Parameters Of Mechanical System Research Articles

Tresca Versus Von Mises: Which Failure Criterion is More Conservative in a Probabilistic Context?

Abstract This tutorial examines the failure theories of Tresca and von Mises, both of which are crucial for designing metallic structures. Conventionally, Tresca is regarded as more conservative than von Mises from a deterministic perspective. This tutorial, however, introduces a different viewpoint, presenting a scenario where von Mises’ theory may appear more conservative when variability in the mechanical system parameters is considered. This often-overlooked aspect is not extensively addressed in standard textbooks on solid mechanics and the strength of materials. The tutorial aims to shed light on the non-negligible probability where von Mises’ criterion yields a smaller equivalent stress than Tresca, thus being more conservative. It underscores the importance of integrating probabilistic considerations into stress analyses of solids, offering valuable insights for the education of structural mechanics.

Rat-Tail Models for Studying Hand-Arm Vibration Syndrome: A Comparison between Living and Cadaver Rat Tails

Over-exposure of the hand-arm system to intense vibration and force over time may cause degeneration of the vascular, neurological, and musculoskeletal systems in the fingers. A novel animal model using rat tails has been developed to understand the health effects on human fingers exposed to vibration and force when operating powered hand tools or workpieces. The biodynamic responses, such as vibration stress, strain, and power absorption density, of the rat tails can be used to help evaluate the health effects related to vibration and force and to establish a dose-effect relationship. While the biodynamic responses of cadaver rat tails have been investigated, the objective of the current study was to determine whether the biodynamic responses of living rat tails are different from those of cadaver rat tails, and whether the biodynamic responses of both living and cadaver tails change with exposure duration. To make direct comparisons, the responses of both cadaver and living rat tails were examined on four different testing stations. The transfer function of each tail under a given contact force (2 N) was measured at each frequency in the one-third octave bands from 20 to 1000 Hz, and used to calculate the mechanical system parameters of the tails. The transfer functions were also measured at different exposure durations to determine the time dependency of the response. Differences were observed in the vibration biodynamic responses between living and cadaver tails, but the general trends were similar. The biodynamic responses of both cadaver and living rat tails varied with exposure duration.

Mechanical properties analysis of cross-linked epoxy resin

Abstract For this study, bisphenol A epoxy resin (DGEBA) was used as the resin matrix, and 3,3’-diaminodiphenyl sulfone (33DDS) was used as the curing agent. The effects of different cross-linking densities on the mechanical properties of epoxy resins were studied by molecular dynamics (MD) simulation, and the changes in the mechanical properties of epoxy resins under five different cross-linking density levels were predicted [1]. The results showed that as the cross-linking density of the epoxy resin increased, the mechanical parameters (such as elastic modulus, shear modulus, and bulk modulus) of the epoxy resin system also increased. This indicates the importance of improving the curing process of epoxy resin to enhance its mechanical properties.

Theoretical analysis of dynamic performance of concrete-filled steel tube pile under vertical load

The concrete-filled steel tube (CFST) pile is a type of composite pile that offers a preferable alternative to the traditional pile owing to its exceptional advantages. In this study, a new theoretical model is established to investigate the dynamic performance of the CFST pile under vertical load. The inner concrete column, outer steel tube and surrounding soil are modelled as axisymmetric elastic continua taking account of both the vertical and radial motions. The interface conditions between different materials and specific mathematical tools are then introduced to obtain the theoretical solution for the dynamic impedance of CFST piles. Existing solutions are involved in the verification of the obtained solution. Furthermore, combined with the defined soil resistance factor of the CFST pile, extensive parametric analysis is conducted to explore the impact of geometric and mechanical parameters of the CFST pile-soil system on its dynamic behavior under various working conditions. It is found that two cut-off frequencies exist during the axial vibration of the CFST pile within the low-frequency range and their characteristics are thoroughly investigated. The observations provide valuable guidance and enhanced interpretation for the dynamic analysis and design of CFST piles.

Design and analysis of LRB base-isolated building structure for multilevel performance targets

According to China's current code for the seismic design of buildings (GB50011-2010), in the course of designing base-isolated building structures, the isolation system and superstructure are designed separately. Hence, the horizontal seismic isolation coefficient in terms of the design-based earthquake (DBE) and horizontal deformation of the isolation system under the maximum considerable earthquake (MCE) cannot be considered simultaneously. Consequently, the optimum mechanical parameters for isolation bearing and the corresponding horizontal seismic isolation coefficient used in the seismic design of the superstructure cannot be obtained. To address these shortcomings, we propose an optimum seismic design procedure for LRB base-isolated building structures to meet multilevel performance fortification criteria, where explicit mathematical formulations for horizontal seismic isolation coefficients and the horizontal deformation of isolation systems in terms of the mechanical parameters of the LRB isolation system are established by combining equivalent linearization and modal decomposition response spectrum methods. Through a parametric study, we find the critical yield strength ratio, i.e., the ratio of the yielding shear of lead core to the total weight of the LRB base-isolated structure, which leads to the minimal value of the horizontal seismic isolation coefficient. Beyond this critical yield strength ratio, an optimum solution is unavailable, as the horizontal seismic isolation coefficient and horizontal displacement of the isolation system are of a conflicting nature. By converting the multi-criterion formulation into an auxiliary problem with a scalar objective, the optimum design method of an LRB base-isolated building structure oriented to multilevel performance fortification criteria is proposed, so as to obtain the optimum yield strength ratio and the optimum second shape coefficient for the seismic design of the superstructure. A numerical example demonstrates that the seismic horizontal seismic isolation coefficient and maximum horizontal displacement of the isolation system calculated from the optimum yield strength ratio and the optimum second shape coefficient agree well with the results from the time-history method. In a comparative study, LRB base-isolated building structures designed by the critical yield strength ratio, the optimum yield strength ratio and the optimum second shape coefficient, the optimum yield strength ratio and the corresponding fixed-base superstructure are subjected to MCE and mega earthquakes, where the LRB base-isolated structure shows good seismic performance in terms of the optimum yield strength ratio, even when subjected to mega earthquakes.

TO ASSESS THE STRUCTURAL AND TECHNOLOGICAL CHANGES IN THE PARAMETERS OF THE PRECISION ROTARY SYSTEM ACCORDING TO THE SPECIFIED FUNCTIONS OF SENSITIVITY AND DEVIATION OF THE SPECTRUM OF OWN FREQUENCIES

The question of precision rotary systems with artificial elements of pretension, which significantly affect the rigidity and displacement of resonance frequencies and, as a result, lead to the appearance of very conditioned sensitivity matrices, has been investigated. The mathematical model of the system is identified. With spatial oscillations of the system, two of the most typical and important are defined: fluctuations in vibration force along the rotor axis and in a direction perpendicular to it. Designed diagnostic operator as a complete sensitivity matrix. The proposed algorithm for the diagnosis of parameters of multidimensional mechanical fluctuation systems using computer technology. In any prefabricated design, the parameters of the system during assembly may differ from the design values and change during operation. In order to predict the consequences of this, it is necessary to know the reaction of the system to these changes. At the same time, in many cases, it is almost impossible to assess experimentally the effect of parameters on the behavior of the system. Therefore, there is a need to study and analyze the effect of changes in parameters on the properties of the system analytically, that is, according to the known mathematical model of the system. Analytical study of the dynamics of such systems is a very difficult task, but determining the sensitivity functions for this type of compound experimentally is another much more complex technological task, so their characteristics should be obtained by different methods of identification. The main purpose of this work is to determine: the identified mathematical model of the system, to offer a methodology and algorithm for the diagnosis of parameters of multidimensional mechanical fluctuation systems using computer technology. Of course, the presented algorithm is most suitable for the diagnosis of parameters of multidimensional fluctuation systems, but of course, in this case, widespread use of modern computer technology is necessary. If in the system it is necessary to determine the degree of influence of various physical parameters on the vector of the state, then it is necessary to consider the matrix of relative sensitivity. Sensitivity matrices allow determining sensitive and invariant parameters to the state vector. This information answers the question of which parameters determine the vibrational characteristics of the object to the greatest extent. In addition, the determination of the sensitivity matrix can significantly simplify the dynamic model of the system, leaving only those parameters that most determine the vibrational state of the system. Keywords: construction, press-threaded connection, dynamic parameters, structural model, deformation, deviation, frequency and amplitude of oscillations, sensitivity of dynamic parameters, algorithm, sensitivity matrix, methodology.

Vibration-collision mechanism of dual-stabilizer bottom hole assembly system in vertical wellbore trajectory

The lateral vibration of drill string causes well deviation and the collision between drill collar and sidewall, and severe lateral vibration even affects the drilling safety or reliability. In view of the problems above, the lateral vibration characteristics of drill string need to be analyzed. Therefore, a newly vibration-collision model of BHA (bottom hole assembly) with random collision characteristics is proposed in this paper. Firstly, the dynamic model of drill collar with double stabilizer is presented by utilizing the Lagrange equations. Secondly, the dynamic characteristics of drill collar in air and mud drilling is analyzed with different collision frequencies. Subsequently, the displacement and motion trajectory of drill collar under different structure parameters of BHA and mechanical parameters of system are investigated by numerical simulation. Finally, the influence of rotation speed of BHA and length of drill collar on lateral vibration of drill collar is discussed. The results indicate that the lateral vibration of drill collar in air drilling is more serious than that in mud drilling; and the higher the collision frequency, the more severe the lateral vibration. Improving rotation speed of BHA, length of drill collar and WOB (weight on bit) have promoting influence on lateral vibration of drill collar; however, increasing stabilizer diameter has suppressing influence on lateral vibration of drill collar. The research findings give reasonable guidance for structure design of BHA and selection of mechanical parameters of system.

Failure mechanism and influencing factors of cement sheath integrity under alternating pressure

The failure of cement sheath integrity can be easily caused by alternating pressure during large-scale multistage hydraulic fracturing in shale-gas well. An elastic-plastic mechanical model of casing-cement sheath-formation (CSF) system under alternating pressure is established based on the Mohr-Coulomb criterion and thick-walled cylinder theory, and it has been solved by MATLAB programming combining global optimization algorithm with Global Search. The failure mechanism of cement sheath integrity is investigated, by which it can be seen that the formation of interface debonding is mainly related to the plastic strain accumulation, and there is a risk of interface debonding under alternating pressure, once the cement sheath enters plasticity whether in shallow or deep well sections. The matching relationship between the mechanical parameters (elastic modulus and Poisson's ratio) of cement sheath and its integrity failure under alternating pressure in whole well sections is studied, by which it has been found there is a “critical range” in the Poisson's ratio of cement sheath. When the Poisson's ratio is below the “critical range”, there is a positive correlation between the yield internal pressure of cement sheath (SYP) and its elastic modulus. However, when the Poisson's ratio is above the “critical range”, there is a negative correlation. The elastic modulus of cement sheath is closely related to its Poisson's ratio, and restricts each other. Scientific and reasonable matching between mechanical parameters of cement sheath and CSF system under different working conditions can not only reduce the cost, but also protect the cement sheath integrity.

Optimization Driven Robust Control of Mechanical Systems with Parametric Uncertainties

This paper presents a control algorithm designed to compensate for unknown parameters in mechanical systems, addressing parametric uncertainty in a comprehensive manner. The control optimization process involves two key stages. Firstly, it estimates the narrow uncertainty bounds that satisfy parameter constraints, providing a robust foundation. Subsequently, the algorithm identifies a control strategy that not only ensures uniform boundedness of tracking error but also adheres to drive constraints, effectively minimizing chattering. The proposed control scheme is demonstrated through the modeling of a single rigid body with parameter uncertainties. The algorithm possesses notable strengths such as maximal compensation for parametric uncertainty, chattering reduction, and consideration of control input constraints. However, it is applicable for continuous systems and does not explicitly account for uncertainty in the control input.

Influence of Extruder Plasticizing Systems on the Selected Properties of PLA/Graphite Composite

Abstract Twin-screw extrusion is a crucial method for the direct inserting of carbon micro- and nanomaterials into a polymer matrix using a dry procedure. The study aimed to determine the influence of the parameters of the twin-screw extruder plasticizing system on the dispersion homogeneity and distribution of graphite filler in the polylactide polymer matrix and overall quality of the composite. As a filler, a graphite micropowder with a 5 μm lateral size of platelets was used at concentration of 1 wt.%. Three configurations of screws with different mixing intensity and various types segments were considered in the extrusion experiments. Morphology and chemical structure of the obtained composites were examined using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy – attenuated total reflectance (FTIR-ATR) and Raman spectroscopy. Differential scanning calorimetry (DSC) and melting flow rate measurements (MFR) were used to asses thermal and rheological properties of the composites. Samples of the polylactide/graphite composites were also subjected to mechanical tests. The results show that the selection of the mechanical parameters of twin-screw extruder plasticizing system plays a key role in the preparation of the homogeneous PLA/graphite composites. Incorrect selection of the screw geometry results in poor mixing quality and a significant deterioration of the mechanical and thermal properties of the composites. Optimised mixing and extrusion parameters can be the starting point for the design of efficient twin-screw extruder plasticizing system for fabrication of PLA composites with carbon nanotube and graphene fillers.

A technology of structural mathematical modelling for engineering objects under vibrational loading: Interaction forms and dynamic invariants

We present a system approach to evaluating dynamic forms of interactions between elements of mechanical oscillatory systems, which can be applied as design diagrams of engineering objects used for transport or technology purposes. The approach of structural mathematical modelling was used, where a mechanical oscillatory system (with the finite number of freedom degrees) is compared to the block diagram of a dynamically equivalent automatic control system. The research object was represented by a family of mechanical oscillatory systems with the finite number of freedom degrees under the action of connected force harmonic disturbances. The main research focus was on a set of dynamic states of an engineering object, which are caused by the application of common-phase external force disturbances at various frequencies and characterised by a connection coefficient. For a family of chain mechanical oscillatory systems with two degrees of freedom, a method for interpreting a set of dynamic states in the form of oriented graphs was developed. A method for constructing a population graph of dynamic states based on the frequency response of system transfer functions was developed. Within the framework of the developed interpretation, the graphs of dynamic states can be considered as peculiar invariants that persist on sets of mechanical oscillatory system parameters. Using the methodology of structural mathematical modelling, a concept of dynamic invariants was developed, according to which the totality of dynamic invariants can be used to provide a general evaluation of the variety of dynamic states and forms of dynamic interactions between the elements of mechanical oscillatory systems. The proposed concept of dynamic invariants extends the methodology of structural mathematical modelling in relation to the problems of system analysis for ensuring the safety of engineering objects for transport and technology purposes under the conditions of connected vibrational loading.

On the mean square displacement of intruders in freely cooling granular gases

We compute the mean square displacement (MSD) of intruders immersed in a freely cooling granular gas made up of smooth inelastic hard spheres. In general, intruders and particles of the granular gas are assumed to have different mechanical properties, implying that non-equipartition of energy must be accounted for in the computation of the diffusion coefficient D. In the hydrodynamic regime, the time decay of the granular temperature T of the cooling granular gas is known to be dictated by Haff’s law; the corresponding decay of the intruder’s collision frequency entails a time decrease of the diffusion coefficient D. Explicit knowledge of this time dependence allows us to determine the MSD by integrating the corresponding diffusion equation. As in previous studies of self-diffusion (intruders mechanically equivalent to gas particles) and the Brownian limit (intruder’s mass much larger than the grain’s mass), we find a logarithmic time dependence of the MSD as a consequence of Haff’s law. This dependence extends well beyond the two aforementioned cases, as it holds in all spatial dimensions for arbitrary values of the mechanical parameters of the system (masses and diameters of intruders and grains, as well as their coefficients of normal restitution). Our result for self-diffusion in a three-dimensional granular gas agrees qualitatively, but not quantitatively, with that recently obtained by Blumenfeld [arXiv: 2111.06260] in the framework of a random walk model. Beyond the logarithmic time growth, we find that the MSD depends on the mechanical system parameters in a highly complex way. We carry out a comprehensive analysis from which interesting features emerge, such a non-monotonic dependence of the MSD on the coefficients of normal restitution and on the intruder-grain mass ratio. To explain the observed behaviour, we analyze in detail the intruder’s random walk, consisting of ballistic displacements interrupted by anisotropic deflections caused by the collisions with the hard spheres. We also show that the MSD can be thought of as arising from an equivalent random walk with isotropic, uncorrelated steps. Finally, we derive some results for the MSD of an intruder inmersed in a driven granular gas and compare them with those obtained for the freely cooling case. In general, we find significant quantitative differences in the dependence of the scaled diffusion coefficient on the coefficient of normal restitution for the grain-grain collisions.Graphic abstract

Further development in modeling fatigue failure in metals with a multi-spring non-linear mechanical system

This paper presents further development of a spring mechanical system, proposed by Guranlick et al, in (1) deriving equations for the determination of the mechanical system parameters in terms of material properties; (2) developing applications for deriving fatigue life relations with consideration for the ratio of the minimum to maximum stress; and (3) extending the model to incorporate the hysteresis behavior of steel under cycling loading. These applications are demonstrated in this paper with numerical illustrations.

The Influence of Nesfatin-1 on Bone Metabolism Markers Concentration, Densitometric, Tomographic and Mechanical Parameters of Skeletal System of Rats in the Conditions of Established Osteopenia.

Simple SummaryNesfatin-1 is an adipokine with little known effect on the skeletal system. In this study, we examined the effect of 8-wk administration of nesfatin-1 on densitometric, tomographic, and mechanical parameters of bones, as well as the concentration of bone metabolism markers in rats with experimentally induced established osteopenia.Our study aimed to evaluate the impact of nesfatin-1 administration on bone metabolism and properties in established osteopenia in ovariectomized female rats. In total, 21 female Wistar rats were assigned to two groups: sham-operated (SHAM, n = 7) and ovariectomized (OVA, n = 14). After 12 weeks of osteopenia induction in the OVA females, the animals were given i.p. physiological saline (OVA, n = 7) or 2 µg/kg body weight of nesfatin-1(NES, n = 7) for the next 8 weeks. The SHAM animals received physiological saline at the same time. Final body weight, total bone mineral density and content of the skeleton were estimated. Then, isolated femora and tibias were subjected to densitometric, tomographic, and mechanical tests. Bone metabolism markers, i.e., osteocalcin, bone specific alkaline phosphatase (bALP), and crosslinked N-terminal telopeptide of type I collagen (NTx) were determined in serum using an ELISA kit. Ovariectomy led to negative changes in bone metabolism associated with increased resorption, thus diminishing the densitometric, tomographic, and mechanical parameters. In turn, the administration of nesfatin-1 led to an increase in the value of the majority of the tested parameters of bones. The lowest bALP concentration and the highest NTx concentration were found in the OVA females. The bALP concentration was significantly higher after nesfatin-1 administration in comparison to the OVA rats. In conclusion, the results indicate that nesfatin-1 treatment limits bone loss, preserves bone architecture, and increases bone strength in condition of established osteopenia.

Experimental Investigation on the Kinematics of an Underactuated Mechanical Finger through Vision-Based Technology

Marker-less vision techniques represent a promising route in the development of experimental methods to study the kinematic and the dynamic parameters of mechanical systems. The knowledge of a great number of these parameters is a fundamental issue in the system behaviour analysis and represents an even more crucial aspect for underactuated mechanical systems. In this paper, a technique is proposed to identify the kinematics of the phalanges of an underactuated mechanical finger, starting from the acquisition of the finger point cloud data by means of contactless vision system devices. The analytical model identified allows to determine the underactuated finger configuration as function of the shaft rotation of the single motor of the mechanical system.

Mathematical modeling in problems about dynamics and stability of elastic elements of wing profiles

The mathematical models describing the dynamics of elastic elements of wing structures and representing the initial-boundary value problems for systems of partial differential equations are proposed. The dynamics and stability of elastic elements of wings, flown around by a gas or liquid stream in a model of an incompressible medium, are investigated. To study the dynamics of elastic elements and a gas-liquid medium, both linear and nonlinear models of the mechanics of a solid deformable body and linear models of the mechanics of liquid and gas are used. On the basis of the constructed functionals for partial differential equations, the sufficient stability conditions are obtained in analytical form. The conditions impose restrictions on the parameters of mechanical systems. The obtained stability conditions are necessary for solving the problems of controlling the parameters of the aeroelastic system. On the basis of the Galerkin method, a numerical study of the dynamics of elastic elements was carried out, the reliability of which is confirmed by the obtained analytical results.

Applications of building information modeling software to HVAC noise prediction

This paper presents a methodology and workflow for utilizing Building Information Modeling (BIM) software to expedite the calculation of duct borne noise according to Chapter 49 of the ASHRAE Handbook – HVAC Applications. Using Dynamo script for Autodesk Revit, relevant building mechanical system parameters are extracted to perform noise calculations with reduced manual input. Resulting predictions for receiver sound pressure levels are compared to other software tools available in the industry. Advantages and limitations of this approach are weighed to assess the utility of Building Information Models in the context of the noise prediction workflow. The results of this effort support the development of more robust duct noise prediction tools that are not only more accurate but also more user-friendly.

Study of dynamics of main drive of pilger pipe cold rolling mill

Elimination of nonstable deformed state of main drive systems of Pilger pipe cold rolling (PCR) mills with distributed parameters is often stipulated by dynamics stabilization of multi-mass in-line mechanical system. Increase of productivity and optimal conditions of PCR mills loading is reached by dynamic synthesis of base mechanisms. Results of study of force line dynamics of PCR mill with embedded doubled elastic clutch or torsion damper presented. A nonlinear dynamic model of the main force line of a PCR mill with compensating doubled elastic clutch created. A solution of the dynamic synthesis of PCR mill force line task was obtained by nonlinear programming application. To decrease dynamic loads level, an optimal synthesis of the damper system of PCR mill force line was accomplished. A methodology of synthesis of parameters of nonlinear mechanical system with elastic clutch and damper proposed, as a mean to decrease destructive torsion oscillations in the main force line of PCR mill. Harmonic linearization of integral equations of mill main force line motion carried out, recorded by pulse-frequency characteristics. It was established that since the number of equations equals to the number of nonlinear effects of the mechanical system, the task solutions practically does not depend on the degree of freedom of the selected model. It was shown that the results obtained were adequate to the results of experimental studies of mill ХПТ 32 force line.

Stochastic dynamic model updating of aerospace thermal structure with a hierarchical framework

Most physical properties and boundary conditions of complex aerospace mechanical systems are temperature dependent. Hence, the test data are exposed to uncertainty in high surface temperature or large temperature gradient environments. However, existing deterministic model updating methods are not applicable under complicated multi-physics fields. Hence, dynamic model updating under a thermal environment from the stochastic perspective is vital. In this study, a dynamic model updating approach that considers thermal effects and uncertainties by using a hierarchical strategy is proposed, and a method for adjusting design parameter means and their covariance matrix from experimental data is demonstrated, which is based on a surrogate model. In contrast to the previous method, an inverse uncertainty propagation of mechanical system parameters under multiple physical fields with probability distributions is conducted, and the thermal parameters and mechanical characteristics to be identified are regarded as temperature dependent. Numerical simulations are used to demonstrate the stochastic model updating procedure, and their associated response prediction variabilities are explored using a fuselage skin structure.

Eigenwaves propagation in three-layer cylindrical viscoelastic shells with a filler non-uniform in thickness

The paper provides the statement of the problem, the development of a calculation method and an algorithm to solve the problems of propagation and absorption of non-axisymmetric natural waves in layered dissipative-inhomogeneous viscoelastic three-layer cylindrical bodies. A detailed analysis of well-known publications devoted to this problem is given. The paper posed the problem of non-axisymmetric natural wave propagation in three-layer cylindrical shells with fillers, taking into account the theory of hereditary viscoelasticity. Dispersion equations were obtained and the dependence of the phase velocity on the wavenumber for the three-layer shells was constructed. A calculation method was developed based on the Muller, Gauss, and orthogonal sweep methods. The program (in C++ language) was compiled based on the developed algorithm. Numerical results were obtained for the complex phase velocity depending on various wavenumbers and parameters of an axisymmetric cylindrical mechanical system for the Kirchhoff-Love and Timoshenko hypotheses. The change in the real and imaginary parts of the complex phase velocity under various parameters of the system was investigated for structurally homogeneous and inhomogeneous mechanical systems. The results obtained by the Kirchhoff-Love and Timoshenko hypotheses are in good agreement but differ in the wave absorbing abilities. It was found that a decrease in filler thickness at a rigid inner shell leads to a rapid increase in the real and imaginary parts of the vibration frequencies.