Theoretical and Applied Mechanics Research Papers (original) (raw)

It has been shown that developing a supercavitating flow around underwater projectiles has a significant effect on their drag reduction. As such, it has been a subject of growing attention in the recent decades. In this paper, a numerical and experimental study of supercavitating flows around axisymmetric cavitators is presented. The experiments are conducted in a semi-open loop water tunnel. According to the Reynolds-Averaged Navier-Stokes equations and mass transfer model, a three-component cavitation model is proposed to simulate the cavitating flow. The corresponding governing equations are solved using the finite element method and the mixture Rayleigh-Plesset model. The main objective of this research is to study the effects of some important parameters of these flows such as the cavitation number, Reynolds number and conic angle of the cavitators on the drag coefficient as well as the dimensions of cavities developed around the submerged bodies. A comparison of the numerical and experimental results shows that the numerical method is able to predict accurately the shape parameters of the natural cavitation phenomena such as cavity length, cavity diameter and cavity shape. The results also indicate that the cavitation number declines from 0.32 to 0.25 leading to a 28 percent decrease in the drag coefficient for a 30 • cone cavitator. By increasing the Reynolds number, the cavity length is extended up to 322% for a 60 • cone cavitator.

- by
- •
- Theoretical and Applied Mechanics

The main aim of the paper is to present the procedure allowing one to determine correct mechanical characteristics of a rubber material compressed within a wide range of strain rates. In order to obtain a satisfactory wide spectrum of material data, a number of tests were conducted both under low and high strain rates with the use of a universal strength machine and split Hopkinson pressure bar setup equipped with polymethyl methacrylate and 7075-T6 alloy bars. During the investigations, the necessity of performing pre-compression tests and the problem of specimen geometry were pointed out as key methodical requirements to guarantee achieving valid experimental data both from quasi-static and high strain rate tests.

- by Jacek Janiszewski
- •
- Theoretical and Applied Mechanics

We present the numerical study of unsteady hydromagnetic (MHD) flow and heat transfer characteristics of a viscous incompressible electrically conducting water-based nanofluid (containing Al 2 O 3 nanoparticles) between two orthogonally moving porous coaxial disks with suction. Different from the classical shooting methodology, we employ a combination of a direct and an iterative method (SOR with optimal relaxation parameter) for solving the sparse systems of linear algebraic equations arising from the FD discretization of the linearized self similar nonlinear ODEs. Effects of the governing parameters on the flow and heat transfer are discussed and presented through tables and graphs. The findings of the present investigation may be beneficial for electronic industry in maintaining the electronic components under effective and safe operational conditions.

- by Kashif Ali
- •
- Theoretical and Applied Mechanics

The prediction of temperature distributions in the tool-chip-workpiece interface is not obvious with the complexity of the induced phenomena. For this purpose, we developed a thermal model in orthogonal metal cutting based on the thermal model of Komanduri and Hou that determines temperature distributions in the tool-chip-workpiece separately, each in its own axes system. The overall distribution is obtained by assembling three temperature distributions at the tool-chip-workpiece interface. Our developed model returns global temperature distributions in the real time throughout the tool-chip-workpiece in the same coordinate system. Our simulation results compared to the original maps showed a perfect correspondence, unlike the computation time and computation steps.

- by Mustapha Belarbi and +1
- •
- Theoretical and Applied Mechanics
- by Mohamed MOKHTARI
- •
- Theoretical and Applied Mechanics

Lorenzo Sanavia Dipartimento di Costruzioni e Trasporti, Universit`a degli Studi di Padova, Via Marzolo 9, 35-131 Padova, Italy, e-mail: lorenzo.sanavia@unipd.it Bertrand François Soil Mechanics Laboratory, Ecole Polytechnique Fédérale... more

- by Lorenzo Sanavia
- •
- Theoretical and Applied Mechanics, Theoretical

This article presents a design process of a single-wheel robot which consists of building a theoretical model, designing a mechanical structure, simulating the design, building a prototype and testing it. It describes the control strategy for this vehicle, developed during the simulation process, and how it works for a ready built prototype. It mainly focuses on the self-stabilisation problem encountered in the single-wheel structure and shows the test rig results for this case. The design of the robot is under patent protection.

- by Tadeusz Uhl
- •
- Theoretical and Applied Mechanics

This work proposes an optimization methodology for the identification of vehicle multibody models for crashworthiness analysis based on the use of plastic hinge approach. The multiple objective functions for the optimal problem are built as the deviation of the model behavior from the required crash responses. The design variables of the problem are the plastic hinge constitutive relations. The constraints are set not only as technological side constraints but also as some of the deviation functions of selected crash responses that would, otherwise, be used as objective functions. The vehicle model identification methodology is demonstrated by its application to the construction of virtual vehicle models, designated as the generic car model, for which the reference is available as a detailed finite element model.

- by Jorge Ambrosio
- •
- Optimization, Theoretical and Applied Mechanics

A computer programhas been developed for design of surface drip irrigation system. It could be applied for calculation of small scale fields with an area up to 10 ha. The program includes two main parts: crop water requirements and hydraulic calculations of the system. It has been developed in Graphical User Interface in MATLAB and gives opportunity for selecting some parameters from tables such as: agro- physical soil properties, characteristics of the corresponding crop, climatic data. It allows the user of the program to assume and set a definite value, for example the emitter discharge, plot parameters and etc. Eight cases of system layout according to the water source layout and the number of plots of the system operation are laid into hydraulic section of the program. It includes the design of lateral, manifold, main line and pump calculations. The program has been compiled to work in Windows.

The paper presents the problem of modelling and simulation of transients during turbulent fluid flow in hydraulic pipes. The instantaneous wall shear stress on a pipe wall is presented in the form of integral convolution of a weighting function and local acceleration of the liquid. This weighting function depends on the dimensionless time and Reynolds number. Its original, very complicated mathematical structure is approximated to a simpler form which is useful for practical engineering calculations. The paper presents an efficient way to solve the integral convolution based on the method given by Trikha for laminar flow. An application of an improved method with the use of the Method of Characteristic for the case of unsteady flow (water hammer) is presented. This method is characterised by high efficiency compared to traditional numerical schemes. Notation c 0 [ms −1 ] -acoustic wave speed p [kg m −1 s −2 ] -pressure s [s −1 ] -Laplace operator t [s] -time v [ms −1 ] -instantaneous mean flow velocity t = νt/R 2 [-] -dimensionless time 136 Z. Zarzycki et al. v [ms −1 ] -average value of velocity in cross-section of pipe v z [ms −1 ] -axial velocity w [-] -weighting function z [m] -distance along pipe axis L [m] -pipe length R [m] -radius of pipe Re = 2Rv/ν [-] -Reynolds number µ [kg m −1 s −1 ] -dynamic viscosity ν [m 2 s −1 ] -kinematic viscosity λ [-] -Darcy-Weisbach friction coefficient ρ 0 [kg m −3 ] -fluid density (constant) τ w , τ wq , τ wu [kg m −1 s −2 ] -wall shear stress, wall shear stress for quasi-steady flow, unsteady wall shear stress, respectively Ω = ωR 2 /ν [-] -dimensionless frequency

- by Kamil Urbanowicz
- •
- Theoretical and Applied Mechanics

Subsonic general configuration aircrafts' unsteady longitudinal aerodynamic stability derivatives can be estimated using finite element methodology based on the Doublet Lattice Method (DLM), the Slender Body Theory (SBT) and the Method of Images (MI). Applying this methodology, software DERIV is developed. The obtained results from DERIV are compared to NASTRAN examples HA21A and HA75H. A good agreement is achieved.

- by Nikola Maricic
- •
- Civil Engineering, Mathematics, Applied Mathematics, Software Development

The three dimensional (3D) flight of a golf ball at taking into account the Magnus effect is studied in the paper. For this purpose it is composed a system of six nonlinear differential equations. To determine the 3D orientation of the ball the rotations around all three axes are given by the so-called Cardan angles instead of classical Euler ones. The high nonlinear system differential equations are solved numerically by a special program created in the MatLab-Simulink environment. It is founded the laws of motion, velocities and accelerations on all six coordinates, as well as the projections of trajectory on the three coordinate planes. The presented analytical base and numerical results in the paper increasing and expanding the knowledge in the theory of general motion of spherical solid and leads to new more extensive research in this complicated area.

In this review, recent advances on the measurement and modeling of elastic properties of cortical and trabecular bone are presented. Bone is a multifunctional material which among its other functions serves as a support for other tissues in the body. As a structural material it is stiff, strong, tough, lightweight and is adaptable. Its excellent mechanical properties are due to its complex, composite and hierarchical structure. In this paper, we outline the experimental approaches that have been used to characterize bone's structure, composition and elastic properties at several different length scales. Then, we discuss different modeling approaches that have been employed to compute bone's elastic moduli. We conclude by discussing the challenges and open issues in this area. Analysis of bone is of importance in orthopedics. Also, gained knowledge on bone can be used by engineers to design new bioinspired composite materials for a wide range of engineering applications.

Empirical relationships are developed for estimating the undrained critical shear strength based on experimental triaxial tests under monotonic loadings. The effect of fines content on the undrained shear strength is analyzed for different combinations of density states. The parametric study indicates that in terms of the soil void ratio and fines content properties, the undrained critical shear strength may increase, or decrease as the amount of fines content increases, consequently showing vulnerability to liquefaction influenced by the fines content percentage. A series of monotonic undrained triaxial tests have been undertaken on a reconstituted saturated sand-silt mixtures specimen. Beyond 30% of fines content, it is shown that a fraction of silt participates in the soil skeleton chain force. In this context, the concept of the equivalent intergranular void ratio may be an appropriate parameter to express the critical shear strength of the soil under investigation. This parameter is able to control the undrained shear strength of non plastic silt and sand mixtures for different density states.

- by Karim Bendani
- •
- Theoretical and Applied Mechanics

Thermal instability in a horizontal layer of Couple-stress nanofluid in a porous medium is investigated. Darcy model is used for porous medium. The model used for nanofluid incorporates the effect of Brownian diffusion and thermophoresis. The flux of volume fraction of nanoparticle is taken to be zero on the isothermal boundaries. Normal mode analysis and perturbation method is employed to solve the eigenvalue problem with the Rayleigh number as eigenvalue. Oscillatory convection cannot occur for the problem. The effects of Couple-stress parameter, Lewis number, modified diffusivity ratio, concentration Rayleigh number and porosity on stationary convection are shown both analytically and graphically.

- by G. C. Rana
- •
- Theoretical and Applied Mechanics

The aim of this paper is to present the design of device for control of new propulsion system with pneumatic artificial muscles. The propulsion system can be used for ankle joint articulation, for assisting and rehabilitation in cases of... more

- by Ivanka Veneva
- •
- Theoretical and Applied Mechanics

Capture of the discrete nature of crystalline solids for the purpose of the determination of their mechanical behavior with high precision is of interest. To achieve this objective, two fundamental contributing factors are on top of the list: (1) formulation in the mathematical framework of an appropriate higher order continuum theory rather than using classical treatment, and (2) incorporation of the true anisotropy of the media. The present work revisits Toupin-Mindlin first strain gradient theory for media with general anisotropy, and then specialize it to cubic crystals of hexoctahedral class. This formulation in addition to 3 classical material constants encountered in classical theory of elasticity, gives rise to 11 additional material parameters

- by Farzaneh Ojaghnezhad
- •
- Surface Science, Fracture Mechanics, Nanomechanics, Micromechanics

In this paper, an effective semi-analytical method is presented for torsion analysis of structural beams with various kinds of junctions such as T, I, H, E and + beams. A fairly simple but precise formulation based on analytical and accurate numerical solutions is presented for evaluating the shearing stress at critical points and computing the torsional rigidity of a member under torsion. The problem is formulated based on Prandtl's stress function. The cross-section is decomposed into several segments, including straight, curved, end, and junction segments. The torsion problem is solved in each segment separately. Standard junction segments are analyzed using the finite element method with a fine mesh. Other segments are analyzed by analytical methods. Closed-form expressions in terms of geometrical parameters are found for the shearing stresses at critical points of each segment. The torsional rigidity of the cross section is also expressed by a closed-form expression. The presented formulations can be used for analysis of a wide range of thin-to moderately thick-walled complicated sections.

- by Mohammad Hematiyan
- •
- Theoretical and Applied Mechanics, Torsion

Continuation of the first part of the paper focuses on implementation issues, computational efficiency and presentation of test calculations. Sample results have been obtained for a viscous flow past a spherical body immersed in an uniform stream. The solution algorithm for the external Neumann boundary problem, the construction of the vortex particles near the material boundary and the evaluation of the stretching effect are described in some details. The problem of design of efficient algorithms for induced velocity computation is discussed briefly. The presented results include patterns of instantaneous velocity and vorticity field as well as selected streamlines showing the complexity of flow near the aft part of the body and inside the aerodynamic wake.

- by Jacek Szumbarski
- •
- Theoretical and Applied Mechanics

The paper reports on current developments in gearbox dynamic modelling. It refers to Müller's one-mass two-parameter (stiffness and damping) gearbox model with rectilinear vibration. The paper shows that there is a need to develop a new model, which would incorporate torsional vibration. The paper refers to the previous papers on gearbox dynamic modelling published by the author in journals and conference proceedings. In the present paper, the influence of the clutch damping coefficient and one random parameter value from the three-parameter error mode, and that of the interaction between error parameters on the vibration generated by a gearbox system, is analyzed.

The paper presents selected aspects of the strength analysis of the selfpropelled tunnelling machine boom. The principles of creating calculation models for numerical simulations with use of the ﬁnite element method are given. The study also presents two ways of conducting numerical calculations in both the static and dynamic range. A detailed example of numerical FEM tests of the telescopic boom is provided.

- by Damian Derlukiewicz
- •
- Theoretical and Applied Mechanics

The flow and heat transfer of Casson fluid from a permeable isothermal sphere in the presence of slip condition in a non-Darcy porous medium is analyzed. The sphere surface is maintained at a constant temperature. The boundary layer conservation equations, which are parabolic in nature, are normalized into non-similar form and then solved numerically with the well-tested, efficient, implicit, stable Keller-box finite-difference scheme. Increasing the velocity slip parameter is found to decrease the velocity and boundary layer thickness and increases the temperature and the boundary layer thickness. The velocity decreases with the increase the non-Darcy parameter and is found to increase the temperature. The velocity increases with the increase the Casson fluid parameter and is found to decrease the temperature. The Skin-friction coefficient and the local Nusselt number is found to decrease with the increase in velocity and thermal slip parameters respectively.

- by B. Vasu and +1
- •
- Chemical Engineering, Civil Engineering, Applied Mathematics, Heat Transfer

The paper presents an inverse kinematic model for a centrifuge motion simulator used to verify newly defined absolute acceleration profiles. The modelling is concerned with a human training centrifuge with three degrees of freedom. The values of kinematic parameters have been obtained for this three-jointed manipulator. Validation of the developed model has been performed by comparing the results obtained from the centrifuge motion simulator with the results of numerical simulations. The simulation revealed that the inverse kinematic model enabled calculation of the angular displacement, velocity and acceleration of the links that are needed for the given linear acceleration of the simulator cabin.

A numerical study of an axisymmetric steady laminar incompressible flow of an electrically conducting micropolar fluid over a stretchable disk is carried out when the fluid is subjected to an external transverse magnetic field. The governing nonlinear equations of motion are transformed into a dimensionless form through Von Karman's logic similarity functions. An algorithm based on a finite difference scheme is used to solve the reduced coupled nonlinear ordinary differential equations with the associated boundary conditions. Effects of the micropolar parameters, the magnetic parameter and the Prandtl number on the flow velocity and temperature distribution are discussed. Investigations predict that the heat transfer rate at the surface of the disk increases with an increase in the values of micropolar parameters. The magnetic field enhances the shear and couple stresses. The shear stress factor is lower for micropolar fluids as compared to Newtonian fluids, which may be beneficial in flow and heat control of polymeric processing.

- by Muhammad Ashraf
- •
- Heat Transfer, Theoretical and Applied Mechanics

In this paper the effect of rapid movement of a heat source inside a two-dimensional infinite body is investigated. Non Fourier heat transfer model is employed and the governing equation is solved using finite difference method. The effect of thermal Mach number on temperature distribution is discussed and the results are compared with analytical results reported in references.

The paper contains a proposal of a new model for the stress-life curve. The new model reflects the nature of the stress curve occurring under current conditions, which means its shape of an inclined letter S. It can be used for both low and high cycle fatigue. Verification of the proposed model was performed on experimental results of ten various materials from three main types that are low-alloy, high-alloy and non-alloy steels.

- by Marta Kurek
- •
- Theoretical and Applied Mechanics

- by Dr. D. Subba Rao
- •
- Chemical Engineering, Civil Engineering, Applied Mathematics, Heat Transfer

The paper presents selected aspects of the strength analysis of the self-propelled tunnelling machine boom. The principles of creating calculation models for numerical simulations with use of the finite element method are given. The study also presents two ways of conducting numerical calculations in both the static and dynamic range. A detailed example of numerical FEM tests of the telescopic boom is provided.

- by Jacek Karliński
- •
- Engineering, Theoretical and Applied Mechanics
- by Marta Kurek
- •
- Theoretical and Applied Mechanics

Recent investigations show that active noise control methods can improve noise reduction capabilities of aircraft-type windows in the low-frequency region. Being a privileged path for external noise transmission and one of the main causes of high interior noise levels in a treated aircraft, a proper design of the aircraft window can significantly contribute to the reduction of cabin noise levels with a minimum impact on the aircraft mass and performances. This is the first part of two companion papers. In this paper (Part 1), the vibro-acoustic design of a triple-pane aircraft-type window prototype is presented. Numerical and experimental activities addressing the structural dynamics and the actuation performances are described in detail. The effectiveness of the piezo-stack actuators in the excitation of the flexural bending modes of the structure by means of adaptive in-plane and eccentric dynamic forces is experimentally investigated. An experimental modal analysis is carried out to determine both single partition and coupled fluid-structure modal frequencies used to validate the finite element model. For the purpose of estimating the sound radiation characteristics of the window prototype, a numerical procedure coupling boundary and finite element methods will be detailed in the second part of this paper (Part 2) to solve the coupled acoustic-structure problem in the exterior acoustic domain.

- by Andrea Vigliotti and +1
- •
- Theoretical and Applied Mechanics, Theoretical

The mechanical behavior of soils has been traditionally described using continuum-mechanics-based models. These are empirical relations based on laboratory tests of soil specimens. The investigation of the soils at the grain scale using discrete element models has become possible in recent years. These models have provided valuable understanding of many micromechanical aspects of soil deformation. The aim of this work is to draw together these two approaches in the investigation of the plastic deformation of non-cohesive soils. A simple discrete element model has been used to evaluate the effect of anisotropy, force chains, and sliding contacts on different aspects of soil plasticity: dilatancy, shear bands, ratcheting, etc. The discussion of these aspects raises important questions such as the width of shear bands, the origin of the stress-dilatancy relation, and the existence of a purely elastic regime in the deformation of granular materials.

- by Hans Muhlhaus
- •
- Civil Engineering, Applied Mathematics, Continuum Mechanics, Shear bands

This survey is concerned oneself with the study of those types of material networks which can be met both in civil engineering and also in electrotechnics, in mechanics, or in hydrotechnics, and of which behavior lead to linear problems, solvable by means of Finite Element Method and adequate algorithms. Here, it is presented a unitary theory of networks met in the domains mentioned above and this one is illustrated with examples for the structural networks in civil engineering, electric circuits, and water supply networks, but also planar or spatial mechanisms can be comprised in this theory. The attention is focused to make evident the essential properties and concepts in the network analysis, which differentiate the networks under force from other types of material networks. To such a network a planar, connected, and directed or undirected graph is associated, and with some vector fields on the vertex set this graph is endowed.

Strength and durability of thin-walled structures are usually calculated with the use of computer simulations. To perform such simulations using Finite Element Method, characteristics of a material subjected to monotonic tension or compression and tension-compression cyclic loading are necessary. Experimental determination of such kind of characteristics is usually performed on specimens cut out from a metal or composite thin sheet. Problems associated with testing on flat specimens under large deformation are discussed in this paper. A new design of fixture proposed by the authors for this kind of testing is shortly described. The results of investigations carried out on brass using the new fixture for flat specimens testing are also presented.

- by G. Socha
- •
- Theoretical and Applied Mechanics

An objective of this paper is to reconcile the "symmetry" approach with the "symmetry groups" approach as these two different points of view presently coexist in the literature. Here we will be concerned exclusively with linearly elastic materials. The starting point for an analysis of the inherent symmetry of elastic materials is the notion of a symmetry transformation. Particularly, we paid attention to the compliance tensor for cubic and hexagonal crystals.

- by jovo jaric
- •
- Civil Engineering, Applied Mathematics, Theoretical and Applied Mechanics

In this manuscript, we discuss the influence of surface and interface stress on the elastic field of a nanoparticle, embedded in a finite spherical substrate. We consider an axially symmetric traction field acting along the outer boundary of the substrate and a non-shear uniform eigenstrain field inside the particle. As a result of axial symmetry, two Papkovitch-Neuber displacement potential functions are sufficient to represent the elastic solution. The surface and interface stress effects are fully represented utilizing Gurtin and Murdoch's theory of surface and interface elasticity. These effects modify the traction-continuity boundary conditions associated with the classical continuum elasticity theory. A complete methodology is presented resulting in the solution of the elastostatic Navier's equations. In contrast to the classical solution, the modified version introduces additional dependencies on the size of the nanoparticles as well as the surface and interface material properties.

- by Demitris Kouris
- •
- Civil Engineering, Applied Mathematics, Nanoparticles, Micromechanics

The requirement of mitigating the environmental impact of helicopters has been addressed globally within the FRIENDCOPTER Project in the sen-se that several aspects (such as noise abatement, vibration reduction, fuel consumption) have been studied in parallel with different approaches among which there is the active blade control. In the work at hand, attention is paid on two topics aimed at mitigating helicopter environmental impact through a morphing strategy: the aerodynamic optimization of a blade section who-se camber can be affected by an actuator and the design of a SMA based static twist concept, aimed at extending the helicopter flight envelope. The latter device is based on a SMA rod which is integrated in the spanwise di-rection within the blade structure at different positions. The actuator, when heated, transmits a torque couple which induces twist onto the blade. The twist variation due to the SMA device activation has been predicted by a FE approach (MSC/Marc software...

- by Antonio Pagano
- •
- Theoretical and Applied Mechanics, Morphing, Sma

This work investigates the vibrational response of thermoelastic nanobeam resonators induced by ramp-type heating and subjected to exponential decaying time varying load via Euler-Bernoulli beam theory. Governing equations are derived in the context of nonlocal generalized thermoelasticity theory with dual phase lags. The nonlocal nanobeam theory incorporates a nonlocal parameter to capture the small scale effect. Using the Laplace transform technique, an analytical solution has been attained. and inversions of the transformed solutions have been carried out by means of calculus of residues. The effects of nonlocal, point load and ramping-time parameters on all studied fields of the nanobeam are investigated and discussed.

The article presents a two-temperature theory to study the thermally insulated stress-free surface of a thermoelastic solid half-space due to an inclined load. The inclined load is a linear combination of a normal load and a tangential load. The normal mode analysis has been employed to solve the present problem. Variations of conductive and thermodynamic temperatures, displacements, and stresses distributions with the horizontal distance have been presented graphically. Some comparisons have been made to estimate the effects due to the two-temperature parameter and the inclination angle on the field quantities. Results of earlier works have been deduced from the present investigation as special cases.

This paper presents a nonlinear robust control design procedure for a micro air vehicle, which uses the singular value (µ) and µ-synthesis technique. The optimal robust control law that combines parametric and lumped uncertainties of the micro UAV (unmanned aerial vehicle) which are realized by serial connection of the Kestrel autopilot and the Gumstix microprocessor. Thus, the robust control feedback loops, which handle the uncertainty of aerodynamics derivatives, are used to ensure the robust stability of the UAV local dynamics in longitudinal and lateral control directions.

- by Arkadiusz Mystkowski
- •
- Theoretical and Applied Mechanics

An approximate analytical model is developed for the evaluation of the interfacial shear and peeling stresses in a bi-material element composed of two elastic plates bonded together by an interface zero thickness material and subjected to monotonically increasing thermal loading. Thermal peeling stress is caused by thermal and elastic mismatch of a two-plate structure undergo a temperature change. The "peeling" stress can be determined from the evaluated interfacial shear stress and is proportional to deflections of the thinner plate of the structure, i.e. to its displacements with respect to the thicker plate. The interface is assumed to exhibit brittle failure at the critical shear stress value. The analytical solution qualitatively shows delamination and ultimate failure. The results are illustrated in figures and discussed.

- by Jordanka Ivanova
- •
- Theoretical and Applied Mechanics, Delamination

The paper presents a methodology of the multiscale bone modeling in which the task of identification of material parameters plays the crucial role. A two-scale analysis of the bone is considered and the problem of identification, formulated as an inverse problem, is examined as an important stage of the modelling process. The human femur bone, built form cancellous and cortical bone, is taken as an example of an osseous tissue, and the computational multiscale approach is considered. The methodology presented in the paper allows one to analyze the two-scale model with the use of computational homogenization. The representative volume element (RVE) is created for the microstructure of the basis of micro-CT scans. The macro and micro model analyses are performed by using the finite element method. The identification of trabeculae material parameters on the micro-level is considered as the minimization problem which is solved using evolutionary computing.

The paper deals with the dynamic phenomena accompanying the wheel rolling over a road (rail, track), with lateral slip effects. They occur in rolling of a wheel and wheelset on a straight track in the case of lateral load and especially on curves. Different curvature radii and rotary oscillations of wheelsets result in skew rolling and, in turn, in lateral slip oscillation in the contact zone between the wheel and rail. It significantly increases noise and wear in real structures. Double periodicity of motion was detected in an underground train. Hitherto, this phenomenon has not been reported in the literature. Experimental investigation was performed on a test stand for various parameters: the angle of skew rolling, velocity and contact pressure. Results were related to a two degree-of-freedom theoretical system. In the case of steel/polyester and polyamide/polyester friction pair, qualitatively similar results were obtained.

Normally, during one-dimensional pipe flow, the friction terms are calculated with the use of a numerical method (for example MOC -method of characteristics) at every computational node along the pipe and at every time step. This procedure tends to increase the computational effort greatly. A considerable increase in computational speed can be archived by calculating the frequency-dependent friction at the end of the pipe only. To avoid possible problems (no damping at closed walls, underestimate damping on high impedance components) the frequency-dependent friction term is calculated from the flow waves. The lumping friction model in this work is based on a modificated Schohl convolution integral solution. In addition, the work examined the impact of using of simplified effective weighting function on the obtained results of numerical simulations. The modified method in conjunction with the use of simplified weighting function allow determination of real-time estimate of the basic parameters representing the fluid flow in complex hydraulic systems, water supply, etc.

- by Kamil Urbanowicz
- •
- Theoretical and Applied Mechanics

Loading conditions and complex geometry have led cylinder heads to become the most challenging parts of diesel engines. One of the most important durability problems in diesel engines is due to cracks in the valves bridge area. The purpose of this study is thermo-mechanical analysis of cylinder heads of diesel engines using a two-layer viscoplasticity model. The results of the thermo-mechanical analysis indicate that the maximum temperature and stress occurr in the valves bridge. The results of the finite element analysis correspond with the experimental tests carried out by researchers, and illustrate cracks in cylinder heads in this region. The results of the thermo-mechanical analysis show that when the engine is running, the stress in the region is compressive, caused by thermal loading and combustion pressure. When the engine is shut off, the compressive stress turns into tensile stress because of assembly loads. The valves bridge is under cyclic tensile and compressive stress state and thus is subject to low cycle fatigue. After several cycles fatigue cracks will appear in this region. The lifetime of this part can be determined through finite element analysis instead of experimental tests. The viscous strain is greater than the plastic strain which is not negligible.

- by BABAK BEHESHTI
- •
- Engineering, Theoretical and Applied Mechanics

Buoyancy driven, adiabatic and compressible flow in relatively high solar chimneys is treated in the paper analytically by using one-dimensional model of flow. General equations written suitably in a non-dimensional form are used for a qualitative discussion pertaining to the mutual effects of gravity, viscosity and varying cross section of the chimney. It is shown that in case of low Mach number flow these equations possess exact solutions obtainable by ordinary mathematical methods for any given chimney shape. Also shown, and demonstrated on an example, is the procedure of evaluation of the chimney shape that satisfies a condition imposed beforehand upon the flow. For better insight into the role of various parameters the solutions are presented in the form of power series expansions.

The main issue taken up in the paper is to find optimal designs of multi-span sandwich panels with slightly profiled steel facings and polyure-thane foam core (PUR), which would satisfy conflicting demands of the market, i.e. minimal variance in types of panels, maximum range of ap-plication and minimum cost. The aim is to find dimensional and material parameters of panels which generate minimum cost and maximum length of span under prescribed loads in ultimate and serviceability limit states. The multi-criterion optimization problem is formulated in such a way, where the length of the span plays two roles, namely a design variable and a component of a vector objective function. An evolutionary algo-rithm is used. Numerous inequality constraints are introduced in two ways: directly and by external penalty functions.