Mechanical Energy Loss Research Articles

The Internal Seiches in Gullmar Fjord. Part II: Contribution to Basin Water Mixing

The mixing in the basin water (the water below sill level) of Gullmar Fjord has been investigated with the main focus on the contribution from internal seiches. A companion paper reports evidence for dissipation of internal seiche energy in the basin water after near-critical reflection from the bottom. In the present paper the magnitude and variation of basin water mixing is investigated, using the budget method. The results are related to variations of three energy sources, namely (i) the internal seiches, (ii) the internal tides, and (iii) the internal waves generated by the external seiche. The mixing efficiency, defined as the irreversible work against buoyancy forces due to mixing divided by the total mechanical energy loss from the sources mentioned above, is about 7%, similar to results obtained for other fjords. Large variations in mixing are shown to be related to large variations of the energy sources. The internal seiches are found to be important for the mixing, with a contribution that is 144% of the internal tide contribution during the most energetic period and 92% on average over the investigated periods. Including contributions from the external seiche, the wind forcing is responsible for 61% of the basin water mixing, while tidal forcing is responsible for 39%.

A new method for studying thermal desorption of hydrogen from metals based on internal friction technique

Many hydrogenated pure metals and industrial alloys with FCC lattices show a distinct internal friction peak above room temperature caused by the thermal desorption of hydrogen. Based on these observations, a new method for studying the hydrogen diffusivity and the interaction of hydrogen with lattice defects is proposed for the temperature range of 250–500 K. The desorption origin of the peak was studied in detail in hydrogen-charged Inconel 600 alloys with different carbon contents. The peak was shown to possess transient and non-relaxation nature. In some cases, a fine structure of the peak caused by hydrogen traps can be observed. A theoretical model of the thermal desorption effects on the losses of mechanical energy, i.e., internal friction, in metals is developed.

Modeling driving force in processes of ultrafiltration of non-Newtonian fluids

A model for longitudinal pressure profile has been developed. Mechanical energy balance is the core of the model. The model, developed for plate-and-frame configuration of the unit, is based on the following conceptual frameworks and assumptions: the flow is to be isothermal, laminar, incompressible and steady-state; fluid manifests time-independent non-Newtonian behavior viz.: field of apparent viscosity has non-isotropic configuration; deformation of velocity and shear stress profiles is correlated with rheological properties through index in the power law. The paper covers pseudoplastic and dilatant flow. The developed model describes mechanical energy losses, transmembrane energy flux and fluxes passing through entry and exit control planes and gives a calculation of these variables along the membrane surface. The model permits the analysis of the influence of rheological properties of the fluid, geometry parameters of the channel and process variables on the longitudinal pressure profile. The submitted solution does not contain digital integration and can be segmented into a more complicated algorithm. The paper includes the algorithm, the array of calculated data and graphic visualization.

Optimum take-off techniques and muscle design for long jump.

A two-segment model based on Alexander (1990; Phil. Trans. R. Soc. Lond. B 329, 3-10) was used to investigate the action of knee extensor muscles during long jumps. A more realistic representation of the muscle and tendon properties than implemented previously was necessary to demonstrate the advantages of eccentric force enhancement and non-linear tendon properties. During the take-off phase of the long jump, highly stretched leg extensor muscles are able to generate the required vertical momentum. Thereby, serially arranged elastic structures may increase the duration of muscle lengthening and dissipative operation, resulting in an enhanced force generation of the muscle-tendon complex. To obtain maximum performance, athletes run at maximum speed and have a net loss in mechanical energy during the take-off phase. The positive work done by the concentrically operating muscle is clearly less than the work done by the surrounding system on the muscle during the eccentric phase. Jumping performance was insensitive to changes in tendon compliance and muscle speed, but was greatly influenced by muscle strength and eccentric force enhancement. In agreement with a variety of experimental jumping performances, the optimal jumping technique (angle of attack) was insensitive to the approach speed and to muscle properties (muscle mass, the ratio of muscle fibre to tendon cross-sectional area, relative length of fibres and tendon). The muscle properties also restrict the predicted range of the angle of the velocity vector at take-off.

Effect of drag and frictional losses on the hydrodynamics of gas‐lift reactors

The purpose of this communication is to examine several assumptions concerning the drag and frictional losses in gas-lift reactors that are common to the Saez et al. (1998) and Marquez et al. (1999) models, and to some other published models. These assumptions are as follows. (1) The friction factor in the downcomer must be adjusted upward with respect to correlations for fully developed, single-phase flow in pipes in order to account for developing flow. (2) Mechanical energy losses in the gas/liquid separator and the straightening vanes can be neglected. (3) Frictional losses in the riser are adequately described by the correlation of Akita et al. (1988), which explicitly accounts for two-phase flow.

Mechanical relaxation spectroscopy of three triepoxide-based polymers

Three network structure polymers formed by the chemical reactions of a triepoxide with aniline, 3-chloroaniline,and 4-chloroaniline were prepared and their shear modulus relaxation spectra studied over the 10−3- to 1-Hz range and temperatures up to their rubber modulus region. The decrease in the unrelaxed modulus with increase in temperature is found to be a reflection of both an increase in volume, and a decrease in the relaxed modulus of the sub-Tg relaxations process. It is quantitatively shown that the increase in the rubber modulus with increase in temperature above Tg is predominantly due to an increase in the entropy and not to a decrease in the number of cross-links density on thermal expansion. The unrelaxed modulus remained unaffected by the change in the overall size of the phenyl groups of the amines and of the steric hindrance to their rotations caused by the proximity of the chlorine atom to the cross-linking N-atom in the network structure, but the rubber modulus was effected. The shear modulus spectra could be fitted to a stretched exponential decay function with a temperature-independent stretch parameter of 0.25 for two polymers and 0.22 for one. The time–temperature superposition of the spectra did not yield a master curve, and a vertical displacement of the data also failed to produce it. This was more clearly demonstrated by the spectra of the mechanical loss tangent. After considering the various contributions to the shear modulus, it was concluded that deviations from the time–temperature superposition of the spectra are intrinsic to these polymers and arise from the change in the viscoelastic functions for segmental dynamics on change in the temperature such that the overall distribution of relaxation times remains unaffected. The mechanical loss tangent of the three polymers is found to be higher than that of polycarbonate at ambient temperature, implying a higher loss of mechanical energy before these polymers may fracture. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3071–3083, 1999

Analysis of Heat, Mass, and Momentum Transfer in the Rain Zone of Counterflow Cooling Towers

The rate of heat, mass, and momentum transfer in the rain zone of three counterflow cooling tower geometries is analyzed using simplifying assumptions and numerical integration. The objective of the analysis is to generate equations for use in a one-dimensional mathematical cooling tower performance evaluations. Droplet deformation is taken into account and momentum transfer is calculated from the air flow’s mechanical energy loss, caused by air-droplet interaction. A comparison of dimensionless semi-empirical equations and experimental data demonstrates the method’s capability to predict the pressure drop in a counterflow rain zone.

Oscillations and mechanical energy losses in a hollow truncated piezoceramic cone

Oscillations and mechanical energy losses in a hollow truncated piezoceramic cone

Experimental analysis of fluid mechanical energy losses in aortic valve stenosis: Importance of pressure recovery

Current methods for assessing the severity of aortic stenosis depend primarily on measures of maximum systolic pressure drop at the aortic valve orifice and related calculations such as valve area. It is becoming increasingly obvious, however, that the impact of the obstruction on the left ventricle is equally important in assessing its severity and could potentially be influenced by geometric factors of the valve, causing variable degrees of downstream pressure recovery. The goal of this study was to develop a method for measuring fluid mechanical energy losses in aortic stenosis that could then be directly related to the hemodynamic load placed on the left ventricle. A control volume form of conservation of energy was theoretically analyzed and modified for application to aortic valve stenosis measurements. In vitro physiological pulsatile flow experiments were conducted with different types of aortic stenosis models, including a venturi meter, a nozzle, and 21-mm Medtronic-Hall tilting disc and St. Jude bileaflet mechanical valves. The energy loss created by each model was measured for a wide range of experimental conditions, simulating physiological variation. In all cases, there was more energy lost for the nozzle (mean = 0.27 J) than for any other model for a given stroke volume. The two prosthetic valves generated approximately the same energy losses (mean = 0.18 J), which were not statistically different, whereas the venturi meter had the lowest energy loss for all conditions (mean = 0.037 J). Energy loss correlated poorly with orifice pressure drop (r2 = 0.34) but correlated well with recovered pressure drop (r2 = 0.94). However, when the valves were considered separately, orifice and recovered pressure drop were both strongly correlated with energy loss (r2 = 0.99, 0.96). The results show that recovered pressure drop, not orifice pressure drop, is directly related to the energy loss that determines pump work and therefore is a more accurate measure of the hemodynamic significance of aortic stenosis.

Numerical study of unsteady, thermally stratified flow in an idealized thermoacoustic stack

A computational model for the simulation of unsteady, thermally stratified flow within an idealized thermoacoustic stack is developed. The model is based on a vorticity-based formulation of the low-Mach-number conservation equations. The numerical scheme combines fast Poisson solvers with domain decomposition/boundary Green’s-function techniques. The model is applied to analyze the response of the stack to imposed, finite-amplitude acoustic oscillations. Computed results are used to visualize the essential features of the vorticity field and temperature distribution, quantify the heat transfer between the gas and plates, and analyze thermal and mechanical energy losses. [The work of A.S.W. and O.M.K. is supported by the Office of Naval Research. R.K. is partially supported by Deutsche Forschungsgemeinschaft (DFG).]

The mechanical energy loss in stressed and -irradiated polycrystalline aluminium

The mechanical energy loss in two very pure (99.9999%) deformed aluminium samples (strain, 2%; stress, 12.6 MPa) was studied using the pulse-echo technique at 10 MHz frequency. These two samples were given several -irradiation doses (up to ) at room temperature and liquid-nitrogen temperature. Two relaxation peaks and , dislocation relaxation peaks, were found at temperatures from 179 to 169 K for peak and from 221 to 210 K for peak , having relaxation strengths of - and - , respectively. Both the peak heights and the peak temperatures decrease as the -irradiation dose increases. These variations are explained in terms of the kink-pair formation model.

Mechanical and Dielectric Energy Loss Related to Viscous Motion and Freezing of Domain Walls

Three dielectric loss (D) and/or three mechanical loss (Q -1 ) peaks (P1,P2,P3) and corresponding susceptibilities for ferroelectric KDP and TGS, and ferroelastic LNPP crystal and Cu-Al-Zn-Ni alloy have been investigated in the kHz range. P 1 and P 2 almost overlap for first order phase transitions. P i , a very narrow peak, is attributed to the dynamic domains due to fluctuations near Tc. P2 is recognized to be related to domain walls (DWs). The formulas of Q -1 and D caused by the viscous motion of DWs are derived, being fairly coincident with the experimental data of P2. The viscous coefficient, pinning force constant of DW and the spontaneous shear strain have been calculated for Cu-Al-Zn-Ni. The susceptibility, e' or ΔJ/J, always shows a high plateau below Tc and drops down rapidly nearly consistent with the low temperature side of P3 peak for poly-domain TGS, KDP and Cu-Al-Zn-Ni. P3 is thought to originate from the freezing of DWs of high density due to a collective pinning of randomly distributed defects, similar to the pinned-vortex glass model suggested for high Tc superconductors.

Long-wavelength acoustic-mode-enhanced electron emission from Se and Te donors in silicon.

An enhancement of the thermal emission rates from Se and Te double donors in silicon was observed by applying external vibrational excitation in the MHz frequency range. The excitation was performed either by resonant sample vibrations at frequencies of the lowest eigenmodes or by Lamb waves in a plate. Emission rates were measured by using both deep-level transient spectroscopy and single-shot capacitance techniques. Possible explanations for the observed enhancement of the emission rates are either thermal disturbances due to thermoelastic losses of mechanical energy or nonlinear effects in conjunction with oscillating stresses in solids. Our data are inconsistent with possible thermal disturbances. A tentative model is therefore proposed, suggesting that changes in the equilibrium position of impurity atoms exhibiting low-frequency oscillations yield enhanced emission rates. These changes depend upon the local surrounding of the impurity atoms and ``hardness'' of the interatomic interaction rather than the strength. Vibrational perturbations as discussed in this paper may be an effective tool to obtain new information on defects in solids.

Theoretical studies of sonoluminescence radiation: Radiative transfer and parametric dependence.

We present results for sonoluminescent (SL) radiation from a strongly modulated air bubble in water. The SL pulse is due to high temperatures in the bubble that are produced by the collapse of a shock wave. The dependence of SL radiation on acoustic pressure and initial bubble size is discussed, as well as the inclusion of various mechanical energy loss mechanisms. We find that the inclusion of loss terms, especially due to radiation, is necessary in order to understand the bubble dynamics, the resulting SL pulse, and some recent experiments.

Viscoelastic properties of short carbon fiber thermoplastic (SBS) elastomer composites

AbstractThe determination of viscoelastic property variation in short fiber‐reinforced composites, as a function of strain, temperature, and frequency, constitutes a useful tool when the existence or the strength of matrix–fiber interfaces are to be examined. In this work, these properties are studied in thermoplastic elastomer matrix materials (SBS) filled with commercial carbon fiber (PAN), oxidated, and subsequently treated with diazide, which generates SO2N3 groups on the fiber surface, theoretically capable of chemical reaction with the polymeric chain. For the composite containing diazide‐treated oxidated fiber, certain phenomena have been proven to occur, such as lesser storing modulus losses in case of increasing strain, greater equivalent interfacial thickness values, and higher mechanical energy loss values than those of composite containing oxidated fiber. An increase in glass transition temperature and apparent activation energy of the relaxation process, with respect to composite‐containing commercial fiber, are also observed, which, altogether, allow for the statement that new matrix–fiber bonds are generated through the sulfonyl azide group, conferring greater strength to the interface, although it is less stiff than the one formed with oxidated fiber. Finally, the experimental results are in agreement with those obtained from Huet's rheological model. © 1995 John Wiley & Sons, Inc.

Dynamic properties of short fiber–EPDM matrix composites as a function of strain amplitude

AbstractThe dynamic properties of composite materials consisting of an ethylene–propylene rubber matrix (EPDM) and short polyester polyethylene‐terephthalate (PET) fiber vary with dynamic stress amplitude applied to the material. These variations support the statement that fiber treatment with 1,4‐carboxy‐sulphonyl‐diazide, which acts as a bridge between the fiber and the matrix and hence enhances the strength of the interface enabling it to resist greater strain applied to the composite and, as a consequence, yielding greater retention values of the storage modulus, measured longitudinally to preferential fiber orientation, E′L. By means of transversal measurements of the storage modulus, E′T, of these materials it is possible to determine a parameter b, which eventually indicates the degree of matrix–fiber bonding and which is consistently higher for materials filled with surface‐treated fiber. This enhanced phase adhesion is further confirmed by higher equivalent interfacial thickness values, ΔR, which, in addition, vary less with increasing dynamic strain amplitude. Finally dissipated energy variation or mechanical energy loss, Eloss, is studied as a function of fiber content and strain amplitude. Experimental findings show Eloss to increase with fiber content and strain amplitude, when measured at constant strain amplitude ϵ0, and to yield higher values for treated fiber samples. © 1994 John Wiley & Sons, Inc.

Hydrodynamics of swirling flow in a circular tube with sudden increase in cross-section and of the flow through a borda mouthpiece

By applying the mass, momentum, and angular momentum conservation laws and the maximum flow rate principle to swirling, effectively inviscid, incompressible flows in a circular tube with a sudden expansion and in direct-flow and reversed-flow Borda mouthpieces the dependence of the flow rate coefficient and mechanical energy losses on the radius ratio and nondimensional circulation is obtained. Several calculating approaches with potential and helical motion are introduced and investigated. In the case of helical motion, as the swirl decreases the axial core of the flow is found to close with a sudden change of the flow parameters.

The effect of a diazide as adhesion agent on composite materials consisting of an elastomeric matrix and short polyester fiber

AbstractThis research reports on the effect of a diazide, i.e., 1.4‐carboxybenzenesulfonyl diazide, which had been incorporated onto fiber by a chemical reaction, on the formation of an interphase between the elastomeric SBR matrix and polyester fiber. The existence of the interphase becomes manifest not only in the variation of the mechanical properties, but especially through swelling measurements and dynamic properties. The effect of the new system based on diazide is similar to that obtained from a conventional adhesive system, but presents certain benefits, such as a shorter curing time due to absence of resin, enhanced tensile strength, and the formation of a more flexible interphase, which entails lesser heat generation due to mechanical energy loss. © 1993 John Wiley & Sons, Inc.

Electrical equivalent circuit parameters for montmorillonite clay film-coated quartz crystal oscillators in contact with air, moisture and electrolyte solutions

The piezoelectric admittance measurements of the quartz crystal oscillators with and without a montmorillonite clay coating have been carried out over the frequency range covering the area of the resonant frequency of each oscillator system. These oscillators are in contact with air, moisture and Na 2SO 4 aqueous media of various concentrations (0.01–1.0 M). The results have been represented in the form of conductance and susceptance spectra, ie plots of the real and imaginary components of the admittance vs. frequency. By use of electrical equivalent circuit model conventionally proposed for a piezoelectric quartz crystal, the relevant circuit parameters resistance R, inductance L, capacitance C and static capacitance C o, have been evaluated, especially as a function of the concentration of Na 2SO 4. R, C, L and C 0correspond to a loss in the crystal mechanical energy, a mechanical elasticity of the vibrating body, a measure of the vibrating mass and a capacitance between the two parallel-plate metal electrodes on the quartz surfaces, respectively. R was found to depend largely on the kind and property of the medium in contact with the oscillator. The values of R obtained for the oscillator with the clay coating were larger in lower concentrations of Na 2SO 4 electrolyte than in higher ones, in contrast to the case of the oscillator without the clay coating where R increases with the electrolyte concentration as expected from a hitherto proposed theory. These results have been explained on the basis of the electrolyte concentration-dependent swelling of the clay film as well as Derjaguin—Landau—Verwey—Overbeek theory being proposed for the interaction forces between colloidal particles. It is demonstrated that in addition to the conventional measurements of the resonant frequency of the quartz oscillator, the estimation of its electrical equivalent circuit parameters provides information concerning the chemical and physical processes on the oscillator.

Application of high temperature superconductors on levitation bearings, torque transmissions and vibration dampers

The transfer of momentum between a permanent magnet and a type II superconductor without mutual physical contact is the central theme behind many mechanical applications of the new class of high-temperature ceramic superconductors. The properties of this momentum transfer and its applications were studied in a series of experiments as a proof of principle. The authors discuss the application of the force between permanent magnets and high-temperature superconductors (HTSs) in three different mechanical devices-a torque coupler, a magnetic bearing, and a vibration damper-based on the following two broad features of this forces. (1) A restoring force is generated by a piece of HTS material to oppose the motion of a magnet if and only if the magnet moves in such a way as to produce a change in the magnetic field in the space occupied by HTS material. (2) Back and forth cyclic motion of a magnet relative to a piece of HTS in the vicinity experiences hysteretic forces with loss of mechanical energy as a result. All the studies refer to melt-textured HTS material.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>