Formulating a simple model structure 401.661 Advanced Construction Technology Moonseo Park Professor, PhD 39동 433 Phone 880-5848, Fax 871-5518 E-mail:
[email protected] Department of Architecture College of Engineering Seoul National University 401.661 Advanced Construction Technology 1 Equilibrium § Stock in equilibrium when unchanging *System in equilibrium when all its stocks are unchanging. § Dynamic Equilibrium e.g., # of US senate inflow = outflow § Static Equilibrium *Same contents. e.g., # of Bach cantatas inflow = outflow = 0 401.661 Advanced Construction Technology 2 Integration & Differentiation 401.661 Advanced Construction Technology 3 Calculus without Mathematics Quantity added during interval of length dt . = R (units/time) * dt (time) *R = the net flow during the interval Concrete Mixer Example § Area of each rectangle= Ridt Net Rate (units/time) § Adding all six rectangles = R1 0 dt Approximation of total water added S2 S1 Stock (units) § How to increase accuracy? t1 t2 401.661 Advanced Construction Technology 4 Fundamental Modes § Positive feedback causes exponential growth, while negative feedback causes goal-seeking behavior. Goal State of the System State of the System Time Time + State of the Goal System (Desired + Net State of System) Increase R State of the - System B Rate Discrepancy + + Corrective Action + §Sterman, J., “Business Dynamics”, Mcgraw-Hill, 2000 401.661 Advanced Construction Technology 5 First-Order Systems § A first-order system contains only one stock. § Linear systems are systems, in which the rate equations are linear combinations of the state variables. dS/dt = Net Inflow = a1S1 + a2S2 … + anSn + b1U1 + b2U2 … + bmUm Where the coefficients ai, bj are constants and any exogenous variable are denoted Uj.