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EDITORIAL

J. Energy Resour. Technol. 1983;105(1):1. doi:10.1115/1.3230869.
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Abstract
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J. Energy Resour. Technol. 1983;105(1):2-5. doi:10.1115/1.3230871.

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.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):6-11. doi:10.1115/1.3230882.

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.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):12-16. doi:10.1115/1.3230867.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):17-25. doi:10.1115/1.3230868.

This paper discusses the importance of environmental driving forces in determining ice loads on Arctic offshore structures. Limits to the environmental driving force in a first-year ice field are analyzed by considering models of ridge formation, wind and current driving forces, and irregularities such as leads and tidal cracks. Average driving forces are estimated to be approximately 10–50 kips/ft for far-field, with some local concentration near fixed structures. These order of magnitude estimates are sufficiently less than failure loads for many ice features to indicate that limited driving force approach may reduce estimated ice loads on Arctic structures.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):26-29. doi:10.1115/1.3230870.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):30-37. doi:10.1115/1.3230872.

The study of conductive heat transfer with phase change — often called the Stefan problem — includes some of the most intractable mathematical areas of heat transfer. Exact solutions are extremely limited and approximate methods are widely used. This paper discusses the heat balance integral approximation using the collocation method. The method is applied to some standard problems of phase change — Neumann’s problem — and a new solution is presented for the case of a semi-infinite body with surface convection. Numerical results are given for soil systems and also for materials of interest in latent heat thermal storage.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):38-42. doi:10.1115/1.3230873.

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.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):43-45. doi:10.1115/1.3230874.
Abstract
Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):46-53. doi:10.1115/1.3230875.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):54-57. doi:10.1115/1.3230876.

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.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):58-61. doi:10.1115/1.3230877.

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.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):62-66. doi:10.1115/1.3230878.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):68-72. doi:10.1115/1.3230881.

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.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):73-77. doi:10.1115/1.3230883.

The efficiency of some recently developed integration schemes, namely, Hilber’s ∝-method, collocation schemes and large time step integration schemes developed by Argyris, is evaluated by applying them to the response analysis of an idealized offshore tower. The tower is fixed at the base, having an additional mass at the top. For the analysis the tower has been modeled as an assemblage of 2-D beam elements. The dynamic degrees of freedom at each node are taken as those corresponding to the rotational and sway degrees of freedom. Using the normal mode theory the equations of motion have been decoupled except for the generalized loading vector which appear nonlinearly coupled, thus requiring iterative solution at every time step. The results of the study show that the large time step integration schemes developed by Argyris are more efficient than other integration methods considered here.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):78-82. doi:10.1115/1.3230884.

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.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):83-89. doi:10.1115/1.3230885.

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.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):90-96. doi:10.1115/1.3230886.

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.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):97-102. doi:10.1115/1.3230887.

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

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1983;105(1):103-107. doi:10.1115/1.3230866.
Commentary by Dr. Valentin Fuster

DISCUSSIONS

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