Structural Modification Technique Research Articles

Analytical modeling of asymmetric multi-segment rotor – bearing systems with Timoshenko beam model including gyroscopic moments

In this study, analytical modeling and an analysis approach for asymmetric multi-segment rotor – bearing systems are presented. Timoshenko beam model which includes the effect of gyroscopic moments is employed for modeling rotor segments. Instead of applying FEM, sub-segment Frequency Response Functions (FRFs) are obtained analytically, and sub-segment FRFs obtained are coupled by using receptance coupling method. Bearing properties are included into system dynamics by employing structural modification techniques. The proposed analytical model is verified by using FEM approach. It is shown that using analytical model and receptance coupling, compared with FEM, reduces computational time drastically without losing accuracy.

Vibration modeling and modification of cutting platform in a harvest combine by means of operational modal analysis (OMA)

Vibration in combine cutting platform causes increase in grain loss, reduction of vehicle lifetime and driver’s comfort, and also affects the machine working precision. In order to determine vibration behavior of a mechanical structure, the model which relates acting forces on the structure with the resulting responses of it plays a significant role. For a great deal of mechanical structures, only response data are measurable while the actual loading conditions are unknown. Therefore, the system identification process will need to build on the output-only data. The use of such processes allows the identification of modal models of structures which are excited by unknown ambient vibration. In this contribution, controlled vibration experiments were conducted on cutting platform of a combine in order to recognize and reduce its vibration problem. A finite element model is constructed representing the vibration behavior of the cutting platform. Also, the frequency domain decomposition (FDD) technique is used to estimate the modal parameters of vibrating structures in operational conditions. Then, the finite element model is successfully updated by comparing the estimated results of the operational modal analysis. It is found that there is a resonance condition around 50Hz. Then, the mass change strategy is used to estimate the scaling-factor and frequency response function (FRF) matrix. Finally, the resonance condition and subsequently vibration of cutting platform is reduced by the structural modification technique. As a result of this modification, natural frequency of fifth mode shape (50Hz) of the combine cutting platform is shifted to 48Hz.

A New Design Approach for Rapid Evaluation of Structural Modifications Using Neural Networks

Design optimization of structural systems is often iterative, time consuming and is limited by the knowledge of the designer. For that reason, a rapid design optimization scheme is desirable to avoid such problems. This paper presents and integrates two design methodologies for efficient conceptual design of structural systems involving computationally intensive analysis. The first design methodology used in this paper is structural modification technique (SMT). The SMT utilizes the frequency response functions (FRFs) of the original model for the reanalysis of the structure that is subjected to structural modification. The receptances of the original structure are coupled with the dynamic stiffness of the components that are added to or removed from the original structure to perform the structural modification. Then, the coupled matrices are used to calculate the mobility matrices of the modified structure in an efficient way. The second design methodology used in this paper is neural networks (NN). Once sufficient input and output relationships are obtained through SMT, a NN model is constructed to predict the FRF curves of the system for further analysis of the system performance while experimenting different design parameters. The input–output sets used for training the network are increased by applying an interpolation scheme to improve the accuracy of the NN model. The performance of the proposed method integrated through SMT and NN technique is demonstrated on a rectangular plate to observe the effect of the location and thickness of stiffeners on the frequency response of the structure. It is observed that both methods combined with the proposed interpolation scheme work very efficiently to predict the dynamic response of the structure when modifications are required to improve the system performance.

Preparation and assessment cytotoxic and hemolytic activities of Complexes from “Chelating Kojic–Lipid Conjugate”

Complex bis (2-Oleicoyloxymethyl-5-hydroxy-gamma-pyrone) copper (II) and tris (2-Oleicoyloxymethyl-5-hydroxy-gamma-pyrone) iron (III) were prepared in ethanol using the structure chelator conjugate kojic -lipid. This ester was obtained from kojic acid by improving their lipophilicity of obtaining metalobioactives with application in Medicinal Bioinorganic Chemistry. Through the technique ATR/FTIR, the values ​​ of the infrared kojic acid has been updated and it was possible to characterize the complex 1567m, 1511w (Cu (II) ← [O=C] 2 ), and 1540m, 1519m (Fe(III) ← [O=C] 3 . These compounds no showed cytotoxic potential against B16 (melanoma) and ACP02 (gastric adenocarcinoma) (IC 50 > 5 μ g mL -1 ) and low hemolytic activity (EC 50 > 250 μ g mL -1 ).The preparation of th ese new molecules by structural modification techniques and these interesting biological results confirm the continuity of this studies related to these coordination complexes to glimpse the possibility of obtaining other derivatives/ analogues with significant biological potential of this metallo-bioactive.

A passive adaptor to enhance chatter stability for end mills

A design procedure is suggested in this paper to enhance the chatter stability of an end mill cutter. Tool chatter is a well recognized self-excited vibration problem where the excitation force is the cutting force required to machine a workpiece. The cutting force magnitude is proportional to the thickness of the chip removed from the workpiece. The thickness of the chip, on the other hand, is affected by two distinct sets of events, namely, the instantaneous oscillations of the tip of the cutter and the undulations left on the surface from the earlier passes of the cutter. Hence, the excitation force, which is the cause of the oscillations, feeds on the oscillations. In this investigation, an end mill is simplified to be a beam cantilevered from a relatively rigid spindle. A local structural modification technique of the authors is then applied to this beam to suppress its proneness to excessive resonance vibrations. An add-on passive adaptor is developed for this purpose. Numerical simulations with random tip excitation and experimental verification with a scaled model are discussed. Suggested designs promise to enhance the chatter stability of a cantilevered cutter. Cutting tests are being planned for the next stage of work.

An Improved Impedance Bandwidth of Modified UWB Antenna With Staircased Parasitic Rings

In this letter, a structural modification technique of simple monopole to improve the input impedance bandwidth by using multiple staircased parasitic rings is suggested. In addition, the shape and size of parasitic rings are optimized to enhance the antenna bandwidth. The final optimized parameter values have been obtained from the parametric studies of the antenna and simple equation evaluating the resonant frequency. The electrical performances of the proposed antenna are verified in terms of the return loss and the radiation pattern by using commercially available softwares, CST MW Studio, and HFSS based on FDTD and FEM algorithms, respectively.

An artificial carbon nano-thorn synthesized by a plasma chemical vapour deposition

We show a structural modification technique which causes the fluctuated surface of multi-wall carbon nanotubes (MWNTs) by using hydrogen sulfide as a reaction-assist medium, which promotes the formation of sp3-hybridized orbitals of carbon and suppresses the formation of sp2-hybridized orbitals in the plasma process. We observed the structure of MWNTs synthesized with the addition of H2S by means of high-resolution transmission electron microscopy and electron energy loss spectroscopy, and found the cornhusk-like surface fluctuations on the surface of MWNTs. In this study, we discuss the mechanism underlying this structural modification of carbon nanotubes precisely.

A Modeling Approach for Analysis and Improvement of Spindle-Holder-Tool Assembly Dynamics

The most important information required for chatter stability analysis is the dynamics of the involved structures, i.e. the frequency response functions (FRFs) which are usually determined experimentally. In this study, the tool point FRF of a spindle-holder-tool assembly is analytically determined by using the receptance coupling and structural modification techniques. Timoshenko's beam model is used for increased accuracy. The spindle is also modeled analytically with elastic supports representing the bearings. The mathematical model is used to determine the effects of different parameters on the tool point FRF and to identify contact dynamics from experimental measurements. The applications of the model are demonstrated and the predictions are verified experimentally.

Structure Dynamic Modification and Optimization for High-Speed Face Milling Cutter

Due to the complexity of high-speed milling process by high relative speed and interrupted cutting, the face milling cutters possess the multi-order modes and the vibrating displacements of the cutting edges under each modes affect adversely both the surface roughness and the life of machine/tool system worse than other structures. In order to improve the stability of milling process, this work focuses on the influence of the variables such as structure geometries and constraint conditions on the eigenfrequencies and modeshapes of cutter. As an example, the dynamic characteristics of several face cutters are analyzed and optimized by structural dynamic modification (SDM) techniques.

Some studies on Al–8.3Fe–0.8V–0.9Si alloy for near net shape casting

With the development of new generation high temperature aluminium alloys, simple techniques to produce them to near net shape by casting route have become necessary. It is well known that near net shape casting not only contributes to material saving but also to reduction of processing steps. Amongst the high temperature aluminium alloys, the Al–Fe–V–Si alloys system has attracted considerable interest due to its potential in automotive and aerospace applications. These alloys are generally prepared through the complex rapid solidification–powder metallurgical processing route. Thus, although the alloys possess good elevated temperature strength, ductility, fatigue and fracture toughness they have not found industrial application. An alternative method of conventional solidification for producing these alloys has been attempted in this work. A novel structural modification technique has been tried out with Mg/Ni–Mg master alloy to bring about alteration and refinement of the precipitate particles, which are otherwise ten-armed star-shaped and adversely affect the mechanical properties, to favourable cuboidal, hexagonal or other compact forms. It was observed that a number of arrest points occur in the cooling curve of the alloy, indicating that a variety of phases such as Al 12(Fe,V,Si) 6(Si,Mg) 5, Al 15(Ni,V,Fe) 6(Si,Mg), Al 3(Fe,V,Ni,Si,Mg) form during cooling. Quenching experiments were performed to identify the details of the phases formed. The features of the phases were studied using scanning electron microscope/EDAX and X-ray diffraction. Important properties required for near net shape casting such as the thermal expansion coefficient, fluidity, etc., have been studied and correlated with the phases.

Structural dynamic modifications via models

Structural dynamic modification techniques attempt to reduce dynamic design time and can be implemented beginning with spatial models of structures, dynamic test data or updated models. The models assumed in this discussion are mathematical models, namely mass, stiffness, and damping matrices of the equations of motion of a structure. These models are identified/ extracted from dynamic test data viz. frequency response functions (FRFs). Alternatively these models could have been obtained by adjusting or updating the finite element model of the structure in the light of the test data. The methods of structural modification for getting desired dynamic characteristics by using modifiers namely mass, beams and tuned absorbers are discussed.

REANALYSIS OF DAMPED STRUCTURES USING THE SINGLE STEP PERTURBATION METHOD

The single step perturbation method is a recently developed structural dynamic modification technique. In the present work, this has been applied to complex structures. A typical machine tool structure in form of an F structure is considered and eigenvalue and response reanalysis are carried out for this structure when modified by constrained viscoelastic damping layer treatment. A comparison of results is made for cases using the single step perturbation method, with the erstwhile perturbation method and the re-solved results, i.e., results obtained by repeated solution. Comparison of computational times taken are also indicated. A variation of coverage ratio is considered for the above structure and the variation in natural frequencies and loss factors in case of free vibration, variation in resonant frequencies and amplitudes in case of forced vibration are also studied.

A Computationally Efficient Objective Function for the Evaluation of the Natural Frequency in Structural Modification and Optimization Problems

A highly computationally efficient objective function for measuring the change in the natural frequency when a structure is modified is introduced. When the optimization of an orthotropic plate is studied, a decrease in CPU time by at least a factor of 40 is obtained when the new objective function is compared to that derived from the minor structural modification technique. The greater the number of finite elements affected by the design changes the higher the factor of improvement will be. This new objective function has the additional advantage that it can be used for substantial modifications to the original design.

Some considerations on modal reanalysis of non-conservative dynamics systems by the generalized receptance method

A structural modification technique which takes into account the damping parameter is introduced in this paper. The applications described are the extensions of a method based on the Receptance Approach initially developed by Palazzolo. Numerous efforts have been made in order to take into consideration the dissipative characteristics of the mechanical structures. Specific cases of modifications can lead to simplified algorithms and, as a consequence, to outstanding results. The conclusions, which have been drawn up, show the important reductions in terms of computational times but also in terms of memory size, that we can expect when this method is implemented in practical engineering design.

A Design Approach for the Systematic Improvement of Support Locations for Vibrating Circuit Cards

This paper approaches the problem of improving an initial guess at support locations for a vibrating circuit card so as to increase the first natural frequency of the card. The finite element method and structural dynamic modification techniques are combined with a simple sequential search algorithm to systematically improve the location of point supports for a circuit card populated with components. It is found that the proposed methodology can be useful for determining the support locations of a circuit card so as to increase its fundamental natural frequency. A case study is presented in which the original support locations on an existing commercial power supply circuit card are systematically improved giving a better than two fold increase in the natural frequency. Additionally, finite element modeling approaches for determining the modal characteristics of a circuit card are compared with experimental results.

Updating model parameters by adding an imagined stiffness to the structure

A mass addition technique for structural parameters updating has recently been described by the authors. It uses eigenvalues of the structure, before and after it is perturbed by adding mass, to adjust selected parameters by sensitivity analysis. The technique avoids the use of noisy mode shape data and overcomes the problem of a non-unique set of parameters when eigenvalues alone are used. However, it is not suitable for a large structure because of the difficulty of adding the necessarily large perturbing mass to the existing structure. This paper presents an alternative technique. An "imagined" stiffness is added to the structure and the FRF of this perturbed structure is obtained from the measured FRF of the original structure by a simple structural modification technique. The eigenvalues of the original and perturbed structures are obtained from the measured and constructed FRFs respectively. These eigenvalues, together with the eigenvalues predicted from an analytical model of the structure, are used to adjust the structural parameters by sensitivity analysis. The technique is demonstrated by a simulated example and by an experiment on an H-frame.

Experimental Modal Analysis and Dynamic Response Prediction of PC Boards With Surface Mount Electronic Components

Abstract Use of modal testing and structural dynamic modification techniques for prediction of the modal parameters of a PC board with a surface-mount component is described. Experimentally determined natural frequencies and mode shapes of a PC board with and without an added component are presented. Several simple dynamic models of the component are evaluated. Results obtained indicate that the component can sometimes be modeled as a point mass.

A new structural modification technique for zeolites: chemisorption of Si 2H 6

Abstract Chemisorption of disilane on H-mordenite small port causes two types of structural modification: 1) homogeneous intracrystalline implantation of additional groups and/or 2) preferential pore entrance and external surface modification. The obtained type depends of the applied reaction conditions. The second modification process causes an efficient pore size reduction without loss of sorption capacity or acidity. The obtained substrates show a high resistance to a steaming treatment. The properties of these modified zeolites have been evaluated by chemisorption kinetics, gas adsorption experiments and FTIR-PAS spectroscopy.