TRAIN NOISE SIMULATION FOR QUIET TRAVEL EXPERIENCES

As a child, you may have enjoyed hearing every clack and screech on a train rushing forward toward distant adventures with friends.

However, as an adult traveling on business with your boss, you might prefer silence in the carriage. And let’s not even talk about how noisy some train cars can be. Clearly, engineers need to address this issue.

Trevor Edwards, Global Business Development Manager at ESI Group, said: “Addressing vehicle noise is very important for customers. Designers view vehicle noise as a target at critical points in transportation. Attention to exterior noise is sometimes legally required—for example, pass-by noise (PBN) regulations for railways or other vehicles near residential areas.”

Engineers are tasked with minimizing noise as much as possible. Unfortunately, much of the noise comes from the tracks and the environment, beyond the control of train designers.

This is why simulation tools like ESI VA One are critical to optimize all possible factors and ensure the comfort of drivers, operators, passengers, and nearby residents during transit.

Each train has multiple noise sources. Engineers need to assess how these factors affect passenger comfort. (Image courtesy of ESI Group)

How Do Engineers Measure Noise?

The main sources of train noise include equipment, rolling noise, aerodynamics, and switch rails. For effective acoustic design, each noise source must be assessed and limited.

Some VA One tools help engineers design quieter vehicles. (Image courtesy of ESI Group)

Robert Fiedler, NVH expert at ESI, notes that noise from wheel/rail irregularities is particularly significant. While engineers cannot control the track, they can design wheels, rails, and assemblies to reduce vibration. First, however, they must measure or model the sound.

“Noise can be quantified using sound antennas with multiple microphones,” Fiedler said. “This is challenging due to expensive equipment and difficulty separating equipment noise from environmental noise during recording.”

Another method is to record noise using a microphone array near the midsection of the vehicle, which is easier but captures both equipment and environmental noise.

“A third approach is to simulate the energy radiated from wheel/rail noise,” Fiedler added. “I have used the Remington method, an analytical approach dividing the rail and wheel into grids with inertia, mass, and spring elements. Alternatively, FEM/BEM methods can be used.”

In short, to characterize noise components quickly, accurately, and reasonably, engineers need computer-aided engineering (CAE) software capable of simulating noise, vibration, and harshness (NVH).

Sergej Italjancev, CAD design specialist for Škoda Transportation’s Mechanical Project, explained that their first subway train design failed the tender noise standards. After applying VA One and adjusting the software design, they won the contract.

They currently provide eight train types, each with six carriages.

How to Simulate NVH for Wheel/Rail Surfaces

Using simulation, engineers can optimize rail component designs to reduce vibration and noise propagation inside and outside the train.

To simulate these noises, they must first model the wheel-rail interaction.

“Previous studies show noise can result from small irregularities on wheel and rail surfaces causing vibration,” Fiedler said.

Representative diagram of wheel/rail interaction. Irregularities increase noise. (Image courtesy of ESI Group)

As wheels move on the rail, they experience stress under the train’s weight. This load produces local deformations in both rail and wheel.

Wheel deformation causes local distortions and rapidly changing contact forces, generating vibrations.

“To represent deformation, engineers can model wheel and rail components as frequency-dependent springs,” Fiedler explained. “Dynamic spring properties and local mobility can be assessed using 1D analytical or 3D FEM/BEM approaches.”

3D modeling allows engineers to control boundary conditions and model any wheel or shape, which is critical as different shapes have varying vibration resistance.

With ESI VA One, using FEM/BEM, engineers can model any wheel shape, such as this one. Simple analytical simulation cannot achieve this. (Image courtesy of ESI Group)

3D modeling also enables exploration of pre-load conditions before axle operation or centrifugal forces.

Fiedler noted: “These methods show how the structure behaves at certain frequencies. Applying the correct forces reveals real structural vibration in the frequency domain, known as the Modal approach.”

Next, engineers calculate energy radiated by the wheel, simulating air around the wheel.

“In BEM simulation, a surface shell is generated around the wheel shape, defining which surfaces are exposed to air,” Fiedler explained. “After solving, engineers can access the radiated sound energy.”

This radiated energy is then used as a reference to compare performance of different wheel shapes.

A rail noise simulation chart in VA One. (Image courtesy of ESI Group)

Radiated sound energy can also be used in system-level modeling via Statistical Energy Analysis (SEA). This predicts interior noise by accounting for all noise sources in the system.

Once wheel radiated energy is identified, similar decomposition can be applied to other sources such as HVAC and structural elements under vibration. All sources can then be integrated into SEA models for total noise assessment.

“This approach helped us identify which structural components of the electric train contribute most to interior noise,” Petr Cuchý, lead field researcher at Škoda Transportation, said. “Focusing on acoustically sensitive components avoids adding unnecessary weight and cost to components with minimal noise impact. Estimating interior noise levels is equally important.”

Simulating Interior vs. Exterior Noise

Once a model calculates vibration and noise at the component or system level, what’s next?

“VA One calculates and ranks all structural and acoustic paths from the source to a selected point,” Edwards said. “For example, a train compartment can be selected so designers can identify where noise is highest and determine corrective measures.”

Fiedler explains the importance of seat layout because it affects and absorbs interior noise. (Image courtesy of ESI Group)

NVH software simulates sound transmission using source, path, and receiver. Vibrations from the source inject energy, transmitted through structures and air to the receiver.

Edwards explained it can be challenging to determine interior cabin noise due to multiple accessories and furnishings.

“The key difference is that interior noise occurs in a confined space, while exterior noise occurs in an open environment,” Edwards said. “The same source, path, and receiver model are used, but different frequencies require different tools in VA One.”

For example, depending on sound frequency, even a seat can absorb noise, while complex paths in walls and open spaces can scatter, echo, or prolong noise.

VA One allows engineers to assess sound levels at receiver locations and determine how features like carpets and curtains absorb noise.

This enables engineers to optimize interior features to minimize noise, crucial for designing train interiors for even whisper-level comfort.

Source: engineering.com

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