Unsteady Aerodynamic Interaction Between Rotor and Ground Obstacle

The mutual aerodynamic interaction between rotor wake and surrounding obstacles is complex, and generates high compensatory workload for pilots, degradation of the handling qualities and performance, and unsteady force on the structure of the obstacles. The interaction also affects the minimum distance between rotorcrafts and obstacles to operate safely. A vortex-based approach is then employed to investigate the complex aerodynamic interaction between rotors and ground obstacle, and identify the distance where the interaction ends, and this is also the objective of the GARTEUR AG22 working group activities. In this approach, the aerodynamic loads of the rotor blades are described through a panel method, and the unsteady behaviour of the rotor wake is modelled using a vortex particle method. The effects of the ground plane and obstacle are accounted for via a viscous boundary model. The method is then applied to a “Large” and a “Wee” rotor near the ground and obstacle, and compared with the earlier experiments carried out at the University of Glasgow. The results show that the predicted rotor induced inflow and flow field compare reasonably well with the experiments. Furthermore, at certain conditions the tip vortices are pushed up and re-injected into the rotor wake due to the effect of the obstacle resulting in a recirculation. Moreover, contrary to without the obstacle case, the peak and thickness of the radial outwash near the obstacle is smaller due to the barrier effect of the obstacle, and an up-wash is observed. Additionally, as the rotor closes to the obstacle, the rotor slipstreams impinge directly on the obstacle, and the up-wash near the obstacle is faster, indicating a stronger interaction between the rotor wake and the obstacle. Also, contrary to the case without the obstacle, the fluctuations of the rotor thrust, rolling and pitching moments are obviously strengthened. When the distance between the rotor and the obstacle is larger than 3R, the effect of the obstacle is small

Static Monopoles and Their Anti-Configurations

Recently, we have reported on the existence of some monopoles, multimonopole, and antimonopoles configurations. In this paper we would like to present more monopoles, multimonopole, and antimonopoles configurations of the magnetic ansatz of Ref.\cite{kn:9} when the parameters $p$ and $b$ of the solutions takes different serial values. These exact solutions are a different kind of BPS solution. They satisfy the first order Bogomol'nyi equation but possess infinite energy. They can have radial, axial, or rotational symmetry about the z-axis. We classified these serial solutions as (i) the multimonopole at the origin; (ii) the finitely separated 1-monopoles; (iii) the screening solutions of multimonopole and (iv) the axially symmetric monopole solutions. We also give a construction of their anti-configurations with all the magnetic charges of poles in the configurations reversed. Half-integer topological magnetic charge multimonopole also exist in some of these series of solutions.Comment: 20 pages with 4 figure

N(HI) and jet power/emission in AGNs

Neutral hydrogen (HI) 21 cm absorption has been detected against more and more powerful radio jets. In this work, based on the Guppta et al. 2006a sample, we present our preliminary study of the correlations between the HI column density N(HI) and the jet power, N(HI) versus the low frequency luminosity at 408MHz, and N(HI) versus the radio luminosity at 1400MHz.Comment: 3 pages, 1 figures, Multiwavelength Variability of Blazars Guangzhou, China, Sept. 22-24, 2010; will be published by JA

Transition Density and Pressure at the Inner Edge of Neutron Star Crusts

Using the nuclear symmetry energy that has been recently constrained by the isospin diffusion data in intermediate-energy heavy ion collisions, we have studied the transition density and pressure at the inner edge of neutron star crusts, and they are found to be 0.040 fm$^{-3}$ $\leq \rho_{t}\leq 0.065$ fm$^{-3}$ and 0.01 MeV/fm$^{3}$ $\leq P_{t}\leq 0.26$ MeV/fm$^{3}$, respectively, in both the dynamical and thermodynamical approaches. We have also found that the widely used parabolic approximation to the equation of state of asymmetric nuclear matter gives significantly higher values of core-crust transition density and pressure, especially for stiff symmetry energies. With these newly determined transition density and pressure, we have obtained an improved relation between the mass and radius of neutron stars.Comment: 7 pages, 3 figures, proceeding of "The International Workshop on Nuclear Dynamics in Heavy-Ion Reactions and the Symmetry Energy (IWND2009)

Pengaruh Variasi Jarak Tulangan Vertikal Terhadap Daktilitas Dan Kekakuan Dinding Geser Dengan Pembebanan Siklik (Quasi-statis)

Indonesia merupakan negara dengan intensitas gempa bumi vulkanik dan tektonik cukup aktif oleh karena itu diperlukan struktur-struktur yang mampu bertahan selama gempa yang terjadi. Dinding geser merupakan dinding struktur yang diaplikasikan untuk menahan gaya momen, geser dan aksial. Pembuatan dan uji pembebanan siklik terhadap tiga spesimen benda uji dengan menggunakan material utama yaitu semen, air, agregat kasar dan agregat halus untuk mutu desain 20 Mpa serta tulangan polos ᴓ8 untuk pondasi dan dinding geser dengan rasio tulangan dinding geser vertikal 2,44% serta rasio tulangan horizontal 5,54%. Dinding geser pertama yaitu dengan jarak antar tulangan vertikal 50 mm. Dinding geser kedua yaitu dengan jarak antar tulangan vertikal 40 mm. Dinding geser ketiga yaitu dengan jarak antar tulangan vertikal 30 mm. Untuk masing-masing spesimen memiliki jarak antar tulangan horizontal 150 mm dengan tingga benda uji 800 mm, lebar 400mm serta tebal 80 mm. Pembebanan aksial yang diberikan sebesar 5% dari kapasitas desain benda uji. Pembebanan lateral yang diberikan berupa pembebanan siklik. Pada penelitian dilapangan dikarenakan berbagai kondisi maka spesimen dengan jarak antar tulangan vertikal 50 mm (jarak tengah tulangan 65mm) memiliki beban lateral 6780 kg, µpeak load =1,645, µSimp max load = 2,742 dan Ktangential= 678,154 kg/mm juga Ksecant= 464,829 kg/mm. Spesimen dengan jarak antar tulangan vertikal 40 mm (jarak tengah tulangan 105mm) memiliki beban lateral 7650 kg, µpeak load =1,137, µSimp max load = 2,274 dan Ktangential= 583,658 kg/mm juga Ksecant= 434,98 kg/mm. Spesimen dengan jarak antar tulangan vertikal 30 mm (jarak tengah tulangan 165mm) memiliki beban lateral 6782 kg, µpeak load =1,959, µSimp max load = 3,919 dan Ktangential= 1090,178 kg/mm dan Ksecant= 553,678 kg/mm

Vortex fluctuations in underdoped Bi2Sr2CaCu2O8+d crystals

Vortex thermal fluctuations in heavily underdoped Bi2Sr2CaCu2O8+d (Tc=69.4 K) are studied using Josephson plasma resonance (JPR). From the data in zero magnetic field, we obtain the penetration depth along the c-axis, lambda_{L,c}(0) = 229 micrometers and the anisotropy ratio gamma(0) = 600. The low plasma frequency allows us to study phase correlations over the whole vortex solid (Bragg-glass) state. The JPR results yield a wandering length r_{w} of vortex pancakes. The temperature dependence of r_{w} as well as its increase with applied dc magnetic field can only be explained by the renormalization of the tilt modulus by thermal fluctuations, and suggest the latter is responsible for the dissociation of the vortices at the first order transition.Comment: 4 pages, 5 figures. Submitted to Phys. Rev. Let

Exact solution of mean geodesic distance for Vicsek fractals

The Vicsek fractals are one of the most interesting classes of fractals and the study of their structural properties is important. In this paper, the exact formula for the mean geodesic distance of Vicsek fractals is found. The quantity is computed precisely through the recurrence relations derived from the self-similar structure of the fractals considered. The obtained exact solution exhibits that the mean geodesic distance approximately increases as an exponential function of the number of nodes, with the exponent equal to the reciprocal of the fractal dimension. The closed-form solution is confirmed by extensive numerical calculations.Comment: 4 pages, 3 figure

Monotonicity results and bounds for the inverse hyperbolic sine

In this note, we present monotonicity results of a function involving to the inverse hyperbolic sine. From these, we derive some inequalities for bounding the inverse hyperbolic sine.Comment: 3 page

Oscillations of General Relativistic Multi-fluid/Multi-layer Compact Stars

We develop the formalism for determining the quasinormal modes of general relativistic multi-fluid compact stars in such a way that the impact of superfluid gap data can be assessed. Our results represent the first attempt to study true multi-layer dynamics, an important step towards considering realistic superfluid/superconducting compact stars. We combine a relativistic model for entrainment with model equations of state that explicity incorporate the symmetry energy. Our analysis emphasises the many different parameters that are required for this kind of modelling, and the fact that standard tabulated equations of state are grossly incomplete in this respect. To make progress, future equations of state need to provide the energy density as a function of the various nucleon number densities, the temperature (i.e. entropy), and the entrainment among the various components

Analisis Modul Produksi Saat Kondisi Transportasi Pada Floating Production System Di Perairan Lepas Pantai Indonesia

Melihat kondisi pada saat ini dimana konsumsi minyak bumi dunia yang cukup besar, maka penyediaan minyak bumi harus terus dioptimalkan, terutama dalam hal efisiensi operasional yang dapat mengurangi biaya maupun waktu produksi. Dalam hal proses produksi, banyak kegiatan produksi yang bisa diefisiensikan, beberapa hal yang bisa diupayakan yaitu membuat dimensi kapal yang lebih ringkas dan mengurangi waktu pengangkatan (lifting).Dalam hal ini konfigurasi modul harus direncanakan ulang sehingga dibutuhkan analisis kembali terhadap struktur baja elemen utama modul. Analisis yang dibahas merupakan analisis struktur modul saat kondisi transportasi untuk mengetahui kinerja struktur modul apabila struktur dikonfigurasi ulang akibat penyatuan beberapa struktur modul pada saat kondisi kapal berjalan. Dalam analisis digunakan software SAP2000 V.18 yang menghasilkan outputberupa momen, gaya geser, dan aksial yang terbesar dari 8 kondisi arah pembebanan yang selanjutnya data tersebut digunakan sebagai angka yang dianalisis dengan manual AISC. Hasil analisis menunjukkan bahwa struktur baja pada elemen utama modul kuat menahan beban-beban yang bekerja yaitu kombinasi beban berat sendiri struktur, beban benda produksi, beban angin, serta beban akibat pergerakan kapal