Split-Flaps – a Way to Improve the Heel Stability of T-Foil Supported Craft

Horizontal T-foils allow for maximum lift generation within a given span. However, the lift force on a T-foil acts on the symmetry plane of the hull, thereby producing no righting moment. It results in a lack of transverse stability during foil-borne sailing. In this paper, we propose a system, where the height-regulating flap on the trailing edge of the foil is split into a port and a starboard part, whose deflection angles are adjusted to shift the centre of effort of the lift force. Similar to the ailerons which help in steering aircraft, the split-flaps produce an additional righting moment for stabilizing the boat. The improved stability comes, however, at a cost of additional induced resistance. To investigate the performance of the split-flap system a new Dynamic Velocity Prediction Program (DVPP) is developed. Since it is very important for the performance evaluation of the proposed system it is described in some detail in the paper. A complicated effect to model in the DVPP is the flow in the slot between the two flaps and the induced resistance due to the generated vorticity. Therefore, a detailed CFD investigation is carried out to validate a model for the resistance due to the slot effect. Two applications of the split-flap system: an Automated Heel Stability System (AHSS) and a manual offset system for performance increase are studied using a DVPP for a custom-made double-handed skiff. It is shown that the AHSS system can assist the sailors while stabilizing the boat during unsteady wind conditions. The manual offset enables the sailors to adjust the difference between the deflection angles of the two flaps while sailing, thus creating a righting moment whenever required. Such a system would be an advantage whilst sailing with a windward heel. Due to the additional righting moment from the manual offset system, the sails could be less depowered by the sailors resulting in a faster boat despite the additional induced resistance. It is shown in the paper that the control systems for the ride height and the heel stability need to be decoupled. The paper ends with a description of a mechanical system that satisfies this requirement.

Theoretical Model and Experimental Study of Dynamic Hot Rolling

At present, the commonly used hot rolling model is only applicable to the static rolling process. However, to study the dynamic rolling process, a dynamic rolling model with roll vertical movement velocity parameters is required. In this study, the influence of the vertical movement velocity of the rolls on the rolling process is considered, and a dynamic rolling process model is proposed when the roll gap is reduced during the hot rolling dynamic rolling process. Mathematically, the model is based on the upper limit method. The model considers the influence of the dynamic rolling process on the length of the deformation zone, establishes a dynamic velocity field model and an average deformation rate model, and then solves the total power of the rolling process. Finally, the dynamic rolling force equation is given. Compared with the experimental results, the dynamic rolling model in this paper has high accuracy with an average error of 4%. In addition, the influence of roll vertical velocity on rolling parameters is discussed, which provides a basis for the study of the dynamic rolling process.

Racing Driver Modeling Based on Driving Behavior

The driver model is an important link in the research of shared autonomy control. In order to simulate the driver’s handling characteristics in the complex human-vehicle-road closed-loop system, the driver model is required to accomplish the driving operation under specific working conditions. In this paper, a lateral-longitudinal combined racing driver model is designed. The lateral control model adopts the preview model with far and near viewpoints and the dynamic velocity controller is added into the longitudinal control model to obtain the expected speed of the target trajectory. Finally, the racing driver model proposed in this paper is validated through simulation on track conditions of FSAE. In the given conditions, the result shows the racing driver model outperforms the typical driver model in lateral path tracking and the speed of racing driver model is higher than typical model on straight and corners. Meanwhile, the representation of driving skills is a key step to enhance the adaptive control of vehicles in the future. The control parameters can be adjusted according to the driver’s skill information to make the vehicle control system adapt to the driver’s skill level. This paper introduces the method of driving skill recognition based on wavelet transform and Lipschitz singularity detection theory and the preliminary test results prove the feasibility of using this method to characterize the driver’s operating skill level.

Obtaining Expressions for Time-Dependent Functions That Describe the Unsteady Properties of Swirling Jets of Viscous Fluid

Previously, it has been shown that the dynamic geometric configuration of the flow channel of the left heart and aorta corresponds to the direction of the streamlines of swirling flow, which can be described using the exact solution of the Navier–Stokes and continuity equations for the class of centripetal swirling viscous fluid flows. In this paper, analytical expressions were obtained. They describe the functions C0t and Г0t, included in the solutions, for the velocity components of such a flow. These expressions make it possible to relate the values of these functions to dynamic changes in the geometry of the flow channel in which the swirling flow evolves. The obtained expressions allow the reconstruction of the dynamic velocity field of an unsteady potential swirling flow in a flow channel of arbitrary geometry. The proposed approach can be used as a theoretical method for correct numerical modeling of the blood flow in the heart chambers and large arteries, as well as for developing a mathematical model of blood circulation, considering the swirling structure of the blood flow.

Physics-based universal outlier detector for flow statistics

Outlier detection for PIV velocity fields is still nowadays an active field of research. In the last decades, several image pre-processing and processing algorithms have been developed aiming at increasing the dynamic velocity range of PIV measurements and reducing the measurement uncertainty. Nevertheless, PIV velocity fields are still often characterised by the presence of outliers, which potentially hamper the correct interpretation of the flow physics and negatively affect the evaluation of the flow statistics. The outlier detection strategies presented in literature are mainly based on the statistical analysis of the velocity vector with its immediate neighbour. Most of these algorithms have been demonstrated to be effective for instantaneous flow fields, where the errors associated with the outliers are order of magnitude larger than the expected measurement uncertainty. However, these approaches are not as effective for the flow statistics, where the outliers yield errors of the same order of the measurement uncertainty. To overcome this limitation, this paper proposed an outlier detection approach based on the agreement of the flow statistics to the constitutive equations, more specifically to the turbulent kinetic energy (TKE) transport equation. The focus is posed on the ratio between the local advection terms of TKE and a robust estimation of the TKE production along the local streamline. It is demonstrated that, in presence of outliers, the proposed principle yields a clear separation between the correct and the erroneous vectors. In order to assess the performance of the proposed principle, three different test cases are considered. For all of them, the results are compared with a reference outlier detection methodology, namely the universal outlier detection method proposed by Westerweel and Scarano (2005). The proposed turbulence transport-based approach exhibits higher performance in terms of percentage of outliers correctly identified in the flow statistics.

High Froude Number Experimental Investigation of the 2 DOF Behavior of a Multihull Float in Head Waves

Dynamic Velocity Prediction Programs are taking an increasingly prominent role in high performance yacht design, as they allow to deal with seakeeping abilities and stability issues. Their validation is however often neglected for lack of time and data. This paper presents an experimental campaign carried out in the towing tank of the Ecole Centrale de Nantes, France, to validate the hull modeling in use in a previously presented Dynamic Velocity Prediction Program. Even though with foils, hulls are less frequently immersed, a reliable hull modeling is necessary to properly simulate the critical transient phases such as touchdowns and takeoffs. The model is a multihull float with a waterline length of 2.5 m. Measurements were made in head waves in both captive and semi-captive conditions (free to heave and pitch), with the model towed at constant yaw and speed. To get as close as possible to real sailing conditions, experiments were made at both zero and non-zero leeway angles, sweeping a wide range of speed values, with Froude numbers up to 1.2. Both linear and nonlinear wave conditions were studied in order to test the limits of the modeling approach, with wave steepness reaching up to 7% in captive conditions and 3.5% in semi-captive ones. The paper presents the design and methodology of the experiments, as well as comparisons of measured loads and motions with simulations. Loads are shown to be consistent, with a good representation of the sustained non-linearities. Pitch and heave motions depict an encouraging correlation which confirms that the modeling approach is valid.

A multi-parameter speed control model of traveling wave ultrasonic motor

This paper presents a multi-parameter model of an ultrasonic motor for speed control. Firstly, the model is divided into the steady-state part and the dynamic part, and then the speed mapping relationship of amplitude, frequency, phase difference is described by linear function, exponential function, and hyperbolic tangent function, respectively in steady-state modeling. The least-square transfer function identification is used in the dynamic velocity modeling. This paper also constructs a modeling flowchart from the discrete models to the state-space function based on the pairwise combination of parameters, which can realize the flexible control of different parameters. Finally, the error box diagram of the model and the comparison between the measured results and simulation ones both verify the effectiveness of the model.

Turbulent flow in rough pipes

Ввиду того, что применяемые в инженерной практике трубы являются шероховатыми, определение гидравлического сопротивления шероховатых труб является важной проблемой. Необходимость повышения точности расчетов коэффициентов гидравлического сопротивления при течении жидкости в трубах с различной степенью шероховатости внутренней поверхности стенок трубы требует постоянного совершенствования инженерных методик расчета. В настоящей работе анализируются формулы для скоростей и сопротивлений при установившемся течении несжимаемой вязкой жидкости в круглой цилиндрической трубе с шероховатыми стенками, в том числе и формула Коулбрука. Рассматриваются предельные случаи проявления шероховатости, а также связь между числами Рейнольдса, вычисляемых по средней и по динамической скоростями. Использован принцип нахождении профилей скорости по закону сопротивления. Приводится алгоритм построения кривой сопротивления по найденному профилю скоростей в универсальных координатах. Для коэффициента сопротивления даётся формула Коулбрука в явном виде. As far as practically used pipes are always have different roughness the problem of practical determination of hydraulic resistance of pipes with roughness is very important. Improving the accuracy of hydraulic coefficients computations for fluid flows in pipes with different roughness of the inner surface requires continuous improvement of calculation methods. In the present article we analyze formulas for velocities and resistance for steady-state incompressible flows of a viscous fluid in a round cylindrical pipe with rough walls, including Colebrook’s formula. The limiting cases of roughness are considered, as well as the relationship between the Reynolds numbers calculated by both average and dynamic velocity. On a basis of resistance law, we have recovered velocity profiles. The algorithm of determination of resistance curve by computed velocity profile in universal coordinates is described. Colebrook’s formula for resistance coefficient is written explicitly.