Vibrations amplitude

Classical ion trajectory computer simulations based on the BCA are a series of evaluations of two-body collisions. The parameters involved in each collision are tire type of atoms of the projectile and the target atom, the kinetic energy of the projectile and the impact parameter. The general procedure for implementation of such computer simulations is as follows. All of the parameters involved in tlie calculation are defined the surface structure in tenns of the types of the constituent atoms, their positions in the surface and their themial vibration amplitude the projectile in tenns of the type of ion to be used, the incident beam direction and the initial kinetic energy the detector in tenns of the position, size and detection efficiency the type of potential fiinctions for possible collision pairs. 

VoHex shedding The vortex-shedding frequency of the fluid in cross-flow over the tubes may coincide with a natural frequency of the tubes and excite large resonant vibration amplitudes. 

Vibration Amplitude and Frequency Speed and amplitude of vibration should be designed to convey the material properly and to prevent blinding of the cloth. They are somewhat dependent upon the size and weight of the material being handled and are related to the angle of installation and the type of screen surface. The object, of course, is to see that the feed is properly stratified for the most efficient separation. 

Appears suddenly at or above rotor critical speed when critical is below one-half operating speed. Increasing speed increases vibration amplitude, blit whirl frequency remains constant. When speed IS decreased, vibration disappears below where it first appeared. Fnction-indnced rotor whirl Encountered m bnilt-np rotors or rotors with shrink fits or rotor disassembly to inspect fits, increase shrink fits Coupling friction has been known to induce whirl... 

Increasing vibration amplitude with speed behavior Unbalance Loose rotor component 3... 

Vibration amplitude varies with time in a definite rhythm (beat). 

EiTatic high-frequency vibration amplitude and possibly an audible sound. Rotor mb Labyrinth mbs generally self-comect Disc mbs due to thrust bearing failure often self-comect temporarily through wean steel on steel shrill noise during wear Rotor deflection is critical speed... 

In a real rotor system the amount and location of unbalances cannot always be found. The only way to detect them is with the study of rotor vibration. Through careful operation, the amount and the phase angle of vibration amplitude can be precisely recorded by electronic equipment. The relation between vibration amplitude and its generating force for an uncoupled mass station is... 

Y t) = vibration amplitude F = generating force A = amplification factor (f) = phase lag between force and amplitude... 

This procedure is based on the observation of the orbital movement of the shaft eenterline. Three signal piekups are employed, of whieh two probes measure the vibration amplitudes of the rotor in two mutually perpendieular direetions. These two signals trace the orbit of the shaft centerline. The third probe is used to register the once-per-revolution reference point and is called the keyphazor. A schematic arrangement of these probes is shown in Figure 17-6. 

Take a blank Data Sheet B. Enter the plane number. Plaee a trial weight at any radius and any angle in that plane. Enter these values on the sheet. Now, operate the maehine at the balaneing speed, and measure the vibration amplitude and phase in eaeh plane. Repeat the proeedure for eaeh plane. (Plaee only one trial weight in only one plane at a time.) When finished, you should have as many Data Sheets B as the number of planes. 

Final Vibration Amplitude and Phase Before Balancing In-Plane... 

Turbine fouling. This is indieated by an inerease in turbine exhaust temperature. Change in vibration amplitude will oeeur when fouling is exeessive and eauses rotor imbalanee. 

Rfpire The relaticmship of displacement, velocity, and acceleration to vibration amplitude and frequency. 

Thermal properties of overlayer atoms. Measurement of the intensity of any diffracted beam with temperature and its angular profile can be interpreted in terms of a surface-atom Debye-Waller factor and phonon scattering. Mean-square vibrational amplitudes of surfece atoms can be extracted. The measurement must be made away from the parameter space at which phase transitions occur. 

The temperature dependence of the mean-square-displacements of Au adatom in the normal to the surface direction is shown in Figure 4 for the three low-index faces of Cu. We note that up to 500"K the MSD s on the three different faces are almost equal, while at higher temperatures the vibrational amplitudes of Au on Cu(llO) present enhanced anharmonicity and become much larger than on the other faces. These results denote that... 

Figure 4-236. Order of magnitude of the vibration amplitudes encountered during drilling.

All vibration amplitude curves, which can represent displacement, velocity, or acceleration, have common elements that can be used to describe the function. These common elements are peak-to-peak, zero-to-peak, and root-mean-square, each of which are illustrated in Figure 43.11. 

In a mechanical system, the degrees of freedom indicate how many numbers are required to express its geometrical position at any instant. In machine-trains, the relationship of mass, stiffness, and damping is not the same in all directions. As a result, the rotating or dynamic elements within the machine move more in one direction than in another. A clear understanding of the degrees of freedom is important in that it has a direct impact on the vibration amplitudes generated by a machine or process system. 

Most vibration monitoring programs rely heavily on historical vibration-level amplitude trends as their dominant analysis tool. This is a valid approach if the vibration data are normalized to remove the influence of variables, such as load, on the recorded vibration energy levels. Valid trend data provides an indication of change over time within the monitored machine. As stated in preceding sections, a change in vibration amplitude is an indication... 

Another configuration, called an unbalanced design, has piston orientations that are neither in-phase nor 180° out-of-phase. In these configurations, the impact forces generated as each piston changes direction are not balanced by an equal and opposite force. As a result, the impact energy and the vibration amplitude are greatly increased. 

Low-limit alert The first alert (i.e., low-limit alerta) should be set at the lowest vibration amplitude that will be encountered from a normally operating machine-train. This value is needed to ensure that valid data are taken with the microprocessor. If this minimum amplitude is not reached, the system alerts the operator, who can retake or verify the data point. Low-limit selection is arbitrary, but should be set slightly above the noise floor of the specific microprocessor used to acquire data. 

Maximum rate of change alert The second alert (i.e., maximum rate of change alert) is used to automatically notify the operator that based on statistical data the rate of degradation has increased above the pre-selected norm. Since the vibration amplitudes of all machine-trains increase as normal wear occurs, the statistical rate of this normal increase should be trended. A drastic change in this rate is a major indication that a problem is developing. 

Absolute-fault limits are typically based on industrial standards for specific classifications of machinery. Generally, these standards are based on a filtered broadband limit and are not adjusted for variables such as speed, load or mounting configuration. However, vibration amplitude and its severity depend on speed and load. Therefore, alert/alarm limits must be adjusted for variations in both of these critical factors. 

Other There are a multitude of other forms of mechanical looseness (besides vertical and horizontal movement of machine legs) that are typical for manufacturing and process machinery. Most forms of pure mechanical looseness result in an increase in the vibration amplitude at the fundamental (lx) shaft speed. In addition, looseness generates one or more harmonics (i.e., 2x, 3x, 4x, or combinations of harmonics and half-harmonics). 

While most stationary machine components move during normal operation, they are not always resonant. Some degree of flexing or movement is common in most stationary machine-trains and structural members. The amount of movement depends on the spring constant or stiffness of the member. However, when an energy source coincides and couples with the natural frequency of a structure, excessive and extremely destructive vibration amplitudes result. 

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