J. Energy Resour. Technol. 1991;113(3):141-146. doi:10.1115/1.2905794.

The Wells turbine is an axial-flow air-turbine designed to extract energy from the ocean waves. The turbine is self-rectifying, i.e., produces an unidirectional time-averaged torque from a reciprocating flow. The paper describes an experimental investigation on the aerodynamic performance of a modified version of the Wells turbine, whose rotor blades can be set at varying angle (as in a Kaplan turbine) while the turbine is in motion. The purpose of the work is to investigate whether, and to what extent, the modification to the turbine can enable it to achieve phase control—a method of tuning the energy-absorbing device to the incident waves—and avoid aerodynamic stall on the turbine rotor blades at peaks of air flow rate under conditions of real irregular ocean waves. Experimental results obtained with a model turbine are compared with predicted values from a quasi-three-dimensional computational method of flow analysis.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):147-153. doi:10.1115/1.2905795.

The isothermal characteristics and high effective thermal conductivity of heat pipes and thermosyphons make them particularly useful in air to air and process to air heat recovery systems. Although previous investigations have developed successful techniques for predicting many of the transport limitations, entrainment remains the least understood. Current entrainment modeling techniques have resulted in a large range in the predicted axial heat flux required for the onset of entrainment. Included here is a review of the present analytical methods used to predict the liquid entrainment as a function of the pipe’s physical parameters and working fluid properties, for both thermosyphons and heat pipes. The results of the models are compared with existing experimental data in an effort to determine the accuracy of the predictive techniques. Using a sample copper/water thermosyphon and a similar screen wicked heat pipe, comparisons of the experimental entrainment limit and those predicted by seven thermosyphon and four heat pipe models were made. The results of this comparison can provide insight for designers developing heat pipe exchangers and will provide a basis for further understanding the phenomena which govern this limit.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):154-156. doi:10.1115/1.2905796.

Well control operations while drilling with an oil-base mud can suffer several unexpected phenomena. One of these is the dispersion (smearing) of the gas in solution whenever a gas kick is being circulated from the well. If the gas influx has gone into solution, it is very important to predict the movement of this gas-contaminated mud as it is circulated from the well. A computer model of non-Newtonian fluids flowing in an annulus of any eccentricity has been developed with which to accurately model this dispersion. The movement of the gas-contaminated mud is predicted as a consequence of the velocity profiles established as the displacement of the annulus progresses.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):157-160. doi:10.1115/1.2905797.

This work is an analysis of non-Newtonian fluid flow in an annulus of any eccentricity with inner pipe motion, for typical petroleum drilling operations. The annular flow geometry and the two-dimensional laminar equation of motion are not approximations, but rather a finite difference method is used to develop a computer model which calculates the velocity profile and flow rate for a given frictional pressure loss. Very accurate velocity profiles of non-Newtonian (Bingham plastic and power law) fluids with inner pipe motion are obtained using exact geometries. Contour plots of the resulting velocity profiles in annuli of varying eccentricities help one visualize the effects of eccentricity as well as the effects of inner pipe movement and rheological properties of a fluid on surge pressures. Example cases show a significant reduction in surge pressure as eccentricity increases. The surge pressures are as much as 50 percent less than a concentric calculation when the inner pipe lays to one side of the hole. Therefore, previous concentric models are found to overpredict surge pressures in directional and horizontal wells. A correlation of frictional pressure is developed based on this model’s results. This correlation, permitting a quick calculation of surge pressures in eccentric annuli, can easily be incorporated into existing concentric models (steady state or unsteady state) to accurately calculate surge/swab pressures at any pipe eccentricity.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):161-164. doi:10.1115/1.2905798.

The injection of hot oil to clean the formation and tubing of accumulated paraffin has been used for many years in petroleum production. Although effective in freeing tubulars immobilized by paraffin deposits, formation damage has been attributed to hot oiling when the oil reaching the formation face is at a temperature below the paraffin cloud point. The differential equations describing hot oil injection through the casing-tubing annulus were solved using finite difference mathematics and the model was verified using data from field studies. Model studies indicated that rapid cooling of the injected fluid frequently results in fluid temperatures below geothermal in the lower reaches of wells of even moderate depth. Injection through centralized tubing provides a conduit for effective transmission of thermal energy along the entire depth of the tubing and to the formation face. Injection through tubing is modeled and verified by field experiment. A parametric study of operating parameters is included.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):165-170. doi:10.1115/1.2905799.

A mathematical model of droplet combustion in surroundings of hot gas with a uniform free stream motion is made from the numerical solution of the conservation equations of heat, mass and momentum in both the carrier and droplet phases. The gas phase chemical reaction between fuel vapor and oxidizer is assumed to be a single-step irreversible one. The phenomena of ignition is recognized by the sudden rise of temperature in the temperature-time histories at different locations in the carrier phase. The relative influences of pertinent input parameters, namely initial Reynolds number Rei , ratio of free stream to initial drop temperature T∞ , and the ambient pressure on: (i) the ignition time lag, (ii) extinction characteristics, and (iii) life histories of burning fuel drops have been established.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):171-175. doi:10.1115/1.2905800.

An analysis model is presented to analyze continuous fiber-reinforced composite structures with some local damage such as matrix cracks. Two separate material properties of fiber and matrix are used in the analysis model instead of a smeared-out global anisotropic material property. Stresses acting on fibers and stresses acting on matrix are computed directly. If there are local matrix cracks in the direction perpendicular to the fiber orientation in a composite structure, the broken matrix is modeled not to sustain any tensile stress in the fiber direction. A finite element formulation is derived for the analysis model. Some numerical problems are presented to test the proposed analysis model.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):176-181. doi:10.1115/1.2905801.

The design of composite rotors for high-energy density pulsed power supplies demands accurate characterization of both the mechanical and electrical properties of fiber-reinforced epoxy. The mechanical properties of S-2 glass-epoxy, IM6 graphite-epoxy, and hybrid graphite-glass epoxy composites were measured in tension and torsion tests, providing strength and stiffness parameters for rotor dynamics modeling. Variable frequency electrical resistivity tests were conducted to allow estimation of eddy current losses arising in carbon-reinforced materials. Volume fraction measurements using electron microscopy and analysis by digestion allow for normalization of the test results with respect to composite fiber content. The experimental results were used to evaluate the micromechanical rule of mixtures and Halpin-Tsai correlations.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):182-188. doi:10.1115/1.2905802.

The objective of this study was to gain a better understanding of the low-velocity impact phenomena of composite pipe. The focus was on test method development, and material and damage characterization. A drop weight tower tester was designed in this investigation. The dynamic tests were conducted using three different impactor geometries, velocities, and masses. It was found that the damage was localized and on the outer surface of the pipe in the case of the conical and wedge tip impactors. On the other hand, the damage zone was larger than the impact zone for the hemispherical impactor, and cracks were first seen within the inner surface of the pipe. This implies that the hemispherical tip impactor caused more damage to the pipe than the conical or wedge tips. The energy absorbed slightly increased with an increase in velocity or in mass. The contact period for the conical impactor was the longest. The velocity and mass of the impactor had only a slight effect on that period. The wedge impactor generated the largest peak force. The energy absorbed by the two composite pipes under low-velocity impact was studied. The specimen-1, Derakane 411-45 resin with less glass fiber, seemed to absorb more energy compared to the specimen-2, Derakane 470-36 resin with more glass fiber. In addition, the specimen-2 exhibited a slightly higher maximum impact force. Therefore, impact response is sensitive to fiber content.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):189-192. doi:10.1115/1.2905803.

An experimental test program is described in which biaxial failure envelopes were generated for unidirectional [0]8 and quasi-isotropic [0/+45/90/−45]s specimens made from Toray T800HY/3910 graphite/epoxy. Data was generated in all four quadrants of the biaxial stress plane. Fiber direction failure strengths were also found by uniaxial tension and compression tests. The quasi-isotropic compressive failure strengths are approximately 50 percent of the tensile strengths. Failure strengths in the tension-tension quadrant were essentially the same as previous tubular specimen tests made of a similar material (Swanson and Christoforou, 1986) indicating that free-edge and stress concentration effects may not preclude using flat cruciform specimens to generate biaxial failure data.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):193-196. doi:10.1115/1.2905804.

A new technique is described for determining all four elastic constants of a lamina from a single laminated specimen of arbitrary, symmetric lay-up. This specimen is subjected to three different loading conditions, and the experimental data is reduced by means of a finite element analysis. The testing procedure for the specimen is relatively easy, which can result in considerable time and cost savings over traditional methods. The new specimen generates biaxial stress states. Thus, the material properties determined from such a configuration may be more appropriate for later use in structural analysis than those determined from traditional specimens with uniform uniaxial stress states.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):197-203. doi:10.1115/1.2905805.

Toughening of ceramics by incorporating strong fibers has become an established technology, resulting in the creation of a new generation of tough ceramic composites. This toughening effect is primarily due to bridging of the crack surfaces by intact fibers when the composite is subjected to tension. The fiber bridging mechanisms, which are contingent upon the stress transfer phenomena between the fiber and the matrix, are reviewed in this paper. The critical role of the properties at the fiber/matrix interface in controlling the stress transfer phenomena is examined. Finally, evaluations of the interfacial properties of the composite by the indentation technique and the corresponding analysis are presented.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):204-209. doi:10.1115/1.2905806.

Response of a cylindrical panel made of layers of composite material and subjected to in-plane loads is investigated. Prebuckling deformations are determined for antisymmetric angle-ply and cross-ply panels having simply supported boundary conditions. Buckling solutions are obtained via the Rayleigh-Ritz method. Nonlinear programming is used to optimize the designs. Design variables are taken as fiber orientations and/or thicknesses of different layers. Numerical results are presented for different materials and different geometrical parameters, including aspect ratio and curvature-to-length ratio.

Commentary by Dr. Valentin Fuster
J. Energy Resour. Technol. 1991;113(3):210-213. doi:10.1115/1.2905807.

Closed-form solutions are not tractable for clamped composite plates due to the boundary conditions and anisotropy of the plate. In the present work, a method based on Lagrange multipliers is developed for the bending analysis of antisymmetric angle-ply clamped plates. The transverse shear flexibility is incorporated in the energy functional. Boundary conditions not satisfied by the assumed series are enforced using Lagrange multipliers. Results are presented to study the influence of shear deformation, anisotropy, aspect ratio and loadings on the deflections and stresses of clamped plates.

Commentary by Dr. Valentin Fuster

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