Large-scale Mechanical Systems Research Articles

Optimal Modeling of an Elevator Chassis under Crash Scenario Based on Characterization and Validation of the Hyperelastic Material of Its Shock Absorber System

A wide variety of hyperelastic rubber-like materials, exhibiting strong nonlinear stress–strain relations under large deformations, is applied in various industrial mechanical systems and engineering applications involving shock and vibration absorbers. An optimal design procedure of an elevator chassis crashing on a hyperelastic shock absorber in a fail scenario, applicable in large-scale mechanical systems or industrial structures of high importance under strong nonlinear dynamic excitation, is presented in this work. For the characterization of the hyperelastic absorber, a Mooney–Rivlin material model was adopted, and a series of in-lab compression quasi-static tests were conducted. Applying a fully parallelizable state-of-the-art stochastic model updating methodology, coupled with robust, accurate and efficient Finite Element Analysis (FEA) software, the hyperelastic behavior of the shock absorber was validated under uniaxial large deformation, in order to tune all material parameters and develop a high-fidelity FE model of the shock absorber system. Next, a series of in situ full-scale experimental trials were carried out using a test-case elevator chassis, representing the crash scenario on the buffer absorber system, after a controlled free fall. A limited number of sensors, i.e., triaxial accelerometers and strain gauges, were placed at characteristic points of the real structure of the elevator chassis recording experimental data. A discrete Finite Element (FE) model of the experimentally tested arrangement involving the elevator chassis and updated buffer absorber system along with all boundary conditions was developed and used in explicit nonlinear analysis of the crash scenario. Steel material properties and the characterized updated Mooney–Rivlin material model were assigned to the elevator chassis and buffer, respectively. A direct comparison of the numerical and experimental data validated the reliability and accuracy of the methodology applied, whereas results of the analysis were used in order to redesign and optimize a new-design elevator chassis, achieving minimum design stresses and satisfying serviceability limit states.

Ill-posedness of reconstruction of stress corrosion cracking and a regularization method using multifrequency eddy current signals

Stress corrosion cracking (SCC) widely occurs in the key structures of large-scale mechanical systems and may cause catastrophic accidents without evident macroscopic deformation. A sufficiently accurate quantitative evaluation of SCC is important to guarantee the safety and efficient operation of large mechanical systems. However, the reconstruction accuracy of SCC shape parameters using eddy current testing (ECT) signals remains a problem, given the complex microstructure of cracks and the properties of the ECT inverse problem. In this study, a two-dimensional numerical model of crack with conductivity distribution is used to calculate the ECT signals due to SCC. The relation between crack parameters and ECT signals is investigated through simulation and experiment. Results show that the ill-posedness of SCC shape reconstruction is mainly manifested in the nonuniqueness of the solution of crack shape parameters. Therefore, a regularization method based on the features of multifrequency ECT signals is proposed to solve ill-posedness by adding prior information to the solution space of the optimization problem. The reconstruction results of the simulated and measured ECT signals from the conductive crack models verify that the proposed strategy can effectively improve the precision of SCC shape reconstruction.

Inverse Eigenvalue Theory-Based Rigid Multibody Modeling Method of Complex Flexible Structures in Large-Scale Mechanical Systems

Increasing attention is paid to modeling flexibility of individual components in the multibody simulation of large-scale mechanical systems. Nevertheless, the high model order of common methods such as FEA restricts efficient explorations, especially in dynamic design and iterative optimization. In this paper, a rigid multibody modeling strategy (RMMS) with low DOFs and explicit physical meaning is proposed, which directly discretizes a continuous structure into a number of rigid finite elements (RFEs) connected by spring-damping elements (SDEs). In the RMMS, a new identification method from the perspective of the inverse vibration problem is particularly put forward to resolve the parameters of SDEs, which is crucial to the implementation of RMMS in complex flexible structures. With decoupling and linearization, this nonlinear problem is transformed into solving the incompatible linear equations in Rn2 vector space based on vectorization operator and Kronecker product, and optimal parameters are obtained by calculating the Moore–Penrose generalized inverse. Finally, the comparison of the experimental results with the simulated ones by the RMMS strongly validates the feasibility and correctness of the RMMS in predicting the dynamic behaviors while with few DOFs and explicit physical meaning; the application in a lithography system exhibits the applicability of the RMMS for dynamic modeling of large-scale mechanical systems.

Optimum design of large-scale systems considering material nonlinearities and uncertainties

A novel optimum design procedure for uncertainty quantification and validation, applicable in large-scale mechanical systems or industrial structures with material or structural nonlinearities is proposed in this work. Its implementation is presented through the research and optimal development of a full glass panoramic car elevator under real operational fail-safe loading scenario, including accurate dynamic analyses, placing emphasis on high fidelity FE models, uncertainty quantification and efficient handling of material nonlinearities. At first, a small-scale laboratory experimental arrangement of a single glass panel was examined, in order to develop high fidelity FE models of the laminated glass system and the point-support contact mechanism based on the level of dynamic excitation forces. Structural identification along with effective computational model updating and uncertainty quantification techniques were applied, in order to finely tune and estimate the parameters (material properties and damping ratios) of the numerical FE models and assess their uncertainties. The material nonlinearity of the natural rubber was examined at three forcing levels and excitation frequencies. Using maximum stress-strain pairs and updated moduli of elasticity a stress-strain curve, defining the nonlinear elastic behavior of the rubber was applied in the implicit nonlinear analysis of the full-scale elevator system. Based on the results of this analysis the elevator chassis was redesigned and optimized, in order to achieve minimum design stresses at the glazing components under emergency safety gear engagement. The stress levels developed on the optimal design of the elevator car were validated, in order to test the reliability of the applied method.

A New Fault Diagnosis Method for a Diesel Engine Based on an Optimized Vibration Mel Frequency under Multiple Operation Conditions.

The diesel engine has been a significant component of large-scale mechanical systems for the intelligent manufacturing industry. Because of its complex structure and poor working environment, it has trouble effectively acquiring the representative fault features. Further, fault diagnosis of the diesel engine faces great challenges. This paper presents a new fault diagnosis method for the detection of diesel engine faults under multiple operation conditions instead of conventional methods confined to a single condition. First, an adaptive correlation threshold process is designed as a preprocessing unit to enhance data quality by weakening non-impact region characteristics. Next, a feature extraction method for sound signals based on the Mel frequency cepstrum (MFC) is improved and introduced into the machinery fault diagnosis. Then, the combination of the improved feature and vibrational mode decomposition (VMD) is proposed to incorporate VMD into an effective adaptive decomposition of non-stationary signals to combine it with an excellent feature representation of the vibration signal. Finally, the vector quantization algorithm is adopted to reduce the feature dimensions and generate codebook model bases, which trains the K-Nearest Neighbor classifiers. Five comparative methods were carried out, and the experimental results show that the proposed method offers a good effect of the common valve clearance fault of diesel engines under different conditions.

Malticriteria design of a large-scale mechanical systems

The design and optimization of a large-scale systems are the most difficalt problems. A large-scale system consists of a number of subsystems. For example, in a harvest for harvesting one can separate the following subsystems: the frame, driver's cab, platform, engine, transmission, and steering system. Different departments of the design office engaged in creating a machine optimize their ‘own’ subsystems, while ignoring others. A machine assembled from ‘autonomously optimal’ subsystems turns out to be far from perfect. A machine is a single whole. When improving one of its subsystems, we can unwittingly worsen others. This implies that it is not always possible to solve optimization problems directly even for determination of the feasible solution set. The correct determination of the feasible solution set was a major challenge in engineering optimization problems. In order to construct the feasible solution set, a method called the Parameter Space Investigation (PSI) has been created and successfully integrated into various fields of industry, science, and technology. The methods of approximation of the feasible solution and Pareto optimal sets and the regularization of the Pareto optimal set are described in our paper. These methods are applied to solving the multicriteria optimization problems of large- scale systems. For example, they were applied in an agricultural engineering to a harvester for harvesting design.

Integrated Reverse Engineering Strategy for Large-Scale Mechanical Systems: Application to a Steam Turbine Rotor

An integrated reverse engineering methodology is proposed for a large-scale fully operational steam turbine rotor, considering issues related to the development of the CAD and FE model and the application of robust and effective computational finite element model updating techniques based on experimental modal analysis procedures. First, using an integrated reverse engineering strategy, the digital shape of the three sections of a steam turbine rotor was developed and the final parametric CAD model was created. The finite element model of the turbine was developed using tetrahedral solid elements. Due to complex geometry of the structure, the developed model consists of about fifty-five million DOFs. The identification of modal characteristics of the frame is based on acceleration time histories, which are obtained through an experimental investigation of its dynamic response in a support-free state by imposing impulsive loading. Experimentally identified modal modes and modal frequencies compared to the FE model predicted ones constitute the actual measure of fit. CMA-ES optimization algorithm is then implemented in order to finely tune material parameters, such as modulus of elasticity and density, in order to best match experi-mental and numerical data. Direct comparison of the numerical and experimental data verified the reliability and accuracy of the methodology applied. The identified finite element model is repre-sentative of the initial structural condition of the turbine and is used to develop a simplified finite element model, which then used for the turbine rotordynamic analysis. Accumulated knowledge of the dynamic behavior of the specific steam turbine system, could be implemented in order to eval-uate stability or instability states, fatigue growth in the turbine blades, changes in the damping of the bearing system and perform necessary scheduled optimal and cost-effective maintenance strategies. Additionally, upon a series of scheduled experimental data collection, a permanent output-only vibration SHM system could be installed and even a proper dynamic balancing could be investigated and designed.

Hierarchical parallel processing for design optimization - a case study

The optimization methods can be applied to design large scale mechanical systems. One popular method for increasing the efficiency of large scale design optimization problem is a hierarchical decomposition of the problem into a number of sub problems each with its own objective function, constraints, and design variables. Then each and every sub problem is optimized by using a powerful tool known as genetic algorithm, to get required optimum solutions. The solutions obtained from sub problems are used to get the required global optimum solution of a large and complex design problem.A well known speed reducer is considered as an example to illustrate the application of the above parallel processing method. Speed reducer includes gear, pinion, two shafts, four bearings enclosed in housing. The design objective is to minimize the overall volume, where 7 variables and 25 constraints are considered.

An efficient parallel algorithm for flexible multibody systems based on domain decomposition method

Recently, a large number of lightweight flexible structures are successfully used in the field of aerospace industry, intelligent robot and 3D printing. Because of the increasing flexibility of elastic components, some large scale mechanical systems will perform typical rigid-flexible coupled dynamic characteristic. Previous studies have indicated that the traditional modeling methods of the flexible multibody system based on the assumptions of small rotations and small deformation, such as the floating frame of reference method, can not lead to correct results for the dynamic response of those large deformation structures. Under the framework of Isogeometric analysis, the basis functions of the NURBS are employed to discretize the displacement field of elastic components with large deformation. Based on the large deformation theory of the continuum mechanics, the geometrical nonlinearity of planar structures undergoing the overall motion and large deformation is accurately taken into account. In order to improve the computational efficiency, some efficient formulations to calculate the elastic force and the tangent stiffness matrix are proposed via the invariant matrix method. Furthermore, based on the finite element tearing and interconnecting (FETI) method, an efficient parallel algorithm is presented to deal with the dynamic equations of motion for flexible multibody systems. First, the governing partial differential equations of multibody systems are transformed into a set of nonlinear algebraic equations after spatial and time discretization. Then, the preconditioned conjugate gradient method is exploited to solve the linearization equation in parallel. Compared with the existing parallel direct methods for flexible multibody systems, the proposed method can improve the computational efficiency significantly. Finally, several numerical examples are given to validate the effectiveness of the proposed parallel algorithm, including the complexity, the speed-up ratio and the scalability.

A graph-theoretic approach to sparse matrix inversion for implicit differential algebraic equations

Abstract. In this paper, we propose an efficient numerical scheme to compute sparse matrix inversions for Implicit Differential Algebraic Equations of large-scale nonlinear mechanical systems. We first formulate mechanical systems with constraints by Dirac structures and associated Lagrangian systems. Second, we show how to allocate input-output relations to the variables in kinematical and dynamical relations appearing in DAEs by introducing an oriented bipartite graph. Then, we also show that the matrix inversion of Jacobian matrix associated to the kinematical and dynamical relations can be carried out by using the input-output relations and we explain solvability of the sparse Jacobian matrix inversion by using the bipartite graph. Finally, we propose an efficient symbolic generation algorithm to compute the sparse matrix inversion of the Jacobian matrix, and we demonstrate the validity in numerical efficiency by an example of the stanford manipulator.

Application of Fault Detection based on Hybrid Intelligent Methods

How to collect information optimally by scheduling a limited number of sensors is one of the key technologies of safety monitoring for large mechanical equipment systems. In this paper, an improved model of Pulse Coupled Neural Network is used for the discretization algorithm of continuous features. And based on classificatory error parameter and approximate dependence degree in Variable Precision Rough Sets theory, a VPRS data model is created by utilizing the measured signals from the multi-sensor Bridge Erecting Machine Safety Monitoring System. Then the corresponding relations between time-frequency characteristics and operating condition classifications are analyzed. Finally, while the determinability of decision making analysis is enhanced, the validity order of safety monitoring information of the multi-sensor sampling points is gained, which can direct optimal scheduling of position of sensors in large-scale mechanical equipment systems. DOI: http://dx.doi.org/10.11591/telkomnika.v10i8.1634 Full Text: PDF

Nonlinear modal analysis of mechanical systems with frictionless contact interfaces

This paper explores mechanical systems undergoing unilateral frictionless contact conditions in the framework of nonlinear modal analysis. The nonlinear eigenproblem is formulated in the frequency domain through the minimization of a Rayleigh quotient subject to non-penetration inequality constraints. An additional equality constraint is introduced for normalization purposes. The resulting constrained minimization problem is then solved using an augmented Lagrangian strategy. Two applications are proposed: a thin longitudinal rod in unilateral contact with a rigid obstacle and a turbomachinery compressor blade in contact with a rigid casing. The first application illustrates the complexity of the nonlinear modal characterization of a system experiencing unilateral contact conditions while the second demonstrates the applicability of the proposed approach to large-scale mechanical systems involving non-smooth nonlinear terms.

Decentralised robust control of interconnected uncertain non-linear mechanical systems

This paper proposes a new method of decentralised robust control for large-scale interconnected uncertain non-linear mechanical systems, by using disturbance observers. Rigorous stability analysis is given for the overall non-linear system. Simulation results on a coupled double pendulum system are presented to confirm the established theoretical results.

Dynamics of Large Scale Mechanical Models Using Multilevel Substructuring

An appropriate substructuring methodology is applied in order to study the dynamic response of very large scale mechanical systems. The emphasis is put on enabling a systematic study of dynamical systems with nonlinear characteristics, but the method is equally applicable to systems possessing linear properties. The accuracy and effectiveness of the methodology are illustrated by numerical results obtained for example vehicle models, having a total number of degrees of freedom lying in the order of a million or even bigger. First, the equations of motion of each component are set up by applying the finite element method. The order of the resulting models is so high that the classical substructuring methodologies become numerically ineffective or practically impossible to apply. However, the method developed overcomes these difficulties by imposing a further, multilevel substructuring of each component, based on the sparsity pattern of the stiffness matrix. In this way, the number of the equations of motion of the complete system is substantially reduced. Consequently, the numerical results presented demonstrate that besides the direct computational savings, this reduction in the dimensions enables the application of numerical codes, which capture response characteristics of dynamical systems sufficiently accurate up to a prespecified level of forcing frequencies. The study concludes by investigating biodynamic response of passenger-seat subsystem models coupled with complex mechanical models of ground vehicles resulting from deterministic or random road excitation.

Supporting Negotiations in the Early Stage of Large-Scale Mechanical System Design

Abstract The development of large-scale mechanical systems involves interactive negotiations among nontechnical and technical design stakeholders. Usually, two types of negotiations exist: (i) those between the nontechnical stakeholders and technical stakeholders with responsibilities for the overall system, such as chief system design engineers and project managers; and (ii) those within the design engineering groups who are responsible for design tasks at different system hierarchical levels, i.e., system, subsystem, and component. This paper addresses the interactive negotiations among the design engineering groups. A direct synthesis (DS) method was developed to support the negotiations by combining adaptive and interactive modeling system based surrogate modeling with a set-based “zoom-in” approach. A vehicle frontal structural system design example is used to demonstrate how to apply the DS method in industrial practice. The preliminary results show that DS has the potential to support the fast synthesis of robust design alternatives that satisfy performance requirements at the system, subsystem, and component level.

Demonstration-scale evaluation of a novel high-solids anaerobic digestion process for converting organic wastes to fuel gas and compost

Early evaluations of the bioconversion potential for combined wastes such as tuna sludge and sorted municipal solid waste (MSW) were conducted at laboratory scale and compared conventional low-solids, stirred-tank anaerobic systems with the novel, high-solids anaerobic digester (HSAD) design. Enhanced feedstock conversion rates and yields were determined for the HSAD system. In addition, the HSAD system demonstrated superior resiliency to process failure. Utilizing relatively dry feedstocks, the HSAD system is approximately one-tenth the size of conventional low-solids systems. In addition, the HSAD system is capable of organic loading rates (OLRs) on the order of 20-25 g volatile solids per liter digester volume per d (gVS/L/d), roughly 4-5 times those of conventional systems. Current efforts involve developing a demonstration-scale (pilot-scale) HSAD system. A two-ton/d plant has been constructed in Stanton, CA and is currently in the commissioning/startup phase. The purposes of the project are to verify laboratory- and intermediate-scale process performance; test the performance of large-scale prototype mechanical systems; demonstrate the long-term reliability of the process; and generate the process and economic data required for the design, financing, and construction of full-scale commercial systems. This study presents conformational fermentation data obtained at intermediate-scale and a snapshot of the pilot-scale project.

Large-Scale Processing Machinery for Fabrication of Composite Hulls and Superstructure

Large-scale mechanical systems for impregnating and positioning composite materials are now permitting efficient manufacturing of composite hulls up to 60 m (200 ft) and greater. Recreational, commercial, and military vessels fabricated from composite materials are gaining acceptance around the world; however, processing of thermosetting resins and fiber reinforcements in quantities exceeding 90 000 kg (200 000 lb) per unit presents a new set of challenges to production engineers responsible for maintaining quality control. Impregnation systems are currently being used at several mine-hunter production shipyards worldwide. Large-to-medium sized recreational yachts are also in production with impregnation systems. This paper reviews some past and current impregnator installations, the selection process used for choosing the systems, and production engineering factors.

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.

Computer Aided Design of Aircraft Flight Control System

A computer implementation of flight control system design method, based on decomposition-aggregation principle and decentralized control of large-scale mechanical systems, is described. Numerical aspects of using the complete nonlinear aircraft model in the synthesis process are considered. Some data about software organization and user interaction are given.

Dynamic analysis of large-scale mechanical systems and animated graphics

This paper presents a computer-based method for formulation and solution of coupled differential and algebraic equations describing large-scale mechanical systems, including feedback control, aerodynamic forces, and other multidisciplinary effects that interact with the mechanical system. A Euler parameter repersentation of the configuration of the mechanical system is employed to obtain singularity free solution for generalized coordinates and a much simplified algebraic formulation of the governing system of equations, compared with the more classical Euler angle generalized coordinate formulation. A generalized coordinate partitioning algorithm is employed to identify independent generalized coordinates automatically and reduce the dimension of the numerical integration problem. Animated graphics output is employed to assist in visualization of dynamic performance of several systems—a parachute descending in air, an aircraft landing on a damaged runway, and a truck with flexible chassis.