•Research results of a 4/3 sectional proportional directional control valve.•A concept of using flow forces for pressure compensation.•Proposition of creating the appropriate spool grooves to obtain ...required jet angle.•Obtaining dependency of spool position on jet angle and thus on flow forces.•Obtaining the required valve characteristics through the spring stiffness selection.
The main subject of this article is pressure compensation in a multi-section proportional directional control valve. The undertaken compensation task was carried out without the use of neither additional compensating valves nor other correcting elements, such as sensors in a feedback control system. The proposed method consists in the appropriate adjustment of forces acting on the valve spool. It requires knowledge of the electromagnet force characteristics and the appropriately matched stiffness and initial tension of the valve spring. In order to achieve the assumed objective, a number of CFD simulations was performed on a 3-D fluid model. The CFD analysis allowed determination of the values of flow resistance through the valve and the axial component of the flow force acting on the spool. The values calculated for various spool positions and flow velocities were approximated using analytical equations. Next, the mathematical model was built and simulations in Matlab/Simulink system were carried out. In the first stage of the research, flow characteristics of a single valve section were determined. The obtained results were then verified on the test bench. In the second stage, the simulation model was used to examine the possibility of pressure compensation in a three-section control valve. In this case, the individual valve sections were loaded unevenly by applying pressure in a wide range of values. It has been demonstrated, that the appropriate shaping of the spool geometry allows usage of the flow forces for pressure compensation in multi-section proportional directional control valves.
This article presents a new control method for a pneumatic cushion for transporting heavy payloads. Pneumatic cushions are particularly useful for moving structural or non-structural components over ...hard, smooth floors. They can be put directly under load, lifted to a small height by applying air pressure and moved. A thin, friction-reducing air film is formed under the cushion during lifting. Currently, pressure is usually controlled manually, which causes difficulty in establishing an appropriate pressure value, especially when the load is distributed unevenly between multiple cushions. In practice, the pressure is often set higher than is necessary to move the load. Excessive pressure does not reduce friction, but increases air consumption. Hence, in this article an effort is described to obtain the minimum allowable pressure. The first part of the article includes the theoretical background, detailed models of the proposed automatic controllers and the parameters of a test bench. Experiments were carried out with a typical manual control system and two automatic controllers, with PID and fuzzy logic algorithms. The results indicate that automation of the control system significantly reduces air consumption and shortens the time needed to obtain the correct pressure. Moreover, it improves the stability of the load by allowing more accurate vertical positioning of individual cushions.
•Presenting transport platform on four pneumatic cushions.•Obtaining characteristics of the platform with manual control system.•Presenting innovative concept of automatic control system for the platform.•Proposing PID and Fuzzy Logic algorithms for the controller.•Carrying out tests of the controllers on the platform and comparing results.
The main objective of this article is to analyse flow coefficient of a proportional directional valve with integrated spool position controller. The valve geometry has been modified by creating ...additional undercuts on the spool, which provide improved flow characteristics, especially at low flow rates. The analysis consisted of two phases, including computer simulations and test bench experiments. At first, flow through the valve was simulated by the means of CFD method in ANSYS/Fluent software, assuming the fixed spool positions. Based on the results, flow coefficient values were determined. The results showed, that in the examined gap width range, the coefficient value is mainly related to the spool position, and to a lesser extent to the volumetric flow rate. Hence, a proposal to formulate the flow coefficient value as a function of spool position or spool position and flow rate was made. Three approximating functions were determined in Matlab system on the basis of the obtained CFD results: a linear curve μ=f(xg), as well as a linear polynomial surface and a quadratic polynomial surface μ=f(xg,Q). Next, the results were verified by experiments conducted at a test bench.
The best fit flow coefficient function was then used in the subsequent simulations on a multi-actuator system comprising three parallel-connected valves supplied by a single pump. In this case, each valve was set a different fixed spool position, which resulted in a different throttle gap width. Analysis of the system was carried out using an own-developed computer software for solving the analytical equations. Finally, the results were compared to those obtained by means of a CFD method, and a satisfactory compliance was achieved.
•Research of a proportional directional control valve with a spool position controller.•A concept of formulating flow coefficient as a function of spool position and flow rate.•CFD simulations in a wide range of spool positions and flow rates.•Determination of flow coefficient functions and verification by test bench experiments.•Analysis of a multi-valve system using the determined flow coefficient function.
The design of the Forward Tracker for the Forward Spectrometer of the PANDA experiment is described. The tracker consists of 6 tracking stations, each comprising 4 planar double layers of straw tube ...detectors, and has a total material budget of only 2% X0. The straws are made self-supporting by a 1 bar over-pressure of the working gas mixture (Ar/CO2). This allows to use lightweight and compact rectangular support frames for the double layers and to split the frames into pairs of C-shaped half-frames for an easier installation on the beam line.
This dissertation consists of four parts that revolve around structured stochastic uncertainty and optimal control/estimation theory. In the first part, we consider the continuous-time setting of ...linear time-invariant (LTI) systems in feedback with multiplicative stochastic uncertainties. The objective is to characterize the conditions of Mean-Square Stability (MSS) using a purely input-output approach. This approach leads to uncovering new tools such as stochastic block diagrams. Various stochastic interpretations are considered, such as Itō and Stratonovich, and block diagram conversion schemes between different interpretations are devised. The MSS conditions are given in terms of the spectral radius of a matrix operator that takes different forms when different stochastic interpretations are considered. The second part applies the developed theory to analyze the mean-square stability and performance of stochastic cochlear models. The analysis is carried out for a generalized class of biomechanical models of the cochlea, that is formulated as a stochastic spatially distributed system, by allowing stochastic spatio-temporal perturbations within the cochlear amplifier. The simulation-free analysis explains the underlying mechanisms that give rise to cochlear instabilities such as spontaneous otoacoustic emissions and/or tinnitus. Furthermore, nonlinear stochastic simulations are carried out to validate the predictions of the theoretical analysis. The third part revisits the development of numerical methods to solve optimal control problems using a function-space approach. This approach has the advantage of unifying the framework upon which the various (existing) numerical methods are based on. In fact, this approach motivates the definition of various system and projection operators that make the derivations conceptually transparent. Furthermore, the function-space approach builds useful geometric intuitions that inspire the development of new projection-based methods. In the last part, we propose a methodology of optimal path design for sensors through a distributed environment. We consider time-limited scenarios where the sensors can only make a small number of measurements, but where some portion of a physics-based model is available for the field of interest (such as temperature). We consider both point-wise and tomographic sensors. The main idea is to recast the sensor path planning problem as a deterministic optimal control problem to minimize metrics related to the optimal estimation error covariance.
This thesis touches upon several topics in cochlear modeling. Throughout the literature, mathematical models of the cochlea vary according to the degree of biological realism to be incorporated. This ...thesis casts the cochlear model as a continuous space-time dynamical system using operator language. This framework encompasses a wider class of cochlear models and makes the dynamics more transparent and easier to analyze before applying any numerical method to discretize space. In fact, several numerical methods are investigated to study the computational efficiency of the finite dimensional realizations in space. Furthermore, we study the effects of the active gain perturbations on the stability of the linearized dynamics. The stability analysis is used to explain possible mechanisms underlying spontaneous otoacoustic emissions and tinnitus. Dynamic Mode Decomposition (DMD) is introduced as a useful tool to analyze the response of nonlinear cochlear models. Cochlear response features are illustrated using DMD which has the advantage of explicitly revealing the spatial modes of vibrations occurring in the Basilar Membrane (BM). Finally, we address the dynamic estimation problem of BM vibrations using Extended Kalman Filters (EKF). Due to the limitations of noninvasive sensing schemes, such algorithms are inevitable to estimate the dynamic behavior of a living cochlea.
We previously reported the benefit of lomustine addition to conventional chemotherapy in older acute myeloid leukemias with nonadverse chromosomal aberrations in the LAM-SA 2007 randomized clinical ...trial (NCT00590837). A molecular analysis of 52 genes performed in 330 patients included in this trial, 163 patients being treated with lomustine in combination with idarubicin and cytarabine and 167 without lomustine, identified 1088 mutations with an average of 3.3 mutations per patient. NPM1, FLT3, and DNMT3A were the most frequently mutated genes. A putative therapeutic target was identified in 178 patients (54%). Among five molecular classifications analyzed, the ELN2017 risk classification has the stronger association with the clinical evolution. Patients not treated with lomustine have an expected survival prognosis in agreement with this classification regarding the overall and event-free survivals. In strong contrast, lomustine erased the ELN2017 classification prognosis. The benefit of lomustine in nonadverse chromosomal aberrations was restricted to patients with RUNX1, ASXL1, TP53, and FLT3-ITD
/NPM1
mutations in contrast to the intermediate and favorable ELN2017 patients. This post-hoc analysis identified a subgroup of fit elderly AML patients with intermediate cytogenetics and molecular markers who may benefit from lomustine addition to intensive chemotherapy.
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