A boundary element method for the strongly nonlinear analysis of surface-piercing hydrofoils

A two-dimensional BEM based scheme is presented for the numerical modeling of the ventilated flow past a surfacepiercing hydrofoil. Fully nonlinear boundary conditions are applied on the free-surface allowing for the modeling of the jets generated as a result of the passage of the hydrofoil through the air-water interface. The scheme is validated through a comparison with self-similar solutions in the case of nonventilating entry and with experiments in the case of ventilating entry. Results are presented for fully wetted and ventilating cases with and without the effects of gravity. Preliminary results are presented for the case of a hydrofoil in rotational motion, simulating the ventilation characteristics of a typical surface-piercing propeller. The fully nonlinear scheme is a step towards quantifying the errors associated with some of the linearizing assumptions made in a 3-D boundary-element tool (PROPCAV) for the modeling of surface-piercing propellers..http://deepblue.lib.umich.edu/bitstream/2027.42/84281/1/CAV2009-final97.pd

Prediction of cavitating flow around 3-D straight/swept hydrofoils

A boundary element method (BEM) model is applied for prediction of cavitating flow around 3-D straight/swept hydrofoils between slip (zero shear) walls. The governing equation and boundary conditions are formulated and solved by assuming piecewise constant distribution of sources and dipoles on the hydrofoil and cavity surfaces, and piecewise constant distribution of dipoles on the trailing wake sheet. Cavity shape determination is initiated with a guessed cavity planform, and the cavity extent and thickness are determined iteratively until the dynamic and kinematic boundary conditions are satisfied on the cavity surface. To account for no-normal flow through the side walls, the method of images is used. For the fully-wetted case, the attached flow results obtained are compared with results from a full-fledged Reynolds-Averaged Navier-Stokes (RANS) solver. The cavitating results for a straight wing between slip walls are compared with results from an existing 2-D BEM solver for cavitating flow around hydrofoils. The RANS solver is also used to study separated flow characteristics around 2-D/3-D hydrofoils at high loading.http://deepblue.lib.umich.edu/bitstream/2027.42/84279/1/CAV2009-final94.pd

VISVE – A VIScous Vorticity Equation Model Applied to Cylinders, Hydrofoils, Propellers

A newly developed numerical tool for Computational Fluid Dynamics (CFD) computations is presented. This method is designed to be spatially compact and computationally efficient, and meanwhile capable of modeling the dynamics of vortices interacting with solid walls. The vorticity transport equation is solved in the Eulerian frame to model only the vortical regions, where the vorticity is concentrated, in the flow field. Therefore, the computational domain can be made rather small without a loss in accuracy. The small computational domain results in a significantly small number of elements in the grid and considerably less simulation time compared with the velocity based methods, such as the Navier-Stokes methods. The method has a wide range of applications, including the flow past a cylinder, sphere, hydrofoil, and propeller. In addition, both Open-MP and MPI are used to parallel the code to further facilitate its performance. Validations against the experimental results and numerical results from other methods have been conducted to verify the correctness, robustness, and computational efficiency of the current method.Texas Advanced Computing Center (TACC

Respon Empat Genotipe Kedelai (Glycine Max (L.) Merril.) terhadap Pemberian Zat Pengatur Tumbuh Ethepon dengan Konsentrasi Berbeda

Kedelai (Glycine max (L) Merril) merupakan komoditas pangan utama setelah padi dan jagung. Kedelai juga merupakan salah satu komoditas tanaman pangan yang penting di Indonesia karena memiliki nilai gizi tinggi selain itu juga dimanfaatkan sebagai campuran pakan ternak, maupun bahan baku industri, terutama minyak dan protein kedelai. Upaya peningkatan produksi kedelai yaitu dengan meningkatkan hasil, yaitu dapat dilakukan dengan pengaturan pertumbuhan mennggunakan zat pengatur tumbuh (ZPT) Ethepon atau ethrel. Ethepon merupakan salah satu zat pengatur tumbuh sintetik penghasil etilen. Etilen umumnya menghambat pemanjangan batang maupun akar, tetapi merangsang pertumbuhan radial terutama untuk tanaman dikotil seperti kedelai. Penelitian ini dilaksanakan selama 4 bulan terhitung mulai bulan Agustus 2020 sampai dengan bulan Desember 2020 di screen house, desa Surajaya, Kecamatan Pemalang. Penelitian ini menggunakan Rancangan Acak Kelompok Lengkap yang terdiri dari 2 faktor yaitu faktor (E) adalah Ethepon terdiri dari 4 taraf perlakuan dan faktor Genotipe (V). Penelitian ini bertujuan untuk mengetahui perbedaan respon dari masing-masing varietas kedelai terhadap penggunaan ethepon terhadap pertumbuhan dan produksi kedelai variabel pengamatan yang diamati adalah tinggi tanaman (cm), umur tanaman berbunga (hst), umur panen (hst), jumlah buku, jumlah cabang produktif, jumlah polong total, jumlah polong bernas, bobot biji pertanaman, bobot 100 biji, bobot segar tanaman, bobot kering tanaman, Panjang akar tanaman. Hasil penelitian ini menunjukan bahwa pemberian ethepon dengan konsentrasi semakin tinggi akan menekan tinggi tanaman, jumlah buku, jumlah polong total, jumlah polong bernas, jumlah biji pertanaman, bobot 100 biji, bobot segar tanaman, panjang akar tanaman dan bobot kering tanaman, namun meningkatkan umur tanaman berbunga, umur panen dan jumlah cabang produktif

A Wake Model for the Prediction of Propeller Performance at Low Advance Ratios

A low order panel method is used to predict the performance of propellers. A wake alignment model based on a pseudounsteady scheme is proposed and implemented. The results from this full wake alignment (FWA) model are correlated with available experimental data, and results from RANS for some propellers at design and low advance ratios. Significant improvements have been found in the predicted integrated forces and pressure distributions

Shape-optimization of 2D hydrofoils using an isogeometric BEM solver

In this paper, an optimization procedure, based on an Isogeometric BEM solver for the potential flow, is developed and used for the shape optimization of hydrofoils. The formulation of the exterior potential-flow problem reduces to a Boundary-Integral Equation (BIE) for the associated velocity potential exploiting the null-pressure jump Kutta condition at the trailing edge. The numerical solution of the BIE is performed by an Isogeometric Boundary-Element Method (BEM) combining a generic B-splines parametric modeler for generating hydrofoil shapes, using a set of eight parameters, the very same basis of the geometric representation for representing the velocity potential and collocation at the Greville abscissas of the knot vector of the hydrofoil's B-splines representation. Furthermore, the optimization environment is developed based on the geometric parametric modeler for the hydrofoil, the Isogeometric BEM solver and an optimizer employing a controlled elitist genetic algorithm. Multi-objective hydrofoil shape optimization examples are demonstrated with respect to the criteria (i) maximum lift coefficient and (ii) minimum deviation of the hydrofoil area from a reference area

Modeling of Unsteady Blade Sheet and Developed Tip Vortex Cavitation

A boundary element method is used for the numerical modeling of unsteady blade sheet and developed tip vortex cavitation on propellers. The objective of this work is to predict more accurately blade sheet and developed tip vortex cavity in the vicinity of the blade tip subject to a non-axisymmetric flow-field. The ultimate goal of this work is to predict more accurately the hull pressures induced by the unsteady cavities on the blade and tip. Initially, we assume that the section of the tip vortex cavity shape is circular and the wake a pure helical surface without contraction and roll-up. Once the fully wetted problem is solved by applying the potential based panel method on the assumed tip vortex cavity and wake geometry, the three-component velocities on the tip vortex cavity are calculated by numerically differentiating the velocity potential, and those on the wake surface are determined from the differentiated Green's formula. The new wake surface and the trajectory of the tip vortex cavity core are determined by aligning the wake surface with the flow velocity, in fully unsteady manner. Once the aligned wake surface is determined in an iterative way, the shape of the blade sheet and tip vortex cavity, having a constant pressure distribution, is determined by applying the dynamic and the kinematic boundary conditions on the cavity surface. The method is applied in the case of simplified 2-D vortex cavity, 3-D elliptic wing, and propeller blades subject to inclined and non-axisymmetric inflows. Comparisons with experiments in terms of unsteady cavity shapes, tip vortex cavity trajectories, and unsteady blade forces, are finally presented

Re-Entrant Jet Modelling for Partially Cavitating Two-Dimensional Hydrofoils

The computational analysis of partial sheet hydrofoil cavitation in two dimensions is performed. Particular attention is given to the method of simulating the flow at the end of the cavity. A fixed-length partially cavitating panel method is used to predict the height of the re-entrant jet, using the values of the cavitation number and the drag coefficient. The jet surface is subsequently constructed and included in an updated cavity shape. A source singularity is introduced in the fluid domain to account for the mass flux through the part of the domain boundary represented by the re-entrant jet surface. Further iterations are performed for fixed cavitation number on the cavity with a re-entrant jet cavity termination model. This model is seen to produce good results and displays quick convergence. A validation is accomplished by conducting a parametric analysis of the model and comparing the present calculations with other numerical schemes. The flow around the partially cavitating hydrofoil with a re-entrant jet has also been treated with a viscous/inviscid interactive method with favourable results

Numerical Modeling of Supercavitating and Surface-Piercing Propeller Flows

A 3-D panel method has been extended to model the flow around fully submerged supercavitating propellers and surface-piercing propellers. Overviews of the formulation and solution methodology is presented. Comparisons of the numerical predictions with measurements from experiments are given. Discussion of the numerical results, and initial work on modeling of impact flows are provided