• Journal of Environmental Health Sciences
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• v.8 no.2
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• pp.13-31
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• 1982

Factors affecting on dewatering characteristics of anaerobically digested or/and elutriated sludges were examined from 15 January 1982 to 30 April 1982, results obtained were as follows 1. Sludges, either anaerobically digested or/and elutriated sludges, which were produced at the Joong Rang Cheon Sewage Treatment Plant wore found to be compressive in its nature, coefficient of compressibility ranged from 0.83 for unelutriated and 1.10 for elutriated. 2. Dosage of FeC13 for the anaerobically digested sludges were difficult to establish for the most favorable dosage rate, though the filterability indicated linear improvement with increased dosage from dosing rate excess of over 15% in terms of dry solids by weight, under the conditions of this examination. Optimum filterability were obtained with 9~11% of $FeCl_3$ for elutriated sludges, and required CaO, as aids, were appeared to be 2.5~3.5 times that of the $FeCl_3$ at that point by weight. 3. The specific resistances for anaerobically digested sludges showed higher value than the elutriated one, being $11 \times 10^{12} ~ 20 \times 10^{12}$ cm/g with no chemical conditioning, and $2 \times 10^{12} ~ 11 \times 10^{12}$ cm/g with conditioned ($FeCl_3$ + CaO) contrast to $0.5 \times 10^{12} ~ 2.0 \times 10cm/g$ for the elutriated. 4. The strength of the alkalinities before and after elutriation were measured to 10,000 ~ 15,000 mg/l and 1,500 ~ 2,000mg/l respectively. These alkalinities affected greatly on the filterabilities together with concentration of the organic matters in the sludges. 5. The yields with 11% $FeCl_3$, by weight to the DS, on the elutriated sludges averaged to $14.7 kg/m^2.hr$, and $3.2kg/m^2.hr$ for unelutriated sludges. Which was 4.6 times of not elutriated sludges. Elutriated sludges without chemical conditioner added showed much better filterabilities than with 15% of $FeCl_3$ added to the anaerobically digested and unelutriated sludges.

• Computational Structural Engineering
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• v.10 no.4
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• pp.291-302
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• 1997

This paper presents an analytical method for evaluating the free vibration of a circular cylindrical tank filled with bounded compressible fluid. The analytical method was developed by means of the finite Fourier series expansion method. The compressible fluid motion was determined by means of the linear velocity potential theory. To clarify the validity of the analytical method, the natural frequencies of a circular cylindrical tank with the clamped-clamped boundary condition, and filled with water, were obtained by the analytical method and the finite element method using a comercial ANSYS 5.2 software. Excellent agreement on the natural frequencies of the liquid-filled tank structure was found. The compressiblity and the fluid density effects on the normalized coupled natural frequencies were investigated. The density of fluid affects on all coupled natural frequencies of the tank, whereas the compressibility of fluid affects mainly on the natural frequencies of lower circumferential modes.

• International Journal of Fluid Machinery and Systems
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• v.3 no.4
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• pp.315-323
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• 2010

This work investigates the influence of water compressibility on pressure pulsations induced by rotor-stator interaction (RSI) in hydraulic machinery, using the commercial CFD solver ANSYS-CFX. A pipe flow example with harmonic velocity excitation at the inlet plane is simulated using different grid densities and time step sizes. Results are compared with a validated code for hydraulic networks (SIMSEN). Subsequently, the solution procedure is applied to a simplified 2.5-dimensional pump-turbine configuration in prototype with different speeds of sound as well as in model scale with an adapted speed of sound. Pressure fluctuations are compared with numerical and experimental data based on prototype scale. The good agreement indicates that the scaling of acoustic effects with an adapted speed of sound works well. With respect to pressure fluctuation amplitudes along the centerline of runner channels, incompressible solutions exhibit a linear decrease while compressible solutions exhibit sinusoidal distributions with maximum values at half the channel length, coinciding with analytical solutions of one-dimensional acoustics. Furthermore, in compressible simulation the amplification of pressure fluctuations is observed from the inlet of stay vane channels to the spiral case wall. Finally, the procedure is applied to a three-dimensional pump configuration in model scale with adapted speed of sound. Normalized Pressure fluctuations are compared with results from prototype measurements. Compared to incompressible computations, compressible simulations provide similar pressure fluctuations in vaneless space, but pressure fluctuations in spiral case and penstock may be much higher.

• Journal of the Korean Society of Safety
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• v.15 no.3
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• pp.115-123
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• 2000

Pneumatic actuators are widely used in a variety of hazardous working environments. Any process that involves pneumatic actuation is also recognized as "eco-friendly". In most cases, applications of pneumatic actuators require only point-to-point control. In recent years, research efforts have been directed toward achieving precise position tracking control. In this study, a tracking position control method is proposed and experimentally evaluated for a linear positioning system. The positioning system is composed of a pneumatic actuator and a 3-port proportional valve. The proposed controller has an inner pressure control loop and an outer position control loop. A PID controller with feedback linearization is used in the pressure control loop to nullify the nonlinearity arising from the compressibility of the air. The position controller is also a PID controller augmented with the friction compensation by a neural network. Experimental results indicate that the proposed controller significantly improves the tracking performance.rformance.

• Journal of the Korean Geotechnical Society
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• v.27 no.3
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• pp.85-94
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• 2011

Mixtures of sand and rubber particles ($D_{sand}/D_{rubber}=1$) are investigated to explore their characteristics under different stain level. Mixtures are prepared with different volumetric sand fractions ($sf=V_{sand}/V_{total}$). Experimental data are gathered from a resonant column, an instrumented oedometer, and a direct shear tests. Results show that sand and rubber differently control the behavior of the whole mixture with strain level. Non-linear degradation of small strain stiffness is observed for the mixtures with $sf{\geq}0.4$, while the mixtures with low sand fraction ($sf{\leq}0.2$) show significantly high elastic threshold strain. Vertical stress-deformation increases dramatically when the rubber particle works as a member of force chain. The strength of the mixtures increases as the content of rubber particle decreases, and contractive behavior is observed in the mixtures with $sf{\leq}0.8$. Rubber particle plays different roles with strain level in the mixture: it increases a coordination number and controls a plasticity of the mixture in small strain; it prevents a buckling of force chain in intermediate strain; it leads a contractive behavior in large strain.

• Magazine of the Korean Society of Agricultural Engineers
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• v.25 no.4
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• pp.50-60
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• 1983

305 samples of alluvial deposit in inland and harbour districts were selected and consolidation charateristics of the alluvium were put in order statiscally. The correlations between them were as follows. 1. The relationships between LL(liguid limit) and Cc (compression index) were explained as Cc=0. 03(LL-21. 7) in case of inland district soil and as Cc=0. 019(LL-19) in case of harbour district soil. As compared with formular proposed by Skernpton, the gradient of this linear line was slight steep. 2. The relationships between PI(plastic index) and Cc were explained as Cc=0. 063 PI-0. 52 in case of inland district soil and Cc=0. 043 PI-0. 31 in case of harbour district soil. 3. As void ratio and natural moisture content were increased, Cc was increased, and as wet density was increased, Cc was decreased with a gentle curve. 4. As LL and P1 increased, mv(coefficient of volume compressibility) was increased but if LL and P1 was increased beyond a certain extend, mv has a tendency of constant value, that is, mv show a tendency to take constant value in the very soft clay. and mv in P=2. 5kg/cm$^2$ was about l${\times}$ l0-$^1$cm$^2$/kg in case of land district soil and 6x 10-$^1$crn$^2$/kg in case of harbour district soil lower than that in P=0. 25kg/crn2. 5. Cv(coefficient of consolidation) was a tendency to decrease with a gentle curve as LL was increased, and Cv in P=0. 25kg/crn2 was about 3x l0-$^1$crn$^2$/min larger than that in P=2. 5kg/crn$^2$. 6. Relationships between Py(pre-consolidation pressure) which is included over consolidation soil and ∑r1h(effective over-burden pressure) were explained as Py=l. 12 ∑r'h in case of land district soil and as Py=l. l5∑r'h in case of harbour district soil. 7. Some of the properties show good correlations between them, practical and effective applications of these correlations are expected in the planning and excution of soil investigation and also in the evaluation of the results.