31 research outputs found
Gerardus van der Leeuw (Sebagai Seorang Theoloog Dan Phenomenoloog)
No full textData biografi dan aktifisnya. Gerardus van der Leeuw dilahirkan pada tanggal 19 Maret 1980 di kotaDen Haag, Negeri Belanda. Putera Sulung Gerardus van der Leeuw Senior, seorang collectant dan diaken Nederlands Hervormde Kark (Gereja Harvormde Belanda) di Den Haag. Setelah tamat sekolah dasar dia melanjutkan belajar pada Stedelijk Haags Gymnasium dari tahun 1902 sampai 1908. Gymnasium tersebut didirikan tahun 1832 dan pada waktu itu direkturnya dr. Th van Aalit. Dan diantara para gurunya antara lain: Dr. A.J Barnouw, Edward B. kostar dan dr. E.F. Korsmann. Dan diantara teman teman sebayanya pada waktu itu antara lain P.J. van Eijck (yang kemudian menjadi Guru besar dalam studi Grafika di Universitas Groningen), Martinus Nijhiff (seorang penyair), Victor van Vriesland (seorang author) dan Alexander Loundon (seorang diplomat). Juga berkenan dengan H.C. Rukma yang kemudian menjadi Guru besar dalam psiater dan neurologi di Universitas Utrecht
The UTwente aeroacoustic wind tunnel upgrade
Full text linkThis paper describes the UTwente Aeroacoustic Wind Tunnel including its recent anechoic chamber renovation and commissioning. This testing facilitywas originally built in the 1970’s as a closed circuit/closed test section aerodynamic wind tunnel and converted into an aeroacoustic open jet/closed circuit facility in 2001. In 2018 this aeroacoustic wind tunnel has been further upgraded with a special focus on reducing the anechoic chamber cut-off frequency. In the current configuration, the UTwente Aeroacoustic Wind Tunnel is an open test-section facility equipped with a 132 kW electric motor able to produce flow up to 60 m/s with turbulence intensity below 0.08%. The 0.7 x 0.9 m2 rectangular jet with Reynolds number of 324.000 based on the criteria of 0:1 √S. This test facility can be used with airfoil models with chord of up to 0.30 m, reaching a chord-based Reynolds number of up to 1.2 million. The anechoic chamber measures 6 x 6 x 4 m3 equipped with a combination of wedges and flat absorbers leading to a cut-off frequency of 160 Hz and is commissioned accordingly to the ISO 3745 norm
Comparison between analog and digital microphone phased arrays for aeroacoustic measurements
No full textMicrophone arrays are useful measurement devices for estimating the location and strength of sound sources. Numerous comparative studies have been conducted regarding the performance of acoustic imaging methods in the past, but literature lacks of a systematic investigation on the role of the hardware on the measurements. This research focuses on the performance differences between two 63-microphone arrays: one with digital MEMS (Micro Electro Mechanical Systems) microphones and the other with analog condenser microphones. Both systems are used on an aeroacoustic experiment performed in an anechoic open-jet wind tunnel featuring two airfoils (NACA 0012 and NACA 0018) equipped with trailing-edge serrations. Whereas both arrays provided similar frequency spectra when analyzing trailing-edge noise emissions (which are in agreement with previous research), the analog array seems to offer source maps of higher quality with a higher dynamic range (lower sidelobe level). Moreover, the results of the digital array featuring trailing-edge serrations show a noise increase at the higher frequencies (4 kHz) with respect to the straight-edge case, which is not expected from the findings of previous experimental research. The results of the analog array do not present such behavior. This manuscript is the result of a collaboration project between the University of Twente (UTwente) and Delft University of Technology (TU Delft).Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aircraft Noise and Climate EffectsWind Energ
Unsteady surface pressure measurements on trailing edge serrations based on digital MEMS microphones
Full text linkThe physics of turbulent flow reaching the airfoil trailing edge is fundamental to the understanding of the Turbulent Boundary Layer (TBL) noise production mechanism. The experimental validation of semi-empirical and computational models requires advances in current experimental techniques and instrumentation to allow accurate determination of turbulent structures. This research investigates the applications of digital MEMS microphones embedded for the experimental determination of unsteady wall pressure in a 3D printed NACA0012 airfoil at chord-based Reynolds number 200,000<Re<700,000. The development of this experimental technique brings challenges regarding the construction since sensors and components must be miniaturized in order to maximize the sensor spatial resolution. This paper discusses the implementation of this novel wall pressure transducer. Results indicate that the proposed approach can be effectively applied to the experimental determination of near-wall turbulence structures and other flow features, which is a major step toward improved TBL noise prediction
Effect of noise control treatments on surfaces near a non-uniform inflow propeller
Full text linkWith the advent of urban air mobility and distributed electric propulsion in aviation, effective noise mitigation for propeller systems has become critical. This study explores the application of noise-mitigating materials in the bottom wall of UTwente's wind tunnel test section, beneath a non-shrouded propeller subject to non-uniform inflow. The objective was to assess the impact of these materials on tonal noise reduction, emitted noise levels, and directivity. Two materials were tested: arrays of additive-manufactured quarter-wavelength resonators (band-stop mitigator) and a slab of metal foam (broadband mitigator). Various geometrical configurations were investigated for the resonators, with the optimal configuration placing resonators everywhere except directly beneath the propeller blades. Applying resonators immediately underneath the propeller, with a critical clearance, induced a spurious hydrodynamic interaction, amplifying tonal noise at higher frequencies. The efficiency of the quarter-wavelength-resonator solution depends heavily on configuration. Performance was compared with a flat plate and the metal foam, with the tuned resonators outperforming the broadband material in noise reduction. The polar directivity of the emitted sound is influenced by the configuration, and the presence of any sound-mitigating material underneath the propeller consistently degrades upstream azimuthal directivity
Wind tunnel testing and modelling of a rod-airfoil setup: validation and 3D acoustic imaging
No full textThis work revisits the rod-airfoil benchmark experiment from Jacob et al. (2004) with the aim of performing a detailed numerical validation in the nearfield and far field as well as to perform 3D acoustic imaging. The setup consists of a rod near the leading edge of a NACA-0012 airfoil and is placed in a semi-open wind tunnel in anechoic conditions. In addition to a far-field microphone array, the setup is equipped with two planar microphone arrays as well as wall-mounted microphones on the closed wind tunnel section and on the airfoil. The setup is modelled using a second-order finite volume method, and particular attention is devoted to including installation effects and sensor response properties in order to guarantee simulation accuracy. Validation examples are provided, including single microphone spectra as well as the acoustic field reconstructed on the test object by means of 3D acoustic imaging using the planar microphone arrays. Finally, the experimentally-validated numerical model is used as a means to gain further insight into the tested object. For instance, the model allows to separate acoustical and turbulent effects present in the sensors located within the flow section
Experimental characterization of vortex generators induced noise of wind turbines
Full text linkThe wind energy industry is progressively aiming towards larger wind turbine size as a means of increasing energy production efficiency. Wind turbine rotor blades are becoming significantly more flexible and have an increased risk of structural failure. Thicker airfoil profiles can be used to increase the structural strength. However, thicker airfoils are more prone to flow separation with adverse effect on power generation. Vortex generators (VGs) are an effective solution to delay flow separation. However, VGs significantly increase radiated noise levels. This presented research experimentally investigates the effect of VGs on blade noise production. Specifically, the influence of the VG geometric shape is evaluated while keeping the dimensions constant. Wind tunnel tests have been carried out on a NACA 0018 that is equipped with triangular vane-type VGs specifically designed for the test conditions. A microphone phased array is used to assess the radiated noise using the beamforming technique. The results show that the VGs significantly contribute to increase the blade noise production with having a predominant role at high-frequencies where the VG acts as a non-compact aeroacoustic source
A note on games corresponding to sequencing situations with due dates
Full text linkconvex cooperative games;one-machine sequencing situations;due dates;ready times
Self priming in face recognition
Full text linkRecently Burton, Bruce and Johnston (1990) have presented an interactive activation and competition model of face recognition. They have shown that this IAC model presents a parsimonious account of semantic and repetition priming effects with faces. In addition, a number of new predictions are evident from the model's structure. One such prediction is highlighted by Burton et al. themselves - that for short prime-target stimulus onset asynchronies (SOAs) a face should prime the recognition of a target name (or vice versa), 'self priming'. This thesis examined this prediction and found that it held for a design in which items were repeated across prime type conditions (same, associated, neutral and unrelated). Further, cross (face prime/name target) and within-domain (name prime/name target) designs were found to produce equivalent degrees of self and semantic priming (Experiments 1 and 2). Closer examination of the Burton et al. model suggested that the effect of domain equivalence for self priming should not hold for a design in which the stimulus items are not repeated across prime type conditions (i.e. subjects are presented with each item only once). This prediction was confirmed in Experiments 3, 4, 5 and 6.The time courses of self and semantic priming were investigated in two experiments where the interstimulus interval (ISI) between prime and target, and prime presentation times were varied. The results proved difficult to accommodate within the Burton et al. model, but it is argued that they did not provide a sufficient basis on which to reject the model. Finally, the self priming paradigm was applied to the study of distinctiveness effects. Faces judged to be distinctive in appearance were found to produce more facilitation than faces judged to be typical in appearance. Similarly, caricatured representation of faces were found to produce more facilitation than veridical or anticaricatured representations. The results of the distinctiveness studies are discussed in terms of the Valentine's (1991a; 1991b) exemplar-based coding model and Burton, Bruce and Johnston's (1990) IAC implementation. It is concluded that the results of these experiments lend support to the Burton et al. model
International law, Arms embargoes and the United Nations security council
Full text linkDue to the political aspects of international law and the political nature of the problems involved in international relations, appreciation of the legal nature of United Nations Security Council arms embargoes is lacking. Based upon a review of the practice of the Council, this thesis explores the operation of arms embargoes within the overall scheme of international law and highlights how these measures provide an interface between the laws of collective security, armed conflict, human rights and arms control. The author outlines existing arms control regimes and the law applicable to the study of arms embargoes; ex amines the law relating to the powers of the United Nations Security Council under Chapter VII of the Charter of the United Nations and the legal limits thereto; identifies the patterns in practice by expounding the nature, scope and functions of arms embargoes and comments on the possible existence of a normative framework; explores the specific legal mandate for arms embargoes and considers possible alternative legal bases; and finally, investigates other issues of international law arising from the use of arms embargoes. The powers of the Security Council exist for the pursuit of one central outcome - the maintenance of international peace and security. This thesis argues that the logical way to achieve this outcome in situations of armed conflict is to remove the tools with which those types of threats are created and sustained. Conventional weapons (in particular, small arms and light weapons) are the principal, although not the exclusive, tools of armed conflict. Arms embargoes imposed in the context of an armed conflict can be legally justified with the simple objective of suppressing conflict by means of arms control
