Dynamic modeling of a fully flexible rotor-stator system with bolt joint and rubbing-induced nonlinear vibration

A new dynamic model for bolted joints in heavy machine structures is proposed. The influence of the bolt pretightening force, the interface dimensions and the surface roughness on joint dynamics (i.e. the stiffness matrix of finite element) were analysed. Each stiffness coefficient in the matrix can be expressed by an exponential function of preload, and a quadratic polynomial function of geometric dimensions. Sixteen specimens were thoroughly designed and analysed. Then, the resulting stiffness matrices were saved as templates, based on which could establish dynamic models of joints with different influence factor values, using curve-fitting and Response Surface Methodology (RSM). The methodology was validated by experiments with a specimen of the new design and a heavy-duty cutting machine.

High-order dynamic modeling and parameter identification of structural discontinuities in Timoshenko beams by using reflection coefficients

In this paper, a robust fuzzy-tuned PID controller is proposed for the trajectory tracking and vibration control of a flexible joint manipulator system (FJMS) with parametric uncertainties. Flexible joint manipulators are widely used in industry due to their flexibility, light in weight and fast response, low cost, and low energy consumption. The dynamic modeling via Euler-Lagrange equation for a single link flexible joint manipulator system (FJMS) is presented first. By analyzing the characteristics of the high order linear system, the Fuzzy-Tuned PID control strategy is utilized. The parameters of classical PID controller are updated by the intelligent method of fuzzy logic. With the adaptivity to the parametric uncertainties from the system stiffness and moment of inertia, the contrived approach provides more efficient results compared to existing techniques in terms of vibration suppressions, time response, and overshoot. Finally, the effectiveness of the controller is corroborated through multiple experiments on the QUANSER's flexible joint manipulator system (FJMS).

Despite recent advances and improvements in modeling and prediction of the dynamics of the machining process, an efficient machining process is limited due to chatter and instability of machining system. In fact, the machining system contains various kinds of joints, which cause difficulties in dynamics modeling, simulation and prediction. Moreover, the flexible support system results in large deformation and violent vibration of the workpiece when machining, and the thin-walled workpiece easily gives rise to the chatter of the machining system. Therefore, the dynamics of the flexible support system was considered to calculate stability lobe diagram in the modeling of milling process. The whole machining system was regarded as a closed loop composed by the machine tool structures, support, workpiece and machining process. In this paper, the receptance coupling (RC) method was introduced to predict the dynamics of the closed machining system. A milling process was taken for example to predict the chatter limitations using the dynamics of closed model. The mathematical model of the machining system (machine tool structures, spindle, holder and tool), together with the details of joint contacts, was given based on the RC method. The RC model was used to obtain the dynamics of the system, while receptance of the tool point was coupled. Based on the coupling model of the machining system, the depth limitations under different speeds were estimated for the technology parameter optimization in milling process. The response was considered to be the sum of the cutting point and the support system. The flexibility of the support system was considered to be the feedback of the cutting stiffness. By this means, the traditional model was modified to calculate the stability lobe diagram based on the dynamics of the spindle and support system. Furthermore, the milling experiment was carried out to verify the prediction results, and the dominant natural frequencies of receptance at tool point were obtained by modal testing to define the stability lobe diagram. It was found that the chatter results matched well with the stability lobes. It was concluded that the support system with poor stiffness might cause violent chatter especially when the workpiece was thin-walled. The cutting depth limitations of the flexible support system were lower than that of the rigid one. Moreover, this closed model of the machining system is appropriate for the chatter prediction of the flexible support system or thin-walled workpiece, so it is helpful for a better parameter optimization.

Guest Editorial: Situational awareness of integrated energy systems

It has gradually become the trend of the world to integrate the individualized and diversified needs of customers into products, which has brought new pressure to enterprises, and the diversification of users’ needs has led to the diversification of the market. Manufacturing industry must adjust the existing production mode to adapt to these changes. This paper puts forward the research and development of product flexible customization experience system based on VR considering users’ customization requirement. Through the research of data modularization modelling and dynamic product family model and configuration for product flexible customization, the functions and operation processes of typical industries are analysed. By using modularization idea, the general rules are found out from customer requirements, and the multi-layer module division and model from production system planning to equipment design are studied. Group coupling technology, explore customer modular customization methods and technologies for equipment manufacturing industry. Combining with a case of customization of logistics equipment system, this paper explores how to combine VR technology application with production system simulation technology, build a digital personalized flexible configuration experience system, provide an immersive visual environment of interactive design for customers, and improve the market competitiveness of enterprises.

As part of a study conducted by Esso Australia investigating means of reducing the high cost of construction of submarine pipelines in Bass Strait, flexible risers connecting bottom-towed steel pipelines and the topsides of freed platforms were identified as a potential means of providing significant cost savings. To assess the concept, an extensive program of dynamic analyses and state model tests in a large wave-current flume were undertaken. This paper presents the findings of these analytical and test studies. Additional dynamic analyses were performed to assess the sensitivity of flexible riser performance to various changes in hydromechanics and other design parameters. A number of recommendations were developed for design criteria and analytical parameters for flexible riser systems, not addressed in current codes of practice for such systems. Introduction The relative remoteness of Australia from major centres of offshore oil and gas activity presents a number of problems to the viability of potential offshore field developments, notably the cost of mobilization of specialist construction vessels, such as derrick and pipelaying barges, pipe reeling vessels and diving support vessels (DSVS). In recent years Esso Australia Ltd. (EAL) has used innovative engineering and new construction techniques, minimizing or avoiding the use of such vessels altogether, to make substantial reductions in the cost of development of offshore structures and facilities in Bass Strait. Most future field developments in Bass Strait involve much smaller reservoirs than in the past, such that the high cost of conventionally installed pipelines, which has References, tables and figures at end of paper been identified as a major component of the total cost of such projects, would either preclude development or would make it a marginal proposition. In view of these considerations, EAL initiated the "Pipeline Cost Reduction Study" (PCRS), investigating novel pipelaying procedures to identify cost effective means of installing pipeline links to new marginal field developments. One of the innovations investigated in the PCRS was the use of single-catenary flexible risers as tie-ins to fixed platforms from on-bottom steel pipelines. This paper describes wave tank testing and dynamic numerical analysis of this concept, and discusses design criteria and analytical parameters for use in the design of such flexible riser systems. The following section introduces the PCRS. Section 3 develops the criteria used for the design of flexible riser systems. Section 4 describes the dynamic numerical analysis and the use of FLEXCOM-3D, while Section 5 describes the physical model studies including the effect of spectral versus regular waves and the influence of the structure. Section 6 discusses the design parameters obtained and compares the capabilities of numerical and physical models this discussion is summarised in Section 7 Conclusions. The Pipeline Cost Reduction Study and Its Application The PCRS identified a number of alternative methods of construction and new pipeline configurations which might offer substantial savings in pipeline cost. The most promising concepts were reviewed and the technical feasibility of specific aspects which offered the possibility of significant reductions in the cost of installation of the pipelines for a number of future projects were established.

Experimental study on the influence of radial internal clearances of the rolling bearings on dynamics of a flexible rotor system

Dynamic modelling and vibration suppression of a single-link flexible manipulator with two cables

The flexible manipulator is widely used in many fields due to its advantages of light weight, fast response, and low energy consumption. However, due to the flexible structure of the flexible manipulator, it is easy to generate tip vibration, and difficult to achieve high-speed and high-precision motion control. In this paper, the dynamics model of the flexible manipulator system with controllable damping is established based on the Lagrange method and damping force constraining equation. Using the singular perturbation principle, the dynamics model is decomposed into fast and slow subsystems, where the slow subsystem represents the large-scale rigid motion, and the fast subsystem represents the small-scale vibration. A two-time scale composite control strategy is proposed, which consists of an adaptive robust controller for the slow system and a LQR controller for the fast system, to achieve tip vibration suppression and precise motion control. Through simulation, the effectiveness of the two-time scale control strategy of the flexible manipulator system with controllable damping is proved.

In this study, an adaptive servo controller based on LQR is designed for flexible master-slave system (FMSS). A dynamics model, observer and servo controller based on LQR is built respectively. According to the parameter sensitive experiments, adaptive servo controller based on LQR is designed. This research focuses on the performance of rapid response and vibration suppression. Experimental results indicate that adaptive servo controller, which suppresses the saturation of the input torque to ensure the stability, has achieved short time delay and adequate vibration suppression.

A possible analysis for failure of U.S. SMAP satellite

The phenomenon of dynamic stiffening is a research field of general interest for flexible multi-body systems. In fact, there are not only dynamic stiffening but also dynamic softening phenomenon in the flexible multi-body systems. In this paper, a non-linear dynamic model and its linearization characteristic equations of a cantilever beam with tip mass in the centrifugal field are established by adopting the general Hamilton Variational Principle. Then, the problems of the dynamic stiffening and the dynamic softening are studied by using numerical simulations. Meanwhile, the modal test is carried out on our centrifuge. The numerical results show that the system stiffness will be strengthened when the centrifugal tension force acts on the beam (i.e. the dynamic stiffening). However, the system stiffness will be weakened when the centrifugal compression force acts on the beam (i.e. the dynamic softening). Furthermore, the equilibrium position of the system will lose its stability when the inertial force reaches a critical value. Through theoretical analysis, we find that this phenomenon comes from the effect of dynamic softening resulting from the centrifugal compression force. Our test results verify the above conclusions and confirm that both dynamic stiffening and softening phenomena exist in flexible multi-body systems.

Mobile robotic systems, which include a mobile platform with one or more manipulators, are of great interest in most applications, e.g. planet explorations, rescuing operations, nursing, book keeping, storing and many others. To manipulate an object with two or more cooperating manipulators, the Multiple Impedance control (MIC) as a model-based algorithm enforces a desired impedance law on each manipulator, the manipulated object, and the moving base itself. However, to apply model-based control laws, it is needed to extract explicit system dynamic model, which of course for such systems may lead to very complicated nonlinear equations of motions. To this end, non-holonomic constraint of a wheeled system is derived, and the obtained dynamics model is reformatted to become a more concise one using natural orthogonal complement method. Next, the MIC law is applied to manipulate an object by two 6-dof cooperating manipulators mounted on a wheeled platform while the moving base is driven with two differentially driver wheels. Obtained results reveal a good tracking performance of the system, i.e. a coordinated smooth motion of the object, manipulators and the moving base, even in the presence of impacts due to contact with an obstacle, and system flexibility.

Identification of linearized oil-film coefficients in a flexible rotor-bearing system, part II: Experiment