The rise of autonomous vehicles and ridesharing mean the passenger experience is firmly in the driving seat for vehicle design. Climate control, noise and seat design all need to be optimized to maximise comfort, safety and energy efficiency—especially for electric vehicles. The hyper-connected world meanwhile makes increasingly heavy demands on on-board computers and wireless internet.

BALANCING VEHICLE COMFORT AND PERFORMANCE WITH SIMULATION-DRIVEN CABIN DESIGN

Modern trends in vehicle cabin design lead to an increasing number of challenges:

• Heating, ventilation and air condition (HVAC) and climate control systems must perform in the harshest conditions

• Energy efficient interior systems for better battery range and fuel economy

• Reducing noise from the HVAC system and create clearer sound system experiences

• Ensuring a comfortable ride and ergonomic seats without impairing crash safety

• Producing durable, touchable interfaces for infotainment controls

• Seamless connectivity for electronic devices and reliable performance

• Meet increasingly demanding regulations such as Worldwide Harmonised Light Vehicle Test Procedure (WLTP)

Bringing a vehicle successfully to market means not only meeting all the regulatory requirements for safety and energy efficiency, but also crafting a passenger experience that sets it apart from competitors’ offerings.

SIMULATION-DRIVEN SOLUTIONS FOR CABIN DESIGN ENABLE TAILORING OF PASSENGER EXPERIENCE

CABIN COMFORTThis eBook focuses on simulation solutions for designing and analyzing vehicle cabins. See examples of how SIMULIA products are used to:

• Decrease the number of prototypes required and turnaround times with virtual cabin testing

• Ensure regulations and passenger expectations are met before any prototypes are built

• Reduce the risk of delays and product recalls

• Increase energy efficiency and battery range

• Optimize vehicle heating and air conditioning performance

• Reduce costly climate wind tunnel and worldwide performance testing

• Digitally validate the flow and thermal performance of HVAC system concepts

• Ensure a quiet ride by minimizing cabin noise

• Ensure device and infotainment connectivity and reliability

The design of vehicle climate control systems is complicated due to the many trade-offs that are required with other design attributes such as styling, comfort, interior space, packaging, noise and vibration, safety and energy efficiency.

No need for a prototype, or testing “world tours”Digital design testing through simulation reduces the number of expensive physical prototypes required. Climate control systems are typically designed using climate wind tunnel tests or real world tests such as solar soaks and cool-downs. Compared to wind tunnels and heat chambers, simulation can more accurately represent the real world without the cost of shipping vehicles and engineering crew for field testing campaigns in very hot or cold locations. Vehicles rarely meet their performance targets on the first try which means that the prototype must be modified and the tests re-run multiple times. If an issue is discovered during physical testing, test variation and limitations on the placement of sensors can make it difficult to isolate and identify the root cause.

Assess comfort levels through realistic and accurate simulationThe SIMULIA Computational Fluid Dynamics (CFD) offering accurately predicts key climate control performance parameters considering details in interior geometry and materials, with unique capabilities such as 9-hour solar soak followed by a 60-minute cooldown. PowerFLOW solutions can go beyond with the implementation of virtual drive cycles to assess cabin performance in real vehicle operations. Using the accurate Lattice Boltzmann Method,

SIMULIA PowerFLOW solutions capture all of relevant physics including radiation, conduction, natural convection, and forced convection as well as a human thermal comfort model. This is key for the tradeoff with energy consumption, as optimal real-world performance can only be achieved by considering human comfort. Only SIMULIA solutions can provide the necessary accuracy for cabin temperature to obtain meaningful human comfort predictions.

Break the silos for HVAC design with the 3DEXPERIENCE platformWorking on the 3DEXPERIENCE® platform, early HVAC designs can be simulated to improve flow performance, leveraging CAD parameterization to design and optimize the HVAC system and ducts in tandem with the rest of the vehicle. Bringing all the design knowledge together on a single platform breaks down the silos that restrain design teams and allows fast, effective cooperation between departments.

Digitally track design improvements to reach your performance targetsThe end result is that engineers can accurately evaluate climate control system design alternatives under a wide range of conditions much earlier in the design process. It enables them to deliver higher performance with reduced prototyping and testing costs as well as shorter time to market. Using Design Verification Methods (DVM) to confirm the performance of a design at all stages of the Digital Verification Plan (DVP), a plan is built to track the evolution of a design towards achieving performance targets.

DESIGN COMFORTABLE, ENERGY EFFICIENT AND SAFE CABINS FOR REAL WORLD CONDITIONS

Rethinking HVAC objectives for EVsThe power required for the cooling fan, blower, compressor and control electronics means that up to 5% of the fuel used in a conventional vehicle goes towards climate control, significantly affecting fuel consumption. In an electric vehicle, more than 30% of the battery energy can be used for passenger comfort, and battery heating and cooling is a serious concern. HVAC is not just for comfort either—defrosting and demisting are safety crucial systems subject to regulations, and can also significantly reduce range in cold conditions.

Understand what really counts for consumersClimate control system performance is usually evaluated based on measuring air and surface temperatures. Understanding these temperatures is important but the actual goal is to improve passenger comfort which is a function of both the cabin conditions and the human thermoregulation that occurs due to physiology, clothing, and activity. SIMULIA PowerFLOW Cabin Thermal Comfort solution incorporates a physiology-based passenger model that

leverages accurate skin temperature and convection predictions to determine localized comfort results for each body segment.

Impact range through holistic HVAC integrationHVAC controls optimization either happens early with inaccurate system models, or late in the design process when a physical prototype is available. It is consequently finalized separately from the HVAC system and cabin development rather than in parallel. However, these can be co-simulated, leveraging vehicle system modelling available with Dymola in the Dassault Systèmes CATIA solution. This allows mature 1D system modeling for vehicle system models coupling to the cabin 3D models. All the vehicle subsystems, including the HVAC system, can be connected for true digital testing of the vehicle power system to optimize energy efficiency against human comfort. This is critical for improving vehicle fuel economy for example, and helps reduce CO2 emissions to comply with the regulations like the Worldwide Harmonised Light Vehicle Test Procedure (WLTP).

BALANCE COMFORT WITH BATTERY RANGE AND FUEL ECONOMY

DESIGN QUIETER CABINSEngineers have made huge strides over the past two decades in reducing powertrain and road noise which previously were the primary sources of vehicle noise. Their reward is an upsurge in consumer complaints over interior noises that were previously drowned out by engine and road noise. For example, owners are bringing electric vehicles in for expensive warranty repairs after hearing noise emanating from the HVAC system even though nothing is functionally wrong with the vehicle.

Meeting overall HVAC noise targetsIn response, automotive Original Equipment Manufacturers (OEMs) are setting increasingly challenging HVAC noise targets. HVAC suppliers are struggling to meet these KPIs while at the same time wrestling with thermal management trade-offs. This task is made more difficult by tighter packaging under the hood and around the dashboard which makes it necessary to reduce the size of HVAC units and run ducts around more obstacles. A further challenge is that even with a HVAC module that is quiet in isolation, interactions between the module and vehicle can cause noise targets to be exceeded. The 3DEXPERIENCE platform catalyzes collaboration between OEMs and suppliers, allowing these interactions to be simulated and avoided.

FIND sources of noise, and suppress themThe SIMULIA PowerACOUSTICS Flow Induced Noise Detection (FIND™) module is uniquely capable of identifying the location and magnitude of flow-induced noise sources—providing engineers with a roadmap to reducing HVAC noise as perceived by the driver and passengers. These software solutions enable engineers to quickly iterate to an HVAC module design that will meet noise targets when integrated with the full vehicle in order to get the design right the first time and minimize expensive design and prototyping iterations.

Seats which are comfortable and safeSeats are responsible for 60-70% of perceived cabin comfort. Designing a comfortable, ergonomic car seat means balancing two competing design requirements – the seat must be firm enough to provide support, particularly to the neck and lumbar region, while also having a soft, cushioning effect for a smoother ride. Seats that protect the back and neck in an accident can also have a major impact on a vehicle’s crashworthiness.

Structural simulation with realistic bodies and complex materialsFinite element analysis with SIMULIA’s mechanical solvers in Abaqus enable the prediction of how different seat filling materials support people sitting in them, plotting the areas of maximum stress and strain within the body. Using realistic body models

offers insight into exactly how passengers sit in the seat and predict comfort for different ages and body shapes. Abaqus can model highly complex non-linear material behavior and contact of the body in the seat allowing virtual hip point (H-point) testing.

Save energy with microclimate systemsSeats also provide individualized climate control through seat-based heating and ventilation. These can be modeled with PowerFLOW Suite in order to calculate not just the thermal sensation but also the resulting comfort level, to ensure that the passenger is neither too cold nor too hot. Optimization of seat heating and radiant panels provides comfortable microclimates without relying on HVAC output. This reduces noise, maximizes perceived comfort and typically saves energy in the process.

DESIGN COMFORTABLE SEATS FOR WELL-BEING AND RIDER EXPERIENCE

An important goal for any interface designer is to make the interaction between people and devices as easy as possible. Traditionally, car systems were controlled with buttons and switches, but increasingly all the on-board systems are integrated into a single touchscreen interface. The experience of using these systems needs to be both satisfying and reliable, not requiring too much pressure to activate but also not being oversensitive or prone to misreading finger position (the “fat finger” effect).

Injection Molded Structural Electronics (IMSE) provides greater freedom of design by integrating printed electronics inside of thin 3D plastic structures. This opens up completely new possibilities as electronics such as circuitry, sensors, antennas, LEDs and special functions are amalgamated with the car’s interior thus providing new experiences in cabin design. Since IMSE products integrate a significant number of various electrical functions into a single product, electromagnetic simulation is required to ensure proper functioning.

Get the right feel for your cabinElectronic systems can be simulated for electrical performance with SIMULIA’s electromagnetic simulation tool CST Studio Suite, while Abaqus can be used to calculate their mechanical performance and

the comfort factor associated with pressing the switch or tapping the screen. Accurate simulations of how the fingertip moves when touching the screen can be used to calculate the exact contact surface, which can then in turn be used in CST Studio Suite to simulate the screen’s electrical response. A wide range of physical sizes can be modeled, simulating the experience for occupants of different ages. This helps engineers overcome the fat finger effect and make touchscreens more precise and more convenient to use.

Simulate electromagnetic interactionsCST Studio Suite can be used to analyze the performance of the touchscreen sensor when it is subjected to Electrostatic Discharge (ESD). ESD may occur if the user is at a different potential to the touchscreen device, causing discharge to the touchscreen sensor when the fingertip approaches the device. This can result in noise currents flowing through the touchscreen electronics and its integrated circuit (IC), which could affect the performance of the sensor, or even damage the electronics. The touchscreen sensor must be immune to common mode (CM) conducted noise that could enter the device through the power cables. CST Studio Suite can be used to analyze the conducted susceptibility and evaluate performance of protection strategies such as CM filtering.

ENSURE DEVICE USABILITY AND COMFORTABLE USER EXPERIENCE

Increasingly connected vehiclesBoth private vehicles and public transit are increasingly integrating wireless technology for internet access, interactivity, keyless entry and vehicle control. The metal body of the vehicle will block, reflect and conduct radio waves, potentially creating dead zones inside the vehicle where the signal is poor. In addition, with so many electronic systems in a typical vehicle—including the passengers’ own devices—controlling electromagnetic interference (EMI) and compatibility (EMC), as well as human exposure to EM fields, is a challenge. Interference issues not only spoil the passengers’ experience, but in the most serious cases they can even pose a safety risk. Government regulators specify limits on the interference and exposure a device can produce, and OEMs often impose even stricter EMI/EMC restrictions on their suppliers.

To analyze and mitigate connectivity and interference issues, engineers can use the SIMULIA electromagnetic simulation package CST Studio Suite. The robust meshing and solver technology allows the entire vehicle model from the mechanical department to be used directly in simulation without the need for simplification, leading to more accurate simulation.

Fix interferences before they occurThe CST EDA import tool enables Printed Circuit Board (PCB) layouts to be analyzed to evaluate Signal Integrity (SI) and Power Integrity (PI). The PCB model can be combined with mechanical models of the

enclosure housing and cable models, to simulate Electromagnetic Compatibility (EMC) performance including; conducted and radiated emissions and susceptibility. For simulations with multiple devices operating simultaneously, the Interference Task offers a quick overview of all potential interference issues between systems. With this engineers can pinpoint and deal with EMI problems, such as electromagnetic noise affecting camera image quality and sound quality, before physical testing.

Optimise EMAG performance and safety with passengersThe presence of people in the cabin also affects device performance in some unexpected ways. The human body can reflect or absorb radio waves. To get an accurate picture of WiFi or Bluetooth coverage inside the vehicle, realistic human body models can be included in the electromagnetic simulation. The results of the simulation inform the placement of antennas to maximize signal coverage and avoid passenger frustration at unreliable connectivity.

To ensure passenger safety, limits are set on the power the human body can be exposed to. There are many high-power EM sources in vehicles spanning the frequency spectrum, but a specific concern for electric vehicles are fields emitted during charging and driving. Simulations can reproduce standard exposure calculations such as the specific absorption rate (SAR) and ensure vehicles meet the International Commission on Non-Ionizing Radiation Protection (ICNIRP) standards.

SEAMLESS ELECTRONIC CONNECTIVITY AND PERFORMANCE

Europe/Middle East/AfricaDassault Systèmes10, rue Marcel DassaultCS 4050178946 Vélizy-Villacoublay CedexFrance

AmericasDassault Systèmes175 Wyman StreetWaltham, Massachusetts02451-1223USA

Asia-PacificDassault Systèmes K.K.ThinkPark Tower2-1-1 Osaki, Shinagawa-ku,Tokyo 141-6020Japan

Our 3DEXPERIENCE® platform powers our brand applications, serving 11 industries, and provides a rich portfolio of industry solution experiences. Dassault Systèmes, the 3DEXPERIENCE Company, is a catalyst for human progress. We provide business and people with collaborative virtual environments to imagine sustainable innovations. By creating ‘virtual experience twins’ of the real world with our 3DEXPERIENCE platform and applications, our customers push the boundaries of innovation, learning and production.

Dassault Systèmes’ 20,000 employees are bringing value to more than 270,000 customers of all sizes, in all industries, in more than 140 countries. For more information, visit www.3ds.com.

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As consumers are looking for refreshing and comfortable experiences, cabin design is taking center stage as a dominant selling factor for the automotive, aerospace and industrial equipment industries.

Balance Cabin Comfort and Performance with Simulation-driven Design

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