Minimum Total Resistance Research Articles

Designing a system of liquid cooling for industrial microwave installations

The paper considers the issue on ensuring a thermal regime of the magnetron's anode unit by replacing an air-cooling system with the system of liquid cooling. It has been argued that a liquid cooling system is most suitable for magnetrons, for which currently an air-cooling system is implied, although they are not designed for a continuous operation in the structure of industrial microwave installations. Arranging the system of liquid cooling would makes it possible for a magnetron to work over long time without overheating and under favorable conditions, which rule out a possibility to clog the heat exchange surface with particles and dust, as well as the occurrence of overheating of the anode unit's surface. The basic element of the proposed system for liquid cooling is a cooling jacket, which represents an annular channel made from a heat-conducting material. Cooling jacket is mounted directly on the anode unit; in this case, a compression ratio of surfaces and the thickness of an air gap must ensure a minimum total thermal resistance. In order to determine heat transfer coefficients, an empirical dependence was established, which reflects the fact that when cooling the anode units the rational regimes are the viscous and transitional motion modes. The basic thermal characteristics of the cooling process have been defined, which include a coefficient of heat transfer, change in a heat-carrier temperature, the maximally permissible temperature at inlet. Calculations were carried out for two types of heat-carriers: water and a 54 % aqueous solution of ethylene glycol. A circuit for the system of liquid cooling has been proposed, which implies cooling from 1 to 6 magnetrons. Applying a given circuitry and choosing the rational estimated modes make it possible to solve the task on improving production efficiency, as well as reliability of microwave equipment.

Optimization of a separator assisted two-phase thermosyphon loop by using entropy generation analysis

In this paper, an optimization model is developed for a separator assisted two-phase thermosyphon loop and basic two-phase thermosyphon loop based on the entropy generation minimization method. The total entropy generation rate of the system is proposed as an optimization objective function and the total heat transfer area of evaporator and condenser is considered as a constraint. The model takes into account the irreversibility due to both irreversible heat transfer and pressure drop. The results show that there always exists minimum total entropy generation rate of the two systems when the heat transfer area ratio varies. The optimal heat transfer area ratios corresponding to the minimum total entropy generation rate also lead to the minimum total thermal resistance of the system and achieve the lowest temperature of the cooled object. Besides, the separator assisted two-phase thermosyphon loop can gain lower total entropy generation rate than the basic two-phase thermosyphon loop. Furthermore, the effects of the heat load, the total heat transfer area, the working fluid charge, the inner diameter of the separator and the height of two-phase tube on the minimum total entropy generation rate and the corresponding area ratio are also evaluated.

Optimization Design of Minimum Total Resistance Hull Form Based on CFD Method

In order to reduce the resistance and improve the hydrodynamic performance of a ship, two hull form design methods are proposed based on the potential flow theory and viscous flow theory. The flow fields are meshed using body-fitted mesh and structured grids. The parameters of the hull modification function are the design variables. A three-dimensional modeling method is used to alter the geometry. The Non-Linear Programming (NLP) method is utilized to optimize a David Taylor Model Basin (DTMB) model 5415 ship under the constraints, including the displacement constraint. The optimization results show an effective reduction of the resistance. The two hull form design methods developed in this study can provide technical support and theoretical basis for designing green ships.

Hull form optimisation in waves based on CFD technique

ABSTRACTThe seakeeping behavior of a ship in waves is different from its behavior in calm water. The resistance and seakeeping performance of a ship must be considered in the early-stage design. Therefore, this paper proposes a hull form optimization framework aiming to achieve the minimum total resistance in waves using a computational fluid dynamics (CFD) technique. A sinusoidal wave is adopted to establish the numerical wave tank and the overset mesh technique is used to facilitate the motions of the ships in question. The total resistance of the hull in waves is regarded as the objective function which is calculated using the Reynolds averaged Navier–Stokes (RANS) method. The arbitrary shape deformation (ASD) technique is used to change the geometry. Under displacement and design variables, a hybrid algorithm is developed to evaluate the objective function combining the optimal Latin hypercube design (Opt LHD) and the non-linear programming by quadratic Lagrangian (NLPQL) algorithm. Finally, two examples of hull form optimization are presented and discussed for David Taylor Model Basin (DTMB) model 5512 and WIGLEY III cases. The results show the effectiveness of the optimization framework developed in the present study, which can lay the foundation for further optimization of full-scale ships.

Integrated flat heat pipe with a porous network wick for high-heat-flux electronic devices

A novel integrated flat heat pipe (IFHP) was constructed, which consists of an evaporator and a condenser with multiple channels fabricated in the fin heat sink. A layer of compressed copper foam was sintered on the inner surface of the evaporator bottom plate, and many copper foam bars were inserted into the channels, both of which formed a porous network wick. Experiments were performed under three inclination angles (θ=0°, 90°, and 180°), using acetone as the working fluid. Air and water cooling methods were used to cool the fin heat sink. Compared with the conventional flat heat pipe (CFHP), the IFHP presents good fin temperature uniformity and heat performance; it eliminates the contact thermal resistance between the heat pipe and the heat sink, expands the condensation area of the heat pipe, and reduces the temperature difference between the fin base and the fin end. When the heat flux reached 161.1W/cm2, the fin efficiency increased to 93% and the temperature at the center of the evaporator bottom surface was merely 68.7°C. For the IFHP, the optimal filling ratio and inclination angle are 30% and θ=0°, respectively, for which the best heat performance was achieved, and the minimum total thermal resistance was 0.33K/W. In the case of water cooling, the heat flux could reach up to 350W/cm2. The results indicate that the IFHP with copper foam as a porous network wick presents excellent heat performance, and is thus suitable for heat dissipation in high-heat-flux electronic devices.

Numerical investigation on the hydrodynamic performance of fast SWATHs with optimum canted struts arrangements

Small Waterplane Area Twin Hulls (SWATHs) are known to have superior seakeeping performance but higher resistance compared to equivalent catamarans or mono-hulls. A way to improve their resistance characteristics is to use unconventional hull forms parametrically defined and optimized by CFD methods. This study builds on previous SWATH optimization studies proposing a comprehensive, systematic investigation on the effect of different shapes and canting angles of the struts. For the first time we demonstrate the importance of considering the shape of the strut that is fully parametrized in our study. The effect of the design speed on the best shape is addressed through a multi-objective optimization targeting the minimum total resistance at two very different speeds, namely the cruise and slow transfer speeds. Optimum hull shapes are discussed in terms of maximum resistance reduction, together with the predicted free waves patterns.

Experimental investigation on a novel multi-branch heat pipe for multi-heat source electronics

This paper proposes a novel multi-branch heat pipe (MBHP) that can be utilized for heat dissipation in multi-heat source electronics. The proposed heat pipe consists of three branches—two with an evaporator and one with a condenser—connected by vapor lines and liquid lines. A test system was implemented to study the filling ratio, the start-up characteristics, the power distribution characteristics, the dynamic characteristics and the thermal resistance of the heat pipe. The experimental results obtained indicate the following: 1) the optimal working fluid filling ratio of MBHP is between 75% and 100%; 2) the MBHP can start up steadily under tested heating load; 3) the ideal heat load of the MBHP (filling ratio 75%) was within a range of 30–160W, in which the minimum total thermal resistance was 0.04°C/W and the maximum temperatures of both evaporators were less than 110°C under the limiting heating load of 160W.

The Design of a Hull form with the Minimum Total Resistance

In order to obtain a hull form which exhibits low resistance and highly-efficient energy-saving performance, the overall resistance should be calculated as the sum of wave-making and viscous resistance, in which the total resistance corresponds to the objective function whereas the hull geometry parameters correspond to design variables. Apart from considering the limited conditions due to appropriate displacement, we further ponder over the boundary-layer viscous separation caused by additional constraints. We then proceed to apply the Nonlinear Programming Method (NLP) to determine the hull form with the minimum total resistance. This paper aims to optimize the streamlined design of the S60 so as to get an improved hull form in which lower resistance and smoother hull lines are evident. This suggests that there is no significant increase in viscous resistance during the process of hull form optimization with the wave-making resistance as the objective function. Therefore, this confirms the feasibility of optimizing the hull form by the NLP method.

Research on theoretical optimization and experimental verification of minimum resistance hull form based on Rankine source method

To obtain low resistance and high efficiency energy-saving ship, minimum total resistance hull form design method is studied based on potential flow theory of wave-making resistance and considering the effects of tail viscous separation. With the sum of wave resistance and viscous resistance as objective functions and the parameters of B-Spline function as design variables, mathematical models are built using Nonlinear Programming Method (NLP) ensuring the basic limit of displacement and considering rear viscous separation. We develop ship lines optimization procedures with intellectual property rights. Series60 is used as parent ship in optimization design to obtain improved ship (Series60-1) theoretically. Then drag tests for the improved ship (Series60-1) is made to get the actual minimum total resistance hull form.

On The Macro Hydrodynamic Design Of Highly Efficient Medium-speed Catamarans With Minimum Resistance

A new class of fuel-efficient and environmentally friendly twin-hull vessels is currently under development. Compared to high-speed catamarans, a significant reduction in speed combined with an increase in deadweight tonnes will lead to a highly efficient medium-speed catamaran design. Recently-built conventional and high-speed ferries are compared to each other in terms of length, speed, deadweight and transport efficiency to classify the new design. The goal of this study is to find a preliminary macro design point for minimum total resistance by considering the main particulars of the catamaran vessel: block coefficient, prismatic coefficient and slenderness and separation ratios of the demihulls. Publications containing recommendations towards the optimum hull form parameters for moderate Froude numbers are reviewed and existing experimental data analysed to identify parameters for this new class of vessel. Designs with varied L/BOA-ratios and constant deck area are compared to find configurations of low total resistance for carrying a nominated deadweight at a particular speed, the associated change of the light ship weight has been taken into account. Two different model test series of catamaran models have been considered and their resistance curves agreed to each other. Recommendations are made; with the most important being the vessel should not exceed a speed of Fr = 0.35, with optimal prismatic coefficients around CP ≈ 0.5 and low transom immersion. This study presents the preliminary design of medium-speed single and twin-hull vessels for operations close to hump speed.

Multiobjective Shape Optimization of the Rigid Shell Moving into a Condensed Media

The problem of optimization of rigid bodies moving in the deformable media is considered. The shape of the axisymmetric impactors has been taken as an unknown design variable. The total resistance force, the mass of material, and the volume are taken as components of the minimized vector functional. The formulated multiobjective minimization problem for the vector functional is investigated analytically. As an example, the Pareto-optimal set of optimal shape and the Pareto front are found for the rigid thin-walled axisymmetric shells having the minimum total resistance force and the mass of the shell material.

종모양 분포 변환함수를 이용한 선형최적화 기법에 관한 연구

A design procedure for a ship with minimum total resistance was developed using a numerical optimization method called SQP(Sequential Quadratic Programming) and a CFD technique based on the Rankine source panel method with the nonlinear free surface boundary conditions. During the whole optimization process the geometry of the hull shape was represented based on the NURBS(Non-uniform rational B-spline) technique and the modification of the hull shape was controlled using the Bell-shaped distribution function to keep the fairness of the hull shape before and after the hull modification. The numerical analysis was carried out using 4000TEU container ship in the towing tank facility installed in the Pusan national university to know the validity of the developed algorithm for this study. As the results of the numerical analysis it proved that the resistance of the optimized hull is conspicuously reduced in comparison with the original hull in a wave-making resistance point of view.

A bulk-micromachined bistable relay with U-shaped thermal actuators

This paper reports a deep-reactive ion etching (DRIE)-through-etched laterally bistable MEMS relay for power applications, with a primary emphasis on the design and modeling of its U-shaped transient thermal actuators, and a secondary emphasis on the design and fabrication of its contact element. In this relay, a contact crossbar is carried by a curved-beam bistable mechanism , which is toggled by transient U-shaped thermal actuators with their hot beam adiabaticly heated by electrical pulses. Each U-shaped thermal actuator comprises uniform-thickness hot and cold beams with a gap between them so they bend differently. This paper develops both a basic model and a complete model for the actuator that are verified by Finite Element Analysis and serve as effective design tools. The DRIE process creates nonideal etched surfaces, which pose challenges for good relay contacts. Both contact design and process development are discussed to help alleviate this problem. The fabricated relay exhibits a minimum total on-state resistance of 60 m/spl Omega/, and a maximum current carrying capacity of 3 A. It switches with a 1 ms actuation pulse, and a maximum 5 Hz repetition rate.

An Optimization Study for the Bow Form of High-Speed Displacement Catamarans

ABSTRACT Interest in high-speed marine transportation has acquired a wide variety of hydrodynamic research activities on catamarans, including shape optimization for minimum total resistance. This study attempts to utilize the mathematical programming in optimizing the bow form of twin hulls for minimum total resistance as well as in analyzing the optimization by physical model tests. The total resistance is assumed to be composed of wave-making and frictional components, which are formulated using Michell's thin-ship theory and ITTC-1957 friction line, respectively. The optimized hull form is analyzed by means of a computational flow solver before going through the experimental analysis. The study demonstrates the capabilities of the optimization procedure, presented for catamarans, in reducing the total resistance, as well as its limitations to be used as a design tool in a relatively high-speed zone.

Abundance of ladder digital-to-analog converters

A general digital-to-analog converter (DAC), which encompasses popularly known weighted-resistor and R-2R ladder DACs as the special cases, is introduced. The weighted-resistor subfamily has been studied in the recent past. This paper presents a detailed study of the sub-family of ladder DACs. Some DACs have very interesting features. It is found that the R-2R ladder DAC not only has the least possible spread but also has the minimum total resistance. Also, there is another DAC which has the same spread of 2 as the R-2R ladder DAC but requires the minimum number of resistors.

Correlations to predict heat transfer characteristics of an inclined closed two-phase thermosyphon at normal operating conditions

This paper describes the effect of dimensionless parameters on heat transfer characteristics of an inclined thermosyphon. The parameters studied in this paper are: Bond numbers, Froude numbers, Weber numbers and Kutateladze numbers, and experiments are conducted to find out their effects on the heat transfer rate and on the total thermal resistance. Copper thermosyphons with an ID of 7.5, 11.1 and 25.4 mm are employed with R22, R123, R134a, ethanol, and water as the working fluids. The selected filling ratios are 50, 80, and 100% and the selected aspect ratios are 5, 10, 20, 30 and 40 respectively. Experiments are conducted by varying the inclination angle from the horizontal axis by 5, 10, 20, 30, 40, 50, 60, 70, 80 and 90°, and the controlled vapor temperature ranged from 0 to 30°C. It is found from the experiments that, the filling ratio has no effect on the ratio of heat transfer characteristics at any angle to that of the vertical position ( Q/ Q 90), but the properties of the working fluid affected Q/ Q 90. Results show that the lower the latent heat of vaporization, the higher the Q/ Q 90. It is also shown that the modified Kutateladze number can be employed to predict the maximum Q/ Q 90, or Q m/ Q 90. Another modified Kutateladze number can also be used to predict the ratio of minimum total thermal resistance to that at vertical position, or R m/ R 90.

Optimised weighted-resistor digital to analogue converter

From the classical weighted-resistor (WR) digital to analogue converter (DAC), two-stage DACs are derived. Conditions for minimum spread and the minimum total resistance for the two-stage DACs are derived. The theory is extended to multistage WR DACs. Thus, an optimised WR DAC is obtained that has minimum spread and the minimum total resistance and is therefore, suitable for economic fabrication in integrated circuit form.

Early adaptations in collateral and microvascular resistances after ligation of the rat femoral artery.

Collateral and microvascular (including feed artery) resistances in the rat hindlimb were determined immediately or 1 wk after ligation of the femoral artery. Collateral-to-microvascular resistance ratios were determined from in vivo pressure measurements proximal and distal to the ligation. Microvascular resistance was 32 +/- 2.5 and 41 +/- 1.5% of the total collateral-dependent vasculature in acutely and chronically ligated limbs, respectively, and decreased 20% in both groups during reactive hyperemia. Minimum resistances of collateral vessels and the microcirculation arising from arterial branches proximal and distal to the ligation were determined by using a modification of the standard hindquarter perfusion technique for determining maximum vascular conductance. One week postligation, minimum total hindquarter resistance was decreased by a reduction in the resistance of the collaterals (approximately 50%) and microcirculation (approximately 33%) proximal to the ligation. The results suggest that the microvasculature distal to the occlusion is able to increase flow by dilation both initially and at 1 wk postligation but that collateral adaptations are primarily responsible for decreases in the minimum total resistance of the collateral-dependent region.

Optimal Ship Forms for Minimum Total Resistance

A numerical scheme is developed by using the "tent" function to compute the hull surface area and then the ship frictional resistance in a quadratic form in terms of ship offsets. Combining with the wave resistance, a total ship resistance formula is derived in a standard quadratic form. With a set of linear-inequality constraints, the optimal solution of ship offsets for minimum total resistance can be obtained by applying a quadratic programming method to the problem. Computations have been carried out for three conditions which have exactly the same constraints as those required to obtain the optimal forms for minimum wave resistance shown in an earlier work [1].3 The optimal forms found for minimum total resistance also have either bow or midship bulbs. The new optimal bulbs have a relatively small size, higher vertical slope to the baseline, and less curvature at the tip of the bulb.

Minimization of Total Resistance of a Surface-Piercing Vertical Strut

An attempt was made to obtain a surface-piercing vertical strut with minimum total resistance by means of nonlinear programming under the constraints that the beam and water plane area of the strut were kept constant. The objective function in the nonlinear programming is the sum of wave-making resistance calculated by Michell's integral and viscous resistance calculated by a higher order boundary layer theory taking the longitudinal curvature effect into consideration.In the minimization process, the strut form with minimum wave-making resistance was used as an initial form. It is a characteristic that the strut form of minimum total resistance has a fine shape near the trailing edge and the fore body has a similar shape as that of the body of minimum wave-making resistance. In the minimization process, it is shown that the viscous pressure resistance is reduced largely whereas the wave-making resistance is increased a little and frictional resistance is kept almost unchanged.