Structural Acoustics Methods

Understanding Structural Acoustics: The Foundation of Sound Engineering

Structural acoustics represents one of the most sophisticated branches of engineering analysis, examining the complex interaction between structural vibrations and acoustic waves. For industries across Atlantic Canada—from shipbuilding in Halifax to manufacturing facilities throughout Nova Scotia—understanding these phenomena is essential for creating environments that meet both performance standards and regulatory requirements.

At its core, structural acoustics bridges two distinct physical domains: the solid mechanics of vibrating structures and the fluid dynamics of sound propagation through air or water. When a structure vibrates, it displaces the surrounding medium, creating pressure waves that we perceive as sound. Conversely, acoustic waves can induce vibrations in structures, a phenomenon particularly relevant for buildings near airports, industrial facilities, or transportation corridors throughout the Maritime provinces.

The field has evolved significantly over the past three decades, driven by advances in computational power and numerical methods. Modern structural acoustics analysis enables engineers to predict noise levels, optimise designs for acoustic performance, and troubleshoot existing installations with unprecedented accuracy. For engineering firms serving Atlantic Canada's diverse industrial base, these capabilities are increasingly essential.

Fundamental Analytical Methods in Structural Acoustics

Several analytical approaches form the backbone of structural acoustics analysis, each suited to particular frequency ranges, structural configurations, and project requirements. Understanding these methods allows engineers to select the most appropriate tool for each unique challenge.

Finite Element Method (FEM) for Low-Frequency Analysis

The Finite Element Method remains the gold standard for low-frequency structural acoustics problems, typically those below 200-500 Hz depending on the structure's size. FEM discretises both the structural and acoustic domains into elements, solving coupled equations that capture the interaction between vibrating surfaces and the surrounding medium.

For a typical industrial enclosure analysis, engineers might employ:

• Shell elements for thin-walled structures with thicknesses ranging from 3-25 mm

• Solid acoustic elements for enclosed air volumes

• Coupling elements at fluid-structure interfaces

• Mesh densities of at least 6 elements per acoustic wavelength

The computational cost of FEM scales rapidly with frequency, as shorter wavelengths require finer meshes. A 1,000 Hz analysis might require 8-10 times more elements than a 200 Hz analysis for the same geometry, making this method impractical for high-frequency problems in large structures.

Boundary Element Method (BEM) for Radiation Problems

The Boundary Element Method offers significant advantages when analysing sound radiation from structures into unbounded domains—a common scenario in Maritime industrial applications such as offshore platform noise or marine vessel acoustics. BEM requires only surface meshing, automatically satisfying radiation conditions at infinity.

Typical BEM applications include:

• Prediction of radiated sound power from vibrating machinery

• Analysis of acoustic scattering from complex geometries

• Environmental noise propagation studies

• Underwater acoustic signatures for marine applications

For Nova Scotia's shipbuilding and offshore industries, BEM proves particularly valuable for predicting how vessel hull vibrations translate into underwater radiated noise—a growing concern given increasing regulations around marine mammal protection in Atlantic waters.

Statistical Energy Analysis (SEA) for High-Frequency Problems

When frequencies exceed approximately 500-1,000 Hz, deterministic methods become computationally prohibitive and increasingly sensitive to manufacturing variations. Statistical Energy Analysis addresses this by treating energy flow between coupled subsystems statistically, providing reliable predictions of average response levels.

SEA models divide complex structures into subsystems characterised by:

• Modal density (modes per Hz per subsystem)

• Damping loss factors (typically 0.001-0.1 for engineering materials)

• Coupling loss factors describing energy transfer between subsystems

• Input power from excitation sources

This approach excels for automotive, aerospace, and building acoustics applications where broadband noise control is the primary objective. Many industrial facilities across Nova Scotia benefit from SEA-based assessments when addressing occupational noise exposure concerns.

Hybrid Methods: Bridging Frequency Ranges

Real-world structural acoustics problems rarely fall neatly into low or high-frequency categories. Modern engineering practice increasingly relies on hybrid methods that combine the strengths of multiple approaches.

FEM-SEA Hybrid Approaches

The mid-frequency range—roughly 200-2,000 Hz for typical industrial structures—presents particular challenges. Some subsystems exhibit deterministic behaviour while others respond statistically. Hybrid FEM-SEA methods address this by:

• Modelling stiff, low-modal-density components with FEM

• Representing flexible, high-modal-density components with SEA

• Coupling the two domains through energy-based interface conditions

For example, analysing a ship's engine room might use FEM for the rigid engine foundation and SEA for the surrounding lightweight bulkheads and deck panels. This approach has proven particularly effective for vessels built in Atlantic Canadian shipyards, where diverse structural configurations demand flexible analytical tools.

Energy Finite Element Analysis (EFEA)

Energy Finite Element Analysis represents another hybrid approach, solving energy-based governing equations on finite element meshes. This method captures spatial variation in high-frequency response while maintaining computational efficiency. EFEA proves especially useful for:

• Large structures with non-uniform damping treatments

• Systems with localised excitation sources

• Configurations where energy flow patterns are complex

Practical Applications in Atlantic Canadian Industries

Structural acoustics methods find diverse applications across Nova Scotia's industrial landscape, addressing challenges unique to the Maritime context.

Marine and Offshore Applications

Atlantic Canada's maritime heritage creates substantial demand for structural acoustics expertise. Key applications include:

Vessel Noise Control: Modern vessels must meet increasingly stringent noise standards. Classification societies such as Lloyd's Register and DNV specify comfort class notations requiring noise levels below 60-65 dB(A) in accommodation spaces and below 75-85 dB(A) in machinery spaces, depending on vessel type and classification.

Underwater Radiated Noise: Growing environmental awareness drives demand for reduced underwater noise signatures. The IMO's guidelines and Transport Canada's emerging regulations require vessels to demonstrate noise levels below specified thresholds at standardised distances, typically measured at 1 metre and referenced to various operating conditions.

Offshore Platform Acoustics: Platforms operating off Nova Scotia's coast must manage noise from multiple sources including turbines, compressors, and HVAC systems. Structural acoustics analysis helps optimise equipment isolation, enclosure design, and accommodation layout to meet occupational exposure limits below 85 dB(A) for 8-hour time-weighted averages.

Industrial Facility Assessment

Manufacturing and processing facilities throughout Nova Scotia face ongoing pressure to reduce noise impacts on workers and surrounding communities. Structural acoustics methods enable:

Source Identification: Using experimental methods such as acoustic intensity mapping and operational deflection shape analysis, engineers can identify dominant noise sources and transmission paths. This diagnostic capability proves essential for cost-effective noise control, ensuring mitigation investments target the most significant contributors.

Barrier and Enclosure Design: Analytical methods predict the acoustic performance of proposed noise control treatments before fabrication. For a typical industrial enclosure, engineers analyse:

• Panel resonances and coincidence frequencies

• Sound transmission loss across the frequency spectrum (typically targeting STC ratings of 35-50)

• Flanking transmission through structural connections

• Ventilation opening treatments

Building Acoustics: Industrial buildings require careful attention to sound isolation between spaces. Nova Scotia Building Code requirements and ASHRAE guidelines establish minimum performance standards that structural acoustics analysis helps achieve.

Transportation Infrastructure

Transportation projects across the Maritime provinces increasingly incorporate structural acoustics considerations from the earliest design stages.

Bridge Vibration and Noise: Traffic-induced vibrations can generate objectionable noise in bridge structures and adjacent buildings. Analysis methods help predict these effects and design appropriate countermeasures such as expansion joint details, bearing selections, and deck surface treatments.

Rail Noise Mitigation: Communities along rail corridors may experience noise from wheel-rail interaction, particularly at curves and crossings. Structural acoustics analysis supports the design of barriers, rail dampers, and track modifications to achieve community noise targets typically set at 55-65 dB(A) during daytime hours.

Measurement and Validation Techniques

Analytical predictions require validation through carefully designed measurement programmes. Modern structural acoustics practice integrates computational and experimental methods throughout the project lifecycle.

Experimental Modal Analysis

Determining a structure's natural frequencies, mode shapes, and damping values provides essential input for analytical models. Typical procedures involve:

• Impact hammer or shaker excitation at multiple drive points

• Accelerometer measurements at 50-500+ response locations depending on structural complexity

• Frequency response function measurements from 0-2,000 Hz or higher

• Modal parameter extraction using curve-fitting algorithms

For critical applications, correlation metrics such as Modal Assurance Criterion (MAC) values exceeding 0.9 confirm agreement between predicted and measured mode shapes.

Sound Intensity and Power Measurements

Sound intensity techniques enable direct measurement of acoustic energy flow, supporting both source identification and sound power determination. These methods comply with ISO 9614 series standards and provide results traceable to international measurement references.

Transfer Path Analysis

When multiple noise sources and transmission paths contribute to a receiver location, transfer path analysis (TPA) helps quantify individual contributions. This technique proves invaluable for complex systems where intuition alone cannot identify the dominant paths requiring treatment.

Software Tools and Computational Resources

Modern structural acoustics analysis relies on sophisticated software platforms, each offering particular strengths:

Commercial FEM/BEM Packages: Industry-standard tools such as COMSOL Multiphysics, ANSYS, and Siemens Simcenter provide comprehensive structural acoustics capabilities. These platforms support model sizes ranging from simple components (thousands of degrees of freedom) to complete vehicles or buildings (millions of degrees of freedom).

Specialised Acoustics Software: Dedicated tools address specific applications including room acoustics prediction, environmental noise propagation, and SEA modelling. Selection depends on project requirements, available computational resources, and team expertise.

High-Performance Computing: Large-scale structural acoustics models benefit from parallel computing resources. Cloud-based platforms increasingly provide cost-effective access to substantial computational power, enabling analyses that would be impractical on standard engineering workstations.

Emerging Trends and Future Directions

Several developments are shaping the future of structural acoustics analysis:

Machine Learning Integration: Data-driven approaches complement traditional physics-based methods, enabling rapid screening of design alternatives and improved uncertainty quantification. Early applications show promise for acoustic material characterisation and source identification.

Digital Twin Implementations: Real-time structural acoustics models integrated with sensor networks enable continuous monitoring and predictive maintenance. This approach proves particularly valuable for critical infrastructure and high-value assets.

Sustainable Design: Growing emphasis on environmental performance drives demand for quieter products and facilities. Structural acoustics analysis supports noise reduction at the source—the most effective and sustainable approach to noise control.

Partner with Experienced Structural Acoustics Specialists

Structural acoustics analysis demands both theoretical expertise and practical experience—understanding not only the mathematical foundations but also the engineering judgement required to apply these methods effectively. From initial problem scoping through final validation, experienced guidance ensures that analytical efforts translate into real-world performance improvements.

Whether your project involves marine vessels, industrial facilities, building systems, or infrastructure, Sangster Engineering Ltd. brings comprehensive structural acoustics capabilities to clients throughout Nova Scotia and Atlantic Canada. Our team combines advanced analytical tools with hands-on measurement expertise to deliver practical solutions that meet your acoustic performance objectives.

Contact Sangster Engineering Ltd. today to discuss how structural acoustics analysis can support your next project. Our Amherst-based team is ready to help you achieve optimal acoustic performance while meeting regulatory requirements and project constraints.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.