Chatter reduction in slender boring bar via a tunable holder with variable mass and stiffness

2017 ◽  
Vol 232 (12) ◽  
pp. 2098-2108 ◽  
Author(s):  
Sajad Hayati ◽  
Mohammad Hajaliakbari ◽  
Yalda Rajabi ◽  
Sajad Rasaee
Keyword(s):  
Time Domain ◽  
Variable Mass ◽  
Stable Condition ◽  
Domain Model ◽  
Machining Process ◽  
Machining Processes ◽  
Stability Lobe Diagram ◽  
Chatter Suppression ◽  
Stability Lobe ◽  
The Time Domain

In this study, a new strategy is presented to increase the machining stability due to chatter suppression for boring and turning machining processes. The proposed approach is based on varying the position of stability lobes via changing mechanical properties of the tool body such as the mass and stiffness. Because of the shape of stability lobe diagrams, having a tool with a tunable stability lobe diagram can be useful to alter an unstable condition to a stable condition. For this purpose, a structure for the tool body is designed that is consisted of a hollow body with a core as a tunable screw inside it. As the core gets in or out, it changes the mass and stiffness of the tool body that leads to change the position of stability lobe diagram. In order to study the effect of designed structure on stability, the structure is simulated using a validated finite element time domain model. The time domain simulation shows a considerable improvement in stability of process. The strategy is experimentally applied to the process via modulation of the tool structure in the machining process to validate the simulation results. The experimental results have a high coincidence with theory and show a good improvement in stability.

Discrete Time-Delay Optimal Control Method for Experimental Active Chatter Suppression and Its Closed-Loop Stability Analysis

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Xingwu Zhang ◽  
Ziyu Yin ◽  
Jiawei Gao ◽  
Jinxin Liu ◽  
Robert X. Gao ◽  
...  
Keyword(s):  
Optimal Control ◽  
Closed Loop ◽  
Control Method ◽  
Trial And Error ◽  
Stability Lobe Diagram ◽  
Weighting Matrix ◽  
Chatter Suppression ◽  
Stability Lobe ◽  
Optimal Control Method ◽  
Discrete Time Delay

Chatter is a self-excited and unstable vibration phenomenon during machining operations, which affects the workpiece surface quality and the production efficiency. Active chatter control has been intensively studied to mitigate chatter and expand the boundary of machining stability. This paper presents a discrete time-delay optimal control method for chatter suppression. A dynamical model incorporating the time-periodic and time-delayed characteristic of active chatter suppression during the milling process is first formulated. Next, the milling system is represented as a discrete linear time-invariant (LTI) system with state-space description through averaging and discretization. An optimal control strategy is then formulated to stabilize unstable cutting states, where the balanced realization method is applied to determine the weighting matrix without trial and error. Finally, a closed-loop stability lobe diagram (CLSLD) is proposed to evaluate the performance of the designed controller based on the proposed method. The CLSLD can provide the stability lobe diagram with control and evaluate the performance and robustness of the controller cross the tested spindle speeds. Through many numerical simulations and experimental studies, it demonstrates that the proposed control method can make the unstable cutting parameters stable with control on, reduce the control force to 21% of traditional weighting matrix selection method by trial and error in simulation, and reduce the amplitude of chatter frequency up to 78.6% in experiment. Hence, the designed controller reduces the performance requirements of actuators during active chatter suppression.

Coupled Time-Domain Hydro-Elastic Simulation for Submerged Floating Tunnel Under Wave Excitations

2021 ◽  
Author(s):  
Chungkuk Jin ◽  
Sung-Jae Kim ◽  
MooHyun Kim
Keyword(s):  
Time Domain ◽  
Domain Model ◽  
Mooring Line ◽  
Wave Forces ◽  
Rod Theory ◽  
Discrete Module ◽  
Simulation Based ◽  
Submerged Floating Tunnel ◽  
The Time Domain ◽  
Elastic Simulation

Abstract We develop a fully-coupled time-domain hydro-elasticity model for the Submerged Floating Tunnel (SFT) based on the Discrete-Module-Beam (DMB) method. Frequency-domain simulation based on 3D potential theory results in multibody’s hydrodynamic coefficients and excitation forces for tunnel sections. Subsequently, we build the time-domain model with the multibody Cummins equation and external stiffness matrix from the Euler-Bernoulli and Saint-Venant torsion theories. We establish the mooring line model with rod theory and couple components with translational springs at their respective connection locations. We then compare the dynamic motions, wave forces, and mooring tensions between the present and Morison-equation-based elastic models under regular wave excitations at different submergence depths. The present model is especially important for the shallowly submerged tunnel in which the Morison model shows exaggerated motions, especially at high-frequency range.

On Vessel Motion Induced Vortex-Induced Vibrations of a Steel Lazy Wave Riser

2021 ◽  
Author(s):  
Decao Yin
Keyword(s):  
Vortex Shedding ◽  
Time Domain ◽  
Oscillatory Flow ◽  
Domain Model ◽  
Time Varying ◽  
Structure Interaction ◽  
Response Characteristics ◽  
Vortex Induced Vibrations ◽  
The Time Domain ◽  
Vessel Motion

Abstract Deepwater steel lazy wave risers (SLWR) subject to vessel motion will be exposed to time-varying oscillatory flow, vortices could be generated and the cyclic vortex shedding force causes the structure vibrate, such fluid-structure interaction is called vortex-induced vibrations (VIV). To investigate VIV on a riser with non-linear structures under vessel motion and oscillatory flows, time domain approaches are needed. In this study, a time-domain approach is used to simulate a full-scale SLWR. Two cases with simplified riser top motions are simulated numerically. By using default input parameters to the time domain approach, the key oscillatory flow induced VIV response characteristics such as response frequency, curvature and displacements are examined and discussed. More accurate VIV prediction could be achieved by using realistic hydrodynamic inputs into the time domain model.

Simulating High Mode Vortex Induced Vibration of Riser in Linear Sheared Current Using an Empirical Time Domain Model

2020 ◽  
Author(s):  
Sang Woo Kim ◽  
Svein Sævik ◽  
Jie Wu
Keyword(s):  
Frequency Domain ◽  
Vortex Shedding ◽  
Time Domain ◽  
Structural Model ◽  
Cross Flow ◽  
Domain Model ◽  
Vortex Induced Vibrations ◽  
The One ◽  
The Time Domain ◽  
Empirical Coefficients

Abstract This paper addresses the performance evaluation of an empirical time domain Vortex Induced Vibrations (VIV) model which has been developed for several years at NTNU. Unlike the frequency domain which is the existing VIV analysis method, the time domain model introduces new vortex shedding force terms to the well known Morison equation. The extra load terms are based on the relative velocity, a synchronization model and additional empirical coefficients that describe the hydrodynamic forces due to cross-flow (CF) and In-line (IL) vortex shedding. These hydrodynamic coefficients have been tuned to fit experimental data and by considering the results from the one of existing frequency domain VIV programs, VIVANA, which is widely used for industrial design. The feature of the time domain model is that it enables to include the structural non-linearity, such as variable tension, and time-varying flow. The robustness of the new model’s features has been validated by comparing the test results in previous researches. However, the riser used in experiments has a relatively small length/diameter (L/D) ratio. It implies that there is a need for more validation to make it applicable to real riser design. In this study, the time domain VIV model is applied to perform correlation studies against the Hanøytangen experiment data for the case of linear sheared current at a large L/D ratio. The main comparison has been made with respect to the maximum fatigue damage and dominating frequency for each test condition. The results show the time domain model showed reasonable accuracy with respect to the experimental and VIVANA. The discrepancy with regard to experiment results needs to be further studied with a non-linear structural model.

Investigation on Fluidelastic Instability Accompanied by Wake Shedding With a Time-Domain Model

2019 ◽  
Author(s):  
Kai Guo ◽  
Yipeng Wang ◽  
Tong Su ◽  
Liyan Liu ◽  
Zhanbin Jia ◽  
...  
Keyword(s):  
Vortex Shedding ◽  
Time Domain ◽  
Domain Model ◽  
Elastic Instability ◽  
Flow Induced Vibration ◽  
Fluid Forces ◽  
Double Peaks ◽  
Critical Instability ◽  
Periodic Characteristic ◽  
The Time Domain

Abstract As the most dangerous flow-induced vibration (FIV) mechanism, fluid-elastic instability is always accompanied by the wake shedding. If both of the two FIV mechanisms are considered, fluid forces in this condition can be quite complex. In this paper, a time-domain model based on unsteady flow theory was used to investigate the fluid-elastic instability in a rotated triangular tube array. The vortex shedding forces were simplified as harmonic forces. Computational fluid dynamics (CFD) was used to get the fluid force coefficients with vortex shedding. The model was established by a finite element code with MATLAB software and simulation results agreed with the experiment results. The results showed the critical instability velocity can be influenced by vortex shedding forces, and double peaks can be found in the frequency spectrum of displacements of tubes. The time-domain displacements showed the phases had been impacted by the shedding and periodic characteristic was found in the displacements results. The model can also be adopted in fluid-elastic instability analysis in other tube arrangements and flow conditions.

Effect of the elastic hysteresis term formulation and response to non-harmonic periodic excitations of a non-linear SDOF dynamical model with weak frequency-dependency in the time domain

2021 ◽  
pp. 095440622110182
Author(s):  
Christos Spitas ◽  
Mahmoud S Dwaikat ◽  
Vasileios Spitas
Keyword(s):  
Correction Factor ◽  
Time Domain ◽  
Hysteresis Loops ◽  
Domain Model ◽  
Viscous Damping ◽  
State Variables ◽  
Hysteretic Damping ◽  
Vibration Responses ◽  
The Time Domain ◽  
Damping Model

We elaborate a SDOF time-domain model for elastic hysteretic damping, by modifying the viscous damping model to introduce an instantaneous correction factor that recursively depends on the state variables of the system, such that the response exhibits weak dependency on frequency, corresponding to a large array of engineering materials. The effect of different formulations for calculating the instantaneous correction factor on the predicted hysteresis loops and the potential manifestation of singularities is studied. Hysteresis loops anticipated by the model are plotted and forced vibration responses to harmonic and other periodic non-harmonic excitations are simulated and discussed, also in comparison to the conventional viscous and Reid’s damping models.

An Improved Time Domain Simulation for Dynamic Milling at Small Radial Immersions and Large Depths of Cut

2001 ◽  
Author(s):  
Marc L. Campomanes ◽  
Yusuf Altintas
Keyword(s):  
Surface Finish ◽  
Time Domain ◽  
Dynamic Models ◽  
Three Dimensional ◽  
Domain Model ◽  
Time Domain Simulation ◽  
Chatter Stability ◽  
Linear Effects ◽  
Deep Cuts ◽  
The Time Domain

Abstract This paper presents an improved time domain model for milling, which can simulate vibratory cutting conditions at very small radial widths of cut and large depths of cut. The improved kinematics model allows simulation of very small radial immersions. The varying dynamics modeled along the cutting depth allows milling with very flexible cutters and/or flexible workpieces at very deep cuts to be simulated. The model can predict forces, surface finish, and chatter stability, accurately accounting for non-linear effects that are difficult to model analytically. The discretized cutter and workpiece kinematics and dynamic models are used to represent the exact trochoidal motion of the cutter, and to investigate the effects of forced vibrations and changing radial immersion due to deflection and vibrations on chatter stability. Three dimensional surface finish profiles are predicted and are compared to measured results. Stability lobes generated from the time domain simulation are also shown for various cases.

Preliminary Study on the Effect of Mass-Induced Damping on Machining Delicate Workpiece Geometry

2013 ◽  
Vol 764 ◽  
pp. 83-89
Author(s):  
A. Kamaruddin ◽  
W.C. Pan ◽  
S.L. Ding ◽  
J. Mo
Keyword(s):  
Machining Process ◽  
Depth Of Cut ◽  
Machining Processes ◽  
Stability Lobe ◽  
Mechanical Factors ◽  
Preliminary Study ◽  
Thin Walled ◽  
Enhance Efficiency ◽  
The Stability ◽  
Minor Increment

Study of predicting chatter has been around for many years. These studies are crucial for our understanding of machining processes and to enhance efficiency in manufacturing. This paper presents a new mechanism affecting the stability of machining process called mass induced damping. This effect is simulated numerically with tested values of initial parameters taken for impact tests of a thin-walled workpiece. Results from the simulation shows minor increment in allowable depth of cut by numerically calculated using stability lobe theory. This effect will open a new understanding how certain mechanical factors would affect the value of damping of a system.

Simulating Riser VIV in Current and Waves Using an Empirical Time Domain Model

2017 ◽  
Author(s):  
Mats J. Thorsen ◽  
Svein Sævik
Keyword(s):  
Frequency Domain ◽  
Vortex Shedding ◽  
Time Domain ◽  
Theoretical Background ◽  
Domain Model ◽  
Wave Period ◽  
Time Variability ◽  
Analysis Tool ◽  
Load Model ◽  
The Time Domain

The theoretical background of an empirical model for time domain simulation of VIV is reviewed. This model allows the surrounding flow to be time varying, which is in contrast to the traditional frequency domain tools. The hydrodynamic load model consists of Morison’s equation plus an additional term representing the oscillating effect of vortex shedding. The magnitude of the vortex shedding force is given by a dimensionless coefficient, and this force is assumed to act perpendicular to the relative velocity between the cylinder and the fluid. The time variability of the vortex shedding force is described by a synchronization model, which captures how the instantaneous frequency reacts to cylinder motion. The parameters in the time domain load model are calibrated against a commonly used frequency domain VIV analysis tool, VIVANA. To do this, a finite element model of a vertical tensioned riser is established, and the structure is exposed to a linearly sheared flow. Key results such as cross-flow displacements along the riser, frequency content, r.m.s. of bending stresses and mean in-line displacements are compared, and it is shown that the frequency and time domain methods are close to equivalent in this simple case with stationary flow. Finally, the time domain model is utilized to study VIV of a riser subjected to regular waves. The characteristics of wave induced VIV are discussed in light of the simulation results. It is seen that VIV is excited in the zone close to the surface, and the energy is transported downwards as traveling waves. The vibrations typically build up as the horizontal water particle velocity is high, and die out as the velocity decreases. The effect of varying the wave amplitude and period is investigated, and it is found that the dominating frequency, mode and r.m.s. stresses increase together with the wave height. The effect of the wave period is however more complicated. For example, reducing the wave period increases the dominating mode but decreases the displacements. Hence the stress may increase or decrease, depending on which of these effects are strongest.

A Complex Frequency Domain Model of Wind Turbine Structures

1995 ◽  
Vol 117 (4) ◽  
pp. 311-317 ◽  
Author(s):  
P. So̸rensen ◽  
G. C. Larsen ◽  
C. J. Christensen
Keyword(s):  
Wind Turbine ◽  
Frequency Domain ◽  
Time Domain ◽  
Domain Model ◽  
Horizontal Axis ◽  
Complex Frequency ◽  
Horizontal Axis Wind Turbine ◽  
The Time Domain

The present paper describes a frequency domain model of the structure of an operating horizontal axis wind turbine with three or more blades. The frequency domain model is implemented along with an analogous time domain model in a PC code. This PC code is used to verify the frequency domain model comparing loads on the structure calculated with the frequency domain model both to loads calculated with the time domain model and to measured loads.

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