Pitch Loop Research Articles

Method for deriving twisting process parameters of large package E-glass yarn by measuring physical properties of bobbin yarn

Abstract Twisting is an important part in the production process of large package E-glass yarn. To derive the twisting process parameters of large package E-glass yarn, a method from the physical properties of bobbin yarn is proposed based on the study of the twisting principle of E-glass yarn. After unwinding the bobbin yarn and measuring its twist, loop pitch, and corresponding diameter, the calculation is completed according to the steps of first determining the descending speed of the traveler, then fitting the spindle speed data, and finally calculating the elevating speed of the traveler. The result is that the twisting spindle speed of D450 E-glass yarn with 31.8 T/m decreases from 5,015 to 4,550 rpm, the elevating speed of the traveler is 0.91 m/min, and the descending speed of the traveler is 1.50 m/min. The accuracy of the calculation is verified by monitoring the rotating speed of the roving cake and measuring the loop pitch of bobbin yarn in the twisting experiment. The result shows that the prediction error of this method is less than 1.1%, which can effectively derive the twisting process parameters of large package E-glass yarn, and provide a reference for the twisting process design scheme of glass fiber strand manufacturers.

Development and Evaluation of AI System to Specify Favourable Launch Windows of Space Vehicles from the MST Radar Data

Weather being a complex Nondeterministic Polynomial time System, forecasting weather parameters has been a major challenge for so long and continues to be so. To address the pressing challenges, new prediction models are developed that vary in the prediction duration and accuracy. Predicting the wind speed, wind direction and turbulence is of significant interest to rocket industry as that would leverage them to time their launches. Launch vehicle trajectory would use the altitude based on mean wind biasing during atmospheric phase of flight to reduce significantly the effect of atmospheric winds on the structural loads experienced by the vehicle. Biasing the open loop pitch and yaw programs to the mean wind condition of launch month is known as monthly mean wind biasing. Atmospheric phase of flight refers to the wind profile up to 20-25 km altitude, the height resolution and accuracy is important. Diurnal variation on the day of launch is critical. Surface winds are measured at various tower heights up to 150 metres. While upper winds are measured with radiosonde mounted to Rawin balloons or with the expensive and difficult to procure Jimsphere or with MST radars. MST radar is far superior to the traditional radiosonde mounted to Rawin balloons in that the MST radar can be operated on a continuous basis to obtain measurements of the wind. MST Radar data is considered in the present study. Usually, numerical methods involving complex mathematical modelling else statistical estimates are employed for weather forecasting. In this article, an appropriate soft computing technique such as the Feed Forward based Back Propagation Neural Networks is proposed. Neural networks are good at fitting any nonlinear nature of function with several mathematical learning co-efficient variables. Analyses are carried out using MATLAB software for assessing the launch windows of space vehicles and its applications.

Stability Analysis of Tailsitters in Vertical Takeoff and Landing Flights

The stability of tailsitters is severely impacted by ground friction/reaction forces when the landing gear contacts the ground. This paper analyzes the stability of tailsitters during taking off from and landing on the ground. A distributed propulsion tailsitter with four electrically driven propellers is studied and modeled. The pitch loop of this tailsitter can be stabilized by both aerodynamic effectors immersed in the propeller slipstream and differential thrust of the propellers installed on upper and lower wing sides. The stability criteria and stability margin of tailsitters in the landing-gear/contact-ground flight stage are defined. The open-loop stability of tailsitters on high-friction and low-friction grounds is analyzed. The closed-loop stability of tailsitters with thrust-vectoring control and trailing-edge elevators control are discussed separately. On high-friction ground or uneven terrain, the tailsitter pivots about the ground contact point instead of the center of gravity. It is shown that the ground friction/reaction forces induced by the trailing-edge elevators generate a reversed pitching moment, which makes the pitch loop of the tailsitter unstable. A Proportional–Derivative controller with thrust vectoring as an effector is given and proved to guarantee the pitch loop stability. The influences of the thrust increase rate are also discussed. The experimental results of a tailsitter unmanned air vehicle verify the conclusions of this paper.

Tower Load Reduction Control by Pitch Loop Individual Gain Scheduling

Tower Load Reduction Control by Pitch Loop Individual Gain Scheduling

Mathematical Model of a Closed Loop Pitch Controlled Turbine in a Wind Energy Conversion System

Mathematical Model of a Closed Loop Pitch Controlled Turbine in a Wind Energy Conversion System

Pitch Loop Control of a VTOL UAV Using Fractional Order Controller

Pitch loop control is the fundamental tuning step for vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAVs), and has significant impact on the flight. In this paper, a fractional order strategy is designed to control the pitch loop of a VTOL UAV. First, an auto-regressive with exogenous input (ARX) model is acquired and converted to a first-order plus time delay (FOPTD) model. Next, based on the FOPTD model, a fractional order [proportional integral] (FO[PI]) controller is designed. Then, an integer order PI controller based on the modified Ziegler-Nichols (MZNs) tuning rule and a general integer order proportional integral derivative (PID) controller are also designed for comparison following three design specifications. Simulation results have shown that the proposed fractional order controller outperforms both the MZNs PI controller and the integer order PID controller in terms of robustness and disturbance rejection. At last, ARX model based system identification of AggieAir VTOL platform is achieved with experimental flight data.

Comparing the thermal performance of horizontal slinky-loop and vertical slinky-loop heat exchangers

The heat pump market in the UK has grown rapidly over the last few years. Performance analyses of vertical ground-loop heat exchanger configurations have been widely carried out using both numerical modelling and experiments. However, research findings and design recommendations on horizontal slinky-loop and vertical slinky-loop heat exchangers are far fewer compared with those for vertical ground-loop heat exchanger configurations, especially where the long-term operation of the systems is concerned. The paper presents the results obtained from a numerical simulation for the horizontal slinky-loop and vertical slinky-loop heat exchangers of a ground-source heat pump system. A three- dimensional numerical heat transfer model was developed to study the thermal performance of various heat exchanger configurations. The influence of the loop pitch (loop spacing) and the depth of a vertical slinky-loop installation were investigated and the thermal performance and excavation work required for the horizontal and vertical slinky-loop heat exchangers were compared. The influence of the installation depth for vertical slinky-loop configurations was also investigated. The results of this study show that the influence of the installation depth of the vertical slinky-loop heat exchanger on the thermal performance of the system is small. The maximum difference in the thermal performance between the vertical and horizontal slinky-loop heat exchangers with the same loop diameter and loop pitch is less than 5%.

Simulation of thermal performance of horizontal slinky-loop heat exchangers for ground source heat pumps

This paper presents results obtained from a numerical simulation for the horizontal slinky-loop heat exchanger of a ground-source heat pump system. A three-dimensional numerical model was developed and the results of the thermal performance of various heat exchanger configurations are presented. The investigation was carried out on five types of loop pitch (loop spacing), three types of loop diameter, three values of soil thermal properties, and allowing continuous and intermittent operation. Comparison was made for the heat transfer rate, the amount of pipe material needed, as well as excavation work required for the horizontal slinky-loop heat exchanger. The results indicate that system parameters have a significant effect on the thermal performance of the system.

Longitudinal Control Law Design and Simulation of Fixed-Wing UAV

Taken some fixed-wing UAV as the study object, the aircraft movement was broken down into the longitudinal movement and lateral movement according to the linearized small perturbation principle, the longitudinal control law design method was discussed using root locus which belonged to classical control theory. The six degrees of freedom nonlinear model simulation result shows that: the control parameters designed are reasonable, the simulation profile is fully consistent with the setting profile, the control effect of pitch angle loop and altitude loop meets with the indices requirements, the method is mature and reliable, easy to realize in engineering.

Adjustable Adaptive Fuzzy Attitude Control using Nonlinear SISO Structure of Satellite Dynamics

This paper presents a method for three-dimensional attitude stabilization of a satellite. The pitch loop of the satellite is controlled by a momentum wheel; whereas the roll/yaw loops are stabilized using two magnetic torques along their respective axes. In order to design an efficient controller, the stability conditions are considered based on a nonlinear model of system. An adjustable adaptive fuzzy system is proposed as the method to design the controller. The span of membership functions are tuned using errors of fuzzy inputs with respect to their references. Results show that fuzzy sets cover all variations of fuzzy inputs and optimal fuzzy output is gained. The Lyapunov synthesis method is used to prove the stability of the closed-loop system. The efficiency of the controller in converging of the position error to close to zero is also shown using some numerical simulations.

Attitude Tracking Control Using an Online Identification and a Linear Quadratic Regulator–Based Strategy in the Presence of Orbital Eccentricity

This paper presents attitude trajectory control for a satellite system. The pitch loop of the satellite is controlled by momentum wheel; whereas the roll/yaw loops are stabilized by two different magnetic torques along their axes. The controller is on the basis of both the linear quadratic regulator (LQR) control theory and recursive least square (RLS) algorithm that is used to identify the equivalent linear canonical second order system for each axis at discrete points on references. Then, the linear identified model is used to design the LQR-based controller. This process is done in each time span. The efficiency of the controller to bring the position error close to zero is shown by some numerical simulations. The performance of the proposed controller is remarkable in stabilizing the satellite attitude even in the presence of orbital eccentricity.

A revised inversion model parameter formulation for fixed wing transmitter loop – towed bird receiver coil time-domain airborne electromagnetic data

The conversion of data to conductivity for fixed wing transmitter loop ? towed bird receiver coil time-domain airborne electromagnetic (AEM) systems, such as TEMPEST, would ideally utilise complete knowledge of the system geometry and measurements for all three mutually perpendicular components of the received signal. In practice, not all of this information is available. We use a layered inversion that integrates TEMPEST survey data with a priori conductivity information from the survey area. Total (primary plus secondary) field data from both the X (horizontal in-line) and Z (vertical) components are used. Receiver coil pitch angle and transmitter loop to receiver coil horizontal and vertical separation parameters are included as unknowns in the inversion. Borehole conductivity data are used to build a reference conductivity model that acts as a constraint to stabilise the partitioning of the measured signal into primary field and ground response contributions. Smoothness constraints are applied to the conductivity values in the 1D model. The quality of the inversion output was assessed through comparison of the conductivity predictions with borehole conductivity values and shallow single-frequency ground EM measurements. This showed that the new formulation more accurately predicted conductivity than two previous sets of conductivity predictions.

Influence of a Pitch Adjustable Foot Restraint on Operator Induced Loads in Zero-Gravity

The zero-gravity environment creates a need for a proper human body restraint system to maintain a comfortable posture which lessens fatigue and maximizes productivity. In addition, restraint systems must be able to meet the loading demands of maintenance and assembly tasks performed on-orbit. The Shuttle's primary intravehicular astronaut restraint system is currently a foot loop design that attaches to flat surfaces. This restraint system allows for variation in mounting locations and ease of ingress and egress. However, this design limits performance because it does not allow for elevation, pitch, or foot loop length adjustment. Several prototype foot restraint systems are being evaluated for use aboard Space Station and the Space Shuttle. A study was initiated using NASA's reduced gravity aircraft quantifying differences observed in operator performance while adjusting the pitch angle of a prototype foot restraint. Pitch angle adjustments were made from 5° to 35°. While operators performed a torque wrench task using a hand hold and foot restraint, the maximum axial forces and moments induced on the restraint systems and torque wrench were recorded. Overall this study did not see any significant difference in the force operators could place on the torque wrench or forces imparted to the foot restraint system due to the pitch orientation of the foot restraint. Thus in a work environment in which hand holds are available, no significant influence of the pitch angle existed for operator performance or forces imparted to the restraint system.

Fast methods for the CELP speech coding algorithm

Special fast procedures for the code excited linear predictive coding (CELP) algorithm have been developed to make implementation on modest hardware possible. The advantages, as well as the disadvantages, of the various fast procedures are discussed. A general formalism for the algorithm is developed, followed by the discussion of the individual procedures which are grouped according to their features. Along with the computational complexity of each procedure, its storage requirement and numerical accuracy are discussed. A large number of the fast procedures are designed to search through a particular type of codebook (most of the codebooks are stochastic in character, while a few are deterministic). Other fast procedures can be used for arbitrary codebooks and are thus also applicable to trained codebooks. Some of the fast procedures designed for stochastic codebooks can also be used for the computation of the closed pitch loop parameters, which can be interpreted as a search through a time-dependent codebook. >

An efficient stochastically excited linear predictive coding algorithm for high quality low bit rate transmission of speech

The Stochastically Excited Linear Prediction (SELP) algorithm for speech coding offers good performance at bit rates as low as 4.8 kbit/s. Linear Predictive Coding (LPC) techniques remove the short-term correlation from the speech. A pitch loop removes long-term correlation, producing a noise-like residual, which is vector quantized. Information describing the LPC filter coefficients, the long-term predictor, and the vector quantization is transmitted. In this paper, we describe improvements to the SELP algorithm which result in better speech quality and higher computational efficiency. In its closed-loop form, the pitch loop can be interpreted as a vector quantization of the desired excitation signal with an adaptive codebook populated by previous excitation sequences. To better model the non-stationarity of speech we extend this adaptive codebook with a special set of candidate vectors which are transform of other codebook entries. The second stage vector quantization is performed using a fixed stochastic codebook. In its original form, the SELP algorithm requires excessive computational effort. We employ a new recursive algorithm which performs a very fast search through the adaptive codebook. In this method, we modify the error criterion, and exploit the resulting symmetries. The same fast vector quantization procedure is applied to the stochastic codebook.