Concentric Tube Research Articles

Autonomous Steering of Concentric Tube Robots via Nonlinear Model Predictive Control

This article presents a model predictive controller (MPC) developed for the autonomous steering of concentric tube robots (CTRs). State-of-the-art CTR control relies on differential kinematics developed by local linearization of the CTRs mechanics model and cannot explicitly handle constraints on robot's joint limits or unstable configurations commonly known as snapping points. The proposed nonlinear MPC explicitly considers constraints on the robot configuration space (i.e., joint limits) and the robot's workspace (i.e., mixed boundary conditions on robot curvature). Additionally, the MPC calculates control decisions by optimizing the model-based predictions of future robot configurations. This way, it avoids configurations it cannot recover from, i.e., joint limits, singular configurations, and snapping. The proposed controller is evaluated via simulations and experimental studies with a variety of trajectories of increasing complexity. Simulation results demonstrate the capability of MPC to avoid singularities while satisfying robot mechanical constraints. Experimental results demonstrate that our solution enables following of trajectories unattainable by state-of-the-art controllers with mean error corresponding to $1\%$ of robot arclength.

Impingement of a counter-rotating vortex pair on a wavy wall

In this paper, we investigate the impingement of a two-dimensional (2-D) vortex pair translating downwards onto a horizontal wall with a wavy surface. A principal purpose is to compare the vortex dynamics with the complementary case of a wavy vortex pair (deformed by the long-wavelength Crow instability) impinging onto a flat surface. The simpler case of a 2-D vortex pair descending onto a flat horizontal ground plane leads to the well known ‘rebound’ effect, wherein the primary vortex pair approaches the wall but subsequently advects vertically upwards, due to the induced velocity of secondary vorticity. In contrast, a wavy vortex pair descending onto a flat plane leads to ‘rebounding’ vorticity in the form of vortex rings. A descending 2-D vortex pair, impinging on a wavy wall, also generates ‘rebounding’ vortex rings. In this case, we observe that the vortex pair interacts first with the ‘hills’ of the wavy wall before the ‘valleys’. The resulting secondary vorticity rolls up into a concentrated vortex tube, ultimately forming a vortex loop along each valley. Each vortex loop pinches off to form a vortex ring, which advects upwards. Surprisingly, these rebounding vortex rings evolve without the strong axial flows fundamental to the wavy vortex case. The present research is relevant to wing tip trailing vortices interacting with a non-uniform ground plane. A non-flat wall is shown to accelerate the decay of the primary vortex pair. Such a passive, ground-based method to diminish the wake vortex hazard close to the ground is consistent with Stephan et al. (J. Aircraft, vol. 50 (4), 2013a, pp. 1250–1260; CEAS Aeronaut. J., vol. 5 (2), 2013b, pp. 109–125).

Behaviour of restrained concrete filled square double-skin and double-tube hollow columns in case of fire

This paper presents the results of an experimental investigation on the fire behaviour of restrained composite columns made with square concrete filled double-skin and double-tube hollow sections. In the fire resistance tests the columns have been tested for different parameters that may influence their behavior, as for example the type of cross-section, the concrete filling of the tubes (ordinary, high-strength and light-weight concrete), the load level and the stiffness of the surrounding structure to the testing columns. These columns had two concentric steel tubes, where the inner one had approximately half the side of the outer one. The double-tube columns had both tubes filled with concrete and the double-skin ones had only concrete between tubes. As major conclusions, it was observed that the load level had a small influence on the reduction of the critical times but some influence on the reduction of the ultimate collapse times of the tested columns. The stiffness showed an insignificant influence on the critical time but again a higher influence on the ultimate collapse time of the columns being those smaller for the higher stiffness values. The concrete infill showed some influence, presenting the columns with high-strength concrete in the inner tube higher ultimate collapse times than those with ordinary concrete. The use of light-weight concrete between tubes did not show advantages when comparing with the ordinary concrete. The double-tube columns presented in general advantages over the double-skin columns being the ultimate collapse times of the first higher than those of the second.

Analogous Diamondene Nanotube Structure Prediction Based on Molecular Dynamics and First-Principle Calculations.

A concentric twin tube (CTT) can be built by placing a carbon nanotube (CNT) in another identical CNT. Different from diamondene nanotubes, a stable CTT has no inter-shell covalent bond. As a prestressed double-walled nanotube, CTT has a lower structural stability at a finite temperature. According to the molecular dynamics and first-principle calculations, (a) CTTs have three types of relaxed configurations. In a type III CTT, the inner tube buckles to produce a V-shaped cross-section, and the outer tube may be convex or concave. (b) The minimal radii of relaxed zigzag and armchair CTTs with concave outer tubes were found. (c) After relaxation, the circumferences and areas of the two tubes in a type III CTT are different from those of the corresponding ideal CNT. The area change rate (A-CR) and circumference change rate (C-CR) of the outer tube are the first-order Gaussian function of the radius of the ideal CNT (which forms the CTT), and tends to be 73.3% of A-CR or 95.3% of C-CR, respectively. For the inner tube of a CTT, the A-CR is between 29.3% and 37.0%, and the C-CR is close to 95.8%. (d) The temperature slightly influences the findings given above.

Evaluation and optimization of melting performance of latent thermal s

In the present work, the phase change materials (PCMs) melting characteristics with partial metal foam filled in horizontal concentric tube heat accumulator are numerically investigated. The thermal response of PCMs is improved by using porous media. By comparing the properties of different porous configurations, the position of porous inserts is optimized. According to the thermal reservoir rate density, the optimal arrangement of porous embeds is determined. The results show that this method can effectively investigate the melting performance of materials, such as complete melting time, thermal storage capacity and total materials mass. The results indicate that the best melting performance of PCMs structure is 18 radial porous fins and the optimal length of radial porous fins is the ring width. Comparing with the no porous media case, the thermal storage rate density has increased over 2.6 times obviously. It's worth noting that compared with the full porous media case, the comprehensive performance is reduced by 46.7%, while the porous material is reduced by 80%. The optimized scheme has better heat storage performance and lower cost.

Novel, Flexible, and Ultrathin Pressure Feedback Sensor for Miniaturized Intraventricular Neurosurgery Robotic Tools

Remote-controlled minimally invasive neuroendoscopic robotic surgical tools can be miniaturized to a size of less than 2 mm while maintaining their dexterity and force required to perform operations in brain without an open-skull surgery. However, these platforms lack haptic information to be received by the surgeons, leading to loss of control over tissue and causing unexpected slippage and trauma. This study presents the design of a small and highly sensitive material-based sensor being integrated to the tool shaft, known as the concentric tube manipulators, to achieve static and quasi-static force sensing and feedback. Through a nine-element design and contact mechanics modeling, the sensor system can generate real-time polar visual pressure profile displays. Optimizations are performed on the subcomponents of the sensor design including microstructures and electrodes to improve detection threshold with reduced hysteresis. The finalized design can sense a force from as low as 14.8 ± 1.22 mN to 1 N with excellent proportionality between the acquired signal and force applied while retaining its flexibility and sterilizability. The sensor will also enhance more intuitive force feedback for surgeons to use the dexterous neurosurgical tool, ensuring safety and quality of operations for minimally invasive surgeries for brain tumor and epilepsy practice.

VaLeNS: Design of a Novel Variable Length Nested Soft Arm

Over the last decade, soft continuum arms (SCAs) have successfully demonstrated the compliance and dexterity needed to operate in unstructured environments and handle fragile objects. However, their inherent soft compliance limits their performance in situations where stiffness and force transfer is required. In this letter, we present a compact design architecture, which is a hybrid between soft arms and rigid links known as Variable Length Nested Soft (VaLeNS) arm. The design architecture involves a novel SCA nested inside a concentric rigid tube. The SCA can undergo a combination of spatial bending (B) and bidirectional axial twist (R2), and can extrude out or retract back into the rigid tube with varying length. The resulting configuration is shown to modulate stiffness up to a factor of ten and exhibits enhanced workspace and dexterity. Furthermore, the VaLeNS arm mounted on a rigid robotic platform allows for bifurcation of the overall workspace into rigid and soft, and can achieve high reachability in constrained environments. The letter demonstrates the effectiveness of the VaLeNS arm system in manipulation tasks that require both the rigid and soft attributes. This design architecture is deemed useful in agricultural applications and in physical human robot interaction.

Numerical Analisis by RNG k-ε Turbulent Model of a Concentric Tube Heat Exchanger with Coiled Wire Turbulator

Bu çalışmada, eşmerkezli iç içe borulu bir ısı değiştiricisinin boyutlarının azaltılması ile ısı transferinin iyileştirilmesi ve sürtünme özelliklerinin belirlenmesi amacıyla yay tipi türbülatör kullanarak, RNG k-ε modeli ile sayısal analizler yapılmıştır. Çalışmalar Reynolds (Re) sayısının 3000 ila 18000 aralığında yapılmıştır. Sonlu Hacimler Metoduna dayalı ANSYS-fluent adlı bir Hesaplamalı Akışkanlar Dinamiği (HAD) kodu ile sayısal simülasyonlar yapılmıştır. Sayısal analizlerde, Model ➀ (RNG-Standard wall function), Model ➁ (RNG-Non-Equilibrium wall function) ve Model ➂ (RNG-Enhanced wall treatment) üç temel türbülans modelleri kullanılmıştır. Bu nedenle, deneysel ve sayısal analizlerle RNG k-ε modelinin üç temel türbülans modelleri arasında karşılaştırma yapılarak, en iyi sonucu Model ➀ türbülans modeli vermiştir.

Identification of the process windows of inclined rotating fixed-bed reactors with concentric tube – A hydrodynamic analysis

The inclined rotating fixed-bed reactor with inner tube is a promising process intensification concept for gas-limited reactions. In order to take full advantage of the reactor concept the installation of an inner concentric displacement tube is proposed to support the wetting intermittency of the whole fixed-bed at stratified flow with different liquid filling levels. The liquid phase distribution is characterized with a capacitance-based wire-mesh sensor, which is designed to cope with organic liquid, porous catalyst packings and reactor rotation. The effects of operating conditions and design parameters on flow stratification, liquid filling level and specific pressure drop are analysed to identify the process windows. Superficial liquid velocity and inclination angle were found to significantly influence the liquid filling level, while rotational velocity and superficial gas velocity have minor effects. Besides, reducing the particle diameter is an effective measure to manipulate the stratification patterns and the associated pressure drop.

Influence of the Water Nature on the Two-phase Flow in an Air-lift Column

The aim of this study is to determine the phase indicator functions of a two-phase flow in an air-lift vacuum column. The outcome of this study is to master the hydrodynamics in a vertical column when determining the size, the velocities of the bubbles and the void rate then the gas-liquid interphase. The functions are the vacuum rate, the interface speed and bubble size, the flow rate and the speed of the liquid phase. The vacuum lift air column that is the subject of this study is based on the principle of air lift and flotation, all under vacuum. In its operation, the column combines hydraulic pumping, solute transfer and particle phase separation functions, which has the particularity of minimizing energy costs. The process of air-lift columns under the vacuum is still at the development stage and the experimental study of its hydrodynamics is one of the determining axes in the course of the exploration with a assessment to optimizing its design and functioning. The experiments were carried out on a vertical column composed of two concentric plexiglas tubes connected to a water recirculation tank and to a vacuum pump. For all experiments performed, demineralized water and salt water are used and the flow rate is measured using a flow meter. The experimental analysis is done using two-phase instrumentation consisting of a bi-probe and the use of experimental techniques has enabled a better understanding of the hydrodynamics of the two-phase flow.

Comparative Study for Thermal and Fluid Flow Peculiarities in Cascading Spiral Inner Tube Heat Exchanger with or without Diverse Inserts over Spiral Tube

Present work deals with experimental analysis in which various observation takes place related to performance characteristics like HTR, effectiveness and fluid flow peculiarities like Nu, Re, f, NTU, TPF etc in a cascaded spiral concentric tube type heat exchanger consisting of a GI shell and a cascaded spiral copper inner tube having conical shape inserts, hemispherical insert and plane profile unit for parallel flow. Five spiral cascades with three turns in each are used for the inner side copper tube unit. Water enters at 304°K from the innermost turn along the cascaded spiral tube, and leaves at the outermost turn. The hot fluid inlet for heat exchanger is from bottom of one end of the shell at 333°K, flowing radically across the cascades, and then leaving the exchanger from the top of another end. This paper based on comparative experimental study of the behavior of such system for parallel flow with different shape of inserts, and then compared with the simulation results for same. In this analysis comparative approach is considered for evaluating optimum fluid flow and thermal properties on the basis of geometrical parameters. The results predicted that out of three profiles of insert, plain, conical and half cut elliptical profile, which located over inner copper tube of exchanger, half cut elliptical profile insert shows best results on fluid flow and thermal peculiarities, for mass flow rate range 0.012 to 0.049 Kg/s and Reynolds number range 4236 to 18540, heat transfer rate varies from 1128.06 to 2374.77, Nusselt number varies from 75.15 to 144.05, Friction factor varies from 0.00376 to 0.00305 and effectiveness varies from 0.77 to 0.40 and Number of transfer unit varies from 2.08 to 0.68 for half cut elliptical profile.

Mechatronic Design of a Two-Arm Concentric Tube Robot System for Rigid Neuroendoscopy.

Open surgical approaches are still often employed in neurosurgery, despite the availability of neuroendoscopic approaches that reduce invasiveness. The challenge of maneuvering instruments at the tip of the endoscope makes neuroendoscopy demanding for the physician. The only way to aim tools passed through endoscope ports is to tilt the entire endoscope; but, tilting compresses brain tissue through which the endoscope passes and can damage it. Concentric tube robots can provide necessary dexterity without endoscope tilting, while passing through existing ports in the endoscope and carrying surgical tools in their inner lumen. In this paper we describe the mechatronic design of a new concentric tube robot that can deploy two concentric tube manipulators through a standard neuroendoscope. The robot uses a compact differential drive and features embedded motor control electronics and redundant position sensors for safety. In addition to the mechatronic design of this system, this paper contributes experimental validation in the context of colloid cyst removal, comparing our new robotic system to standard manual endoscopy in a brain phantom. The robotic approach essentially eliminated endoscope tilt during the procedure (17.09° for the manual approach vs. 1.16° for the robotic system). The robotic system also enables a single surgeon to perform the procedure - typically in a manual approach one surgeon aims the endoscope and another operates the tools delivered through its ports.

Learning the Complete Shape of Concentric Tube Robots.

Concentric tube robots, composed of nested pre-curved tubes, have the potential to perform minimally invasive surgery at difficult-to-reach sites in the human body. In order to plan motions that safely perform surgeries in constrained spaces that require avoiding sensitive structures, the ability to accurately estimate the entire shape of the robot is needed. Many state-of-the-art physics-based shape models are unable to account for complex physical phenomena and subsequently are less accurate than is required for safe surgery. In this work, we present a learned model that can estimate the entire shape of a concentric tube robot. The learned model is based on a deep neural network that is trained using a mixture of simulated and physical data. We evaluate multiple network architectures and demonstrate the model's ability to compute the full shape of a concentric tube robot with high accuracy.

Performance ratings of concentric and lateral (taped, brazed and extruded) capillary tube suction line heat exchangers running with isobutane

This paper is aimed at studying the thermal performance of counterflow capillary tube suction line heat exchangers (CTSLHX) commonly used in household refrigerating appliances. Conventional and novel CTSLHX configurations, with different capillary tube and suction line geometries and made of different materials, were evaluated by means of a purpose-built testing facility designed to provide a strict control of the thermodynamic conditions of the refrigerant at the CTSLHX inlet ports. In total, 220 tests were performed with isobutane under typical operating conditions of household applications. The results pointed out that the extruded lateral configuration presented the highest thermal performance in terms of temperature effectiveness, followed by the lateral-brazed, the concentric, and the lateral-taped, respectively. Furthermore, it was also observed that the thermal performance of the latter is more affected by the tape tightness than that by its thermal conductivity.

Heat transfer enhancement in concentric tube heat exchanger with tangential injection and twisted tape inserts

Heat exchanger has many engineering applications such as air conditioning, chemical reactor and refrigeration systems, etc. The performance of this industries mainly depends on the performance of heat exchanger. So, to increase the performance of heat exchanger many techniques have been investigated on enhancement of heat transfer rate and decrease the size and cost of the heat exchangers. In most of applications and key areas like power plants, process & chemical industries uses surface enhancement methods. Present work mainly emphasis on the both passive and active methods of heat transfer enhancement. In this work, to enhance the heat transfer rate with the help of twisted tape insert in passive method in which aluminium twisted tapes are used. In the active method fluid is injected in annulus space to generate turbulence through tangential injectors. There are six injectors are used to generate turbulence. Water is used as a working fluid in both types of heat exchanger. From the experiment it shows that, as Reynolds number increases heat transfer coefficient also increases

Mathematical Modelling of a Three Tube Heat Exchanger for Hot Two Pass and Cold one Pass Flow (Both from Front end) Arrangement

A three tube heat exchanger is a special type of H.E having three concentric tubes with multi-pass arrangements for one of the fluid. This is a mixed type of heat exchanger which is neither pure counter flow nor pure parallel flow. Simultaneously it gives both parallel and counter flow arrangements for any flow directions of two fluids. This is also a type of multi-pass and a compact type of heat exchanger. The work involved in this investigation is to analyze the performance of 3-tube heat exchanger by formulating differential equations using energy balance in differential form. These differential equations are solved by using a numerical technique viz., by 4th order Runge-Kutta method with boundary conditions. Figure numbers 5 to 8 shows the temperature plots along the length of the three tube heat exchanger in dimensionless form. The plots are obtained for four different values of F, which is a capacity rate ratio. The temperature profile nature is as expected for different arrangements resulting from entry of hot and cold fluids. By using this temperature plots effectiveness and NTU are determined for different capacity rate ratios. The results are concluded at the end.

Adaptive boundary observer design for linear hyperbolic systems; Application to estimation in heat exchangers

In this work, we consider the estimation of temperature along the pipes of concentric heat exchanger tubes in which CO2 is the working fluid. The transport phenomenon is modeled using (2x2) linear hyperbolic partial differential equations, with one rightward equation for the hot flow and one leftward equation for the cold flow. Both flows exchange energy through the wall interface, which physically induces a coupling between the two dynamics. Our objective is to estimate the temperature distribution along the flows from measurements at the tubes boundaries only. In this framework, we propose an adaptive boundary observer that can estimate not only the full state of the system, but also unknown in-domain parameters. The design is based on transforming the error system via a finite-dimensional backstepping-like transformation into a desired filter-based system, for which standard backstepping observer techniques and adaptation laws can be used. The theoretical results are evaluated against the temperature measurements taken from a CO2 refrigeration apparatus built at CERN, Switzerland.

SLAM-Based Follow-the-Leader Deployment of Concentric Tube Robots

This paper deals with an original combination of navigation by simultaneous localization and mapping (SLAM) and follow-the-leader (FTL) deployment for the control of concentric tube robots (CTRs). The objective is to make possible the automatic navigation of such continuum robots within an anatomical structure, by simultaneously managing both collision avoidance and map updating of the environment, i.e. , of the surrounding anatomical structures. Indeed, CTRs designed to achieve a FTL deployment to date were deployed on path identified during a planning task. In this work, this limitation is overcome by embedding, in the control scheme, an online trajectory estimation, therefore allowing an autonomous deployment of CTRs with an approximate FTL behavior. The proposed hybrid control law integrates a stability criterion to ensure at the same time CTR stability during deployment, required for a FTL deployment. The interest of the approach is demonstrated through simulation using realistic anatomical data and experiments, with a 3 degrees-of-freedom CTR.

Acoustic Behavior Prediction and Analysis of Resonators in the Presence of Low Mach Number Flow

The frequency-domain linearized Navier–Stokes equations (LNSEs) are used to describe the sound field of Helmholtz resonators and concentric perforated tube resonators in the presence of low Mach number flow. The numerical procedure of LNSEs method is performed in three steps, computational fluid dynamics (CFD) calculation, data transfer and acoustics calculation. The transmission loss predictions of the resonators exhibit good agreement with measurements published in the literature. The results show that the low Mach number flow shifts the resonance frequencies of resonators and changes the acoustic attenuation behavior, which may be attributed to the change of acoustic impedance of the opening and orifices. In order to weaken the effect of flow on the resonance frequency, the modified configurations of resonators are proposed by using the conical tubes to reduce the flow velocity passing the opening and orifices. Numerical results demonstrated that the influence of flow velocity on the resonance frequency of the modified resonators is less sensitive than the original configurations.

Numerical study on a novel parabolic trough solar receiver-reactor and a new control strategy for continuous and efficient hydrogen production

In this paper, a novel parabolic trough solar receiver-reactor is proposed for continuous and efficient hydrogen production via the methanol-steam reforming reaction. With a concentric through-type tube introduced for thermal energy storage, this novel system canbe effectively applied for better solar thermochemical energy conversion and management. The proposed novel system and the corresponding original system, as well as direct/indirect control strategies and parameter optimizations, were then fully investigated. This was numerically carried out by a proposed three-dimensional comprehensive model based on the finite volume method, combined with the Monte Carlo ray-tracing method and the comprehensive kinetic model of the methanol-steam reforming reaction. It is revealed that the proposed novel system has much better comprehensive characteristics and performance than that of the corresponding original system. These previously incompatible requirements, both an affordable temperature rise per unitreceiver-reactor length and a nearly complete methanol conversion rate, can be achieved simultaneously in this novel system. It is also found that the previously sensitive process of the methanol-steam reforming reaction can be controlled separately or jointly, by adjusting more control variables introduced in the novel system. Moreover, this novel system could also have great potential to be improved, by tuning corresponding key operating parameters such as the inlet temperature, the flowmodel and the concentric tube geometry. The energy distribution of the collected solar radiation and working temperature characteristics could also be further controlled or optimized. It could provide significant guidance for similar solar-driven thermochemical applications for continuous and efficient hydrogen production.