Flood control systems

The Ramsar site and the important bird area Lonjsko Polje Nature Park (510 km2) represent mainly palustrine-riverine wetlands located within the flood-plains of the Middle Sava river basin (Central Posavina, Croatia). It represents the largest maintained inundation area of all the Danube River catchment and, at the same time, the key facility of the flood control system of the entire Sava river basin (including Bosnia and Herzegovina, and Serbia and Montenegro). 

Che Wu, Lu Fangfang, Li Junqi, Li Haiyan, Wang Jianlong, 2009, Typical Rainwater and Flood Control System of Developed Countries and Inspiration, China Water Supply and Drainage, (10)1-6. 

Harder, J.A. (1963). Analog models for flood control systems. Trans. ASCE 128(1) 993-1004. Harder, J.A, Nelson, J.O. (1966). Analog modeling the California Delta Tidal System. Journal ofthe Hydraulics Division AS E91QAYA). 1-10 93(HY2) 77-78. http //www.universityofcahfomia.edu/senate/inmemoriam/jamesharder.html P... 

Modern flood control systems are barrage weirs, clusters of barrage weirs, or high-water reservoirs. Besides protection from floods, these often present advantages of an ecological or economic nature. Difficulties in planning and dimensioning flood control systems are often caused by the fact that a number of random variables must be taken into account as input data. 

Infrastructure impacts every person in one or more of three roles for any specific system. Users are those directly served by an infrastructure system. Examples include drivers on a highway or families whose homes are protected by a flood control system. Producers of infrastructure products and services... 

As designs progress through phases, the cost estimates become more accurate. Using the watershed flood control system as an example, cost estimates in the preliminary design might have an accuracy of plus or minus 25 percent while cost estimates prepared for the final design of each individual flood control facility would be accurate to plus or minus one to five percent. 

A nation s quality of life is heavily dependent on its infrastmcture which includes, but is not limited to, its water supply and wastewater systems, transportation systems (e.g., highways, bridges, tunnels, railroads, airports, ports), stormwater management and flood control systems, communication systems, power generation and distribution systems, and other structures, facilities, and systems supportive of daily life. The infrastructure is built and maintained by the constmction industry. Annual U.S. constmction is on the order of a trillion (1,000 billion) dollars making it the largest product-based, contrasted with service-based, industry in the country (Halpin 2006). 

Pressure can also be controlled by variable heat transfer coefficient in the condenser. In this type of control, the condenser must have excess surface. This excess surface becomes part of the control system. One example of this is a total condenser with the accumulator running full and the level up in the condenser. If the pressure is too high, the level is lowered to provide additional cooling, and vice versa. This works on the principle of a slow moving liquid film having poorer heat transfer than a condensing vapor film. Sometimes it is necessary to put a partially flooded condenser at a steep angle rather than horizontal for proper control response. 

Submerged electrode hot water boilers operate in a totally flooded condition, and electrode insulating shields are mechanically adjusted by an automatic control system to provide the required HW temperature. As the insulating shields are adjusted between the electrodes and the neutral walls, so the current path is lengthened and heat generation (and thus output) is decreased. 

Funds for water retention systems, flood control, Irwestmentsln alternative irrgatlon techniques... 

Derive a dynamic mathematical model of the flooded-condenser system. Calculate the transfer function relating steam flow rate to condensate flow rate. Using a PI controller with tj = 0.1 minute, calculate the closedloop time constant of the steam flow control loop when a closedloop damping coefTident of 0.3 is used. Compare this with the result found in (u). 

All single-screw extruders have several common characteristics, as shown in Figs. 1.1 and 1.2. The main sections of the extruder include the barrel, a screw that fits inside the barrel, a motor-drive system for rotating the screw, and a control system for the barrel heaters and motor speed. Many innovations on the construction of these components have been developed by machine suppliers over the years. A hopper is attached to the barrel at the entrance end of the screw and the resin is either gravity-fed (flood-fed) into the feed section of the screw or metered (starve-fed) through the hopper to the screw flights. The resin can be in either a solid particle form or molten. If the resin feedstock is in the solid form, typically pellets (or powders), the extruder screw must first convey the pellets away from the feed opening, melt the resin, and then pump and pressurize it for a down-... 

The extensive quality control tests of raw materials, intermediate and final products represent a flood of data which have to be evaluated and documented according to the different aims of the quality control system. Considering the fact, that quality control often has to work under deadline pressure this work can only be done by using powerful electronic labour information and management systems (TIMS). 

The use of high or low limits for process variables is another type of selective control, called an override. The feature of antireset windup in feedback controllers is a type of override. Another example is a distillation column with lower and upper limits on the heat input to the column reboiler. The minimum level ensures that liquid will remain on the trays, while the upper limit is determined by the onset of flooding. Overrides are also used in forced-draft combustion control systems to prevent an imbalance between airflow and fuel flow, which could result in unsafe operating conditions. 

Operational constraints The various types of equipments used in a chemical plant have constraints inherent to their operation. Such constraints should be satisfied throughout the operation of a plant. For example, pumps must maintain a certain net positive suction head tanks should not overflow or go dry distillation columns should not be flooded the temperature in a catalytic reactor should not exceed an upper limit since the catalyst will be destroyed. Control systems are needed to satisfy all these operational constraints. 

EXAMPLE 9.1. Consider the process with a series cascade control system sketched in Fig. 9.le. A typical example is a secondary loop in which the flow rate of condensate from a flooded reboiler is the manipulated variable M, the secondary variable is the flow rate of steam to the reboiler, and the primary variable is the temperature in a distillation column. We assume that the secondary controller Gci and the primary controller Gci are both proportional only. 

Intermediate component accumulation may interfere with the control system. For instance, a component trapped in the upper part of the column may warm up the control tray. The controller will increase reflux, which pushes the component down. As the component continues accumulating, the control tray will warm up again, and reflux will increase again eventually, the column will flood. One case describing a similar sequence has been reported (352). 

Improved stability. When columns operate close to their capacity limits, even small disturbances can carry the column beyond the flood point (152). Once flooding sets in, it may be difficult to return the column to normal operation unless vapor and liquid traffic are largely reduced. In order to operate the column at a point close to maximum capacity, stable operation and reduction of the magnitude and frequency of outside disturbances are essential. The column control system and instrument tuning play a major role in achieving maximum column capacity. It has been the author s experience that the improved stability can usually enhance capacity by 2 to 5 percent, and sometimes by up to 10 percent. 

Minimum throughput tests are usually carried out by reducing the feed rate to the column while at the same time reducing reflux and reboil rates in proportion until the separation falls off sharply or until an instability is observed. The procedure for reducing the reflux and reboil rates should take the control system into account, and should be carried out in a manner similar to that used for flood testing (see Sec. 14.1.4). 

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