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This paper studies the dynamic deployment of cylindrical thin-shell structures with open cross section, attached to a rigid base. The structures are elastically folded and then released. Previous experiments have shown that the total energy decreases while a fold moves back and forth along the structure, which was explained in terms of energy losses related to the fold "bouncing" against the boundary. This paper uses a rigorous numerical simulation, based on an in-house isogeometric shell finite element code that simultaneously eliminates shear locking and hourglassing without any intrinsic energy dissipation, to show that the total energy of the system is conserved during deployment. The discrepancy with the previous results is explained by showing that energy transfers from low-frequency, "rigid body" modes, to higher frequency modes. [ABSTRACT FROM AUTHOR]

An in-depth understanding of stall behavior is essential to improve the safe and stable operation of the pump turbine. In this research, the detached eddy simulation (DES) is used to investigate the various characteristics and propagation mechanism of the rotating stall of the hump instability region. The frequency characteristics and spatial intensity distribution of the stall cells are studied by adopting the proper orthogonal decomposition (POD) method. The results indicate that the energy loss at 0.80QDES and 0.75QDES are induced by the rotating stall with three cells that occur in the diffuser flow channel, and the corresponding high amplitude frequencies are St0.0074 and St0.0111, respectively. The effect of the stall cells is particularly severe near the hub. When the flow rate is further reduced to 0.68QDES, the three rotating stall cells develop into two symmetrically distributed stable stall cells with no definite characteristic frequencies, and the blocking phenomenon is concentrated near the shroud. With the stall cells losing their rotational characteristics, they have less impact on the flow field and contribute less energy. This paper also reveals that the energy loss in the diffuser contributes significantly to the hump formation on the performance curve. [ABSTRACT FROM AUTHOR]

Under near-vacuum conditions, the fluid frictional dissipation or approximately the inverse of the quality factor of a microcantilever once the intrinsic dissipation can be neglected is proportional to the low pressure. We shall investigate the dynamic behavior of micro-electromechanical systems (MEMS) devices via the calculation of the quality factor or frictional damping forces resulting from surrounding gases. Here, we illustrated some specific examples relevant to the computation of the quality factor or dynamical friction for an oscillating microcantilever in air via measurements of the paper of Okada et al. (Okada, H., Itoh, T., and Suga, T., 2008, Wafer Level Sealing Characterization Method Using Si Micro Cantilevers,Â" Sens. Actuators A, 147(2), pp. 359-364) considering the quality factors of the CM (a label for a microcantilever: 500 × 90 × 5 μm³ Si microcantilever (the measured resonance frequency: 23.7 kHz) and the paper of Kara et al. (Kara, V., Yakhot, V., and Ekinci, K. L., 2017, Generalized Knudsen Number for Unsteady Fluid Flow, Phys. Rev. Lett., 118(7), p. 074505) in rarefied gases regime. We present the corrected quality factor or dynamical friction over the whole range of the Knudsen number considering the CM part by Okada et al. Our new plot considering the quality factor which is proportional to the inverse of the dissipative friction parameter per unit length, pressure as well as the Knudsen number over the whole range should be useful to researchers in this field. [ABSTRACT FROM AUTHOR]

Dielectric elastomers (DEs) are a class of highly deformable electroactive polymers (EAPs) employed for electromechanical transduction technology. When electrostatically actuated dielectric elastomer actuators (DEAs) are subjected to an input signal comprising multiple Heaviside voltage steps, the emerging inherent residual vibrations may limit their motion accuracy in practical applications. In this paper, the systematic development of a command-shaping scheme is proposed for controlling residual vibrations in an electrically driven planar DEA. The proposed scheme relies on invoking the force balance at the point of maximum lateral stretch in an oscillation cycle to bring the actuator to a stagnation state followed by the application of an additional electric input signal of predetermined magnitude at a specific time. The underlying concept of the proposed control scheme is articulated for a single Heaviside step input-driven actuator and further extended to the actuator subjected to the multistep input signal. The equation governing the dynamic motion of the actuator is derived using the principle of virtual work. The devised dynamic model of the actuator incorporates the effects of strain stiffening of elastomer and viscous energy dissipation. The nonlinear dynamic governing equation is solved using matlab ode solver for extracting the dynamic response of the actuator. The applicability of the devised command-shaping control scheme is illustrated by taking a wide range of parameters including variations in the extent of equilibrium state sequences, damping, and polymer chain extensibility. The proposed scheme is found to be adaptable in controlling the vibrations of the actuator for any desired equilibrium state. The results presented in this paper can find its potential application in the design of an open-loop control system for DEAs. [ABSTRACT FROM AUTHOR]

The numerical simulation was carried out to investigate mechanism of the heat transfer enhancement in the fin-and-tube heat exchangers. As known, the vortex generators (VGs) were widely used to improve the thermal performance with bad flow resistance characteristics and led to bad comprehensive performance. This paper aims to expound the mechanism of thermal hydraulic characteristics and explore the effect of VGs position on the comprehensive performance. Three types of fins (type 1, type 2, and type 3) were discussed in this paper. The j factor, f factor, and performance evaluation (PEC) of three types of VGs in different positions were discussed and compared. Based on the numerical results, a detailed description of the effect of three types of VGs on the heat transfer performance and flow resistance characteristics was presented at different Reynolds number in the range between 1300 and 2000. In addition, local velocity distribution, local temperature distribution, and local pressure drop distribution were analyzed and discussed. And the effect of VG angle on the thermal performance and flow resistance was presented. It can be concluded that the main heat transfer occurred in the region before the tube, and the wake region behind the tube was harmful to improve the thermal performance and reduce the flow resistance. Besides, VG in the wake region was obviously beneficial to the enhancement of the thermal performance with less energy loss. [ABSTRACT FROM AUTHOR]

The paper investigates the effect of nonequilibrium behavior of boundary layers on the profile loss of a compressor. The investigation is undertaken using both high fidelity simulations of a midheight section of a compressor blade and a reduced order model, MISES. The solutions are validated using experimental measurements made in the embedded stage of a multistage low speed compressor. The paper shows that up to 35% of the suction surface boundary layer of the compressor blade exhibits nonequilibrium behavior. The size of this region reduces as the Reynolds number is increased. The nonequilibrium behavior was found to reduce profile loss in cases of attached transition and raise loss where transition occurs through separation. [ABSTRACT FROM AUTHOR]

This paper has revisited the roof deformation and collapse of stamps with isolated grooves based on a contact mechanics approach, with emphasis on establishing the nonadhesive and adhesive contact solutions for surfaces containing a shallow rectangular groove with the effects of applied load and interfacial adhesion taken into account. By solving singular integral equations and using the energy release rate approach, closed-form solutions are derived analytically for the deformed groove shapes, interfacial stress distributions, and equilibrium relations between load and contact size, which reduce to the previously proposed solutions without adhesion or without applied load. Finite element (FE) analysis is performed to validate the nonadhesion solutions, while experiment results of stamp collapse reported in the literature are adopted to examine the adhesion solutions. By introducing the Johnson parameter a to represent a competition between surface energy and elastic strain energy of the groove, four kinds of contact behaviors of the groove roof can be characterized appropriately: nonadhesion, weak adhesion, intermediate adhesion, and strong adhesion. Hysteresis loop and energy loss due to distinct load/unloading paths are revealed in the cases of intermediate and strong adhesion. We have also provided the critical applied pressure to achieve roof collapse and the corresponding equilibrium contact size for full range of a. [ABSTRACT FROM AUTHOR]

In this paper, identification of energy dissipation in the joints of a lab-scale structure is accomplished. The identification is carried out by means of an energy flow analysis and experimental data. The devised procedure enables to formulate an energy balance in the vicinity of the joints to obtain local energy dissipation. In this paper, a damping matrix based on the locally identified damping coefficients is formulated. The formulated damping matrix is later used in a five-degrees-of-freedom (5DOF) system for validation. The results obtained with the proposed method are in good agreement with the experimental data, especially in the low frequency range. [ABSTRACT FROM AUTHOR]

Prior to the detailed design of components, turbomachinery engineers must guide a mean-line or throughflow design toward an optimum configuration. This process requires a combination of informed judgement and low-order correlations for the principle sources of loss. With these requirements in mind, this paper examines the impact of key design parameters on endwall loss in turbines, a problem which remains poorly understood. This paper presents a parametric study of linear cascades, which represent a simplified model of real-engine flow. The designs are nominally representative of the low-pressure turbine blades of an aero-engine, with varying flow angles, blade thickness, and suction surface lift styles. Reynolds-averaged Navier-Stokes (RANS) calculations are performed for a single aspect ratio (AR) and constant inlet boundary layer thickness. To characterize the cascades studied, the two-dimensional design space is examined before studying endwall losses in detail. It is demonstrated that endwall loss can be decomposed into two components: one due to the dissipation associated with the endwall boundary layer and another induced by the secondary flows. This secondary-flow-induced loss is found to scale with a measure of streamwise vorticity predicted by classical secondary flow theory. [ABSTRACT FROM AUTHOR]

Energy addiction is regarded as the primary obstacle to humanity's sustainable future. The need to change lifestyles in consumer societies to become more sustainable is advocated without a clear understanding of what elements of modern life must undergo major transformations. One of the most overlooked aspects of this question is the role of buildings that serve as homes and workspaces. The energy use for maintaining such infrastructure, especially in urban areas, and operating key services like heating or cooling, lighting, delivering water, and collecting wastewater will inevitably grow as global population becomes increasing more affluent. This paper investigates the energy costs of several aspects of these key services in urban areas, specifically delivering and heating water and heating residential spaces in the five boroughs of New York City. It provides detailed geospatial calculations as an example of assessing energy costs based on physical principles (e.g., accounting for the effects of topography and building floor elevation to deliver water and heat, and energy losses in the water distribution system). The paper also serves as a demonstration of much-needed research to price out the cost of modern life in energy terms in order to identify major inefficiencies in our current urban infrastructure, as well as the potential for efficiency improvements. While these calculations do not directly incorporate observed data, the principles demonstrated here highlight the use of quantitative geospatial analyses (based on fundamental physics) in order to look at urban infrastructures, particularly for planning and designing new cities or rebuild existing ones. [ABSTRACT FROM AUTHOR]

The direct heat exchange network (direct flow mixing network) and the indirect heat exchange network (exchanger network) are two of the elements that constitute a water network where heat and mass are transferred. When designing these systems, it is important to consider different aspects such as thermodynamics and equipment costs. This paper analyzes different design options within the framework of heuristic methodologies on a case study taken from the open literature. Two design methodologies are compared on the basis of exergy losses. It also enunciates a series of considerations in heuristic design for the heat and mass exchange networks. A very helpful tool in relation with the considerations set out herein is the composite curve; special focus will be given during its construction. This paper shows how to incorporate the exergy component in design seeking to minimize the thermal irreversibility. [ABSTRACT FROM AUTHOR]

Recently developed laboratory and numerical techniques reveal that the very thin, nearwall (assumed) "laminar" fluid layer, an essential feature of all turbulent flow conditions, houses a world of identifiable jetlike structures including bursts generated from the near-wall regions and lumps of fluids projected back onto the wall zones. This activity, identified as "coherent structures" (CS), is recognized as an important mechanism for radial mass transport and energy dissipation, particularly in near-wall or fluid-bed zones. Buoyancy-, adhesion-, hydrodynamic-, and CS-related updraft forces act on particles positioned in the fluid-bed interface zone. Depending on the particle nature, bulk fluid properties, and transport velocity, three pairs of forces were identified corresponding to the equilibrium condition of deposit particles in each of the three size ranges with respect to the onset of entrainment into the bulk flow. This mechanistic approach using a set of force equilibrium equations to assess the potential entrainment of particles was first suggested in 1980 by Phillips and was later (2006) applied by Toma and a research team from ARC and PETRONAS to explain the aging of wall-deposit layer occurring during waxy crude transportation as an effect of size-selective removal of paraffin crystals formed from a mixture of crystalized alkanes. The merit of this paper, regarded as an extension of the 2006 publication, is to introduce a more general selective extraction rate function that enables calculations of both the rate of paraffin aging and size alteration of any fine, polydisperse particulate matter exposed to bulk turbulent flow, gas or liquid. Without any adjustment of the process or physical constants, the modeling results presented in this paper compared satisfactorily with the experimental results obtained independently by the Texaco Research (aging of waxy crude) and laboratoiy data from the University of Alberta on the effect of size-selective extraction of fine sand or glass beads (GB) initially deposited on the bottom of a pipe and exposed to a turbulent bulk flow of water. An overarching objective of this paper is to stir interest in mechanistic modeling and prediction of size-selective radial transport and separation for a broad range of industrial and environmental applications and studies and specifically in the recognition and use of burst-sweep CS structures for calculating radial transport of small particle sizes, particularly in near-interface zones exposed to turbulent flow conditions. [ABSTRACT FROM AUTHOR]

Capture of a prey by spider orb webs is a dynamic process with energy dissipation. The dynamic response of spider orb webs under prey impact requires a multi-scale modeling by considering the material microstructures and the assembly of spider silks in the macro-scale. To better understand the prey capture process, this paper addresses a multi-scale approach to uncover the underlying energy dissipation mechanisms. Simulation results show that the microstructures of spider dragline silk play a significant role on energy absorption during prey capture. The alteration of the microstructures, material internal friction, and plastic deformation lead to energy dissipation, which is called material damping. In addition to the material damping in the micro-scale modeling, the energy dissipation due to drag force on the prey is also taken into consideration in the macro-scale modeling. The results indicate that aerodynamic drag, i.e., aero-damping, plays a significant role when the prey size is larger than a critical size. [ABSTRACT FROM AUTHOR]

Fracture of polymer gels is often time- and rate-dependent. Subject to a constant load, a gel specimen may fracture immediately or after a delay (time-dependent, delayed fracture). When a crack grows in a gel, the fracture energy may depend on the crack speed (rate-dependent). The underlying mechanisms for the time- and rate-dependent fracture of gels could include local molecular processes, polymer viscoelasticity, and solvent diffusion coupled with deformation (poroelasticity). This paper focuses on the effects of poroelasticity. A path-independent, modified J-integral approach is adopted to define the crack-tip energy release rate as the energetic driving force for crack growth in gels, taking into account the energy dissipation by solvent diffusion. For a stationary crack, the energy release rate is time-dependent, with which delayed fracture can be predicted based on a Griffith-like fracture criterion. For steady-state crack growth in a long-strip specimen, the energy release rate is a function of the crack speed, with rate-dependent poroelastic toughening. With a poroelastic cohesive zone model, solvent diffusion within the cohesive zone leads to significantly enhanced poroelastic toughening as the crack speed increases, rendering a rate-dependent traction-separation relation. While most of the results are based on a linear poroelastic formulation, future studies may extend to nonlinear theories with large deformation. In addition to the poroelastic effects, other mechanisms such as viscoelasticity and local fracture processes should be studied to further understand the time and rate-dependent fracture of polymer gels. [ABSTRACT FROM AUTHOR]

In this paper, a general torque distribution strategy is proposed to improve the drivetrain efficiency of four-wheel-drive electric vehicles (EVs). The strategy allows the same or different motors to be equipped in the front and rear wheels. The model of the drivetrain considers the loss properties of four permanent magnet synchronous motors (PMSMs) and four inverters over a wide range of torque and speed. The relationship between the drivetrain efficiency and the torque split ratio at any given speed is proven to be convex under both traction and regenerative braking conditions. It is shown that, when all four motors are identical, the maximum efficiency can be achieved if the total torque is equally shared. An equivalent loss strategy, which is a general method and can solve many optimization problems of multi-PMSM applications, is proposed to maximize the drivetrain efficiency when different PMSMs are used in the front and rear wheels. The effectiveness of the proposed strategy is verified using an urban dynamometer driving schedule (UDDS). In addition, the acceleration process of EVs is optimized using a dynamic programming approach to minimize acceleration duration and energy consumption. Simulation results show that, with the proposed strategy, the energy loss during the acceleration can be reduced by up to 15%. [ABSTRACT FROM AUTHOR]

The objective of this study focuses on the energy dissipation by friction on the interface of a braking system and the effects of roughness and granular plateaus on heat propagation. Faced with the difficulty of defining velocity accommodation and thermal partition between the two bodies in contact (disk and pad, for example,), the authors model the third body (friction) layer with circular particles detached from the pad. From a numerical point of view, this paper proposes a strategy of storing mechanical calculations in steady-state and using it for successive thermal processing in discrete element method (DEM) code. Thus, the heat is generated due to interparticle friction and is dissipated in the disk/pad interface by conductance. Accordingly, this coupling micro-macro model aims to determine the temperature rise of the pad/disk interface and to identify the equivalent thermal resistance. In line with that, the authors provide discussions of these parameters compared to experimental/empirical data as reported in the literature review and limitations of the model. [ABSTRACT FROM AUTHOR]

The ever-growing interest toward energy efficiency imposes the optimization of mechanism design under an energetic point of view. Even if the benefit of using spring balancing systems to reduce energy consumption is intuitive, the relation between spring design and electrical energy consumption has never been systematically addressed in the literature, which is mainly focused on static compensation of gravity forces. This paper tackles this novel and important issue and proposes an analytical method for model-based design of springs minimizing the energy required in rest-to-rest motion. The method relies on the model of energy dissipation that accounts for the characteristics of the mechanical, electrical, and power electronic components of a servo-actuated mechanism. The theory is developed with reference to a single rotating beam. The proposed solution ensures significant energy saving compared with the traditional static balancing design of springs and is particularly suitable for repetitive (cyclic) motion tasks. [ABSTRACT FROM AUTHOR]

This paper presents a new energy dissipation system composed of multistable cosine-curved domes (CCD) connected in series. The system exhibits multiple consecutive snap-through and snap-back buckling behavior with a hysteretic response. The response of the CCDs is within the elastic regime and hence the system's original configuration is fully recoverable. Numerical studies and experimental tests were conducted on the geometric properties of the individual CCD units and their number in the system to examine the force-displacement and energy dissipation characteristics. Finite element analysis (FEA) was performed to simulate the response of the system to develop a multilinear analytical model for the hysteretic response that considers the nonlinear behavior of the system. The model was used to study the energy dissipation characteristics of the system. Experimental tests on 3D printed specimens were conducted to analyze the system and validate numerical results. Results show that the energy dissipation mainly depends on the number and the apex height-to-thickness ratio of the CCD units. The developed multilinear analytical model yields conservative yet accurate values for the dissipated energy of the system. The proposed system offered reliable high energy dissipation with a maximum loss factor value of 0.14 for a monostable (self-recoverable) system and higher for a bistable system. [ABSTRACT FROM AUTHOR]

This paper presents a method to achieve high deformability levels in dielectric elastomer actuators (DEAs) by applying a modulated voltage waveform. The method relies on supplying the electrostatic energy during the specific phase of the oscillation cycle, resulting in the enhanced travel range at a relatively low driving voltage. We consider a standard sandwich configuration of the DE actuator with neo-Hookean material model and outline an energy-based approach for delineating the underlying principles of the proposed method. A comparison of the deformability levels achieved using the quasi-static, Heaviside step, and the modulated input waveforms is presented. Significant reduction in instability voltages together with a considerable increase in the stable actuation limit is observed in the case of the modulated voltage input. The estimates of the stability thresholds are validated by integrating the equation of motion obtained using Hamilton's principle. The effect of energy dissipation is assessed by considering variations in the quality factor. Further, a qualitative comparison with experimental observations is presented highlighting the practical feasibility of the method. This investigation can find its potential use in the design and development of DEAs subjected to a time-dependent motion. [ABSTRACT FROM AUTHOR]

In this paper, an acoustomechanical constitutive model is developed to describe the heating effect of a tissue-mimicking gel by cavitation in exposure to high-intensity focused ultrasound (HIFU). An internal variable, representing the evolution of cavitation process, is introduced into the Helmholtz free energy under the framework of thermodynamics that combines the acoustic radiation stress theory and the nonlinear elasticity theory together. Thus, the internal variable is related to the cavitation process and the mechanical energy dissipation of a tissue-mimicking gel from a macroscopic viewpoint. Since the temperature rise of cavitation phenomenon is more remarkable than that of heating waves, the temperature inside the tissue-mimicking gel rises rapidly mainly due to large amounts of cavitation bubbles. This phenomenon can be quantitatively described by the present model, which fits the existing experimental data well. [ABSTRACT FROM AUTHOR]

The structure of pomelo peel arouses research interest in recent years because of the outstanding damping and energy dissipating performance of the pomelo peel. Researchers found that pomelo peel has varying pore size through the peel thickness; the pore size gradient is one of the key reasons leading to superior energy dissipation performance of pomelo peel. In this paper, we introduce a method to model pomelo peel bioinspired foams with nonuniform pore distribution. We generate the skeletal open cell structure of the bioinspired foams using Voronoi tessellation. The skeleton of the bioinspired foams is built as three-dimension (3D) beam elements in a full-scale finite element model. The quasi-static and dynamic mechanical behaviors of the pomelo peel bioinspired foams could be derived through a finite element analysis (FEA). We illustrate our method using a case study of pomelo peel bioinspired aluminum foams under quasi-static compression and free fall impact circumstances. The case study results validate our method and demonstrate the superior impact resistance and damping behavior of bioinspired foam with gradient porosity for designers. [ABSTRACT FROM AUTHOR]

In this research paper, fully developed natural convection flow in a vertical parallel plate's micro-channel in the presence of viscous dissipation is theoretically examined by using a perturbation series method. The effects of velocity slip and temperature jump are taken to consideration. Due to the presence of viscous dissipation, the momentum and energy equations are coupled system of ordinary differential equations. The influences of Knudsen number, fluid wall interaction parameter, and viscous dissipation on the flow formation and heat transfer aspects are demonstrated through graphs and tables. This result indicates that increasing the value of rarefaction parameter decreases the effect of viscous dissipation on the Nusselt number. Furthermore, it is found that the effects of rarefaction parameter as well as buoyancy parameter on temperature and velocity are significantly pronounced in the case of symmetric heating [ABSTRACT FROM AUTHOR]

This paper is the second part of a two part paper that reports on the improvement of efficiency of a one and a half stage high work axial flow turbine. The first part covered the design of the endwall profiling, as well as a comparison with steady probe data; this part covers the analysis of the time-resolved flow physics. The focus is on the timeresolved flow physics that leads to a total-to-total stage efficiency improvement of 1.0%±0.4%. The investigated geometry is a model of a high work (Δh/ U2 = 2.36), axial shroudless HP turbine. The time-resolved measurements have been acquired upstream and downstream of the rotor using a fast response aerodynamic probe (FRAP). This paper contains a detailed analysis of the secondary flow field that is changed between the axisymmetric and the nonaxisyminetric endwall profiling cases. The flowfield at the exit of the first stator is improved considerably due to the nonaxisymmetric endwall profiling and results in reduced secondary flow and a reduction in loss at both hub and tip, as well as a reduced trailing shed vorticity. The rotor has reduced losses and a reduction in secondary flows mainly at the hub. At the rotor exit, the flow field with nonaxisymmetric endwalls is more homogenous due to the reduction in secondary flows in the two rows upstream of the measurement plane. This confirms that nonaxisymmetric endwall profiling is an effective tool for reducing secondary losses in axial turbines. Using a frozen flow assumption, the time-resolved data are used to estimate the axial velocity gradients, which are then used to evaluate the streamwise vorticily and dissipation. The nonaxisymmetric endwall profiling of the first nozzle guide vane show reductions in dissipation and streamwise vorticity due to the reduced. trailing shed vorticity. This smaller vorticity explains the reduction in loss at midspan, which is shown in the first part of the two part paper This leads to the conclusion that nonaxisymmetric endwall profiling also has the potential of reducing trailing shed vorticity. [ABSTRACT FROM AUTHOR]

Compliant contact force modeling has become a popular approach for contact and impact dynamics simulation of multibody systems. In this area, the nonlinear viscoelastic contact force model developed by Hunt and Crossley (1975, "Coefficient of Restitution Interpreted as Damping in Vibroimpact," ASME J. AppI. Mech., 42, pp. 440-445) over 2 decades ago has become a trademark with applications of the model ranging from intermittent dynamics of mechanisms to engagement dynamics of helicopter rotors and implementations in commercial multibody dynamics simulators. The distinguishing feature of this model is that it employs a nonlinear damping term to model the energy dissipation during contact, where the damping coefficient is related to the coefficient of restitution. Since its conception, the model prompted several investigations on how to evaluate the damping coefficient, in turn resulting in several variations on the original Hunt-Crossley model. In this paper the authors aim to experimentally validate the Hunt-Crossley type of contact force models and furthermore to compare the experimental results to the model predictions obtained with different values of the damping coefficient. This paper reports our findings from the sphere to flat impact experiments, conducted for a range of initial impacting velocities using a pendulum test rig. The unique features of this investigation are that the impact forces are deduced from the acceleration measurements of the impacting body, and the experiments are conducted with specimens of different yield strengths. The experimental forces are compared with those predicted from the contact dynamics simulation of the experimental scenario. The experiments, in addition to generating novel impact measurements, provide a number of insights into both the study of impact and the impact response. [ABSTRACT FROM AUTHOR]

One of the main interests of gas foil bearings lies in their superior rotordynamic characteristics compared with conventional bearings. A numerical investigation on the stability limit and on the unbalanced response off oil bearings is presented in this paper The main difficulty in modeling the dynamic behavior of such bearings comes from the dry friction that occurs within the foil structure. Indeed, dry friction is highly nonlinear and is strongly influenced by the dynamic amplitude of the pressure field. To deal with these nonlinearities, a structural dynamic model has been developed in a previous work. This model considers the entire corrugated foil and the interactions between the bumps by describing the foil bearing structure as a multiple degrees of freedom system. It allows the determination of the dynamic friction forces at the top and at the bottom of the bumps by simple integration of ordinary differential equations. The dynamic displacements of the entire corrugated sheet are then easily obtained at each time step. The coupling between this structural model and a gas bearing prediction code is presented in this paper and allows performing full nonlinear analyses of a complete foil bearing. The bearing stability is the first investigated problem. The results show that the structural deflection enhances the stability of compliant surface bearings compared with rigid ones. Moreover when friction is introduced, a new level of stability is reached, revealing the importance of this dissipation mechanism. The second investigated problem is the unbalanced response of foil bearings. The shaft trajectories depict a nonlinear jump in the response of both rigid and foil bearings when the value of the unbalance increases. Again, it is evidenced that the foil bearing can support higher masts unbalance before this undesirable step occurs. [ABSTRACT FROM AUTHOR]

Enriched by the nonlinear Onsager reciprocal relations and thermodynamic equilibrium points (Onsager, Phys. Rev., 37, pp. 405-406; 38, pp. 2265-2279), an extended normality structure by Rice (1971, J. Mech. Phys. Solids, 19, pp. 433-455) is established in this paper as a unified nonlinear thermodynamic theory of solids. It is revealed that the normality structure stems from the microscale irrotational thermodynamic fluxes. Within the extended normality structure, this paper focuses on the microscale thermodynamic mechanisms and significance of the convexity of flow potentials and yield surfaces. It is shown that the flow potential is convex if the conjugate force increment cannot not oppose the increment of the rates of local internal variables. For the Rice fluxes, the convexity condition reduces to the local rates being monotonic increasing functions with respect to their conjugate forces. The convexity of the flow potential provides the thermodynamic system a capability against the disturbance of the thermodynamic equilibrium point. It is proposed for time-independent behavior that the set of plastically admissible stresses determined by yield conditions corresponds to the set of thermodynamic equilibrium points. Based on that viewpoint, the intrinsic dissipation inequality is just the thermodynamic counterpart of the principle of maximum plastic dissipation and requires the convexity of the yield surfaces. [ABSTRACT FROM AUTHOR]

The starting point in the formulation of most acoustic problems is the acoustic wave equation. Those most widely used, the classical and convected wave equations, have significant restrictions, i.e., apply only to linear, nondissipative sound waves in a steady homogeneous medium at rest or in uniform motion. There are many practical situations violating these severe restrictions. In the present paper 36 distinct forms of the acoustic wave equation are derived (and numbered W1–W36), extending the classical and convected wave equations to include cases of propagation in inhomogeneous and/or unsteady media, either at rest or in potential or vortical flows. The cases considered include: (i) linear waves, i.e., with small gradients, which imply small amplitudes, and (ii) nonlinear waves, i.e., with steep gradients, which include “ripples” (large gradients with small amplitude) or large amplitude waves. Only nondissipative waves are considered, i.e., excluding and dissipation by shear and bulk viscosity and thermal conduction. Consideration is given to propagation in homogeneous media and inhomogeneous media, which are homentropic (i.e., have uniform entropy) or isentropic (i.e., entropy is conserved along streamlines), excluding nonisentropic (e.g., dissipative); unsteady media are also considered. The medium may be at rest, in uniform motion, or it may be a nonuniform and/or unsteady mean flow, including: (i) potential mean flow, of low Mach number (i.e., incompressible mean state) or of high-speed (i.e., inhomogeneous compressible mean flow); (ii) quasi-one-dimensional propagation in ducts of varying cross section, including horns without mean flow and nozzles with low or high Mach number mean flow; or (iii) unidirectional sheared mean flow, in the plane, in space or axisymmetric. Other types of vortical mean flows, e.g., axisymmetric swirling mean flow, possibly combined with shear, are not considered in the present paper (and are left to follow-up work together with dissipative and other cases). The 36 wave equations are derived either by elimination among the general equations of fluid mechanics or from an acoustic variational principle, with both methods being used in a number of cases as cross-checks. Although the 36 forms of the acoustic wave equation do not cover all possible combinations of the three effects of (i) nonlinearity in (ii) inhomogeneous and unsteady and (iii) nonuniformly moving media, they do include each effect in isolation and a variety of combinations of multiple effects. Altogether they provide a useful variety of extensions of the classical (and convected) wave equations, which are used widely in the literature, in spite of being restricted to linear, nondissipative sound waves in an homogeneous steady medium at rest (or in uniform motion). There are many applications for which the classical and convected wave equations are poor approximations, and more general forms of the acoustic wave equation provide more satisfactory models. Numerous examples of these applications are given at the end of each written section. There are 240 references cited in this review article. [ABSTRACT FROM AUTHOR]

This paper presents a novel asymptotic framework to obtain detailed solutions describing the propagation of hydraulic fractures in an elastic material. The problem consists of a system of nonlinear integro-differential equations and a free boundary problem. This combination of local and nonlocal effects leads to transitions on a small scale near the crack tip, which control the behavior across the whole fracture profile. These transitions depend upon the dominant physical process(es) and are identified by simultaneously scaling the associated parameters with the distance from the tip. A smooth analytic solution incorporating several physical processes in the crucial tip region can be constructed using this new framework. In order to clarify the exposition of the new methodology, this paper is confined to considering the impermeable case in which only the two physical processes of viscous dissipation and structure energy release compete. [ABSTRACT FROM AUTHOR]

In Part I of this two-part paper on swirling gas--liquid two-phase flow, correlations have been developed for the continuous liquid-phase velocity field under swirling conditions, such as that occurring in the lower part of the Gas--Liquid Cylindrical Cyclone (GLCC©) compact separator. The developed correlations, including the axial, tangential, and radial velocity distributions, are applicable for swirling flow in both cyclones and pipe flow. The first objective of this paper is to extend the study of Part I by developing correlations for the turbulent quantities of the continuous liquid phase, including the turbulent kinetic energy and its dissipation rate and Reynolds shear stresses. The second objective is to study experimentally and theoretically two-phase swirling flow gas-core characteristics and stability. The first objective has been met utilizing local LDV measurements acquired for swirling flow. The developed turbulent quantities correlations have been tested against data from other studies, showing good agreement. For the second objective, experimental data have been acquired under swirling two-phase flow conditions. A model for the prediction of the gas-core diameter and stability in swirling flow field has been developed, based on the turbulent kinetic energy behavior predicted by the developed correlations. Good agreement is observed between the model predictions and the data. [ABSTRACT FROM AUTHOR]

Geomaterials such as vuggy carbonates are known to exhibit multiple spatial scales. A common manifestation of spatial scales is the presence of (at least) two different scales of pores with different hydromechanical properties. Moreover, these pore-networks are connected through fissures and conduits. Although some models are available in the literature to describe flows in such media, they lack a strong theoretical basis. This paper aims to fill this gap in knowledge by providing the theoretical foundation for the flow of incompressible single-phase fluids in rigid porous media that exhibit double porosity/permeability. We first obtain a mathematical model by combining the theory of interacting continua and the maximization of rate of dissipation (MRD) hypothesis, and thereby provide a firm thermodynamic underpinning. The governing equations of the model are a system of elliptic partial differential equations (PDEs) under a steady-state response and a system of parabolic PDEs under a transient response. We then present, along with mathematical proofs, several important mathematical properties that the solutions to the model satisfy. We also present several canonical problems with analytical solutions which are used to gain insights into the velocity and pressure profiles, and the mass transfer across the two pore-networks. In particular, we highlight how the solutions under the double porosity/permeability differ from the corresponding ones under Darcy equations. [ABSTRACT FROM AUTHOR]

Switch-mode hydraulic control is a compact and theoretically efficient alternative to throttling valve control or variable displacement pump control. However, a significant source of energy loss in switch-mode circuits is due to throttling during valve transitions. Hydraulic soft switching was previously proposed as a method of reducing the throttling energy loss, by absorbing, in a small variable volume chamber, the flow that would normally be throttled across the transitioning high-speed valve. An active locking mechanism was previously proposed that overcomes the main challenge with soft switching, which is a lock mechanism that releases quickly and with precise timing. This prior work demonstrated a reduction in energy losses by 66% compared to a control circuit. In this paper, a numerical model is developed for a switch-mode virtually variable displacement pump (VVDP) circuit, utilizing the proposed soft switch. The model is then used as a means of designing a proof of concept prototype to validate the model. The prototype design includes methods for controlling the soft switch spring preload, travel distance, piston displacement required to unlock the soft switch, valve command duty cycle, switching cycle period, and load pressure. Testing demonstrated that the soft switch circuit performed as expected in a baseline condition. The operating region for this prototype was found to be quite narrow. However, the model does a good job of predicting the displacement of the soft switch. [ABSTRACT FROM AUTHOR]

This paper presents a novel adaptive thermal management technique to improve the efficiency of solid-state power amplifier (SSPA) for geo-synchronous satellites. The thermal management for space segment is very important as it determines the reliability of the satellite. The microwave power amplifiers (MPAs), either traveling wave tube amplifiers (TWTAs) or SSPAs, are the maximum power consuming and heat dissipative elements in the satellite and their power efficiency determines weight, volume, cost, and reliability of the satellite. So, it is necessary to improve the efficiency of the SSPA. A novel technique is presented, which improves the efficiency of the SSPA and hence, saving of costly DC power generation on-board and reduction of the heat dissipation. [ABSTRACT FROM AUTHOR]

Vibration is an environmental factor with hazardous effects on the instruments' precision, structural stability, and service life in engineering fields. Many kinds of energy dissipation devices have been invented to reduce the dynamic responses of structures and instruments due to environmental excitations. In this paper, a new kind of vibration isolation and suppression device with high damping performance, fine deformation recoverability, and bearing capacity for platform structures is developed, which is designed by considering the combination of the energy dissipation mechanisms of viscoelastic material, viscous fluid, and air spring. A series of dynamic properties tests on the device are carried out under different excitation frequencies and displacement amplitudes, and a mathematical model considering the coupling effects of energy dissipation of viscoelastic material, viscous liquid, and air spring is proposed. The research results indicate that the vibration isolation and suppression device has high damping capacity, and the proposed mathematical model can well describe the mechanical properties affected by excitation frequency and displacement amplitude. [ABSTRACT FROM AUTHOR]

The phosphor and die bonding configuration affect the optical efficiency and thermal performance in phosphor-coated white light emitting diodes (LEDs). In this paper, light emission studies reveal that the chromaticity shift and light extraction losses depend on the uniformity of phosphor particles deposited over the LED surface. A nonuniform and sparse phosphor layer affects the correlated color temperature (CCT) and the spectral Y-B ratio due to the disproportionate contribution of light emission between the LED device and the phosphor layer. Furthermore, the Y-B ratio was observed to reduce with temperature due to higher Stoke's energy and light extraction losses in the phosphor layer. As a result, the Y-B ratio exhibits an inverse relationship with the package's thermal resistance as a function of temperature. On the other hand, the thermal performance of a LED package is dependent on the die-bonding configurations (conventional and flip-chip). Due to the improved heat dissipation capabilities in flip-chip bonding, the temperature rise and thermal resistance of the package were observed to reduce with temperature. By alleviating the heat accumulation in the package, more stable colorimetric properties such as CCT and Y-B ratio can be achieved. [ABSTRACT FROM AUTHOR]

In this paper, we consider the interlayer slidable friction structures on soft-substrate as the hardcover book-like-laminated-plates with internal friction on the Winkler foundation. For a quasi-static problem, a detailed analysis of the bending response and energy dissipation is carried out for a three-point-supported layered plate on the Winker foundation. Our numerical investigations show that the hardcover, friction, and substrate have a great influence on bending response, and in particular, the friction can cause a considerable amount of energy dissipation within per loading-unloading cycle. The study is not only to predict the mechanical interactions behavior in-between of geometry, friction, elasticity, and substrate but also as a representative case to help finding some clue on the universal behaviors of interlayer slidable friction structures on soft-substrate. [ABSTRACT FROM AUTHOR]

Impulse mistuning is an alternative approach for the reduction of vibration stresses of blades and vanes. In contrast to most other approaches, it is not a direct energy dissipation approach but a mistuning based one. However, the approach is not aimed at making use of the geometrical mistuning of the structure (e.g., a blade or a vane stage). Mistuners, specially designed small bodies are placed at specific locations inside of the component, e.g., of a blade or of a vane. They do not directly dissipate enough energy to cause relevant damping like a friction or friction-impact damper, because of the small mass involved, but rather mistune the eigen frequencies of the structure using impulses (impacts). As a result, the structure absorbs less energy at the original resonance and hence answers with lower vibration amplitude. In fact, impulse mistuning is a special case of absorption--the so-called targeted energy transfer (TET) with "vibro-impact nonlinear energy sinks" (VI-NES)--with very small impact mass involved, and thus, a negligible role of dissipation while experiencing a significant amount of absorption. The energy will be transferred (or "pumped") to other resonances, sometimes outside of the primary resonance crossing and partially dissipated. We use the names "impulse mistuning" or "mistuners" instead of TET or VI-NES because (in our opinion) it better describes the physics of this special kind of absorption. In the paper, the design and validation of two impulse mistuning systems, for a blade stage and a vane cluster of a lower power turbine, are presented. [ABSTRACT FROM AUTHOR]

In this paper, the necessary and sufficient conditions for fulfilling the thermodynamic consistency of computational homogenization schemes in the framework of hierarchical multiscale theories are defined. The proposal is valid for arbitrary homogenization based multiscale procedures, including continuum and discontinuum methods in either scale. It is demonstrated that the well-known Hill-Mandel variational criterion for homogenization scheme is a necessary, but not a sufficient condition for the micro-macro thermodynamic consistency when dissipative material responses are involved at any scale. In this sense, the additional condition to be fulfilled considering that the multiscale thermodynamic consistency is established. The general case of temperature-dependent, higher order elastoplasticity is considered as theoretical framework to account for the material dissipation at micro and macro scales of observation. It is shown that the thermodynamic consistency enforces the homogenization of the nonlocal terms of the finer scale's free energy density; however, this does not lead to nonlocal gradient effects on the coarse scale. Then, the particular cases of local isothermal elastoplasticity and continuum damage are considered for the purpose of the proposed thermodynamically consistent approach for multiscale homogenizations. [ABSTRACT FROM AUTHOR]

In this paper, we consider the evolution of decaying homogeneous anisotropic turbulence without mean velocity gradients, where only the slow pressure rate of strain is nonzero. A higher degree nonlinear return-to-isotropy model has been developed for the slow pressure-strain correlation, considering anisotropies in Reynolds stress, dissipation rate, and length scale tensor. Assumption of single length scale across the flow is not sufficient, from which stems the introduction of length scale anisotropy tensor, which has been assumed to be a linear function of Reynolds stress and dissipation tensor. The present model with anisotropy in length scale shows better agreement with well-accepted experimental results and an improvement over the Sarkar and Speziale (SS) quadratic model. [ABSTRACT FROM AUTHOR]

Regions of three-dimensional separations are an inherent flow feature of the suction surface-endwall corner in axial compressors. These corner separations can cause a significant total pressure loss and reduce the compressor's efficiency. This paper uses wall-resolved LES to investigate the loss sources in a corner separation, and examines the influence of the inflow turbulence on these sources. Different subgrid scale (SGS) models are tested and the choice of model is found to be important. The σ SGS model, which performed well, is then used to perform LES of a compressor endwall flow. The time-averaged data are in good agreement with measurements. The viscous and turbulent dissipation are used to highlight the sources of loss, with the latter being dominant. The key loss sources are seen to be the 2D laminar separation bubble and trailing edge wake, and the 3D flow region near the endwall. Increasing the freestream turbulence (FST) intensity changes the suction surface boundary layer transition mode from separation induced to bypass. However, it does not significantly alter the transition location and therefore the corner separation size. Additionally, the FST does not noticeably interact with the corner separation itself, meaning that in this case the corner separation is relatively insensitive to the FST. The endwall boundary layer state is found to be significant. A laminar endwall boundary layer separates much earlier leading to a larger passage vortex. This significantly alters the endwall flow and loss. Hence, the need for accurate boundary measurements is clear. [ABSTRACT FROM AUTHOR]

A typical switched inertance buck converter includes digital valves controlling the flow of fluid to the load from the pressure supply and also from the reservoir. These valves are typically located at the same position, often packaged in the form of a single three-way valve, but also sometimes in the form of a two-way high-pressure supply valve and check valve from tank. This results in the situation where attempts to increase flow boosting performance by exploiting reflected pressure waves to draw additional fluid from tank will also tend to draw additional fluid through the valve from the high-pressure supply, causing increased energy loss at the valve. This paper presents a strategy that avoids this tradeoff by locating the tank flow valve along the length of the inertance tube such that the timing of pressure waves arriving at the tank valve can be optimized separately from those arriving at the high-pressure supply valve. A simulation study is presented, in which valve placement and inertance tube resonance are optimized for flow gain or energy efficiency, with results in both cases better than a conventional system with colocated valves. Two strategies for avoiding cavitation are also presented. [ABSTRACT FROM AUTHOR]

The tabulated premixed conditional moment closure (T-PCMC) method has been shown to provide the capability to model turbulent, premixed methane flames with detailed chemistry and reasonable runtimes in Reynolds-averaged Navier-Stokes (RANS) environment by Martin et al. (2013, "Modeling an Enclosed, Turbulent Reacting Methane Jet With the Premixed Conditional Moment Closure Method," ASME Paper No. GT2013-95092). Here, the premixed conditional moment closure (PCMC) method is extended to large eddy simulation (LES). The new model is validated with the turbulent, enclosed reacting methane backward facing step data from El Banhawy et al. (1983, "Premixed, Turbulent Combustion of a Sudden-Expansion Flow," Combust. Flame, 50, pp. 153-165). The experimental data have a rectangular test section at atmospheric pressure and temperature with an inlet velocity of 10.5 m/s and an equivalence ratio of 0.9 for two different step heights. Contours of major species, velocity, and temperature are provided. The T-PCMC model falls into the class of table lookup turbulent combustion models in which the combustion model is solved offline over a range of conditions and stored in a table that is accessed by the computational fluid dynamic (CFD) code using three controlling variables: the reaction progress variable (RPV), variance, and local scalar dissipation rate. The local scalar dissipation rate is used to account for the affects of the small-scale mixing on the reaction rates. A presumed shape beta function probability density function (PDF) is used to account for the effects of subgrid scale (SGS) turbulence on the reactions. SGS models are incorporated for the scalar dissipation and variance. The open source CFD code OpenFOAM is used with the compressible Smagorinsky LES model. Velocity, temperature, and major species are compared to the experimental data. Once validated, this low "runtime" CFD turbulent combustion model will have great utility for designing the next generation of lean premixed (LPM) gas turbine combustors. [ABSTRACT FROM AUTHOR]

Recently, patterned surfaces (elastodynamic meta-surfaces) were shown to cause mechanical wave depolarization resulting in conversion of uniaxial waves to multiaxial vibrations. Frictional oscillators loaded in multiple directions provide more tailorable damping scheme when compared to uniaxially loaded equivalents. This paper utilizes wave depolarization properties of patterned surfaces in tuning frictional damping. In particular, two-dimensional (2D) motion achieved by anisotropic wave reflection and depolarization across patterned surfaces is exerted on a simple friction oscillator; and frictional energy dissipation is studied using the homogenization theory and mechanics of a simple friction oscillator under macro and microslip conditions. The degree of depolarization is shown to control the extent of frictional shakedown (no-dissipation) zones and magnitude of energy dissipation for different incident wave frequencies and amplitudes. Transmission of the depolarized waves from the patterned surface to the friction oscillator enables higher and more uniform frictional damping for broader loading conditions. Uniform damping facilitates predictive linear dynamic models, and tuning the magnitude of damping permits efficient and robust wave attenuation, and energy transfer and localization in dynamic applications. A discussion on modeling assumptions and practical utilization of this potential is also provided. The presented potential of tuning frictional dissipation from very low to high values by simple surface patterns suggests that more sophisticated surface patterns can be designed for spatially varying frequency-dependent wave attenuation. [ABSTRACT FROM AUTHOR]

This paper proposes an ammonia-water Kalina cycle driven by low-grade waste energy released from the combustion reactions of mill's rejection which is coupled with 500 MWe coal-fired thermal power plant to quantify the additional electrical power. Energy of combustion for mill rejection is computed by combustion modeling equations. A thermodynamic property calculator for the binary mixture and a computer simulation program have been developed by MS-Excel and Visual Basic for Application (VBA) to calculate and optimize the Kalina cycle operating parameters based on thermodynamic modeling equations. Variation of key operating parameters, namely, turbine inlet pressure, mass flow rate of binary mixture, and ammonia mass fraction in mixture is studied and filters the optimum value accordingly to maximize the cycle efficiency. Technocommercial feasibility is also done through economic analysis. The results show that about 562.745 kWe power generation can be added with total plant generation for organization profit. This will enhance the combined plant efficiency from 38.559% to 38.604%. Maximum net Kalina cycle efficiency o f24.74% can be achieved with ammonia mass fraction of 0.4 at condenser back pressure of 1.957 bar and turbine inlet pressure and temperature of 20 bar and 442.40 K, respectively. Ammonia mass fraction of 0.4 is the optimum choice for 20 bar turbine inlet pressure to get maximum output after maintaining minimum 50 K degree of superheat compared to ammonia mass fraction of 0.3. The cycle peiformance at ammonia mass fraction of 0.4 is better than 0.5 due to less condenser back pressure. Kalina cycle operating with less mass flow rate performs higher cycle efficiency when dryness fraction at turbine exhaust is less than 1 and performance deteriorates at above 1. This deterioration is due to higher condenser energy loss carried away by cooling water (CW) flow. The simple payback period of this system is around 5.5 years if the system is running with 80% plant availability factor and 100% plant load factor. [ABSTRACT FROM AUTHOR]

Critical heat flux (CHF) is a key design consideration for the systems involving heat dissipation through boiling application. It dictates the maximum limit of performance of heat transfer systems. Abrupt and substantial decrease in heat transfer coefficient is an indirect indication of occurrence of the CHF, which may cause complete burnout of heat transfer surface. Unlike conventional channels, CHF correlations for microchannels are limited and associated with significant variations. In the present paper, effort has been made to develop new CHF models applicable to a frequently occurring scenario of flow boiling in microchannels. The approach combines nondimensional analysis and an energy analysis based bubble growth model at an arbitrary nucleation site. Two separate CHF correlations for refrigerants and water have been developed following a semi-empirical approach. The proposed correlations show good agreement with available experimental data. The mean errors for the refrigerant and water cases are, respectively, found to be 21% and 27% for seven and six relevant datasets. Around 77% data of the refrigerant and 60% data of water are predicted within error band of ±30%. It is also found that influence of a certain energy ratio term (gravity to surface tension, denoted as πE4) is negligible for examined water CHF conditions. [ABSTRACT FROM AUTHOR]

The energy equation for constant density fluid flow with the viscous dissipation term is often used for the governing equations of gas flow with low velocity in microchannels. If the gas is an ideal gas with low velocity, the average temperatures at the inlet and the outlet of an adiabatic channel are the same based on the first law of the thermodynamics. If the gas is a real gas with low velocity, the average temperature at the outlet is higher or lower than the average temperature at the inlet. However, the outlet temperature which is obtained by solving the energy equation for constant density fluid flow with the viscous dissipation term is higher than the inlet gas temperature, since the viscous dissipation term is always positive. This inconsistency arose from choice of the relationship between the enthalpy and temperature that resulted in neglecting the substantial derivative of pressure term in the energy equation. In this paper, the energy equation which includes the substantial derivative of pressure term is proposed to be used for the governing equation of gas flow with low velocity in microchannels. The proposed energy equation is verified by solving it numerically for flow in a circular microtube. Some physically consistent results are demonstrated. [ABSTRACT FROM AUTHOR]

Electrohydrostatic actuators are increasingly finding applications in different fields due to their numerous advantages with respect to electromechanical and conventional hydraulic systems. To understand their behavior, potentialities, limitations, and design aspects, the present paper deals with the modeling of such devices. The discussed phenomena are experimentally validated through the stationary and dynamic characterization tests of a rotary electrohydrostatic prototype. Results emphasize the role of mechanical and hydraulic dissipative effects and the fluid bulk modulus. [ABSTRACT FROM AUTHOR]

Nonviscously damped vibrating systems are characterized by dissipative mechanisms depending on the time-history of the response velocity, introduced in the physical models using convolution integrals involving hereditary kernel functions. One of the most used damping viscoelastic models is the Biot's model, whose hereditary functions are assumed to be exponential kernels. The free-motion equations of these types of nonviscous systems lead to a nonlinear eigenvalue problem enclosing certain number of the so-called nonviscous modes with nonoscillatory nature. Traditionally, the nonviscous modes (eigenvalues and eigenvectors) for nonproportional systems have been computed using the state-space approach, computationally expensive. In this paper, we address this problem developing a new method, computationally more efficient than that based on the state-space approach. It will be shown that real eigenvalues and eigenvectors of viscoelastically damped system can be obtained from a linear eigenvalue problem with the same size as the physical system. The numerical approach can even be enhanced to solve highly damped problems. The theoretical results are validated using a numerical example. [ABSTRACT FROM AUTHOR]

Impact dampers (IDs) provide an effective, economical, and retrofittable solution to the vibration problem in several engineering applications. An ID typically consists of a single or multiple masses constrained between two or more stops and attached to a primary system to be controlled. The latest developed type in the IDs family is the linear particle chain (LPC) ID. It consists of a linear arrangement of two sizes of freely moving masses, constrained by two stops. The high number of impacts among the damper masses leads to rapid energy dissipation compared to the common IDs. This paper presents an experimental study on the effectiveness of the LPC ID in reducing the vibrations of a single degree-of-freedom (SDOF) frame structure under different shock excitations. Prototypes of the LPC and conventional IDs with different geometric parameters are fabricated. The structure is excited by either an impact at the top floor or pulses at its base. The damping effect of the LPC ID is compared with that of conventional IDs. The experimental outcomes clearly show that the LPC ID can effectively reduce the response of simple structures under shock excitation. Additional investigations are conducted to examine the LPC ID sensitivity to the main damper parameters, such as the chain length, damper mass ratio, and damper clearance. [ABSTRACT FROM AUTHOR]

The energy balance equation consisting of mechanical and electrical parts of a mechatronic elevator system is studied in this paper. The total input energy is equal to the mechanical and electrical energies, where a weighting factor should he added for the mechatronic system. The calculus of variation is implemented to find the minimum input electrical energy control (M1EEC) and minimum dissipation energy control (MDEC), which are compared and found to have the same results. From numerical simulations, it is confirmed to demonstrate that the energy balance equation must contain a weighting factor in a mechatronic system. [ABSTRACT FROM AUTHOR]

When interacting with a virtual object (VO) through a haptic device, it is crucial to feedback a contact force to the human operator (HO) that displays the VO physical properties with high fidelity. The core challenge, here, is to expand the renderable range of these properties, including larger stiffness and smaller inertia, at the available sampling rate. To address this challenge, a framework entitled high-fidelity contact rendering (HFCR) has been developed in this paper. The framework consists of three main strategies: an energy-based rendering of the contact force, smooth transition (ST) between contact modes, and remaining leak dissipation (LD). The essence of these strategies is to make the VO emulate its continuous-time counterpart. This is achieved via physically meaningful modifications in the constitutive relations to suppress artificial energy leaks. The strategies are first developed for the one-dimensional (ID) canonical VO; then, generalization to the multivariable case is discussed. Renderability has been analyzed exploring different stability criteria within a unified approach. This leads to stability charts and identification of renderable range of properties in the presence and absence of the HO. The framework has been validated through simulation and various experiments. Results verify its promising aspects for various scenarios including sustained contact and sudden collision events with or without the HO. [ABSTRACT FROM AUTHOR]