ReliaSim® vs FlexSim
3D Process Simulation and a Rate-Based Line Simulator

FlexSim is 3D simulation software for modeling and improving almost any system or process. ReliaSim is built for production lines, especially high-speed ones, modeled as flow from each line’s own stop history. Both answer what-if questions before the real system changes. This page sets out where each fits.

What FlexSim is built for

FlexSim calls itself “3D Simulation Modeling and Analysis Software” and promises to help you “understand and improve any system or process” (FlexSim home page). It lists manufacturing, warehousing, material handling, supply chain, healthcare, airports and container terminals among its applications, with dedicated products for healthcare and container terminals. It presents its 3D view as a second level of validation, because people can see whether the model behaves like the real system. FlexSim is now an Autodesk product: the site is copyright Autodesk, and its free trial is offered through autodesk.com.

Where FlexSim is the better fit

• Layout and movement matter. Warehouses, material handling, AGVs and operators walking a floor are problems where space and travel decide the answer, and a 3D environment shows them directly.
• Persuading people visually. A realistic 3D model is a strong way to win agreement for a layout change.
• Systems beyond the line. Hospitals, airports and terminals are outside ReliaSim’s scope.

ReliaSim doesn’t try to match FlexSim’s 3D environment or its range of applications.

Where ReliaSim fits

The price is on the page

A ReliaSim desktop license is $8,000 per user per year, and you can buy it online. ReliaStats, the companion tool that fits failure and repair distributions from your stop data, is $1,800 per user per year, and its Designer is free. The Sandbox and the desktop demo cost nothing. Every price is on the pricing page.

Discrete rate, built for high-speed lines

A discrete event model moves each unit through the line as its own event. On a line that makes hundreds of units a minute, that’s a great many events per simulated hour. ReliaSim uses discrete rate simulation, which models material as flow at rates and changes state only when a rate changes: a machine stops or restarts, or a buffer fills or empties. The work grows with the number of stops, not the number of units. A thousand one-year runs of the five-machine demo bottling line take about two and a half minutes on a laptop, or 0.154 seconds per simulated year. That speed is what makes sweeps practical: the buffer study behind how big should a buffer be? is 7,770 runs in 31.8 seconds. Discrete rate vs discrete event explains the difference in full.

Validated before it predicts

A published food plant model, from Fischel and Lange at the 2020 Winter Simulation Conference, was rebuilt in ReliaSim and independently validated by Tom Lange. It came within 1% of the plant’s measured OEE (the validation study). Every ReliaSim model follows the same order: reproduce the line’s own history, failure mode by failure mode, then ask what-if. How to check a digital twin’s accuracy claim sets out the test, for any vendor.

Your data stays on your machine

ReliaSim is desktop software for Mac and Windows. Models are files on the modeler’s own machine, and it works air-gapped. Security and deployment covers what IT usually asks.

At a glance

Using both

A layout study in a 3D tool and a throughput study in ReliaSim answer different questions about the same plant. One shows whether people and equipment fit and move well. The other shows what the line will make given its stops and buffers, and what each fix is worth.

How to choose

If the answer depends on space, travel and what people will see, start with 3D. If it depends on stops, buffers and line speed on a fast line, start with a rate-based model built from the line’s own stop data and checked against its measured OEE. FlexSim and Autodesk are referenced here for identification only; no affiliation or endorsement is implied.