Reduction Of Kinetic Energy Research Articles

A diagnostic study on the energetics aspects of hiatus in the advance of southwest monsoon

Advance of southwest monsoon, after its onset, often gets stalled for a week or more causing concern to the farmers and other community whose activities are weather dependent. The present study on the energetics aspect of hiatus in the advance of southwest monsoon over India aims at understanding the dynamical reasons for this. Nine cases of hiatus of duration more than 10 days during 1982-2006 have been selected. For each hiatus case, different energy terms, their generation and conversion among different terms have been computed during the hiatus period and also during the pre-hiatus pentad over a limited region between 65° E to 90° E, 5° N to 30° N. These computations are based on NCEP 2.5° × 2.5° re-analysed daily composite data during different hiatus period and during corresponding pre-hiatus pentad.
 
 From this study it is found that :
 
 (i) In most of the cases there is a reduction in the generation of zonal available potential energy [G(AZ)] during hiatus period compared to pre-hiatus pentad.
 
 (ii) Drop in the conversion from zonal available potential energy to zonal kinetic energy [C(AZ, KZ)] during hiatus period has been observed in most of the cases.
 
 (iii) In most of the cases there is a reduction in zonal kinetic energy (KZ) and in eddy kinetic energy (KE) during hiatus period compared to pre-hiatus pentad.

Measurements of Secondary Losses in a Turbine Cascade With the Implementation of Nonaxisymmetric Endwall Contouring

An approach to endwall contouring has been developed with the goal of reducing secondary losses in highly loaded axial flow turbines. The present paper describes an experimental assessment of the performance of the contouring approach implemented in a low-speed linear cascade test facility. The study examines the secondary flows of a cascade composed of Pratt & Whitney PAKB airfoils. This airfoil has been used extensively in low-pressure turbine research, and the present work adds intrapassage pressure and velocity measurements to the existing database. The cascade was tested at design incidence and at an inlet Reynolds number of 126,000 based on inlet midspan velocity and axial chord. Quantitative results include seven-hole pneumatic probe pressure measurements downstream of the cascade to assess blade row losses and detailed seven-hole probe measurements within the blade passage to track the progression of flow structures. Qualitative results take the form of oil surface flow visualization on the endwall and blade suction surface. The application of endwall contouring resulted in lower secondary losses and a reduction in secondary kinetic energy associated with pitchwise flow near the endwall and spanwise flow up the suction surface within the blade passage. The mechanism of loss reduction is discussed in regard to the reduction in secondary kinetic energy.

Electronic correlations in the iron pnictides

In correlated metals derived from Mott insulators, the motion of an electron is impeded by Coulomb repulsion due to other electrons. This phenomenon causes a substantial reduction in the electron's kinetic energy leading to remarkable experimental manifestations in optical spectroscopy. The high-Tc superconducting cuprates are perhaps the most studied examples of such correlated metals. The occurrence of high-Tc superconductivity in the iron pnictides puts a spotlight on the relevance of correlation effects in these materials. Here we present an infrared and optical study on single crystals of the iron pnictide superconductor LaFePO. We find clear evidence of electronic correlations in metallic LaFePO with the kinetic energy of the electrons reduced to half of that predicted by band theory of nearly free electrons. Hallmarks of strong electronic many-body effects reported here are important because the iron pnictides expose a new pathway towards a correlated electron state that does not explicitly involve the Mott transition.

A heat engine based moist convection parametrization for Jupiter

We have developed a parametrization of Jovian moist convection based on a heat engine model of moist convection. In comparison to other moist convection schemes, this framework allows the computation of the total available convective energy TCAPE and the corresponding mass flux M as dynamic variables from the mean atmospheric state. The effects of this parametrization have been investigated both analytically and numerically. In agreement with previous numerical experiments and observations, the inclusion of moist convection leads to heat and water vapor transport from the water condensation level into higher altitudes. The time development of the modeled convective events was found to be strongly influenced by a rapid reduction of kinetic energy and a subsequent lowering of the cumulus tower's top in response to convective heating. We have tested the sensitivity of the scheme to different variations in the fractional cloud coverage and under the inclusion of external radiative forcing towards a stable/unstable temperature profile. While the time development of convective events differs in response to these variations, the general moist convective heating and moistening of the upper troposphere was a robust feature observed in all experiments.

Vertical electrical conduction in pentacene polycrystalline thin films mediated by Au-induced gap states at grain boundaries

Vertical electrical conduction in Au/(polycrystal-line pentacene)/Al diode structures and the influence of the kinetic energy of incident Au atoms on the conduction property have been comprehensively studied using current–voltage–temperature (I–V–T) measurements, ultraviolet photoelectron spectroscopy (UPS), atomic-force-microscope (AFM) current imaging, etc. In the I–V characteristics, a symmetrical ohmic current component appeared when a low voltage was applied, and a super-linear one appeared when a high positive voltage was applied to Au. The component in the high-forward-voltage region was concluded to be a thermionic emission of holes from Au with a 0.23-eV injection barrier, which is the normal hole conduction through the highest occupied molecular orbital of pentacene. On the other hand, the ohmic component was concluded to be a metal-like electron transport through high-density gap states at grain boundaries which were induced by the Au penetration into pentacene. UPS and I–V–T measurements clearly indicated the generation of the gap states and the enhancement of their density by the reduction of Au kinetic energy. For vertical-type devices with polycrystalline organic films, the ohmic conduction through the grain boundary will increase the leakage current. On the contrary, it possibly enhances the carrier injection in lateral-type transistors in the case of top-contact configuration.

RANS Analyses of Turbofan Nozzles With Internal Wedge Deflectors for Noise Reduction

Computational fluid dynamics (CFD) was used to evaluate the flow field and thrust performance of a promising concept for reducing the noise at take-off of dual-stream turbofan nozzles. The concept, offset stream technology, reduces the jet noise observed on the ground by diverting (offsetting) a portion of the fan flow below the core flow, thickening and lengthening this layer between the high-velocity core flow and the ground observers. In this study a wedge placed in the internal fan stream is used as the diverter. Wind, a Reynolds averaged Navier–Stokes (RANS) code, was used to analyze the flow field of the exhaust plume and to calculate nozzle performance. Results showed that the wedge diverts all of the fan flow to the lower side of the nozzle, and the turbulent kinetic energy on the observer side of the nozzle is reduced. This reduction in turbulent kinetic energy should correspond to a reduction in noise. However, because all of the fan flow is diverted, the upper portion of the core flow is exposed to the freestream, and the turbulent kinetic energy on the upper side of the nozzle is increased, creating an unintended noise source. The blockage due to the wedge reduces the fan mass flow proportional to its blockage, and the overall thrust is consequently reduced. The CFD predictions are in very good agreement with experimental flow field data, demonstrating that RANS CFD can accurately predict the velocity and turbulent kinetic energy fields. While this initial design of a large scale wedge nozzle did not meet noise reduction or thrust goals, this study identified areas for improvement and demonstrated that RANS CFD can be used to improve the concept.

Application of Al 2O 3-based polyimide composite thick films to integrated substrates using aerosol deposition method

Al 2O 3-based polyimide composite thick films were successfully fabricated with reduction of residual stress and improvement in plasticity for integrated substrates at room temperature by aerosol deposition method. Scanning electron microscopy and energy dispersive spectroscopy mappings exhibited a high content of Al 2O 3 evenly distributed in the composite thick films. The relative dielectric permittivity and loss tangent of Al 2O 3-based polyimide composite thick films were 7.6 and 0.007, respectively. There was almost no change in the crystallite size of Al 2O 3-based polyimide composite thick films compared with that of starting powder due to the reduction of kinetic energy by polyimide during collision on the substrates. Moreover, it was confirmed that the residual stress of Al 2O 3-based polyimide composite thick films remarkably decreased compared with that of Al 2O 3 thick films.

The effects of induced dissipative small-scale motions and mixing on optical distortion in a plane shear layer

Optical distortion through a plane shear layer between two uniform streams of unequal temperatures is investigated using imaging of scalar mixing by planar laser-induced fluorescence (LIF). Simultaneous fluorescence intensity measurements of disodium fluorescein and rhodamine B (the fluorescence of the latter is temperature dependent) are used to extract the temperature distribution within the plane of a laser sheet. This planar imaging technique allows a direct measurement of the index of refraction field, which is used to determine optical distortions in the imaging plane. While a given ray within the sheet is refracted at a cumulative angle that depends on the local index of refraction gradient along its path, LIF measurements in the cross-stream plane of the flow show substantial optical distortions near the upstream and downstream edges of the primary vortices where the angle between the local temperature (or index) gradient and the wavevector of the incident light is large. These distortions are manifested by the appearance of low- and high-intensity streaks that are advected with the flow and whose characteristic spatial scales significantly diminish with the onset of small-scale (mixing) transition. The formation of secondary (streamwise) vortical structures leads to substantial spanwise variations in index of refraction and consequently to optical distortions that vary with the phase of the base flow and can exceed the distortions in the cross-stream plane. An important aim of the present research is the investigation of the effects of direct actuation of small-scale motions on the mixing and consequently on optical distortion within the shear layer. The actuation suppresses the formation of the large coherent vortical structures and leads to localized enhancement of dissipation and reduction in turbulent kinetic energy. The actuation enhances mixing across the entire width of the forced shear layer and leads to significant reduction of optical distortion, suggesting that active small-scale mixing can play a significant role in the mitigation of aero-optical effects through turbulent shear flows.

Multidimensional Longwave Forcing of Boundary Layer Cloud Systems

Abstract The importance of multidimensional (MD) longwave radiative effects on cloud dynamics is evaluated in an eddy-resolving model (ERM)—the two-dimensional analog to large-eddy simulation (LES)—framework employing multidimensional radiative transfer [Spherical Harmonics Discrete Ordinate Method (SHDOM)]. Simulations are performed for a case of unbroken, marine boundary layer stratocumulus and a broken field of trade cumulus. “Snapshot” calculations of MD and independent pixel approximation (IPA; 1D) radiative transfer applied to simulated cloud fields show that the total radiative forcing changes only slightly, although the MD effects significantly modify the spatial structure of the radiative forcing. Simulations of each cloud type employing MD and IPA radiative transfer, however, differ little. For the solid cloud case, relative to using IPA, the MD simulation exhibits a slight reduction in entrainment rate and boundary layer total kinetic energy (TKE) relative to the IPA simulation. This reduction is consistent with both the slight decrease in net radiative forcing and a negative correlation between local vertical velocity and radiative forcing, which implies a damping of boundary layer eddies. Snapshot calculations of the broken cloud case suggest a slight increase in radiative cooling, although few systematic differences are noted in the interactive simulations. This result is attributed to the fact that radiative cooling is a relatively minor contribution to the total energetics. For the cloud systems in this study, the use of IPA longwave radiative transfer is sufficiently accurate to capture the dynamical behavior of boundary layer clouds. Further investigations are required to generalize this conclusion for other cloud types and longer time integrations.

Flow-Induced Sound of Wall-Mounted Cylinders with Different Geometries

The objective of this work was to investigate the influence of changes in geometry of a wall-mounted square cylinder in crossflow on the generated aerodynamic noise. The flowfield and acoustic field of several geometries are obtained and their interaction is analyzed. The results of the subset of geometries investigated indicate that the reduction in turbulent kinetic energy does not necessarily also lead to a reduction in radiated noise. Reducing the fluctuations of the stagnation point in front of the cylinder, maintaining a fixed separation line, and reducing the symmetry of the vortex street and its stability seem to be effective measures for reducing aerodynamic noise, among other known approaches.

Experimental modeling of gravity underflow in a sinuous submerged channel

This paper describes the results of an experimental study involving density driven gravity underflow in a submarine sinuous channel. A single bend channel with sine generated planform was constructed inside a laboratory basin. Saline density flow was released at a constant rate at the upstream end of the channel which was submerged under fresh water. Instantaneous velocity data recorded within the body of the developed current were used to derive the vertical structures of the streamwise and cross‐stream velocity. The vertical distributions of the streamwise and lateral velocity were found to vary modestly between cross sections and also within an individual cross section. The distance of the maximum velocity position from the bed was found to vary between 0.4 and 0.6 times the local current thickness. In the vicinity of the bend apex the curvature effect led to the development of two helical flow cells with one forming on top of the other. The sense of rotation of the bottom cell was similar to that observed in curved open channel flow, while the upper circulation cell had an opposite sense of rotation. Turbulent kinetic energy profiles were derived from the instantaneous velocity data. The observed turbulent kinetic energy profiles confirm some previous observations that the location of the maximum velocity in a density underflow also corresponds to significant reduction in turbulent kinetic energy.

The performance trade off of decentralised, distributed and centralised controllers

Direct velocity feedback control of structures is well known to increase structural damping and thus reduce vibration. In multichannel systems the way in which the velocity signals are used to inform the actuators ranges from decentralised controller through distributed or clustered controllers to the fully centralised controller. The objective of distributed controllers is to exploit the anticipated performance advantage of the centralised controller whilst maintaining the ease of implementation and robustness of the decentralised controller. It has been observed, however, that in many vibration control systems the centralised controller struggles to perform significantly better than a decentralised controller. This paper compares a number of distributed controllers and optimisation techniques for the reduction of kinetic energy and radiated sound power and identifies the conditions under which the centralised and distributed controllers offer a significant performance advantage.

Reduction of Axial Kinetic Energy Induced Perturbations on Observed Cyclotron Frequency

With Fourier transform ion cyclotron resonance (FTICR) mass spectrometry one determines the mass-to-charge ratio of an ion by measuring its cyclotron frequency. However, the need to confine ions to the trapping region of the ion cyclotron resonance (ICR) cell with electric fields induces deviations from the unperturbed cyclotron frequency. Additional perturbations to the observed cyclotron frequency are often attributed to changes in space charge conditions. This study presents a detailed investigation of the observed ion cyclotron frequency as a function of ion z-axis kinetic energy. In a perfect three-dimensional quadrupolar field, cyclotron frequency is independent of position within the trap. However, in most ICR cell designs, this ideality is approximated only near the trap center and deviations arise from this ideal quadrupolar field as the ion moves both radially and axially from the center of the trap. To allow differentiation between deviations in observed cyclotron frequency caused from changes in space charge conditions or differences in oscillation amplitude, ions with identical molecular weights but different axial kinetic energy, and thus amplitude of z-axis motion, were simultaneously trapped within the ICR cell. This allows one to attribute deviations in observed cyclotron frequency to differences in the average force from the radial electric field experienced by ions of different axial amplitude. Experimentally derived magnetron frequency is compared with the magnetron frequency calculated using SIMION 7.0 for ions of different axial amplitude. Electron promoted ion coherence, or EPIC, is used to reduce the differences in radial electric fields at different axial positions. Thus with the application of EPIC, the differences in observed cyclotron frequencies are minimized for ions of different axial oscillation amplitudes.

Assessing Curve Severity and Design Consistency Using Energy- and Friction-Based Measures

Numerous published models can be used to predict curve speed based on geometric and operational characteristics like radius, superelevation rate, and approach tangent speed. Speed-based design consistency measures have also been developed to help identify which curves on a roadway are the most severe. However, the use of speed reduction alone can result in improper assessment of curve severity because drivers are more reluctant to reduce speed on roadways with higher speeds and thus accept speeds associated with higher crash risk. New measures of curve severity are suggested, based on considerations of side friction demand and kinetic energy. The increase in side friction demand above drivers’ comfort thresholds is shown to be roughly proportional to the kinetic energy reduction associated with speed reduction. Agencies can use these curve severity measures to assist in identifying curves in their jurisdictions that would most likely benefit from safety improvements.

Transit of Blood Flow Through the Human Left Ventricle Mapped by Cardiovascular Magnetic Resonance

The transit of blood through the beating heart is a basic aspect of cardiovascular physiology which remains incompletely studied. Quantification of the components of multidirectional flow in the normal left ventricle (LV) is lacking, making it difficult to put the changes observed with LV dysfunction and cardiac surgery into context. Three dimensional, three directional, time resolved magnetic resonance phase-contrast velocity mapping was performed at 1.5 Tesla in 17 normal subjects, 6 female, aged 44+/-14 years (mean+/-SD). We visualized and measured the relative volumes of LV flow components and the diastolic changes in inflowing kinetic energy (KE). Of total diastolic inflow volume, 44+/-11% followed a direct, albeit curved route to systolic ejection (videos 1 and 2), in contrast to 11% in a subject with mildly dilated cardiomyopathy (DCM), who was included for preliminary comparison (video 3). In normals, 16+/-8% of the KE of inflow was conserved to the end of diastole, compared with 5% in the DCM patient. Blood following the direct route lost or transferred less of its KE during diastole than blood that was retained until the next beat (1.6+/-1.0 millijoules vs 8.2+/-1.9 millijoules, p<0.05); whereas, in the DCM patient, the reduction in KE of retained inflow was 18-fold greater than that of the blood tracing the direct route. Multidimensional flow mapping can measure the paths, compartmentalization and kinetic energy changes of blood flowing into the LV, demonstrating differences of KE loss between compartments, and potentially between the flows in normal and dilated left ventricles.

Proportional-derivative energy-based control for manipulator using normalized quasi-velocities

This paper presents a proportional-derivative (PD) controller for rigid manipulators whose dynamics is expressed in terms of the normalized quasi-velocities (NQV) described by Jain and Rodriguez. It is shown that using the NQV it is possible to shape the kinetic energy reduction of the manipulator and at the same time to realize the PD control in its joint space. The energy-based strategy gives an insight into the position control and allows a different method to be used instead of the classical PD controller in order to change the behaviour of the system. The controller uses quasi-velocities arising from a decomposition of the manipulator mass matrix. Its use yields a globally asymptotically stable closed-loop system. The performance of the controller is illustrated via experiment on a two-degree-of-freedom robot arm and in simulation on a three-degree-of-freedom spatial manipulator.

Investigation of impact fracture behavior of automobile laminated glass by 3D discrete element method

A three-dimensional discrete element model of laminated glass plane is presented and a 3D numerical analysis code, which can simulate the impact fracture behavior of automobile laminated glass, is developed. The impact process of a single glass plane and a laminated glass plane are calculated in the elastic range by the code. Comparing its results with those calculated by the commercial FEM code LS-DYNA in the same condition, the validity of the 3D laminated glass model and the 3D discrete element method are proved. Furthermore, the impact fracture process of a single glass plane and a laminated glass plane are simulated respectively. The entire failure processes in detail are presented. By comparing the impact force and reduction of kinetic energy of impact body between those two models, the numerical method is applied to demonstrate the advantage of laminated glass in passenger’s safety.

Centralized and decentralized control of structural vibration and sound radiation

This paper examines the performance of centralized and decentralized feedback controllers on a plate with multiple colocated velocity sensors and force actuators. The performance is measured by the reduction in either kinetic energy or sound radiation, when the plate is excited with a randomly distributed, white pressure field or colored noise. The trade-off between performance and control effort is examined for each case. The controllers examined are decentralized absolute velocity feedback, centralized absolute velocity feedback control and linear quadratic Gaussian (LQG) control. It is seen that, despite the fact that LQG control is a centralized, dynamic controller, there is little overall performance improvement in comparison to decentralized direct velocity feedback control if both are limited to the same control effort.

Energetic balance of the superconducting transition across the BCS—Bose Einstein crossover in the attractive Hubbard model

We investigate by means of Dynamical mean-field theory the crossover from BCS superconductivity to Bose-Einstein (BE) condensation of preformed pairs which occurs in the attractive Hubbard model by increasing the attraction strength. Fixing the density to a generic value $n=0.75$, we follow the evolution of the two energy scales underlying the superconducting phenomenon, the gap ${\ensuremath{\Delta}}_{0}$, and the superfluid stiffness ${D}_{S}$, which controls the phase coherence. The BCS--BE crossover is clearly mirrored in a change in the hierarchy of these two scales, the smallest of the two controlling the critical temperature. In the whole intermediate-to-strong-coupling region ${T}_{c}$ scales with ${D}_{S}$, while ${T}_{C}$ is proportional to ${\ensuremath{\Delta}}_{0}$ only in the BCS regime. This evolution as a function of the interaction qualitatively resembles what happens in the cuprates when the doping is decreased towards the Mott insulator. This continuous change reflects also in the energetic balance at the superconducting transition. While, as it is well known, superconductivity is stabilized by a potential energy gain in the BCS regime, the strong-coupling superconductivity is made stable by a reduction of kinetic energy. Interestingly the intermediate-coupling region, where the maximum ${T}_{c}$ is achieved, behaves similarly to the strong-coupling regime, and its gain in kinetic energy is the largest as a function of the coupling. Since the integral of the optical conductivity is proportional to the kinetic energy, the above finding implies that the attractive Hubbard model can account qualitatively for the anomalous behavior of optical spectra around ${T}_{c}$, where an increase of spectral weight is observed in under and optimally doped cuprates, while the overdoped samples have a more standard behavior. This qualitative agreement is lost in the normal phase, specifically at strong coupling, calling for the inclusion of strong correlation effects in the theoretical description.

Energy Based Indexes for Manipulator Dynamics Improvement

Several indexes for evaluation of nonlinear effects during the motion of rigid multi-body systems are proposed in this paper. All of them are based on the kinetic energy and arise from an analysis of equations of motion expressed in terms of inertial quasi-velocities (IQV). Such equations are first-order and have a diagonal mass matrix of the system. The IQV depend on configuration of the system and take into consideration also its geometrical and inertial parameters. The indexes enable to detect deformation of joint velocity as a consequence of manipulator motion, the kinetic energy resulting from dynamical couplings and the energy transferred by each link individually. Because calculation of these indexes allow to determine influence of couplings on behavior of the manipulator then they can be used in the design phase for analysis and reduction of nonlinear effects in any motion. Simulation and experimental results demonstrate that the proposed indexes are significant for evaluation of nonlinear effects and kinetic energy reduction during the manipulator motion.