Simulation of Block Diagram Schematics Project

Greetings everyone

I have created a project using block diagram schematic in quartus ii software. The project is a simple multiplexing system. I have downloaded the project into the target FPGA on Altera DE2 board. The project runs without problem and the LEDs show the blinking correctly. But I just can't Simulate the project using Quartus II waveform editor. So, what is the reason for that???? I mean if the project runs correctly that means there is no problem, so why not giving output in Simulation??? Thanks!