Technical Problems of Electric Analog Model for Ground Water Analysis Part 2 A discrete analog model

Abstract

An unsteady state, two dimensional flow is simulated by the discrete analog model, that is R - C network composed of a series of resistors and capacitors. In this model, a given problem is solved on the nodes and lines of the grid expressing the actual field.
The simulation of this model is based on the analogy between the unsteady state ground water flow and kirchhoff's law of electric current. Considering the four scale factors, aquifer constants, boundary conditions and pumping conditions are converted to the values of resistors and capacitors, pulse width and pulse amplitude. Therefore, the aquifer constants and boundary conditions are most important factors of this model. After all, resistors are analogous reciprocally to the coefficients of transmissibility of the aquifer, and capacitors are analogous to the coefficients of storage. When the field boundary does not coincide with the lines of the network grid, the values of R- C circuit are calculated by vector - area technic.
The equipments for analysing R-C network analog model are formed of sawtooth generator, pulse generator, synchroscope, analog model and calibrate resistor. Analog model is constructed on an acrylic board. It is 3 mm thick, and is perforated in square grid with 2.5 cm intervals. Eyelets are inserted in the holes to make terminals. Resistors and capacitors are connected to the terminals by solder, and one side of the capacitors is connected to the earth.
Pulse generator produces rectangular pulse. It is send to the pumping well junction of the analog model. The sawtooth generator gives the excitation to the pulse generator to produce pulse. Pulse width is analogous to the pumping period and pulse amplitude is analogous to the pumping rate. The probe of the synchroscope is touched to the observation well junction of the analog model. Then, on the screen of synchroscope, the response wave is drawn in obedience to the distance between pumping well and observation well.
As the response wave is time-voltage curve, it is converted to time-drawdown curve by the four scale factors and the scale of the synchroscope.