Sudhir Kaul

Frame Flexibility Effects on Engine Mount Optimization for Vibration Isolation in Motorcycles

This paper examines the influence of frame flexibility on the optimization of an engine mounting system for enhanced vibration isolation in motorcycles. A theoretical model is developed to represent the structural dynamics of an engine mount system in motorcycles. The model consists of the power-train assembly, modeled as a six-degree-of-freedom (DOF) rigid body; the swing arm assembly, connected to the power-train through a coupler shaft assembly; and the frame, connected to the power-train by elastomeric mounts and to the swing-arm through the rear suspension. Two models of the flexible frame are developed for analysis. The first model uses an equivalent stiffness matrix of the frame, derived from its finite element model, in terms of the nodes connecting the frame to the other subsystems. The second model is based on a dynamic model of the frame as well as the swing arm derived from their respective finite element models. The optimization procedure minimizes the load transmitted to the frame while constraining the engine displacement due to imposed loads within prescribed limits. The mount stiffnesses, locations and orientations are used as design variables. Examples are presented to demonstrate the influence of frame flexibility on the force transmitted to the frame.

Crack diagnostics in beams using wavelets, kurtosis and skewness

This paper presents a diagnostic technique using wavelets, kurtosis and skewness for detecting crack location and severity in beams. The first three mode shapes of a damaged beam are used for detecting crack locations in beams with varying boundary conditions. Damage due to an edge-crack is modelled by a conventional macroscopic torsional spring element. Multiple families of wavelets with varying scales and vanishing moments are used so as to distinguish between their ability to detect crack locations by using the mode shapes of the damaged beam. Crack detection is followed by determination of the crack size by using statistical measures of the mode shapes such as kurtosis and skewness. These two measures are highly sensitive to small changes in mode shapes resulting from crack initiation or crack propagation, and have been used in other fields of damage detection. Several simulations are presented to showcase the application of the proposed technique, and to highlight the differences between multiple wavelets and the parameters associated with the wavelets. The proposed diagnostic technique is also tested for robustness by adding noise to the mode shapes. The simulation results and preliminary experimental results indicate that the statistical measures of kurtosis and skewness can be used in conjunction with wavelets in order to provide a viable crack diagnostic technique for beam structures.

Use of wavelets for damage diagnostics in truss structures

Purpose Wavelets are being increasingly used for damage diagnostics. The purpose of this paper is to present an algorithm that uses the wavelet transform for detecting mixed-mode, also known as combined mode, cracks in large truss structures. Design/methodology/approach The mixed-mode crack is modeled by superposing two damage modes, and this model is combined with a finite element model of the truss. The natural modes of the truss are processed through the wavelet transform and then used to determine the damage location. The influence of multiple parameters such as truss geometry, crack geometry, number of truss members, orientation of truss members, etc. is investigated as part of the study. Findings The proposed damage detection algorithm is found to be successful in detecting single mode as well as mixed-mode cracks even in the presence of significant end effects, and even when a relatively coarse sampling of natural modes is used. Results from multiple simulations that involve three commonly used truss structures are presented. A correlation between damage severity and the magnitude of wavelet coefficients is observed. Originality/value The proposed algorithm is found to be successful in accurately detecting damage, but direct determination of damage severity is found to be challenging.

Influence of Fractional Damping and Time Delay on Maxwell-Voigt Model for Vibration Isolation

Models of vibration isolators are very commonly used for the design and analysis of isolation systems. Accurate isolator modeling is critical for a successful prediction of the dynamic characteristics of isolated systems. Isolators exhibit a complex behavior that depends on multiple parameters such as frequency, displacement amplitude, temperature and loading conditions. Therefore, it is important to choose a model that is accurate while adequately representing the relationships with relevant parameters. Recent literature has indicated some inherent advantages of fractional derivatives that can be exploited in the modeling of elastomeric isolators. Furthermore, time delay of damping is also seen to provide a realistic representation of damping. This paper examines the Maxwell-Voigt model with fractional damping and a time delay. This model is compared with the conventional Maxwell-Voigt model (without time delay or fractional damping) and the Voigt model in order to comprehend the influence of fractional damping and time delay on dynamic characteristics. Multiple simulations are performed after identifying model parameters from the data collected for a passive elastomeric isolator. The analysis results are compared and it is observed that the Voigt model is highly sensitive to fractional damping as well as time delay.Copyright

Magnetorheological (MR) Damping for Vibration Mitigation: Experimental Analysis

Magnetorheological (MR) dampers have emerged as a viable means of semi-active damping in multiple industry applications. The semi-active nature of these dampers is a significant attribute since the damper functions as a passive damper in the event of a failure. While there have been other smart materials like ferroelectric, piezoelectric, shape memory alloys, etc. that have been successfully used, MR fluids exhibit a unique combination of completely reversible effect, very low response time, high durability and very low energy requirements that make them suitable for vibration control in a wide variety of applications. This paper presents results from an experimental investigation that has been carried out to evaluate the performance of a MR damper for vibration mitigation. The capability of a commercial MR damper to isolate a payload from base excitation is analyzed and the damper parameters are identified to simulate the capability of the damper with regards to transmissibility. Multiple iterations of testing are performed in order to evaluate the influence of variables such as input current to the electromagnet, mass of the payload, excitation frequency and excitation amplitude. Results indicate that the MR damper is successful in mitigating vibrations transmitted to the payload. Vibration mitigation is quantified through multiple means such as comparing the root mean square (RMS) of the time history of acceleration of the base with that of the payload, comparing the frequency response and evaluating the hysteresis plots. Displacement transmissibility results directly demonstrate the variable damping capability of the MR damper. Although the stiffness constant of the damper may also change, it is not seen to vary appreciably in this study since the excitation amplitude is limited to a low threshold. The damper is found to be robust with an inherent ability of handling payload and excitation variability. It is observed that increasing the input current to the electromagnet around the MR fluid results in an increase in damping, therefore, making the use of these dampers viable in applications where payloads and excitation inputs are expected to change during operation.Copyright

Thermo-Mechanical Analysis of Mixed-Mode Damage: Cohesive Zone Modeling

Damage detection and diagnostics is a key area of research in structural analysis. This paper presents results from the analysis of mixed-mode damage initiation in a composite beam under thermal and mechanical loads. A finite element model in conjunction with a cohesive zone model (CZM) is used in order to determine the location of joint separation as well as the contribution of each mode in damage (debonding) initiation. The composite beam is modeled by using two layers of aluminum that are bonded together through a layer of adhesive. Simulation results show that the model can successfully detect the location of damage under a thermo-mechanical load. The model can also be used to determine the severity of damage due to a thermal load, a mechanical load and a thermo-mechanical load. It is observed that integrating thermal analysis has a significant influence on the fracture energy.Copyright

A Comparative Study of Passive Vibration Isolator Modeling and Analysis

Passive vibration isolators are extensively used in wide ranging applications such as automotive, aerospace, railroad and earth moving equipment in the mechanical industry, and in structural applications in the civil industry. These isolators serve as spring-damper units that isolate specific parts of a system from external dynamic loading, or from other sub-systems that cause vibration excitation. Passive isolators exhibit very complex behavior that depends on excitation frequency, displacement amplitude, ambient temperature and pre-load in addition to geometry, design features as well as material composition of the isolator. Various models are prevalent in the existing literature for the design and analysis of such isolators, ranging from the basic Voigt model to more complex models such as the Maxwell-Voigt model with multiple Maxwell elements, the Maxwell ladder model, the three dimensional viscoelastic model, the fractional derivative model, and models specifically used for capturing the hysteresis behavior or the displacement limiting behavior. However, each of these models is successful in representing certain characteristics of the isolator while being unable to capture other key attributes. This paper provides a comparative study of some of the main models that are commonly used for the design and analysis of passive vibration isolators. Experimental data collected from a passive elastomeric isolator under varying excitation conditions is used to identify parameters associated with some of the commonly used models. The analysis results are compared and specific highlights and shortcomings of each model are identified and discussed.Copyright

Use of Wavelets for Mixed-Mode Damage Diagnostics in Warren Truss Structures

The use of the wavelet transform has been gaining widespread acceptance over the last decade as a valuable tool for damage detection. This paper investigates the use of wavelets for detecting mixed-mode, also known as combined mode, cracks in truss structures. The propagation of an open, mixed-mode crack is simulated by using a macroscopic model of damage that is combined with a finite element model of the Warren truss. The natural modes of the truss with varying levels of damage are then used to determine crack location on a specific member of the truss. A damage detection algorithm is developed and the influence of multiple parameters such as truss geometry, crack geometry, number of truss members, etc. is investigated. A direct correlation between damage severity and the magnitude of wavelet coefficients is found for a predefined damage location. It is observed that the proposed damage detection algorithm can be used to successfully detect mixed-mode cracks even in the presence of noise, and even when a relatively coarse sampling of natural modes is used. Multiple simulations are presented and some shortcomings of the proposed algorithm are also discussed in detail.Copyright

Magneto-Rheological (MR) Damper Design for High-Flowrate Suspensions

This paper presents the design of a magneto-rheological (MR) damper for an off-road vehicle where large suspension travel and high flow rates, as compared to typical passenger car suspensions, are required. The MR damper is expected to enhance the capability of the suspension system by allowing variable damping due to inherent properties of the MR fluid. MR fluids exhibit a reversible behavior that can be controlled with the intensity of a magnetic field, allowing a change in the effective viscosity and thereby in the damping characteristics of the fluid. A mathematical model of the proposed damper has been developed using the Bingham plastic model so as to determine the necessary geometry for the damper designed in this study, using the fluid flow rate and current to the electromagnet as the input variables. The model is used to compute the damping force, and the analytical results show that the designed MR damper provides the required range of damping force for the specific vehicle setup that is being used for this study. A valve-mode MR fluid channel has been designed such that the required minimum damping is reached in the off-state, and the desired maximum damping is reached in the on-state. For manufacturing and size considerations, the final design incorporates a triple pass layout with the MR fluid flowing through the three passages that are arranged in an S-shape so as to minimize the cross section of the electromagnet core.Copyright

Kinematic and Dynamic Analysis of V-Twin Powertrains: Design Trade-Offs

This paper examines the influence of multiple design parameters on the kinematics and dynamics of a V-twin powertrain. Two models are presented to study the design trade-offs in order to provide an analytical tool that can be used for the top-level design of a V-twin powertrain. Shaking forces and bearing loads are evaluated to quantitatively comprehend the influence of design parameters such as banking angle, crank pin, piston off-set, etc. Furthermore, the influence of parameters associated with the use of conventional Lanchester balance shafts is also investigated as part of the analysis. These parameters include support bearing locations and balancing mass location on the balance shaft. The analysis results are compared to some of the studies on balancing of shaking forces and shaking moments in the literature. While the design trade-offs associated with parameters such as banking angle are well understood in the available literature, the analysis performed in this study shows interesting results for piston off-set and crank pin design, as well as for parameters associated with the balance shaft.Copyright