2-DOF Model Research Articles

Synchronous Position Control of Gantry Table Using Adaptive Fraction-Order Dynamic Surface Control With Dendritic Neuron Model

This article introduces a three-degree-of-freedom (3DOF) model-based adaptive fractional-order dynamic surface control (AFODSC) system for a synchronous position control of a gantry table. First, the 3DOF model of the gantry table is investigated considering the rotational dynamics caused by inter-axis mechanical coupling and synchronous error. Then, a new fractional-order dynamic surface control (FODSC) approach is introduced using a fractional-order low-pass filter to provide an extra degree of freedom for the existing dynamic surface control (DSC) method. Because it is arduous to know the system uncertainty, the AFODSC is further elaborated by incorporating an adaptive mechanism and an uncertainty observation into the FODSC. In the proposed AFODSC, a modified dendritic neuron model observer (DNMO) is proposed to identify uncertainties, whereas an exponential compensator is designed to compensate for the observation error. Multiple adaptation laws are derived to adapt the parameters of DNMO on the basis of the Lyapunov stability theorem. Experimental results confirm that the proposed AFODSC system demonstrates favorable position tracking and synchronization accuracies for the gantry table compared with the conventional DSC system.

Effects of Deflection Mode on Flared-Maneuver Performance of Unpowered Heavy Airdrop System

For the landing process of a large-scale airdrop system, flared-maneuver is a common approach to decelerate to prevent huge impacts while touching down. A 6-DOF model of parafoil-load system is used to investigate the effects of different deflection modes on airdrop system’s landing performance. By numerical simulation, three main factors, distance of deflection, rate of deflection and the pattern of rate changing, are discussed according to the results. The conclusion derived is of some significance in assisting control and design of landing procedure of such unpowered heavy airdrop systems.

An improved 2DOF model for dynamic behaviors of RC members under lateral low-velocity impact

Under lateral low-velocity impact, the RC slender members, i.e., beams and columns, commonly exhibit the local punching-shear as well as the global shear, flexural, flexure-shear and instability failure modes. However, the existing theoretical models are incapable of simultaneously predicting the above failure modes and the corresponding dynamic responses of RC members. This study aims to develop a two-degree-of freedom model (2DOF) model to predict the dynamic behaviors of RC members exhibiting the above-mentioned failure modes under the lateral low-velocity impact. Firstly, the combined dynamic flexural and shear resistance function of RC members is established and verified by rapidly concentrated loading tests on RC beams. Secondly, an improved 2DOF model is proposed by incorporating the combined dynamic resistance function, P-δ effect and the shear wave propagation effect for the local and global response stages of members. Then, the improved 2DOF model is comprehensively validated by eight series of existing drop hammer tests (165 scenarios), in terms of the failure modes, impact forces and mid-span deflections of RC members. It is further found that, under impact loadings, the failure mode of the static flexure-critical RC beams would transit to the punching-/flexure-shear failure, which is more sensitive to the impact velocity than the impactor mass, and can be effectively inhibited by increasing sectional shear capacity. Finally, aiming to assist the impact-resistant design and evaluation of RC members, the corresponding flowchart is given.

Evaluating the performances of PI controller (2DOF) under linear and nonlinear operations of DFIG-based WECS: A simulation study

Owing to different stochastic characteristics of wind energy systems, there would commonly be uncertainties in the processes of wind energy conversion that may ultimately cause to severely degrade the quality of electric power production. These uncertainties include time-varying fluctuations of mechanical & electrical parameters that can be generated during both linear, and nonlinear operating behaviors of doubly fed induction generator-based wind energy conversion system (DFIG WECS). In order to handle a wind power quality problem, the previous studies largely focused on adjustment of mechanical parameters particularly based on blade pitch angle control by proposing different control strategies, and controller models. This work proposes a rarely studied electrical parameter control method that is particularly used to implement the regulation of rotor current components & electromagnetic torque in a DFIG WECS, based on Indirect Field Oriented Control (IFOC) strategy. Accordingly, a novel Proportional Integral controller model that employs a 2-Degree-of-Freedom [PI (2DOF)] is illustrated for an enhanced control of the rotor current components (quadrature & direct currents), electromagnetic torque under a 2MW DFIG WECS, which is operationally assumed to behave both linearly & nonlinearly. Herein, nonlinear operating behavior signifies a voltage dip that was assumed to be resulting when the system's normal (linear) voltage would suddenly drop by 90%. Furthermore, the overall model of the DFIG system was simulated in MATLAB-SIMULINK environment to evaluate the performances of PI controller (2DOF) under the system's stated operating behaviors. Based on the simulation signal statistics, the quadrature current distortion levels & DC mean values were mainly considered as the criteria for evaluating the controller performances. Finally, the proposed PI controller (2DOF) model has been tested to achieve an enhanced power quality in comparison with the traditional PI controller model.

Stable and unstable curves in vehicle three-dimensional state space

In the field of vehicle system dynamics, revealing the dynamic characteristics of nonlinear vehicle models with high degrees of freedom is a key point in current research. In the classic 2-DOF (degrees of freedom) model, the dynamics is analysed and represented in two-dimensional state space. However, it is necessary to reveal the three-dimensional state characteristics of the system when analysing high-DOF vehicle models. The concept of equilibrium points in two-dimensional space will be extended to curves in three-dimensional space, including stable curves and unstable curves, which can qualitatively reveal the evolvement characteristics of the system under different control parameters. In addition, because the dissipation of energy method can quantitatively reveal the global dynamic characteristics of the vehicle, this paper combines the (un)stable curves in the three-dimensional space with dissipation of energy to better analyse the global dynamics characteristics and mutually verify the correctness of conclusions. In this paper, first, the connection between (un)stable curves and region boundary is established. Second, the theoretical analysis of relationship between dissipation of energy and phase trajectories convergence characteristics is perfected. Third, the static and dynamic characteristics of vehicle system are analysed. Therefore, this paper proposed the concept of stable and unstable curves to intuitively reveal the global dynamics characteristics and system evolvement characteristics in three-dimensional state space.

Dynamic modelling of parafoil system based on aerodynamic coefficients identification

This study focuses on the identification of aerodynamic coefficients through airdrop data based on a known six-degree-of-freedom (6-DOF) model. Since the precise modelling of the parafoil system is a prerequisite for design of guidance, navigation and control systems, the accurate calculation of aerodynamic coefficients is vital. This paper first presents a rigid 6-DOF nonlinear model and simplifies it by linearizing the equations around the equilibrium point, which facilitates the acquisition of aerodynamic parameters next. Then, the recursive weighted least square method is applied to identify roll and yaw coefficients from airdrop test data. At last, simulations in the wind environment are implemented to analyse the dynamics of gliding and turning. The airdrop experiment also verifies the effectiveness of the dynamic model and the accuracy of identification.

Sensitivity analysis on the vertical motion of heavy machine due to changing tires characteristics

In this paper the author presents some aspects about the motion of a heavy machine with tires in moving on the irregular roads. Based on the spatial 3-DOF model of machine it was evaluated all eigen pulsations and simulated the tire-road interaction only for the vertical motion of a wheel loader. The influence of the tire characteristics to the dynamic behavior of the loader was studied.

A Numerical Analysis of Hybrid Spur Gears with Asymmetric Teeth: Stress and Dynamic Behavior

Hybrid gears are composed of high-strength steel, carbon fiber reinforced plastic (CFRP), and adhesive bond to join these materials. In this study, the effect of rack tip radius (TR), drive side pressure angle (DSPA), and rim thickness (RT) on the stress of hybrid gears is investigated numerically. In addition, the stress results of hybrid gears are compared with steel gears that are used for validation of the numerical results. Single tooth stiffness (STS) values are calculated based on tooth deformations obtained from numerical analyses. The 2-DOF model is used to observe the influence of DSPA and RT on the dynamic factor (DF) and static transmission error (STE). According to the results, increasing RT has a positive effect on stress, STS, and STE, while DSPA is effective on the dynamic factor at most.

Cross-story installation of viscous dampers in timber frame houses for earthquake damage reduction

Timber frame structures are commonly used in housing construction that use squared-off timber beams, columns, and walls as lateral load-bearing members. A small-size viscous damper can be applied to timber frame houses to reduce damage caused by major earthquakes. Dampers are normally installed inter-story (between adjacent floors) to absorb vibration energy and reduce seismic response. Another method is the cross-story installation wherein a damper is installed between the rooftop and base of the structure across intermediate floors. This study investigated the effectiveness of cross-story installation of a viscous damper by conducting eigenvalue analyses of 2DOF models and earthquake response analyses of a two-story timber frame house subjected to the 2016 Kumamoto earthquake and other major earthquakes. We compared the damping factors and response reduction effects of the cross-story installation with those of conventional inter-story installations. The results showed that the cross-story installation of dampers was more effective than the inter-story installation in terms of reducing story drift. Furthermore, the cross-story installation reduced the number of dampers required for preventing severe damage by half. Finally, the cross-story installation allowed the viscous damper in the first story to absorb vibration energy nearly twice as much as that of the inter-story installation. Therefore, while the cross-story damper is typically installed on an outer frame fixed to the house, our results conclude that it can be applied to an existing house as a seismic retrofitting measure.

Hydrodynamic interactions between waves and cylinder arrays of relative motions composed of truncated floating cylinders with five degrees of freedom

The hydrodynamic interactions between waves and a truncated floating circular cylinder array were examined in this work. Each cylinder of the array is allowed to oscillate with five degrees of freedom (DOFs), and there can be relative motions among different cylinders. The hydrodynamic responses of such arrays in the presence of ambient incident waves were studied using a semi-analytical technique, in which, the unknown coefficients of radiation–diffraction velocity potentials caused by array motions were expressed by the linear combination of each cylinder’s to-be-calculated oscillation amplitudes in each direction. Then, for each cylinder in the array, the amplitude of each degree of freedom was computed. Variations in the oscillation amplitudes of the cylinders in the array with wavenumbers for various incidence angles and column spacing, and amplitude distributions of free surface elevation for various wavenumbers were given. Additionally, extensions to the situation of multidirectional irregular waves were presented. Last but not least, we examined the effects of other DOFs (nonheave) on hydrodynamic responses and wave energy extraction performances (capture width w and interaction factor q) by comparing the results obtained by the 5-DOF and the 1-DOF (heave) models. In terms of response amplitude and wave energy extraction performance, the 5-DOF model’s results were significantly different from those of the 1-DOF model. Therefore, it is suggested to use the 5-DOF model to analyze such cylindrical arrays.

Numerical simulation analysis of the flow field in the bore of a two-stage light gas gun

In order to study the effect of different launch tube diameters of gas-driven two-stage light gas guns on the flow field during the launch process, a model of the piston movement in the pump tube to the projectile launch was established using Fluent. Using the dynamic mesh technology and 6DOF model, a numerical simulation of the projectile launch process of the two-stage light gas gun was carried out, and the effects of different launch tubes on the projectile velocity and the flow field in the bore were obtained. The results show that when the mass difference between the piston and the projectile is large, appropriately increasing the diameter of the launch tube is conducive to the flow of gas in the high-pressure cone and increases the projectile launching speed. The numerical simulation analysis of the flow field in the bore provides a basis for the design and optimization of the two-stage light gas gun.

Autonomous Maneuver Decision of Air Combat Based on Simulated Operation Command and FRV-DDPG Algorithm

With the improvement of UAV performance and intelligence in recent years, it is particularly important for unmanned aerial vehicles (UAVs) to improve the ability of autonomous air combat. Aiming to solve the problem of how to improve the autonomous air combat maneuver decision ability of UAVs so that it can be close to manual manipulation, this paper proposes an autonomous air combat maneuvering decision method based on the combination of simulated operation command and the final reward value deep deterministic policy gradient (FRV-DDPG) algorithm. Firstly, the six-degree-of-freedom (6-DOF) model is established based on the air combat process, UAV motion, and missile motion. Secondly, a prediction method based on the Particle swarm optimization radial basis function (PSO-RBF) is designed to simulate the operation command of the enemy aircraft, which makes the training process more realistic, and then an improved DDPG strategy is proposed, which returns the final reward value to the previous reward value in a certain proportion of time for offline training, which can improve the convergence speed of the algorithm. Finally, the effectiveness of the algorithm is verified by building a simulation environment. The simulation results show that the algorithm can improve the autonomous air combat maneuver decision-making ability of UAVs.

Dynamics Modeling and Characterization of Sunk Screw Connection Structure in Small Rockets

Bolted flange joints are widely used in engineering structures. Sunk screw connection structures commonly used in small rockets and missiles exhibit significant nonlinear characteristics when subjected to forces. In this article, a study of the dynamic characteristics of sunk screw connection is conducted. A 3-dof trilinear dynamic model is proposed, based on the study of the stiffness characteristics of the connection structure and considering contact nonlinearities. The connection surface is simplified as two axial trilinear springs and a lateral linear spring. The motion of the system can be divided into nine regions by the turning point of the trilinear springs. So that the motion of the system in each region can be completely resolved, the dynamic characteristics of the 3-dof trilinear system under impulse load and simple harmonic load are studied by means of semi-numerical analytical method. It is found that the response frequency of the system remains unchanged under a small impulse load, and the response can be obtained by approximate analytical expressions. When the impulse load is large, the response frequency is fluctuant, which reflects the sensitivity of the nonlinear system to the magnitude of impulse load. Under the simple harmonic excitation of bending moment, the response frequency curve of the system presents good single peak characteristics when the excitation amplitude is small. When the amplitude is large, the peak frequency of the system shifts, and the phenomenon of multi-peak resonance is shown in a certain range.

On the short-term and long-term acceleration failure probability of a container ship in irregular waves

ABSTRACT The evaluation of the acceleration response are required in ship intact stability analysis. The nondimensional response-amplitude operators of lateral acceleration in beam long-crested waves of a large container ship are compared by four calculation methods, three of which are the 5-DOF model in the time domain. The nonlinear restoring force and nonlinear diffraction force are considered. In irregular waves, the short-term and long-term acceleration failure probability of a large container ship are compared, and the influence of different frequency range integration of wave spectrum on the excessive acceleration failure probability is discussed. The results show that the lateral acceleration response obtained by the modification 2 method is the closest to the experimental value, and the short-term and long-term acceleration failure probability calculated by the modification 2 method is the largest among the prediction methods. In addition, increasing the integral range of wave spectra will increase the failure probability of acceleration.

Drill-string with cutting dynamics: A mathematical assessment of two models

In this paper, a new model to study drill-string dynamics is developed. Some of the novelties of the paper are: (1) the use of a new bit-rock interaction relation that does not restrict backward rotation of the bit nor bit-bounce; (2) the use of an advection equation to avoid dealing with a system of delay-differential equations in the simulation of the cutting process; (3) the extension of the advection approach treated in previous works to allow rotation in both directions; (4) the combination of the previous items with a distributed approach for the torsional dynamics; (5) the inclusion of the 2-DOF model as a limiting case of the continuous model. For this purpose, a strategy considering an extra parameter α is used. All these aspects lead to a coupled non-linear formulation that can exhibit self-sustained vibrations associated with the regenerative cutting process. The new model is compared, from a numerical point of view, with an established 2-DOF approach. Five scenarios considering a 1200 m column with different friction parameters and top drive conditions are simulated. Dissimilar predictions are observed, showing a more complex response for the continuum model where higher frequencies are excited as well. These results indicate that the more sophisticated model could capture other aspects of the dynamics that are neglected in the 2-DOF approach.

COLREGs-Compliant Multi-Ship Collision Avoidance Based on Multi-Agent Reinforcement Learning Technique

The congestion of waterways can easily lead to traffic hazards. Moreover, according to the data, the majority of sea collisions are caused by human error and the failure to comply with the Convention on the International Regulation for the preventing Collision at Sea (COLREGs). To avoid this situation, ship automatic collision avoidance has become one of the most important research issues in the field of marine engineering. In this study, an efficient method is proposed to solve multi-ship collision avoidance problems based on the multi-agent reinforcement learning (MARL) algorithm. Firstly, the COLREGs and ship maneuverability are considered for achieving multi-ship collision avoidance. Subsequently, the Optimal Reciprocal Collision Avoidance (ORCA) algorithm is utilized to detect and reduce the risk of collision. Ships can operate at the safe velocity computed by the ORCA algorithm to avoid collisions. Finally, the Nomoto three-degrees-of-freedom (3-DOF) model is used to simulate the maneuvers of ships. According to the above information and algorithms, this study designs and improves the state space, action space and reward function. For validating the effectiveness of the method, this study designs various simulation scenarios with thorough performance evaluations. The simulation results indicate that the proposed method is flexible and scalable in solving multi-ship collision avoidance, complying with COLREGs in various scenarios.

İki Bacaklı Yürüyüşün Ters Dinamiği : Basınç Merkezinin Bir Ani Dönme Merkezi Olduğu Varsayımı

In the study, an alternative 7-dof dynamical model that can be used in gait analysis of human, bipedal robots and exoskeleton systems is proposed. The dimensions and kinematic data of the model are specified on the basis of anthropometry and kinematic data of real human gait. The 7-link model consists of the trunk, two thighs, two shanks and two feet links. The movement is examined in the sagittal plane and during the single support phase (SSP). Unlike the rotation about a fixed point, it is assumed that the right foot rotates about the center of pressure (COP). The part between the COP and the tip of the toe is considered to be a passive limb which is horizontally on the ground. The effect of this part on dynamic analysis is neglected. The equations of motions are derived by applying Lagrange equations. Using the kinematic data obtained in clinical gait analysis (CGA) conducted by Winter [1], the net joint torques are calculated and then compared with CGA torque data. As a result of the comparisons, it is seen that the curves are overlapped significantly.

Dynamic model and earthquake response of a hybrid isolated system with tuned inerter dampers for nuclear power plants

Considering the benefits of tuned inerter damper (TID), a hybrid control system (TIDISO system) for third-generation NPPs consisting of an un-isolated outer containment structure, an isolated inner containment structure and a connecting TID system was proposed. First, governing equations of motion for the 3-degree-of-freedom (3DOF) model were derived and the seismic response variances of TIDISO system under white noise excitation were obtained. Next, an optimization study on inertance, frequency and damping parameters was conducted, and then simplified expressions were provided as a function of the various structural parameters for the optimal TID parameters. Through simulation comparisons, the accuracy of the expressions was further verified. Finally, a case study was conducted to demonstrate the proposed rapid-determining formula for optimal TID parameters and to estimate the effectiveness of the proposed TIDISO system under seismic waves. The results illustrate the proposed system is effective to suppress acceleration and story draft responses, especially for isolation displacement. Under artificial wave 1, the displacement of isolation layer has declined from 475 mm to 327 mm, nearly 32.7%.

A continuous-time walking pattern generator for realizing seamless transition between flat-contact and heel-to-toe walking

A planning algorithm that can generate continuous-time walking patterns including the seamless transition between flat-contact and heel-to-toe walking gaits is proposed. The planner makes use of the closed-form solution of a modified linear inverted pendulum mode which includes the ZMP and the weight ratio of each foot explicitly in its dynamics. The heel-to-toe movement of each foot is directly parameterized by the ZMP, and therefore consistency between the foot movement and the low-dimensional dynamics is ensured. In simulations with a 32 DoF model of a life-sized humanoid robot, fast human-like walking at the maximum speed of 4.6 km/h was achieved.

Performance analysis of the SJTU-WEC based on the wave-to-wire model and the wave tank experiment

The development of wave energy has attracted wide attention. This paper proposes a conceptual design of a station featuring direct drive 3-degree-of-freedom (3-DoF) wave energy converter (SJTU-WEC), of which the numerical and experimental performances are studied. This article first introduces the power generation principle of the SJTU-WEC, of which the wave-to-wire (W2W) model is simplified and established as a 2-DoF model, including frequency domain and time domain. Then a 1:12.5 prototype is manufactured and tested in wave tank to study its performance. By comparing numerical and experimental results, the accuracy of the W2W model is verified. The experimental results show that the energy conversion efficiency reaches up to 28% under the specific wave condition. Finally, based on the W2W model, the power generation performance of the full-scale SJTU-WEC is obtained. In Lianyungang Sea areas, the average annual power generation of a single SJTU-WEC is calculated to be 108W.