ATTI investigates how the Praga Bohema’s simulation plan went to new lengths, further than the bounds of what was initially planned

In March, Czech model Praga documented that the last phase of advancement for its road-authorized hypercar, Bohema, had commenced. The application for the company’s most recent development threw up a multitude of technical, innovative and mental hurdles. The vehicle’s very carefully crafted aero deal and its performance qualifications are the end result of an intense virtual technique that finished up actively playing a increased position than was to begin with envisioned.


// –>


// –>

Substantially of Bohema’s style and design language, such as the shape of the motor vehicle, came off the back of CFD simulations. According to Jan Martinek, challenge leader and main engineer, “In the original stages there were a lot of suggestions loops – heading from a clay model to a 3D scanned shape optimized for CFD and back again to clay to uncover a useful design that doesn’t lose its distinguished and potent mix of variety and functionality.”

CFD was also applied closely when honing the hypercar’s performance as the group strove to get the optimum out of its bundle. Significant emphasis has been positioned on the conversation amongst auto dynamics and aerodynamics.

Virtual instruments employed incorporated TotalSim, Icon CFD software package, ChassisSim, OptimumG and Ansys. In accordance to Martinek, Praga believes these are some of the ideal-value platforms offered on the computer software market.

Software program aside, recognised quantities could be rather effortlessly simulated, this kind of as the structural integrity of a part bearing a outlined load or the actions of air when introduced with the dynamic ailments of a fixed body design.

“What is more difficult to simulate are the issues you do not know – the HVAC program, for instance,” Martinek claims. “The Bohema interior is fairly compact, for this reason the packaging wasa authentic problem. It correctly meant that pretty considerably all components experienced to be developed bespoke.

“The HVAC process experienced to be defined very early on as it usually takes up a major volume of space, when most interior components and even important attributes these kinds of as the seats and center console did not exist. Luckily for us, the disorders we modeled in the early simulations proved mainly accurate, conference the packaging [requirements]and only necessitating a insignificant correction to optimize the air movement.”

Four dimensional

The actual-globe testing part of the software was break up into four features: composite structural tests, motor analysis, wind tunnel analysis and general performance validation.

Novel manufacturing strategies have been used in the course of Bohema’s construction, and these had to be assessed comprehensively. “We tested samples of composite materials and layups. We have integrated Zylon panels into the car’s composition and we have carried out a good deal of producing optimizations,” Martinek notes. “We also analyzed versatility as [the car has]one of the widest mounted rear wings [in the industry]and it is important to understand the wing’s behavior beneath aerodynamic loads.”

This was the initial time that the existing staff at Praga had to handle emissions benchmarks as harsh as Euro 6d, which Martinek admits proved to be a problem. In-depth engine scrutiny and code composing were crucial to attain the stipulated values.

At Praga’s growth centre, engineers can use an motor dyno and rolling highway. The OEM also has near ties with the Czech Complex University in Prague and the Brno College of Technologies, where by a raft of other methods are obtainable.

Moreover, Praga operator Tomas Kasparek has long-standing interactions with associates of F1. This meant the workforce ended up equipped to obtain a Method 1 team’s wind tunnel, which gave them an option to verify their CFD computation designs and input new information. “It was good to be ready to confirm and sign off the final layout with a wind tunnel report from engineers in F1, and also search at future solutions using our knowledge to make your mind up where by to go upcoming with the bundle,” Martinek feedback.

3 prototypes and two pre-production prototypes ended up fabricated. For a bespoke enterprise like Praga, which options to make just 89 cars and trucks, that is sufficient.

Bohema has been assessed on airfields, racetracks and general public roadways across Europe. The the vast majority of observe and public street analyses took location in Slovakia, at and close to the Slovakia Ring, with which Praga maintains a potent connection, which means engineers can test there a lot more or fewer each time they have to have to.

“It is a wonderful track for tests as our improvement and carbon center is nearby, so we can on a regular basis entry [the track], which has a technological and speedy format,” Martinek suggests. “The roadways [in Slovakia]characteristic a fantastic mix of new, sleek asphalt on the highways and incredibly improperly maintained rural back again roadways.”

Monitor do the job was split into two parts: stamina and performance. Examination on racetracks started again in 2019. All through the previous leg of Bohema’s progress, the staff committed a year to general public street screening.

It’s not distinct-reduce

Martinek says it’s impossible to attract a line in between how considerably digital and how considerably actual physical screening has been done, mainly because the simulation routine grew to become gradually additional iterative all over the hypercar’s engineering. “There was a period at the beginning of the challenge when there was a accurate combine of very best practices – with simulation actively playing a supporting position – simply because the primary group powering Bohema was made up largely of folks with wide useful working experience but comparatively little simulation history,” he explains.

Street assessment concentrated on toughness, testing of new merchandise and concentrate on performance checks, which usually meant tweaks to the set up of the hypercar. The full routine was underpinned by a variety of sorts of simulation
and modeling

This approach bit by bit transformed, with Bohema’s design and style turning into a lot more heavily affected by digital examination as the days went on. In the course of the latter task levels, the workforce employed digital equipment in which doable to make refinements, squeezing out people all-crucial cumulative effectiveness enhancements from Bohema’s deal – the part and functionality of simulation escalating all the whilst.

“Looking back again, the virtual part of the plan ultimately grew way past what we initially expected, nevertheless really small of the authentic all round architecture had to be modified. This by yourself is a sturdy statement that evidences the know-how within just the Praga staff. Nonetheless, the significant, incremental overall performance updates we ended up ready to make via additional simulation and optimization is as great of a statement on recent simulation software ability and requirement,” Martinek concludes.

Puzzle to resolve

To outline the motor vehicle dynamics traits of the hypercar, general overall performance targets have been established very first and an understanding of the tire founded, Martinek points out.

“Then we started out putting the parts of the puzzle with each other. We made use of resources for simulating tire functionality and the habits of the automobile in phrases of the auto dynamics and aerodynamics to achieve our targets.

“We were then equipped to simulate the best aero equilibrium in the course of diverse situations on the observe and maximum worth of downforce to not overload the tires, and so on.”

Curiously, Pirellis proved to be far additional effective on the car or truck than any other manufacturer, Martinek notes.

“Once happy we experienced realized the targets, we made use of this details in simulations of
the structural parts, enabling us to figure out theoretical hundreds and enhance the components in terms of stiffness and pounds.”

By Tara