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The fundamental principle of the transient state control method for turbofan engines, which is based on the acceleration ratio of high-pressure rotational speed (N-dot), involves sacrificing a portion of the safety margin to obtain satisfactory acceleration performance. However, it could induce surge in the engine's compressor. To prevent the destructive damage caused by surge to both the engine and its components, a surge-elimination control strategy for the engine based on an N-dot controller is proposed. First, the engine mathematical model, which incorporates the effects of engine volumetric dynamics, stall zone characteristics, and combustion chamber flameout characteristics, is established to simulate surge mechanism. Subsequently, the acceleration schedule of the N-dot is calculated by employing sequential quadratic programming (SQP) algorithm to solve the multiconstraint optimization problem, while designing the transition state controller of N-dot based on a high-order filter. Finally, the surge detection logic and surge-elimination strategy based on the µ-correction method are proposed and designed to realize active control of surge elimination. The simulation results demonstrate that the N-dot control method offers significant advantages in mitigating the steady-state errors resulting from inevitable engine degradations. The surge state is effectively suppressed by the proposed surge-elimination control method, and the surge duration is significantly shorten during the acceleration phases. Furthermore, compared to the one without any surge-elimination control, the proposed method decreases the acceleration time by 5.53%. [ABSTRACT FROM AUTHOR]

In order to overcome the problem of significant drop in operational efficiency remarkably while power turbine speed varies among a large range, an optimal speed control method of multiple turboshaft engines based on sequential shifting control (SSC) algorithm is proposed. Firstly, combined with multispeed gearboxes, a sequential shifting control algorithm of multiple turboshaft engines is proposed and designed to accomplish continuously variable speed control. Then, selecting the minimum engine fuel flow as the optimization objective, an integrated optimization method of optimal speed based on multiple engines and multispeed gearboxes is proposed to promote the operational economy. Finally, the simulation tests of the optimal speed control method of twin and triple turboshaft engines are conducted separately. The results demonstrate that the optimal speed control method of multiple turboshaft engines based on SSC algorithm can change the power turbine speeds by no more than 7% and the main rotor speed by over 8% simultaneously. In addition, compared with the fixed-ratio transmission (FRT), engine fuel flows decrease by more than 2% under different cruise states. It proves that the optimal speed control method is beneficial to obtain more superior overall performances of the integrated helicopter/multi-engine system without considerable loss of compressor surge margin. [ABSTRACT FROM AUTHOR]

Ball-end milling is widely used in five-axis high-speed machining. The abrupt change of tool orientations or rotary axes movements will scrap the workpiece. This research presents a smoothing method of rotary axes movements within the feasible domains of the rotary-axes space. Most existing smoothing methods of tool orientation or rotary axes movements employ the Dijkstra's shortest path algorithm. However, this algorithm requires extensive computations if the number of the cutter locations is large or the sampling resolution in the feasible regions is high. Moreover, jumps in the results obtained with the Dijkstra's shortest path algorithm may occur, because the optimization problem has to be converted from a continuous problem into a discrete problem when using this algorithm. The progressive iterative approximation (PIA) method incorporating smoothness terms is established as a gradient-based optimization method to smooth the rotary axes movements in this research. Then a gradient-based differential evolution (DE) algorithm, combining the global exploration feature of the DE algorithm and the local searching ability of the gradient-based optimization method, is developed to solve the smoothing model. The validity and effectiveness of the proposed approach are confirmed by numerical examples. [ABSTRACT FROM AUTHOR]

This study reports an experimental investigation of two planar jets in a crossflow in a tandem arrangement. Tests were conducted in an open-jet wind tunnel facility using two-dimensional (2D)-particle imaging velocimetry (PIV) measurement. Using the terminology in the dual jets in a quiescent ambient, the mean flow field of the crossflow arrangement was divided into a converging region, a merging region, and a combined region. An approach to determining the range of these three regions was proposed based on the mean characteristics of horizontal velocity profiles of the flow field, validated by the experimental data. The momentum-dominated near field (MDNF) for the rear jet in the dual-jet configuration was recognized using the horizontal offset of mean jet trajectory, which accordingly gives a quantitative definition of the MDNF range. Discussions were made on the effects of different parameters on the three regions and MDNF. Finally, snapshot proper orthogonal decomposition (POD) analysis was conducted, characterizing the coherent structures of the flow field, particularly the large-scale vortices. It was observed that the large-scale vortices mainly occur in the shear layers of the jets and their occurrence is affected by the parameters of the jets. In addition, compared with the single-jet configuration, the introduction of the front jet was found to contribute to the occurrence and development of the large-scale vortices. [ABSTRACT FROM AUTHOR]

Inspired by the phenomenon of localized response intensification in wideband random vibration, a novel procedure is proposed to determine the optimal locations of piezoelectric patch attaching on wideband random point-driven beam for vibration energy harvesting application. The optimization objective is to maximize the mean output voltage, and the optimal locations lie on the vicinities of the excited point and its symmetric point. The optimal locations keep invariable regardless of typical symmetric boundary conditions (such as the clamped, simply supported, free, and torsional spring supports), the lower and upper cutoff frequencies of the band-limited white noise, and the external damping provided that the excited point is not too close to boundaries and the bandwidth of excitation covers enough modes of primary structure. The robustness of optimal locations is illustrated from an electromechanical coupling model and is qualitatively verified through experimental testing on a random-excited aluminum beam with piezoelectric patches attached on its surface. [ABSTRACT FROM AUTHOR]

In this paper, we develop and apply feature extraction and selection techniques to classify tool wear in the gear shaving process. Because shaving tool condition monitoring is not well-studied, we extract both traditional and novel features from accelerometer signals collected from the shaving machine. We then apply a heuristic feature selection technique to identify key features and classify the tool condition. Run-to-life data from a shop-floor application is used to validate the proposed technique. [ABSTRACT FROM AUTHOR]

The impacting and rehounding behaviors of straight elastic components are investigated and a unified approach is proposed to analytically predict the whole process of the collision and rebounding of straight elastic bars and beams after each of them impinges on ideal (massless) elastic spring(s). The mathematical problems with definitive solution are formulated, respectively, for both the constrained-motion and free-motion stages, and the method of mode superposition, which is concise and straightforward especially for longtime interaction and multiple collision cases, is successfully utilized by repeatedly altering boundary and initial conditions for these successive stages. These two stages happen alternatively and the collision process terminates when the constrained motion no longer occurs. In particular, three examples are investigated in detail; they are: a straight bar impinges on an ideal elastic spring along its axis, a straight beam vertically impinges on an ideal elastic spring at the beam's midpoint, and a straight beam vertically impinges on two ideal springs with the same stiffness at the beam's two ends. Numerical results show that the coefficient of restitution (COR) and the nondimensional rebounding time (NRT) only depend on the stiffness ratio between the ideal spring(s) and the elastic barI beam. Collision happens only once for the straight bar impinging on spring, while multiple collisions occur for the straight beam impinging on springs in the cases with large stiffness ratio. Once multiple collisions occur, COR undergoes complicated fluctuation with the increase of stiffness ratio. Approximate analytical solutions (AASs) for COR and NRT under the cases of small stiffness ratio are all derived. Finally, to validate the proposed approach in practical collision problems, the influence of the springs' mass on the collision behavior is demonstrated through numerical simulation. [ABSTRACT FROM AUTHOR]