Hydrogeologic Electric Analog ComputerS

Electric analog computers are versatile and simple equipment that allow ground-water development schemes to be rapidly and accurately tested and allow the relative merits of alternate choices of development to be appraised. The electric analog computer consists of an analog model and excitation-response apparatus, i.e., waveform generator, pulse generator, and oscilloscope. The analog model is a regular array of resistors and capacitors whose values vary in accordance with the irregular physical dimensions and properties of nonhomogeneous aquifers. The behavior of the electrical network is described by an equation that has the same form as the finite-difference equation for nonsteady state three-dimensional flow of ground water. Electrical and hydraulic units are connected by four scale factors. Excitation-response equipment force electrical energy in the proper time phase into the analog model and measure energy levels within the energy-dissipative resistor-capacitor network. Close agreement between analog computer and exact analytical solutions for three selected idealized aquifer situations is noted.