Constant Rotation Research Articles

Preparation of Iron Oxide Magnetic Nanoparticles Natural Sand of Rokan River Synthesis with Ball Milling

Natural sand samples taken from the Rokan river, Riau Province, Indonesia, have been ball milled for 100 (one hundred) hours using a ball with a diameter of 1.5 cm and a constant rotation angular velocity of the tube of 100 revolutions / minute. Neodymium Iron Boron (NdFeB) strong magnets are used to separate magnetic minerals from their non-magnetic minerals. Magnetic induction was measured using the Pasco PS-2162 probe and its value was used to calculate the magnitude of magnetic susceptibility, it turns out that the magnetic susceptibility value of the 100-hour Ball Milling results increased significantly when compared to the magnetic susceptibility before Ball Milling, 968,245x 10−5 becomes 19.471x 10−5. The results of the X-Ray Fluorescence (XRF) test showed that the percentage of Fe milled increased from 1.669% to 35.187%, the particle size obtained from the scanning electron microscope (SEM) results was in the nanometer order of 78 nm and the X-Ray Difractometer (XRD) results.) shows that the magnetic nanoparticles produced are dominated by the hematite phase (α-Fe2O3) and the others are in the magnetite (Fe3O4) phase..

Performance of a cold storage air-cooled heat pump system with phase change materials for space cooling

This paper studies the performance of a cold storage heat pump system integrated with phase change materials (PCMs) for space cooling. An air-cooled heat pump unit comprising of two constant rotation speed compressors is selected. The PCM is an organic material that is commercially available, and has a phase change temperature of 10–12 °C. A coupled computational heat transfer model of the heat pump unit, fan coil units, and a cold storage tank filled with PCM slabs is developed. The simulations are performed under the climatic condition of Fuzhou, China. The operational behaviors of the cold charging and discharging processes of the system are analyzed. Furthermore, the overall electrical energy and electricity charge consumptions at various indoor temperature set points are compared. The results indicate that, the electrical energy consumption of the cold storage heat pump system increases as the indoor temperature increases. However, there is very little difference in the electrical energy consumption of the conventional heat pump system and the cold storage system. While under the demand tariff, the electricity charge saving ratio of the cold storage system over the conventional system is 9.07%-11.28%. In general, as the indoor temperature set point reduces, the electricity charge saving ratio increases. Moreover, the effect of cold charging temperature is also discussed. It is found that higher cold charging temperature consumes less electrical energy, however, takes longer to store the same amount of cold, and the differences relies on the required amount of cold.

Three-Link Mechanism as a Model of a Person on a Swing

We model movements of a person swinging on a swing. We consider a flat three-link hinged mechanism as the main mechanical model of the person sitting on the swing. The first, second, and third links model the human body, two hips that are rigidly connected to the swing, and two shins, respectively. The hinge between the first and second links models two hip joints, while the hinge between the second and third links models two knee joints. In each of the interlink hinges, a control moment, limited in magnitude, is applied. At the point of the support of the swing, the moment of viscous friction acts. A mathematical model of a controlled three-link mechanism is built. In solving the problem of synthesizing the control of a three-link model, the law of the control of a simpler (auxiliary) two-link swing model is preconstructed. Then this law is used to control the three-link model. Motion equations with the control built in the form of feedback, have periodic orbitally asymptotically stable solutions. Depending on the parameters of the model, such solutions describe the oscillations of a swing with a constant amplitude or rotation. The control that damps the swing is also built.

PI Controller Untuk Mengatur Kecepatan Motor Induksi 1 Fasa

Induction motors are widely used in the industrial world, home-based businesses as well as in households. Currently in the process of making tofu an induction motor is used as a motor to drive soy blending blades. At this time the use of induction motors is still manually by requiring the operator to regulate the speed of the motor. To reduce operator work, it is necessary to apply PI control as a motor speed controller so that a constant motor rotation is obtained. 1 phase induction motor can be adjusted with variable speed drive (VSD) 0.75KW 1 phase. Blending blade drive uses 0.5HP 1 phase induction motor. In the application of PI control requires some hardware namely Arduino Uno as a minimum system that gives PWM circuit input commands. And the speed sensor as a motor blending speed reader. PI tuning values obtained from the application of the Ziegerl-Nichols I method with the best Kp and Ki tuning values are 1.35 and 0.02673. This research was conducted with 3 speed variables namely 1400 rpm, 1300 and 1200 rpm. From the application of Kp and Ki tuning values, the smallest error value is 4.08% at 1400 rpm with the system response time peak (tp) 5s, rise time (tr) 3s faster, delay time (td) 3s, and settling time (ts) 9s , and a maximum overshoot of 9.8%.

Modified load sharing rip-stop technique in patients with traumatic transtendinous rotator cuff tear: Surgical technique and clinical outcomes

BackgroundTranstendinous rotator cuff tear is likely to occur due to trauma in sports activities, with a frequency of <2% of total rotator cuff tears. These tears are difficult to treat because of limited tendon tissue in the proximal stump, and standard repair techniques are sometimes ineffective. Few studies have reported on the repair technique and clinical outcomes for transtendinous rotator cuff tear, and an appropriate repair technique has, therefore, not been established. The purpose of this study was to use our modified load sharing rip-stop technique to repair transtendinous rotator cuff tear and to clarify the clinical effectiveness of this technique. MethodsThis was a retrospective case series review of eight patients who underwent the modified load sharing rip-stop technique for repairing traumatic transtendinous rotator cuff tear between January 2013 and June 2017. The eight patients were followed up for at least 2 years (range: 24–41 months). Cuff integrity was evaluated using magnetic resonance imaging at 12 months after surgery using the Sugaya classification. We evaluated the pre- and postoperative ranges of motion, American Shoulder and Elbow Surgeons score, Constant Shoulder Score, and muscle strength at 90° abduction. Data were analyzed using the Mann–Whitney U test and Fisher's exact tests. P < .05 was considered to indicate statistical significance. ResultsSix patients were classified as Sugaya I and two as Sugaya II. ASES score (38.5–90.2, P = .0008), Constant shoulder score (36.5–79, P = .002), flexion (85°–158.1°, P = .002), abduction (85°–157.5°, P = .001), external rotation (38.8°–55°, P = .024), and muscle strength at 90° abduction (2.95–5.39 kg, P = .028) improved significantly. Six patients were able to return to their previous sports activity. ConclusionUsing our modified load sharing rip-stop technique for repair of transtendinous rotator cuff tear, patients obtained good clinical outcomes and could return to sports activities.

Friction stir welding of 2060–T8 Al[sbnd]Li alloy. Part I: Microstructure evolution mechanism and mechanical properties

2 mm thick rolled 2060–T8 AlLi alloy plates were subjected to friction stir welding (FSW) under rotation rates of 400–1200 rpm and welding speeds of 50–200 mm/min. In the nugget zone (NZ), FSW resulted in the dissolution of the precipitates and the formation of δ′ (Al3Zr) precipitates, as well as the formation of Guinier–Preston (GP) and Guinier–Preston–Bagaryatsky (GPB) zones except for at 400 rpm–200 mm/min. In the heat affected zone (HAZ), FSW led to the dissolution and coarsening of T1 (Al2CuLi) and S′ (Al2CuMg), and the subsequent formation of new θ′ (Al2Cu) and σ (Al5Cu6Mg2) precipitates. The lowest hardness zones (LHZs) of the FSW joints were located at either the NZ or the HAZ under varied welding parameters. Different from the FSW joints of conventional precipitation–hardened aluminum alloys, the ultimate tensile strength of FSW 2060–T8 joints increased as the rotation rate increased from 400 to 800 rpm, but was unchanged with further increasing the rotation rate from 800 to 1200 rpm under a constant welding speed of 200 mm/min. On the other hand, the joint strength increased as the welding speed increased from 50 to 200 mm/min under a constant rotation rate of 1200 rpm. While the FSW joints fractured at the LHZs under 400 rpm–200 mm/min and 1200 rpm–50 mm/min, abnormal fracture at the thermo–mechanically affected zone (TMAZ) was observed under 800 rpm–200 mm/min and 1200 rpm–200 mm/min.

TECHNOLOGY OF WELL TRAJECTORY CONTROL APPLYING STEM ASSEMBLY ROTATION AND ELIMINATING ROTARY CONTROLLED SYSTEMS

The article discusses the traditional stem assembly consisting of a bit, a screw downhole motor, a telemetry system and a drilling string. This system is relatively simple, however, it has significant drawbacks which are in the non-measured zone of 15 - 20 m, and in demand of a slide mode. The slide mode has significant drawbacks: increased friction forces, which makes it difficult to transfer the load on the bit, clean the wellbore and therefore form landings during the tripping down and drill pipe drag when tripping the drill string up, and contributes to the formation of oil seals. The stem assembly consisting of: a bit, a rotary steerable system, a telemetry system and then a drilling string with a top drive has a significant advantage over the above: it illuminates the non-measured zone, which increases the accuracy of hole making, the curvature of the well is controlled with constant rotation of the drill string, which helps to improve the cuttings lifting, reducing the coefficient of friction, improving the transfer of load on the bit. The complications when wells drilling can be minimized as well. However, the stem assembly with a rotary steerable system has a high cost of operation, up to half the cost of well construction. Based on the analysis of the assemblies, a fundamentally new drill string assembly is proposed, which includes an above-bit module that excludes non-measured zone, a screw downhole motor, a telemetry system, and a top drive. The rotation of the drill string is carried out «left-right» due to the spring turned by the drill string during operation of the top drive. By adjusting the magnitude of the torque, it is possible to achieve a state where the torque decays before reaching the telemetry system and the screw downhole motor. As a result, when the drill string is rotated, the screw downhole motor can control the zenith and azimuth angles in the slide mode. Moreover, the sensors (magnetometers, accelerometers and gamma ray logging) are located in the above-bit module within the distance of 1.5 - 2.0 m from the bit.

Off-Line Detection of Static Eccentricity of PMSM Robust to Machine Operating Temperature and Rotor Position Misalignment Using Incremental Inductance Approach

In this article, an incremental inductance approach is used for static eccentricity detection under off-line condition. This method uses the DC values of the $q$ -axis voltage, which makes it independent of the bandwidth of the controller. In this work, a new feature, the height of hump of the incremental inductance curve, along with the known feature, saturation current in the $d$ -axis, was used for fault detection. It is shown that this new feature is independent of the machine operating temperature, which makes the method robust with respect to machine operating temperature. It is also shown that the proposed method is robust to the rotor position misalignment. A new controller for off-line testing was designed, which controls both the speed and saturation of the machine. Using this controller, the hardware requirements for constant rotation of the machine are reduced while keeping the method independent of the bandwidth of the controller. Finally, a MATLAB-based computer program was developed to calculate the features: saturation current in the $d$ -axis and height of hump of the incremental inductance curve. Six different machines, combinations of two stators and three rotors, were used to validate the proposed method through experiments.

Studies on thermal and interface optimization for CdZnTe crystals by unseeded Traveling Heater Method

A stable thermal field and a controlled convex growth interface are essential for the stable growth of large-size CdZnTe crystals by the Traveling Heater Method (THM). However, the crucible wall temperature always increases due to the deposition of CdZnTe crystals with low thermal conductivity at the bottom of the crucible. A comprehensive two-dimensional simulation model for THM growth of CdZnTe is developed and implemented to study the heat and mass transfer. The effect of increasing wall temperature on interface shape and concentration distribution is discussed. Experimental results show that a dummy crystal with a thermal conductivity similar to that of the CdZnTe crystal helps to stabilize the wall temperature. In a stable thermal field, low constant rotation is assumed to be sufficient to weaken natural convection flow and to make the interface convex in THM. Simulation results show that low constant rotation rates of 2.5 RPM for 2-in. crystal and of 1.25 RPM for 3-in. crystal are effective in interface optimization. Several ingots with a diameter of 2 in. and 3 in. were grown by unseeded THM. Convex interfaces were observed both in 2-in. and 3-in. crystals by applying simulated rotation rates after fast cooling.

Nugget Formation and Mechanical Behaviour of Friction Stir Welds of Three Dissimilar Aluminum Alloys.

The aim of this research was to investigate the influence of the properties of the base materials and welding speed on the morphology and mechanical behavior of the friction stir welds of three dissimilar aluminum alloys in a T-joint configuration. The base materials were the AA2017-T4, AA5083-H111, and AA6082-T6 alloys in 3 mm-thick sheets. The AA6082-T6 alloy was the stringer, and the other alloys were located either on the advancing or retreating sides of the skin. All the T-joint welds were produced with a constant tool rotation speed but with different welding speeds. The microstructures of the welds were analyzed using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and the electron backscatter diffraction technique. The mechanical properties were assessed according to micro-hardness, tensile, and fatigue testing. Good quality welds of the three dissimilar aluminum alloys could be achieved with friction stir welding, but a high ratio between the tool’s rotational and traverse speeds was required. The welding speed influenced the weld morphology and fatigue strength. The positioning of the skin materials influenced the nugget morphology and the mechanical behavior of the joints. The joints in which the AA2017 alloy was positioned on the advancing side presented the best tensile properties and fatigue strength.

Swirling Flow of Jeffrey Fluid by a Spiraling Disk

Swirling flows are frequently detected in nature such as combustion chambers, meteorological systems, turbomachines and their associated ducting, and cyclone separators. Due to the ability of rate type fluid to show time retardation and relaxation in their flow phenomenon. The current research is focused on the Jeffrey liquid flowing normally to a spiraling disk with constant rotation and radial stretching. The constitutive relationship is followed, and the partial system of equations is obtained which is further transformed into ordinary ones by employing a similarity reduction. A numerical finite difference approach is executed to estimate the approximate numerical solutions in tabular and graphical forms. The analysis concludes that the ratio parameter boosts the fluid velocity near the wall, while the retardation parameter deteriorates the fluid velocity radially.

A condition that produces sensory recalibration and abolishes multisensory integration

We examined the influence of extended exposure to a visuomotor rotation, which induces both motor adaptation and sensory recalibration, on (partial) multisensory integration in a cursor-control task. Participants adapted to a 30° (adaptation condition) or 0° (control condition) visuomotor rotation by making center-out movements to remembered targets. In subsequent test trials of sensory integration, they made center-out movements with variable visuomotor rotations and judged the position of hand or cursor at the end of these movements. Test trials were randomly embedded among twice the number of maintenance trials with 30° or 0° rotation. The biases of perceived hand (or cursor) position toward the cursor (or hand) position were measured. We found motor adaptation together with proprioceptive and visual recalibrations in the adaptation condition. Unexpectedly, multisensory integration was absent in both the adaptation and control condition. The absence stemmed from the extensive experience of constant visuomotor rotations of 30° or 0°, which probably produced highly precise predictions of the visual consequences of hand movements. The frequently confirmed predictions then dominated the estimate of the visual movement consequences, leaving no influence of the actual visuomotor rotations in the minority of test trials. Conversely, multisensory integration was present for sensed hand positions when these were indirectly assessed from movement characteristics, indicating that the relative weighting of discrepant estimates of hand position was different for motor control. The existence of a condition that abolishes multisensory integration while keeping sensory recalibration suggests that mechanisms that reduce sensory discrepancies (partly) differ between integration and recalibration.

Limiting treatment plan complexity by applying a novel commercial tool.

PurposeA recently introduced commercial tool is tested to assess whether it is able to reduce the complexity of a treatment plan and improve deliverability without compromising overall quality.MethodsTen prostate and ten oropharynx plans of previously treated patients were reoptimized using the aperture shape controller (ASC) tool recently introduced in Eclipse TPS (Varian Medical Systems, Palo Alto, CA). The performance of ASC was assessed in terms of the overall plan quality using a plan quality metric, the reduction in plan complexity through the analysis of 14 of the most common plan complexity metrics, and the change in plan deliverability through 3D dosimetric measurements. Similarly, plans optimized limiting the total number of delivered monitor units was assessed and compared. The two strategies were also combined to assess their potential combination.ResultsThe plans optimized by exploiting the ASC generally show a reduced number of total Monitor Units, a more constant gantry rotation and a MLC modulation characterized by larger and less complicated shapes with leaves traveling shorter overall lengths.ConclusionsThis first experience suggests that the ASC is an effective tool to reduce the unnecessary complexity of a plan. This turns into an increased plan deliverability with no loss of plan quality.

Determination of total and fine airborne dust in coals

Issues on evaluation of coals ability to liberate airborne dust during transportation and transloading are nowadays relevantly current. In the current work, a new method was presented for evaluation of dust contents in coals. It is based on modeling of the processes of coals transloading and transportation. The essence is to stir coals sample of size &lt;3mm at a constant rotation rate with a simultaneous passing a fixed volume of air through a filter system and determining the total airborne dust content and dust class sizes more or less than 10 microns. During the tests, a sample of commodity coal is used as a residue of a sieve analysis of the representative coal sample after the sieve of 3 mm. Experiments were held at two hard coals of the Kuznetsk coal basin differing in their metamorphism degree and petrographic composition. It was established that within the measurement error, the total amount of airborne dust able to be released during transloading for both the considered samples is comparable. On the other hand, the size classes distribution for dust particles over or less than 10 microns varies significantly and depends on the coals rank and petrographic composition. High inertinite contents determines, presumably, the increase of fine dust particles (less than 10 microns) in the total airborne dust released.

Turbine Generator Rotor Vibrations with Rubbing in the Span and Supports

The article presents an algorithm for and results from studying the motion of a rotor involving its simultaneous rubbing against the stator elements in the turbine set span and supports. The aim of the study was to develop the mathematical model describing vibration of the rotor resting in a few supports and to select the main assumptions regarding the contact interaction between the rotor and stator that will make it possible to model a real vibrational process that involves rubbing. An abrupt loss of balancing in the rotor’s second span section at the angular rotation speed is taken as the initial disturbance upsetting the turbine set’s normal operation. The case of a constant rotor rotation speed with loss of balancing followed by development of contact interaction between the rotor and stator elements is considered. This scenario seems to be the most plausible because the interaction persists for a short period of time during which the safety system still remains silent in producing the command to disconnect the steam supply to the turbine, and the torque on its shaft remains constant. It is shown that with the adopted clearances in the turbine set span and supports, with the loss of balancing corresponding to detachment of the mass of one turbine blade, and with increased damping in the supports, the rotor motion is accompanied by rubbing in the turbine set supports and span. If the damping coefficient in the supports does not exceed the value of this parameter in the plain bearing oil film, asynchronous reverse whirl of the rotor develops, which is characterized by self-excited vibration caused by the effect of contact interaction forces between the rotor and stator. Owing to consideration of the rotor design features, its frequency characteristics, including the change in the frequency characteristics of the rotor–supports system due to additional reactions arising at the moments in which the rotor comes into contact with the stator, it becomes possible to model the vibration development process not only during strong (when whirl is excited) but also during weak (possible excitation of low-frequency vibration) interactions between the rotor and stator and to analyze the influence of detuning from resonances and other factors on the development of self-excitation processes in systems closer to real ones.

Rototaxis: Localization of active motion under rotation

The ability to navigate in complex, inhomogeneous environments is fundamental to survival at all length scales, giving rise to the rapid development of various subfields in bio-locomotion such as the well established concept of chemotaxis. In this work, we extend this existing notion of taxis to rotating environments and introduce the idea of roto-taxis to bio-locomotion. In particular, we explore both overdamped and inertial dynamics of a model synthetic self-propelled particle in the presence of constant global rotation, focusing on the particle's ability to localize near a rotation center as a survival strategy. We find that in the overdamped regime, the swimmer is in general able to generate a self restoring active torque that enables it to remain on stable epicyclical-like trajectories. On the other hand, for underdamped motion with inertial effects, the intricate competition between self-propulsion and inertial forces, in conjunction with the rototactic torque leads to complex dynamical behavior with non-trivial phase space of initial conditions which we reveal by numerical simulations. Our results are relevant for a wide range of setups, from vibrated granular matter on turntables to microorganisms or animals swimming near swirls or vortices.

Structure, Adhesion Strength and Corrosion Resistance of Vacuum Arc Multi-Period NbN/Cu Coatings

The influence of deposition modes on the phase-structural state, corrosion resistance, and adhesive strength of vacuum-arc multi-period NbN/Cu coatings is studied. It was found that in thin layers (about 8 nm, in a constant rotation mode), regardless of the change in the pressure of the nitrogen atmosphere, a metastable δ - NbN phase forms (cubic crystal lattice of the NaCl type). At a layer thickness of ~ 40 nm or more, a phase composition changes from the metastable δ - NbN to the equilibrium ε - NbN phase with a hexagonal crystal lattice. In the presence of the ε - NbN phase in the niobium nitride layers, the highest adhesive strength is achieved with a value of LС5 = 96.5 N. Corrosion resistance tests have shown that for all the studied samples the corrosion process has mainly an anodic reaction. The highest corrosion resistance was shown by coatings obtained at a pressure of 7·10-4 Torr, with the smallest bias potential of -50 V and the smallest layer thickness; with a thickness of such a coating of about 10 microns, its service life in the environment of the formation of chloride ions is about a year.

Design, fabrication of a semi-automatic welding fixture for circumferential joining of cylinders using tig welding

This paper presents the systematic approach of design, fabrication of a semi-automatic welding fixture for circumferential joining of cylinders and testing the welded samples obtained. The TIG welding unit is used to make a circumferential joining on tank and piping, which are fixed onto the welding fixture and several parameters such as the setting of voltage, current and travel speed (rotational speed) is used for fabrication setup. The fabrication fixture with a constant rotation speed is obtained by revolving the tank or pipe with an electrical adjustable speed control motor. The report is focused on the welding of the aluminum workpiece using TIG welding. The joint of mechanical properties is determined by a static tensile test, impact test, and hardness test. This fixture, all the parameters can be determined, and it's an easy way to get the constant shape of welding joint at all joining by using the welding fixture, the evaluation by determination of joining quality can easily be used, especially for circumferential joint on tank and piping with a cylindrical shape.

Economy Mode Setting Device for Wind-Diesel Power Plants

The article is devoted to the problem of reducing fuel consumption in a diesel generator set (DGS) as a part of a wind-diesel power plant (WDPP). The object of the research is a variable speed DGS. The goal is to develop the WDPP intelligent control system, providing an optimal shaft speed of an internal combustion engine (ICE). The basis of the intelligent control system is an economy mode setting device (EMSD), which controls the fuel supply to the ICE. The functional chart of EMSD has been presented. The main EMSD blocks contain a controller and an associative memory block. The associative memory block is a software model of an artificial neural network that determines the optimal shaft speed of the ICE. An algorithm for the WDPP intelligent control system has been developed and tested using the WDPP Simulink model. The EMSD prototype has been created, and its research has been conducted. Dependences of the change in specific and absolute fuel consumption on the load power have been obtained for two 4 kW DGS: with constant rotation speed and variable rotation speed DGS with EMSD. It has been established that the use of EMSD in the mode of low loads allow one to reduce fuel consumption by almost 30%. The error in determining the optimal engine speed using EMSD prototype is not more than 15%.

Spectral finite element method for wave propagation analysis in smart composite beams containing delamination

PurposeThe purpose of the study is to present a frequency domain spectral finite element model (SFEM) based on fast Fourier transform (FFT) for wave propagation analysis of smart laminated composite beams with embedded delamination. For generating and sensing high-frequency elastic waves in composite beams, piezoelectric materials such as lead zirconate titanate (PZT) are used because they can act as both actuators and sensors. The present model is used to investigate the effects of parametric variation of delamination configuration on the propagation of fundamental anti-symmetric wave mode in piezoelectric composite beams.Design/methodology/approachThe spectral element is derived from the exact solution of the governing equation of motion in frequency domain, obtained through fast Fourier transformation of the time domain equation. The beam is divided into two sublaminates (delamination region) and two base laminates (integral regions). The delamination region is modeled by assuming constant and continuous cross-sectional rotation at the interfaces between the base laminate and sublaminates. The governing differential equation of motion for delaminated composite beam with piezoelectric lamina is obtained using Hamilton’s principle by introducing an electrical potential function.FindingsA detailed study of the wave response at the sensor shows that the A0 mode can be used for delamination detection in a wide region and is more suitable for detecting small delamination. It is observed that the amplitude and time of arrival of the reflected A0 wave from a delamination are strongly dependent on the size, position of the delamination and the stacking sequence. The degraded material properties because of the loss of stiffness and density in damaged area differently alter the S0 and A0 wave response and the group speed. The present method provides a potential technique for researchers to accurately model delaminations in piezoelectric composite beam structures. The delamination position can be identified if the time of flight of a reflected wave from delamination and the wave propagation speed of A0 (or S0) mode is known.Originality/valueSpectral finite element modeling of delaminated composite beams with piezoelectric layers has not been reported in the literature yet. The spectral element developed is validated by comparing the present results with those available in the literature. The spectral element developed is then used to investigate the wave propagation characteristics and interaction with delamination in the piezoelectric composite beam.