141 research outputs found
Pemodelan Inundasi (Banjir Rob) Di Pesisir Kota Semarang Dengan Menggunakan Model Hidrodinamika
Fenomena banjir rob yang terjadi di Semarang sudah sangat memprihatinkan, karena banjir ini tidak hanya terjadi pada daerah pesisir pantai saja tetapi sudah menggenangi wilayah pariwisata, pemukiman, maupun industri. Tujuan penelitian ini adalah untuk menghitung jarak dan luas genangan rob di pesisir Kota Semarang akibat kondisi pasang surut pada saat purnama dan perbani.Metode yang digunakan dalam penelitian ini adalah metode kuantitatif. Penelitian dibagi menjadi tiga tahap, yaitu pengumpulan data sekunder, pengambilan data lapangan, dan pengolahan data. Pengambilan data lapangan dilakukan di perairan Kota Semarang yang dilaksanakan dari tanggal 5 - 20 Juli 2010 pada koordinat 6052'30â- 6057'30â LS dan 110019'45â-110027'30â BT. Pengolahan data serta proses pemodelan dilakukan di BPPT, Yogyakarta. Berdasarkan hasil penelitian diketahui bahwa arus di daerah penelitian didominasi oleh arus pasang surut sebesar 74,3%, dimana pergerakannya condong dari arah utara ke selatan dengan kecepatan rata-rata terhadap kedalaman mencapai 0,024 m/s. Sedangkan dari hasil analisis banjir rob (inundasi), jarak terjauh terjadi di kecamatan Genuk yang mencapai 4,295 km dari garis pantai pada saat pasang purnama dan jarak terdekat terjadi di kecamatan Semarang Barat yang mencapai 488,93 m dari garis pantai pada saat pasang perbani. Selain itu berdasarkan hasil penelitian didapat luas banjir maksimal terjadi di kecamatan Tugu dengan luas 3450,1 Ha pada saat pasang purnama. Sedangkan wilayah yang paling sedikit terendam terjadi di kecamatan Gayamsari dengan luas 71,228 Ha pada saat pasang perbani. Hasil verifikasi bathimetri mempunyai tingkat kebenaran sekitar 73,69%, pasut sekitar 84,87%, vektor u dan v arus lapangan sekitar 93,58% dan model sekitar 92%
Experimental study of Taylor's hypothesis in a turbulent soap film
An experimental study of Taylor's hypothesis in a quasi-two-dimensional
turbulent soap film is presented. A two probe laser Doppler velocimeter enables
a non-intrusive simultaneous measurement of the velocity at spatially separated
points. The breakdown of Taylor's hypothesis is quantified using the cross
correlation between two points displaced in both space and time; correlation is
better than 90% for scales less than the integral scale. A quantitative study
of the decorrelation beyond the integral scale is presented, including an
analysis of the failure of Taylor's hypothesis using techniques from
predictability studies of turbulent flows. Our results are compared with
similar studies of 3D turbulence.Comment: 27 pages, + 19 figure
Tropical polyhedra are equivalent to mean payoff games
We show that several decision problems originating from max-plus or tropical
convexity are equivalent to zero-sum two player game problems. In particular,
we set up an equivalence between the external representation of tropical convex
sets and zero-sum stochastic games, in which tropical polyhedra correspond to
deterministic games with finite action spaces. Then, we show that the winning
initial positions can be determined from the associated tropical polyhedron. We
obtain as a corollary a game theoretical proof of the fact that the tropical
rank of a matrix, defined as the maximal size of a submatrix for which the
optimal assignment problem has a unique solution, coincides with the maximal
number of rows (or columns) of the matrix which are linearly independent in the
tropical sense. Our proofs rely on techniques from non-linear Perron-Frobenius
theory.Comment: 28 pages, 5 figures; v2: updated references, added background
materials and illustrations; v3: minor improvements, references update
Scaling and universality in turbulent convection
Anomalous correlation functions of the temperature field in two-dimensional
turbulent convection are shown to be universal with respect to the choice of
external sources. Moreover, they are equal to the anomalous correlations of the
concentration field of a passive tracer advected by the convective flow itself.
The statistics of velocity differences is found to be universal, self-similar
and close to Gaussian. These results point to the conclusion that temperature
intermittency in two-dimensional turbulent convection may be traced back to the
existence of statistically preserved structures, as it is in passive scalar
turbulence.Comment: 4 pages, 6 figure
Statistical geometry in scalar turbulence
A general link between geometry and intermittency in passive scalar
turbulence is established. Intermittency is qualitatively traced back to events
where tracer particles stay for anomalousy long times in degenerate geometries
characterized by strong clustering. The quantitative counterpart is the
existence of special functions of particle configurations which are
statistically invariant under the flow. These are the statistical integrals of
motion controlling the scalar statistics at small scales and responsible for
the breaking of scale invariance associated to intermittency.Comment: 4 pages, 5 figure
Universality and saturation of intermittency in passive scalar turbulence
The statistical properties of a scalar field advected by the non-intermittent
Navier-Stokes flow arising from a two-dimensional inverse energy cascade are
investigated. The universality properties of the scalar field are directly
probed by comparing the results obtained with two different types of injection
mechanisms. Scaling properties are shown to be universal, even though
anisotropies injected at large scales persist down to the smallest scales and
local isotropy is not fully restored. Scalar statistics is strongly
intermittent and scaling exponents saturate to a constant for sufficiently high
orders. This is observed also for the advection by a velocity field rapidly
changing in time, pointing to the genericity of the phenomenon. The persistence
of anisotropies and the saturation are both statistical signatures of the
ramp-and-cliff structures observed in the scalar field.Comment: 4 pages, 8 figure
Universal decay of scalar turbulence
The asymptotic decay of passive scalar fields is solved analytically for the
Kraichnan model, where the velocity has a short correlation time. At long
times, two universality classes are found, both characterized by a distribution
of the scalar -- generally non-Gaussian -- with global self-similar evolution
in time. Analogous behavior is found numerically with a more realistic flow
resulting from an inverse energy cascade.Comment: 4 pages, 3 Postscript figures, submitted to PR
Dynamical equations for high-order structure functions, and a comparison of a mean field theory with experiments in three-dimensional turbulence
Two recent publications [V. Yakhot, Phys. Rev. E {\bf 63}, 026307, (2001) and
R.J. Hill, J. Fluid Mech. {\bf 434}, 379, (2001)] derive, through two different
approaches that have the Navier-Stokes equations as the common starting point,
a set of steady-state dynamic equations for structure functions of arbitrary
order in hydrodynamic turbulence. These equations are not closed. Yakhot
proposed a "mean field theory" to close the equations for locally isotropic
turbulence, and obtained scaling exponents of structure functions and an
expression for the tails of the probability density function of transverse
velocity increments. At high Reynolds numbers, we present some relevant
experimental data on pressure and dissipation terms that are needed to provide
closure, as well as on aspects predicted by the theory. Comparison between the
theory and the data shows varying levels of agreement, and reveals gaps
inherent to the implementation of the theory.Comment: 16 pages, 23 figure
Intermittency in Dynamics of Two-Dimensional Vortex-like Defects
We examine high-order dynamical correlations of defects (vortices,
disclinations etc) in thin films starting from the Langevin equation for the
defect motion. We demonstrate that dynamical correlation functions of
vorticity and disclinicity behave as where is the
characteristic scale and is the fugacity. As a consequence, below the
Berezinskii-Kosterlitz-Thouless transition temperature are
characterized by anomalous scaling exponents. The behavior strongly differs
from the normal law occurring for simultaneous correlation
functions, the non-simultaneous correlation functions appear to be much larger.
The phenomenon resembles intermittency in turbulence.Comment: 30 pages, 11 figure
- âŠ