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In this paper, path following control of an unmanned ground vehicle is presented based on the feedback of position and orientation errors. The measurement unit of this autonomous vehicle prototyped for such tasks contains a real-time kinematic global positioning system (RTK-GPS), an inertial measurement unit (IMU) and an absolute encoder to accurately define the position and orientation of the car. A model predictive control was proposed for the path following of the mobile robot based on the successive linearized and discretized kinematic model. This optimal control method performs on the lowest position and orientation errors with respect to a non-holonomic virtual vehicle that is considered to move flawlessly on a given reference path and the smoother steering angle. The paths followed here are defined by rationally based splines or known geometric curves created with control points from a digital mapping program. This paper includes both simulation and real-time experimental studies. The outcomes were examined in terms of the design performance and control strategy of the vehicle. Despite the physical constraints on the vehicle prototype, it has been observed that position and orientation errors occur within satisfactory limits. In particular, the fact that the steering angle is not subjected to excessive oscillations indicates that the control method has a good performance. [ABSTRACT FROM AUTHOR]

Abstract: A new predictive formula for the total longshore sediment transport (LST) rate was developed from principles of sediment transport physics assuming that breaking waves mobilize the sediment, which is subsequently moved by a mean current. Six high-quality data sets on hydrodynamics and sediment transport collected during both field and laboratory conditions were employed to evaluate the predictive capability of the new formula. The main parameter of the formula (a transport coefficient), which represents the efficiency of the waves in keeping sand grains in suspension, was expressed through a Dean number based on dimensional analysis. The new formula yields predictions that lie within a factor of 0.5 to 2 of the measured values for 62% of the data points, which is higher than other commonly employed formulas for the LST rate such as the CERC equation or the formulas developed by Inman–Bagnold and Kamphuis, respectively. The new formula is well suited for practical applications in coastal areas, as well as for numerical modeling of sediment transport and shoreline change in the nearshore. [Copyright &y& Elsevier]

This paper presents a new relationship between the roughness height and the main hydrodynamic and sediment parameters for plane beds under steady current conditions. In order to derive such a formula, a large data base involving plane-bed experiments was compiled from previous investigations and analyzed. Comparisons between the data and different existing predictive formulas for the bed roughness obtained from the literature were also made. A relationship with the Shields parameter only, which is commonly proposed, appeared to be insufficient. The roughness was also found to be a function of a Froude number and a dimensionless settling velocity. A critical Shields parameter was identified up to which the equivalent roughness ratio is proportional to the Shields parameter. The new empirical equation that was developed yields the best results for all conditions investigated, and should improve the understanding of the total shear stress. [ABSTRACT FROM AUTHOR]

Presents information on a study which examined the characteristics of the scour holes that developed around a group of vertical piles in the field exposed to oscillatory waves. Nondimensional parameters that control scour hole properties; Parameters that described the scour hole; Conclusions.

Abstract: A new relationship between the roughness height and the main hydrodynamic and sediment parameters for plane beds under oscillatory conditions is presented. In order to derive such a relationship, a large data base encompassing plane-bed experiments was compiled from previous investigations and analyzed. Different methods to estimate the roughness height were investigated. Comparisons between the data and different existing predictive formulas for the bed roughness obtained from the literature were also performed. A relationship involving the grain size and Shields parameter only, which is commonly proposed, appeared to be insufficient to characterize the roughness. The roughness height was also found to be a function of the sediment density and the settling velocity. A critical Shields parameter was identified up to which the effective roughness ratio is proportional to the Shields parameter only. The new empirical equation developed in this study provides the highest predictive skill for all conditions investigated. [Copyright &y& Elsevier]