Summary. This paper describes simulations of the effects of microscopic heterogeneity present in rock pore structures or resulting from high water saturations on the performance of one-dimensional (1D) CO2 floods. In the simulations, microscopic heterogeneity was represented by dividing the nonaqueous portion of the pore space into flowing, dendritic, and trapped fractions. A 1D simulator, previously shown to model quantitatively the effects of phase behavior in slim-tube displacements, was modified to include effects of the isolated or trapped fraction unavailable for mixing with injected fluids and the dendritic fraction, which exchanges material with the flowing fraction by mass transfer. Model formulation, numerical solution, and validation tests are described. Results of simulations with no water present indicate that performance of a 1D CO2 flood is sensitive to deviations from performance of a 1D CO2 flood is sensitive to deviations from complete local mixing. Calculated oil recovery decreases as the flowing fraction, Peclet number, and Damkohler number decrease. Comparisons of calculated and measured residual oil saturations (ROS's) in CO2 corefloods support this observation. Simulations of secondary and tertiary displacements by continuous CO2 injection and alternate and simultaneous injection of CO2 and water are compared. Performance of secondary displacements is not strongly affected by incomplete local mixing. In tertiary displacements, however, total oil recovery and the rate of recovery are reduced if effects of trapped and dendritic saturations are included. Introduction High local displacement efficiency in a CO2 flood requires mixing between injected CO2 and the oil in place. When the pressure is high enough that the CO2-rich phase has a density close to that of the oil, the CO2-rich phase extracts hydrocarbons from the oil to form a mixture that displaces oil more efficiently than pure CO2. It is clear that extraction cannot take place unless the CO2 mixes with the oil. Accepted theoretical descriptions of the underlying mechanism of a CO2 flood are based on the assumption that fluids are locally well mixed. Hutchinson and Braun's explanation of the mechanism of a vaporizing gas drive treated phases as completely mixed locally, as did Helfferich's analysis of 1D flow with phase behavior. In those analyses, fluid at some location in a plane phase behavior. In those analyses, fluid at some location in a plane normal to the flow direction is treated as completely mixed and at chemical equilibrium, but fluid in that plane does not mix at all with fluid in planes just upstream or downstream. Those descriptions indicate that composition path controls local displacement efficiency in 1D flows in which effects of dispersion, viscous instability, or other nonlocal mixing are absent. In such flows, if the oil composition lies outside the region of tie-line extensions on a pseudoternary phase diagram, the ROS is zero. Subsequent investigation by pseudoternary phase diagram, the ROS is zero. Subsequent investigation by Gardner et al. showed that dispersive mixing reduces local displacement efficiency and leads to a nonzero ROS. Simulations of viscous instability in a CO2 flood by Gardner and Ypma showed that mixing between CO2 in a finger and oil in adjacent unswept areas alters composition paths in a way that also reduces recovery. Thus, deviations from complete local mixing influence the performance of processes that depend on the transfer of components performance of processes that depend on the transfer of components between phases to generate high local displacement efficiency. In real porous media, such deviations (which are referred to as incomplete or restricted mixing) can arise from at least two sources: heterogeneity of the pore structure and the presence of water in a portion of the pore space. If the pore space is heterogeneous at the microscopic level, injected fluid will flow faster through sequences of large pores. Because the resultant displacement front are not uniform, it is clear that in the neighborhood of the displacement front, the fluids present are not completely mixed unless the flow is so slow that diffusion can eliminate the nonuniformity. Given the complexity of real pore structures, attempts to model flow have relied on much simpler representations of heterogeneity, as we do here. For instance, Deans proposed a model of single-phase flow in which the pore space was divided into flowing and stagnant fractions. In Deans' model, exchange of material between flowing and stagnant fractions is governed by a lumped mass-transfer coefficient. Coats and Smith extended Deans' model to include effects of dispersion in the flowing stream. Baker, Batycky et al., and Spence and Watkins interpreted single-phase miscible displacements in reservoir cores with the Coats-Smith model. Spence and Watkins found that cores with wide pore-size distributions--i.e., with significant microscopic pore-size distributions--i.e., with significant microscopic heterogeneity-also showed flowing fractions less than 1 when miscible displacement results were fit to the Coats-Smith model. A flowing fraction less than one is an indication that a stagnant volume was required in the model to fit the observed displacement data. They also found experimentally that cores with flowing fractions less than I also showed higher ROS's after CO2 floods. Salter and Mohanty also used the Coats-Smith model to interpret steady-state two-phase displacements. They found that high water saturations caused effluent composition curves that could be duplicated by use of both trapped and dendritic PV's in the Coats-Smith model description of the flow in the nonwetting phase. Stalkup and Shelton and Schneider observed that high water saturation reduced the effectiveness of miscible floods, particularly in water-wet rocks. Campbell and Orr also observed trapped and dendritic oil ganglia in flow visualization experiments. In those experiments in two-dimensional pore networks, water isolated some oil droplets from contact with injected solvent. Other droplets were given the shape of dead-end pores by surrounding water, even though the pore network contained no actual dead-end pores. Oil in those dendritic droplets was recovered by diffusion into the flowing stream. Thus there is also experimental evidence that the presence of water alters mixing between injected fluid and residual oil from a waterflood. None of the previous studies attempted to investigate in detail the interaction between incomplete local mixing and phase behavior. This paper examines the impact of nonuniform flow on the performance of 1D CO2 floods. performance of 1D CO2 floods. SPERE P. 531

This paper applies Reynolds-averaged Navier-Stokes (RANS) method to study propulsion performance in head and oblique waves. Finite volume method (FVM) is employed to discretize the governing equations and SST k-ω model is used for modeling the turbulent flow. The free surface is solved by volume of fluid (VOF) method. Sliding mesh technique is used to enable rotation of propeller. Propeller open water curves are determined by propeller open water simulations. Calm water resistance and wave added resistances are obtained from towing computations without propeller. Self-propulsion simulations in calm water and waves with varying loads are performed to obtain self-propulsion point and thrust identify method is use to predict propulsive factors. Regular head waves with wavelengths varying from 0.6 to 1.4 times the length of ship and oblique waves with incident directions varying from 0° to 360° are considered. The influence of waves on propulsive factors, including thrust deduction and wake fraction, open water, relative rotative, hull and propulsive efficiencies are discussed.

Free running model tests and a system-based method are employed to evaluate maneuvering performance for a Small Waterplane Area Twin Hull (SWATH) ship in this paper. A 3 degrees of freedom Maneuvering Modeling Group (MMG) model is implemented to numerically simulate the maneuvering motions in calm water. Virtual captive model tests are performed by using a Reynolds-averaged Navier-Stokes (RANS) method to acquire hydrodynamic derivatives, after a convergence study to check the numerical accuracy. The turning and zigzag maneuvers are simulated by solving the maneuvering motion model and the predicted results agree well with the experimental data. Moreover, free running model tests are carried out for three lateral separations and the influence of the lateral separations on maneuvering performance is investigated. The research results of this paper will be helpful for the maneuvering prediction of the small waterplane area twin hull ship.

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This paper describes the application of computational fluid dynamics rather than a towing tank test for the prediction of hydrodynamic derivatives using a RANS-based solver. Virtual captive model tests are conducted, including an oblique towing test and circular motion test for a bare model scale KVLCC2 hull, to obtain linear and nonlinear hydrodynamic derivatives in the 3rd-order MMG model. A static drift test is used in a convergence study to verify the numerical accuracy. The computed hydrodynamic forces and derivatives are compared with the available captive model test data, showing good agreement overall. Simulations of standard turning and zigzag manoeuvres are carried out with the computed hydrodynamic derivatives and are compared with available experimental data. The results show an acceptable level of prediction accuracy, indicating that the proposed method is capable of predicting manoeuvring motions.