Semi-open Loop Research Articles

Uniformly high-speed semi-open loop polarization control and PMD suppression

We propose and demonstrate a novel scheme of semi-open-loop polarization control (SOL-PC), which controls the state of polarization (SOP) with high accuracy and uniform high speed. For any desired SOP, we first adjust the initial SOP using open-loop control (OLC) based on the matrix model of a three-unit piezoelectric polarization controller, and quickly move it close to the objective one. Then closed-loop control (CLC) is performed to reduce the error and reach precisely the desired SOP. The response time is three orders faster than that of the present closed-loop polarization control, while the average deviation is on par with it. Finally, the SOL-PC system is successfully applied to realize the suppression of the polarization mode dispersion (PMD) effect and reduce the first-order PMD to near zero. Due to its perfect performance, the SOL-PC energizes the present polarization control to pursue an ideal product that can meet the future requirements in ultrafast optical transmission and quantum communication.

Role of hydrodynamic shear layer stability in driving combustion instability in a premixed propane-air backward-facing step combustor

With numerical methods and analysis of existing experimental results we show that combustion instability in a backward-facing step combustor can be maintained either with weak coupling between acoustic and hydrodynamic modes (semi-open loop) or with strong coupling (fully closed loop).

A Semi-Open Loop GNSS Carrier Tracking Algorithm for Monitoring Strong Equatorial Scintillation

Strong equatorial ionospheric scintillation of radio signals is often associated with simultaneous deep amplitude fading and rapid random carrier phase fluctuations. It poses a challenge for satellite navigation receiver carrier phase tracking loop operation. This paper presents a semi-open loop algorithm that utilizes the known position of a stationary receiver and satellite orbit information to estimate carrier phase variations during deep signal fading. Strong GPS scintillation data collected on Ascension Island in March 2013 are processed to reveal fast phase changes of half and full cycles over tens of milliseconds on all three GPS frequencies. Simulated signals are used to validate the algorithm and confirm that the fast phase changes are true scintillation effects rather than receiver processing artifacts. The algorithm performance is demonstrated through comparison with several closed-loop implementations. Potential errors associated with receiver clock bias and other environmental factors are also analyzed. A statistical summary of the concurrent fast phase changes and deep fades based on the processing results of the Ascension Island data is presented.

In-flight tracking and vibration control using the DLR’s multiple Swashplate system

This paper discusses the design, integration, and test of a higher harmonic control algorithm capable of both vibration control and in-flight blade tracking in conjunction with DLR’s multiple swashplate control system (META), while honoring predefined limits in usable control authority. The design of the control algorithm is described in detail and the results of coupled numerical investigations with both a general purpose multibody code by Politecnico di Milano and DLR’s comprehensive rotor code to determine the algorithm’s performance are presented. The integration of the control algorithm into the real-time control software is shown for the META system, where, for safety reasons, a semi-open loop approach was implemented. First tests of the controllers in-flight tracking mode to reduce 1/rev loads during hover yielded an almost complete reduction in 1/rev vibratory loads while maintaining constant rotor thrust. Following the experiments at DLR’s own facility, extensive wind-tunnel tests were performed in 2016 with META and a 5-bladed rotor system at the large low-speed facility of the German Dutch Wind Tunnels. The control algorithm was adapted to the 5-bladed rotor and successfully applied for in-flight blade tracking as well as the reduction of 5/rev hub loads using multi-harmonic pitch inputs with frequencies from 4/rev to 6/rev in cruise and high-speed flight condition. In both cases, the controller showed excellent performance and yielded satisfactory reductions of 1/rev rotor imbalances as well as a reduction of 5/rev hub vibrations by more than $$80\%$$ , while, at the same time, adhering to user set limits for the higher harmonic control amplitudes.

Cooling tests, numerical modeling and economic analysis of semi-open loop ground source heat pump system

Ground source heat pump (GSHP) systems are serving the heating and cooling demands of buildings worldwide. However, the widespread usage of these systems is limited because of their higher initial costs compared with conventional heating and cooling systems, especially in countries with high drilling costs like Japan. The semi-open loop GSHP system was introduced by authors and the results of heating tests and numerical modeling have been published. This system comprises two ungrouted vertical Ground heat exchangers (GHEs) in which groundwater is pumped from one well and injected to another using a water pump. The purpose of the water pumping and injection is to create an artificial groundwater flow around the GHEs to increase the heat advection between the GHEs and the surrounding environment.In this study, cooling tests on the semi-open loop GSHP system were performed and the thermal performance of the system was measured in each test. The developed numerical model was validated using the results of the cooling tests. Then, a sensitivity analysis was performed to evaluate the system performance under different operational and geological conditions during cooling operation. The results showed that in comparison with conventional GSHP operation, cooling coefficient of performance (COP) and system coefficient of performance (COPsys) can be enhanced by 13.1% and 6.6%, respectively, under fast groundwater flow conditions, as expected at the experimental site. In the absence of groundwater flow, the semi-open loop system is estimated to boost the cooling COP and COPsys by 101% and 62%, respectively, for cooling operations. Finally, an economic analysis was performed, considering the capital and running costs of the system and also the additional equipment costs associated with semi-open loop systems. The results of the economic analysis showed that water pumping and injection can reduce GSHP system costs by 22–36%.

An experimental and numerical study of supercavitating flows tric cavitators

It has been shown that developing a supercavitating flow around under-water projectiles has a significant effect on their drag reduction. As such, it has been a subject of growing attention in the recent decades. In this paper, a numerical and experimental study of supercavitating flows around axisymmetric cavitators is presented. The experiments are conducted in a semi-open loop water tunnel. According to the Reynolds-Averaged Navier-Stokes equations and mass transfer model, a three-component cavitation model is proposed to simulate the cavitating flow. The corresponding governing equations are solved using the finite element method and the mixture Rayleigh-Plesset model. The main objective of this research is to study the effects of some important parameters of these flows such as the cavitation number, Reynolds number and conic angle of the cavitators on the drag coefficient as well as the dimensions of cavities developed around the submerged bodies. A comparison of the numerical and experimental results shows that the numerical method is able to predict accurately the shape parameters of the natural cavitation phenomena such as cavity length, cavity diameter and cavity shape. The results also indicate that the cavitation number declines from 0.32 to 0.25 leading to a 28 percent decrease in the drag coefficient for a 30◦ cone cavitator. By increasing the Reynolds number, the cavity length is extended up to 322% for a 60◦ cone cavitator.

Cycle slip detection and repair with a circular on-line change-point detector

In this article, we propose a circular change-point detector for on-line processing of the phase and the frequency of a GPS-L1 signal. The aims of this processing are to get an accurate estimation of the phase and to use it to get centimeter precise position estimates every millisecond. We propose to track the phase of the GPS signal in an open loop and the frequency in a semi-open loop. In an open loop, the phase delay evolves as a circular random variable. Furthermore, the phase is subject to cycle slips. These abrupt changes must be detected and repaired. We propose a circular generalized likelihood test for the on-line detection of changes in the phase measurements. With the estimation and detection being non-linear, we propose a particle filter defined according to the circular von Mises distribution for the estimation of the phase and frequency. The proposed architecture is assessed using synthetic and real data.

GNSS dataless signal tracking with a delay semi-open loop and a phase open loop

In this article we propose to process the code and phase delay of a dataless GNSS signal in open and semi-open loops. The aims of this processing are to get an accurate estimate of the phase and code delays by integration of the GNSS signal. We show that in an open loop the code delay evolution is a piecewise stationary process and we propose to model the phase delay as a circular random variable distributed according to a von Mises distribution. In this context the code tracking is realised on the GNSS signal by estimating the abrupt changes in the code discriminator values. We propose a Bayesian modeling of the problem in order to define the change point estimator. The proposed estimator involves in its definition the inaccurate prior information of Doppler and signal to noise density ratio provided by the phase delay tracking loop. Furthermore we propose a circular Bayesian modeling of the observations provided by the phase open loop. From this model, we derive a circular recursive filter for the estimation of phase delay and frequency of the carrier. The proposed tools are assessed using synthetic and real data.

Dimensioning the EVITA semi-open loop at BR2 for qualification of full size JHR fuel elements

The Jules Horowitz Reactor (JHR) is the next generation research reactor from CEA and which commissioning is foreseen in 2014. Prior to acquiring the exploitation license, the fuel elements have to be qualified for their intended functioning power. The only facility capable to perform this task is the Belgian research reactor BR2, due to its similar thermal-hydraulic parameters. At the moment, one has already tested the fuel plates separately. The preparation of the JHR safety report still needs the test of full size elements.This JHR fuel element is broader and more powerful than a standard BR2 fuel element, and one cannot perform an irradiation by simply interchanging them. However, BR2 has 200mm channels at its disposal, which can be adapted to give the correct hydraulic diameter. One also needs an additional pump to deliver the necessary cooling flow rate for the higher power.This paper describes the dimensioning of the EVITA semi-open loop, which has been built at BR2 to irradiate full size JHR fuel elements and qualify them for the foreseen exploitation parameters. One explains here the followed methodology to quantify the required additional head for the booster pump and to determine the pressure profile along the circuit and the safety margin on the fuel. This methodology relies only on a priori calculations without any measurement on full size installation subpart as usual before the assembly in controlled zone. The article also explains how the original JHR thermal hydraulic safety calculation scheme was adapted to the BR2 environment. One also compares the measurement results on the fully built installation with our previsions. Our models compare well with the experimental results, excepted for the pressure loss on the fuel plates.

Simulation of Vibration Damage in Produce Transportation

ABSTRACT MODUS operandi of measuring, recording and synthesizing transportation vibration environments for produce damage simulation in the laboratory is described. Based on measurements of typical produce transport routes, realistic simulation of damage in containers and unit loads of fresh produce may be achieved in a fraction of the real journey's time, by reproducing maxi-max envelope peak acceleration spectra. A semi open loop control strategy, for an electrohydraulic vibration testing machine was developed, utilizing commonly available and relatively inexpensive analog instrumentation and components, while digital hardware and software is implemented on a microcomputer. Once a control signal, simulating a given transport environment is developed, for a particular brand and type of vibration machine, it can be stored on FM analog magnetic cassette tape. Copies of this tape may be played back, as command signals on similar machines, for simulating that environment, hence further reducing cost and complexity. Simulation experiments are reported, wherein columns of containers filled with dummy fruit and oranges, were subjected to a typical maxi-max acceleration envelope spectrum. These show, that the highest acceleration levels are encountered in the bottom tier containers, whether the load is strapped down or not. The low frequency end of the spectrum is significantly amplified in the top tier containers, when the column is strapped down. The high frequency end of the spectrum is generally attenuated from the bottom to the top tier containers.