A new synthetic metamodel methodology for liquid‐propellant engine's cooling system optimization

The present paper strives for optimization of the cooling system of a liquid‐propellant engine (LPE). To this end, the new synthetic metamodel methodology utilizing the design of experiment method and the response surface method was developed and implemented as two effective means of designing, analyzing, and optimizing. The input variables, constraints, objective functions, and their surfaces were identified. Hence, the design and development strategy of combustion chamber and nozzle was clarified, and 64 different experiments were carried out on the RD‐161 propulsion system, of which 47 experiments were approved and compatible with the problem constraints. This engine used all three modes of cooling: the radiation cooling, the regenerative cooling, and the film cooling. The response surface curves were drawn and the related objective function equations were obtained. The analysis of variance results indicate that the developed synthetic model is capable to predict the responses adequately within the limits of input parameters. The three‐dimensional response surface curves and contour plots have been developed to find out the combined effects of input parameters on responses. In addition, the precision of the models was assessed and the output was interpreted and analyzed, which showed high accuracy. Therefore, the desirability function analysis has been applied to LPE's cooling system for multiobjective optimization to maximize the total heat transfer and minimize the cooling system pressure loss simultaneously. Finally, confirmatory tests have been conducted with the optimum parametric conditions to validate the optimization techniques. In conclusion, this methodology optimizes the LPE's cooling system, a 2% increase in the total heat transfer, and a 38% decrease in the pressure loss of the cooling system. These values are considerably large for the LPE design.     

Numerical and experimental investigation of vortex breaker effectiveness on the improvement in launch vehicle ballistic parameters

The focus of the present study is to investigate the effectiveness of installing vortex breakers at the outlet of launch vehicle tanks on postponing vortex formation and decreasing the critical height of propellants while discharging. Analytical results in the absence of a vortex breaker show that the effects of the Weber and Reynolds numbers in the flow field can be ignored for values greater than 720 and 1.1 × 10⁵, respectively; and critical height can be considered as a function of Froude number under aforementioned conditions. The analytical criteria are verified by two-dimensional, axis symmetrical, transient and two-phase numerical model. Eventually, some experiments are conducted to examine the effectiveness of the applied vortex breakers in reduction of the critical height of propellant. Experimental results show that a 30% decrease can be achieved in critical height by using a particular type of vortex breaker. Additionally, the carried out simulations for an existing two-stage launch vehicle indicate a 13% increase in orbital altitude, which in turn proves the considerable improvement in launch vehicle mass/energetic capabilities.     

Power management and nonlinear control of a fuel cell–supercapacitor hybrid automotive vehicle with working condition algorithm

This paper deals with the problem of controlling a multi-source system applied in hybrid electrical vehicles. The system consists of a proton exchange membrane fuel cell (PEMFC) and a super capacitor (SC). Fuel cell (FC) provides energy for load as a main power source, and SC helps the system in a load peak or in fast transients. The system is modeled as Port controlled Hamiltonian (PCH), and interconnection and damping assignment passivity based controller (IDA-PBC) is used for a typical hybrid vehicle. The aim is first to support the load power in all circumstances without interruption by combination of FC and SC production, and second to control the DC bus voltage. The purposed system analyzed under standard driving cycle consists of off-load, over-load, and charging conditions of SC. Simulations are accomplished in MATLAB/Simulink software for validation of control strategy and new represented algorithm. The results illustrate that both control method and algorithm can manage power among PEMFC, SC, and the load whereas the DC bus voltage remains near its reference.     

Effects of hot-carrier stress on the performance of the LC-tank CMOS oscillators

The effects of hot carrier stress on a fully integrated negative resistance LC-tank CMOS oscillator are investigated. The major effect is the decrease of the amplitude of the oscillation due to degradation in the I-V characteristics of the MOSFETs. The oscillator phase noise increases with stress duration since the amplitude of the oscillation decreases. A change in the biasing of the circuit due to the stress affects the parasitic capacitances in the circuit which in turn cause a slight change in the oscillation frequency.     

A 6-GHz capacitively-coupled Colpitts CMOS quadrature voltage controlled oscillator

In this work a new low-noise low-power Colpitts quadrature voltage controlled oscillator (QVCO) made by coupling two identical current-switching differential Colpitts voltage controlled oscillators (VCO) is proposed; coupling of the VCOs is done using some capacitors in an “in-phase anti-phase” scheme. In this coupling configuration first harmonics (as well as higher harmonics) from each VCO are injected to the other VCO, as opposed to coupling schemes in which only even harmonics are injected. An analysis of the linearized circuit which confirms 90° phase difference between output signals of the proposed circuit is presented. Since no extra noise sources or power consumption are introduced to the core VCOs, the proposed QVCO achieves low phase noise performance and low power consumption. The proposed circuit is designed and simulated in a commercial 0.18 μm CMOS technology. The simulated phase noise of the proposed QVCO at 3 MHz offset frequency is ?138.3 dBc/Hz, at 6 GHz. The circuit dissipates 8.16 mW from a 1.8 V supply and its frequency can be tuned from 5.6 to 6.3 GHz.     

On hillocks generated during anisotropic etching of Si in TMAH

Hillocks on etched Si{100} surfaces produced by anisotropic etching are a common irritant in the creation of micromachined devices. Close inspection of typical pyramidal hillock shapes reveals that they are usually bounded by convex 〈101〉-directed edges and {111} or near-{111} planes. Underetch experiments at varying TMAH etchant composition confirm that the etch rates of {101} planes and {100} planes vary with etchant conditions. Hillocks are suppressed when {101} etches faster than {100}, which occurs when the TMAH concentration is low. A simple model involving kinks and ledges is proposed and allows direct relation of hillock features to etch anisotropy. Hillocks are hypothesized to be stable due to a lower etch rate for 〈101〉 ledges adjacent to the etched surface. The apex of the pyramids may be protected by impurities or defects. Re-etch experiments indicate that hillock-producing conditions are quite sensitive to etchant conditions     

A new 1.4-GHz soil moisture sensor

Moisture content determination in agriculture and civil engineering is a common process which needs special sensors with high accuracy, durability and compatibility with the measurement environment. A new 1.4-GHz soil moisture sensor using microstrip transmission line is presented. The proposed sensor consists of two separate parts: (1) A sensor head, which is a microstrip transmission line to be placed in the soil, and (2) an electronic transceiver which sends a sinusoidal wave into the sensor head at one end of the transmission line, and receives the traveled wave from the other end. Transmitter is basically a Colpitts oscillator, and the receiver is a phase detector that measures the phase shift due to velocity variation caused by the moisture content of soil. At a certain frequency, the velocity of a microwave traveling through a media depends on the permittivity of that media. The proposed sensor is implemented and tested on one sample of typical soil. The main advantages of the proposed sensor are its high accuracy, quickness of measurement, its low cost and ease of implementation. Since the sensor has low power consumption, it can be recommended for low-power applications such as wireless sensor network.     

A second-harmonic LC-quadrature voltage controlled oscillator with direct connection of MOSFETs’ substrate

This work introduces a new low noise second-harmonic quadrature voltage controlled oscillator (QVCO) made by coupling two identical cross-connected LC voltage controlled oscillators. In each of the core oscillators the substrate nodes of the MOS varactors, and also the substrate nodes of the cross-connected MOSFETs are configured in such a way that they act as common mode nodes. Then the core oscillators are coupled together via direct connection of the substrates of the MOS varactors in one of the core oscillators to the substrates of the cross-connected MOSFETs in the other core oscillator, and vice versa. No extra elements are used for coupling of the two core oscillators and therefore no extra noise sources are imposed on the circuit. Operation of the proposed QVCO was investigated with simulation using a commercial 0.18 μm RF CMOS technology: it shows a power dissipation of 9.7 mW from a 1.8 V supply voltage and a simulated phase noise of −125.5 dBc/Hz at 1 MHz offset from center oscillation frequency of 5 GHz. Since the tail transistor can be eliminated, the proposed QVCO can operate with supply voltages as low as 0.5 V, as confirmed with simulation.     

Effects of different silicon-based surface active additives on degradability of clearcoats exposed to bird droppings

A series of clearcoats separately loaded with different concentrations of functional silicon–polyacrylate and polydimethyl siloxane additives were prepared. Optical performances of the cured films were studied by gonio-spectrophotometry. Dynamic mechanical thermal analysis was used in order to investigate viscoelastic properties of the additive-containing films. Contact angle measurements, (FTIR) spectroscopy, scanning electron microscopy equipped with energy-dispersive analysis of X-ray, and atomic force microscopy techniques were utilized to evaluate surface properties of the clearcoats. It was shown that clearcoat surface free energy decreased and its crosslinking density increased in the presence of the additives. Results revealed that addition of both additives to the clearcoat enhanced its resistance against pancreatin (simulated bird droppings). A decrease in surface degradation was observed in the presence of the additives. Results also showed that functional polydimethyl siloxane influenced coating viscoelastic, surface chemistry, and biological resistance more effectively compared to that of the functional silicon–polyacrylate one.