Simulation and Modelling - Old Questions

5. What is analog computer? Design a basic analog computer that represents a simple dynamic system.

Analog computers are those computers that are unified with devices like adder and integral so as to simulate the continuous mathematical model of the system, which generates continuous outputs.

Analog method of system simulation is for use of analog computer and other analog devices in the simulation of continuous system. The analog computation is sometimes called differential analyser. Electronics analog computers for simulation are based on the use of high gain dc amplifiers called operational amplifier (op amps). In such analog computer, voltages are equated to mathematical variables and the op amps can add and integrate the voltages. The proper configurations can handle addition of several input voltages each representing the input variables. The analog computer provides limited accuracy because op amps have many assumptions which can never be true in reality.

Now, 

Designing analog computer for Automobile Suspension system:

The general method by which analog computers are applied can be demonstrated using second order differential equation.

    M x" + D x' + K x = K F(t)

Solving the equation for the highest order derivate gives,

    M x" = K F(t) – D x' - K x

        Fig: Automobile suspension problem

Suppose a variable representing the input F(t) is supplied, assume there exist variables representing -x and -x'. These three variables can be scaled and added to produce Mx". Integrating it with a scale factor 1/M produces X'. Changing sign produces -x', further integrating produces -x, a further sign inverter is included to produce +x as output.