Mechanical Energy Loss Research Articles

Prediction of excess pressure drop in contraction–expansion flow by molecular dynamics: Axisymmetric and planar configurations

In this paper, non-equilibrium molecular dynamics is used to simulate the flow of a dilute solution of linear molecules (Boger fluid) and a simple fluid (Lennard-Jones) through axisymmetric and planar contraction–expansion geometries. The pressure flow condition is generated by adding an external force field Fe to the equation of motion for the velocity, which is coupled to Nose–Hoover dynamics to keep the temperature constant. According to the monomer-spring model of Kremer and Grest, linear molecules are represented; and the simple fluid consists of spherical particles, which interact by means of a Lennard-Jones potential. The rheological response of the fluids indicates that the Boger fluid and the simple fluid exhibit constant viscosity in the interval (0.002⩽γ̇⩽0.5); additionally, the Boger fluid presents elastic effects under shear (first normal stress difference, N1) which are quadratic at low shear rates. In pressure flow through the expansion–contraction, results indicate that when both fluids have the same viscosity, pressure profiles P(x1) in the axisymmetric geometry reveal a higher pressure drop (ΔP) in the Boger fluid, while in the planar geometry ΔP was the same for both fluids. Results also reveal that ΔP is closely related to the extensional strain rate (ε̇) experienced by the fluid at the contraction entrance. The pressure drop is higher in the axisymmetric geometry because the change in the molecular conformation, as measured by the mean-square mass distribution tensor 〈I22〉, is 80% higher than in the planar case, resulting in an increase in the energy required to deform the molecule and the loss of mechanical energy. In the planar geometry, under the same extensional strain rate, the conformational change of the molecules in the Boger fluid at the contraction is then lower than in the axisymmetric geometry.

Computational study of the dynamics of a bileaflet mechanical heart valve in the mitral position.

A computational study of the flow-structure interaction of a bileaflet mechanical heart valve in the mitral position is presented. Flow in a simple model of the left ventricle is simulated using an immersed boundary method, and the dynamics of the valve leaflets are solved in a fully-coupled manner with the flow. Simulations are conducted for two distinct valve orientations and multiple valve hinge locations, and the performance of the valve is compared in terms of metrics associated with leaflet motion, mitral regurgitation, and mechanical energy losses through the valve. Results indicate that a bileaflet mechanical heart valve with a more centrally located hinge, and implanted in the anatomical orientation provides the best overall performance. The fluid and leaflet dynamics, as well as the clinical implications underlying these findings are discussed.

Incompressible impulsive wall impact of liquid bodies

Analytical leading-order solutions are given for various liquid bodies in translational motion that hit a plane wall in impulsive impact at constant velocity. The initial velocity field and the associated virtual masses are calculated for selected liquid bodies of uniform density. We consider 2D and 3D wedges, a cone, the semi-circle and the hemisphere. Sideways force impulses are obtained for 2D bodies. The loss of mechanical energy during impact is calculated for a 2D wedge.

Water Level Rise Upstream a Permeable Barrier in Subcritical Flow: Experiment and Modeling

This work addresses the dependence of water depth upstream a permeable barrier, h1, with discharge per unit channel width, Q/W, in sub-critical flow regime. The barrier, that extends over the entire width of the channel, is composed by smooth cylinders of small aspect ratio vertically mounted on the bottom in a staggered pattern and fully submerged in the flow. The height of the cylinders above the bottom was kept constant for all runs. Several configurations were considered by varying systematically the cylinders diameter, dv, the number of cylinders per unit area of the bed, or density, m, and the length of the barrier in the stream direction, Lv. A one-dimensional model was developed to predict the observed values of h1 and to obtain a sound basis taking into account the incidence of Q/W, m, dv and Lv. This model is based on fluid mechanics equations applied on a finite control volume for the flow in the test section, and it was deduced under simplifying assumptions physically-based. Finally, and based on the experimental results and the model predictions, the mechanical energy losses of the flow are analyzed. The main role played by a dimensionless number R, that takes into account the barrier's resistance to the flow, is highlighted.

Quantum Markovian master equation for scattering from surfaces

We propose a semi-phenomenological Markovian Master equation for describing the quantum dynamics of atom-surface scattering. It embodies the Lindblad-like structure and can describe both damping and pumping of energy between the system and the bath. It preserves positivity and correctly accounts for the vanishing of the interaction of the particle with the surface when the particle is distant from the surface. As a numerical test, we apply it to a model of an Ar atom scattered from a LiF surface, allowing for interaction only in the vertical direction. At low temperatures, we find that the quantum mechanical average energy loss is smaller than the classical energy loss. The numerical results obtained from the space dependent friction master equation are compared with numerical simulations for a discretized bath, using the multi-configurational time dependent Hartree methodology. The agreement between the two simulations is quantitative.

도서지역 소형풍력발전기 에너지 발생량 평가

This paper presents how to determine AEP(Annual Energy Production) by a small wind turbine in DuckjeokDo island. Evaluation of AEP is introduced to make a self-contained island including renewable energy sources of wind, solar, and tidal energy. To determine the AEP in DuckjeokDo island, a local wind data is analyzed using the annual wind data from Korea Institute of Energy Research firstly. After the wind data is separated in 12-direction, a mean wind speed at each direction is determined. And then, a small wind turbine power curve is selected by introducing the capacity of a small wind turbine and the energy production of the wind turbine according to each wind direction. Finally, total annual wind energy production for each small wind turbine can be evaluated using the local wind density and local energy production considering a mechanical energy loss. Throughout the analytic study, it is found that the AEP of DuckjeokDo island is about 2.02MWh/y and 3.47MWh/y per a 1kW small wind turbine installed at the altitude of 10 m and 21m, respectively.

The calculation of mechanical energy loss for incompressible steady pipe flow of homogeneous fluid

The calculation of the mechanical energy loss is one of the fundamental problems in the field of Hydraulics and Engineering Fluid Mechanics. However, for a non-uniform flow the relation between the mechanical energy loss in a volume of fluid and the kinematical and dynamical characteristics of the flow field is not clearly established. In this paper a new mechanical energy equation for the incompressible steady non-uniform pipe flow of homogeneous fluid is derived, which includes the variation of the mean turbulent kinetic energy, and the formula for the calculation of the mechanical energy transformation loss for the non-uniform flow between two cross sections is obtained based on this equation. This formula can be simplified to the Darcy-Weisbach formula for the uniform flow as widely used in Hydraulics. Furthermore, the contributions of the mechanical energy loss relative to the time averaged velocity gradient and the dissipation of the turbulent kinetic energy in the turbulent uniform pipe flow are discussed, and the contributions of the mechanical energy loss in the viscous sublayer, the buffer layer and the region above the buffer layer for the turbulent uniform flow are also analyzed.

Quantum Cherenkov radiation and noncontact friction

We present a number of arguments to demonstrate that a quantum analog of Cherenkov effect occurs when two dispersive objects are in relative motion. Specifically we show that two semi-infinite plates experience friction beyond a threshold velocity which, in their center-of-mass frame, is the phase speed of light within their medium. The loss in mechanical energy is radiated away through the plates before getting fully absorbed in the form of heat. By deriving various correlation functions inside and outside the two plates, we explicitly compute the radiation, and discuss its dependence on the reference frame.

Thermal crisis of a vorticity source with a compression shock

A study is made of the thermal crisis of a vorticity source fl owing out into a rarefi ed space with the supersonic-tosubsonic transition in the compression shock followed by the deceleration of the subsonic fl ow in a submerged space. Consideration is given to a perfect gas with a constant heat capacity and with negligible thickness of the shock and thickness of the energy-release region. Dependences of the fl ow parameters on the parameter of mechanical-energy loss, the circulation, the coordinate of the energy-release region, and on the energy-supply parameter are studied.

Interphasial energy transfer and particle dissipation in particle-laden wall turbulence

AbstractTransfer of mechanical energy between solid spherical particles and a Newtonian carrier fluid has been explored in two-way coupled direct numerical simulations of turbulent channel flow. The inertial particles have been treated as individual point particles in a Lagrangian framework and their feedback on the fluid phase has been incorporated in the Navier–Stokes equations. At sufficiently large particle response times the Reynolds shear stress and the turbulence intensities in the spanwise and wall-normal directions were attenuated whereas the velocity fluctuations were augmented in the streamwise direction. The physical mechanisms involved in the particle–fluid interactions were analysed in detail, and it was observed that the fluid transferred energy to the particles in the core region of the channel whereas the fluid received kinetic energy from the particles in the wall region. A local imbalance in the work performed by the particles on the fluid and the work exerted by the fluid on the particles was observed. This imbalance gave rise to a particle-induced energy dissipation which represents a loss of mechanical energy from the fluid–particle suspension. An independent examination of the work associated with the different directional components of the Stokes force revealed that the dominating energy transfer was associated with the streamwise component. Both the mean and fluctuating parts of the Stokes force promoted streamwise fluctuations in the near-wall region. The kinetic energy associated with the cross-sectional velocity components was damped due to work done by the particles, and the energy was dissipated rather than recovered as particle kinetic energy. Componentwise scatter plots of the instantaneous velocity versus the instantaneous slip-velocity provided further insight into the energy transfer mechanisms, and the observed modulations of the flow field could thereby be explained.

Analysis of condenser shell side pressure drop based on the mechanical energy loss

The condenser performance is strongly affected by the tube arrangement. The steam pressure drop in the tube bundle influences the condenser back pressure, which is an important indicator of the condenser performance used to compare different condenser tube arrangements. The condenser shell side pressure drop is studied here using the mechanical energy loss of the steam flow in the condensers. The mechanical energy loss is due to the flow resistance of the tube bundle and the steam condensation. Three typical tube arrangements are analyzed numerically. The results show that a higher condenser shell side pressure drop for different tube arrangements always corresponds to a larger mechanical energy loss. The mechanical energy loss is mainly in the periphery of the tube bundle, indicating that the flow pattern and the mechanical energy losses are markedly determined by the tube bundle profile. The condenser shell side pressure drop can be reduced by reducing the total mechanical energy loss when the steam enters the tube bundle more uniformly. Thus, a well designed tube arrangement will reduce the mechanical energy loss, and also the shell side pressure drop.

Experimental Analysis of 1-3 Piezocomposites for High-Intensity Focused Ultrasound Transducer Applications

Piezocomposites with 1-3 connectivity have been extensively used in medical imaging transducers and high-intensity focused ultrasound transducers, but most studies of 1-3 piezocomposites address medical imaging applications. The purpose of this study was to completely investigate 1-3 composites specifically for high-power ultrasonic transducer applications via a series of experimental analyses. PZT4-epoxy composite focused transducers with various aspect ratios and volume fractions were constructed in-house for the evaluation of the coupling factor, dielectric loss tangent, quality factor, bandwidth, acoustic impedance, and electroacoustic efficiency. The experimental analyses demonstrated that although the coupling factor of composite transducers was higher than that of the ceramic transducer, the composite transducers had a lower efficiency due to the high dielectric loss and high mechanical energy loss of the composites. In addition, the bandwidth and acoustic impedance of composite transducers were superior to the ceramic transducer. For the composite transducers, the efficiency and acoustic impedance were inversely proportional to the aspect ratio and linearly proportional to the volume fraction. The coupling of inter pillars that are too close to each other could cause a significant decrease in the efficiency of the composite transducer. With an appropriate design in terms of the aspect ratio, volume fraction, and PZT-pillar spacing, a high-efficiency composite high-intensity focused ultrasound transducer can be achieved.

Effect of the working liquid compressibility on the picture of volumetric and mechanical losses in a high pressure displacement pump used in a hydrostatic drive part ii mechanical losses in a pump

ABSTRACT Working liquid compressibility may considerably change the values and proportions of coefficients of the volumetric and mechanical energy losses in the displacement pump used in a hydrostatic drive system. This effect can be particularly seen in the operation under high pressure and also in the system, where aeration of the working liquid can occur. In the Part II the mathematical model is presented of the torque of mechanical losses in the pump and its laboratory verification. Conclusions are drawn regarding the effect of working liquid compressibility on the mechanical and volumetric losses in the pump.

High Transvalvular Gradients Across a Prosthetic Valve in the Mitral Position: Not Ignoring the Bigger Picture

High Transvalvular Gradients Across a Prosthetic Valve in the Mitral Position: Not Ignoring the Bigger Picture

Mechanical energy losses in plastically deformed and electron plus neutron irradiated high purity single crystalline molybdenum at elevated temperatures

AbstractMechanical spectroscopy (MS) and transmission electron microscopy (TEM) studies have been performed in plastically deformed and electron plus neutron irradiated high purity single crystalline molybdenum, oriented for single slip, in order to study the dislocation dynamics in the temperature range within one third of the melting temperature. A damping peak related to the interaction of dislocation lines with both prismatic loops and tangles of dislocations was found. The peak temperature ranges between 900 and 1050 K, for an oscillating frequency of about 1 Hz.

Dynamic Analysis of the Nonel Rotary Piezoelectric Generator

The method to transfer energy by less-contact magnetic force can decrease mechanical energy loss comparing with that by mechanical contact. In this paper, a novel piezoelectric rotary generator was designed based on the theory of the transition from less-contact magnetic force to the mechanical energy. ANSYS software was used to calculate the driving forces for the piezoelectric cantilever beam from the rotary wheel rotate in the different positions. The periodic driving force for the piezoelectric cantilever beam was obtained by the methods of fitting and Fourier transform. Laws of dynamic performance for piezoelectric cantilever beam were obtained by dynamic analysis. The results show that the low-frequency and variable rotational mechanical energy in the natural environment can be harvested by this novel rotary piezoelectric generator.

Numerical investigation on the mixing process in a steam ejector with different nozzle structures

The effects of different nozzle structures on the performance of a steam ejector have been investigated numerically with the computational fluid dynamics (CFD) technique. The performance of the steam ejectors with five different nozzle structures, namely, conical, elliptical, square, rectangular and cross-shaped nozzles, have been compared under the same conditions. It is found that, compared with the CFD results of the ejector equipped with the conical nozzle, the entrainment ratio (ER) and critical back pressure (CBP) of the rectangular nozzle is 7.1% and 21.3% lower respectively; the ER and CBP of the elliptical nozzle is 7.9% and 21.3% lower respectively; the square nozzle has improved the ER by 2.0% and decreased the CBP by 2.1%; the ER and CBP of the ejector utilizing cross-shaped nozzle is 9.1% higher and 6.4% respectively lower. Based on the simulation results of the streamwise vortex and spanwise vortex distributions in the mixing chamber and the internal energy variations along the streamwise distance, the characteristics of the mixing process and the main factors accounting for the ejector performance change are clarified. The ER increase can be achieved by efficient mixing due to the interactions between the streamwise vortex and the spanwise vortex. The streamwise vortex helps to deform and rupture the spanwise vortex which has greater strength. Collides of the vortices to the mixing chamber wall at early stage would increase mechanical energy loss and reduce “effective area” for secondary flow to pass through, resulting in great decrease of the ER and CBP. This scenario should be avoided in the design of nozzles.

Dynamic analysis of impact in swing-through crutch gait using impulsive and continuous contact models

The dynamics associated with the impact of the crutch with the ground is an important topic of research, since this is known to be the main cause of mechanical energy loss during swing-through gait. In this work, a multibody system representing a subject walking with crutches is used to investigate the behavior of two different contact models, impulsive and continuous, used for impact analysis. In the impulsive (discrete) approach, the impact interval is considered to be negligible and, therefore, the system configuration is constant. The postimpact state is directly obtained from the preimpact one through algebraic equations. In the continuous approach, the stiffness and dissipation characteristics of the contact surfaces are modeled through nonlinear springs and dampers. The equations of motion are integrated during the impact time interval to obtain the postimpact state, which, in principle, can differ from that obtained by means of the impulsive approach. Although both approaches have been widely used in the field of biomechanics, we have not found any comparative study in the existing literature justifying the model chosen for impact analysis. In this work, we present detailed numerical results and discussions to investigate several dynamic and energetic features associated with crutch impact. Based on the results, we compare the implications of using one contact model or the other.

Effect of the working liquid compressibility on the picture of volumetric and mechanical losses in a high pressure displacement pump used in a hydrostatic drive

Effect of the working liquid compressibility on the picture of volumetric and mechanical losses in a high pressure displacement pump used in a hydrostatic drive Working liquid compressibility may considerably change the values and proportions of coefficients of volumetric and mechanical energy losses in the displacement pump used in a hydrostatic drive system. This effect can be particularly seen in the operation under high pressure and also in the system, where aeration of the working liquid can occur. In the Part I a diagram is presented, proposed by the author, of power increase in a hydrostatic drive system (hydraulic motor, pump) opposite to the direction of power flow, replacing the Sankey diagram of power decrease in the direction of power flow. Mathematical model is presented of volumetric losses in the pump and its laboratory verification.

Elastic deformation and energy loss of flapping fly wings

During flight, the wings of many insects undergo considerable shape changes in spanwise and chordwise directions. We determined the origin of spanwise wing deformation by combining measurements on segmental wing stiffness of the blowfly Calliphora vicina in the ventral and dorsal directions with numerical modelling of instantaneous aerodynamic and inertial forces within the stroke cycle using a two-dimensional unsteady blade elementary approach. We completed this approach by an experimental study on the wing's rotational axis during stroke reversal. The wing's local flexural stiffness ranges from 30 to 40 nN m(2) near the root, whereas the distal wing parts are highly compliant (0.6 to 2.2 nN m(2)). Local bending moments during wing flapping peak near the wing root at the beginning of each half stroke due to both aerodynamic and inertial forces, producing a maximum wing tip deflection of up to 46 deg. Blowfly wings store up to 2.30 μJ elastic potential energy that converts into a mean wing deformation power of 27.3 μW. This value equates to approximately 5.9 and 2.3% of the inertial and aerodynamic power requirements for flight in this animal, respectively. Wing elasticity measurements suggest that approximately 20% or 0.46 μJ of elastic potential energy cannot be recovered within each half stroke. Local strain energy increases from tip to root, matching the distribution of the wing's elastic protein resilin, whereas local strain energy density varies little in the spanwise direction. This study demonstrates a source of mechanical energy loss in fly flight owing to spanwise wing bending at the stroke reversals, even in cases in which aerodynamic power exceeds inertial power. Despite lower stiffness estimates, our findings are widely consistent with previous stiffness measurements on insect wings but highlight the relationship between local flexural stiffness, wing deformation power and energy expenditure in flapping insect wings.