Additional Dynamic Loads Research Articles

SELF BALANCING SYSTEM FOR ROTATING MECHANISMS

INTRODUCTIONThe rotation of unbalanced rotor produces vibration andintroduces additional dynamic loads. Particular angularspeeds encountered in presently built modern rotatingmachinery, impose rigorous requirements concerningthe unbalance of rotating mechanisms. In the system,however, where the distribution of masses around thegeometric axis of rotation varies during the operationof a machine or each time the machine is beingrestarted, the conventional balancing method becomesimpracticable. Therefore, self balancing methods arepracticed in such systems where the role of fixedbalancing bodies is performed, either by a body ofliquid or by a special arrangement of movable balancingbodies (balls or rollers) which are suitably guided forfree movement in predetermined directions. In the casewhen a body of liquid is self balancing the attainabledegree of balance does not exceed 50% of initialunbalance of rotating parts [1]. In fact, however, thereare a lot of reasons rendering the attainment of such ahigh degree of balance practically impossible. Selfbalancing systems are used to reduce the imbalance inwashing machines, machining tools and optical diskdrives such as CD-ROM and DVD drives. In selfbalancing systems, the basic research was initiated byThearle [2], [3], Alexander [4] and Cade [5]. Analysisfor various self balancing systems can be encounteredin references [6-9]. Equations obtained are for non-autonomous systems, these equations have limitationson complete stability analysis.Chung and Ro [9] studied the stability and dynamicbehavior of an ABB for the Jeffcott rotor. They derivedthe equations of motion for an autonomous system byusing the polar coordinates instead of the rectangular

A method of biomechanical testing the suspensory apparatus of the third phalanx in cattle: a technical note.

There are a number of differences between the claws of the front and hind limbs in cattle concerning macroscopic shape, chemical and physical properties of claw horn and epidemiological data. Front claws have superior data in almost every respect. Virtually no information is available on the mechanical stability of the suspensory apparatus of the third phalanx. It was the objective of this study to develop a method to measure the maximum strength (N/mm2) of the suspensory apparatus of the bovine distal phalanx. This apparatus includes all layers of tissue such as bone, corium, corioepidermal junction and wall horn. The feet of 13 clinically healthy beef bulls were collected from the local abattoir. Testing was performed in three locations of the wall segment (dorsal, abaxial, axial) in a material testing machine. The corium and the corioepidermal junction were set under increasing tension until failure occurred. Maximum stress was recorded. The values ranged between 2.47-3.13 N/mm2 (dorsal), 4.08-4.87 N/mm2 (abaxial) and 2.27-2.66 N/mm2 (axial). No differences could be validated statistically between front and hind claws and between lateral and medial claws respectively. Abaxial ultimate stress values were significantly higher than dorsal and axial ones. Between the two a statistical difference could not be validated. Most of the specimens (57.1%) were torn apart at the corioepidermal junction, almost a quarter of the samples (27.6%) were to a degree disrupted at the corioepidermal junction and to a certain extent in the deeper layers of the corium. A few samples showed disruption within the horn (11.5%) or at the attachment of the third phalanx (3.8%). Biomechanical features of the experimental set-up are discussed. The biological significance of these findings is that the body weight and the additional dynamic loading is predominantly taken over by the abaxial part of the claw, while the dorsal and axial aspects are less loaded.

Scour under Submarine Pipelines in Waves in Shoaling Conditions

Submarine pipelines, one of the most important subjects in coastal engineering, are widely used in coastal structures. In order to ensure these pipelines are stable and functional during their project life, attention must be paid to their design and coastal processes. In the design phase, the possibility of local scouring under submarine pipelines must be taken into consideration. If local scour occurs under the submarine pipelines, the pipelines may either vibrate due to the hydrodynamic forces or induce additional static or dynamic loads due to self-burial. Moreover, they might be destroyed partially or fully and thus be unable to perform their functions. This paper presents experimental investigations of scour depth with respect to water depth using regular waves. The investigations encompass shoaling region conditions. Results of the measurements of velocities and beach profiles are enlightening, both for understanding of the mutual interaction between the disturbed flow field around the pipe and the seabed morphology as well as in making predictions of scour depth around submarine pipelines. Based on the present experimental data, a new equation is proposed, relating the maximum equilibrium scour depth to the modified Ursell number for the live bed condition for a rigid pipe fixed initially in contact with the bed.

The testing and repair of steel silo

The characteristic damage and repair of four silo cells for white soya flakes are described in the paper. Cylindrical steel cells, with 6 m diameters and 15 m high, are placed upon RC structure composed of a ring beam supported by eight columns 7.5 m high. The silo is so designed that the loading is transmitted and distributed uniformly on the ring beam. Filling and emptying of the silo is automatic by use of vibrating exemptor. After 10 years of service, the following damage was registrated on the structure: buckling of the vertical steel stiffening ribs of the steel envelope in the supporting zone, strains and cracks on the horizontal leg of the steel angle bar. On that basis the causes of damage were identified, among which the most important are: 1) imperfection at contact between the supporting part of the cell and the RC ring, so that instead of the contact along the total surface, concentrated supporting occurred along the beam; 2) eccentricity of the cell in horizontal plane in relation to the RC ring which caused uneven loading of the ring; 3) additional dynamic loading caused by the emptying equipment. By the repair design two variants were considered. In the first variant, the strengthening of the supporting part of the cell is proposed by welding additional steel plates to form a ring of box section with corresponding stiffening ribs. Besides, the way the cell leans on the steel structure is changed, so that centrally above the columns neoprene bearings are designed. For their installation the elevation of the cell is assumed by means of hydraulic jacks. Thus the static system is changed, i.e. the way of loading transmission by unloading the RC ring. According to the second variant, the repair should include strengthening of the RC ring by additional reinforcement and by concreting a new layer after injecting the cracks. Cost analysis of the variant solutions showed that the first one was more acceptable, and consequently it was realized. Inspection of damage, testing of structure, production of design and repair works were done in the period June–October 1992.

Nearly-uniform deployment strategy for space tether systems

The nearly-uniform deployment strategy is applicable to many types of prospective space tether systems of two satellites connected with a long flexible tether (cable, wire). The basic idea is to control the tether tension such as to maintain a desired deployment rate. Under perturbations, the deployment rate is adjusted to compensate for the additional dynamic loads.

Oscillations of an ice sheet under a periodically varying load

The factors affecting flexure-gravitation wave (FGW) parameters, and thus, the icebreaking ability of an ACV for uniform rectilinear motion of the latter were considered in [2]. As large scale model and field experiments with ACV's have shown, the capabilities of the resonant method can be improved, if the dimensions of the body of water or the vessel parameters do not permit excitation of waves of sufficient intensity to destroy the ice during uniform rectilinear motion, the ice cover can be broken by an additional dynamic load produced by periodic change of the pressure in the air cushion. The vertical oscillations of the vessel produced in this manner at some resonant frequency w lead to excitation of a flexuregravitation wave which destroys the ice over a significant area. The character of the ice damage is shown in Figure i.

Repair And Strengthening Of The Eastern FacadeWall Of The Western Range Of Cells At The ByzantineMonastery Of St. Luke In Boeotia/Greece

The four-story eastern fagade wall of the western range of cells at the byzantine monastery of St. Luke in Boeotia, according to recent architectural and structural survey, consists of approximately 20 different structural phases, dated from the byzantine period (11th century AD) until today. Its strengthening and partial restoration, which became necessary during the recent strengthening and restoration works at the second floor cells, will be carried out: First, by increasing the existing mechanical strength of its elements, with the use of cement grouting and repointing, the partial reconstruction of the masonry walls and the seaming of cracks or structural joints. Second, by reinforcing the wall and its elements, in order to undertake additional dynamic loads, using a system of horizontal zones of stainless steel ties and steel bars in the random stone masonry wall. Transactions on the Built Environment vol 15, © 1995 WIT Press, www.witpress.com, ISSN 1743-3509 146 Dynamics, Repairs & Restoration