SETTING UP A PROBLEM OF AIR-BORNE SOUND IN-SULATION CALCULATION FOR DOUBLE LAYER MASSIVE ENCLOSURES ON THE BASE OF THE MODELS WITH THE CONCENTRATED PARAMETERS

The calculation methods on the base of the concentrated parameters models, which were formed in the XX century, allowed to get simple and theoretically consistent solutions for the problems of one-layered building partitions sound insulation finding. The sound insulation estimation for the double-layered massive building partitions also is of scientific and practical interest, as double layer partitions are the particular case of the single layer enclosure's application. The concept of concentrated parameters includes the concentrated and the reduced masses, as well as the concentrated elasticity. The criteria for the object application as a specified kind of the concentrated parameters in the acoustical problems is the presence or the absence of the oscillation movement in it. The three calculation models with the application of the concentrated (discreet) parameters that to define the sound insulation of the massive double layer enclosures are given. The equations for sound insulation computation for one layer partition are represented. They were derived on the base of momentum law and energy conservation formulas under the continuity of energy flow conditions at the interface of different media. The three main paths of sound propagation from the room with the air-borne noise to the isolated room are shown. The two frequency range are separated on the way of the direct sound propagation: at the first, the surface density of the one of two layers and the air elasticity in the inter-layer gap influence on isolation; at the second one, the predominant role belongs to the summarized insulation by the "Mass Action Law" of the two layers. The indirect way's insulation is taken in account through the additional sound insulation graph drawing. The compound insulation curve is defined by the ways, where the sound energy transmittance is maximal at the standard frequency spectrum. The method of sound insulation calculation for the double layer partitions on the base of the concentrated parameters model application is revealed. As an example, the calculation of a prefabricated double layer inter-flat wall in the panel building was performed.

Study of the dynamics of ТПА 350 automatic mill working stand elements

To form a necessary geometry of a hollow billet to be rolled at a pipe rolling line, stable dynamics of the base equipment of the automatic mill working stand has a practical meaning. Among the forces, acting on its parts and elements, significant by value short-time dynamic loads are the least studied phenomena. These dynamic loads arise during transient interaction of the hollow billet, rollers, mandrel and other mill parts at the forced grip of the hollow billet. Basing of the calculation scheme and dynamic model of the mechanical system of the ТПА 350 automatic mill working stand was accomplished. A mathematical model of dynamics of the system “hollow billet (pipe) – working stand” within accepted calculation scheme and dynamic model of the mechanical system elaborated. Influence of technological load of the rolled hollow billet variation in time was accounted, as well as variation of the mechanical system mass, and rigidity of the ТПА 350 automatic mill working stand. Differential equations of oscillation movement for four-mass model of forked sub-systems of the automatic mill working stand were made up, results of their digital calculation quoted. Dynamic displacement of the stand elements in the inter-roller gap obtained, which enabled to estimate the results of amplitude and frequency characteristics of the branches of the mill rollers setting. It was defined by calculation, that the maximum amplitude of the forced oscillations of elements of the ТПА 350 automatic mill working stand within the inter-roller gap does not exceed 2 mm. It is much higher than the accepted value of adjusting parameters of the deformation center of the ТПА 350 automatic mill. A scheme of comprehensive modernization of the rollers setting in the ТПА 350 automatic mill working stand was proposed. It was shown, that increase of rigidity of rollers setting in the ТПА 350 automatic mill working stand enables to stabilize the amplitude of forced oscillations of the working stand elements within the inter-rollers gap and considerably decrease the induced nonuniform hollow billet wall thickness and increase quality of the rolled pipes at ТПА 350.

The Application of Double Elastic Band Exercise in the 90/90 Arm Position for Overhead Athletes

Background: Traditional exercises performed with the shoulder in the position of 90° abduction and external rotation with elbow flexion (90/90) while using a single elastic band showed moderate activity of both the lower trapezius (LT) and infraspinatus (IS) muscle. The purpose of this study was to investigate activity of the teres minor (TMi) and the LT muscles during standing external rotation exercise with the shoulder in the 90/90 position with 2 elastic bands in both the frontal and the scapular plane. Hypothesis: TMi, IS, and LT muscle activities will vary depending on whether the shoulder is positioned in the frontal or scapular plane with the application of 2 elastic bands. Also, the serratus anterior (SA) and teres major (TMa) muscles will produce different muscular activity patterns during exercises performed with 2 elastic bands in the frontal plane compared with the TMi and LT muscles. Study Design: Controlled laboratory study Level of Evidence: Level 4. Methods: A total of 21 collegiate baseball players volunteered to participate. The electromyography (EMG) activities of the TMi, IS, LT, SA, TMa, middle deltoid (MD), posterior deltoid, and upper trapezius (UT) muscles were measured with the 90/90 arm position during both isometric and oscillation resistance exercises with 2 elastic bands oriented in the frontal and scapular planes. Results: A significant difference was observed in EMG activity of both the TMi and the LT muscles between single and double elastic band applications in the frontal plane ( P < 0.05). In contrast, EMG activity of the IS, SA, and TMa muscles was significantly increased in the scapular plane compared with the frontal plane ( P < 0.05). Conclusion: The standing 90/90 position effectively increased both TMi and LT muscle EMG activity with the double elastic band in the frontal plane while minimizing UT and MD muscle activity. EMG activity of the IS, SA, and TMa muscles increased with exercise in the scapular plane as compared with the frontal plane. Clinical Relevance: Oscillation movement under double elastic band application differentiated external rotator muscle and scapular muscle activities between the frontal and scapular plane during the 90/90 exercise in the frontal plane compared with the scapular plane. Clinicians can utilize each of the scapular and frontal positions based on their desired focus for muscular activation.

A review on micro-electron beam welding with a modernized SEM: Process, applications, trends and future prospect

Electron beam welding (EBW) is a well-established joining method in the field of manufacturing. If this technology is downscaled to a micro-level (i.e., micro-EBW (µ-EBW)), it will be able to solve a variety of problems. The necessity of adopting µ-EBW technology lies with the fact that it can be used from micro-mechanical fabrication to micro-electronics components joining, micro-electro-mechanical system (MEMS), medical instrument, etc. µ-EBW has some special properties like the possibility of obtaining exact focussing of the beam and conducting measurement up to micrometer level, accurate control of energy input, inertia-free manipulation, high-frequency oscillation movement and ability to work under high vacuum chamber. µ-EBW has several important applications like micro-joining and micro-fabrication, which is welding of dissimilar materials. This article deals with a review of the recent developments, significant applications, and advantages of µ-EBW, multiple modes of joining and also some new technologies such as scanning electron microscope, function generator, control software, etc. Finally, the current challenges of this emerging technology and the scopes for future studies have been presented in this article.

An Investigation on Two-Dimensional Nonlinear Sloshing in Rectangular Tank

Two-dimensional liquid sloshing in rectangular tank of FLNG system is investigated both numerically and experimentally. In numerical simulation, a time-domain scheme has been developed based on potential flow theory in boundary element method. Tank movement is defined by wall boundary condition to produce a reciprocating oscillation. Nonlinear free surface condition is adopted to capture free surface elevation. Energy dissipation caused by viscous effects is considered by applying artificial damping term to the dynamic free surface condition, which is also vital to achieve a steady-state solution. For comparison, experiments of a rectangular tank filled with water subjected to specified oscillation are carried out. As coupling effects between sloshing and tank motion is not included in this research, the testing apparatus is required to produce consistent oscillation movement and not affected by the change of filling condition and sloshing load. Liquid surface elevations in several typical places of the tank were measured. Sloshing related parameters including oscillation amplitude, frequency and filling level are analyzed systematically. It’s found that numerical simulation results have good agreement with phenomenon observed under small amplitude excitation, and this nonlinear analysis method is proved to be effective in capturing liquid surface elevation. It is found that sloshing in tank is sensitive to filling level as well as excitation frequency, especially in the crucial combination cases of them. For given filling level, sloshing tends to be violent near corresponding natural frequencies, and viscous damping has limited contribution to sloshing amplitude when resonance occurs. This fundamental investigation also paves path for the study of more complicated sloshing problems.