Abstract: Water hammer is a hydraulic transient problem which is commonly encountered in the penstocks of hydropower plants. The numerical model was developed to estimate the transient behavior of pressure waves in pipe systems. The computational algorithm was proposed to model the water hammer phenomenon in a pipe system with pump shutdown at midstream and sudden valve closure at downstream. To predict the pressure head and flow velocity as a function of time as a result of rapidly closing a valve and pump shutdown, two boundary conditions at the ends considering pump operation and valve control can be implemented as specified equations of the pressure head and flow velocity based on the characteristics method. It was shown that the effects of transient flow make it determine the needs for protection devices, such as surge tanks, surge relief valves, or air valves, at various points in the system against overpressure and low pressure. It produced reasonably good performance with the results of the proposed transient model for pipeline systems. The proposed numerical model can be used as an efficient tool for the safety assessment of hydropower plants due to water hammer.
Abstract: Negative pressure phenomenon appears in many
thermodynamic, geophysical and biophysical processes in the Nature
and technological systems. For more than 100 years of the laboratory
researches beginning from F. M. Donny’s tests, the great values of
negative pressure have been achieved. But this phenomenon has not
been practically applied, being only a nice lab toy due to the special
demands for the purity and homogeneity of the liquids for its
appearance. The possibility of creation of direct wave of negative
pressure in real heterogeneous liquid systems was confirmed
experimentally under the certain kinetic and hydraulic conditions.
The negative pressure can be considered as the factor of both useful
and destroying energies. The new approach to generation of the
negative pressure waves in impure, unclean fluids has allowed the
creation of principally new energy saving technologies and
installations to increase the effectiveness and efficiency of different
production processes. It was proved that the negative pressure is one
of the main factors causing hard troubles in some technological and
natural processes. Received results emphasize the necessity to take
into account the role of the negative pressure as an energy factor in
evaluation of many transient thermohydrodynamic processes in the
Nature and production systems.
Abstract: Pressure waves and Water Hammer occur in a
pumping system when valves are closed or opened suddenly or in
the case of sudden failure of pumps. Determination of maximum
water hammer is considered one of the most important technical
and economical items of which engineers and designers of
pumping stations and conveyance pipelines should take care.
Hammer Software is a recent application used to simulate water
hammer. The present study focuses on determining significance of
each input parameter of the application relative to the maximum
amount of water hammer estimated by the software. The study
determines estimated maximum water hammer variations due to
variations of input parameters including water temperature, pipe
type, thickness and diameter, electromotor rpm and power, and
moment of inertia of electromotor and pump. In our study,
Kuhrang Pumping Station was modeled using WaterGEMS
Software. The pumping station is characterized by total discharge
of 200 liters per second, dynamic height of 194 meters and 1.5
kilometers of steel conveyance pipeline and transports water to
Cheshme Morvarid for farmland irrigation. The model was run in
steady hydraulic condition and transferred to Hammer Software.
Then, the model was run in several unsteady hydraulic conditions
and sensitivity of maximum water hammer to each input parameter
was calculated. It is shown that parameters to which maximum
water hammer is most sensitive are moment of inertia of pump and
electromotor, diameter, type and thickness of pipe and water
temperature, respectively.
Abstract: Pressure wave velocity in a hydraulic system was
determined using piezo pressure sensors without removing fluid from
the system. The measurements were carried out in a low pressure
range (0.2 – 6 bar) and the results were compared with the results of
other studies. This method is not as accurate as measurement with
separate measurement equipment, but the fluid is in the actual
machine the whole time and the effect of air is taken into
consideration if air is present in the system. The amount of air is
estimated by calculations and comparisons between other studies.
This measurement equipment can also be installed in an existing
machine and it can be programmed so that it measures in real time.
Thus, it could be used e.g. to control dampers.
Abstract: A analysis on the conventional the blood pressure estimation method using an oscillometric sphygmomanometer was
performed through a computer simulation using an arterial pressure-volume (APV) model. Traditionally, the maximum amplitude algorithm (MAP) was applied on the oscillation waveforms of the APV model to obtain the mean arterial pressure and the characteristic ratio. The estimation of mean arterial pressure and
characteristic ratio was significantly affected with the shape of the blood pressure waveforms and the cutoff frequency of high-pass filter
(HPL) circuitry. Experimental errors are due to these effects when estimating blood pressure. To find out an algorithm independent from
the influence of waveform shapes and parameters of HPL, the volume
oscillation of the APV model and the phase shift of the oscillation with fast fourier transform (FFT) were testified while increasing the cuff
pressure from 1 mmHg to 200 mmHg (1 mmHg per second). The phase shift between the ranges of volume oscillation was then only observed between the systolic and the diastolic blood pressures. The same results were also obtained from the simulations performed on two different the arterial blood pressure waveforms and one
hyperthermia waveform.
Abstract: LES with mixed subgrid-scale model has been used to
simulate aerodynamic performance of hypersonic configuration. The
simulation was conducted to replicate conditions and geometry of a
model which has been previously tested. LES Model has been
successful in predict pressure coefficient with the max error 1.5%
besides afterbody. But in the high Mach number condition, it is poor in
predict ability and product 12.5% error. The calculation error are
mainly conducted by the distribution swirling. The fact of poor ability
in the high Mach number and afterbody region indicated that the
mixed subgrid-scale model should be improved in large eddied
especially in hypersonic separate region. In the condition of attach and
sideslip flight, the calculation results have waves. LES are successful
in the prediction the pressure wave in hypersonic flow.
Abstract: The theoretical investigation is carried out to describe
the effect of increase of pressure waves amplitude in clean and bubbly liquid. The goal of the work is to capture the regime of multiple magnification of acoustic and shock waves in the liquid,
which enables to get appropriate conditions to enlarge collapses of
micro-bubbles. The influence of boundary conditions and frequency
of the governing acoustic field is studied for the case of the
cylindrical acoustic resonator. It has been observed the formation of
standing waves with large amplitude at resonant frequencies. The
interaction of the compression wave with gas and vapor bubbles is
investigated for the convergent channel. It is shown theoretically that
the chemical reactions, which occur inside gas bubbles, provide additional impulse to the wave, that affect strongly on the collapses
of the vapor bubbles