Damping ratio - Wikipedia
undamped and damped vibration, linear and nonlinear vibration, and an stringed harp with a gold-decorated, bull-headed sounding box, found at Ur in a . that he had a clear understanding of the relationship between the frequency. Here we use ultrafast laser pulses to impulsively launch acoustic phonons in single gold nanodisks with variable titanium layer thicknesses. from the relationship between the cardiovascular system and the transducer itself, if the natural frequency and the damping coefficient have suitable values. Although intra-arterial measurement is considered the gold standard of BP.
Most commonly the upper arm is used although it is possible to use the forearm or leg when the upper arm is inaccessible, for example due to surgical requirements. The cuff is inflated to a pressure above that of the arterial systolic pressure. At this point, the walls of the artery are opposed preventing blood flow. The cuff is then deflated below systolic pressure allowing blood flow to resume; this flow can then be detected using various means.
Doppler Systolic pressure can also be determined using the Doppler principle. Blood flow towards or away from the Doppler probe, reflects sound waves causing a change in frequency that is detected using the same Doppler probe. As Doppler is so sensitive, this technique is usually reserved for the measurement of low pressures, e.
Auscultation Auscultation over the brachial artery while using a Riva Rocci cuff was first described in by Nicolai Korotkoff, a Russian army sergeant. A fifth sound was later described Fig. The cause of the sounds is uncertain but may be due to formation of bubbles within the blood cavitation theorysudden stretching of the vessel wall arterial wall theoryturbulence within the vessel turbulence theoryor a most likely a combination of factors.
In the past, there has been controversy around which Korotkoff sound represents true diastolic pressure. However, the current consensus is to use the fifth sound unless the pulsation continues to be audible on complete deflation of the cuff when the fourth sound should be used.
Oscillotonometry The Von Recklinghausen Oscillotonometer uses two cuffs and two bellows connected to a measurement gauge. The two cuffs overlap, one occludes the artery occluding cuff and the other senses the arterial signal sensing cuff. Pressure from both cuffs is transmitted to the two bellows which is in turn displayed via a single gauge, alternating between the two bellows using a lever. With the lever in the sensing position, the occlusive cuff is inflated above systolic pressure.
The cuff is then deflated using a bleed valve until the needle suddenly starts to move vigorously. The lever is then switched to measure the occluding cuff pressure. This is the systolic blood pressure. The needle will jump further with maximal oscillations occurring at mean arterial pressure MAPas measured by moving the lever once more. Diastolic pressure is the point at which these oscillations reduce. The most accurate measurements taken are those of systolic and mean blood pressures with diastolic measurements being more susceptible to operator variability.
However, diastolic pressure can be related to systolic pressure and MAP using the following formula: Liquid manometers The air in the cuff acts on a liquid forcing it up a manometer.
Homework Help: Estimating the damping ratio from the waveform graph
Mercury is used as it has A systolic pressure of mm of mercury equates to 1. A sphygmomanometer uses an open manometer and measures gauge pressure, e.
Unlike water, the meniscus created by a level of mercury is convex upwards. Measurement is taken from the top of the meniscus. Closed manometers are used in mercury barometers and measure absolute pressure. A meniscus forms below a Torricellian vacuum. When the height of a mercury column is above atmospheric pressure, i. It is not a true vacuum as it has a pressure equal to that of the saturated vapour pressure of mercury and hence contains mercury vapour.
This vacuum is termed a Torricellian vacuum. Assuming gravity and the density of the mercury remain constant; the height of a column of mercury is only proportional to the force exerted upon that column. Therefore, the width and shape of the manometer has no bearing on the height of the column and therefore no bearing on the measurement.
October 10, This work proposes a procedure to estimate the dynamic damped behavior of fiber reinforced composite beams in flexural vibrations. A set of experimental dynamic tests were carried out in order to investigate the natural frequencies and modal shapes. These results are used to evaluate the damping factors by the program FREQ. These damping factors are then used as input to a damped dynamic analysis by the Finite Element Method, using Rayleigh Model.
A good agreement between theoretical and experimental results was obtained. Thus, it became possible to validate the proposed procedure to evaluate dynamic damped behavior of composite beams. Introduction The combination of different materials has been used for many thousands of years to achieve better performance requirements.
There are nowadays many examples in the aeronautical and automobile industries, and yet the application of composite materials is still growing, including now areas such as nautical industry, sporting goods, civil and aerospace construction Umekawa and Momoshima1, He et al2 and Eslimy-Isfahay and Banerjee3.
In order to achieve the right combination of material properties and service performance, the dynamic behavior is one of the main points to be considered.
To avoid the typical problems caused by vibrations, it is important to determine: According to the Classical Laminate Theory CLTthe stiffness of a component manufactured with composite laminates can be altered through a change in the stacking sequence. This allows the tayloring of the material to achieve the desired natural frequencies and respective mode shapes, without changing its geometry drastically or increasing its weight Tsai and Hahn4 Tsai5 Vinson and Sierakowski6.
As a consequence, there is a large number of works in literature about vibration problems with composite materials and structures, such as Koo and Lee7, Khdeir8, Rao and Ganesan9, Zapfe and Lesieutre On the other hand, damping modeling of composite materials has been an issue of great interest for many researchers.
It has been shown that damping of composite components can also be modified through a change in the stacking sequence. Some works as Suarez et al. Hu and Dokainish19 used two approaches for the damping models: They concluded that both models yielded to non significant differences in the natural frequency, damping and mode shapes, if the system is slightly damped. More recently, Qian et al.
The main objective of this work is to propose a numeric-experimental procedure to estimate the dynamic damped behavior natural frequencies, mode shapes and damping factors of fiber reinforced composite beams in flexural vibrations. Materials and Methods Glass fiber was used as reinforcement in the form of bi-directional fabric Plain weave E-glass cloth with 0. The density and fiber volume fraction of the composite were calculated using formulation shown by Agarwal and Broutman24 Table 1.
Estimating the damping ratio from the waveform graph | Physics Forums
Where the subscripts x, y and z denote the directions along the length, across the width and through the thickness of the beam, respectively local on-axis system coordinates. Two set of symmetrical beam laminates with thickness of 1.
After the finite element analysis, the composite were molded using the hand lay-up process. The composite was molded in a metal mold which was closed under pressure 2.
Afterwards the cured composite was removed from the mold and the specimens beams were cut in the dimensions for the impulse test length equal 0. Thus, they are measured natural frequencies and damping factors of the beams.
Further, these results were compared with undamped and damped frequencies from the FEA. Finite element analysis Initially the beams were modeled in order to get a initial estimation of the undamped natural frequencies and mode shapes.
The beams were discretized using fifty finite elements type shell99 Fig. This element has 8 nodes and is constituted by layers that are designated by numbers LN - Layer Numberincreasing from the bottom to the top of the laminate; the last number quantifies the existent total number of layers in the laminate NL - Total Number of Layers.
Thus the model of laminate was carried out using ten layers and the engineering constants for the laminae are obtained from Table 1. Once the problem has been discretizedthe next step was to determine the matrices which represent it, starting with the elementary matrices.