Proceedings of the Institution of Mechanical Engineers,Part C: Journal of Mechanical Engineering Science

In this article, the achievement of a uniform elastic contact pressure in a frictionless, keyless, shaft–hub interference fit obtained by properly shaping the mating profiles is examined. The peculiarity of the hub mechanical response according to which, under the effect of a uniform pressure applied to the hub bore, the bore axial profile moves radially without any distortion, is exploited to simplify the determination of the mating profiles that return a uniform pressure. In particular, the hub radial deflection may be computed with a simple plane model, whereas only the shaft radial deflection requires a more complex analysis in cylindrical coordinates. Explicit approximate expressions are reported for the shapes to be conferred to the mating profiles to achieve a uniform pressure. Selected examples are presented to clarify the proposed design procedure and to preliminarily explore the effect on the pressure profile of simple shape errors.

Recently, the demands for eco-friendly and effective energy systems have rapidly increased due to global environment problems. A heat exchanger is a well-known mechanical rig that has been used for a long time in many energy systems to reduce heat energy loss and to increase energy efficiency. However, till now, there have been few attempts to install a heat exchanger inside of an airliner engine. In such a case, the heat exchanger should be designed to be compact, lightweight, and highly reliable; therefore, the issue of the mechanical integrity of the heat exchanger becomes very important. In this study, we suggest a method by which it is possible to evaluate the mechanical integrity of a tube-type heat exchanger using global and local analysis. In the global analysis, fluid–structure interaction was introduced to get global behavior of a tube, which was used as boundary conditions in the local analysis. Also, local material properties near a brazing joint were measured using a nano-indentation test, and then they were utilized in the local analysis to evaluate clearly stress distribution around the joint. Through this study, a U-shaped single tube brazed on a manifold, which is a segment of a tube-type heat exchanger, was used as an example; its fatigue limit and stress concentration on the joint depending on the change of fillet radius were estimated by the proposed approach.

Many elements of machines, like shafts, blades, connecting rods, etc., are often modeled using the so-called beam theory and, when these elements rotate with respect to an inertial reference frame, this rotation can deeply affect their dynamic behavior. The position of the beam with respect to the rotation axis and the possibility that the rotation is more complicated than a simple constant-rate rotation about a fixed axis influence this effect, and different models are usually employed. As a result, different phenomena, like gyroscopic effect, centrifugal stiffening or softening, and instability due to rotation are often mentioned in reference to the different cases. The aim of this article is that of building a much simplified beam model, and to subject it to a compound, nonconstant rate rotation. Since the model can be solved in closed form, at least in several cases, a general discussion of the revant phenomena can be done to shed some light on some aspects, like the instability ranges due to rotation and to the damping of the system.

Active power control in wind farm, implemented with hierarchical structure (including the central wind farm active power control system and the control system of variable speed wind generation system), has significantly improved the wind-farm-generated power. However, the interaction between the control system of variable speed wind generation system and the central wind farm active power control system has not been considered in the control system design of both sides. The wind generation system with active power control in wind farm, as a high-order nonlinear large-scale system, will not only autonomous operating with maximum power capture, but also being demanded to regulate power output according to the power set points ordered by the central wind farm active power control system. Therefore, robust active power control of wind farm is clearly necessary. In this article, sliding mode is used to design the active power control system for wind farm, which makes the output power of wind farm track the active power order from the power grid operator asymptotically. Particularly, the control system of the variable speed wind generation system is designed with cascaded structure: the input of the internal rotational speed control loop of the wind generation system is controlled by the external power loop which tracks the specified power set point. Then, based on the dynamic model of wind farm, the central wind farm active power control system is designed to control the total output power of wind farm by using the sliding mode control method. Furthermore, in order to ensure the given power set point is within the regulation capability of the wind generation system, the proportional distribution strategy is utilized to specify the power set point according to the available output power of each wind generation system, which is quantified by ultra-short term power prediction model. The proposed approach is illustrated by implementing it to the active power control of a wind-farm model in simulation. The simulation results demonstrate that the proposed method outperforms the method based on proportional-integral control.

Noise reduction in axial piston pumps has been attempted by many researchers with different design approaches and techniques. However, most traditional structures on valve plate for noise reduction are at the cost of efficiency to different extent. In this article, a new distribution method with pressure equalization mechanism composed of check valve and pressure recuperation chamber is discussed. A simulation model for the analysis of noise excitation sources is developed, and is verified by comparison of flow ripple between simulation and experiment. The working principle of pressure equalization mechanism is analyzed in detail. Compared with reference commercial axial piston pump, the simulation results indicate that the flow ripple and the torque pulsation are sharply reduced with the pressure equalization mechanism. Moreover, the volumetric efficiency of axial piston pump is also improved. The power of variable-displacement control mechanism will be reduced and the control accuracy can be improved easily due to the swash-plate torque reduction. The analysis shows that the check-valve frequency and the pressure recuperation chamber volume are vital for the pressure equalization mechanism. The optimal pressure recuperation chamber volume is about three times the size of the minimum piston chamber dead volume. The optimal maximum displacement of check valve is about 1 mm. The pressure equalization mechanism is promising in the design of high-performance axial piston pump with low noise emission.

This article describes a series of development tests of a turbopump, which can be applied to a gas generator cycle rocket engine with liquid oxygen and kerosene propellants. A turbine drives both an oxidizer pump and a fuel pump in the turbopump assembly. In the tests, liquid oxygen and kerosene are supplied to the oxidizer pump and the fuel pump, respectively, while either cold hydrogen gas or hot gas from the gas generator is supplied to the turbine. The turbopump is operated reliably at both on-design and off-design conditions, meeting all the performance requirements. The test results are compared with those of the turbopump component tests, where model fluids are used, that is, water for the oxidizer pump and the fuel pump, and cold air for the turbine. The turbopump tests results agree well with the turbopump component test results. The speed buildup of the turbopump at start period is calculated when pressurized gas is used to initially spin the turbine. A differential equation which represents the torque balance between the turbine and the pumps is solved. The calculation shows a good agreement with the test result. When the mechanical loss of the turbopump is considered, a better estimation is obtained.

The flow and heat transfer characteristics of flat and blocked surfaces were experimentally examined under the influence of the free stream velocity of 3, 5, 10 and 15 m/s encompassing laminar, transitional and turbulent flows. A constant-temperature hot wire anemometer was used for the velocity and turbulent intensity measurements, and copper-constant thermocouples and a micro-manometer for temperature and static pressures measurements, respectively. The flow over blocked surface separated in front of the first block and attached on it, then circulated between blocks, and then reattached behind the last block. The results showed that the flow separation before the first block occurred earlier in laminar–laminar separated–reattached flow than the transitional and turbulent flows and turbulent–turbulent separated–reattached flow leading to a shorter reattachment region with high free-stream turbulence. The presence of the separation and reattachment caused the heat transfer enhancement, which was more pronounced in the laminar flow and new empirical equations were developed for the local Stanton numbers.

A new algorithm is proposed based on semi-analytical methods to solve the conjugate heat transfer problems. In this respect, a problem of conjugate forced-convective flow over a heat-conducting plate is modeled and the integro-differential equation occurring in the problem is solved by two lately-proposed approaches, Adomian decomposition method and differential transform method. The solution of the governing integro-differential equation for temperature distribution of the plate is handled more easily and accurately by implementing Adomian decomposition method/differential transform method rather than other traditional methods such as perturbation method. A numerical approach is also performed via finite volume method to examine the validity of the results for temperature distribution of the plate obtained by Adomian decomposition method/differential transform method. It is shown that the expressions for the temperature distribution in the plate obtained from the two methods, Adomian decomposition method and differential transform method, are the same and show closer agreement to the results calculated from numerical work in comparison with the expression obtained by perturbation method existed in the literature.

The paper addresses experiments and modeling studies on the use of producer gas, a bio-derived low energy content fuel in a spark-ignited engine. Producer gas, generated in situ, has thermo-physical properties different from those of fossil fuel(s). Experiments on naturally aspirated and turbo-charged engine operation and subsequent analysis of the cylinder pressure traces reveal significant differences in the heat release pattern within the cylinder compared with a typical fossil fuel. The heat release patterns for gasoline and producer gas compare well in the initial 50% but beyond this, producer gas combustion tends to be sluggish leading to an overall increase in the combustion duration. This is rather unexpected considering that producer gas with nearly 20% hydrogen has higher flame speeds than gasoline. The influence of hydrogen on the initial flame kernel development period and the combustion duration and hence on the overall heat release pattern is addressed. The significant deviations in the heat release profiles between conventional fuels and producer gas necessitates the estimation of producer gas-specific Wiebe coefficients. The experimental heat release profiles are used for estimating the Wiebe coefficients. Experimental evidence of lower fuel conversion efficiency based on the chemical and thermal analysis of the engine exhaust gas is used to arrive at the Wiebe coefficients. The efficiency factor a is found to be 2.4 while the shape factor m is estimated at 0.7 for 2% to 90% burn duration. The standard Wiebe coefficients for conventional fuels and fuel-specific coefficients for producer gas are used in a zero D model to predict the performance of a 6-cylinder gas engine under naturally aspirated and turbo-charged conditions. While simulation results with standard Wiebe coefficients result in excessive deviations from the experimental results, excellent match is observed when producer gas-specific coefficients are used. Predictions using the same coefficients on a 3-cylinder gas engine having different geometry and compression ratio(s) indicate close match with the experimental traces highlighting the versatility of the coefficients.

In this study, the influence of tool rotation speed and feed rate on the forming limit of friction stir welded Al 6061-T651 sheets has been investigated. The forming limit curve was evaluated by limit dome height test performed on all the friction stir welded sheets. The welding trials were conducted at a tool rotation speed of 1300 and 1400 r/min and feed rate of 90 and 100 mm/min. A third trial of welding was performed at a rotational speed of 1500 r/min and feed rate 120 mm/min. It is found that with increase in the tool rotation speed, from 1300 to 1400 r/min, for a constant feed rate, the forming limit of friction stir welded blank has improved and with increase in feed rate, from 90 to 100 mm/min, for a constant tool rotation speed, it has decreased. The forming limit of friction stir welded sheets is better than unwelded sheets. The thickness gradient after forming is severe in the cases of friction stir welded blanks made at higher feed rate and lower rotation speed. The strain hardening exponent of weld (n) increases with increase in tool rotation speed and it decreases with increase in feed rate. It has been demonstrated that the change in the forming limit of friction stir welded sheets with respect to welding parameters is due to the thickness distribution severity and strain hardening exponent of the weld region during forming. There is not much variation in the dome height among the friction stir welded sheets tested. When compared with unwelded sheets, dome height of friction stir welded sheets is higher in near-plane-strain condition, but it is lesser in stretching strain paths.

Noncircular bevel gear can achieve variable transmission between intersecting axes. This article proposes the design method of high-order noncircular bevel gear with concave pitch curve. The parametric equations for driving and driven gear, addendum and dedendum surface under given transmission ratio and axis angle are established in a spherical polar coordinate system. The tooth profile equation of noncircular bevel gear is derived according to the generation method by using bevel gear cutter. The three-dimensional model for noncircular bevel gear is developed to verify the correctness of the design method.

Dental implants have been extensively utilized on edentulous patients for many years. The fatigue life of dental implants is critical for them being approved to use in human body because they are within the area of biomedicine. To perform a preliminary investigation of fatigue life of dental implants, this article reports a method of fatigue life estimation based on the combination of computer simulation and limited test data. The method is developed based on a probabilistic form of fatigue life given according to the properties of material fatigue strength. The procedure is carried out by shifting of the regression line (representing the fatigue–life curve) to the desired value of the probability of occurrence. Computer simulation includes both stress analysis and life estimation which are done using the ANSYS software. This estimation model offers a method for fatigue life evaluation and yields the life distribution in respect to the scatter of the cyclic properties of dental implants. Furthermore, the reliability of lifetime is calculated based on the probabilistic form. The purposes of this study are to predict fatigue life using a small amount of testing data and to provide a risk assessment for dental implants in use.

This article proposes a deployable frame for a morphing wing. The frame is redundantly constrained in structure, and therefore it has both merits of high structural stiffness and strength of a truss structure and motion flexibility of a mechanism. The primary element of the foldable frame is synthesized from the viewpoint of identical strength principle. The major structures of previous deployable wings are mostly based on prismatic joints. However, the deflections of the cantilevered links might not satisfy the primary geometry requirements of the prismatic joint. Therefore revolute joints are used in our deployable frame to avoid violating the geometry conditions for prismatic joints resulting from the different deflections of its contacting two parts. The deflection and slope of every joint node of the foldable frame is investigated within the deploying/folding process. Numerical analysis indicates that the deployment ratio of the foldable frame can be designed much larger than that of the existing morphing wing even considering the allowable deflection under the completely unfolded situations.

A novel type of mechanical presses design driven by three servo motors in parallel is proposed to develop high stamping capacity based on the theory of generalized function sets, and then is improved to enhance its practicability in engineering practice. The inverse and forward kinematics analyses are conducted later. Based on the fuzzy probability theory, the computing method of fuzzy reliability of kinematic accuracy of slider is then obtained. Finally, with a set of optimized length parameters of the presses given, the fuzzy reliability is calculated, on the basis of which a typical deep-drawing process is simulated.

Variable displacement vane-type oil pumps represent one of the most innovative pump types for industrial applications, especially for engine lubrication systems. This article deals with a mathematical modeling method for theoretical performance investigation of a typical variable displacement vane-type oil pump. This theoretical model is based on the pump geometric design and dynamic analyses. It can be considered as a generation step for a deeper understanding of the pump operation as well as for effectively implementing the pump control mechanisms to satisfy the urgent demands of engine lubrication systems. The developed theoretical pump model is finally illustrated by numerical simulations.

Water hydraulic piston motor is one of the important transmission components in a water hydraulic system. For lack of enough experimental information to analyze the reliability in water hydraulic motor design, the convex model is chosen as wear reliability model for hydraulic friction pairs, which is more economical and reasonable than the interval model. The non-probabilistic reliability index based on the convex model is established using first-order Taylor series expansion, and the non-probabilistic reliability model of wear reliability analysis for the friction pair of swash-plate/slipper in water hydraulic piston motor is introduced based on the convex model. For the non-probabilistic reliability model, only the bounds on uncertain parameters are needed, instead of probabilistic density distribution or statistical quantities. Numerical examples are used to illustrate the validity and feasibility of the presented method.

This article presents a novel 3-DOF parallel manipulator extracted from an origami fold in the context of mechanisms. The parallel manipulator consists of a base, a platform and four chain-legs that connect the platform to base through revolute joints. Each chain-leg contains a closed-loop sub-chain, which is spherical 6R linkage with symmetrical angle lengths. The geometry of the parallel manipulator is revealed according to the configuration design and specifics of the origami fold. This leads to unravelling of the symmetric plane which is determined by the common points of spherical 6R linkages in the four chain-legs. Based on geometric approach, the solutions for both inverse and forward kinematics are derived and the reachable workspace is then analyzed.

Nonlinear dynamic behaviour of a cantilever microbeam actuated by a combination of DC and AC loading are investigated in presence of squeeze-film damping. A reduced order model formulated accounting for the nonlinearities of the system arising out of electrostatic forces and squeeze-film damping is numerically simulated to observe the large amplitude dynamic characteristics near primary and superharmonic resonances. The emphasis is on the significance of nonlinear damping in capturing the true dynamic characteristics of microsystems formulated as distributed parameter model. The damping nonlinearity is found to considerably affect the dynamics with a profound stabilising effect on the microsystem. Under the effect of large DC bias voltage, frequency–response curves obtained for different amplitudes of AC excitation exhibit local and global bifurcations. Response sensitivity to initial conditions is investigated near bifurcation points. Findings in the superharmonic resonance domain are emphasised.