Subjects -> PHYSICS (Total: 857 journals)     - ELECTRICITY AND MAGNETISM (10 journals)    - MECHANICS (22 journals)    - NUCLEAR PHYSICS (53 journals)    - OPTICS (92 journals)    - PHYSICS (625 journals)    - SOUND (25 journals)    - THERMODYNAMICS (30 journals) PHYSICS (625 journals)            First | 1 2 3 4 | Last

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 MeccanicaJournal Prestige (SJR): 0.814 Citation Impact (citeScore): 2Number of Followers: 1      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1572-9648 - ISSN (Online) 0025-6455 Published by Springer-Verlag  [2469 journals]
• Link between externally excited nonlinear system and parametrically
excited Duffing oscillator via bursting oscillations and phase transitions

Abstract: Abstract New types of bursting oscillations in the Duffing oscillator with a slow parametric excitation are introduced. By treating low-frequency parametric excitation as a bifurcation parameter in a novel way, two-stage bifurcation is determined. The first is a modified form of a supercritical pitchfork, while the second is supercritical cusp bifurcation. Cusp bifurcation is considered in a topologically equivalent system, where the effect of damping on the creation of three types of bursting oscillations is explained. These three types of oscillations represent a new phenomenon in the Duffing system and here the active and silent phases are clearly distinguished and governable. A new system with external excitation is developed which is equivalent to the parametrically excited Duffing system. In such a system, “bursting like behavior” and its connection with external excitation are established. Also, the base excited real mechanical system and the conditions under which its behavior can be analysed using the developed model are presented. The explanation of the observed phenomena is given based on the first and second phase transitions. Possible applications of the presented approach for low-frequency energy harvesting and detection of external ultra-low frequency excitations and signals are indicated.
PubDate: 2022-06-01

• Tunable dissipation in elastic metamaterials via methodic reconfiguration
of inertant mechanical networks

Abstract: Abstract Elastic metamaterials have proposed transformative solutions to applications in structural mechanics owing to their unique capabilities in the domain of wave propagation and control. Notable among them are inertant metamaterials which augment their locally resonant mechanism with mechanical inerters, thereby expanding their dispersion profiles and versatility. In this work, we provide a comprehensive analysis of the different ways such profiles can be shaped via an informed reconfiguration of a hierarchical mechanical network comprising the inerter element. Through a series of examples, we demonstrate the pivotal roles played by the network components, architecture, as well as damping placement on the response, bandgap characteristics, and emergent dissipation. Using the finite element method, band structures are computed for locally resonant flexural beams with six inertant networks representative of the design spectrum, via a free wave propagation approach, i.e., waves that are not driven at a given frequency. Predictions of the infinite medium reveal that each configuration is associated with its own dissipative characteristics which are depicted using a set of unique wavenumber-free band structures directly relating Bloch damping ratios to oscillatory damped frequencies. We show that the implemented framework enables a direct comparison with the finite metamaterial counterparts via modal damping ratios obtained at discrete frequencies, providing a straightforward yet firm validation of the resultant behavior across the entire frequency spectrum. Depending on the frequency range of interest, the choice of the inertant network combined with appropriate damping deployment within the host structure or the resonating substructure can be tailored to instigate an efficient damped response which is best suited for a given application. The presented work provides a new perspective on elastic metamaterials with inertant networks, elucidating the interplay between prescribed damping and emergent dissipation and changing the current paradigm from one that merely looks at damping amount to a cost-effective, placement-based strategy which maximizes the aggregate dissipation corresponding to a given amount of damping material.
PubDate: 2022-06-01

• A note on the catenary arch bending-moment-free paradox

Abstract: Abstract Based on the analogy between a hanging chain and a masonry arch, catenary has been for centuries considered to be an ideal arch shape, since it involves pure axial thrust. In recent studies, the equilibrium analysis of the catenary arch of finite uniform thickness under self-weight is revisited under Thrust line theory. Accordingly, it is the only shape in which a shear-free state is possible, but a bending-moment-free state cannot be attained since the thrust line coincident with the arch midline (geometrical axis) is not admissible. In the present research, the true location of centres of gravity of infinitesimal voussoirs—which are not coincident with the arch midline, is introduced into the consideration regarding bending-moments. It is shown that for a catenary arch, with rectangular cross-section, constant mass density and normal stereotomy, there is an admissible shear-free thrust line coincident with the arch centroidal axis. Since it is at a finite distance from the geometrical axis, such a shear-free state is not bending moment-free. However, since the deviation between the centroidal axis and the geometrical axis is small, the catenary shape can be rather viewed as a quasi-ideal shape.
PubDate: 2022-06-01

• Swelling of pH-sensitive hydrogel pressure vessel under altered-pH coupled
with inflation, extension, and torsion

Abstract: Abstract pH-sensitive hydrogels are a unique class of hydrophilic polymers with fascinating characteristics that can be harnessed for future innovative applications such as drug delivery and tissue engineering. To employ hydrogels in various applications, the swelling behavior of these materials are required to be well studied. In this research, the mechanical swelling response of pressure vessels composed of the pH-sensitive hydrogel is studied in response to pH-variation as well as combined inflation, extension, and torsion loading. In this regard, an analytical solution is proposed to inspect this problem, which is utilized as a common experimental protocol for the characterization and modeling of polymeric materials. Evaluating the analytical solution, a 3D finite element study was conducted for the same problem. The consistency of the results in both FE analysis and the proposed method confirms the accuracy of our method. However, considering the much lower computational cost of analytical solutions compared to FEM (< 1%), proposing such solution for this complex problem is of great interest. Therefore, the developed solution can be employed as a beneficial tool for calibrating the material parameters, and examining the swelling behavior of pH-sensitive hydrogels under various factors such as mechanical properties, geometric dimensions, and loading parameters.
PubDate: 2022-06-01

• Investigating the multiple scales method based on a new scaling for energy
harvesting from a double cantilever beam with internal resonance

Abstract: Abstract Nowadays, energy harvesting by piezoelectric materials has become one of the important fields for researchers. In this research, energy harvesting from double cantilever beams is investigated by an approximate analytical solution based on the multiple scales method (MMS). First, the technique to solve the equations of motion by the method of multiple scales is explained, which is performed based on two different scalings. MMS based on scaling 1 is similar to those reported by other researchers, but MMS based on scaling 2 solution has been solved based on a new scaling. The results show that the MMS based on scaling 2 has higher speed and accuracy than the MMS based on scaling 1 with respect to the numerical reference solution. This is due to the correct selection of scaling parameters. Next, the experimental results are compared with the MMS based on scaling 2 results. Finally, the effect of adding a magnet on the bandwidth of the system is comprehensively investigated. The results show that by proper selection of system parameters, it is possible to have a system with wide bandwidth or high voltage peak depending on the values of the initial distance between the magnets and electrical resistance.
PubDate: 2022-06-01

• Stability of heterogeneous beams with three supports through Green
functions

Abstract: Abstract The present paper is devoted to the issue how the critical load of some heterogeneous beams with three supports can be determined by using Green functions. The stability problems of these beams are equivalent to three-point boundary value problems, paired with homogeneous boundary conditions. If the Green functions of these boundary value problems are known, the eigenvalue problems that provide the critical load can be transformed into eigenvalue problems governed by homogeneous Fredholm integral equations. The later eigenvalue problems can be reduced to algebraic eigenvalue problems which then can be solved numerically with effective algorithms.
PubDate: 2022-06-01

• Blocking dynamics of capillary-gravity waves in a two-layer fluid in the
presence of surface and interfacial tensions

Abstract: Abstract In the present study, capillary-gravity wave blocking in a two-layer fluid in the presence of surface and interfacial tensions are analyzed under the assumption of the linearized theory of water waves. In the presence of surface and interfacial tensions, two propagating capillary-gravity wave modes exist, namely barotropic (surface) and baroclinic (internal) modes. However, the inclusion of an opposing current often leads to the vanishing of the group velocity for two different wavenumbers, which are referred to as primary (high frequency) and secondary (low frequency) blocking points within which wave energy flux becomes negative. Moreover, within the primary and secondary blocking points, there exist four/six propagating wavenumbers which depend upon the current speed and frequency. For specific values of opposing current and stratification ratio, both phase and group velocities vanish for the same wavenumber. Beyond that limit, the phase velocity becomes negative, leading to negative energy waves in both surface and internal modes or in one mode. The occurrences of wave blocking and negative energy waves are demonstrated for the internal waves when an upper layer fluid moves over the lower layer fluid in a two-layer system under the deepwater approximation. In addition, the occurrences of Kelvin–Helmholtz instability in the internal mode and analogous dead water effect for capillary-gravity waves in a two-layer fluid are demonstrated. Finally, a few theoretically obtained results related to blocking dynamics are validated using a time-domain simulation.
PubDate: 2022-06-01

• Non-linear frequency-matching of the centrifugal distance to optimize the
rotating frequency range by stabilizing non-linear oscillations

Abstract: Abstract Non-linear bistable energy harvesters (BEH) can generate higher velocity responses compared with linear systems, leading to large-amplitude output voltages by stabilizing high-energy orbital oscillations of a tip magnet. Considering the centrifugal effects due to rotations shows that BEH can further maintain higher performances with wider bandwidths. However, BEH is sensitive to the centrifugal distance and can only perform well over a narrow range. Considering the need to set the centrifugal distance for the tip magnet in experiments and simulations, it is necessary to calculate an optimal centrifugal distance under different parameters. In theory, the relationship of non-linear frequency-matching between the jump-down frequency of the monostable state and the rotating frequency of the external circumstances can be utilized to solve for the optimal centrifugal distance under different parameters. The BEH performance and bandwidth are sensitive to variations in the centrifugal distance, and responses under an optimal distance are improved significantly. The non-linear system has advantages in terms of its effective operational bandwidth and capacity, especially considering the centrifugal effect. The different centrifugal distances of the installation position affect the stabilization of high-energy orbital oscillations, and the optimal installation of the centrifuge depends on a variety of corresponding physical characteristics. The simulation results for the velocity responses verify the optimal centrifugal distance to effectively broaden its frequency range.
PubDate: 2022-06-01

• Analysis of dynamic modeling and solution of 3-RPS parallel mechanism
based on conformal geometric algebra

Abstract: Abstract In this paper, the dynamic modeling and generalized force analysis of three-(rotation pair)-(prismatic pair)-spherical pair (3-RPS) parallel mechanism were carried out for the first time based on the five-dimensional geometric algebra space—(4,0,1) conformal geometric. Compared with the traditional homogeneous matrix method, the maximum error values of generalized force of the three branch chains are $$1.90 \times 10^{ - 4} \,{\text{N}}$$ , $$1.39 \times 10^{ - 4} \,{\text{N}}$$ and $${6}{\text{.0}} \times {10}^{{ - {5}}} \;{\text{N}}$$ ,respectively. The results are basically consistent with the homogeneous matrix method. For composite rigid body transformation of two rotational motions, the rotation matrix method needs 27 times of multiplication and 18 times of addition, while the conformal geometric method only needs 16 times of multiplication and 15 times of addition. The computational efficiency of this method can be improved. In five-dimensional space, derivative operation can be linearly mapped to multiplication operation in three-dimensional space, so that dynamic equation has no derivative term. The dynamic model can separate variables of known and unknown, and realize parallel computation. This method provides a new idea for dynamic modeling and solving of parallel mechanism.
PubDate: 2022-06-01

• Effects of machine-tool parameters on geometry and contact pattern for
face hobbed hypoid gears

Abstract: Abstract Machine-tool parameters (MTP) were one of the most relevant factors on the design of the tooth surface topography (TST) and meshing characteristics for face hobbed hypoid gears. In this paper, the tooth surface mathematical model has been solved based on the cutting trace of the gear blank, meshing equation, kinematic association and tooth surface discretization. The influence of MTP on the TST and magnitude of deviation from midpoint has been researched by the discrete points on the tooth surface. Furthermore, a finite element model (FE model) has been developed to study, in detail, the effect of MTP deviation on the contact pattern. The results show that the diagonal, tooth direction and composite are three main forms of TST for the changing MTP. The deformation direction of radial distance and sliding base is tooth direction and that of work offset is composite. Others MTP are diagonal. Meanwhile, the movement direction of contact pattern is divided into three categories, such as diagonal, tooth profile and tooth direction. The movement direction of contact pattern is diagonal including the tile angle, work offset, machine root angle, horizontal and the radial distance. The tooth profile direction involves the swivel angle and initial cradle angle. The sliding base is in the tooth direction.
PubDate: 2022-06-01

• The interface debonding in particle-reinforced nonlinear viscoelastic
polymer composites

Abstract: Abstract To conveniently and feasibly characterize the interface debonding in particle-reinforced nonlinear viscoelastic polymer composites (PRNVPCs), a micromechanical model is proposed based on a normalization method that can convert the rate-dependent constitutive relationship of a nonlinear viscoelastic matrix into a rate-independent linear viscoelastic constitutive relationship. With this treatment, a linear homogenization scheme is used to achieve closed-form solutions for the critical particle stress and the critical time at the initiation of interface debonding in PRNVPCs. The change in the particle debonding stress versus the debonding angle is theoretically predicted with the new model, and the predicted change is qualitatively consistent with the experimental data. Furthermore, it is found that the particle debonding stress increases monotonically with decreasing particle size. The increase of the applied strain rate leads to an increase of the particle debonding stress but a decrease in the critical debonding time. This demonstrates that a smaller particle and a higher loading rate are both beneficial for improving the interfacial adhesion, while the latter will shorten the time needed to initiate interface debonding. The present research provides a convenient approach to theoretically characterize the interface debonding in PRNVPCs, which should be of guiding value for the design of advanced polymeric composites with a good load bearing capacity.
PubDate: 2022-06-01

• Dynamics of a vibro-impact self-propelled capsule encountering a circular
fold in the small intestine

Abstract: Abstract Given the anatomy of the small intestine, this paper investigates the dynamics of a vibro-impact capsule moving on an intestinal substrate with the consideration of a circular fold which provides the main resistance for the capsule’s progression. To this end, a new mathematical model of the capsule-fold contact that can depict the entire procedure of fold crossing is proposed. Our bifurcation analyses suggest that the capsule always performs period-1 motion when the driving force is small, and fold crossing requires a large excitation amplitude, especially when the duty cycle ratio is small. By contrast, the excitation period of the capsule does not have a strong influence on fold crossing. It is found that the inner mass, capsule mass, frictional coefficient and fold’s height have a significant influence on capsule’s crossing motion. We also realise that Young’s modulus of the tissue has a critical influence on the bifurcation pattern of the capsule, where a stiffer tissue may lead to the co-existence of three stable attractors. On the contrary, the capsule’s length and stiffness of the impact springs have less influence on the capsule’s dynamics. The findings of this study can help with the optimisation and control of capsule’s locomotion in the small intestine.
PubDate: 2022-05-08

• A new shear formula for tapered beamlike solids undergoing large
displacements

Abstract: Abstract In many engineering applications it is often necessary to determine the flow of shear stresses in the cross-sections of beamlike bodies. Taking a cue from Jourawski's well-known formula, several scholars have proposed expressions for evaluating the shear stresses in non-prismatic linear elastic beams, where longitudinal variations in the size and shape of the cross-sections produces complex stress fields. In the present paper, a new shear formula, derived using a mechanical model developed in a previous work, is presented for tapered beams subject to even large displacements and small strains. Numerical examples and comparisons with results obtained using other formulas in the literature and non-linear 3D-FEM simulations show how the new formula constitutes an important generalization of the previous ones and is able to provide particularly accurate results.
PubDate: 2022-05-08

• Design of a path generating compliant mechanism using a novel
rigid-body-replacement method

Abstract: Abstract Flexure-hinge compliant mechanisms have developed rapidly in precision engineering and robotics, especially in the context of micro aerial vehicles, where researchers employ such mechanisms for generating flapping-wing paths. This paper focuses on the design of a fully compliant mechanism for generating different bio-inspired 3D wing paths. A novel design algorithm was developed based on the rigid-body replacement method. The rigid-body replacement typically involves searching a rigid-body mechanism that accomplishes the desired path and converting it into a compliant mechanism by replacing the rigid joints with flexural hinges or using the Pseudo-Rigid-Body model. In the new method, the 3D mechanism was designed in two perpendicular planes. First, the main path was developed using the four-bar mechanism synthesis methods. Then, the mechanism was dynamically designed by flexural elements in the other plane. The governing dynamic equations were derived, and the main parameters were investigated. The mechanism was prototyped by the SCM (Smart Composite Manufacturing) process. For verification, the wing path was captured by a high-speed camera and compared with the analytical path.
PubDate: 2022-05-06

• Acknowledgement to Reviewers 2021

PubDate: 2022-05-01

• A bone-wise approach for modeling the human hind-midfoot. Part I:
kinematics

Abstract: Abstract Multi-line segment foot models propose a triple-line segmentation into hindfoot, midfoot and forefoot; oftentimes, the midfoot is regarded as a rigid line segment. We here begin our presentation of a new model of the hind-midfoot bone complex, regarded as a system of rigid blocks, the bones, with perfect mutual constraints, the bone joints. Firstly, we give a qualitative description of the deformations of the foot per se, as if it were severed from the body or made to move passively in vivo, the talocrural joint being kept locked; the descriptive capabilities of our model are illustrated by progressively locking more and more bone joints. Secondly, we derive two interdependent systems of nonlinear algebraic equations which render the geometrical and kinematic complexity of the hind-midfoot complex: one system locates individual bones in space, the other selects all location sets classifiable as unbroken kinematic chains, that is to say, all admissible hind-midfoot configurations. We define the relative multi-parameter configuration manifold, indicate how to inspect it hierarchically, and furnish a representative example amenable to geometrical description. The accompanying dataset document features graphical information and configurational data helping to motivate our modelling choices, as well as analytical information concerning certain mathematical developments we here omit.
PubDate: 2022-05-01

• Dynamic modeling and vibration control of a large flexible space truss

Abstract: Abstract Dynamic equivalent modeling is convenient to the vibration controller design of large space truss structures. Consequently, it is important to study the effectiveness of designed vibration controller of the original truss structures based on the equivalent dynamic models. In this study, the dynamic modeling and vibration control for a large flexible space truss are investigated. The space truss is typical periodic triangular prism structure which consists of beams and rods. Considered the transverse deformation of the whole structure, the equivalent dynamic model of the space truss is established using energy equivalence principle. The fourth-order governing equations of the cantilevered equivalent beam model are derived and solved by adopting the Hamilton principle and the Galerkin method to achieve its discrete dynamic model. To obtain analytical mode shapes of the established equivalent model, an exact analytical approach is exploited for purpose of constructing state space equation of the space truss. Then the validity and accuracy of the equivalent beam model are demonstrated by comparing the natural frequencies and mode shapes with the original space truss finite element model. More importantly, to further design the active vibration controller of the space truss based on the equivalent beam model, the LQR vibration controller is designed when the space truss is subjected to periodic and impulse excitations. The control moment is applied to the full-scale finite element model of the space truss and the numerical simulations prove the effectiveness of the designed LQR vibration controller for the vibration suppression of the space truss. Results indicate that the established equivalent beam model is valid and particularly convenient for the vibration suppression of the large space truss, which can successfully settle the difficulty caused by the high degree of freedom of the finite element model of the large truss to its vibration controller design.
PubDate: 2022-05-01

• Iterative inverse kinematics for robot manipulators using quaternion
algebra and conformal geometric algebra

Abstract: Abstract This paper presents a set of generalized iterative algorithms to find the inverse position kinematics of n-degree-of-freedom kinematic chains with revolute joints. As a first approach, an iterative algorithm is developed using the gradient descent method in Quaternion Algebra to find both the inverse position and velocity kinematics solution in redundant systems closest to their initial configuration. Additionally, a generalized extension of this approach is developed employing screw rotors and Conformal Geometric Algebra, where efficient update rules are obtained to solve the problem of inverse position kinematics. Simulation experiments using different degree-of-freedom models as well as real-time experiments using a Geomagic Touch Haptic device are carried out to demonstrate the effectiveness of the proposed methods.
PubDate: 2022-04-13

• Topology optimization using the discrete element method. Part 2: Material
nonlinearity

Abstract: Abstract Structural Topology Optimization typically features continuum-based descriptions of the investigated systems. In Part 1 we have proposed a Topology Optimization method for discrete systems and tested it on quasi-static 2D problems of stiffness maximization, assuming linear elastic material. However, discrete descriptions become particularly convenient in the failure and post-failure regimes, where discontinuous processes take place, such as fracture, fragmentation, and collapse. Here we take a first step towards failure problems, testing Discrete Element Topology Optimization for systems with nonlinear material responses. The incorporation of material nonlinearity does not require any change to the optimization method, only using appropriately rich interaction potentials between the discrete elements. Three simple problems are analysed, to show how various combinations of material nonlinearity in tension and compression can impact the optimum geometries. We also quantify the strength loss when a structure is optimized assuming a certain material behavior, but then the material behaves differently in the actual structure. For the systems considered here, assuming weakest material during optimization produces the most robust structures against incorrect assumptions on material behavior. Such incorrect assumptions, instead, are shown to have minor impact on the serviceability of the optimized structures.
PubDate: 2022-04-08

• Topology optimization using the discrete element method. Part 1:
Methodology, validation, and geometric nonlinearity

Abstract: Abstract Structural Topology optimization is attracting increasing attention as a complement to additive manufacturing techniques. The optimization algorithms usually employ continuum-based Finite Element analyses, but some important materials and processes are better described by discrete models, for example granular materials, powder-based 3D printing, or structural collapse. To address these systems, we adapt the established framework of SIMP Topology optimization to address a system modelled with the Discrete Element Method. We consider a typical problem of stiffness maximization for which we define objective function and related sensitivity for the Discrete Element framework. The method is validated for simply supported beams discretized as interacting particles, whose predicted optimum solutions match those from a classical continuum-based algorithm. A parametric study then highlights the effects of mesh dependence and filtering. An advantage of the Discrete Element Method is that geometric nonlinearity is captured without additional complexity; this is illustrated when changing the beam supports from rollers to hinges, which indeed generates different optimum structures. The proposed Discrete Element Topology Optimization method enables future incorporation of nonlinear interactions, as well as discontinuous processes such as during fracture or collapse.
PubDate: 2022-04-08

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