentrates on a nonimpact condition in a uniform landfast ice field. The load scenario considered is one of initial breaking out. The effects of nonhomogeneities in the ice field are not included.
Characteristics of Digging Depth With Air-Bubble Water Jet
Authors: Ohnishi M. , Miyamoto T. , Arioka R.
Published: November 2009

For burying submarine cables under a seabed by a water jet cable burier, it is important to improve digging depth of water jet. This paper discusses digging properties with air-bubble water jet, and clarifies the relation between digging depth and water jet parameters such as traverse speed of nozzle Vn (m/s), air content ratio C, and jet momentum per unit time M (N). It is found from experiment results that the digging depth H* (m) is represented by H*=(1+0.26C0.65)(10.31−4.54Vn)M0.44×10−2.
Collapse of Oil Well Casing With Ovality
Authors: Pattillo P. D. , Huang N. C.
Published: November 2009

The nonlinear response and eventual collapse of an initially imperfect cross section of a cylinder of infinite length is analyzed. The cylinder is loaded by external pressure and axial load and is intended to model oil well casing in a service environment. Results from the analysis agree well with experimental data and provide an interesting alternative to current empirical/statistical methods for determining the minimum collapse resistance of casing for use in design calculations.
Finite Element Modeling of the Response of Long Floating Structures Under Harmonic Excitation
Authors: Georgiadis C.
Published: November 2009

The response of long floating structures to a harmonic excitation is the basis for the response calculation in a short-crested wave field. This paper will present consistent formulas for obtaining the nodal loads in a finite element analysis. The accuracy of the method used is compared with the results obtained using a Rayleigh-Ritz approximation of the response with continuous eigenfunctions. The error of using an irrational finite element model is demonstrated for comparison, and to indicate to designers of similar structures the large effects which they may be overlooking.
Stochastic Modeling and Data Analysis of a Prototype Wave Energy Convertor
Authors: Conroy J. , Dooley T. , McNamara J. F.
Published: November 2009

This study describes the application of the techniques of stochastic modeling to random data obtained from the sea trials of the wave energy device Kaimei, and the interpretation of the results in terms of device efficiency. Two models of the power absorption system are developed and the relationships derived between them yield information on the influence of the vessel motions on the absorbed power. The theory of multiple frequency response functions is applied to the data, and it is shown that the motions of the Kaimei have a detrimental effect on its energy absorption capacity and the reasons for this are investigated.
Deterioration of Floating Ice Covers
Authors: Ashton G. D.
Published: November 2009

The deterioration of floating ice covers is analyzed to determine under what conditions the ice cover loses strength due to internal melting. The analysis considers the interaction between sensible heat transfer and long wave radiation loss at the surface, the surface albedo, the short wave radiation penetration and absorption and the unsteady heat conduction within the ice. The thermal analysis then leads to a determination of the porosity of the ice that allows strength analysis to be made using beam-type analyses. The results provide criteria to determine when and how rapidly the ice cover loses strength and under what conditions it will regain the original strength associated with an ice cover of full integrity.
Dynamics of a Pipe Aspirating Fluid Such as Might be Used in Ocean Mining
Authors: Paidoussis M. P. , Luu T. P.
Published: November 2009

This paper presents an investigation into the dynamics and stability of a long, vertically disposed, cantilevered pipe, submerged in and aspirating fluid from the free lower end, and conveying it upwards to the supported upper end; the pipe has a large mass attached to its free end. The arrangement represents an idealization of an ocean mining system. This paper reports on the first phase of this work, in which the following simplifications have been made: (i) the pipe is straight at equilibrium; (ii) the effects of marine currents and wave action are not considered. It is shown that under the action of the internal flow, the system is inherently unstable, by flutter, and that it does not lose stability at vanishingly small flow velocities, only because of dissipation, through friction with the external fluid medium. Effective passive stabilization of the system may be achieved through artificial augmentation of this form of dissipation.
A Review of Explicit Friction Factor Equations
Authors: Zigrang D. J. , Sylvester N. D.
Published: November 2009

A review of the explicit friction factor equations developed to replace the Colebrook equation is presented. Explicit friction factor equations are developed which yield a very high degree of precision compared to the Colebrook equation. A new explicit equation, which offers a reasonable compromise between complexity and accuracy, is presented and recommended for the calculation of all turbulent pipe flow friction factors for all roughness ratios and Reynold’s numbers.
Stability of a String in Axial Flow
Authors: Triantafyllou G. S. , Chryssostomidis C.
Published: November 2009

The equation of motion of a long slender beam submerged in an infinite fluid moving with constant speed is derived using Hamilton’s principle. The upstream end of the beam is pinned and the downstream end is free to move. The resulting equation of motion is then used to perform the stability analysis of a string, i.e., a beam with negligible bending stiffness. It is found that the string is stable if (a) the external tension at the free end exceeds the value of a U2, where a is the “added mass” of the string and U the fluid speed; or (b) the length-over-diameter ratio exceeds the value 2Cf/π, where Cf is the frictional coefficient of the string.
Adaptive Prediction of the Motion of Marine Vehicles
Authors: Jefferys E. R. , Samra B. S.
Published: November 2009

A predictor of the future motion of a vessel subject to random wave and wind forces, would have a variety of applications in ocean engineering. Most previous work has assumed that the wave spectrum is known and that the vessel is modeled accurately; both factors affect the predictor performance strongly. In practice, the relevant data is difficult to measure on a manoeuvering vessel and can change significantly with operating conditions. Here were describe the application of an adaptive algorithm which predicts the future of a signal from its history. The predictor adapts to the signal and varies its parameters to optimise the prediction. Operating on a signal with a stationary spectrum, the predictor tends to a steady performance; if the spectrum changes, the predictor quickly adjusts to the new situation. We illustrate the performance of the system with examples.
Vertical Relative Motion Between Two Adjacent Platforms in Oblique Waves
Authors: Kim C. H. , Fang M. C.
Published: November 2009

The paper presents a strip theory and its correlation with experiment and analysis on the relative motions of two ships. The ships are in close proximity and in parallel position in oblique waves. The two-dimensional procedure takes account of the hydrodynamic interaction between two cylindrical bodies. It was found that the strip method is a useful technique to predict the hydrodynamically coupled motions of two ships.
Experimental Study on Wave-Induced Structural Responses of Semisubmersibles
Authors: Yoneya T.
Published: November 2009

This paper describes experimental studies on the motion, mooring tension and structural responses of a typical semisubmersible in regular waves. A 1/50-scale structural dynamic model of two-pontoon type was made of acryl and the tank tests were carefully carried out. The measured platforms motions of the model were compared with calculations and close agreement was obtained. As to the structural responses the measured values of the test model agree approximately with the calculated results of a full-scale model. The close experimental results of structural responses presented here are expected to be valuable for the design of similar types of semisubmersibles.
In-Ice Calibration Tests for an Elongated, Uniaxial Brass Ice Stress Sensor
Authors: Johnson J. B.
Published: November 2009

An elongated, uniaxial brass ice stress sensor has been developed by the University of Alaska and used in several field experiments. Laboratory calibration tests have been conducted, in a 60 × 29.5 × 8.5 in. (1524 × 750 × 216 mm) ice block into which the sensor was frozen, to determine the sensor’s response characteristics. Test results indicate that the sensor acts as a stress concentrator with a stress concentration factor of 2.4 and transverse sensitivity of −1.3 at stresses below 30 lbf/in2 (207 kPa). At stresses greater than 30 lbf/in2 (207 kPa) the stress concentration factor increased and the sensor exhibited a time delay response to load. Differences of 22 percent were measured between the measured sensor stress immediately after a constant ice load was applied and the asymptotic stress limit. Interpretation of measured sensor stresses can be considered reliable at ambient ice stress levels below 30 lbf/in2 (207 kPa).
Ice Sheet Indentation Resistance in the Creep Domain
Authors: Ladanyi B.
Published: November 2009

The force exerted by a moving ice sheet on an offshore structure is known to vary strongly with the geometrical conditions at the contact with the structure and with the rate of ice movement, resulting in a wide spectrum of failure modes including both in-plane and out-of-plane failures of either brittle or plastic type. In this paper attention is concentrated to only one limiting case, in which the ice sheet moves so slowly that no fracture occurs at the contact with the structure, but the ice undergoes only in-plane creep deformations.
Vortex-Induced Vibration and Drag Coefficients of Long Cables Subjected to Sheared Flows
Authors: Kim Y.-H. , Vandiver J. K. , Holler R.
Published: November 2009

The vortex-induced vibration response of long cables subjected to vertically sheared flow was investigated in two field experiments. In a typical experiment, a weight was hung over the side of the research vessel by a cable that was instrumented with accelerometers. A typical experiment measured the acceleration response of the cable, the current profile, the tension, and angle of inclination at the top of the cable. Total drag force was computed from the tension and angle measurements. Two braided Kevlar cables were tested at various lengths from 100 to 9,050 ft. As a result of these experiments, several important conclusions can be drawn: (i) the wave propagation along the length of the cable was damped, and therefore, under most conditions the cable behaved like an infinite string; (ii) response spectra were quite broad-band, with center frequencies determined by the flow speed in the region of the accelerometer; (iii) single mode lock-in was not observed for long cables in the sheared current profile; (iv) the average drag coefficient of long cables subjected to sheared flow was considerably lower than observed on short cables in uniform flows; (v) the r.m.s. response was higher in regions of higher current speed. A new dimensionless parameter is proposed that incorporates the properties of the cable as well as the sheared flow. This parameter is useful in establishing the likelihood that lock-in may occur, as well as in estimating the number of modes likely to respond.
Time Domain Simulation of Ship Steering Gear Control Systems
Authors: Reid R. E. , Zheng J. Y.
Published: November 2009

Considering the effects of oil compressibility, leakage, hydrodynamic damping and friction, in addition to other nonlinearities, such as bang-bang relay, pump saturation and limiters of oil pressure and pump flow, the performance of five different types of ship steering gear control systems are examined using digital computer simulation techniques. Three of the controllers examined are “bang-bang” controllers, while the remaining two are “analog”. The behavior and performance of the various systems on three ship configurations are compared. It is shown that the analog steering gear controllers can be expected to demonstrate superior performance of the ship/steering system in calm water operations.
A Nonlinear Compaction Model for Sandstone
Authors: Fahrenthold E. P. , Gray K. E.
Published: November 2009

Constitutive relations for the compaction behavior of porous sandstone have been formulated to describe the results of uniaxial and triaxial tests under reservoir pressure and temperature conditions. An expression for loading behavior in uniaxial compression is derived by treating the loading modulus as an independent variable. Similar relations are derived for uniaxial and triaxial compaction tests. Elastic unloading takes a quadratic form when described by incremental stresses and strains. The constitutive equations relate the values of the incremental stress and strain on loading and unloading using parameters that are a function of the state of prestress in the material. Published data on samples cored from three different wells at various depths exhibited a similar dependence of rock properties on mechanical and pore pressure loads.
Frictional Flow Properties of Coal-Oil Slurries at Low Reynolds Number
Authors: Beans E. W. , Masiulaniec K. C.
Published: November 2009

The pipe friction factor (f) and the pressure loss coefficient for a 90-deg EL (K90) were measured for coal-oil slurries at Reynolds numbers less than 100. A range of mass fractions (0 to 0.4) was examined for a single particle distribution. The pipe friction factor correlated well with the established relationship for laminar flow (f = 64/ReD) where Reynolds number is based on slurry properties. The loss coefficient for the elbow has a similar correlation.
Some Factors Influencing Iceberg Scour Estimates
Authors: Prasad K. S. R. , Chari T. R.
Published: November 2009

The phenomenon of seabed scouring by icebergs is a major threat to buried structures on the Canadian East Coast and is of immediate concern to the petroleum operators. The design of a suitable production and transportation system for the development of the Hibernia field is very much influenced by the potential size of iceberg scours. Several factors influence the theoretical estimates of scour size and some of these have been discussed in the mathematical and laboratory models proposed earlier. In this paper, an appraisal is made of the potential error in iceberg scour predictions caused by assuming a linear velocity variation during scour. The influence of an initial penetration of the iceberg prior to scour is examined. Upper and lower bounds of initial penetration depths are shown to exist which influence the resulting scour type.
The Effect of Moisture on the Structural Stability of a Coal Cavity
Authors: Mortazavi H. R. , Emery A. F. , Corlett R. C. , Lockwood W. R.
Published: November 2009

The drying of coal and the associated thermal and moisture-induced stresses are examined with a numerical model to estimate the rate of surface regression in underground coal gasification. The model includes internal convection, diffusion, conduction and flow of liquid, vapor and gas. The structural failure is modeled by three different mechanisms based upon a strength reduction due to heating, drying, or crack formation. Using properties and boundary conditions appropriate to Western United States coal, the model predicts a regression rate which is in qualitative agreement with measured results. Using the model, it is possible to examine different thermal and failure modes and to gain an understanding of some of the mechanisms which may control the surface regression of coal during gasification. These results may be applicable to the formation of rubble during gasification and to internal cavity collapse.
A Numerical Study of Turbulent Axisymmetric Jets Flowing Into Closed Tubes
Authors: Amano R. S.
Published: November 2009

A numerical study is reported on the turbulent jet flowing into closed tubes. In the computation the finite volume method is employed to solve the continuity and momentum equations with the use of the second-order closure model of turbulence. The computations were made for tube depths and tube widths ranging from 2 to 30 jet diameters and from 2 to 8 jet diameters, respectively. The computed decay of the jet centerline velocity agrees reasonably well with the experimental data (within 10 percent). With the use of the second-order closure model, it became clear that an isotropic assumption is still valid in the main mixing region in the tube. Moreover, the wall shear stress distributions were obtained along the side wall of a tube. Finally, it was found that the terminal stagnation pressure at the tube bottom depends strongly on the diameter of the tube for DT/DN of less than 5.
Life Models for Small-Diameter Polycrystalline Diamond Compact Bits in Hard Abrasive Media
Authors: Hough C. L. , Das B. , Rozgonyi T. G.
Published: November 2009

Mathematical models for bit life of polycrystalline diamond compact (PDC) drill bits were developed for drilling small holes in hard abrasive media. Based on the wear-out criterion of an average 0.060 in. (1.5 mm) flank wear land, bit life equations were formulated in three forms: bit life versus rotary speed and feed rate, bit life versus rotary speed and penetration rate, and wear rate versus cutting speed and cutter engagement area. The traditional linear-logarithmic model proved inadequate to describe bit life, whereas the quadratic-logarithmic model provided the best bit life prediction equation. Consequently, it would be possible to predict the optimum economical drilling conditions more accurately by employing a quadratic-logarithmic based bit life equation. The equation demonstrated the ability to predict the bit life precisely under different modes of wear.
The Thermal Conductivity of Oil Sands Using a Transient Method
Authors: Hanafi A. , Karim G. A.
Published: November 2009

Measurements have been made of the effective thermal conductivity of some samples of oil sands using a transient technique over the relatively wide temperature range of −100°C to 200°C at atmospheric pressure. These results included samples in which the bitumen content was deliberately altered from the natural values. The thermal conductivity values tended to increase as the temperature was lowered. However, these values were relatively unaltered in the temperature range below 0°C. The thermal conductivity values appear to be influenced by variation in the oil content of the sample and whether the sample was from naturally occurring oil sands or artificially prepared with the same nominal oil concentration in the sand.
Free Convection From a Vertical Plate With Nonuniform Surface Temperature and Embedded in a Porous Medium
Authors: Gorla R. S. R. , Zinalabedini A. H.
Published: November 2009

A procedure is described for the calculation of heat transfer due to free convection flow along a vertical plate embedded in a porous medium with an arbitrarily varying surface temperature. By applying the appropriate coordinate transformations and the Merk series, the governing energy equation is expressed as a set of orindary differential equations. Numerical solutions are presented for these equations which represent universal functions and the surface gradients of these universal functions are tabulated. Several computational examples are provided and the results are compared with published data in the case of two examples.
Natural Convection of Non-Newtonian Fluids About a Horizontal Surface in a Porous Medium
Authors: Chen H. T. , Chen C. K.
Published: November 2009

The problem of natural convection of a non-Newtonian power-law fluid about a horizontal impermeable surface in the porous medium is considered, where the plate is assumed with a nonuniform heat flux distribution. The present study is based on the boundary layer approximation and only suitable for a high Rayleigh number. Similarity solutions are obtained by using the fourth-order Runge-Kutta method and the Nachtsheim-Swigert iteration scheme. The effects of the nonuniform wall heat flux qw(x) and the new power-law index n on the heat transfer characteristics are discussed.
A Thermodynamically Based Model for Ash Fusion Temperature
Authors: Rhinehart R. R. , Attar A. A.
Published: November 2009

This paper describes a thermodynamically based correlation between coal ash fusion temperatures and ash composition. A wide range of data from the literature was used to obtain the values of model parameters. A seven-parameter correlation is proposed which permits predicting the ash fusion temperature with a standard error ± 65°C or better.
A Laboratory Study of Two Straddle-Packer Systems Under Simulated Hydrofrac Stress-Measurement Conditions
Authors: Evans K.
Published: November 2009

The mechanical behavior of two straddle-packer systems subjected to pressure histories which replicated hydrofracture stress-measurement procedures has been investigated. The systems were pressurized in borehole simulators consisting of lengths of steel casing instrumented with strain gages. From the strain histories, the stresses applied to the casing by the packer elements could be calculated. The systems studied differed in the manner in which the packer elements were coupled; in one system the packers were rigidly coupled end-to-end (rigid coupling), whereas in the other, the tops of the two packers were rigidly coupled leaving the bottom of the upper packer free to slide on the mandrel (sliding coupling). The elements that featured in the two systems were also greatly different. The results indicate that the sliding coupling system tested exhibited nearly ideal behavior up to the maximum interval pressure attained in the tests of 25 MPa. This is accredited to intrinsic superiority of the sliding coupling design.
The Development Study of a Centrifuging Technique for Oilfield Production Pit Closure
Authors: Osterman M. C. , Wojtanowicz A. K. , Field S. D.
Published: November 2009

A full-scale study was performed of a centrifuge-based process for dewatering oilfield production waste sludges in order to investigate an application of the process to an oilfield production pit closure. Full-scale experiments were performed to analyze the centrifugal sedimentation of both raw and chemically destablized production pit sludge. The two-stage process was tested: primary solids removal by centrifugal classification followed by chemical conditioning and dewatering. Also, full-scale tests were run to understand the effects of the fundamental centrifuging parameters (the bowl-scroll differential speed and the centrifugal force) on the composition and quality of the dewatering products. The concentration of metals in the production pit sludge, before and after dewatering, was analyzed in terms of the present environmental regulations. The removal of heavy metals from the centrifuge overflow was also evaluated. This study provided qualitative information on how to design an on-site, centrifuge-based system for oilfield production pits closure. The system yielded up to 60 percent volume reduction, the solids-free effluent, and the low-moisture (42 percent vol.) cake discharge. The side-product of the process was an oily, low-solids emulsion (skim layer). The study revealed a technique for minimizing the skim layer through a compromise between the centrifugal force and the differential speed.
Collapse of Deepwater Pipelines
Authors: Yeh M. K. , Kyriakides S.
Published: November 2009

The paper describes a series of full-scale collapse experiments using X-42 and X-65 grade steel tubes. The initial geometric imperfections of the tubes were measured using a specially designed scanning facility prior to collapsing them under external pressure. Geometric deviations from a circular shape were recorded at 90 points around the circumference. The wall thickness was also recorded at the same points. At least 31 circumferential scans were made over lengths of 9 diameters. The stress-strain characteristics in the axial and circumferential directions were measured for each tube. The measured parameters were used to calculate numerically the collapse pressures of the tubes. The biggest deviation between the experimental and calculated values was less than 8 percent. These are compared with the results obtained from the same analysis using various idealized imperfection measures.
Critical Mass Flow Gas Meters—The Role of Errors due to the Presence of a Restriction Downstream
Authors: Teodorczyk A. , Karim G. A. , Tawfiq H.
Published: November 2009

An analysis, supported by experiment, is presented of the performance of a typical critical flow meter having a restriction in the form of another nozzle or orifice downstream of its discharge. Guidelines are then presented to establish the conditions for guarding against errors arising in such an arrangement.
Technoeconomic Model for Offshore Supply Operations
Authors: Rahman S. S.
Published: November 2009

The vital role of logistic support for maintaining uninterrupted drilling operations is well known to offshore petroleum engineers. Moreover, its importance is growing as exploration and production activities are extended to progressively deeper water and harsher weather conditions. However, no systematic approach for ensuring effective logistic support has yet been realized. A method of studying the characteristics of logistic support and of designing a system for securing effective supply to an offshore rig is proposed. It is based on event simulation modeling of offshore supply operations, together with more conventional technical and economic models for yielding economic criteria which take into account a possible interruption of drilling operations. The method has been developed through a detailed investigation of each component of the supply operation and of the inherent problems. To evaluate the feasibility of the approach, an example has been provided.
Analysis of Transient Gas-Liquid Two-Phase Flow in Pipelines
Authors: Kohda K. , Suzukawa Y. , Furukawa H.
Published: November 2009

A new method is developed to analyze transient gas-liquid two-phase flow in natural gas pipelines. This method utilizes the two velocity mixture model to derive the basic equations. Also, a new model, which expresses phase conditions for multicomponent natural gas-condensate system, is presented to derive mass conservation equations for each hypothetical component. Transient air-water two-phase flow experiments were conducted using a test pipeline 105.3 mm in diameter and 1436.5 m long. Experimental conditions include, increasing or decreasing air flow rate with constant water flow rate, and transition from single-phase air flow to air-water two-phase flow. Experimental data were compared with calculated results, and the agreement was very good. Furthermore, calculated results agreed very well with a published field data.
Thermal Modeling of POL Bulk Storage Tanks
Authors: Hodge B. K.
Published: November 2009

A lumped-mass surface-temperature thermal model for POL (petroleum, oil, lubricants) bulk storage tanks is developed. The model utilizes twelve ordinary, coupled, first-order differential equations, obtained from energy balances, to describe the time-dependent variation of the surface temperatures (top and eight wall segments) of a partially filled POL tank. One-dimensional transient conduction in the soil is considered below the tank. Convective heat transfer and direct and diffuse irradiation are modeled as energy transfers into/out of the twelve lumped masses. The model is implemented in a computer simulation. Comparisons of the predicted tank surface temperatures with the available data show that the correct trends and salient features are predicted. In most instances predicted and measured temperatures agree within a few degrees centigrade. Preliminary model performance indicates that the technique incorporates much of the correct physics and is capable of being developed into a reliable predictive model. Recommendations are made for further development and validation.
Development of High-Strength Steel Plates for Low-Temperature Use
Authors: Nakano Y. , Saito Y. , Amano K. , Koda M. , Sannomiya Y. , Kobayashi E.
Published: November 2009

This paper describes the metallurgical approaches for producing 415MPa and 460MPa yield strength offshore structural steel plates and the mechanical properties of the steel plates and their welded joints. A thermo-mechanical control process (TMCP) was adopted to manufacture YP415MPa and YP460MPa steel plates with weldability comparable to conventional YP355MPa steel plates. The Charpy impact and CTOD tests of the steel plates and their welded joints proved to be very good.
Modeling Rate Effects and Cyclic Loads With the Pressuremeter
Authors: Cosentino P. J. , Briaud J.-L. , Terry T. A.
Published: November 2009

A relatively new tool, the cone pressuremeter (CPMT), was used in order to evaluate its usefulness in predicting the effects on soil due to various rates of loading and to repetitive loading. Field tests were conducted in two phases. The first phase included 24 CPMT tests, at the Texas A&M University research annex, which were designed to show 1) if the CPMT could be used to predict the effects on the soil due to both rate effects and repetitive loads; and 2) if the CPMT should be inserted into a prebored hole to the desired test depth or if the CPMT should be driven to the desired test depth. The soils at the research annex were a clay and a sand. The second phase included 32 CPMT tests at three sites throughout the state of Texas. Two of the sites were clay and the third site was sand. The CPMT test used at these sites was devised so that both rate effect and cyclic effect could be determined from a single test. Rate effects on the soil modulus were modeled using a viscoelastic model of the form EstEso=ttto−ncrp(1) while repetitive load effects on the soil modulus were modeled using a power law of the form EsNEs1=N−n(2) It was concluded that a single CPMT test could be used to model both rate effects and cyclic effects on the soil modulus and that the most consistent method of inserting the probe was to place it in a prebored hole. It was also concluded that a linear relationship exists between the exponents n in both modeling equations and the normalized CPMT stress level.
Pipeline Incidents and Emergency Repair in the North Sea
Authors: Wood G. D.
Published: November 2009

The failures of submarine pipelines in the North Sea, and the response of pipeline operators are first discussed. Against this background, the methods currently available for submarine pipeline repairs are reviewed. The Emergency Pipeline Repair Services available are described, and some future developments in the field of submarine pipeline repair are briefly outlined.
Effects of Location and Direction of Diluent Injection on Radiation and Pollutant Emissions of a Burning Spray
Authors: Puri R. , Gollahalli S. R.
Published: November 2009

Introduction of diluents into diffusion flames is an effective method of changing their combustion and pollutant emission characteristics. Since the dominant thermochemical processes vary from region to region of a burning spray, diluent injection at different locations of a flame can affect its overall characteristics differently. This study examines the effects of location and orientation of N2 injection into an air-atomized kerosene spray flame. Flame length, radiant emission, temperature profiles, flame opacity, and concentration profiles of NO, CO, and soot are measured. The overall emission indexes of NO, CO, and soot are calculated. Results show that the diluent injection in the axial downstream direction is superior to the radial injection from the point of reducing heat loss to the combustor walls. The location of injection affects flame characteristics substantially. Injection of diluent into midflame region produces largest reductions in radiation, flame length, and emissions of soot and CO. Nitric oxide emission does not depend significantly on the location of injection.
A Critical Review of Second Law Costing Methods—I: Background and Algebraic Procedures
Authors: El-Sayed Y. M. , Gaggioli R. A.
Published: November 2009

The following report reviews the development and state of engineering economic applications of the second law of thermodynamics. It encompasses virtually all of the work carried out publicly in the United States, and to the best of our knowledge that done in other countries (but also see Tsatsaronis, 1987). The ultimate objective here is to provide direction for future research on the fundamentals and applications of this subject, and for the support thereof. We begin with a historical review, which is important for better comprehension of second law costing, its objectives, its state, and its prospects. Following the history, further relevant background, on cost accounting, is presented in Part II. Part III describes in general terms the different exergy costing methods which are in existence. Parts IV and V constitute the nucleus of the report. Therein the various techniques are analyzed and critiqued, generally by considering successive publications developing and/or based on a technique. Part IV is devoted to algebraic methods for determining and applying exergy costs and Part V, to be presented in the sequel to this article, to calculus methods. These two parts do refer to each other, and the relationships between them are developed. Suggestions regarding further research are incorporated into both sections. It should be mentioned that the references we cite are not intended to be exhaustive. However, it is our intention to refer to the most recent work of each author, so that the reader may trace back to earlier publications. Also, the bibliographies of Wepfer (1979) and Liu and Wepfer (1983) are quite exhaustive.
The Effect of Inlet Conditions on the Performance of Wells Turbine
Authors: Raghunathan S. , Setoguchi T. , Kaneko K.
Published: November 2009

Experimental investigations on the effect of inlet turbulence and flow distortion on the performance of a monoplane and a biplane Wells turbine are reported. The performance of biplane Wells turbine is more sensitive to turbulence when compared with a monoplane. The primary effect of increase in turbulence on the performance of Wells turbine is the postponement of stall.
Leak Detection Implementation: Modeling and Tuning Methods
Authors: Griebenow G. , Mears M.
Published: November 2009

This paper contains an overview of the Williams Pipe Line computerized dynamic leak detection system, including the basic calculation methods used in the system, instrumentation support requirements, and various operational situations encountered during the implementation process. Special emphasis is given to enhanced modeling techniques required for complex pipeline configurations. Sample performance test results are also presented with a discussion focused primarily on the system response time.
The Non-Nuclear Conversion of the Montalto BWR/6-Mark III Plant: A Technical and Economical Assessment of the Proposed Options
Authors: Sciubba Enrico
Published: November 2009

The 2×981 MW, GE-BWR/6-Mark III Montalto plant was commissioned in the late 1970s by the Italian Public Utility (ENEL), in a context—the “Nuclear Option Plan,” “PUN”1—which called for the construction of about 10 nuclear powerplants of various types in several sites across Italy, to cover approximately a 15 percent share of the baseload requirements by the year 2000. For several reasons, both technical and political, the ambitious PUN failed, to a point in which, following a National Conference on Energy Generation Systems and Strategies (Feb. 1987), the citizens were called to decide in a national ballot whether they wanted such a plan to be discontinued or enforced (Nov. 1987). The decision having been to discontinue the PUN (by a 66-percent to 34-percent margin), the problem arose about the destination of the two plants which were under construction: “Trino 2”—midway between Torino (Turin) and Milano (Milan)—and “Montalto”—about 70-km from Roma (Rome). Trino, being in the initial construction stages, was promptly halted. The decision about Montalto (70 percent completed) was a more difficult one. Six alternatives were formally presented to a specially appointed Government Committee: (i) the original nuclear option as envisioned by the PUN; (ii) and (iii) two different reconversions to a gas-fired, combined cycle plant, both of which have been proposed earlier (1986) on the basis of objections to the safety procedures related to the reactor’s operation; (iv) a substitution with a series of 7 modular, gas-fired combined cycle plants (also proposed before the national ballot); (v) a reconversion to a multi-fuel, custom-design steam powerplant (also proposed before the national ballot); (vi) a substitution with four modular units, each standard steam multi-fuel (proposed by the Public Utility as the only valid alternative to the completion of the nuclear plant). This paper presents an independent, comparative analysis of the six alternatives, taking into account both technical and economical issues. On the basis of a cost structure deduced by the Public Utility’s published data, an average cost for the kilowatthour is determined for each of the six options, and compared to that corresponding to the completion of the nuclear plant. The final decision of the Italian Government was made public in June 1988 and is also discussed in this final version of the paper.
SUPERTARGETING: Different Process Structures for Different Economics
Authors: Ahmad S. , Linnhoff B.
Published: November 2009

Pinch technology has recently introduced techniques for optimizing integrated energy systems before design. The procedures apply to heat exchanger networks, heat pumps, combined heat and power schemes, and utility systems. They allow overall energy and capital cost targets to be compared and varied ahead of design to seek the optimum cost tradeoff. Near global optimality of the final design is virtually guaranteed, even for complex and highly constrained industrial problems. A key concept is that of supertargeting. This paper describes a case study application involving supertargeting and compares the approach to conventional techniques for optimal design. The example used is the heat exchanger network for a chemical solvents process. To demonstrate the approach fully, the design is carried out more than once. The prevailing economic conditions are varied to examine their influence on design. It is shown how fundamentally different network structures are optimal under different economic situations. Finally, topology traps are identified which prevent such different solutions evolving from each other through conventional design techniques.
The Effects of a Decaying Heat Source in a Rectangular-Shaped Rock Repository
Authors: Small J. C. , Booker J. R.
Published: November 2009

Schemes for the disposal of medium to high level atomic waste involve placing the spent material in repositories deep within stable rock formations. The waste will continue to generate heat after storage underground, and it is of interest to be able to predict the effects of this heating on the surrounding rock, as this may lead to cracking of the rock and the potential contamination of ground water. A solution method is presented for problems involving decaying heat sources of rectangular shape which lie within horizontally layered materials. The method requires very little computer storage (unlike finite element and finite difference techniques) and may easily be implemented on microcomputers. Solution of the time-dependent problem is achieved by applying Laplace transforms to the field variables, solving the resulting equations, and then using numerical inversion to obtain the solution in real time.
Motion and Structural Response of a Hydroelastic Semi-Submersible Model to Waves and Ice Impacts
Authors: El-Tahan H. , Arockiasamy M. , Swamidas A. S. J.
Published: November 2009

This paper presents the motion and structural responses of a model that is structurally and dynamically similar to a typical semi-submersible platform. The model is fabricated of high impact polystyrene sheets, 0.78 mm (0.03 in.) thick, and cellulose acetate butyrate (CAB) tubes (for bracings), 1.58 mm (0.06 in.) thick. The response of the model to regular and irregular waves under operating/survival conditions and impacts of modeled bergy-bits (prototype weights of 1000 t and 2000 t traveling at speeds of 1.0 to 4.0 m/s) was determined. In addition, the response of a damaged-corner-column semi-submersible to survival wave conditions was also examined. The motion and structural responses were monitored using 30 strain gages, an accelerometer and four potentiometer devices. The impact loads were simulated by weights swinging in a pendulum mode in still water. The motion RAOs, stress RAOs, PSDs of stresses, impact loads versus time histories, etc., are computed and compared with published values. There is a very good agreement between the present experimental/analytical results and other results published earlier for the motion response. It was found that the theoretical models tend to overestimate the structural response at short wave periods and underestimate it at long periods.
Vortex-Induced Vibrations due to Steady and Wave-Induced Currents of a Flexible Cylinder Near a Plane Boundary
Authors: Tsahalis D. T.
Published: November 2009

Model tests were performed in a wave tank to determine the effect of combined steady and wave-induced currents and/or proximity of a plane boundary (seabottom) on the vortex-induced vibrations of a flexible pipe. The first mode response of the pipe in both the transverse and in-line directions was measured using a biaxial accelerometer positioned inside the pipe at the midpoint of its span. Results are presented for a wide range of steady flow velocities with superimposed wave-induced flow corresponding to Keulegan–Carpenter numbers of 0, 5, 10, 15, 20, 25 and 30 and pipe-to-wall gaps of 1, 2, 4, 6 and ∞ (isolated pipe) pipe diameters.