Hydraulic induced vibration starts with a continuous flowdisturbance that creates a periodic pressure pulse and changes in direction (elbow, tee, bend) or changes in flow cross section (valve, orifice, reducer) this pressure pulse causes pulsating forces on the pipe and makes it vibrate the complexity of the vibro-acoustic behavior of flexible, fluid-filled pipe systems is predominantly determined by two parameters, the frequency and the ratio of the masses per unit pipe length of fluid and pipe wall. The number of simultaneously propagating waves in the pipes increases with frequency. The mass ratio determines whether fluid borne and structure-borne waves may be treated separately. If this ratio is close to one, fluid pulsations and mechanical vibrations will be strongly coupled, so that it becomes necessary to consider their interaction when analyzing the dynamic behavior therefore, it is vitally important that the evaluation of natural frequency of a pipe be accurately to prevent any resonance condition. There have been extensive studies on the modeling and analysis of fluid conveying pipes over the past half-century, as the pipe conveying fluid has established itself as a generic paradigm of a kaleidoscope of interesting dynamical behavior. The effect of internal flow on transverse vibration of a pipe was studied. Coriolis acceleration of the internal fluid was taken into account, the geometry of fluid
Within its life cycle, a copepod goes through drastic changes in size, shape and swimming mode. In particular, there is a stark difference between the early (nauplius) and later (copepodid) stages. Copepods inhabit an intermediate Reynolds number regime (between ~1 and 100) where both viscosity and inertia are potentially important, and the Reynolds number changes by an order of magnitude during growth. Thus we expect the life stage related changes experienced by a copepod to result in hydrodynamic and energetic differences, ultimately affecting the fitness. To quantify these differences, we measured the swimming kinematics and fluid flow around jumping Acartia tonsa at different stages of its life cycle, using particle image velocimetry and particle tracking velocimetry. We found that the flow structures around nauplii and copepodids are topologically different, with one and two vortex rings, respectively. Our measurements suggest that copepodids cover a larger distance compared to their body size in each jump and are also hydrodynamically quieter, as the flowdisturbance they create attenuates faster with distance. Also, copepodids are energetically more efficient than nauplii, presumably due to the change in hydrodynamic regime accompanied with a well- adapted body form and swimming stroke.
Figure 1 shows that the piping system consists of 50.8 cm diameter pipe (ID = 48.6 cm), a 90 degree elbow, flanges, an orifice plate and a butterfly valve. The distribution of the flow velocity and shear stress are analyzed to understand the effect of flowdisturbance on the piping wall of a 90 degree bended elbow. The present study is conducted using four difference cases. Case 1 is the current arrangement: 60% valve open angle and L/D ≈ 1for the present operating case. Case 2 is the reference configuration, L/D ≈ 8, recommended with 60% valve open angle. This will be used as reference data for evaluation presented by EPRI , and Danbon and Sollice . Case 3 is 100% valve open angle and L/D ≈ 1. Case 4 is 60% valve open angle and L/D ≈ 5. Summary of the numerically analyzed test apparatus applied in this study is given in Table 1.
The subject of this Bachelor Assignment is acoustic particle velocity sensing based on thermal sen- sors. There are various configurations for these sensors, most of them relying on either two heated wires, or one heated wire and two measurement wires [3, 4]. These sensors work as follows, a current is put through the heating wire(s) and power is dissipated as heat. The heat will cause a thermal pro- file over the sensor. When an acoustic particle velocity, aka a sound wave, travels over the sensor, the thermal profile will be disturbed. This flowdisturbance leads to a temperature difference between the measuring wires that causes a change in resistance which is then measured by measuring the voltage over the wires when an equal current flows through the wires. For the configurations with either two heated wires, or one heated wire and two measurement wires an analytical model has al- ready been developed.
Sequences of four instantaneous side-view velocity fields generated by a solitary free-swimming E. superba are shown in Fig.4. The E. superba flow field has multiple, non-uniform, separated regions of high velocity produced by the beating motion of the pleopods. The flow in these regions is generally directed downward and rearward. Fluid is entrained from several directions (i.e. above, behind and from the side of the krill) into the region surrounding the pleopods and into the resulting fluid disturbance. The flow field of the krill penetrates a small distance in the vertical direction and is not visible beyond a distance of a half of a body length below the specimen. The restricted vertical extent of the krill flow field is roughly a half of a body length (Table2). The flow field persists in the horizontal direction at a mean value of nearly four body lengths (Fig.4, Table2). Dorsal views of E. superba (not shown) indicate that the transverse width of the flowdisturbance is again limited to approximately the width of the krill. The high velocity regions in the flowdisturbance are associated with high values of vorticity (Fig.5B). The mean maximum velocity is similar to the swimming speed of the krill (Tables1, 2) and the mean maximum value of vorticity varies substantially among individuals (Table2). Opposing positive and negative vorticity regions align horizontally in the krill flow field, and again no distinct vortices are present (Fig.5B).
We analyzed the flow fields characterized by chord-based Reynolds numbers of 5000 to 15,000 over a stationary model of a hummingbird (Calypte anna) wing. Utilizing two experimental techniques, constant-temperature anemometry and stereo particle image velocimetry, the high-fidelity results depict a laminar-to-turbulent transition process that develops over the wing. At both zero and non-zero angles of attack the spectrum of the velocity signals is wide. At non-zero angles of attack the flow separates from the wing surface and a shear layer forms. As a result, unsteady flow disturbances amplify at a chord-based Reynolds numbers as low as 5000. Nevertheless, only at a Reynolds number of 15,000 is the flowdisturbance growth rate sufficient to bring enough momentum from the outer region of the boundary layer to reattach the flow to the wing surface. For a Reynolds number of 5000, a comparison between the observed growth rates and a theoretical approximation concludes that flow disturbances of a Strouhal number of unity (and above) are no longer two-dimensional. In view of these conclusions, this study could serve as the first step towards a better understanding of the flow mechanisms over steady revolving and periodically flapping wings at this Reynolds number regime.
In general, experimental results presented in this paper show that an external disturbance, generated in conditions which can strongly differ from those found in the tube bank flow, will maintain its original frequency while transported through the bank. The propagation frequency is the shedding frequency or its first harmonic. The value of the predominant frequency in spectra seems to depend on the P/D-ratio and the Reynolds number, but in the cross-correlation measurements the period of the oscillation corresponded only to the shedding frequency. The ratio of the scale of the disturbance to the size of the gap spacing between the tubes of the rows seems to play an important role too. By reducing the gap spacing, the disturbance was dissipated after the second row for the largest vortex generator used (#2), while with the smallest vortex generator (#3) as well as with both vortex generators (#2 and #3) in the largest P/D-ratio studied, it subsisted until the 4 th or 5 th rows.
Tests in the zone from ground surface to 0.3 m.b.g.l. have been made using three different methods, which allows comparison of the test methods (Fig. 8). The double ring infiltrometer (DRI) measured greater values of hydraulic conductivity than obtained from the Guelph and single ring apparatus. This may reflect the greater volume of soil measured using the double ring test (the inner ring of the DRI has plan area of 7 times that of the single ring apparatus used, and 35 times the plan area of the borehole used for Guelph measurements). The values of hydraulic conductivity measured at 0.6 m depth by the Guelph and single ring are consistent with laboratory values obtained using triaxial apparatus to conduct constant head tests on small 38 mm diameter samples (also plotted in Fig. 8); it is likely that these particular tests did not incorporate macro structures such as desiccation cracks. Also plotted in Fig. 8 are the results from two sets of bailout tests carried out in unlined boreholes about 3.0 m deep; values are plotted at mid-depth of lowest and highest water levels on the recharge curve. These measure mainly horizontal radial flow out of the borehole, and the larger values of hydraulic conductivity obtained (of about 5x10 -9 m/s) are likely to be representative of larger volumes of soil incorporating structural features including thin silty bands encountered in the London Clay at Newbury (Smethurst et al. 2012). It can be concluded that the measured hydraulic conductivity may be a function of the method of measurement, with methods measuring a larger volume of soil likely to give greater values of hydraulic conductivity, particularly for a limited number of tests (there are few Guelph and single ring results for Newbury). The coefficient of variation for all three cutting sites is high (i.e. 1.9 to 2.6), which is indicative of the spatial variability of macro structures found in these natural materials further modified in the near-surface by vegetation roots and desiccation features.
Laminar–turbulent transition in boundary layers is a fundamental topic, the understanding of which has special significance in science and engineering. However, modelling the transition process from laminar to turbulent flow poses considerable theoretical and numerical challenges due to the complex nature of the nonlinear breakdown, disparate length and time fluctuations arising and uncertainties regarding the inflow or so-called receptivity process (Morkovin 1969). In a flat-plate boundary layer, laminar–turbulent transition can be triggered by growth of small-amplitude perturbations, such as Tollmien–Schlichting (TS) waves. The linear stage of the TS disturbance evolution can be described by the Orr–Sommerfeld (OS) equation (Orr 1907). Since the existence of TS waves was experimentally verified by Schubauer & Skramstad (1948), there have been numerous detailed theoretical and numerical studies undertaken, to corroborate experimental observations of the transition process. While good agreement of eigenvalues based theory with experiment was achieved quite early (Schubauer & Skramstad 1948), the use of linear and nonlinear theories to predict the breakdown process and precisely where transition occurred remained elusive, until the realisation that the environment (initial conditions) played a crucial role in the transition modelling and hence turbulence tripping process. A presently accepted tenant of the main actors involved in the transition processes are receptivity, linear eigenmode growth and nonlinear breakdown. TS waves and their evolution is now known to be influenced by multiple physical factors such as non-parallelism, free-stream environment, surface geometry and surface roughness. To correctly predict where and how transition occurs, such complexity are therefore required to be included in the modelling.
The flow reversal occurred abruptly but not uniformly across the shelf. We used the time at which the speed goes to a minimum (Table 2) as the approximate time of the rever- sal at each mooring. Generally the reversal proceeded up the coast from southwest to northeast and inshore to offshore. OB3 was first, OB27 second, then OB1 and the two offshore moorings. The greatest difference between times was 03:45 between OB3 and OB2. Each of these time differences im- plies a propagation speed and direction. This information is presented in Fig. 12. We can think of the CORMP moorings as an array through which a signal has propagated and been received at each mooring at the time of the flow reversal. The speed of propagation is the projection of the velocity vectors shown in Fig. 12 onto the real direction of propagation. If the signal were a pure unidirectional plane wave going with con- stant direction and speed, each velocity derived from a moor- ing pair would have the same projection. Thus all would lie on the a line and the direction of propagation would be per- pendicular to that line.
The prediction of the behaviour of disturbance waves is of sig- ni ﬁ cant importance for researchers due to their dominant role in the heat and mass transfer characteristics of the annular ﬂow regime [5,8]. More speciﬁcally, the presence of disturbance waves inﬂuence the shear stress at the gas-liquid interface, together with the wall shear stress underneath them. Moreover, it has been established that liquid en- trainment into the gas core is linked to the presence of the disturbance waves. These factors ultimately have an impact on the overall pressure drop across the system. Furthermore, it has been found that heat transfer rates are enhanced in the areas where disturbance waves are present, whereas the laminar regions in between consecutive dis- turbance waves display much lower heat transfer values . As a result, the study of annular ﬂows in a variety of conﬁgurations has been conducted in an attempt to improve the understanding of such types of ﬂ ows and to advise the di ﬀ erent industries about integral character- istics such as pumping requirements, the fraction of liquid that is en- trained, or the onset of ﬂooding conditions. The achievements are still far from proper generalisations due to the mostly empirical character of the research and the huge number of ﬂow parameters which vary in diﬀerent experiments and aﬀect the properties of the disturbance waves and integral ﬂ ow characteristics. Such ﬂ ow parameters include the physical properties of both liquid and gaseous phases; size and shape of the duct; ﬂow orientation; distance from the inlet; presence of heat ﬂux, phase transitions, chemical reactions, etc.
The numerical assessment of rise time (s), settling time (s) after the disturbance and overshoot (%) for non-filtered and filtered control signal of SWPID controller is given in Table. II. From the table, it can be seen that SWPID controller produced less overshoot of 5.8287% while IF-SWPID and FF- SWPID has an overshoots of 14.3958% and 8.1932%. However, FF- SWPID controller responds faster than IF- SWPID and SWPID with a rise time of 3.1583s as against the 3.3629 and 3.8415s of the latter. Furthermore, FF-SWPID controller settles faster than IF-SWPID and SWPID with a settling time of 125.8280s as against the 127.9643 and 129.7340s of the latter.
In systems theory the problem stated in the introduction is known as the disturbance decoupling problem (DDP) and has been solved by W. Murray Wonham and others using linear algebra, see e.g. [1, Chapter 4]. Therefore it is useful to first show the known solution to this problem for a discrete time system and then use this solution to answer the research question.
The word break down implies that the spot originates from a small volume and suggests the im p o r t a n ce o f t h e d ist u r b a n ce p r e se n t immediat ely before break down to occur. It is important to note that it may be unjustified to ne glect t he charact er of flow far upstream of the bre ak down point. The role of upstream flow is to produce and amplify dist urbance s which satisfy certain local conditions that cause break down to turbulence.
The Fisheries Department has established a Trout Fish Farm in 1905. Since then it is a source of continuous disturbance to Dachigam National Park. The feed provided to the fish is having adverse effects on physico-chemical characteristics of Dagwan Stream. A variety of chemicals are used to inhibit the growth of organisms which foul netting and other structures, reducing water flow through the cages. An increasingly significant effect of intensive fish culture is eutrophication of the water receiving aquaculture effluent. Fish excretion and fecal wastes combine with nutrients released from the breakdown of excess feed to raise nutrient levels well above normal, creating an ideal environment for algal bloom formation.
Comparing with analyzing power quality disturbance signals in frequency domain, the method presented by this paper has some advantages. First, if one feature or some features satisfied some conditions, a disturbance or mixed disturbances can be sure. That is to say, the disturbance classification would not be probable, but be de- finitive. Second, the features extracted won’t change a lot for the existence of the other disturbances. This cha- racteristic is the key of classifying the mixed disturbances. Third, the features have clear physical meanings. So it profits the evaluation of the disturbance parameters.
Similar to the output regulation theory, each unknown external disturbance d i is supposed to be generated by an exogenous system, model (2) we define as in form (3) can represents sinusoidal disturbance with unknown phase and magnitude. In application, many kinds of disturbances encounter- ed in engineering can be described by this sinusoidal model, for example, the control of aircraft control , magnetic bearing control , robotic systems , etc.
For dynamic stiffness enhancement, this paper presents a new method for synthesizing repetitive controllers capable of rejecting periodic vibration disturbance. Dynamic stiffness of the control system is analyzed. Direct and quadrature dynamic stiffness are defined for the repetitive con- trollers’ design. A trade-off method between the determinations of the controller’s parameters is necessary such that both the rejecting performance and stability can be achieved simultaneously. An illustrated example of a twin linear drive system is given to verify the performance of the pro- posed control design. The control performance of the present method is evaluated in the experi- mental disturbance rejecting control system, where the real-time control algorithms are imple- mented using a floating-point digital signal processor. Both computer simulation and experimen- tal results are presented to illustrate the effectiveness of the proposed repetitive controller de- sign.