Trapezoidal Profile Research Articles

Integrated Design Method of Linear PM Machines Considering System Specifications

The system specifications should be considered in the practical design of linear machines, albeit mostly neglected in the previous studies. The main objective of this article is to propose a systematic design method of a coreless-type permanent magnet linear synchronous machine (PMLSM), satisfying all the constraints resulting from the system specifications. Based on the trapezoidal motion profile, an electromagnetic design model is developed by utilizing the 2-D field solutions and energy conversion principle. The thermal effects are incorporated into the design model by measuring the hot-spot temperature of the static winding coil, thereby setting the upper limits of current density. The differential evolution (DE) is then applied to the design model to search for optimal solutions without violating any of the constraints. As a result, the proposed model combined with DE provides the Pareto-optimal front belonging to the feasible regions where all system specifications (e.g., acceleration profile, maximum speed, maximum allowable temperature, load mass, and supply voltage) are satisfied. Finally, the validity of the design model is verified by both the finite element (FE) and experimental results.

Performance analysis of optomechanical‐based microcantilever sensor with various geometrical shapes

AbstractThis paper presents a performance analysis of different microcantilever shapes integrated with the optical MEMS system in different fluid mediums. Microcantilevers such as rectangular, trapezoidal, and triangle profile are coupled with optical sensing layers. Here, the concept of integration of optical sensing layer with different shapes of microcantilever is novel. The cantilever is designed and developed in CAD tools. Numerical analysis of different shapes of microcantilever was carried out with the help of Ansys Workbench. Optimal design of the regular microcantilever is considered during the analysis. The pressure is applied to the free end of the cantilever in the range of 100 to 250 kPa. The complete photonic sensing layer is analyzed with the help of an finite difference time domain (FDTD) tool called MIT Electromagnetic Equation Propagation (MEEP). The transmission spectrum is obtained for each microcantilever model. The pressure‐induced refractive index is calculated for the equivalent maximum stress generated. The result shows that a remarkable Q factor was obtained for rectangular, trapezoidal, and triangular profile microcantilevers with an optical system. Triangular and rectangular profiles have shown remarkable contribution over quality factor for air mediums such as 10 120, 1300, respectively. High pressure sensitivity of 1.92 nm/kPa was obtained for rectangular microcantilever in air. Least sensitivity of 0.16 nm/kPa was obtained for triangle microcantilever in the water medium. The proposed work successfully distinguishes various shapes of microcantilever in terms of sensitivity and Q factor. It is having tremendous application in sensing biofluids and in device miniaturization.

Thermal Performance Evaluation of Longitudinal Fins with Various Profiles Using Homotopy Perturbation Method

The thermal performance of longitudinal radiative–convective fins with rectangular, trapezoidal, and concave parabolic profiles was analyzed by the homotopy perturbation method (HPM). The governing equation of the problem was obtained by establishing the energy balance for a longitudinal element on the longitudinal radiative–convective fin. In addition, thermal conductivity, convective heat transfer coefficient, and surface emissivity were assumed to change with temperature. Given its nonlinear nature, the governing equation was solved relying on the HPM. Validating the results from this method with those of the differential transform method, a good agreement was achieved between the two. In parametric studies, the fins were compared in terms of heat transfer rate, effectiveness, and efficiency. Further, the effects of changes in thermal conductivity, emissivity, convection–conduction parameter, and the radiation–conduction parameter were also investigated on the fin performance. The results were suggestive of the potentials of HPM as a reliable tool for solving nonlinear equations such as the energy equation for radiative–convective fins without compromising accuracy or speed. Further, the concave parabolic fin was found to have a higher heat transfer rate, efficiency, and effectiveness than its rectangular and trapezoidal counterparts.

Energy and exergy analyses of LiBr/H2O absorption cooling system having recto-trapezoidal profile absorber plate

This paper develops a theoretical model for energy and exergy analyses of a solar-powered Lithium-water absorption refrigeration system using a recto-trapezoidal flat plate solar collector. The effect of collector fluid inlet temperature is to examine the overall performance of the solar collector and the vapour absorption system for a wide range of design variables. The parameters computed are energy and exergy efficiencies of the solar collector plate, coefficient of performance, cooling efficiency, exergy destruction rates, thermal exergy loss rates, irreversibility, and exergetic efficiency of the absorption refrigeration cycle. The simulation results indicate that there exists an optimum inlet temperature of collector fluid for the maximum system coefficient of performance and exergetic efficiency. When the cooling system runs at this temperature, the absorber plate volume attains a minimum value. Furthermore, the performance results are significantly better when a higher absorber plate thickness parameter is for the recto-trapezoidal profile. Finally, a comparative study analyzes the collector performance parameters of an absorber plate having rectangular, triangular, or trapezoidal profile by selecting their respective parameters of geometries. When an additional constraint imposes on the plate volume, it found that using a recto-trapezoidal profile instead of a rectangular profile saves at least 30% or more collector material, and also it may have better performance than a triangular or trapezoidal profile.

Рhysical simulation of erosion of bottom pits

The present paper is devoted to research of the erosion of large-scale sand pits in the water flow. The investigations were performed in the hydrodynamic flume with sandy bottom. To provide suitable conditions for sediment transport in the flume, the analysis of the factors leading to the motion of sediments was carried out in accordance with the Shields diagram. It was shown that the flow regime created in the laboratory channel promotes the development of natural bed forms such as ripples. Estimations of the velocity of movement of the ripples were obtained. The experiments with large sand pits on the flume bottom demonstrated that those disturb the balance of sediments and cause the reformatting of the water flow. To assess the influence of the pit configuration on the erosion process, two-dimensional triangular and trapezoidal pits were considered. It was found that the longitudinal profile of the triangular pit changes due to sediment deposition on its upper slope and erosion of the lower slope. The pit upper slope levels out and shifts forward due to the continuous flow of sediment in this region. The depth of the unevenness also decreases owing to deposition of the sediment directly on its bottom. Due to the blow of water jet to the pit lower slope, the zone of maximum erosion of the bottom surface is observed here. The bottom reformatting leads to the displacement of the pit downstream. Studies of the erosion of the trapezoidal pit have shown that its upper slope is first shifted toward the lower slope until the trapezoidal profile turns into a triangular one. The pit erosion causes also the deformation of natural forms of the channel bed and destabilization of sediment discharge. The analysis of the obtained data demonstrated that the reformation of channel bed is a durable process depending of the ratio of pit scales to the volume of sediment. The present study is useful for development of engineering solutions directed to reduction of risks caused by the interaction of sand quarries with hydraulic structures in rivers.

Optimization of beam profiles for improved piezoelectric energy harvesting efficiency

Piezoelectric cantilever beams are among the most popular vibration energy harvesting devices. Homogenization of the spatial distribution of axial strain along those beams increases harvesting efficiency. The general approach to minimize axial strain variation is to use triangular or trapezoidal width profiles. In this study, a width profile function that includes curved shapes is proposed and a finite element–based optimization scheme is constructed to maximize harvesting efficiency. A distribution parameter is defined for quantifying the strain uniformity. Optimization is performed for various tip mass values, using this parameter as the objective function. It is shown that curved beam profiles exhibit less variation in axial strain, compared to triangular and rectangular beams. Optimized shapes for minimal strain variation at resonance are determined. Experimental results also validate the findings of the optimization. At least 22% increase in strain uniformity is obtained with the optimized-shaped beam, compared to a triangular beam when no tip mass is used. The increase in strain uniformity becomes 29% when the tip mass is increased to 5 g. The results indicate the potential of employing beam-type piezoelectric energy harvesters with optimized width profiles.

Side NSM CFRP strips with different profiles for strengthening reinforced concrete beams

The efficiency of using side near-surface mounted (SNSM) carbon fiber reinforced polymer (CFRP) strips with a variable profile in strengthening reinforced concrete (RC) beams is studied. RC beams (150 × 250 × 1400 mm) were strengthened using straight, trapezoidal, and parabolic profiles of SNSM CFRP strips inserted within 25 and 35 mm of the beams' parallel side covers. The mechanical behavior of the beams is evaluated under a four-point loading test setup before the collected data is analyzed for mechanical response. This includes load-deflection diagrams and their characteristics, as well as strain in SNSM CFRP strips at the failure point. Cracking and failure modes were also monitored and characterized. The results show that strengthening RC beams with SNSM CFRP strips at variable profiles helps improve the overall mechanical performance, especially ultimate load capacity and toughness. Trapezoidal profiles of SNSM CFRP strips impart the best improvements to structural performance, followed by the parabolic profiles. Furthermore, inserting SNSM CFRP strips within the concrete side covers at the larger thickness had a limited impact on enhancing the structural performance. An analytical model for the prediction of the load capacity of the present strengthened beams is proposed and used to validate the experimentally obtained data.

FPGA-Based Architecture for Sensing Power Consumption on Parabolic and Trapezoidal Motion Profiles

The objective of this work is to design and implement a scalable Field-Programmable Gate Array (FPGA)-based motion control system for DC servo motors using a parabolic velocity profile for industrial applications. The implementation in this device allows the obtaining of a fast, flexible and low-cost system. The system is divided into control, communication and closed-loop coupling. The work also addresses a comparative analysis of the most used profiles, the trapezoidal and parabolic. The comparison is made considering the energy consumption of both profiles. As a consequence of the comparison made, the velocity profile can be selected to reduce production costs by saving energy and reducing wear on machinery. The discrete models of the velocity profiles are obtained through numerical methods that permit the control blocks to be implemented in an FPGA. To reduce maintenance costs and energy consumption in servo mechanisms, the derivation of the acceleration or jerk of the motor is shown. A Graphic User Interface (GUI) is presented, which allows monitoring the position, velocity and angular acceleration of the motor shaft. In addition, the developed interface supports modification of parameters of the final position and maximum velocity in the motor. The delivered current is compared, evaluating its decrease using a parabolic velocity profile. Finally, the experimental results are illustrated.

A fast processing method to perform transient analysis for vibration control

Transient vibration analyses of structures with complex shapes are performed by finite element (FE) methods. Transient vibration analyses take long processing times for the systems having large number of degrees of freedom. A method performing the transient analyses very fast using the Fast Fourier Transform (FFT) is introduced in this work, and it is applied to a curved manipulator. Various analyses are required to determine the input parameters for vibration control, and each analysis takes long FE solution times.In this work, an FFT method is developed where the samples of the impulse response of the system under study is obtained by the FE software ANSYS first. The samples of the transfer function are then obtained by FFT, and transient responses are found for various vibration control parameters by using FFT. Transient response results for the complex system considered in this study are obtained approximately in 1 s with FFT method, while it takes 36 h with ANSYS.A one degree of freedom system is considered to verify the results of FFT method. Newmark's numerical, ANSYS, and FFT method results are compared, and it is observed that the results are in good agreement. A curved non-uniform steel manipulator with a complex shape is considered after the verification. The samples of the impulse response of the manipulator is found by ANSYS. Then, FFT method is used to obtain transient responses. A trapezoidal velocity profile is considered to analyze the residual vibration. The effect of the deceleration time on the root-mean-square (rms) values of the residual vibration is studied experimentally and using FFT method. It is observed that the results are in good agreement, and it is concluded that FFT method introduced in this study is very effective to study transient vibration problems in complex systems.

Robotic Deep Rolling With Iterative Learning Motion and Force Control

Large industrial robots offer an attractive option for deep rolling in terms of cost and flexibility. These robots are typically designed for fast and precise motion, but may be commanded to perform force control by adjusting the position setpoint based on the measurements from a wrist-mounted force/torque sensor. Contact force during deep rolling may be as high as 2000 N. The force control performance is affected by robot dynamics, robot joint servo controllers, and motion-induced inertial force. In this letter, we compare three deep rolling force control strategies: position-based rolling with open-loop force control, impedance control, and gradient-based iterative learning control (ILC). Open loop force control is easy to implement but does not correct for any force deviation. Impedance control uses force feedback, but does not track well non-constant force profiles. The ILC augments the impedance control by updating the commanded motion and force profiles based on the motion and force error trajectories in the previous iteration. The update is based on the gradient of the motion and force trajectories with respect to the commanded motion and force. We show that this gradient may be generated experimentally without the need of an explicit model. This is possible because the mapping from the commanded joint motion to the actual joint motion is nearly identical for all joints in industrial robots. We have evaluated the approach on the physical testbed using an ABB robot and demonstrated the convergence of the ILC scheme. The final ILC tracking performance of a trapezoidal force profile improves by over 70% in terms of the RMS error compared with the impedance controller.

Performance enhancement of ultrathin graded Cu(InGa)Se2 solar cells through modification of the basic structure and adding antireflective layers

Traditional Cu ( InGa ) Se2 (CIGS) solar cells consist of an Mo bottom contact, p-type CIGS absorber layer, n-type CdS buffer layer, and ZnO window layer including a very thin intrinsic ZnO layer topped with an Al-doped ZnO transparent conducting oxide layer that was simulated by an Silvaco technology computer aided design simulator. The thickness of the layers and other parameters were limited to the values reported in the literature. The simulator was examined to affirm its functionality, and a step-by-step method was applied to optimize the baseline structure. The first modification was the substitution of the conventional CdS buffer layer with a nontoxic n-type ZnO buffer layer. The substituted ZnO buffer layer showed an effective band alignment and led to a remarkable improvement in cell performance. The second modification was the inclusion of different antireflective coatings, such as Al2O3, MgO, SnO2, and CdO, to enhance light trapping. Among them, CdO caused the highest efficiency. The optimization process was followed by replacing a very-thin (750 nm) CIGS layer containing three sublayers with dual-graded Ga contents. A trapezoidal gradient profile was tested and showed a significantly increased internal electric field, which assisted in raising the efficiency of the device. The last simulation concluded that the efficiency of a CIGS solar cell was 19.21% and the efficiency related to the baseline structure was enhanced by 36.24%.

Trapezoidal Well Structures for Improving the Light Efficiency in Algainp-Based LEDs

(AlxGa1-x)0.5In0.5P-based LEDs have a small conduction band offset that limits their electron confining potential.1 This weaker electron confinement subsequently leads to electron heterobarrier leakage in AlGaInP heterostructure LEDs, especially in short-wavelength devices, where a fraction of the electrons injected into the active region have a sufficient thermal energy to escape into the cladding layer. To overcome this problem, trapezoidal well structures are introduced in the active region in order to prevent carrier overflow and to gain a higher light output power (Pout). In the field of AlGaInP-based LEDs that emit a short peak wavelength at around 590 nm, however, the effects of the trapezoidal well profile in the active region on LED performance has yet to be systematically studied.In this study, we investigate the behaviors of optical and electrical characteristics according to their trapezoidal well profile in the active region through the analysis of optical behaviors and device performances.To investigate the optical behaviors according to the trapezoidal well shape, the sloped barrier (SB) is inserted between well and flat barrier (FB) and the thickness of SB (dSB) is changed from 2.5 nm to 10 nm. And, the FB thickness is adjusted from 15 to 0 nm to maintain the total barrier thickness 20 nm. The schematic diagram of MQW structures of a trapezoidal-shaped well is depicted in Fig. 1(b).Fig. 2 shows the device performances having different sloped barrier profiles in the MQW LED structures. As the current is increased to 600 mA, the current-voltage (I-V) curves show different behavior according to the SB thickness. In Fig. 1(a) inset, the forward bias voltage at 350 mA decreases from 2.86 V to 2.62 V with an increase in the thickness of SB from 0 to 10 nm. Fig. 1(b) then shows the light output power (Pout)-current characteristics of LEDs on the dSB and the normalized efficacy of the same LEDs at 350 mA operating current is shown in the figure inset. As the dSB between the well and the barrier is increased from 0 to 5.0 nm, the normalized efficacy improves from 1.0 to 1.16 and the maximum Pout increases from 400 to 500 mA, though at a further increase of the dSB to 10 nm, the normalized efficacy degrades to 0.98.AcknowledgmentThis work was supported by a Korea Research Foundation Grant from the super-saving-LED convergence development project (20004475, Development of high power red micro light-emitting diode for full color RGB) funded by the Ministry of Trade, Industry and Energy, Korea.

Effect of the Focusing of a SEM Probe on the Formation of Relief Structure Images

The effect of focusing a scanning electron microscope probe on the formation of relief structure images is studied in secondary slow electron and backscattering electron collection modes. Protrusions and grooves in silicon with a trapezoidal profile and large inclination angles of lateral walls are used in the experiments. In the defocusing process the probe diameter is increased up to 8 times. It is shown that the image obtained in the secondary slow electron mode greatly varies, while the image acquired in the backscattering electron mode remains unchanged within the noise. The areas of signals strongly affected by the SEM probe are specified as well. According to the results, SEM focusing is necessary for only the secondary slow electron collection mode.

Design Optimization for the Thin-Walled Joint Thread of a Coring Tool Used for Deep Boreholes

Threaded joints are key components of core drilling tools. Currently, core drilling tools generally adopt the thread structure designed by the API Spec 7-1 standard. However, fractures easily occur in this thread structure due to high stress concentrations, resulting in downhole accidents. In this paper, according to the needs of large-diameter core drilling, a core barrel joint was designed with an outer diameter of Φ135 mm and a trapezoidal thread profile. Subsequently, a three-dimensional simulation model of the joint was established. The influence of the external load, connection state and thread structure on the stress distribution in the joint was analyzed through simulations, from which the optimal thread structure was determined. Finally, a connection test was carried out on the threaded joint. The stress distribution in the joint thread was indirectly studied by analyzing gas leaks (i.e., the sealing effect) under axial tension. According to the test data and the simulation results, the final joint thread structure was optimized, which lays a good foundation for the design of a core barrel.

Thermal-Controlled Frictional Behaviour of Nanopatterned Self-assembled Monolayers as Triboactive Surfaces

Friction is an important limitation of energy efficiency performances of MEMS/NEMS but is, in the same time, a great opportunity for harvesting energy by designing optimized tribo-electric nano-Generators (TENG). Thus, frictional behaviour can be accurately controlled in real time by using thermally sensitive periodic patterned self-assembled monolayers of n-octadecyltrichlorosilane (OTS) grafted on MEMS surfaces. Nanopatterns are currently used in order to limit the wear rate without modifying the frictional behaviour. In this work, patterns have been created by micro-contact printing ($$\upmu \hbox {CP}$$) using a polydimethylsiloxane (PDMS) stamp displaying a trapezoidal profile. Hence, pattern periodicity can be continuously changed—and then optimized from discontinuous to pseudo-continuous—by applying a controlled normal load on the soft PDMS stamp. A multiscale tribological study has been carried out on these nanopatterns by using both single-asperity and multi-asperity nanotribometers. Lateral force microscopy (LFM) provides the individual frictional behaviour of each pattern’s component, whereas the multi-asperity nanotribometer rather gives the emerging frictional behaviour induced by the patterning according to temperature. As a macroscopic crucial parameter while designing TENG’s devices, this macroscopic behaviour has to be carefully optimized for each practical applications at the molecular scale. Thus, the microscale frictional behaviour can be precisely optimized by the pattern’s periodicity, whereas the macroscopic one can be accurately controlled with values of friction coefficient ranging from 0.12 to 0.04 by varying the contact temperature. In addition, any inertial effects observed in the thermal-controlled frictional behaviour of nanopatterns can be drastically reduced using infra-red emission as thermal source.

A new design of induced-charge electrokinetic micromixer with corrugated walls and conductive plate installation

Abstract In this paper, a new design of induced-charge electrokinetic micromixer is suggested. The corrugated walls with different profiles, including rectangular, trapezoidal, sinusoidal, and triangular profiles, are used to disrupt the flow and enhance the mixing efficiency. Moreover, the conductive plate is installed inside the micromixer to induce the vortices and improve the mixing process inside the micromixer. The effects of different parameters on the mixing efficiency of the micromixer are investigated. The mixing efficiency enhances by usage of corrugated walls as compared with the straight one. There are about 59.86%, 59.59%, 48.56%, and 47.81% enhancements in the mixing efficiency by using rectangular, trapezoidal, triangular, and sinusoidal micromixers, respectively instead of straight micromixer. The mixing efficiency enhances more than 200% by placing a conductive plate inside the micromixers. The mixing efficiencies in the range of 85.45% to 97.53% can be achieved by placing a conductive plate near the inlet section of the micromixers. The mixing efficiency improves up to 9% inside the micromixer equipped with the conductive plate by increasing the electric field intensity in the range of 20 to 40 V/cm, while, it reduces about 0.38% as the electric field intensity increases in the range of 40 to 50 V/cm.

Reduced-order modeling of composite slabs in fire. II: Thermal-structural analysis.

This paper describes a reduced-order modeling approach for thermal and structural analysis of fire effects on composite slabs with profiled steel decking. The reduced-order modeling approach, which uses alternating strips of layered shell elements to represent the thick and thin portions of the slab, allows both thermal and structural analyses to be performed using a single model. The modeling approach accounts for the trapezoidal profile of the concrete in the ribs; the structural resistance provided by the steel decking, including the webs of the decking; and the orthotropic behavior of the decking, which provides greater resistance along the ribs than transverse to the ribs. The modeling approach is validated against experimental data from one-way composite slabs tested under ambient-temperature, a one-way composite slab tested under fire conditions, and a two-way composite slab tested under fire conditions. Both implicit and explicit solution schemes are evaluated for the structural analysis, and the results show that it is feasible to scale down the hours-long fire duration to a simulation time of seconds in an explicit dynamic analysis, without adversely affecting the accuracy of the results. The steel decking contributes significantly to the structural resistance at ambient temperature, but as expected, its contribution is found to decrease rapidly under fire exposure. The modeling approach can account for the location of reinforcing bars (i.e., at a specified depth in either the thick or thin portion of the slab), and it is found that reinforcement location can have a significant effect on the structural response, because heat transfer in the composite slab results in higher temperatures in the thin portions of the slab between the ribs.

Effect of Secondary Vortex Flow Near Contact Point on Thermal Performance in the Plate Heat Exchanger with Different Corrugation Profiles

The present study numerically investigates thermal performance and turbulent flow characteristics of chevron-type plate heat exchangers with sinusoidal, trapezoidal, triangular, and elliptical corrugation profiles. The commercial code of ANSYS Fluent (v. 17.0) is used for computational fluid dynamics (CFD) simulation with the realizable k-ε model. In particular, we focus on the influence of configuration shape on a substantial change in flow direction near the contact point, yielding local vorticity. As a result, secondary vortical motions are observed in the flow passage with vorticity that is distributed locally and which changes near the contact point. Higher flow mixing generated and distributed by the secondary vortical motions contributes to the increase of the Colburn j-factor as well as the friction factor. The highest Colburn j-factor and friction factor are obtained for an elliptical profile, compared to other shapes, because of the increase in the vortex strength near the contact point.

Dynamic Behaviour of Spindle on Large EDM Machine Induced by High-Speed Jump Motion with Different Control Strategies

High-speed jump motion in electrical discharge machining (EDM) has been proven to be an important reason for flexible impact and vibration on EDM machine tools. Especially for large EDM machines, the moving parts possess large mass, and different jump control strategies cause different vibration characteristics. However, little attention has been paid to the kinematic comparison between different strategies, and the effect of jump motion on EDM spindle dynamics behaviour is also neglected. In this paper, the dynamic behaviour of spindle on a large EDM machine induced by high-speed jump motion has been investigated. Control strategies including trapezoidal velocity profile, constant jerk profile and sinusoidal jerk profile are considered. The kinematic characteristics of these jump control strategies and corresponding dynamic behaviour of EDM spindle were studied. As a result, under the same maximum velocity of 80 mm/s and maximum jerk of 128 m/s3, the jump period and height of sinusoidal jerk profile are about 0.05 s longer and 1.2 mm larger than that of the other two strategies, respectively. Trapezoidal control strategy causes the largest vibration amplitude of 48.7 μm on spindle during jump motion and thus the strongest forced vibration. The experimental measurement platform for vibration displacement was established. Comparing simulation and experiment data, the relative error is lower than 14%, which verifies the simulation model. Moreover, it can be found that large jump velocity increases vibration amplitude of spindle significantly during machining. When the velocity is 80 mm/s, the maximum vibration amplitude is 23.0 μm. And large velocity of jump motion makes spindle amplitude attenuate faster.

Enhancing Energy Efficiency of a 4-DOF Parallel Robot Through Task-Related Analysis

Enhancing energy efficiency is one of the main challenges of today’s industrial robotics and manufacturing technology. In this paper a task-related analysis of the energetic performance of a 4-DOF industrial parallel robot is presented, and the optimal location of a predefined task with respect to the robot workspace is investigated. An optimal position of the task relative to the robot can indeed reduce the actuators’ effort and the energy consumption required to complete the considered operation. The dynamic and electro-mechanical models of the manipulators are developed and implemented to estimate the energy consumption of a parametrized motion with trapezoidal speed profile, i.e., a pick-and-place operation. Numerical results provide energy consumption maps that can be adopted to place the starting and ending points of the task in the more energy-efficient location within the robot workspace.