Parental resource allocation among offspring varies with increasing brood age in Black-legged Kittiwakes Rissa tridactyla

Capsule: Black-legged Kittiwakes Rissa tridactyla breeding at a North Sea colony allocated more resources to younger chicks with increasing brood age.<p></p> Aims: Examine how feeding, attendance and resource allocation change with increasing brood age and how allocation of feeds affects growth rate and fledging success.<p></p> Methods: Broods of two were observed on Coquet Island to compare feeding rates and fledging success between chicks of different hatching order.<p></p> Results: Growth and feeding rates were similar between chicks of different hatching order. The relationship between growth and feeding rate may have differed between siblings, although this relationship was not strong. Feeding rate per brood and nest attendance decreased nonlinearly as brood age increased. First-hatched chicks were fed more frequently at the beginning of multiple feeds and received a higher proportion of feeds during early chick-rearing. However, during late chick-rearing second-hatched chicks received proportionally more feeds.<p></p> Conclusion: Parents reduced overall feeding rate as brood age increased, while increasing the proportion of resources allocated to younger offspring. This may explain general similarities in growth rate and fledging success between chicks of different hatching order. By considering resource allocation throughout development we can better understand parental investment strategies in asynchronous species.<p></p&gt

Descriptors of Sound from HVAC&R Equipment

A test was conducted to investigate how people describe HVAC&R equipment noise. Twenty-eight recordings and modified recordings were played to 42 subjects who wrote down descriptions as they heard the sounds. Subjects also rated these and 12 other sounds on an annoyance scale. The words used by subjects were categorized into 9 groups and the occurrences of the words within a group were counted for each sound. The results of the word analysis were compared to results of a sound quality metric analysis of the sounds, and to the results of the annoyance test. There was a high degree of correlation between the word scores and the corresponding metric values. The performance of linear models of metrics as predictors of annoyance was examined and loudness was the strongest contributor because of the large range of loudness used in the test. There were two significant outliers to the general trend of the predictions; these were sounds that were described by subjects as “sharp” and “high pitched”. The results of this test are being used in the design of a semantic differential test to examine the relationship between sound characteristics and annoyance further

Results of a Semantic Differential Test to Evaluate HVAC&R Equipment Noise

HVAC and Refrigeration (HVAC&R) equipment designers would like to have better noise criteria to guide their designs to reduce customer complaints and to understand what characteristics of sounds people dislike. To develop a robust sound evaluation model, the main sound characteristics that influence overall judgments of the sounds need to be determined. A semantic differential test was conducted using twenty-two sounds that were a mixture of recordings and modified recordings of two types of HVAC&R units. Sound descriptions provided by subjects in another test were used to develop seventeen rating scales. A factor analysis was performed on the ratings of thirty-nine subjects with normal hearing. Three strong factors were identified that are related to loudness, tonal content or sharpness, and fluctuation or irregularity. The correlation between sound metrics and average responses on each scale was examined. The highest correlations were always for the metric that is supposed to measuring the attribute associated with a particular rating scale. Models to predict annoyance ratings from sound metrics were also examined, and models that included a loudness and sharpness term gave very good results, but these need further development and need to be tested on a greater variety of HVAC&R sounds. The results of this test have also inspired development of signal modification techniques to separate tonality and sharpness attributes so that their individual influences on overall judgments of the sounds can be examined

Sound Quality Evaluation of Refrigerated Truck Noise

Noise from refrigeration units on trucks can be a problem, particularly when the trucks are parked near residences. The development of a sound evaluation method that takes into account the strength of all sound attributes affecting people’s responses, including level, is described here. Such a model, coupled with a sound prediction methodology, would be helpful to unit designers who are concerned with optimizing a unit’s acoustical performance. The analysis of human subject responses to a variety of refrigerated truck sounds (in the third of a series of three subjective tests) is described. Sixty participants rated 25 recorded and digitally modified refrigerated truck sounds as well as 25 residential HVAC equipment sounds. Fourteen sound quality metrics were evaluated as potential variables in a model to predict the average annoyance ratings of the refrigerated truck sounds. A rate-change-of-level metric that captured the impulsive character of the refrigerated truck unit noise was developed, and the best performing model comprised it, a level metric and a spectral balance metric. The performance of the model when used with signals and ratings taken from other tests is described

The Design and Evaluation of Microphone Arrays for the Visualization of Noise Sources on Moving Vehicles

The present work was directed towards the design of a sideline microphone array specifically adapted to the visualization of automotive noise sources in the 500 Hz to 2000 Hz range. The particular design philosophy followed here involved the minimization of the array redundancy: i.e., the minimization of the number of pairs of microphones that are separated by the same distance in the same directions. The performance of sixty-four element microphone arrays designed according to this principle will be illustrated through the use of simulated motor vehicle passbys. In addition, their performance will be compared with more conventional array designs: e.g., elliptical, and spiral arrays

Sound Quality Evaluation of Residential HVAC&R Equipment

HVAC and Refrigeration (HVAC&R) equipment designers would benefit if there were better noise criteria for optimization of noise control treatments. Development of a model that can predict the average annoyance ratings of residential HVAC&R equipment sound is described. Three sets of subjective tests were performed, and the results from part of the third test are described. Three rating exercises were designed for the 60 subjects who participated. In each of the three parts the 50 sounds were a mixture of recordings and recordings that were digitally modified to decrease the correlation between sound metrics. In Part A the sounds tended to be louder, in Part B quieter sounds were rated and in Part C the sounds covered a wider range of loudness, similar to that used in the previous two tests. Thirteen sound quality metrics were tested as parameters in a linear model that predicts average annoyance ratings. The best performing model contained a tone-adjusted level, a spectral balance, a tonality and a roughness metric. The model was also used to predict average annoyance ratings in previously conducted tests and R2 values ranged from 0.90 to 0.94. Ongoing work includes examination of model deficiencies to identify potential sound attribute levels that cause actual ratings to be higher than those predicted

Perception of Diesel Engine Gear Rattle Noise

Component sound quality is an important factor in the design of competitive diesel engines. One component noise that causes complaints is the gear rattle that originates in the front-of-engine gear train which drives the fuel pump and other accessories. The rattle is caused by repeated tooth impacts resulting from fluctuations in differential torsional acceleration of the driving gears. These impacts generate a broadband, impulsive noise that is often perceived as annoying. In most previous work, the overall sound quality of diesel engines has been considered without specifically focusing on predicting the perception of gear rattle. Gear rattle level has been quantified based on angular acceleration measurements, but those measurements can be difficult to perform. Here, the emphasis was on developing a metric based on subjective testing of the perception of gear rattle. In the first part of the present work, a method to simulate gear rattle noise and incorporate it into a no-gear-rattle (baseline) recording was developed. That procedure enabled controlled variation of rattle within the total engine noise signal. The simulations were then used in a psychoacoustic test that was designed to quantify detectable levels, perception of growth, and increase in annoyance due to the presence of gear rattle noise. Forty subjects participated in the threshold detection tests and a paired comparison annoyance test. The responses of people who reported having experience with diesel engines were compared to those of a more general population. The subjects with diesel engine experience were found to be better at detecting gear rattle noise and found rattle more annoying than the other subjects, particularly at high rattle levels. Current work is focused on development of metrics that accurately reflect human responses to gear rattle

Noise Source Identification and Noise Directivity Analysis of Bladeless Fans by Combined CFD and CAA Method

The bladeless fan is a new concept of fan that does not have visible impellers. It features low noise level, uniform airflow, and improved safety. It has been widely applied in household appliances. Since the customers are particularly sensitive to the noise generated by the fan, the aeroacoustics performance of the fan needs to be accurately characterized in the design stage. In this study, computational fluid dynamic (CFD) and computational aeroacoustics (CAA) are applied to investigate the aeroacoustics performance and identify the major noise source of the bladeless fan. A prototype of the bladeless fan, including a wind channel, a base cavity, a rotor and a stator inside the base, is set in a computational domain of 4m × 2m × 2m and the airflow through the fan is simulated. The hybrid mesh is generated, the unstructured mesh in the near field, and the structured at the far field. To compute the flow field, steady RANS simulation (standard k–ε turbulence model) and Large Eddy simulation (Smagorinsky-Lilly model) are carried out. Ffowcs Williams and Hawkings (FW-H) analogy is used to predict the acoustic field. Experiments, including air velocity measurement and sound pressure measurement, are conducted to validate simulation results. Sound pressure level results at the near-field receiver illustrate that the blade passage frequency can be captured by combined CFD and CAA method. Noise source analysis shows that the combination of the rotor and stator contributes most to the noise produced by the bladeless fan. The wind channel is the secondary source. Sound pressure level contours at different distances and different heights are generated to investigate the directivity pattern of the noise generated by the bladeless fan. At the near field, the produced noise at the front and the back of the bladeless fan are louder than those at left and right; at the far field, the noise at the front is much larger than the other three sides. In addition, at the near field, with the increase of the height, two separated hotspots appear over 2,500Hz and the sound pressure level at these two hotspots increases; at the far field, the noise distribution at different heights is similar and the peak near 3,000Hz can be estimated. A possible reason to cause this peak is vortex shedding at the trailing edge of the rotor’s blades. The aeroacoustics analysis is helpful to develop strategies to reduce noise and guide the improved design of the bladeless fan

Influence of Geometric Parameters on Aerodynamic and Acoustic Performances of Bladeless Fans

In recent years, the bladeless fan that does not have visible impellers have been widely applied in household appliances. Since the customers are particularly sensitive to noise and the strength of wind generated by the fan, the aerodynamic and acoustic performances of the fan need to be accurately characterized in the design stage. In this study, computational fluid dynamic (CFD) and computational aeroacoustics (CAA) are applied to investigate the performances of different designs of a bladeless fan model. The influence of four parameters, namely the airfoil selection for cross-section of the wind channel, the slit width, the height of cross-section and the location of the slit, is investigated. The results indicate the streamwise air velocity increases significantly by narrowing the outlet, but the noise level increases simultaneously. In addition, the generated noise increases while the height of fan cross-section increases, and a 4mm height of the cross section is optimal for aerodynamic performance. When the slit is closer to the location of maximum thickness, the performances of the bladeless fan increases. Moreover, the performance is not changed significantly by changing the cross-sectional profile. Finally, the optimal geometric parameters are identified to guide the future design of the bladeless fan