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RESEARCH PAPERS: Offshore Mechanics/Ocean Engineering/Arctic Engineering

J. Energy Resour. Technol. 1983;105(3):263-270. doi:10.1115/1.3230912.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):271-276. doi:10.1115/1.3230913.

Resistance to pipeline motions in cohesive soils is shown to change with time. The following time effects are distinguished: aging of disturbed soil, duration of constant loading on the pipeline (consolidation time) and rate of external loading. Theoretical treatment of the two latter of these effects is compared with experimental results available in the literature. These experiments confirm the increase of the soil resistance with increasing consolidation time as shown by the theory. They are, however, insufficient to demonstrate the effect of loading rate set forth by the theoretical considerations herein.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):277-281. doi:10.1115/1.3230915.

Open-ended tubular columns may buckle globally as Euler columns due to the action of internal fluid pressure even while they are in tension along their entire length. Hydraulic columns, marine drilling and production risers are, therefore, prone to such static instability. This paper explains this phenomenon, defines the critical riser length for which this instability may occur and provides graphs with values of the critical length which can readily be used for design purposes. Risers with nonmovable boundaries are considered; namely, hinged-hinged, clamped-hinged, hinged-clamped and clamped-clamped risers.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):282-289. doi:10.1115/1.3230916.

This paper is concerned with the problem of longitudinal resonant vibration of a 3000-m-long disconnected riser. Theoretical investigations of natural frequencies and induced displacements and dynamic tensions are presented, as well as practical investigations of riser longitudinal hydrodynamic damping and of short period heave excitation, likely to be communicated to such a riser, by a typical drillship. Analytical expressions, useful for describing and understanding resonant behavior, are developed in the Appendix.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):290-295. doi:10.1115/1.3230917.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):296-299. doi:10.1115/1.3230918.

The Guyed Tower is a system designed for use in relatively deep waters (more than 1000 ft (300m)). A model is described that mimics the response of the tower. This model calculates the response by a single degree of freedom (SDOF). The properties of the simple model are derived from stiffness, mass and hydrodynamic properties of more detailed models. The simple model is used to evaluate different mooring system configurations, and to determine the influence of dynamic mooring system properties on overall dynamic tower response.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):300-309. doi:10.1115/1.3230919.

Three different algorithms are presented for simulating a time series which is compatible with a given power spectrum of ocean waves. The first algorithm generates the current value of the time series as the sum of a linear combination of its past values and a white noise deviate. The second algorithm produces the values of the time series as a linear combination of white noise deviates. The third algorithm is a combination of the first and second algorithms. These algorithms are applied to the Pierson-Moskowitz (P-M) spectrum, exclusively. The third algorithm is associated with simple analog filter approximations of the P-M spectrum. The advantages and disadvantages of each of the three algorithms are discussed in context with their applicability to offshore engineerng problems.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):310-317. doi:10.1115/1.3230920.

The statistical properties of second-order wave-induced response processes are investigated theoretically. Emphasis is placed on the slow-drift components. The assumed forcing waves are irregular with continuous frequency spectra. A spectral analysis of the response of a general system is made. It is shown that the slow-drift components are closely connected to the complex analytical signal and the Hilbert envelope of the wave elevation. A simple mathematical expression exists for the slow-drift components, based on the complex wave signal and the second-order impulse response of the system. By use of this explicit formula, the theoretical probability functions of slow-drift responses are investigated. The analysis is based on the Kac-Siegert method. A similar approach has earlier been applied to study the sum of both the low-frequency and the high-frequency second-order responses. Final calculations of the probability density functions are in general very complicated, but it can be simplified by the use of a simple idealized model for the second-order transfer function. Probability density curves for a few simple cases are presented.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):318-324. doi:10.1115/1.3230921.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):325-332. doi:10.1115/1.3230922.

Minimization of energy losses associated with the steering control of modern ship types is discussed on the basis of frequency-domain sensitivity analyses and time-domain simulation studies. A high-speed containership and large tankers in the full-load condition are analyzed. A new performance criterion for minimization of steering-related propulsion losses is presented, and controllers designed to it using linear quadratic Gaussian (LQG) techniques. In the case of the containership, the resulting controller is shown to have the potential to reduce the net losses related to steering below those of the uncontrolled ship through proper use of the rudder in some conditions. While this does not seem possible for the tankers, the results indicate that a controller designed to the new criterion results in lower losses than a controller based on a form of criterion to which new autopilots for tankers are presently being designed. The implications for both autopilot and steering gear servo-design based on these results are discussed.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):333-336. doi:10.1115/1.3230923.

Since the first Single Buoy Storage System (SBS) installed in Aquitaine-Tunisia in 1974 [1, 2], many similar systems have been installed. To facilitate oil production in Gulf Bohai, China, a model test of a SBS to investigate its motion and the forces under the action of regular waves has been carried out. Consulting the test results, this SBS “OFFSHORE 621” has been designed and launched. In this paper, the methods for determining the static characteristics of the multichain anchoring buoy system (MABS) and the measure for decreasing the chain force are given.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):337-340. doi:10.1115/1.3230924.

A theory is presented which will predict the stresses in a multilayered cable, subjected to axial, bending and torsional loads. In the axial case, the axial force and axial twisting moment are represented as linear combinations of the axial strain and the rotational strain. An analyisis is also made of a cable subjected to axial loads and wrapped around a drum. The analysis involves a superposition of the stresses caused by the axial loads and the bending loads.

Topics: Cables , Stress , Force
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):341-345. doi:10.1115/1.3230925.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):346-351. doi:10.1115/1.3230926.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):352-355. doi:10.1115/1.3230927.

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

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Drilling/Pipeline Transportation

J. Energy Resour. Technol. 1983;105(3):356-361. doi:10.1115/1.3230928.

A kinematic model of a roller cone bit is developed and integrated with a rock fracture description to simulate test data from a study on the effects of bit offset. The model predicted bit tooth patterns on the rock face similar to those in the experiment. Larger cutter offsets induced increased dragging action to the motion of the bit teeth. For a given bit-rock system, volume removal also increased with bit offset up to a limiting offset value beyond which lower drilling rates were predicted.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):362-371. doi:10.1115/1.3230929.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):372-378. doi:10.1115/1.3230930.

The vertical flow of mud and gas-mud mixtures in long pipes is of interest in the design and operation of subsea well control equipment where long choke lines are required. Heretofore, the question of two-phase flow of non-Newtonian drilling muds has not been investigated experimentally in full-scale well systems. Frictional-pressure losses were measured in a 2 3/8-in., 3000-ft long, vertical tubing when flowing drilling mud alone, and flowing mud-gas mixtures. The single-phase data was compared to values predicted by both the Bingham plastic and power law rheological models, which are commonly used to describe non-Newtonian fluids. The multiphase pressure loss data were used to evaluate various published correlation techniques.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):379-387. doi:10.1115/1.3230931.

An LPG pipeline break flow model has been develped to evaluate the flammability hazards associated with a pipeline rupture. The model estimates the time-dependent flow rate of LPG from a pipeline rupture, the gravity spreading of the LPG vapor layer over the ground, and the dispersion of the vapor cloud downwind of the break location. Examples of model predictions are presented to illustrate the effects of pipeline isolation valve spacing, and shutdown reaction time on the flammable cloud boundaries that could result from a partial break in a propane pipeline.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Equipment Manufacturing/Hydrocarbon Processing

J. Energy Resour. Technol. 1983;105(3):388-393. doi:10.1115/1.3230934.

A procedure for designing optimized ejector-diffuser systems for recovering natural gas vapor from oil storage tanks is presented. The system utilizes high pressure gas from the separator to entrain the ambient pressure gas from the tanks and then pumps the mixture to the sales line. The analysis predicts the minimum separator pressure and the optimum nozzle Mach number and ejector area ratio required to accomplish this task. The results of a parametric study suggest that this system is feasible and that the higher the required ejector compression ratio the more critical is the use of an optimized design.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):394-395. doi:10.1115/1.3230935.

This paper investigates valve hammer as opposed to water hammer in triplex pumps, both of which produce knocking under certain distinctly different hydraulic operations. The occurrence of water hammer is reviewed and the development of valve hammer is discussed and documented.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):396-400. doi:10.1115/1.3230936.

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

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Energy Recovery From Solid Wastes

J. Energy Resour. Technol. 1983;105(3):401-406. doi:10.1115/1.3230937.

This paper describes the Albany New York Solid Waste Energy Recovery System (ANSWERS), which consists of two plants — a City-owned refuse-derived fuel (RDF) plant, and a State-owned boiler plant in which RDF is burned. This paper is chiefly concerned with the City-owned RDF plant, and describes shakedown tests, problems encountered and solutions developed. Operational statistics and operations policies for the City-owned plant are discussed. Laboratory measurements of the heating value of RDF samples are compared with results actually achieved in the State boilers.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):407-411. doi:10.1115/1.3230938.

This paper describes an innovative fume incinerator which supplies all the steam needs of an industrial plant by burning waste liquid fuels, yet is flexible enough to match the instantaneous, hourly, weekly and seasonal variations in steam usage of the plant. Even though fume input is nearly constant, the load can be followed by adjusting the fuel input while furnace temperatures vary in a range above that needed to destroy the selected wastes. A steam accumulator reduces peak steam demand on the boilers. Ash from the waste oils accumulates on the furnace refractory, and boiler and air preheater tubes, requiring periodic cleaning. By maintaining sufficient minimum temperatures, effective atomization and mixing, these systems can destroy liquid wastes containing difficult chemicals such as chlorinated phenol and benzene compounds. The required temperatures can be determined by plug-flow thermal destruction in the laboratory, and confirmed by testing typical materials in the full-scale oxidizer.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(3):412-416. doi:10.1115/1.3230939.

The paper describes derivation of data and guidelines for coburning of municipal sludges and unprepared solid waste, giving approximate limits of applicability using direct coburning model with minimum sludge preparation. No attempt is made to evaluate or compare direct coburning with alternate codisposal concepts such as flash drying, indirect drying, coburning with refuse-derived fuel, etc.

Commentary by Dr. Valentin Fuster

ERRATA

Commentary by Dr. Valentin Fuster

DISCUSSIONS

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