Constant Forward Speed Research Articles

Ride and roll/yaw stability analysis of articulated frame steer vehicle with torsio-elastic suspension

An articulated frame steered vehicle model with torsio-elastic suspension is established in Adams/View. The model considered the influence of the hydraulic steering system on the yaw stability of articulated vehicles, thus, the hydraulic steering system is formulated and modeled in MATLAB/Simulink. The ride and roll/yaw stability of the vehicle model is investigated via co-simulation of Adams and Simulink. The Adams vehicle model is verified based on the vibration acceleration responses near the seat position at constant forward speeds. The hydraulic steering system model is validated through the steady-state steering maneuver. Relative ride performance of unsuspended and fully suspended vehicle is investigated in terms of unweighted and frequency-weighted root-mean-square accelerations. The roll and yaw stability of vehicle model with and without suspension at loaded and unloaded conditions are subsequently analyzed in terms of roll angle, roll safety factor, lateral acceleration, critical speed, and so on. The results show that the torsio-elastic suspension can efficiently reduce the vibrations of the vehicle, and the articulated frame steer vehicles applied with torsio-elastic suspension yield slightly lower roll/yaw stability but substantial reductions in the ride vibration levels. The results provide some reference for the suspension and steering system design of articulated engineering vehicle.

Impact of Approach Angle of an Impinging Cyclone on Generation of Storm Surges and Its Interaction with Tides and Wind Waves

AbstractDetailed investigation is made on the effect of cyclone's approach angle on generation of storm surges and its nonlinear interaction with tides and wind waves using a standalone 2DDI ADCIRC and a coupled ADCIRC+SWAN model. Numerical experiments are executed using 17 idealized straight cyclone tracks of same intensity moving at constant forward speed. The study domain considers an idealized bathymetry with straight coastline and uniform shelf width. All cyclones make landfall at the same location with angles approaching from 10° to 170° with an increment of 10°. The simulations show that the maximum storm surge is computed for tracks land falling with 60o–90o. Increase in the peak storm surge is seen about 15% from 10o–60o, while it decreases by about 13% from 90o–170o. Surge‐wave interaction modifies the maximum water level by about 21–26%. The maximum wave contribution is seen for track with 90o followed by 160o and 20o. During different phases of tide, surge‐tide interaction modifies peak surge, its occurrence, and location as cyclone makes landfall at different angles. The extent of affected coastal stretch is maximum on either side of the landfall for the tracks moving close to the coast, while it is minimum for the perpendicular track (90o), confined only to the right of the landfall. The peak surge‐tide‐wind wave interaction along the coast at both high and low tide is seen about 2–4 hr after the landfall. The interaction along the coast depends on approach angles of the cyclone; however, the total water level is mainly modified by both tidal phase and approach angle.

Performance evaluation of a manual and a motor-operated maize seeder

A motor-operated maize seeder was designed and fabricated. The performance of the seeder was tested in laboratory and compared with a manual-operated seeder. Hybrid maize seed variety, Sunshine NK40 by Syngenta, was used for the performance test of the seeder during January to April/2017. The two seeders, manual-operated and motor-operated, provided an average seed spacing of 22.48 cm and 20.94 cm, respectively, while the standard seed spacing for maize is 20 cm. The seed spacing of the motor-operated seeder varied from the standard value because of the trapping of seed between the seed hopper and metering device. The missing rate of the manual seeder was 13.2% while the motor-operated seeder provided a missing rate of 5.9%. Due to constant forward speed, the motor-operated seeder resulted in 2.3 times lesser missing rate than the manual seeder. The seed rate of the manual- and motor-operated seeder was found to be 30 kg/ha and 25.7 kg/ha, respectively, although both the seeders were calibrated to maintain a constant seed rate of 25 kg/ha. The field capacity and field efficiency of the existing manual seeder was found 0.128 ha/h and 76.65%, respectively, whereas the field capacity and field efficiency of the motor-operated seeder was found 0.135ha/h and 74.76%, respectively. The motor-operated seeder has a limitation of time loss during turning and the required time loss resulted in low field capacity and field efficiency. Break-even analysis shows that at the yearly use of 0.23 hectares, the operation cost of manual seeder and hand application method were the same. Therefore, manual seeder will be beneficial to the farmers when the annual use exceeds 0.23 hectares of land. Compared to manually-operated seeder, the motor-operated seeder can reduce seed requirement by reducing missing rate and save labor and time of operation if the time loss during turning can be minimized.
 J. Bangladesh Agril. Univ. 17(2): 251–257, June 2019

Structures and Mechanisms of Air-Entraining Quasi-Steady Breaking Ship Waves

The overall objective of this study is to develop a fundamental understanding of the quasi-steady breaking wave regions present in surface ship wakes. Our approach uses direct numerical simulation (DNS) and implicit large eddy simulation. Building on our previous efforts looking at three-dimensional canonical dry transom sterns, we focus on the flow structure, air entrainment, and incompressible highly variable density turbulent characteristics in the wake of a fully submerged lifting body. This article represents the first steps of this study. Here, we perform DNS of the wake of a fully submerged lifting body with constant forward speed. Depending on the geometry and flow conditions, the wake of the submerged body contains a quasi-steady breaking-wave region downstream of the body that entrains air. We show that the simulations accurately predict the force and vortex wake frequency of the submerged body. Lagrangian analysis of the wake shows a frequency of peak entrainment that aligns with the frequency of the vortex wake. Finally, we establish that the power law of the air cavity density spectrum during the peak entrainment periods is predicted by r−10/3, consistent with experiments and theory. 1. Introduction Air-entraining quasi-steady breaking waves are prominent and highly observable features associated with surface ships and (nearsurface) submarines. They are important to the overall understanding of ship hydrodynamics with significant implications to the design operations of naval vessels. A systematic research effort elucidated many aspects of the complex three-dimensional highly mixed flows for a canonical dry transom stern (Weymouth et al. 2010; Hendrickson et al. 2012, 2016). In particular, we 1) identified wake and flow characteristics and obtained scaling with ship-scale parameters; 2) quantified the volume and scaling of the entrained air in the near wake; 3) characterized nature of the incompressible highly variable density turbulence (IHVDT) in the wake; and 4) developed explicit turbulent mass flux closure models (Hendrickson et al. under review; Hendrickson and Yue under review). Despite recent advances in large-scale state-of-the-art simulations of these flows, there remain fundamental issues and gaps in our knowledge and modeling capabilities. The main challenge of the canonical stern flow is that it contains regional complexity (convergent corner waves, rooster tails, diverging breaking waves) and many concurrent entrainment mechanisms and processes that limit our ability to isolate and address them fundamentally with sufficient numerical resolution.

Circular Formation Algorithms for Multiple Nonholonomic Mobile Robots: An Optimization-Based Approach

This paper revisits the circular formation control problem proposed in [G. S. Seyboth, J. Wu, J. Qin, C. Yu, and F. Allgower, “Collective circular motion of unicycle type vehicles with nonidentical constant velocities,” IEEE Transactions on Control of Network Systems , vol. 1, no. 2, pp. 167–176, Jun. 2014.] for multiple nonholonomic mobile robots with nonidentical constant forward speeds. Specifically, we study two types of circular formations: First, a circular motion with synchronized/balanced phase configuration; and second, a concentric circular formation with both circular orbits control and phase synchronization/balancing. Existing works on the above problems utilize a fixed-gain control input, which increases the workload of the engineers for selecting favorable algorithm parameters. To reduce this workload, we study the above problems from a new perspective by utilizing optimization methods, based on which two variable-gain control algorithms are proposed such that much greater flexibility on the selection of algorithm parameters is acquired. The global convergence properties of the proposed algorithms are analyzed under some mild assumptions. Both simulations and field experiments are presented to validate the effectiveness of the proposed formation algorithms.

A PROTOTYPE SWING MECHANICAL ARM WEEDER FOR WEED CONTROL OF ORCHARD TREES

A weeder with controlled swing mechanical arm was developed to control and remove the weeds intra-rows orchards tree. The swing mechanical arm constructed from steel, ground wheel carried the arm. The DC Electric motor with 12 V was used as the source of power to operate the rotary blades Weeder. Three rotational speed 1600 rpm, 2200 rpm and 2600 rpm was adjusted and controlled by the short resistor circuit. The prototype electric Weeder was evaluated under three forward speed 3.2 kmh-1, 4.1 kmh-1 and 5.7 kmh-1 at three rotational speed 1600 rpm, 2200 rpm and 2600 rpm for weeder and two different blades. The result indicated that it could be able to use the electric power produced from the tractor can be used to operate of the electric weeder. The electric Weeder with controlled swing mechanical arm may be applied to control of the weeds in citrus orchards tree field. The rotational speed 2600 rpm and forward speed 3.2km. h-1gave the maximum weeding efficiency under orange orchards tree field conditions. The blades weeder was more effective in controlling weeds than the Tines. The developed electric weeder may be ideal for weeding under orchard trees. The type of blades was non-effect on fuel consumption at constant forward speed.

A time domain boundary element method for wave added resistance of ships taking into account viscous effects

Linear boundary element methods generally provide accurately enough predictions of ship motions in small amplitude waves. However, when the wave-induced added resistance is investigated, nonlinear effects are to be accounted for. Higher order effects, such as second order wave-induced drift forces, depend largely on ships forward speed. This article presents a nonlinear time-domain Rankine source method to calculate the wave-induced added resistance of ships advancing at constant forward speed in regular head waves. The fully nonlinear steady flow was computed. Nonlinear Froude-Krylov and hydrostatic forces were obtained by integrating pressures over the instantaneous wetted surface (undisturbed incident wave). Radiation forces were computed in time domain using convolution integrals (Cummins approach); diffraction forces, were computed using the complex force amplitude resulting from the linear seakeeping problem of incident wave diffraction. Radiation and diffraction effects caused by the changing wetted surface were accounted for. An empirical approach to account for the viscous wave added resistance was introduced. Numerical results for a 14,000TEU container ship and a very large tanker were compared to results from a frequency domain method, CFD calculations, and experimental towing tank measurements.

Potential of three-dimensional footprint mold in investigating the effect of tractor tire contact volume changes on rolling resistance

In the present study a method is developed to estimate the three-dimensional (3D) footprint of pneumatic agricultural tires based on molding the tire footprint by liquid plaster and converting these molds to three-dimensional models using a 3D scanner. A Goodyear 12.4–28, 6 ply tractor drive tire was operated on a clay loam soil in a soil bin under three vertical loads, using three inflation pressures and three soil moisture contents at a constant forward speed of 0.45 ms-1. The results showed the rut depth and contact volume increased by increasing the vertical load and inflation pressure and soil moisture content. Contact volume was increased by increasing the vertical load, inflation pressure, and soil moisture content. A multiple regression model was presented with a coefficient of determination (R2) of 0.88 to predict the contact volume based on vertical load, inflation pressure, and soil moisture content. Finally, a univariate regression model was presented to predict the rolling resistance based on the contact volume with a relatively high R2 of 0.93. It was also found that in deformable surfaces, vertical penetration and soil contact volume are the main reasons for the increase in rolling resistance.

On the weakly nonlinear seakeeping solution near the critical frequency

We study theoretically and numerically the nonlinear seakeeping problem of a submerged or floating body translating with constant forward speed $U$ parallel to the undisturbed free surface while at the same time undergoing a small oscillatory motion and/or encountering small-amplitude waves at frequency $\unicode[STIX]{x1D714}$. It is known that at the critical frequency corresponding to $\unicode[STIX]{x1D70F}\equiv \unicode[STIX]{x1D714}U/g=1/4$, where $g$ is the gravitational acceleration, the classical linear solution is unbounded for a single point source, and the inclusion of third-order free-surface nonlinearity due to cubic self-interactions of waves is necessary to remove the associated singularity. Although it has been shown that the linear solution is in fact bounded for a body with full geometry rather than a point source, the solution still varies sharply near the critical frequency. In this work, we show theoretically that for a submerged body, the nonlinear correction to the linear solution due to cubic self-interactions of resonant waves in the neighbourhood of $\unicode[STIX]{x1D70F}=1/4$ is of first order in the wave steepness (or body motion amplitude), which is the same order as the linear solution. With the inclusion of nonlinear effects in the dispersion relation, the wavenumbers of resonant waves become complex-valued and the resonant waves become evanescent, with their amplitudes vanishing with the distance away from the body. To assist in understanding the theory, we derive the analytic nonlinear solution for the case of a submerged two-dimensional circular cylinder in the neighbourhood of $\unicode[STIX]{x1D70F}=1/4$. Independent numerical simulations confirm the analytic solution for the submerged circular cylinder. Finally, we also demonstrate by numerical simulations that similar significant nonlinear effects for a surface-piercing body exist in the neighbourhood of $\unicode[STIX]{x1D70F}=1/4$.

Estabilización Automática de una Bicicleta sin Conductor mediante el Enfoque de Control por Rechazo Activo de Perturbaciones

<p>Este trabajo propone una estrategia de Control por Rechazo Activo de Perturbaciones (ADRC), usando observadores extendidos de perturbación, para estabilizar una bicicleta en movimiento, sin conductor y con una velocidad de avance variable. Aunque la bicicleta tiene una dinámica inestable y no lineal alrededor de su posición vertical, que puede modelarse como un sistema Lineal de Parámetros Variantes (LPV) dependientes de la velocidad, el diseño del controlador usa un modelo simplificado de parámetros concentrados invariantes en el tiempo y una velocidad nominal constante. El esquema ADRC agrupa las discrepancias entre el modelo simplificado y la planta, junto con las perturbaciones externas en una señal aditiva unificada, que es estimada a través del observador y realimentada mediante una ley de control lineal para rechazarla. La efectividad de la estrategia es validada mediante una co-simulación entre ADAMS y MATLAB, la cual exhibe un alto desempeño y robustez sobre un modelo dinámico virtual de la bicicleta, sometida a perturbaciones externas severas y variaciones de parámetros.</p>

Iterative Rankine HOBEM analysis of hull-form effects in forward-speed diffraction problem

A time-domain numerical algorithm based on the higher-order boundary element method and the iterative time-marching scheme is proposed for seakeeping analysis. The ship waves generated by a hull advancing at a constant forward speed in incident waves and the resultant diffraction forces acting on the hull are computed to investigate the hull-form effects on the hydrodynamic forces. A rectangular computational domain travelling at ship's speed is considered. An artificial damping beach for satisfying the radiation condition is installed at the outer portion of the free surface except the downstream side. An iterative time-marching scheme is employed for updating both kinematic and dynamic free-surface boundary conditions for numerical accuracy and stability. The boundary integral equation is solved by distributing higher-order boundary elements over the wetted body surface and the free surface. The hull-form effects on the naval hydrodynamics are investigated by comparing three different Wigley models. Finally, the corresponding unsteady wave patterns and the wave profiles around the hulls are illustrated and discussed.

Transient and steady-state rotation center of vehicle dynamics

The purpose of this paper is to show the effect of acceleration -variable forward velocity-, on the steady-state and transient responses of turning vehicles and the resulted path of motion of the vehicle. Comparing the responses of the vehicle will be used to prove that there is a negligible difference between the steady-state and transient center of rotation of the vehicle in engineering applications.To show that vehicles are working close to their steady-state conditions even at transient stage, we examine a vehicle in two maneuvers. In the first one, the vehicle is assumed to be moving at a constant forward speed and experiencing a step steer angle change. In the second maneuver, the vehicle experiences a lane change steering input. The transient response of the vehicle, as well as the required time to achieve the steady-state conditions will be analyzed.

수중정찰용 자율무인잠수정의 운동 모델링 및 시험을 통한 계수 조정

This paper presents the dynamic model of an AUV called HW200 for underwater surveillance. The mathematical model of HW200 is briefly introduced, considering its shape. The maneuvering coefficients were initially estimated using empirical formulas and a database of vehicles with similar shapes. A motion simulator, based on Simulink of Mathworks, was developed to evaluate the mathematical model of the vehicle and to tune the maneuvering coefficients. The parameters were finely tuned by comparing the experimental results and simulated responses generated with the simulator by applying the same control inputs as the experiment. The velocity of HW200 in the tuning process was fixed at a constant forward speed of 1.83 m/s. Simulations with variable speed commands were conducted, and the results showed good consistency in the motion response, attitude, and velocity of the vehicle, which were similar to those of the experiment even under the speed variation. This paper also discusses the feasibility of its application to a model-based integrated navigation system (INS) using the auxiliary information on the velocities generated by the model.

The effect of tyre and rider properties on the stability of a bicycle

To work towards an advanced model of the bicycle-rider-environment system, an open-loop bicycle-rider model was developed in the commercial multibody dynamics software ADAMS. The main contribution of this article to bicycle dynamics is the analysis of tyre and rider properties that influence bicycle stability. A system identification method is used to extract linear stability properties from time domain analysis. The weave and capsize eigenmodes of the bicycle-rider system are analysed. The effect of tyre properties is studied using the tyre’s forces and torques that have been measured in several operating conditions. The main result is that extending simplified models with a realistic tyre model leads to a notable decrease in the weave stability and a stabilization of the capsize mode. This effect is mainly caused by the twisting torque. Different tyres and tyre inflation pressures have little effect on the bicycle’s stability, in the case of riding straight at a constant forward speed. On the other hand, the tyre load does have a large effect on bicycle stability. The sensitivity study of rider properties shows that body stiffness and damping have a small effect on the weave and capsize mode, whereas arm stiffness destabilizes the capsize mode and arm damping destabilizes the weave mode.

Bottom-following control for an underactuated unmanned undersea vehicle using integral-terminal sliding mode control

The bottom-following problem of an underactuated unmanned undersea vehicle (UUV) is addressed. A robust nonlinear controller is developed by using integral-terminal sliding mode control (ITSMC), which can exponentially drive an UUV onto a predefined path at a constant forward speed. The kinematic error equations are first derived in the Serret-Frenet frame. Using the line of sight (LOS) method, Lyapunov’s direct technique and tracking differentiator, the guidance law is established. Then, the kinematic controller, the guidance law, is expanded to cope with vehicle dynamics by resorting to introduce two integral-terminal sliding surfaces. Robustness to parameter perturbation is addressed by incorporating the reaching laws associated with the upper bound of the parameter perturbation. The proposed control law can guarantee that all error signals globally exponentially converge to the origin. Finally, a series of numerical simulation results are presented and discussed. In these simulations, wave, constant unknown ocean currents (for the purposes of the controller) and the parameter perturbation are added to illustrate the robustness and effectiveness of the bottom-following control scheme.

Pursuit Formation of Double-Integrator Dynamics Using Consensus Control Approach

This paper deals with cyclic pursuit of double-integrator multiagent systems (MASs) in regular polygon formations. In kinematics level, based on a leaderless architecture, each agent pursues another one in a regular polygon formation with cyclic pursuit around a centroid. Then, in dynamics level, the agents reach consensus on a centroid around which they pursue each other. Despite introduced cyclic pursuit approaches in the literature based on agents with kinematic models and constant forward speeds, the proposed approach is based on agents with double-integrator dynamics without speed constraints. Moreover, based on the proposed approach, it is feasible to control the cyclic pursuit angular velocity. Numerical simulations for a MAS including seven agents confirm the usefulness of the proposed formation control strategy.

A numerical study of the second-order wave excitation of ship springing by a higher-order boundary element method

ABSTRACT This paper presents some of the efforts by the authors towards numerical prediction of springing of ships. A time-domain Higher Order Boundary Element Method (HOBEM) based on cubic shape function is first presented to solve a complete second-order problem in terms of wave steepness and ship motions in a consistent manner. In order to avoid high order derivatives on the body surfaces, e.g. mj-terms, a new formulation of the Boundary Value Problem in a body-fixed coordinate system has been proposed instead of traditional formulation in inertial coordinate system. The local steady flow effects on the unsteady waves are taken into account. Double-body flow is used as the basis flow which is an appropriate approximation for ships with moderate forward speed. This numerical model was used to estimate the complete second order wave excitation of springing of a displacement ship at constant forward speeds.

An iterative Rankine boundary element method for wave diffraction of a ship with forward speed

A 3-D time-domain seakeeping analysis tool has been newly developed by using a higher-order boundary element method with the Rankine source as the kernel function. An iterative time-marching scheme for updating both kinematic and dynamic free-surface boundary conditions is adopted for achieving numerical accuracy and stability. A rectangular computational domain moving with the mean speed of ship is introduced. A damping beach at the outer portion of the truncated free surface is installed for satisfying the radiation condition. After numerical convergence checked, the diffraction unsteady problem of a Wigley hull traveling with a constant forward speed in waves is studied. Extensive results including wave exciting forces, wave patterns and pressure distributions on the hull are presented to validate the efficiency and accuracy of the proposed 3-D time-domain iterative Rankine BEM approach. Computed results are compared to be in good agreement with the corresponding experimental data and other published numerical solutions.

Autonomous formation flight of multiple flapping-wing flying vehicles using motion capture system

This study demonstrates an autonomous formation flight of multiple flapping-wing flying vehicles for the first time. In order to extract the position and attitude information of each flying vehicle, an external motion capture system is applied. A path-following controller is designed so that each flapping-wing flying vehicle has a time-independent circular path with the predetermined radius, and the constant forward flight speed and altitude. Due to the variations in flight characteristics among four different flapping-wing flying vehicles, the gain of the directional control, which generates nonlinear rolling moment using the changes of the tension in flexible membrane wings, is individually tuned for each vehicle. The rotational speed of the circular path is kept constant by controlling the desired radius rather than the forward flight speed so that the formation angles between two closest flapping-wing flying vehicles are maintained at 90 degrees. The performances of the individual path-following controllers and the circular formation controller are statistically evaluated in terms of the mean and standard deviation of the flight state variables.

Experimental and numerical investigation of wave resonance in moonpools at low forward speed

In order to study the behavior of resonant piston-mode resonance in a moonpool at low forward/incoming current speed, we performed a series of experiments and compared them to a nonlinear hybrid method which couples potential and viscous flow. The setting is a 2D box section with a moonpool gap in the middle, forced to oscillate in heave with a given amplitude and frequency, while simultaneously travelling at a given constant forward speed. The numerical method couples a Navier–Stokes (CFD) solver using the Finite Volume Method (FVM), with a potential flow method using the Harmonic Polynomial Cell method (HPC). It is found that the moonpool behavior is slightly reduced with a low forward velocity, and the reduction is dependent on the heave forcing amplitude.