Transient Dynamics of Helicopter Rotor Wakes Using a Time-Accurate Free-Vortex Method

A second-order accurate predictor-corrector type algorithm has been developed to obtain a time-accurate solution of the vortical wake generated by a helicopter rotor. The rotor blade flapping solution was fully integrated with the wake geometry solution using the same time-marching algorithm. The analysis was used to predict the locations of wake vortex filaments under transient flight conditions, where the rotor wake may not be periodic at the rotational frequency. Applications of this analysis include prediction of the rotor induced velocity field and blade airloads during transient flight and maneuvers. The stability of the rotor wake structure is important from the perspective of free-vortex wake models. The wake stability was examined using a linearized stability analysis, and the rotor wake was shown to be physically unstable. Therefore, the stability of the numerical algorithm is an important consideration in developing robust wake methodologies. Both the stability and accuracy of the numerical wake solutions algorithms was rigorously examined. The straight-line vortex segmentation used in the present analysis was shown to be second-order accurate. The overall numerical solution was also demonstrated to converge with a second-order accuracy. A technique for increasing the order of accuracy for high resolution solutions is also described. Along with a formal (mathematical) verification of solution accuracy, the numerical solution for the rotor wake problem was compared with experimental results for both steady-state and transient operating conditions. The steady-state wake model was shown to give good predictions of rotor wake geometry, induced inflow distribution as well as performance trends. Under transient conditions, such as those following a pitch input during a maneuver, the time-accurate wake model was shown to correctly model the dynamic response of rotor wake. In axial descent passing through the vortex ring state, the present analysis was shown to properly model the associated power losses as shown by experimental results. The present analysis was also shown to give improved predictions of wake distortions during simulated maneuvering flight with various imposed angular rates of the rotor

Transposition in Translating Proverb Book of New King James Version Bible Into Kitab Amsal of Alkitab Bahasa Indonesia by Lai

Transposisi merupakan salah satu prosedur yang harus diperhatikan dalam proses penerjemahan. Secara linguistik, transposisi berarti perpindahan posisi atau hasil Perubahan fungsi atau kelas kata yang bertujuan untuk dapat menghasilkan suatu karya terjemahan yang mudah dipahami dalam bahasa sasaran. Dalam proses penerjemahan, transposisi memiliki peranan penting karena seringkali ditemukan perbedaan struktur bahasa dari struktur bahasa sasaran. Tujuan penulisan jurnal ini adalah untuk menjabarkan penggunaan transposisi dalam proses penerjemahan khususnya dalam penerjemahan Kitab Amsal dari New King James Version Bible ke dalam Alkitab Bahasa Indonesia. Lewat jurnal ini, penulis juga ingin mengetahui apakah seharusnya penerjemah menggunakan transposisi dalam menerjemahkan teks atau bacaan. Selain itu, kapan seharusnya penerjemah menggunakan transposisi dan kapan seharusnya penerjemah tidak menggunakan transposisi dalam menerjemahkan suatu teks. Dalam jurnal ini, penulis menggunakan metode purposive sampling untuk mendapatkan data, dan metode padan dan agih untuk menganalisis data. Hasil penelitian menunjukkan bahwa penerjemah menggunakan transposisi dikarenakan adanya perbedaan struktur bahasa sumber ke bahasa sasaran tanpa mengubah makna teks. Dalam hasil analisis penulis menemukan bahwa terkadang dalam satu kalimat terdapat beberapa jenis transposisi yang digunakan oleh penerjemah

Supercriticality to subcriticality in dynamo transitions

Evidence from numerical simulations suggest that the nature of dynamo transition changes from supercritical to subcritical as the magnetic Prandtl number is decreased. To explore this interesting crossover we first use direct numerical simulations to investigate the hysteresis zone of a subcritical Taylor-Green dynamo. We establish that a well defined boundary exists in this hysteresis region which separates dynamo states from the purely hydrodynamic solution. We then propose simple dynamo models which show similar crossover from supercritical to subcritical dynamo transition as a function of the magnetic Prandtl number. Our models show that the change in the nature of dynamo transition is connected to the stabilizing or de-stabilizing influence of governing non-linearities.Comment: Version 3 note: Found a sign-error in an equation which propagated further. Section 4 and Fig. 3,4,5 are updated in Version 3 (final form

Field theoretic calculation of scalar turbulence

The cascade rate of passive scalar and Bachelor's constant in scalar turbulence are calculated using the flux formula. This calculation is done to first order in perturbation series. Batchelor's constant in three dimension is found to be approximately 1.25. In higher dimension, the constant increases as $d^{1/3}$.Comment: RevTex4, publ. in Int. J. Mod. Phy. B, v.15, p.3419, 200

Aperiodicity Correction for Rotor Tip Vortex Measurements

The initial roll-up of a tip vortex trailing from a model-scale, hovering rotor was measured using particle image velocimetry. The unique feature of the measurements was that a microscope was attached to the camera to allow much higher spatial resolution than hitherto possible. This also posed some unique challenges. In particular, the existing methodologies to correct for aperiodicity in the tip vortex locations could not be easily extended to the present measurements. The difficulty stemmed from the inability to accurately determine the vortex center, which is a prerequisite for the correction procedure. A new method is proposed for determining the vortex center, as well as the vortex core properties, using a least-squares fit approach. This approach has the obvious advantage that the properties are derived from not just a few points near the vortex core, but from a much larger area of flow measurements. Results clearly demonstrate the advantage in the form of reduced variation in the estimated core properties, and also the self-consistent results obtained using three different aperiodicity correction methods