Cumulative Momentum Research Articles

Research on Momentum Parameters of Tailings Dam-break Mortar

The tailings dam-break mortar with high potential energy will cause impact damage to the downstream buildings, and the momentum parameters of mortar can effectively reflect its impact on buildings. Taking the distribution status of downstream geomorphology and production and living facilities of Yangjiawan tailing pond as the calculation background, Numbering 4 sensitive analysis points from 1 to 4 in line with the distance between the key protected structures and the breach of the tailing pond from the near to the distant, The three-dimensional fluid simulation software FLOW 3D was used to simulate the evolution process of dam-break mortar under the full-break condition of the accumulation dam above the initial dam, and the variation characteristics of the flow mortar momentum at the key protection structures in the evolution process were analyzed. The results show that the momentum of dam-break mortar at the sensitive points decreases from the near to the distant, Compared with instantaneous momentum, cumulative momentum could reflect the cumulative impact effect of mortar on buildings, and the distinction of impact effect was more obvious.; The peak inundation depth of dam-break mortar at each sensitive point was 1, 3, 2 and 4 sensitive points in descending order, the momentum and submergence depth were inconsistent, The momentum could clearly distinguish the difference of mortar impact effect, and the research results could provide some reference for dam - breaking mortar disaster assessment of tailing pond

Kinematics of powerful jets from intermediate-mass protostars in the Carina nebula

We present measurements of proper motions and radial velocities of four powerful Herbig-Haro (HH) jets in the Carina nebula: HH 666, HH 901, HH 902, and HH 1066. Two epochs of Hubble Space Telescope (HST) imaging separated by a time baseline of ~4.4 years provide proper motions that allow us to measure the transverse velocities of the jets, while ground-based spectra sample their Doppler velocities. Together these yield full three-dimensional space velocities. Aside from HH 666, their identification as outflows was previously inferred only from morphology in images. Proper motions now show decisively that these objects are indeed jets, and confirm that the intermediate-mass protostars identified as the candidate driving sources for HH 666 and HH 1066 are indeed the origin of these outflows. The appearance of two new knots in the HH 1066 jet suggest recent (~35 yr) changes in the accretion rate, underscoring the variable nature of accretion and outflow in the formation of intermediate-mass stars. In fact, kinematics and mass-ejection histories for all the jets suggest highly episodic mass loss, and point toward pronounced accretion fluctuations. Overall, we measure velocities similar to those found for low-mass protostars. However, the HH jets in Carina have higher densities and are more massive than their low-mass counterparts. Coarse estimates suggest that the heavy jets of intermediate-mass protostars can compete with or even exceed inject ~10 or more times the cumulative momentum injection of lower-mass protostars.

Revisit on dynamic radiation forces induced by pulsed Gaussian beams

Motivated by the recent optical trapping experiments using ultra-short pulsed lasers [Opt. Express 18, 7554 (2010); Appl. Opt. 48, G33 (2009)], in this paper we have re-investigated the trapping effects of the pulsed radiation force (PRF), which is induced by a pulsed Gaussian beam acting on a Rayleigh dielectric sphere. Based on our previous model [Opt. Express 15, 10615 (2007)], we have considered the effects arisen from both the transverse and axial PRFs, which lead to the different behaviors of both velocities and displacements of a Rayleigh particle within a pulse duration. Our analysis shows that, for the small-sized Rayleigh particles, when the pulse has the large pulse duration, it might provide the three-dimensional optical trapping; and when the pulse has the short pulse duration, it only provides the two-dimensional optical trapping with the axial movement along the pulse propagation. When the particle is in the vacuum or in the situation with the very weak Brownian motion, the particle can always be trapped stably due to the particle's cumulative momentum transferred from the pulse, and only in this case the trapping effect is independent of pulse duration. Finally, we have predicted that for the large-sized Rayleigh particles, the pulse beam can only provide the two-dimensional optical trap (optical guiding). Our results provide the important information about the trapping mechanism of pulsed tweezers.

Comparison of Wake Model Simulations with Offshore Wind Turbine Wake Profiles Measured by Sodar

Abstract This paper gives an evaluation of most of the commonly used models for predicting wind speed decrease (wake) downstream of a wind turbine. The evaluation is based on six experiments where free-stream and wake wind speed profiles were measured using a ship-mounted sodar at a small offshore wind farm. The experiments were conducted at varying distances between 1.7 and 7.4 rotor diameters downstream of the wind turbine. Evaluation of the models compares the predicted and observed velocity deficits at hub height. A new method of evaluation based on determining the cumulative momentum deficit over the profiles is described. Despite the apparent simplicity of the experiments, the models give a wide range of predictions. Overall, it is not possible to establish any of the models as having individually superior performance with respect to the measurements.

A theory of local and global processes which affect solar wind electrons, 1. The origin of typical 1 AU velocity distribution functions—Steady state theory

A new detailed first principle kinetic theory for electrons is presented which is neither a classical fluid treatment nor an expospheric calculation. This new theory illustrates the global and local properties of the solar wind expansion that shape the observed features of the electron distribution function fe, such as its bifurcation, its skewness, and the ‘differential’ temperatures of the thermal and suprathermal subpopulations. Our approach starts with the Boltzmann equation and retains the effects of Coulomb collisions via a Krook collision operator without recourse to wave‐particle effects. We conclude that Coulomb collisions determine the population and shape of fe in both the thermal (E <kT) and suprathermal (E >kT) energy regimes. We find that electrons with E >7kT constitute a special subpopulation of the suprathermals, insofar as Coulomb collisions are concerned; these we call ‘extrathermals.’ The electrons in the thermal portion of fe have undergone ∼10‐20 Coulomb collisions for cumulative momentum transfer en route to the observer at 1 AU; this population is thus more removed from the properties of coronal electrons than the suprathermal population. This latter group retains a strong memory of coronal conditions, since they have undergone only a few momentum transfer collisions. The thermal population is most nearly in collisional contact with the local dynamics (compressions, rarefactions, etc.) of the solar wind. The suprathermal portion of fe is determined by Coulomb collisional interactions with the distribution of solar wind material on radial scale of the heliopause itself. In this respect the suprathermal portion of fe is found to be responsive to the consequences of the global dynamics of the solar wind expansion. We find that this subpopulation is an attenuated vestige of collisional populations deep in the corona (1.03–10 Rs) which has been redistributed via Coulomb multiple pitch angle scattering on magnetically open field lines. The suprathermal particles moving toward the sun are computed to be observed as a result of Coulomb‐collision‐induced backscattering at larger (1–10 AU) heliocentric distances than that of the observer. Based on this theoretical picture, quantitative estimates for the partition of thermal and suprathermal phase density, the break in the velocity distribution, and the magnitude of the skewness (heat flux density) agree well with those typically observed near 1 AU. These calculations predict that the extrathermal fraction of the phase density, the extrathermal temperature, and the net heat flux density carried by electrons should be anticorrelated with the local bulk speed in quasi‐steady‐state flows and that the radial variation of extrathermal temperature inside 1 AU should be essentially independent of heliocentric distance. Our work also shows that the observation of suprathermal particles cannot be taken as a priori evidence for in situ wave particle interaction(s), since we can theoretically calculate a suprathermal population of solar wind electrons at 1 AU by assuming wave‐particle interactions are not present anywhere in the heliospheric cavity; the combination of inhomogeneity and the Coulomb ‘window’ above E*=7kTc naturally gives rise to this leakage of nonlocal collisional populations in superposition with local collisional populations. This work suggests that the local cause and effect precept which permeates the physics of denser media must be relaxed for electrons in sparse and radically inhomogeneous plasmas such as those found in the solar wind between the lower corona and the interstellar medium. The local form of transport laws and equations of state (e.g., Q =−κ ▽,T,P=NkT), which are familiar from collision‐dominated plasmas, must be replaced with global relations that explicitly depend on the relative position of the observer to the boundaries of the system.