Public transport provision in sparsely populated arid areas

Arid areas are characterized by dispersed patterns of population and economic activities in a hot and dry environment. Although basic human needs are identical everywhere, patterns of travel behaviour in arid lands are different from the patterns in more humid areas. The different behavioural patterns imply somewhat different demand patterns for transport services in general and transit services in particular. Good access to the scattered small communities and more so to the remote urban centres is of prime concern in the sparsely populated arid areas. And the demand patterns themselves raise the need to develop unusual types of service based on local conditions. This article presents the effects of the arid spatial and climatic conditions on transit demand and supply. After examining the service standards required in the sparselands and using the Israeli Negev region as an example, guidelines for developing regional transit systems in these arid areas are put forward.     

URANS simulations of static and dynamic maneuvering for surface combatant: part 2. Analysis and validation for local flow characteristics

Part 2 of this two-part paper presents the analysis and validation results of local flow characteristics for a surface combatant Model 5415 bare hull under static and dynamic planar motion mechanism simulations. Unsteady Reynolds averaged Navier–Stokes (URANS) computations are carried out by a general-purpose URANS/detached eddy simulation research code CFDShip-Iowa Ver. 4. The objective of this research is to investigate the capability of the code in relation to the computational fluid dynamics-based maneuvering prediction method. In the current study, the ship is subjected to static drift, steady turn, pure sway and pure yaw motions at Froude number 0.28. The free surface, three dimensional vortical structure and, the validation of two dimensional local flow quantities together with the available experimental data are of the interest in the current study. Part 1 provides the verification and validation results of forces and moment coefficients, hydrodynamic derivatives, and reconstructions of forces and moment coefficients from resultant hydrodynamic derivatives.     

URANS and DES analysis for a Wigley hull at extreme drift angles

Vortical structures and associated instabilities for flows around the Wigley hull for a wide range of drift angles (10° ≤ α ≤ 60°) with free surface are identified and analyzed. Quantitative verification and validation are conducted on three systematically refined grids with comparison to the experimental data for α = 10°. Analysis of the flow pattern shows a strong correlation between the vortical structures and free-surface wave elevation. For α = 10° and 30°, the flows remain steady and vortices are generated at the keel and fore and aft perpendiculars of the hull. The strength and complexity of these vortices increase with increasing α. At α = 45°, flow becomes unsteady without any significant change in the main flow pattern. At α = 60°, a complex and unsteady flow field on the leeward side of the hull is formed with a large recirculation region from the aft to the fore end, which prevents the flow coming from below the keel from moving up and generating the keel vortices observed at lower drift angles. Karman-like and helical instabilities are analyzed. The effect of Froude number is more apparent for large than for small drift angles.     

EFD and CFD for KCS heaving and pitching in regular head waves

The KCS container ship was investigated in calm water and regular head seas by means of EFD and CFD. The experimental study was conducted in FORCE Technology’s towing tank in Denmark, and the CFD study was conducted using the URANS codes CFDSHIP-IOWA and Star-CCM+ plus the potential theory code AEGIR. Three speeds were covered and the wave conditions were chosen in order to study the ship’s response in waves under resonance and maximum exciting conditions. In the experiment, the heave and pitch motions and the resistance were measured together with wave elevation of the incoming wave. The model test was designed and conducted in order to enable UA assessment of the measured data. The results show that the ship responds strongly when the resonance and maximum exciting conditions are met. With respect to experimental uncertainty, the level for calm water is comparable to PMM uncertainties for maneuvering testing while the level is higher in waves. Concerning the CFD results, the computation shows a very complex and time-varying flow pattern. For the integral quantities, a comparison between EFD and CFD shows that the computed motions and resistance in calm water is in fair agreement with the measurement. In waves, the motions are still in fair agreement with measured data, but larger differences are observed for the resistance. The mean resistance is reasonable, but the first order amplitude of the resistance time history is underpredicted by CFD. Finally, it seems that the URANS codes are in closer agreement with the measurements compared to the potential theory.     

Computational fluid dynamics-based multiobjective optimization of a surface combatant using a global optimization method

The main objective of this article is to describe the development of two advanced multiobjective optimization methods based on derivative-free techniques and complex computational fluid dynamics (CFD) analysis. Alternatives for the geometry and mesh manipulation techniques are also described. Emphasis is on advanced strategies for the use of computer resource-intensive CFD solvers in the optimization process: indeed, two up-to-date free surface-fitting Reynolds-averaged Navier-Stokes equation solvers are used as analysis tools for the evaluation of the objective function and functional constraints. The two optimization methods are realized and demonstrated on a real design problem: the optimization of the entire hull form of a surface combatant, the David Taylor Model Basin—Model 5415. Realistic functional and geometrical constraints for preventing unfeasible results and to get a final meaningful design are enforced and discussed. Finally, a recently proposed verification and validation methodology is applied to assess uncertainties and errors in simulation-based optimization, based on the differences between the numerically predicted improvement of the objective function and the actual improvement measured in a dedicated experimental campaign. The optimized model demonstrates improved characteristics beyond the numerical and experimental uncertainty, confirming the validity of the simulation-based design frameworks.     

Verification and validation study of URANS simulations for an axial waterjet propelled large high-speed ship

The accurate prediction of waterjet propulsion using computational fluid dynamics (CFD) is of interest for performance analyses of existing waterjet designs as well as for improvement and design optimization of new waterjet propulsion systems for high-speed marine vehicles. The present work is performed for three main purposes: (1) to investigate the capability of a URANS flow solver, CFDSHIP-IOWA, for the accurate simulation of waterjet propelled ships, including waterjet–hull interactions; (2) to carry out detailed verification and validation (V&V) analysis; and (3) to identify optimization opportunities for intake duct shape design. A concentrated effort is applied to V&V work and performance analysis of waterjet propelled simulations which form the focus of this paper. The joint high speed sealift design (JHSS), which is a design concept for very large high-speed ships operating at transit speeds of at least 36 knots using four axial flow waterjets, is selected as the initial geometry for the current work and subsequent optimization study. For self-propelled simulations, the ship accelerates until the resistance equals the prescribed thrust and added tow force, and converges to the self propulsion point (SPP). Quantitative V&V studies are performed on both barehull and waterjet appended designs, with corresponding experimental fluid dynamics (EFD) data from 1/34 scale model testing. Uncertainty assessments are performed on iterative convergence and grid size. As a result, the total resistance coefficient for the barehull case and SPP for the waterjet propelled case are validated at the average uncertainty intervals of 7.0 and 1.1%D, respectively. Predictions of CFD computations capture the general trend of resistance over the speed range of 18–42 knots, and show reasonable agreement with EFD with average errors of 1.8 and 8.0%D for the barehull and waterjet cases, respectively. Furthermore, results show that URANS is able to accurately predict the major propulsion related features such as volume flow rate, inlet wake fraction, and net jet thrust with an accuracy of ~9%D. The flow feature details inside the duct and interference of the exit jets are qualitatively well-predicted as well. It is found that there are significant losses in inlet efficiency over the speed range; hence, one objective for subsequent optimization studies could be maximizing the inlet efficiency. Overall, the V&V work indicates that the present approach is an efficient tool for predicting the performance of waterjet propelled JHSS ships and paves the way for future optimization work. The main objective of the optimization will be reduction of powering requirements by increasing the inlet efficiency through modification of intake duct shape.     

URANS simulations of static and dynamic maneuvering for surface combatant: part 1. Verification and validation for forces, moment, and hydrodynamic derivatives

Part 1 of this two-part paper presents the verification and validation results of forces and moment coefficients, hydrodynamic derivatives, and reconstructions of forces and moment coefficients from resultant hydrodynamic derivatives for a surface combatant Model 5415 bare hull under static and dynamic planar motion mechanism simulations. Unsteady Reynolds averaged Navier–Stokes (URANS) computations are carried out by a general purpose URANS/detached eddy simulation research code CFDShip-Iowa Ver. 4. The objective of this research is to investigate the capability of the code in regards to the computational fluid dynamics based maneuvering prediction method. In the current study, the ship is subjected to static drift, steady turn, pure sway, pure yaw, and combined yaw and drift motions at Froude number 0.28. The results are analyzed in view of: (1) the verification for iterative, grid, and time-step convergence along with assessment of overall numerical uncertainty; and (2) validations for forces and moment coefficients, hydrodynamic derivatives, and reconstruction of forces and moment coefficients from resultant hydrodynamic derivatives together with the available experimental data. Part 2 provides the validation for flow features with the experimental data as well as investigations for flow physics, e.g., flow separation, three dimensional vortical structure, and reconstructed local flows.     

Factors Influencing the Participation of Local Governmental Officials in the National Estuary Program

Participation by local governmental officials is not given the same attention in the literature as that of citizens, publics, technical experts, or stakeholders. Yet, local governments are often a keystone to successfully implementing and enforcing coastal management policies. Qualitative analysis of open-ended interviews with local government officials from three national estuary program applications in New England revealed factors related to nine themes that shaped decisions to participate or not. Three categories of factors help to clarify the different types of influence agencies have over local government officials' decisions about whether or not to participate: factors associated with the character of individuals, with the context, and with the process. This taxonomy helps to clarify the kinds of opportunities available to project leadership to influence local government officials toward participating in regional coastal management processes. An important finding is that project staff should listen and learn about the concerns of local government officials and then create a process that accommodates and overcomes barriers to their participation.