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This study focuses on the development of time-marching procedures for efficient and accurate fluid-thermal-structural analysis with time-accurate computational fluid dynamics. The developed procedu...

In the community of computational fluid dynamics, pressure Poisson equation with Neumann boundary condition is usually encountered when solving the incompressible Navier–Stokes equations in a segre...

A time-marching aeroelastic method developed for the study of propeller flutter is presented\ud and validated. Propeller flutter can take many forms with stall, whirl and classical flutter\ud being the primary responses. These types of flutter require accurate capture of the non-linear\ud aerodynamics associated with propeller blades. Stall flutter in particular, due to the highly\ud detached nature of the flow, needs detailed unsteady flow modelling. With the development of modern propeller designs potentially adjusting the flutter boundary and the development of faster computing power, CFD is required to ensure accurate capture of aerodynamics. This\ud paper focuses on the validation of the aeroelastic method using the Commander propeller\ud blade.

In this work, an unconditionally stable family of time marching procedures is proposed, in which the time integration parameters of the method are locally computed, considering the properties of the model. Thus, the technique adapts to the characteristics of the problem, enabling enhanced analyses. Here, adaptive dissipation control is explored, allowing spurious modes to be more effectively dissipated. The proposed technique is second-order accurate, L -stable, truly self-starting and very easy to implement. Numerical results are presented along the paper, illustrating the good performance of the novel single-step technique.

Finding efficient and accurate solution methods for nonlinear equilibrium equations is a challenging task. This is the case of systems with friction-induced nonlinearities, e.g., friction-damped turbomachinery assemblies and automotive applications such as brakes. In order to tackle this strategic task, several methods have been developed, both in the time and in the frequency domains. Time marching methods are regarded as the most accurate option, but their computational cost becomes prohibitive when friction nonlinearities are present. This poses a problem in all those cases where alternative frequency domain methods cannot be applied effectively, e.g., if transients, non-periodic excitation/solution, or highly nonlinear systems are of interest. The purpose of this paper is to propose three independent methods to make time-marching more competitive. Two of these methods can be applied to any existing direct integration scheme with minimal adjustments, but the computational time cut they introduce is significant. The last method is instead tailored for systems where the inertia force contribution is negligible. All methods are thoroughly validated numerically using a standard Newmark- β integration scheme as a reference.

A stable method for the analysis of lossy transmission lines with nonlinear loads is presented. The simulation employs the time marching (TM) method for solving the convolution equations in the time domain. To cope with the late-time instability of the TM method, a novel approach based on the application of Z-transform analysis and cepstrum is presented. The efficiency of the proposed method is demonstrated by comparing its results with simulations obtained using (i) a full-wave FDTD approach, and (ii) CST Cable Studio.

The present research introduces a technique to determine the location of pollution sources in urban areas through the use of inverse CFD modeling. The technique depends primarily on the solution of...

The unsteady panel and time-marching free wake are applied to the rotor aerodynamics and wake behaviour. Numerical results of panel and free wake are compared and validated with experimental data. Using these methods, unsteady rotor aerodynamics in BVI condition is analyzed and discussed in detail.

A nonlinear mathematical model capable of prediction load and motions of high speed planing craft in the longitudinal plane has been developed. The development of the model is based on the mathematical model presented by Zarnick (1978). Following the principle of 2D strip theory and wedge water entry problem, a high speed planing hull is divided into a number of transverse sections. Sectional forces are evaluated, and then, integrating along the ship length, total force and moment are obtained which leads to corresponding instantaneous acceleration. By integration using a time marching scheme, velocity and displacement are obtained. Solution of the motions of a planing craft based upon strip theory and wedge water impact is well known and offers fast computational times useful for simulation and design. However it is necessary to understand the balance between rapid computation and accuracy of this approach. Thus, The influence of the controlling parameters, such as number of sections and time step, in the accuracy, stability and computational times of the simulation in calm water and regular waves is investigated. The optimum model is finally validated against the original model of Zarnick (1978) and the experiments of Fridsma (1969)

5Huang, X. Z., and Zan, S., “Wing and Fin Buffet on the Standard Dynamic Model,” RTO, RTO-TR-26 AC/323(AVT)TP/19, Neuilly-sur-Seine, France, Oct. 2000. 6Goura, G. S. L., “Time Marching Analysis of Flutter Using Computational Fluid Dynamics,” Ph.D. Dissertation, Dept. of Aerospace Engineering, Univ. of Glasgow, Glasgow, Scotland, U.K., Sept. 2001. 7Goura, G. S. L., Badcock, K. J., Woodgate, M. A., and Richards, B. E., “A Data Exchange Method for Fluid-Stucture Interaction Problems,” Aeronautical Journal, Vol. 105, No. 1046, 2001, pp. 215–221. 8Goura, G. S. L., Badcock, K. J., Woodgate, M. A., and Richards, B. E., “Implicit Method for the Time Marching Analysis of Flutter,” Aeronautical Journal, Vol. 105, No. 1046, 2001, pp. 199–214. 9Melville, R., “Nonlinear Simulation of Aeroelastic Instability,” AIAA Paper 2001-0570, Jan. 2001. E. Livne Associate Editor

This paper presents the modelling and simulation of a solar water heating system using a time marching model. The results of simulations performed on an annual basis for a solar system, constructed and operated in Yugoslavia, which provides domestic hot water for a four-person family are presented. The solar water heater consists of a flat-plate solar collector, a water-storage tank, an electric heater, and a water-mixing device. The mathematical model is used to evaluate the annual variation of the solar fraction with respect to the volume of the storage tank, demand hot water temperature required, difference of this temperature and preset storage tank water temperature, and consumption profile of the domestic hot water demand. The results of this investigation may be used to design a solar collector system, and to operate already designed systems, effectively. The results for a number of designs with different storage tank volumes indicate that the systems with greater volume yield higher solar fraction values. The results additionally indicate that the solar fraction of the system increases with lower hot water demand temperature and higher differences between the mean storage water and the demand temperatures. However, when a larger storage tank volume is used, the solar fraction is less sensitive to a variation of these operation parameters.

Use of solar energy through passive heating is numerically evaluated for different passive designs of weekend houses with one wall made completely of masonry and with other walls made of two layers: a masonry layer and a thermal-insulation layer. To access this problem, the heating and cooling load is determined by using a dynamic, thermal, building model newly constructed on the basis of finite volumes and time marching. The investigation is performed for two days: one winter day for the weekend house with the masonry wall facing south, and for one summer day for the weekend house with the masonry wall facing north. The heating and cooling loads are evaluated for different thicknesses of masonry by using two investigation procedures where in the first procedure the insulation thickness is kept constant, and in the second procedure the U value of the two-layer walls of the house is kept constant. When the thermal-insulation layer faces the outside of the house, this investigation reveals that the use of the passive house instead of the non-passive house for the winter day gives an energy saving of around 1.5%, and for the summer day gives the maximum energy saving of around 4% for a masonry thickness of 30 cm. When the thermal-insulation layer faces the inside of the house, the investigation reveals that passive heating is not possible at all.

In this paper, analysis of an aircraft crash upon an outer containment of a nuclear power plant is presented. The effect of target yielding is considered simultaneously by calculating the reaction time in a time marching scheme. The concrete model employed is capable of predicting the cracking and yielding. The response for different cracking strains and different locations of aircraft strike for different aircraft has been studied. Critical location of aircraft strike for the containment has been investigated. The analytical procedure and the material model used are found to be capable of representing the aircraft impact response of the containment structure.

Severe rubs between gas turbine blades and engine casings can in extreme cases result in damaging blade vibration levels and rapid loss of casing lining material. Even for more minor rubs, the wear in the lining material will result in increase tip gaps and a consequent loss in efficiency. Major rub events are extremely rare in practice, and there is seldom any useful diagnostic evidence of the root cause of the behaviour. Moreover, traditional analysis methods are not suitable for exploring the wide range of potential conditions under which an unstable vibration response might be initiated. A new modelling technique has been developed for modelling blade casing rubs which includes a detailed model of the interaction with liner wear. The method is time based, but is very efficient, enabling a wide range of initiating conditions to be explored. A series of examples have been developed to firstly: demonstrate the method is robust and reliable, and secondly: to investigate potential interaction phenomena under representative simulated conditions. The method has been applied to a real blade example, for which severe wear is known to have occurred. The method predicts that instability may occur above a threshold level of tip rub severity, and also demonstrates the improvement in an alternative blade design for which rub tolerance is known to be superior.

An approach is formulated to treat the behavior of composites subjected to impact as the sequential effect of a number of events. The sequence for the analysis of im pact presented here is as follows. First, a global analysis of impact of the structure is con ducted. In this study, a plate is analyzed in a time marching scheme to properly account for nonlinearities during the impact event. This provides loads introduced into the struc ture during impact. These loads are then introduced into a local deformation and strain re sponse model just below the impactor to refine the analysis in the local region where damage occurs. Damage is predicted in the laminate on a ply-by-ply basis. Excellent agreement between the models and test data taken during the impact event is found. This is denoted as the Damage Resistance portion of the problem. Given the pre-existing damage, an analysis of the damaged structure is conducted. This entails using an average strain criterion for fiber-dominated fracture around the damage and a sublaminate buck ling analysis for compression loading. Good agreement is found between the analysis and experimental data. This is denoted as the Damage Tolerance portion of the problem. Finally, all of the models are combined to provide combined Damage Resistance/Damage Tolerance curves for useful design data.

Subgrid and subcell FDTD (S-FDTD) methods are described. They can be used for the fast and accurate simulation of mask electromagnetic effects in sub-45nm lithography. The accuracies of the S-FDTD methods are verified by comparison with FDTD and with a very accurate pseudospectral reference solution. The S-FDTD methods are an order of magnitude or more faster than FDTD. Furthermore, the S-FDTD methods require much less memory than FDTD for time marching. Hence, much larger mask areas can be simulated with S-FDTD than with FDTD.

Before using a high-accuracy Computational Aeroacoustics (CAA) code, it is desirable to verify that the code is actually solving the governing equations to the design order of accuracy. In this work, the External Verification Analysis (EVA) method is presented, which allows the Verification of unsteady time-accurate CFD or CAA codes without requiring modifications to the source code of the CAA code. Currently, the EVA tool Verifies only the interior equation solver and does not test boundary conditions. The EVA tool can determine the computed order of accuracy of the CAA code in time and space. Verification results are presented for the Air Force Research Laboratory FDL3DI code.

This paper focuses on the time integration of the nonlinear EOM associated with a very ∞exible aircraft in ∞ight. Various integration methods exist for linear structural dynamics problems. However, a review of the literature indicates little material associated with the integration of nonlinear structural EOM of relatively large order. Moreover, for the problem of simulation of very ∞exible aircraft, a combination of ∞ight dynamics and aeroelastic degrees of freedom must be solved. A modifled flrst and second order Generalizedfi Method along with an implicit sub-iteration scheme were developed. It has shown good agreement with predictor/corrector integration schemes for a reduced set of linear EOM. The method is also seen to be numerically stable when compared to non-dissipative time marching integration schemes and requires less computational time compared to predictor/corrector methods for the full set of nonlinear EOM.

Validation of CRUNCH CFD ® for problems of relevance to modeling coupled VSTOL-Ship Airwake flow fields is presented. The basic numerical framework consists of an edge based multi-element unstructured Navier-Stokes solver. The governing equations are solved using an upwind biased MUSCL scheme and an implicit scheme is used for time marching. Validation of the spatial and temporal aspects of the numerical framework are presented here, with a special emphasis on bluff body shedding problems as these are of particular relevance to the VSTOL-Ship airwake problem. Results from simulations of several unit problems are presented along with preliminary results from airwake flow field modeling.

Validation of CRUNCH CFD® for problems of relevance to modeling coupled VSTOL-Ship Airwake flow fields is presented. The basic numerical framework consists of an edge based multi-element unstructured Navier-Stokes solver. The governing equations are solved using an upwind biased MUSCL scheme and an implicit scheme is used for time marching. Validation of the spatial and temporal aspects of the numerical framework are presented here, with a special emphasis on bluff body shedding problems as these are of particular relevance to the VSTOL-Ship airwake problem. Results from simulations of several unit problems are presented.Copyright © 2004 by ASME

Complex constitutive equations including non‐linear kinematic as well as isotropic hardening rules are introduced in the framework of the finite element method to analyse the behaviour of structures in quasi‐static elasto‐viscoplasticity under cyclic loadings. An implicit time marching process is developed together with a substructuring technique and the corresponding numerical details are underlined. Practical examples are treated to demonstrate the capabilities of the proposed finite element code.

A numerical method using the method of characteristics for a one-dimensional flow model is used for predicting the flow through a convergent-divergent nozzle operating at any pressure ratio. The numerical solutions are compared with the analytical solution and with the results of Marsh and Merryweather; good agreement is found.

Time marching solutions of transonic flow are widely used for the analysis of turbomachinery cascades. Attempts to increase efficiency, accuracy and computational speed are, at present, the main goal of research in the field of two dimensional flow. The aim of the paper is the presentation of a new pseudo-time dependent method to try to achieve these goals. The method, basic idea and procedure used to develop the new formulation are described and discussed in brief. Some applications of the method to transonic turbine cascades are presented against experimental results. The accuracy and speed of the method is discussed and possibilities for further developments are shown.Copyright © 1985 by ASME

In order to clarify the transonic flow characteristics of a turbine cascade with high stagger, low solidity and small deflections, experimental studies were carried out by shortening the chord length of a “Laval-nozzle shaped” blade with thick trailing edge. The behavior of the shock system depends on the amount of overlap between the blades. The relations between the behavior and the performances were discussed in detail. The results may be applied to more standard sections. Lastly, validity of an appropriate time marching analysis for the highly staggered cascade was investigated by comparing with the experiment.Copyright © 1979 by ASME

A time marching method is described which generates the blade profiles in a cascade corresponding to a prescribed pressure distribution (with or without shock waves) around the blade surfaces. The method can be used either to generate entire blade shapes or to modify regions of suction and pressure surfaces. The method enables a reduction in overall aerodynamic design time.Copyright © 1986 by ASME