Simulation

An exploratory concept investigating AI-assisted debugging workflows for scientific and engineering simulations.

Most battery models fail not because the equations are wrong - but because the assumptions smuggled in with them are wrong. Fifteen years working with battery models across the stack: from ECM spreadsheets that needed to survive a BMS real-time loop, to full electrochemical models trying to capture what actually happens inside the cell during a fast charge. The gap between “runs on paper” and “works in a vehicle” is where most of the interesting problems live. ...

GitHub Repository CFD-based battery simulation is powerful and routinely impractical. OpenFOAM can model the coupled thermal-flow behavior of a battery pack in detail that lumped models can’t touch. It can resolve cell-to-cell temperature gradients, coolant channel flow distribution, and transient heat propagation through complex pack geometries. It can also take an experienced CFD engineer a day to set up a single case, another day to run it, and significant effort to extract anything useful from the output. ...

Most battery simulation work happens inside large OEM simulation frameworks - tools with hundreds of subsystems, long setup times, and infrastructure built for full-vehicle analysis. Useful when you need the full vehicle. Counterproductive when you need to iterate quickly on battery-specific questions. At Volvo Trucks, the problem was clear: the battery and BMS teams needed a simulation environment they could actually use - fast iteration, battery-focused, not dragging a full vehicle model along for every run. ...

The DC junction box doesn’t get much attention in EV thermal discussions. People focus on the battery pack, the inverter, the motor. The junction box is a metal enclosure with some contactors, fuses, and busbars - it switches current and protects the circuit. How hot can it get? Hotter than you expect, under the conditions that matter most. Why the Junction Box Gets Hot The DC box carries the full HV current whenever the vehicle is driving or charging. The heating is straightforward: I²R losses in the busbars and contactors. At peak power - high speed driving or DC fast charge - this current is large. ...

The Situation Nobody Talks About Here is a situation that happens more often than you would think in battery development. An EV company has a working cell from Supplier A - tested, characterised, reliable. But for their next programme, they need a different cell: larger capacity, different form factor, different thermal profile. They ask the supplier: “Can you make us a 21700 version with 4000 mAh from the same chemistry?” ...

What This Was This wasn’t a project with a start date and a delivery date. It was three to four years of incremental work on a living codebase that had to keep working while being extended. Mercedes-Benz R&D, in collaboration with other European OEMs, built an in-house full-vehicle simulation framework on top of CarSim — initially scoped for IC engine vehicles. When I joined in 2015, the task was to extend that framework for EV, HEV, and PHEV architectures, improve the existing model libraries, and build the component models that didn’t yet exist. ...

An EV thermal management system is not one problem. It’s eight problems that happen to share coolant. The battery wants to stay between 15 and 35°C. The power electronics want active cooling at high load. The cabin wants heat in winter and cooling in summer, and it’s competing for the same refrigerant circuit the battery uses. The motor generates heat during aggressive driving. The DC-DC converter has its own overtemperature failure mode. All of these are connected - through coolant loops, refrigerant circuits, and control logic - and all of them interact dynamically. ...

After spending years working in battery simulation across Mercedes-Benz, Caterpillar, Volvo Trucks and later A123 Systems, I slowly realised something that was not obvious to me in the beginning. Most battery engineers think they are building battery models. In reality, they are usually building battery infrastructure. The distinction sounds subtle. It isn’t. A battery model answers a question. A battery simulation framework enables an organisation to ask thousands of questions. Those are completely different engineering problems. ...

After spending years working in battery simulation across Mercedes-Benz, Caterpillar, Volvo Trucks and later A123 Systems, I slowly realised something that was not obvious to me in the beginning. Most battery engineers think they are building battery models. In reality, they are usually building battery infrastructure. The distinction sounds subtle. It isn’t. A battery model answers a question. A battery simulation framework enables an organisation to ask thousands of questions. Those are completely different engineering problems. ...