On The Accuracy Of Tidal Waves Analysis

Analysis of tidal waves is a very crucial step when designing coastal structures. The forces on the structure, the top elevation of the structure and the interaction between waves and structure are largely depended on water fluctuation due to tidal wave. Normally tidal waves are analyzed using either Fourier series or least square method. Both methods are basically replacing a periodic function (tidal waves) with a number of harmonics. The decomposition of tidal waves into harmonics depends on the length of the tidal waves record. Two harmonics of very close frequencies need a longer observation. Therefore a limited duration of survey may produce only a few harmonics and hence less accurate prediction. The paper discusses the error of tidal waves analysis based on Fourier method and least square method based on various length of observation and the number of harmonic involved. Hypothetical tidal waves are generated and then decomposed (analyzed) to produce its harmonics. The accuracy of the analysis is investigated for some possible combination between semi-diurnal and diurnal groups of harmonics. The least square method was found to be more advantageous than the other and therefore the method was investigated further for analyzing 1000 hypothetical tidal waves containing nine major harmonics. The study concluded that the accuracy depends on the frequency of the harmonics to be separated, the length of the observation, and the initial and end phase of tidal waves. The nine major harmonics should be established using 30 days of observation

Model Berkurangnya Klorin (Chlorine Decay) Pada Jaringan Air Bersih Dalam Pipa

Abstract Along the distribution main, water quality may be degrading due to temperature, contact with pipe wall, external contaminant etc. Therefore, although the quality of water has been assured in the Water Treatment Plant (WTP), continuous assurance is required along the pipe. Chlorine (Clz) is commonly usedfor water disinfectant. Along the pipe residual active chlorine provide assurance that the water is free from undesirable pathogenic microorganism. However, Cl2 decay along the pipeline due to interaction with surrounding (substance within the water and the pipe wall). Hence, monitoring is necessary to assure enough chlorine in the water. At least there are two water quality model namely DVEM (Discrete Volume Element Method) and Lagrangian method that are used in many available software in the market. The Lagrangian method is said to be superior to the DVEM although it has some weakness especially when the traveling distance of the water(s) is considerably less than the element size (L). In this paper Lagrangian method is developed. The program is calibrated to simulate simple transmission system transmitting water containing certain amount of chlorine. The systems were constructed both mathematically and physically. The chlorine residual the down stream end of the transmission systems were recorded after certain time steps. Various slL were used to study the performance of the model. Analytical solutions were carried out to assured that the numerical approach is consistent to the mathematical formulation. The calibration indicates that the program has been able to simulate the chlorine decay through the pipe. The weakness of the method was found during small slL where the result of the simulation fluctuates. The relative fluctuations are small and negligible as slL close to or higher than unity. Even in small slL value the absolute amplitude of the fluctuation may be ignored. The numerical approach was shown to be in good agreement with the analytical one. It was found that in normal condition, Kb value for clean water in Gadjah Mada University Campus is small but significant for accurate simulation. Keywords: water, quality, chlorine, WTP, DVE

Smulasi Kinerja Pompa Pada Sistem Jaringan Air Bersih

Distribution main is the most important part of water distribution system as most of the investment of distribution system is allocated for it. Yet, for years engineers tend to take the design and construction of the system lightly. Many assumptions and simplifications have made the distribution main work unsatisfactorily. The need for pumping stations for example, is faced by most water companies. The operation for pumping stations may consume a large part of the total operation budget. Such situation should become the central consideration of the engineers. There are many possibilities of water transmission and distribution system designs that require pumping station. The use of tanks is an option that may improve pumping station efficiency. The layout of the system play an important role in cutting the operational cost. This paper discuss about mathematical modelling to simulate distribution system comprising reservoir, pipes, pumps, tanks, and demand-nodes. The demand fluctuation is based on Directorate General Cipta Katy(\u27 Department of Public Work Indonesia (CK) average maximum daily peak and the demand coefficient fluctuation according to Gupta. Pump performance is based on a simple quadratic equation. The pipe flow model is based on Darcy-Weisbach equation, where the friction factors are defined dynamically depending on Reynold number. Six lay out of simple distribution mains yet represent the more complex situation of real distribution systems are tested to study pump performance (efficiency) on these different situations. The results show that the model has been able to simulate the pump characteristic in respond to demand as well as tank water level fluctuations. The existence of the tank significantly improve the efficiency of the pumps. Pump efficiency is slightly reduced when by pass pipe is installed from upstream to down stream of the tank. Finally, installation of a tank near and down stream of distribution area may improve pressure fluctuation at demand-nodes

SIMULASI KEMUNGKINAN TERJADINYA PRIMING DEPRIMING REPRIMING SIPON (KOMBINASI SIPON DAN SPILLWAY TERBUKA) PADA RESERVOIR BERBENTUK PERSEGI

The combined ,spillway (Free flow spillway and siphon) may create oscillation within the reservoir during operation. Large approach velocity of water toward the siphon is quickly dampened as the siphon is depriming.. The kinetik energy of the water is transformed into potensial energy and hence create higher water level in. ront of the siphon. Consequently, such high water level at the siphon will trigger there priming condition to start. The siphon and the free.flow spillway will reduce the water level quickly. This may in turn create another possibility of depriming condition. The cycle may then start again from depriming-priminngreperirning due to oscillation within the reservoir. The paper studies the oscillation within the reservoir of different size and shape of rectangular reservoir (although the shapeof the reservoir is kept rectanglar the ratio between the width and the length is varied). Simulation of the oscilation in the reservoir were conducted using the Method of Characteristicinflow into the reservoir is assumed zero to represent the situation where the oscillation is less possible. The different of priming and depriming elevation is 1.0 meter. The priming level (EP) is set at +2.0m whilst the depriming level is at +1.0m. The spillway is of Ogee type.. The study shows that oscillation in the reservoir due to priming-depriming-repriming of siphon is possible. However, the peak time of the surge (time where the surgeelevation at its maximum) is so small where there is no or very little chance for physical repriming to occure. However, as the priming level (Er) is lowered to +1.5m, there is sufficient time for physical repriming. The study also conclude that different ratio of length and width of rectangular reservoir result in similar surge shape

Studi Efisiensi Pompa Air Laut Energi Gelombang Tipe Flap

There are many sources of energy in nature such as solar. radiation, petroleum, coals, wind, tides and waves. The use of energy resources must consider its availability, influence on the environment, efficiency, and cost of operation. Sea waves provide a large amount of energy, but its recovery is limited. A water pump technology making use of wave energy comprising a flap, a piston and valve sistem can be used to increase sea water potential energy for various use. This research was done using physical model tests with various pipe piston, water depth, wave .period and head. The discharge obtained was measured three times for each combination. The model used a scale of approxiamately 1:20, based on the availability of facilities. Pump efficiency was measured by comparing output power with the input wave power. Results of the research indicate that the for first model (diameter of 11 cm), maximum pump efficiency was 7.87 %, it provide discharge of 0.0294 L/s at head of 35 cm, wave height of 3.35 cm and wave period of 1.79 second. The second model (diameter of 7 cm), produced maximum pump efficiency at 11.05 %, the maximum discharge 0.0393 lt/ s at total head of 30 cm, wave height of 6.63 cm, and wave period of 2.68 second. Keywords : Wave energy, Pump and Efficienc

Cost Comparison of Drainage Channel Construction Considering Uncertainty of Rainfall Distribution

Rainfall data is the main parameter to design drainage channel. The accuracy of rainfall data determines the accuracy of peak discharge estimation that is used for designing the drainage channel for flood mitigation purpose. The previous study presented that uncertainty of peak discharge is associated with the uncertainty of rainfall distribution and uncertainty of water holding capacity. The main purpose of this study is for understanding the sensitivity of rainfall data by comparing the estimated cost to construct drainage channel based on different values of peak discharges using two different rainfall data set which one rainfall data is created by considering 10% uncertainty of rainfall distribution. This study area is located on Plampang, Sumbawa Besar, West Nusa Tenggara. Results showed that the total cost to construct drainage channel increased by 15% if considering 10% uncertainty of rainfall

Optimasi Pompa Air Laut Energi Gelombang

Among energy resources, sea waves is one which is renewable. Sea waves provide an alternative energy which is available largely. This type of energy however, has not been explored in Indonesia. Flap-type wave energy pump is a new technology to elevate sea water and flow it to land, utilizing the wave energy. The method is described in this paper. Pump optimization was conducted using experimental method utilizing wave flume in which piston, valve and piston tube were redesigned. Regular and not breaking wave was used. The pump characteristic was tested with variation of depth (d), wave height (H), wave period (T), weight of valve ball (w), and displacement of valve ball (yk) with constant z. Results of this research indicated that an optimum efficiency (lip) was found at w = 0,93 and yk = 0,14. Using wave height (H) from 2,225 to 12,25 cm at water depth (d) of 50, 55, and 60 cm, wave period (T) of 1,79, 2,24, 2,68, 3,13, 3,58, and 4,03 s, showed that flap-type wave energy pump gained high efficiency. Pump efficiency reached 34,7% at (H/he)(Lb/ A) = 20,86 and z/d = 0,54, and will decrease along with the increasing wave length (L), wave height (H), flap wide (b) and the decreasing head (he), and piston diameter (D). Using a flap-type wave energy pump instead of the conventional electrical motor pump, may give some additional benefits : no fuel and pollution free Key words : wave energy, pump, efficiency

Minimum Jet Velocity for Unbounded Domain Fluidization as a New Dredging Methods

Unlike for the bounded domain, the minimum fluidization velocity of the unbounded fluidization domain has not been well developed. The aimed of the research is to formulate the minimum jet (holes) velocity (voc) theoretically and experimentally as the criteria for unbounded domain fluidization. Physical experiments were conducted for bounded and unbounded fluidizations of 20 cm to 45 cm thickness of sand bed. The bounded fluidization was carried out using a transparent vertical tube, whilst the unbounded fluidization was conducted on a transparent box. The fluidization discharge and pressure were measured. Empirical equations on jet holes velocity based on the experiment was developed. It was found that voc depends on the required superficial velocity at the surface of sediment deposit (vc) and flow rate loose factor (y) due to unbounded domain conditions. The vc is greater than the minimum fluidization velocity in bounded domain (vmf). The conservative values of velocity conversion factor (ks) were found to be approximately 2.0