Simulation of High Frequency Sound Propagation in Duct Systems Simulering av högfrekvent ljudutbredning i kanalsystem Protection of the environment is a concern of global interest. It is universally acknowledged that the steady rise in all kinds of pollution cannot be allowed to continue indefinitely. The acoustical environment has likewise suffered from the increase in use and power of machines in the workplace, increasing road traffic, larger aircraft, etc. High intensities of noise have been associated with numerous harmful health effects including noise-induced hearing loss and other nervous system diseases. In 1970, the Occupational Safety and Health Administration (OSHA) set limits on the levels of noise to which workers may be exposed in their work environments. Many countries and communities have followed suit making it a legal requirement to measure community noise level, to reduce noise at the source, and to maintain acceptable noise levels in factories. Furthermore, noise has become a major factor influencing the marketability and competitiveness of industrial products such as cars, machinery, office equipment, and buildings. In many applications, the amount of sound power produced by a product is indicated by a label giving the customer additional information to help decide which product to choose. Several products, e.g. cars, trucks and heavy equipment, need to pass a certain noise certification in order to be admitted to certain markets. For other products (HVAC and generator sets), the produced noise has to be measured in several spots after installation to conform to limits set by customer regulations. Accordingly, manufacturers and researchers have become increasingly concerned with better ways to attenuate or reduce noise. Traditionally, noise control engineers have identified noise problems experimentally and have solved them in a trial and error manner. However, the automotive, heavy equipment, and HVAC industries are now gravitating towards the use of numerical noise prediction early in the design phase. If computer models can adequately model the physics of the real problem, design changes can be anticipated before a prototype is even fabricated, reducing product delivery time and engineering effort. In IC-engine exhaust and inlet systems and HVAC systems, acoustic waves propagate inside ducts. At lower frequencies, the duct cross-sectional dimensions are small compared to the acoustic wavelength. Accordingly, it can be assumed that plane waves propagate inside the duct system simplifying the analysis. Several university codes have been developed to predict sound attenuation in complex duct networks assuming plane wave propagation. Examples of 1D codes include Davies, LAMPS, SID and SIDLAB. SIDLAB is the 1D software which has been developed by the Egyptian and Swedish research teams. It is based on two-port theory and has benefited from their previous research, teaching and consulting experience. However, SIDLAB and other 1D codes are limited. In some applications, such as HVAC or muffler systems for large diesel engines in ships or generator sets, the duct dimensions are large compared to the frequency of interest. The plane wave assumption is no longer applicable and more complicated techniques like finite and boundary element methods are used. However, both methods are CPU intensive requiring considerable effort to build the model. The main objective of this project is to investigate the use of simple analytical methods even in the high frequency region with a new model. The new model will be validated against FEM calculations and measurements. Several products, e.g. cars and trucks, need to pass a certain noise certification in order to be admitted to certain markets. For other products, e.g. HVAC and generator sets, the produced noise has to be measured in several spots after installation to conform to the limits set by the customer regulations. This project deals with the reduction of noise from the source when acoustic waves propagate inside ducts. For 1D analysis of duct systems it is usually assumed that only plane waves can propagate, which limits the frequency range of the simulation. This technique is valid for several applications such as automotive mufflers. In some applications, such as HVAC or muffler systems for large diesel engines in ships or generator sets, the duct dimensions are large compared to the frequency of interest. Therefore, the simple methods fail and it is important in this case to use some other complicated techniques such as Finite (FEM) or Boundary Element Methods (BEM) which are time consuming and require experience to build the model. The main objective of this project is to investigate the use of simple analytical methods even in the high frequency region. The new model will be validated against FEM calculations and measurements. The measurements will be conducted by the Egyptian team at Ain Shams University (ASU). ASU will derive and code the new simplified technique whereas KTH will perform the validation with FEM.