Acoustic Analysis of an Automobile Horn

 

Horn Assembly

Objective: D65 is a type of horn of Diameter 65mm and  mainly consists of a resonator and a diaphragm which are separated by an air column which is responsible for the functioning of the horn. The resonator of the horn is 0.6mm in thickness and attached to the diaphragm with the help of a washer. The resonator consists of three humps in its design. The functioning will be best when the frequency of the air gap and resonator match or are almost equal and this is analyzed by various FEM methods.

FEA Model-hexahedral elements-Diaphragm

Stress Contours

Methodology and Analysis: By using FEM  we can easily find out the frequency of the resonator but the frequency of the air column is a fluid-solid interaction(FSI) problem. Advanced FEM algorithm was used for the air column frequency and then by iterative method the frequency of both were matched . From the analysis done, some factors which can improve the design are modifying the dimension  of the washer between resonator and diaphragm, like 0.5, 0.8, 1.0 etc and modification in the thickness of the resonator. Analysis is done  by using different thickness of the resonator for different dimension of the washer. Few of the results are shown in the image.

Result and Conclusion: From various analysis done  it can be concluded that the dB and quality of sound depends on the natural frequency of the air column and natural frequency of the resonator. Smaller the gap the better  will be the quality of sound in the particular range. Since 0.6mm is the actual thickness of the resonator which upon analysis was modified to 0.4mm so that the air column volume was increased and hence the quality of sound improved. After  changing the thickness and the profile the output is found to be good i.e. 0.4mm thickness and base is up from second hump and outer side by 0.8mm.   Hence the resonator design was optimized to produce maximum sound  with high quality.

CFD Analysis to Study the Wind and Heat-Island Effect due to Outdoor A.C. Units in an High Rise Building

Objective: To study the airflow around the project building & other buildings due to the effect of wind and effect of heat generated by outdoor air conditioners installed in high rise project building on other surrounding buildings in worst case scenario.For wind flow analysis the predominant wind direction of SW with average wind velocities of 3 m/sec in Mumbai is considered based on the ISHRAE weather data. Hence, in worst case scenario all 30 floors with 20 outdoor AC units in each floor were considered for total heat dissipation from the project building. The worst case conditions were simulated for 21st March at 22:00 which is assumed to be a condition when all the ACs were working. At that moment as per ISHRAE weather data the ambient temperature in Mumbai is 26.9 C, same was considered in the CFD analysis.

Modelling and Analysis: Based on the provided CAD drawings details of the “Kahprideo project building & surrounding buildings”, the 3D CFD model was prepared. The area of interest for the project building & its surrounding building is 305m width, 340m length & 125.5m height. After preparing the 3 D geometry, the high quality mesh with different hexagonal & tetrahedral mesh was generated with total mesh cells of 8.8 million cells were obtained. The meshed geometry was used for solving the flow & energy equations in “project building & surrounding buildings” with applying the suitable boundary conditions in worst case conditions to see the effect of wind flow around buildings and heat dissipated by outdoor air conditioners on other buildings.

Conclusion: Thus CFD Analysis was carried out to study the airflow around the project building & other buildings due to the effect of wind and also the effect of heat generated by outdoor air conditioners installed in high rise project building on the other surrounding buildings in worst case scenario. From the analysis it was found that the temperatures created due to outdoor air conditioners located in project building were reaching at lower levels to other buildings, however the temperature of this heat wave is 0.8 C above the ambient temperature & this temperature difference is very negligible. However while closely observing all the temperature results it reveals that just few meters away from the project building the temperature dropped to 27.6 C, then after 45m of distance the temperature is dropped to 27.2 C and then after 480m of distance the temperature  dropped to ambient conditions. Hence it was concluded that the outdoor air conditioning units placed in the building were slightly affecting the surrounding buildings however it was almost negligible.