Volume 1 (2017)

Volume 1, Issue 3

Download.：https://lhscientificpublishing.com/Journals/JVTSD-Download.aspx

1. On The Temporal and Spectral Characteristics of Micro-Milling Dynamics

Abstract：Due to different chip formation mechanisms, increased tool-radius to feed-rate ratio, and higher spindle speeds, micro-milling is a highly nonlinear process which can produce multiple and broadband frequencies that negatively impact the process. Micro-milling is investigated through the development and analysis of a nonlinear micromilling dynamic model. A lumped mass-spring-damper system is assumed for modeling the dynamic properties of the tool. The force mechanism utilized is a slip-line field model that provides the advantage of being highly dynamic by accounting for the constantly changing effective rake angle and slip-line variables. Accurate prediction of the chip thickness is important in correctly predicting the dynamics of the system since the force mechanism and its variables are a function of the chip thickness. A novel approach for calculating the instantaneous chip thickness which accounts for the tool jumping out of the cut and elastic recovery of the workpiece is presented. The derivation for the effective rake angle is given and the helical angle is accounted for resulting in a three dimensional micro-milling model. The model generates the high frequency force components that are seen in experimental data available in literature. The effect that the helical angle and system stiffness has on the resulting cutting forces is also investigated. It is shown that dynamic instability has the greatest impact on tool performance and improving the dynamic response is a necessity for achieving high speed ultra-stable micro-machining.

2. Evaluation of 3D Measurement Performance of Laser Scanner with Simplified Receiver Optics

3. A Generalized Lattice Boltzmann Model for Simulating Axisymmetric Convective Flow in Porous Media

Abstract：Axisymmetric convective flow in porous media is frequently encountered in nature and industry applications. In recent years, Lattice Boltzmann method has been developed as a powerful tool for such kind of flow and heat transfer. Despite its success in many problems regarding to porous flow, the existing LB model for the axisymmetric thermal flow in porous media at the representative volume scale suffers from a serious drawback. That is, it can not handle the cases where the heat capacitance of porous media varies spatially obviously. In this paper, a generalized LB model for axisymmetric temperature field is proposed to remedy this shortcoming. Chapman-Enskog analysis demonstrates that the energy equation in the cylindrical coordinates system can be recovered by the proposed model. Natural convection in a vertical annulus filled with saturated porous media, natural convection in a vertical annulus without porous media, have been carried out, and the results predicted by the present LB model agree well with the existing numerical data. More, natural convection in a vertical annulus with spatially varying heat capacitance shows that the present model can address the problem where the heat capacitance varies spatially obviously successfully.

4. Steering Control for a Class of Nonholonomic Wheeled Mobile Robots Using Adaptive Back Stepping

Abstract：This paper presents a simple method of steering control strategy for a class of Nonholonomic wheeled mobile robots. The strategy is based on adaptive Backstepping technique and does not require the conversion of the model into a “chained form”, and so it does not depend on any special transformation methods. Control laws have been developed for five different types of mobile robot models. The control laws and the adaptive laws are derived in the sense of Lyapunov functions, so that the closed loop system’s stability can be guaranteed.

5. Steering Control of an Underwater Vehicle using Adaptive Back Stepping Approach

Abstract：This paper presents a simple and systematic approach to steer an underwater vehicle model by considering two different cases: (i) when all actuators are functional, and (ii) when one actuator is not working. In first case, the model of an underwater vehicle is steered by using adaptive Backstepping technique. The first actuator is necessary for the operation of the system so any of the other three actuators can be non-operational. So, the second case itself contains three different cases. Adaptive Backstepping is then used to steer the system with one non-working actuator. The synthesis method is general, in that it applies to a large class of drift free, completely controllable systems, for which the associated controllability Lie algebra is locally nilpotent.

6. Mathematical Framework and Non-Linear Modeling of the Mechanical System. Part I: Rigid Body Kinematics

Abstract：In the present paper, a problem of a free rigid body motion in mechanical system is analyzed from a video capture webcam (Sony Cybershot 10.1 M.P). The problem subjected to kinematic characteristics and relative trajectories are theoretically and analytically solved. Subsequently, the solution is quantitatively verified by a new experiment procedure, constructed by the authors. The geometrical treatments of the absolute experimental trajectories of two points of the body, allow determining the relative trajectory of a point from the other point. The kinematic parameters optimization, i.e., translational velocity, instantaneous velocity of rotation and initial kinematic conditions, are obtained, solving non-linear least-squares problems, based on Levenberg-Marquardt’s algorithm. On the other hand, the response surfaces of the objective function and the sensitivity analysis of the different initial estimates of the analytical model parameters are also discussed. The comparison of the theoretical study results with experimental output shows that there are instruments to directly verify rather abstract mathematical theories even on the general mechanics program. Moreover, combining the theoretical description of the problem with an appropriate laboratory experiment and computational optimization procedures, gives a more exhaustive view of the physical problem as a whole.

Volume 1 (2017)

Volume 1, Issue 2

Download.：https://lhscientificpublishing.com/Journals/JVTSD-Download.aspx

1、Complete Bifurcation Trees of a Parametrically Driven Pendulum

Abstract：In this paper, the complete bifurcation trees of a parametrically driven pendulum are investigated using discrete implicit maps obtained through a mid-point scheme. Based on the discrete maps, mapping structures are developed for periodic motions in such a parametric system. Analytical bifurcation trees of periodic motions to chaos are developed through the nonlinear algebraic equations of such implicit maps. The stability and bifurcation of periodic motions is carried out through eigenvalue analysis. For a better understanding of the motion complexity in such a system, the corresponding frequency-amplitude characteristics are presented. Finally, numerical results of periodic motions are illustrated in verification. Many new periodic motions in the parametrically excited pendulum are discovered.

2、Three-component Parallel and Synchronous Seismic Data Acquisition Based   on Time-division Sampling System

Abstract：To economize power dissipation and volume of the three-component parallel and synchronous seismic data acquisition system, under the inspiration of sampling rate conversion theory in the digital signal processing, a project of three-component parallel and synchronous seismic data acquisition method is proposed based on time-division sampling system, in which triple interpolation is implemented in the three sets of data acquired by time-division sampling. Then another interpolation or decimation is carried out to aim at converting sampling rate of the system into the target value. Results of the error analysis show that the accuracy of numerical calculation in this conversion process is superior to the resolution ratio of hardware system. the prominent dominant of this project is that power dissipation and volume of parallel and synchronous acquisition system applied to band-limited signal are optimized and performance of the whole system is improved.

3、Experimental Research on Surge Characteristics of Centrifugal Compressors

Abstract：Centrifugal compressors are widely used in many process industries. The stability is one of the most important characteristics of centrifugal compressor. When the compressor operates under the condition of small mass flow rate, the working conditions of rotating stall and surge will occur. The surge of the centrifugal compressor is researched by experiment. The signals are tested and analyzed when surge condition occurs in this paper. The suction and discharge pressures are tested under the surge working conditions. The pulsation frequency of the pressures is very small (6Hz), and it is about 0.03 of the rotating speed frequency. The vibration of the inlet pipes is researched as a parameter of the surge of compressor. The vibration test results show that it can be as an important signal to estimate the surge working condition. When the surge occurs, the pipe vibration amplitude at the low frequency is bigger, and it is about four times of that at the working frequency. However, the maximum amplitude of pipe vibration is not change with rotation speeds.

4、Advances in Modal Analysis Application

Abstract：Realization of modal analysis in a wide spectrum of applications has been established since decades. The dynamic characteristics obtained from analytical and experimental modal analysis helped researchers as well as engineers to determine the dynamic behavior of structures and assemblies. Extensive research work is given to the detection and evaluation of damages in mechanical structures using knowledge of modal frequencies and mode shapes. The fact that the dynamic characteristics thus obtained, are influenced by the structure’s physical and mechanical properties has inspired many researchers, recently to use modal analysis as a tool for the identification of mechanical properties and remaining life prediction of manufactured components. It is not the intention of the authors in this paper to investigate the knowhow of each of the applications mentioned within the scope of the paper; since the reader can obtain detailed information of most of the applications from the respective references written at the end of this paper. The main objective of this paper, is to summarize different important applications of modal analysis and classify these applications into three main categories; quality assessment, material characterization, and life prediction. The work also describes what has been studied in each category and provides an insight for researchers on what still needs to be achieved. Accordingly; the authors introduce a new application that will revolutionize the basis on which engineering design is traditionally used, by the fact that it is better testing the product instead of testing the material from which the product will be made. This new philosophy is currently worked upon by the authors.

5、Design and Dynamic Analysis of Bending Waves Waveguide Based on Coordinate Transformation Theory

Abstract：The finite embedded coordinate transformation theory is introduced into the elastic dynamic equation of bending waves, a design of bend waveguide to control bending waves to bend at arbitrary angel is proposed. The formula to describe the transformed materials properties in an elastic thin plate is obtained, which contains anisotropic heterogeneous Young modulus and a radially dependent mass density. Through homogenization of layered periodic composite materials, the anisotropic materials are dispersed into discrete layered isotropic materials. The simulation model of the waveguide is built, and full-wave dynamic simulations of the model are analyst with finite element method. Numerical analysis results show that the waveguide consisting of 10 layers alternating two types of isotropic elastic materials can achieve effective control of the bending wave propagation in thin plates, it works over the frequency range [1500, 10000] hertz with ultra-wideband characteristics. The study can provide technological approaches to bending waves control in thin plates, and it is expected to provide potential applications in isolating structures from vibrations.

Volume 1 (2017)

Volume 1, Issue 1 

Download.：https://lhscientificpublishing.com/Journals/JVTSD-Download.aspx

1.The Use of the Fitting Time HistoriesMethod to Detect the Nonlinear Behaviour of Laminated Glass

Abstract：The experimental free vibrations of a laminated glass beam are inves- tigated with the aim of extracting the nonlinear characteristics of the dynamical behaviour, by an appropriate post-processing of data en- suing from the tests. An updated version of the Fitting Time History (FTH) technique is used. It is based on the least square approx- imation of the measured damped free vibrations of the laminated glass, and provides the optimal values of the natural frequencies and damping coefficients. While in a previous work attention was mainly devoted to the determination of the linear dynamical properties, here the focus is on the nonlinear behaviour, in particular on the nonlinear relationship between the excitation amplitude and: (i) the natural frequencies, a fact that is commonly encountered in nonlinear dy- namics and known as ‘backbone curve’; (ii) the damping coefficient, a fact that is somehow unexpected and commonly not reported in the literature.

2.Dynamics of Turning Operation Part I: Experimental Analysis Using Instantaneous Frequency

 Abstract：

The workpiece and tool vibrations on a lathe are experimentally stud- ied to establish improved understanding of cutting dynamics that would support efforts in exceeding the current limits of the turning process. A Keyence laser displacement sensor is employed to monitor the workpiece and tool vibrations during chatter-free and chatter cut- ting. A procedure is developed that utilizes instantaneous frequency (IF) to identify the modes related to measurement noise and those innate of the cutting process. It is found that IF thoroughly charac- terizes the underlying turning dynamics and identifies the exact time when chatter is fully developed. That IF provides the needed reso- lution for identifying the onset of chatter suggests that the stability of the process should be monitored in the time-frequency domain to effectively detect and characterize machining instability. It is deter- mined that for the cutting tests performed chatter of the workpiece and tool are associated with the changing of the spectral components and more specifically period-doubling bifurcation.

3.Dynamics of Turning Operation Part II: Model Validation and Stability at High Speed

Abstract：

A comprehensive three-dimensional turning model is validated by comparing numerical simulations to the experimental data obtained in Part 1 using instantaneous frequency. Comparison of chatter-free cutting demonstrates that the model effectively captures the work- piece natural frequency, tool natural frequency, a nonlinear mode, and the spindle speed, which are main components of the underlying dynamics observed experimentally. The model accurately simulates chatter vibrations characterized as increased vibration amplitude and the appearance of coupled tool õworkpiece vibrations at a chatter frequency. The stability diagram constructed by running the model at various spindle speeds and depth-of-cuts demonstrates a general increase in the chatter-free critical depth-of-cut as the spindle speed increased. This chatter-free limit levels out as the spindle speeds exceeded 1500 rpm. At high spindle speeds the workpiece motions dominate the cutting dynamics, resulting in cases of excessive work- piece vibration amplitude and highly nonlinear frequencies which af- fect the efficiency of the process. The excessive workpiece amplitude cases create a second stability limit to be considered as a result of imbalance and configuration of the workpiece. Thus, workpiece dy- namics should not be neglected in mathematical and experimental analyses for the design of machine tools and robust

4.Model Reduction for Second Order in Time Nonlinear Dissipative Autonomous Dynamic Systems

Abstract：

In light of Approximate Inertial Manifolds stemmed from nonlinear dynamics and Mode Analysis Technique in linear structural dynam- ics, a combined method is presented to reduce the second order in time nonlinear dissipative autonomous dynamic systems with higher dimension or many degrees-of-freedom to lower dimensional systems, and the ensuing error estimate is investigated theoretically. By this method, the system is studied in the phase space with a distance definition which can describe the distance between the original and reduced systems, and the solution of the original system is then pro- jected onto the complete space spanned by the eigenvectors of the linear operator of the governing equations. With the introduction of an Approximate Inertial Manifolds, the interaction between lower and higher modes or the influence of higher modes on the long-term behaviors, which will be ignored if the traditional Galerkin proce- dure is used to approach the governing equation, is considered to improve the distance between the original and reduced systems. Ad- ditionally, the error estimate for the approximation to the attractor is presented, and an explicit iterative scheme is then proposed to ap- proach the Approximate Inertial Manifolds. Finally, a comparison between the traditional Galerkin method and the method presented has been given and discussed. The results show that the method presented can provide a better and acceptable approximation to the long-term behaviors of the second order in time nonlinear dissipative autonomous dynamic systems with many degrees-of-freedom, espe- cially for the numerical analysis of complex bifurcation and chaos in complicated dynamical systems.

5.Redundant Control of A Bipedal Robot Moving from Sitting to Standing

Abstract

To control a multi-joints bipedal robot, it is necessary to choose a proper law of control that ensures the safe and stable motions of the robot. Even for the simplest postures, such as sitting and stand- ing, there are constraints to respect so that the inverse geometric model (MGI) would not have innitive solutions. In this paper, a particular task of sitting-to-standing is simulated for a bipedal robot using MATLAB. The articulation evolution and the variation of the shoulder position are evaluated using typical control and hierarchical redundant control in which the cases of with and without constraints are both considered. The simulation results show that the hierarchi- cal redundant control has a better effect than the typical one, and when considering the constraints, the articulations' angular velocities vary more smoothly so that the motor is better protected.

6.Time-delay effects on periodic motions in a periodically forced, time-delayed, hardening Duffing oscillator

Abstract

In this paper, time-delay effects on periodic motions in a periodi- cally forced, time-delayed, hardening Duffing oscillator are discussed. One often considers the time-delay interval is very small compared to the oscillation period. In engineering application, the time-delay interval is often very large. Bifurcation trees of periodic motions to chaos varying with time-delay are presented for such a time-delayed, Duffing oscillator. Using the nite discrete Fourier series, harmonic amplitude varying with time-delay for stable and unstable solutions of period-1 to period-4 motions are developed. From the analytical prediction, numerical results of periodic motions in the time-delayed, hardening Duffing oscillator are completed. Through the numerical illustrations, time-delay effects on period-1 motions to chaos in non- linear dynamical systems are strongly dependent on the distributions and quantity levels of harmonic amplitudes.