Large-scale Mechanical System Research Articles

Extended Balancing of Continuous LTI Systems: A Structure-Preserving Approach

In this article, we treat extended balancing for continuous-time linear time-invariant systems. We take a dissipativity perspective, thus, resulting in a characterization in terms of linear matrix inequalities. This perspective is useful for determining a priori error bounds. In addition, we address the problem of structure-preserving model reduction of the subclass of port-Hamiltonian systems. We establish sufficient conditions to ensure that the reduced-order model preserves a port-Hamiltonian structure. Moreover, we show that the use of extended Gramians can be exploited to get a small error bound and, possibly, to preserve a physical interpretation for the reduced-order model. We illustrate the results with a large-scale mechanical system example. Furthermore, we show how to interpret a reduced-order model of an electrical circuit again as a lower dimensional electrical circuit.

Multi-Sensor Fusion by CWT-PARAFAC-IPSO-SVM for Intelligent Mechanical Fault Diagnosis.

A new method of multi-sensor signal analysis for fault diagnosis of centrifugal pump based on parallel factor analysis (PARAFAC) and support vector machine (SVM) is proposed. The single-channel vibration signal is analyzed by Continuous Wavelet Transform (CWT) to construct the time–frequency representation. The multiple time–frequency data are used to construct the three-dimension data matrix. The 3-level PARAFAC method is proposed to decompose the data matrix to obtain the six features, which are the time domain signal (mode 3) and frequency domain signal (mode 2) of each level within the three-level PARAFAC. The eighteen features from three direction vibration signals are used to test the data processing capability of the algorithm models by the comparison among the CWT-PARAFAC-IPSO-SVM, WPA-PSO-SVM, WPA-IPSO-SVM, and CWT-PARAFAC-PSO-SVM. The results show that the multi-channel three-level data decomposition with PARAFAC has better performance than WPT. The improved particle swarm optimization (IPSO) has a great improvement in the complexity of the optimization structure and running time compared to the conventional particle swarm optimization (PSO.) It verifies that the proposed CWT-PARAFAC-IPSO-SVM is the most optimal hybrid algorithm. Further, it is characteristic of its robust and reliable superiority to process the multiple sources of big data in continuous condition monitoring in the large-scale mechanical system.

Research on Creep Deformation and Control Mechanism of Weak Surrounding Rock in Super Large Section Tunnel

In order to solve the difficulties of creep deformation of surrounding rock in super large section tunnel, taking Letuan tunnel of Binlai expressway, a typical super large cross-section tunnel as research background, the creep mechanical characteristics of surrounding rock are taken into consideration, and the influence of different supporting forms such as bolt reinforcement, rock grouting, high-strength arch and concrete lining on surrounding rock deformation and failure mechanism is comprehensively studied. The creep failure mechanism and high strength control mechanism of surrounding rock are obtained. Research results show that the surrounding rock shows obvious creep mechanical characteristics, the continuous growth of surrounding rock deformation has brought severe challenges to the tunnel support; the surrounding rock of super large cross-section tunnel shows unstable creep deformation failure mechanism with obvious acceleration of creep stage under the condition of no support; the influence mechanism of different support forms on the control effect of surrounding rock creep deformation is systematically studied, and the evaluation indexes of deformation control rate and creep control rate of surrounding rock prove that confined concrete, as a high-strength support type, has significant advantages for surrounding rock creep control. Based on the large-scale mechanical test system of tunnel, the mechanical test of confined concrete arch is carried out, and the bearing mechanism and mechanical characteristics of confined concrete arch are clarified. The field application results show that the confined concrete arch can effectively control the creep deformation. The research results can provide theoretical basis for relevant projects.

Macroscopic model of fluid structure interaction in cylinder arrangement using theory of mixture

In the framework of the theory of mixture, the dynamic behaviour of solid cylinder bundles submitted to external hydrodynamic load exerted by surrounding viscous fluid flow is described. Mass conservation and momentum balance formulated on an elementary domain made of a given volume of mixture give rise to a system of coupled equations governing solid space-averaged displacement, fluid velocity and pressure provided that near-wall hydrodynamic load on each vibrating cylinder is expressed as a function of both fluid and solid space-averaged velocity fields.Then, the ability of the macroscopic model to reproduce over time an averaged flow surrounding vibrating cylinders in a large array in the context of small magnitude displacements is pointed out. Numerical solutions obtained on a two-dimensional configuration involving an array of several hundreds of cylinders subjected to an impulsional load are compared to those provided by averaged well-resolved microscopic-scale solutions. The relative error is less than 3% in terms of displacement magnitude and 5% for frequency delay.The proposed macroscopic model does not include any assumption on relative effect contributions to mechanical exchanges occurring in the full domain. Therefore it features interesting properties in terms of fluid solid interaction prediction capabilities. Moreover it contributes to a significant gain in terms of computational time and resources. Further developments are now required in order to extent the formulation to large magnitude displacements including three-dimensional effects. This could be recommended for investigations on fuel assembly vibration risk assessment in Pressure Water, Fast Breeder reactors at a whole core scale or any other large-scale mechanical system involving some kind of periodic geometry.

Study on mechanical properties and influencing factors of confined concrete arch in underground engineering with complex conditions

Confined concrete (CC) is a new form of high-strength support. To verify it, the authors have developed a large-scale mechanical test system. With the test system, a full-scale laboratory experiment is conducted in this paper to compare the mechanical properties of CC and traditional U-shaped steel arches in a straight-wall semicircle. Both of the CC and the U-shaped steel contain the same amount of steel. The experiment is also developed to study the deformation characteristics and the bearing mechanism of various arch types. Based on the numerical calculation, the variation law of bearing capacity of the CC arch is studied under different influencing factors. The factors include wall thickness of steel tube, concrete strength, lateral pressure coefficient, and others. The results show that (1) The U-shaped steel arch is prone to local buckling instability, resulting in failure of the entire arch. In contrast, the CC arch has an ultimate bearing capacity of 1072.4 kN, which is more than 2 times that of the U-shaped steel arch; and it also has high later bearing capacity. (2) Under the action of compression and bending, the arch is damaged with the key failure position on its legs. The bending moment is the main factor for the arch failure, and its action effect is enhanced with the increase in the lateral pressure coefficient. In field application, arch legs should be reinforced to reduce the peak of the bending moment and increase the overall strength of the arch. (3) Compared with the strength of core concrete, the wall thickness of the steel tube has a more significant effect on the mechanical properties and economy of CC arches. In the arch design, the field geological conditions and construction convenience should be considered. So, the steel tube should be used with the minimum wall thickness which meets the requirements of the bearing capacity of arches; and the common brand concrete should be used. Based on the above research, CC arches are designed for support in underground engineering with complex geological conditions. The control effect is remarkable with an average deformation of the surrounding rock controlled within only 72.2 mm.

Global Sensitivity Analysis and Dynamic Optimization of Multi-motor Driving Transmission System

The multi-motor driving transmission system (MMDTS) is a nonlinear, complex large-scale mechanical system that includes the drive subsystem (DS) and the gear transmission subsystem (GTS); the GTS is one of the most important units that can transmit motion and power from the DS to the working machine. A dynamic optimization approach is proposed to improve the dynamic performance of the MMDTS by improving its vibration displacement root mean square (VDRMS) value in this work. To avoid using the time-consuming dynamic model of the MMDTS in the optimization process, a surrogate model that imitates the behavior of the MMDTS is used as a replacement. Candidate surrogate models are constructed by the kriging, radial basis function, and support vector machine methods by employing sample points obtained by the Max-Min distance Latin hypercube sampling method and the original dynamic model of the MMDTS. The adjusted error-squared (R2 adjusted) is used to validate the accuracy of these surrogate models, and the kriging surrogate model is consequently selected as the final surrogate model for the subsequent Sobol’ global sensitivity analysis and particle swarm optimization (PSO). The most important design parameters are selected using the Sobol’ global sensitivity analysis, and they are set as the optimization variables in order to reduce the problem dimension and improve the computational efficiency. Subsequently, the weighted-combination and non-domination sorting methods are used to obtain the optimal parameter solution, and the VDRMS values of the system that are obtained before and after optimization are compared. The optimization results indicate that the proposed dynamic optimization approach not only can significantly improve the computational efficiency, but also can be successfully applied to the parameter optimization design of the MMDTS in order to improve its dynamic performance.

Plug-and-play model predictive control based on robust control invariant sets

We consider the problem of designing decentralized controllers for large-scale linear constrained systems composed by a number of interacting subsystems. As in Riverso et al. (2013b), (i) the design of local controllers requires limited transmission of information from other subsystems and (ii) the addition/removal of a subsystem triggers the design of local controllers for child subsystems only. These properties enable Plug-and-Play (PnP) operations, and we show how to perform them while preserving global stability of the origin and constraint satisfaction. We improve several aspects of the PnP design procedure proposed in Riverso et al. (2013b) and, using recent results in the computation of Robust Control Invariant (RCI) sets, we show that all critical steps in the design of a local controller can be solved through Linear Programming (LP). Finally, an application of the proposed design procedure to a large-scale mechanical system is presented.

Investigation on Slider Structure Deformation and Crowning System of Large-Scale Press Brake

Improving the straightness accuracy of bending workpieces becomes an urgent problem for the development of bending equipment with large size and high precision. In order to obtain the characteristics of slider deformation, a three-dimensional finite element model was developed according to the mechanic characteristics of large-scale press brake and obtained the small deformation using FEM (finite element method). The numerical results are in good agreement with the experimentation. Then based on the simulation results we design a large-scale mechanical crowning system through which the press brake could be automatically compensated in the bend direction by means of a CNC (Computer Numerical Control)-powered motor and could also be compensated for local parts by adjusting the side screw nuts manually. The system has been successfully applied in production and its accuracy was increased 33% compared with the traditional ones. It is proved that the present investigation can provide a technical support and reliable system for the improvement of accuracy of the press brakes.

Study on Subspace Control Based on Modal Analysis (1st Report: Application to Swing-Up Control of an Inverted Pendulum System)

As a new control technique called the subspace control method is developed in an effort to carry out finely tuned control easily and efficiently for a complicated and large-scale mechanical system. In the subspace control method, the minimum and optimum subspace suited for the control specification is extracted from the entire state space by applying the concept of modal analysis, and feedback control based on the modal coordinate is performed in the subspace. The subspace control method takes advantage of the dynamic characteristics of the controlled object in the design of control system. In addition, decreasing the dimension of the controlled object based on the dynamic characteristics leads to simplification of the design of control system, reduction of mechanical overload caused by the control, and a reduction in consumed electric power. In the present study, in order to clarify the fundamental concept, the subspace control method is formulated for swing-up and stabilizing controls of an inverted pendulum system. The effectiveness of the proposed method is verified by numerical simulations and experiments.

Study on Subspace Control Based on Modal Analysis (1st Report, Application to Swing-up Control of Inverted Pendulum System)

As a new control technique, subspace control method is developed in an effort to carry out the finely-tuned control easily and efficiently for a complicated and large-scale mechanical system. In the subspace control method, the minimum and optimum subspace suited for the control specification is extracted from the whole state space by applying the concept of modal analysis and the feedback control based on the modal coordinate is carried out in the subspace. It is a feature of the subspace control method to make positive use of the dynamical characteristics of the controlled object in the design of control system. In addition, decreasing the dimension of controlled object based on the dynamical characteristics leads to simplification of the design of control system, reduction of mechanical overload caused by the control and saving in consumed electric power. For the clarification of the fundamental concept, in this report, the subspace control method is formulated for swing-up and stabilizing controls of an inverted pendulum system. The effectiveness is verified from the numerical simulation and the experiment.

Implicit Runge-Kutta Integration of the Equations of Multibody Dynamics in Descriptor Form

ABSTRACT Implicit Runge-Kutta integration algorithms based on generalized coordinate partitioning are presented for numerical solution of the differential-algebraic equations of motion of multibody dynamics. Second order integration formulas are derived from well known first order Runge-Kutta integrators, defining independent generalized coordinates and their first time derivative as functions of independent accelerations. The latter are determined as the solution of discretized equations of motion that are obtained by inflating underlying state space, second order ordinary differential equations of motion in independent coordinates to descriptor form. Dependent variables in the formulation, including Lagrange multipliers, are determined using kinematic and kinetic equations of multibody dynamics. The proposed method is tested with a large-scale mechanical system that exhibits stiff behavior. Results show that the algorithm is robust and has the capability to integrate the differential-algebraic equations of motion for stiff multibody dynamic systems.

An Algorithm for Synthesis of Decentralized PID Controller for Large-Scale Mechanical Systems

The synthesis of decentralized dynamic controller for large-scale nonlinear mechanical systems with variable parameters is considered in the paper. The large-scale mechanical system is considered as a set of subsystems each associated to one degree of freedom of the system. The model of the subsystem includes the model of the actuator which drives the corresponding joint. For each subsystem local dynamic controller is synthesized. The dynamic controller is synthesized to be robust to variations of parameters of the subsystem and to external perturbations acting upon the decoupled (free) subsystem. The local feedforward is also introduced in each controller to compensate for changes of accelerations along the desired (imposed) trajectory. The practical stability of the local (decoupled) subsystem is considered and then the coupling among the subsystems is estimated. Using the aggregation-decomposition method the practical stability of the complete mechanical system with variable parameters (when interconnections between the subsystems are taken into account) is analyzed. On the basis of this stability analysis we have been able to establish an algorithm for iterative synthesis of the decentralized dynamic controller which can guarantee practical stability of the global system and which is capable to withstand assummed parameter variations. The algorithm is used for computer-aided synthesis of decentralized dynamic control for large-scale mechanical system. The algorithm is described in the paper. The control synthesis is presented for one manipulation robot. For this robot decentralized PID controller is synthesized which is roubst to variation of the payload parameters.

Suboptimal synthesis of a robust decentralized control for large-scale mechanical systems

For a large-scale nonlinear mechanical system, a set of nominal trajectories is prescribed together with a region of allowable parameter values. The system is viewed as a set of decoupled linear time-invariant subsystems and a local controller is synthesized for each subsystem neglecting, in the first step, nonlinear coupling among subsystems. An iterative procedure is established to choose unique linear local controllers which can accommodate all nominal trajectories and withstand parameter variation. If such controllers cannot be found a force feedback is implemented as a global control in order to compensate for the influence of nonlinear and variable coupling. An example of a six-degree-of-freedom industrial manipulator is presented.