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This paper presents the modeling and robust H ∞ control of a novel ultra-quiet spacecraft which employs the non-contact Stewart platform to actively control its support module (SM) and payload module (PM). The SM and PM are mechanically separated such that the disturbances and vibrations from the SM can be perfectly suppressed. However, this novel spacecraft has internal instability. To overcome the instability, this paper derives the dynamics model of the non-contact Stewart spacecraft using Newton–Euler approach at first. Then, the mixed sensitivity robust H ∞ control is developed to guarantee both the attitude stability and precision pointing. Finally, simulation studies are provided to validate the effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

A computational study treating cavitation phenomenon within a single bubble undergoing various controlled ultrasonic waveforms is presented in this paper. Numerical simulations using sinusoidal, square, triangular and sawtooth waves crossing an aqueous media, saturated with oxygen, are conducted upon various operational conditions of frequency and amplitude. Bubble radius, temperature and pressure were estimated over time for 64 combined cases. The obtained results show that at relatively low acoustic pressure, i.e. 1.5 and 2 atm, the square wave is proved to generate the highest temperature and pressure inside the bubble, while triangular and sawtooth ones remain the less interesting waveforms for sonochemical application within the same operational conditions. At higher amplitudes above 2.5 atm, this trend is changed, especially at low frequencies, i.e. 200 and 300 kHz, where square wave showed some limitations in attaining the optimal values of the strong collapse within one acoustic cycle. [ABSTRACT FROM AUTHOR]

This paper presents a new S trajectory kinematic measurement method to evaluate the dynamic accuracy of five-axis machine tools based on R-test measurements. The S trajectory is obtained by scaling the machining path of the S-shaped test piece to the measuring stroke of the R-test. A geometric and dynamic accuracy simulation model is established to analyze the influence of various error factors on the S trajectory test and compare with the conical kinematic test described in ISO10791.6 quantitatively. The simulation results shown that the S trajectory test is more sensitive to most geometric errors and dynamic errors than the conical test. Particularly, to reflect the dynamic error factors such as poor rigidity of machine tools, servo mismatch, reverse error and nonlinear error, the S trajectory test has obvious advantages. Meanwhile, compared with the actual S-shaped piece machining, which is under development for inclusion in ISO 10791.7, the proposed non-cutting kinematic test method can simply reflect the dynamic accuracy of five axis machine tools itself without the interference of other factors and does not require additional workpiece and testing equipment. The proposed method is verified through experiments on a five-axis machine tool. [ABSTRACT FROM AUTHOR]

This paper first presents a highly flexible 3D manipulator with links of arbitrary shape, then develops a closed-form dynamic model that best describes it. The model is based on a Newton–Euler formulation and the substructuring method is used to account for large deformations. The formulation of the motion equations starts from a data set which can be either analytically or numerically computed by finite elements(FE) codes. Simulation has been used to validate the model and compare the results with those of two different multibody software and one experimental, which was obtained from the Multi-Elastic-Link Robot Identification Dataset (MERIt), developed by the TU Dortmund. Then, thanks to the approach here adopted, an integral manifold model is derived, suitable for advanced control system design. [ABSTRACT FROM AUTHOR]

Combustion of fossil fuels in the transport sector represents the second largest source of greenhouse gas emissions. For this reason, governments are fostering diversification of energy sources by creating a set of governmental environmental policies and initiatives. In this context, biofuels are expected to represent a substantial part of source diversification, but it is necessary to assess the sustainability of their market to explore its effect on economical, technological, social, political and environmental dimensions. This research presents a dynamic simulation modelling of the Colombian biodiesel market and analyzes the policy support instruments for creating and managing it. A system dynamics based model is proposed to enable decision-makers to understand the influences between the different variables that describe the system and the impact of the biodiesel government policy in Colombia. The primary focus of this paper is to establish the characteristics of each sustainability dimension for the case of study and apply the system dynamics methodology with different types of validation. Finally, the Colombian market status and a sensitivity analysis are developed. The results show that in order to support the development of this sector, it is necessary to diversify the raw materials for the production of biodiesel in the medium term, which means raw materials without competence for the primary rainforest or competition with food productive lands. [ABSTRACT FROM AUTHOR]

A mathematical model describing the dynamics of road transport vehicle is proposed in this paper. The system consists of a cab, a carriage, a chassis, the road, and mounts/suspensions between them. The coupled correlations between substructures are studied using the state space theory. A factor, coupling coefficient, for describing the coupling effect in the subsystem and a factor, vibration attenuation coefficient, for characterizing the vibration reduction of the substructures are derived. The joint location, the stiffness, and the damping of the mount/suspension, as well as the mass and inertia moment of the substructures are considered as design variables affecting system vibration coupling and reduction. The contribution of design variables is analyzed using Latin hypercube sampling and quadratic regression, top ten contributing variables are obtained, and their effects on the subsystem coupling are analyzed and discussed. The back propagation neural network is employed to investigate the nonlinear correlation between subsystem coupling and substructure vibration reduction. The results show the cab vibration reduction achieves optimum when the cab–chassis coupling is high and the carriage–chassis coupling is low. However, the optimal carriage vibration reduction requires the exact opposite coupling correlations. [ABSTRACT FROM AUTHOR]

In this paper the construction and dynamic modeling of a mobile ball robot is represented. The unique mechanical structure of this robot results more reliable and stable motion with respect to previous similar robots. Driving mechanism is placed within a hollow spherical case, and consists of three sets of actuated omni–wheels for omni-directional motion of the robot. This mechanism decreases relative slip between the inner actuation system and outer ball case, and results more precise control of the robot in different paths and places. At first, the mechanical structure, actuation and control system, and process of different components assembling to work as a robot is explained. Then, based on the Newton–Euler formulation, mathematical model of motion is derived and dynamic equations of the robot are evaluated. These equations have differential algebraic equations (DAEs) formation. Consequently, a computational method to solve ADEs has been developed. Finally, in a case study, the robot performance in passing through a linear path with two perpendicular segments is studied. Simulation and experimental results demonstrate that robot moves through the desired and predefined trajectory. [ABSTRACT FROM AUTHOR]

This paper presents a new methodology for on-line inertia parameters estimation for a rigid space debris captured by a tethered system, based on a new dynamics model of the system where the base satellite (chaser) and the space debris (target) are modeled as rigid bodies and the attachment points of the tether are offset from the centers of mass of the two bodies. Parameters estimation of unknown debris is critical for subsequent tasks in the space debris remediation mission, in particular, for debris retrieval and de-orbiting. In the proposed algorithm, the chaser and target are modeled as rigid bodies, the latter with unknown inertia parameters. Then, the parameters identification problem is formulated and solved in three phases. First, a coarse estimate of the target mass is obtained during the post-capture phase, while the length of tether is much longer than the offsets of base and target satellite, and the rigid body model is degenerated to a mass point model. Then, with a proper tension control scheme and the coarse estimate used as an initial guess, the debris is retrieved smoothly and a precise mass estimate is achieved during the first half of the retrieval. Finally, when the tether is retrieved relatively short and the rigid body model is used, moments of inertia and the offsets of the space debris will be estimated with a proper tension control scheme for rigid body model. [ABSTRACT FROM AUTHOR]

This paper deals with the computational modeling and numerical simulation of contact problems at finite deformations using the finite element method. Quasi-static and dynamic problems are considered and two particular frictional conditions, full stick friction and frictionless cases, are addressed. Lagrange multipliers and regularized formulations of the contact problem, such as penalty or augmented Lagrangian methods, are avoided and a new direct elimination method is proposed. Conserving algorithms are also introduced for the proposed formulation for dynamic contact problems. An assessment of the performance of the resulting formulation is shown in a number of selected benchmark tests and numerical examples, including both quasi-static and dynamic contact problems under full stick friction and frictionless contact conditions. Conservation of key discrete properties exhibited by the time stepping algorithm used for dynamic contact problems is also shown in an example. [ABSTRACT FROM AUTHOR]

Abstract: In order to improve the efficiency and accuracy of soft-landing dynamic calculation of lunar lander, this paper proposed a new soft-landing dynamic model with seven free degrees and the inertia force was also taken into consideration during the landing process. The force condition of lander during soft-landing was investigated; moreover dynamics and kinematics equations were deduced. Besides, the landing process was studied by mathematical model, which is verified by results of scale lander prototype and landing test platform. The result shows that the calculation could match the test results effectively, which verifies accuracy and availability of seven free degrees soft-landing dynamic model. [Copyright &y& Elsevier]

In the last few years, the observation of gravitational waves by means of LIGO and Virgo interferometers and the success of LISA Pathfinder, gave a significant boost to the development of space-based gravitational wave observatories. The European Space Agency confirmed LISA as the third large class mission of the Cosmic Vision program. The present work is part of the Drag Free and Attitude Control System (DFACS) preliminary prototyping study, which aims at the development of mathematical models and advanced controllers for the science phases of the LISA mission. Nonlinear modelling is a fundamental step for the derivation of linearized and decoupled models as well as for the development of suitable linear and nonlinear controllers. In this paper, an analytical nonlinear model is derived, which describes all the relevant dynamics of a LISA spacecraft, representing an effective compromise between accuracy and complexity. The model is extensively validated through linearization analysis and Monte Carlo simulations. [ABSTRACT FROM AUTHOR]