This paper presents a numerical study of a low Reynolds number flow around a thick airfoil (Eppler's E863 airfoil) with and without an upper-surface vortex-trapping cavity. The numerical model of flow is constructed using an O-grid computational domain around the airfoil and analyzed using four different turbulence models: namely standard k-epsilon, RNG k-epsilon, SST k-omega and the one-equation Spallart-Almaras (SA). Enhance wall treatment is employed for the two-equation turbulence models with the non-dimensional first cell height y(+) at the wall region kept close to 1. The Reynolds number is kept constant at 354000. Results of lift & drag coefficient as well as velocity profiles are presented for four different angles of attack from 0 to 15 deg. The RNG k-epsilon model is found to better predict the flow field and airfoil lift and drag characteristics as compared to the other turbulence models taken into consideration in this paper.. The presence of the vortex-trapping cavity midway on the upper-surface of the airfoil is found to yield higher lift coefficients as well as prevent flow separation but at the cost of increase the drag coefficient.

Linear constitutive equations of a thermopiezomagnetic medium involving mechanical, electrical, magnetic, and thermal fields are presented with the aid of a thermodynamic potential. A thermopiezomagnetic medium can be formed by bonding together a piezoelectric and magnetostrictive composite. Two energy functionals are defined. It is shown via Hamilton's principle that these functionals yield the equations of motion for the mechanical field, Maxwell's equilibrium equations for the electrical and magnetic fields, and the generalized heat equation for the thermal field. Finite element equations for the thermopiezomagnetic media are obtained by using the linear constitutive equations in Hamilton's principle together with the finite element approximations. The finite element equations are utilized on an example two-layer smart structure, which consists of a piezoceramic (barium titanate) layer at the bottom and a magnetoceramic (cobalt ferrite) layer at the top. An electrostatic field applied to the piezoceramic layer causes strain in the structure. This strain then produces magnetic field in the magnetoceramic layer.

For a multiple carbon-carbon composite aircraft disk brake system, a transient heat transfer analysis is numerically carried out using temperature-dependent thermophysical properties. Operations of the antiskid control brake system are simulated by considering variations of pressure and angular speed during the braking action. The heat developed during that process is assumed to be convectively released. Maximum temperatures are found to occur around the middle disk and on the disk mid-radii. Maximum and minimum temperature differences amounting to 350 degrees C are found to occur inside the brake assembly.

In this work, the weather conditions and wind power in the eastern part of Saudi Arabia over a period of 36 years (1961-1996) are studied and modelled. The study involves temperature, relative humidity, fog, wind speed, wind power and dust storms. A regression analysis is carried out by using the linear regression technique to model the weather parameters. The models developed can be used in any study related to weather and its effect on the environment and energy. Copyright (C) 1999 John Wiley & Sons, Ltd.

An artificial neural network (ANN) model for predicting the failure rate of Fokker F-27 airplane tires utilizing the backpropagation algorithm as a learning rule is presented. A comparison of the neural model with the Weibull model is made for validation purposes. The results show that the failure rate predicted by the ANN is closer in agreement with the real data than the failure rate predicted by the Weibull model.

Electrical energy consumption in the eastern province of Saudi Arabia is modeled as a function of weather data, global solar radiation, population, and gross domestic product per capita. Five years of data have been used to develop the energy consumption model. Variation selection in the regression model is carried out by using the general stepping-regression technique. Model adequacy is determined from a residual analysis technique. Model validation aims to determine if the model will function successfully in its intended operating field. In this regard, new energy consumption data for a sixth year are collected, and the results predicted by the regression model are compared with the new data set. Finally, the sensitivity of the model is examined. It is found that the model is strongly influenced by the ambient temperature.

Univariate Box-Jenkins time-series analysis has been used for modeling and forecasting monthly domestic electric energy consumption in the Eastern Province of Saudi Arabia. Autoregressive integrated moving average (ARIMA) models were developed using data for 5 yr and evaluated on forecasting new data for the sixth year. The optimum model derived is a multiplicative combination of seasonal and nonseasonal autoregressive parts, each being of the first order, following first differencing at both the seasonal and nonseasonal levels. Compared to regression and abductive network machine-learning models previously developed on the same data, ARIMA models require less data, have fewer coefficients, and are more accurate. The optimum ARIMA model forecasts monthly data for the evaluation year with an average percentage error of 3.8% compared to 8.1% and 5.6% for the best multiple-series regression and abductory induction mechanism (AIM) models, respectively; the mean-square forecasting error is reduced with the ARIMA model by factors of 3.2 and 1.6, respectively.

The wear/failure data of brake assemblies of a commercial type airplane (Fokker F-27) is statistically analyzed, and interpreted in a reliability framework. A three parameter Weibull model is used for reliability characterization of the brake assemblies. A spreadsheet format of analysis is proposed to analyze the data. This reliability model can be effectively integrated into an aviation facility computerized material requirement planning system to forecast the number of brake assemblies needed for a given planning horizon.

Abductive network machine learning is proposed as an alternative to the conventional multiple regression analysis method for modelling and forecasting monthly electric energy consumption. The AIM (abductory induction mechanism) is used to model the domestic consumption in the eastern province of Saudi Arabia in terms of key weather parameters and demographic and economy indicators. Models are synthesized by training on data for 5 years and forecasting new data for the sixth year. Compared to regression models previously developed for the same data, AIM models require fewer input parameters, are more accurate and are easier and faster to develop. An AIM model that uses only the mean relative humidity and air temperature gives an average forecasting error of about 5.6% over the year. Our study demonstrates the advantage of using actual values for monthly average weather data rather than means of such averages over a few years.

The optimal dimensions of circular fins with variable profile, and temperature-dependent thermal conductivity are obtained. A profile of the form y = (w2)[1 + (r0r)n] is studied, while the thermal conductivity considered is of the form k = k0[1 + ε (T−T∞)/T0. The results have been expressed in terms of suitable dimensionless parameters. A correlation for the optimal dimensions of a constant and variable profile fins is presented in terms of reduced heat-transfer rate. It is found that a parabolic circular fin with n = 2 gives an optimum performance. For example, an increase in heat-transfer rate (as compared to constant thickness fin) by about 20% for the optimal fin profile is observed. The effect of thermal conductivity on the optimal dimensions is negligible for the variable profile fin. It is also observed that in general, the optimal fin length is greater for the optimal fin profile.

This article presents a comparative study for cooling aerospace planes, using liquid H-2, CH4, He, Ne, N-2, and Ar. The ascending optimized trajectory to minimize the heat load in the hypersonic part is used to perform the study. The study includes the cooling for the stagnation point, the leading edges for wings and engine, and other parts of the aerospace plane that are close to the leading edges. The laminar case for the stagnation point and both laminar and turbulent cases for the leading-edge heating have been considered. The amount of heat rate (total, radiative, and convective) and the mass of liquid coolant needed for cooling are calculated. A design of minimum inlet-outlet areas for the amount of liquid needed for cooling is made with the consideration of the coolant's physical constraints in liquids and gaseous states. The comparison shows that the hydrogen is a clear winner as a candidate for coolant and it saves mass as compared to all other five coolants. The study shows that there are no fundamental barriers for the cooling system of the vehicle in terms of its coolant mass and area size for coolant passage, especially if H-2 is used.

This is a study of performance and control for transatmospheric (TAV) aerospace planes, that use air-breathing propulsion. The study is structured in two parts and considers the heat load near the stagnation point. The first part is analytical and consists of two cases, it seeks closed form solutions for the non-linear feedback controls (aerodynamic and thrust), which are necessary to transfer the (TAV) from one specified state to another specified state, while satisfying pairs of equality constraints (that is, Case I: constant acceleration with constant dynamic pressure and Case II: constant rate of climb with constant dynamic pressure). This leads to closed form solutions for the controls in feedback form and also for the heat rate and load. The analytical approach gives a reasonable approximation of the general ascent trajectory to orbit, where the two cases can be used in combination with different constant values of the constraints in different levels of the hypersonic trajectory. The analytical results were a useful guide in the numerical studies. The second part describes numerical simulation and optimization. The control laws, which minimize the heat load, are found in feedback form. A numerical example is worked out for illustration. The trajectory corridor and, in general, all the constraints are satisfied for heat load ≤ 350 kJ/cm2 using feasible controls.

The present study was conducted to investigate the tribological and mechanical properties of plasma-nitrided Ti6Al4V alloy. Specimens were nitrided in an H2N2 (1:8 ratio) plasma. The nitrogen concentration along the nitrided zone was obtained using the nuclear reaction analysis technique. The workpiece temperature was varied from 450 to 520 °C during the nitriding process. Pin-on-disc wear tests were carried out to evaluate the wear properties of the resultant samples and a ball-on-disc experiment was conducted to measure the friction coefficient. Microhardness tests, Scanning electron microscopy and X-ray diffraction were carried out to investigate the phases developed in the nitrided zone. It was found that the wear resistance improved considerably after the nitriding process. Three distinct layers were identified: (i) an inner layer where δ-TiN + ε-Ti2N phases formed, (ii) an intermediate layer where α-(TiN) with or without ε phase developed and (iii) an outer layer where precipitations were dominant.

A comparative study was conducted to measure turbulence parameters and to evaluate some of the velocity-bias correction techniques in the near field of a turbulent freejet, The overall objective of this investigation was to develop a reliable technique for obtaining nonintrusive measurements of the mean now velocity components and turbulence and to construct a complete set of data in the developing region of a turbulent freejet.

This paper studies active cooling of an aerospace plane using liquid hydrogen, liquid methane, liquid oxygen and liquid fluorine. An ascending optimized trajectory to minimize the heat load in the hypersonic part is used to perform the study, which includes cooling of the stagnation point, the leading edges of wings and engine and other parts of the aerospace plane that are close to the leading edges. The laminar case of the stagnation point and both laminar and turbulent cases for the leading edge heating have been considered. The amount of liquid coolant mass needed for cooling is calculated. A design of minimum inlet–outlet areas for the amount of liquid needed for cooling is made with consideration of the coolant's physical constraints in the liquid and gaseous states. The study shows that the ratio of masses of coolant to the initial total mass (initial total mass of the vehicle including fuel and coolant masses) is in the limit of the reachable range. The comparison shows that the hydrogen is a clear winner as a candidate for coolant and saves mass as compared to the other three coolants. The study shows that there are no fundamental barriers for the cooling system of the vehicle in terms of its coolant mass and area size for coolant passage.

The present study deals with an analytical model for any vehicle (e.g., aircraft, rocket and aerospace plane). This study produces dosed-form solutions of two (aerodynamic and thrust) nonlinear feedback controls, heat rate, heat load, and integrates most of the state variables for flight vehicles. The analytical solutions require pairs of equality, constant constraints. These include seven pairs of equality, constant constraints (i.e., constant rate of climb with constant dynamic pressure, constant flight path angle with constant dynamic pressure, constant speed with constant dynamic pressure, constant speed with constant rate of climb, constant acceleration with constant dynamic pressure, constant acceleration with constant rate of climb and constant acceleration with constant flight path angle). This analytical study can be helpful in the general numerical solution of the system, where the numerical study has its classical errors and gives a less general picture than this analytical study does.

Friction welding of Al-Al, Al-steel, and steel-steel studs is compared. Transient heat generation and temperature rise during the welding process were modeled. Tensile tests and microhardness measurements across the weld zone were carried out. The metallurgical changes in the heat-affected zone were examined by SEM. Temperature rise at the interface plane was computed and related to weld properties. The affecting parameters on weld quality were identified by statistical analysis. Results show that interaction of weld parameters significantly affect yield, tensile, and breaking strength, and the heat-affected zone on the Al side is wider for Al-steel welds.

A heal pump of domestic capacity and applicable for a water-powered system is studied. A design of the necessary parts is carried out, and realization of the heat pump system is achieved. In realization of the system, output power of a small-scale water turbine is considered, and an electrical motor requiring similar power is employed. The estimation of capital cost and payback period is not included in the study.

This paper studies the cooling of an aerospace plane using liquid hydrogen, liquid methane, and liquid water. An ascending optimized trajectory to minimize the heat load in the hypersonic part of the flight is used to perform the study. The study includes cooling for the stagnation point, the leading edges of the wings, the engine and other parts of the aerospace plane that are close to the leading edges. The laminar case for the stagnation point and both laminar and turbulent cases for the leading edge heating have been considered. The heat rate (total, radiative and convective) and the mass of liquid coolant needed for cooling are calculated. A design for minimum inlet-outlet areas for the amount of liquid needed for cooling, is made with consideration of the coolant's physical constraints in the liquid and gaseous states. The comparison shows that liquid hydrogen is the clear winner over liquid methane or liquid water as a candidate for the coolant.

Laser induced heating processes are important when a laser is used as a machine tool in industry, since the quality of the machining process strongly depends on the heating mechanism. The present study examines a heat transfer model that provides useful information on the laser induced interaction mechanism. Steady state and time dependent heating models are introduced and temperature profiles inside the materials are predicted. Using appropriate assumptions, the time for the surface temperature to reach 90% of its steady state value is estimated. To validate the theoretical predictions, experiments are performed to measure the surface temperature of the irradiated spot during the laser heating pulse. It is found that, during the use of a pulsed laser in the drilling process, as the heating progresses the drilling velocities rise while the liquid depth and time to reach steady state fall, in this case, the energy consumed for evaporation is higher than losses through conduction.