Verification of flow velocity measurements using micrometer-order thermometers

In flow velocity measurements, resolution, miniaturization, and accuracy of measuring devices are important issues because the measuring devices significantly affect the flow in the micro-space, sonic flow, and turbulent flow. We studied recovery temperature anemometry (RTA) using micrometer-order thermometers and evaluated its validity in two velocity ranges (40–90 and 315–420 m/s) by conducting two experiments and a numerical simulation. The results confirmed that the difference between the reference velocity and RTA was within 5% in the velocity range 60–90 m/s for both the thermocouple and platinum thermometer given the same recovery temperature coefficient of 0.83. It is a valuable finding that velocity measurement by RTA is independent of the type of thermometer used. This suggests that the accuracy of about 5% can be guaranteed even without calibration by giving the recovery temperature coefficient according to the thermometer geometry, which is an excellent advantage not found in other anemometers. Furthermore, the supersonic flow measured using RTA agrees well with the simulation results and theoretical trends. Our findings ensure that the micrometer-order point measurement of flow velocity, which is difficult with existing anemometers, using RTA is possible over a wide range of flow velocities.

Switched Optimal Control of a Heavy-Duty Hybrid Vehicle

This work investigates the fuel energy and emission reductions possible with the hybridization of a Class 8 tractor-trailer. The truck tractor has two drive axles: one powered by an internal-combustion-engine-based powertrain (CP) and the other powered by an electric powertrain (EP) consisting of an electric drive system supplied by a battery pack, resulting in a through-the-road hybrid. The EP has two modes of operation depending on the direction of power flow: motoring/battery discharging and generating/battery recharging. Switched optimal control is used to select between the two modes of EP operation, and a recently developed distributed switched optimal control is applied. The control is distributed between the CP, the EP, and the vehicle motion operation components. Control-oriented, component-specific power flow models are set forth to describe the dynamics and algebraic relationships. Four different tractor-trailers are simulated: the original CP and three hybrids with engine sizes of 15 L, 11 L, and 7 L. Simulations are performed over a short test cycle and two regulatory driving cycles to compare the fuel use, total energy, and emissions. Results show that the hybrids have reduced fuel use, total energy, and emissions compared to the original CP; the reductions and reference velocity tracking error increases as the engine size is decreased. Particularly, fuel use is reduced by at least 4.1% under a charge sustaining operation and by 9.8% when the battery energy can be restored with an off-board charger at the end of the cycle.

Advanced deep flux weakening operation control strategies for IPMSM

This paper proposes an advanced flux-weakening control method to enlarge the speed range of interior permanent magnet synchronous motor (IPMSM). In the deep flux weakening (FW) region, the flux linkage decreases as the motor speed increases, increasing instability. Classic control methods will be unstable when operating in this area when changing load torque or reference speed is required. The paper proposes a hybrid control method to eliminate instability caused by voltage limit violation and improve the reference velocity-tracking efficiency when combining two classic control methods. Besides, the effective zone of IPMSM in the FW is analyzed and applied to enhance stability and efficiency following reference velocity. Simulation results demonstrate the strength and effectiveness of the proposed method.

Double-Loop Sliding Mode Controller with An Ocean Current Observer for the Trajectory Tracking of ROV

To solve the trajectory tracking problem of insufficient response and the large tracking error of remotely operated vehicles (ROVs) under the interference of large ocean currents, this paper proposes a double-loop sliding mode controller with an ocean current observer. The designed controller consisted of an outer-loop controller (the position controller) and an inner-loop controller (the velocity controller): the outer controller was designed by the position error, and a reference velocity was created for the inner loop to achieve accurate positioning and attitude tracking. The reference control input was treated as a new target to design the inner-loop controller, enabling the ROV to achieve accurate reference velocity tracking. Based on the theoretical idea of active disturbance rejection control, a kinematic equation-based ocean current observer was designed to estimate and compensate for large unknown currents to ensure accurate trajectory tracking performance under large currents. The simulation results proved that the double-loop sliding-mode control scheme with an ocean current observer always showed good tracking performance, demonstrating the excellent control performance and high robustness of the scheme. Compared with the high-complexity control schemes such as neural network-based PID control or fuzzy sliding mode control, it effectively improves the robustness to ocean current disturbances without increasing the computational effort excessively, and is more practical in ROV systems with limited computational power.

Weak-anisotropy approximation of P-wave geometrical spreading in horizontally layered anisotropic media of arbitrary symmetry: TTI specification

Understanding the role of geometrical spreading and estimating its effects on seismic wave propagation play an important role in several techniques used in seismic exploration. The spreading can be estimated through dynamic ray tracing or determined from reflection traveltime derivatives. In the latter case, derivatives of non-hyperbolic moveout approximations are often used. We offer an alternative approach based on the weak-anisotropy approximation. The resulting formula is applicable to P-waves reflected from the bottom of a stack of horizontal layers, in which each layer can be of arbitrary anisotropy. At an arbitrary surface point, the formula depends, in each layer, on the thickness of the layer, on the P-wave reference velocity used for the construction of reference rays, and on nine P-wave weak-anisotropy (WA) parameters specifying the layer anisotropy. Along an arbitrary surface profile, the number of WA parameters reduces to five parameters related to the profile. WA parameters represent an alternative to the elastic moduli, and as such can be used for the description of any anisotropy. The relative error of the approximate formula for a multilayered structure consisting of layers of anisotropy between 8% and 20% is, at most, 10%. For models including layers of anisotropy stronger than 20%, the relative errors may reach, locally, even 30%. For any offset, relative errors remain under a finite limit, which varies with anisotropy strength.

Design of Variable Damping INS for Ships Based on the Variation of Reference Velocity Error

Schuler oscillation damping is one of the key technologies to improve the long-term precision of inertial navigation systems (INSs). Generally, a ship introduces the reference velocity to work on the external horizontal damping status to avoid the effects caused by maneuvers. However, the navigation accuracy is sensitive to the reference velocity error which will be affected by sea conditions and the ship’s maneuver. It is necessary to adjust the damping status dynamically as the change of the reference velocity error to ensure the accuracy and stability of INS. To address this problem, a novel variable damping system based on the variation of the reference velocity error is designed in this paper. First of all, this proposed method switched the damping status according to the variation of the reference velocity error in a certain period of time based on the principle of window detection. In addition, this paper designed a fuzzy controller to avoid the overshoot caused by the frequent switching of the damping status. What is more, a method of overshoot suppression was applied in this system. Simulation experiments were conducted to validate the theoretical analysis and the effectiveness of this method. Compared with the undamping system, constant damping system, and traditional variable damping system, the simulation results verified that the designed variable damping system can attenuate the system error caused by reference velocity error most effectively, thus improving the navigation accuracy of INS.

A Fault-Tolerant Level Damping Algorithm for Marine INS

When the measurement error of the external reference velocity changes dramatically, the traditional level damping for marine INS needs to cut off the damping to maintain the navigation accuracy. The level channel has a large overshoot oscillation during the variable damping instantaneous, which results in obvious position deviation. In order to solve this practical problem, a damping model is established outside the INS. The most obvious advantage of the algorithm is that the damping algorithm does not affect the inertial navigation solution. The fault-tolerant algorithm realizes the automatic damping switch according to the external reference velocity error variation criterion, which avoids the velocity oscillation and position deviation. Compared with traditional methods, the algorithm presented in this paper has higher reliability and better environmental adaptability. The effectiveness of the algorithm is verified by the actual navigation test data.

Experimental Flow-Induced Vibration Analysis of the Crossflow Past a Single Cylinder and Pairs of Cylinders in Tandem and Side-by-Side

Flow-induced vibration of a single cylinder and two cylinders in tandem and side-by-side configurations is experimentally investigated in this paper in the subcritical regime. The natural frequency of the system varied from 8.8 Hz to 46.2 Hz. The mass ratio, m*, ranged between 158 and 643 while the damping ratio, ζ, between 0.0005 and 0.009. The pairs of cylinders present a spacing ratio of 1.26 (P/D and L/D). In all cases, one and both cylinders (BV) were free to vibrate. Experiments were performed in an aerodynamic channel with a constant height and a variable width, for the evaluation of the influence of the blockage ratio (BR), using accelerometers and hot wire anemometry. The reference velocity, measured at the entrance of the test section was used to calculate the reduced velocity, Vr = U/fnD, with values from 4 to 132 and the Reynolds number between 3 × 103 and 8 × 104. The root-mean-square-values of the displacement amplitudes, Y/D, were obtained through the integration of the acceleration signals. Fourier and continuous wavelets were employed in the analysis. For a single cylinder free to vibrate, the higher amplitudes occur at two distinct reduced velocities, associated with the vibration modes of the cylinder. The vibration amplitude of a single cylinder increased as the blockage ratio increased, decreasing for the highest blockage ratio investigated. For the case of cylinders in tandem, the presence of the fixed cylinder in the wake of the cylinder free to vibrate amplifies the vibration response at high reduced velocities. When the blockage ratio is increased, a sudden increase in the vibration amplitude is observed. When both cylinders are free to vibrate, the relation between the natural frequencies of both cylinders influences the response amplitudes. In the case with two cylinders side-by-side, the vibration amplitude remains similar to a single cylinder, but when both cylinders are free to vibrate, the presence and the influence of flow bistability is observed.