Optimizing Circular Side-Resonators to Reduce Computer Fan Noise

One of the main noise sources in computers are the cooling fans. Tonal noise at the rotational frequency of the fan, the blade passing frequency (BPF) and its higher harmonics are important in fan noise. So called 'side-resonators' integrated in the duct of an in-duct axial fan cause an impedance change in the duct and, having proper dimensions and correct position, act as an acoustic mirror reflecting the noise back to the fan. As a result, noise emitted from the computer can be reduced. In this paper, a model describing viscothermal wave propagation in the duct and side-resonator is outlined. The model can be used to determine the resonator dimension and position to optimally reflect noise near the BPF. The developed model is compared with the models for prismatic tube and cylindrical resonators and the physical differences between these three resonators are explained. Preliminary results of a parameter study are presented. The results point out that the range and magnitude of the effective frequency band of a resonator setup can be successfully manipulated by changing the different dimensions of the setup

Temperature dependence of spin-cluster resonance intensity in RbFeCl3·2H2O

The spin-cluster resonance intensity is observed as a function of temperature in the pseudo-one-dimensional canted Ising metamagnet RbFeCl3·2H2O. For T 0.7 TN a pure one-dimensional Ising model gives a good description of the observed intensities. For T TN the intensity decreases rapidly as a function of temperature due to the destruction of the local ordering around a spin-cluster. The measured value of the intrachain interaction Ja/k of -36 K is in good agreement with earlier measurements on spin-cluster excitations

Elliptical side resonators for broadband noise reduction: theory and experiments

Previous research of the authors pointed out that side-resonators can be applied to reduce fan noise. However, the noise reduction capabilities of most resonator geometries, e.g. tube resonators, cylindrical resonators (cylindrical air layers) and circular resonators (disc shaped air layers), are relatively narrow banded. This is disadvantageous in case resonators are used in combination with a noise source that emits broadband noise or tonal noise at varying frequencies (for instance a speed controlled fan). It was found that the choice of the resonator geometry influences the broadband reduction capabilities (circular resonators offering the best broadband reduction capabilities). In the present study, it is investigated to what extent elliptical resonators, consisting of an elliptically shaped air layer, can be used to achieve broadband noise reduction. A semi-analytical model is proposed that describes the wave propagation in the elliptically shaped air layer. This model is connected to the analytical solution for wave propagation in a tube. The dimensions of the elliptical resonator can be optimized for broadband\ud noise reduction using this model. In addition, an experimental setup was built to verify\ud the semi-analytical model of the elliptical resonator

An acoustic finite element including viscothermal effects

In acoustics it is generally assumed that viscous- en thermal boundary layer effects play a minor role in the propagation of sound waves. Hence, these effects are neglected in the basic set of equations describing the sound field. However, for geometries that include small confinements of air or thin air layers, this assumption is not valid. Special models that include viscous and thermal effects are available (for example the Low Reduced Frequency model) but only for a limited number of geometries. To overcome these limitations and provide a solution that can be used for arbitrary geometries, an acoustic finite (2D) element that includes viscous and thermal effects is developed. The model is based on the linearized Navier stokes equations (including shear), the equation of continuity, the equation of state for an ideal gas and the energy equation. The method of weighed residuals is used in combination with a mixed formulation of pressure, temperature and particle velocity degrees of freedom. The results of the developed element code are compared with the results of an existing (analytical) Low Reduced Frequency solution and a viscothermal element that was found in literature

Role Profiles of HRD Practitioners in the Netherlands

This study of HRD practitioners and experts in the Netherlands was executed in 1993 and based on an earlier US role profile study. Two types of profiles were identified for eleven different roles that an HRD practitioner might perform within her or his job. Both profiles consist of core outputs of the different roles and the core competencies required for achievement of the outputs. Comparisons were drawn between current and future profiles and between the results of the expert study and the outcomes of the US study. The American role profiles appeared to be largely valid for the Dutch context

Measuring the implementation of codes of conduct. An assessment method based on a process approach of the responsible organisation

More and more organisations formulate a code of conduct in order to stimulate responsible behaviour among their members. Much time and energy is usually spent fixing the content of the code but many organisations get stuck in the challenge of implementing and maintaining the code. The code then turns into nothing else than the notorious “paper in the drawer”, without achieving its aims. The challenge of implementation is to utilize the dynamics which have emerged from the formulation of the code. This will support a continuous process of reflection on the central values and standards contained in the code. This paper presents an assessment method, based on the EFQM model, which intends to support this implementation process

The myth of self-managing teams: A reflection on the allocation of responsibilities between individuals, teams and the organisation

Concepts that include the participation and empowerment of workers are becoming \ud increasingly important nowadays. In many of these concepts, the formal responsibility is delegated to teams. Does this imply that the normative responsibility for the actions of teams is also delegated? In this article we will reflect on the difference between holding a person accountable and bearing responsibility. A framework is elaborated in order to analyse the accountability and responsibility of teams. In this framework, the emergence of a collective mind, and the organisational factors that influence the extent to which teams have the possibility of acting in a responsible way play an important role. It shows that teams can bear responsibilities that could never be carried by a group of individuals. The framework is used to analyse two sample cases with self-managing teams in production facilities. The authors discuss the implications for the theory and practice of self-managing teams and the allocation of responsibility between individuals, teams and the organisation

Exploration of an agenda for transparency in the construction industry

Purpose In enhancing the market operation of the building sector, transparency is of great importance. The objective of this article is to propose an inventory of aspects of the relationships between public clients and executing parties that have the most urgent need for greater transparency. Methodology / approach The main methods used include a conceptual analysis and twenty interviews with managers of various organisations in the construction industry. Findings Based on this study, four essential points for transparency have been determined: openness about risks and costs, measuring of quality-price ratios, reasons for award or rejection and enhancement of the reputation mechanism. Research limitations / implications This study takes the Dutch context as a reference point for the analysis. When the findings are used also in other settings, it is necessary to address the differences in characteristics of the building sector. Practical implications The essential points for transparency addressed in this paper have consequences for especially the interaction between public clients and executing parties. Furthermore, conditions for transparency - like possibilities to judge quality in a more robust and transparent manner and methods for enhancing the reputation mechanism - point at necessary future research for improving transparency in the construction industry. Originality / value of the paper The Dutch construction industry is working through a transition process focused on improving its market operation, integral processes and societal added value. In this transition, transparency between clients and executing parties is of great importance.Transparency; construction sector; trust; reputation; integrity