178 results about "Earthquake simulation" patented technology

An earthquake simulating vibration table includes a vibration machine having a vibration table provided on the topside. Paper models are assembled on a model fundamental base that is fixed on the vibration table. The vibration machine is controlled by a computer to produce simulated various-degree earthquakes. A test of anti-seismic strength of the paper models begins with a smallest seismic strength and then the seismic strength increases by degrees until it reaches to a largest level to have all the paper models collapse. The earthquake simulating vibration table is convenient and quick in assembling, economical in cost and able to be popularized to schools to serve as a course of vibration resistance education to elevate students' learning interest.

The invention discloses a model test device for simulating the instability failure of rock and soil slopes under complex conditions, and belongs to the technical fields of geotechnical engineering andmining engineering. The model test device comprises a wind and rain simulation system, an earthquake simulation system, a similar model test system and a monitoring system. Through the adoption of the device, similar model test of rock and soil slope bodies such as waste dumps and tailings dams can be carried out efficiently, and the stability and failure modes of the slope bodies under rainfall,earthquake and the coupling action thereof can be researched and analyzed.

The invention discloses an electric servo cylinder earthquake simulation vibrating table in a small engineering structure, which comprises a vibrating table base, a servo motor, an electric servo actuator, a vibrating table top and a prestress gapless connection mechanism, wherein the vibrating table base is connected with the vibrating table top by a linear guide rail pair; a tested piece is placed on the vibrating table top; the servo motor is mounted below the vibrating table base; an output shaft of the servo motor is connected with an input shaft of the electric servo actuator used for converting rotation into linear motion; an output shaft of the electric servo actuator is connected with a piston rod; a motion direction of the piston rod is consistent with a motion direction of the linear guide rail pair; a table top driving connection seat and the prestress gapless connection mechanism are mounted at the front end of the piston rod; and the upper end of the table top driving connection seat is fixedly connected with the vibrating table top. The electric servo cylinder earthquake simulation vibrating table in the small engineering structure can simplify a structure, lower the cost, and shorten a production period and a single test period.

Provided is a five-freedom-degree earthquake simulation vibrating table for on-bridge railway tracks. The end portion of each bridge body of a bridge is arranged on a side plate of a box type base, and the tracks are installed on the upper surface of the bridge bodies. a horizontal electro-hydraulic servo actuator, a left-side vertical electro-hydraulic servo actuator and a right-side vertical electro-hydraulic servo actuator are hinged to a base plate of the box type base. The actuating end of the horizontal electro-hydraulic servo actuator is sequentially hinged to the side faces of the bridge bodies of the bridge through a vertical connecting rod and a horizontal connecting rod, and the middle of the vertical connecting rod is further hinged to a support block of the box type base. The actuating ends of the left-side vertical electro-hydraulic servo actuator and the right-side vertical electro-hydraulic servo actuator are hinged to the bottoms of the bridge bodies. The five-freedom-degree earthquake simulation vibrating table can achieve five-freedom-degree movements including vertical translation, horizontal translation, rolling, nodding and shaking of the tracks, completely simulate seismic waves of the on-bridge railway tracks and large road distortion deformation caused by an earthquake and further obtain incentive data of the seismic waves, and provides an important test basis for railway train operation safe and structural earthquake-resistant design and safe operation management.

The invention discloses an earthquake simulator capable of carrying out an earthquake drill, which comprises a simulating cabin (1), a basic platform (9) and a cabin shaking device, wherein the basic platform (9) is arranged under the simulating cabin (1), and the cabin shaking device is arranged between the simulating cabin and the basic platform. A small shaking device comprises a horizontal shaking device and a longitudinal shaking device. Under the condition of earthquake, the earthquake simulator can help people to understand and learn emergency shock-proof knowledge, improve the abilities of emergency risk avoidance, self-help and self-protection and change adaptability when the earthquake disaster occurs.

The invention relates to an earthquake experiencing device, comprising an experiencing room, a first oil cylinder, an electro-hydraulic servo valve, a hydraulic pressure power source and an oil source auxiliary equipment which is used for guaranteeing constant output of the hydraulic pressure; the experiencing room is arranged on a desk frame; the desk frame can be arranged on a first motion guide in a horizontal slipping way; a rod of the first oil cylinder is in rigid connection with the desk frame; the first oil cylinder is the double-rod cylinder; the first oil cylinder is connected with the electro-hydraulic servo valve which is connected with the hydraulic pressure power source; the hydraulic pressure power source is connected with the oil source auxiliary equipment; the electro-hydraulic servo valve is connected with a seismic modeling controller which is used for calculating a valve port opening signal according to the seismic displacement data and outputting the valve port opening signal to the electro-hydraulic servo valve. The invention provides the earthquake experiencing device which can reproduce the real earthquake well and strengthen the experience effect, and has the advantage of rational structure.

The invention discloses a suspension tunnel dynamic response test device and method under the coupling of an earthquake and a wave flow. The test device comprises a test water tank and a sensing and measuring device; and a wave and flow making device, an earthquake simulation vibrating table and a restraining device for restraining the motion of a test tube are arranged in the test water tank. Thetest method is realized through the steps of mounting a wave height meter and a flow meter in the test water tank, and carrying out wave flow sequence check and wave elimination treatment on the waveflow; connecting the test tube with the earthquake simulation vibrating table, and mounting a gyro sensor, a GPS-RTK combined measuring device, a tension sensor and a pressure sensor; carrying out wave and flow making by using the wave and flow making device, and after the wave flow is stabilized, starting the earthquake simulation vibrating table; and measuring various dynamic indexes of the test tube, and dynamically acquiring the data through a data acquisition unit. The device and method are capable of truly and effectively simulating the structural three-dimensional motion and stress conditions of the underwater suspension tunnels under the load action of the wave flow, the earthquake and the like.

The invention discloses a large simulation test system for simulating combined effects of earthquakes, waves and ocean current, belonging to the technical field of a marine structure power test. The simulation test system comprises a test wave gutter channel, an absorption wave-maker device, a test water circulating device, an adjustable speed block platform, an earthquake simulation device, a two-way flow simulation device and a waterproof sealing device, wherein the upper plane of a vibration table body of the earthquake simulation device is parallel and level to the bottom plane of the test wave gutter channel; the waterproof sealing deice is arranged between the periphery of the upper plane of the vibration table body and the bottom plane of the test wave gutter channel; the absorption wave-maker device is arranged at the initial end of the test wave gutter channel; a flow making pump of the two-way flow simulation device is connected with an initial-end flow equalizing box and a tail-end flow equalizing box through a pipeline. The system is complete in test simulation function, different input excitation test conditions of the marine structure under combined effects of various loads can be simulated, the test simulation of the earthquakes, the waves and the ocean current is in full-digital control, and the large simulation test system is high in control accuracy and diverse in test function.

A vibration table simulating earthquake consists of support frame, test table and exciting system to make test table simulate earthquake. It is featured as setting contact roll of bottom translation table (BTT) on outer support bottom rail and contact roll of top translation table (TTT) on BTT rail in exciting system, connecting level Y direction spring set to BTT and inside face of outer support frame, level X direction one to TTT and inside face of inner support frame and vertical spring set to TTT and test table bottom.

The invention provides a comprehensive system of a horizontal two-way earthquake simulation shaking table. The comprehensive system consists of a table surface unit of the well-shaped rail beam-stiffened horizontal two-way earthquake simulation shaking table, a support operation mechanism unit of the horizontal two-way earthquake simulation shaking table and a vibration exciter connecting device of the horizontal two-way earthquake simulation shaking table; the table surface unit has light self-weight and large effective load, the large internal damping causes small local vibration and low noise; the vibration exciter connecting device of the shaking table has no geometric coupling, easy ensured rigidness of a connector and small extra work of the vibration exciter; the support operation mechanism unit carries a heavy model test piece, the table surface of the table surface of the shaking table can slide in any direction on the horizontal plane, the operation friction is small and the horizontal displacement ability of the shaking table is not constrained by overturning moment. The maximum displacement which can be achieved by the horizontal two-way earthquake simulation shaking table is that X is equal to plus or minus 300mm and Y is equal to plus or minus 300mm, and the horizontal two-way earthquake simulation shaking table has simple structure, low cost, small energy consumption, high energy efficiency, easy upgrade and ability of realizing the further development of loading and displacement abilities.

The invention discloses a tunnel cast-in-place concrete lining anti-seismic property testing method. The method is characterized by comprising the following steps: manufacturing a cast-in-site concrete lining local test-piece; installing the cast-in-site concrete lining local test-piece into a purpose-made test-piece loading box; applying static load to the test-piece loading box through a static force loading system; installing the test device onto a vertical electro-hydraulic servo drive type seismic modeling vibration table and inputting vibration load; sequentially unloading the vibration load and the static load, and recording damage conditions of the test-piece so as to estimate the anti-seismic property of the test-piece. According to the method, the actual stress state of cast-in-place concrete lining is simulated through the special loading mechanism, and an existing earthquake modeling vibration table is combined to test the anti-seismic property of the local test-piece, so that the overall anti-seismic property of a circular or a quasi-circular tunnel cast-in-place concrete lining structure can be better reflected. Compared with a whole fracture surface experiment, the method greatly saves experiment cost due to the fact the cast-in-place concrete lining local test-piece is used for test.

The invention provides a method for monitoring the seismic deformation of a building curtain wall based on digital speckle marks, and the method comprises the following basic steps: 1) fixing a test piece frame on an earthquake simulation vibration platform, assembling a to-be-detected curtain wall on the frame, and manually marking speckle patterns with random characteristics on the surface of the curtain wall; 2) erecting two industrial digital cameras to image speckle patterns on the surface of the test piece; 3) fitting artificial seismic waves according to the characteristics of a plannedconstruction site, carrying out graded loading for multiple times, and collecting speckle images at the same time; 4) performing three-dimensional digital image correlation matching calculation of the acquired digital image sequence in a computer to obtain full-field displacement and deformation information of the surface of the building curtain wall under the action of a seismic load. Through the digital speckle image marking and optical measurement method, the quantitative data of the full-field deformation of the curtain wall under the earthquake load effect is obtained, the measurement result is more accurate, the measurement steps are simpler, and the application range is wider.

The invention discloses a vibration table substructure test method based on three-parameter control AMD, which belongs to the technical field of structure test and can be used in anti-seismic test ofmulti-story and high-rise building structures. On the basis of the existing hybrid experimental research, an AMD loading device (also called an active mass driver) is used as a means of applying an interface force between a numerical substructure and an experimental substructure, and the control precision of the AMD loading device is improved through a three-parameter control algorithm. Compared with the existing vibration table substructure test method, the test method disclosed by the invention has the advantages as follows: the test conditions can be easily met (no additional counterforce wall is needed); a vertical self-weight effect is provided while the problem of inertia mass loading is solved and the influence of the high-order vibration mode of an upper substructure is neglected (the mass of the AMD loading device can provide a weight); the test precision is high (the high-frequency performance of three-parameter control is excellent); the requirement on the stroke of an actuator is low (there is no need to track the displacement of the board of a seismic simulation vibration table).

The present invention discloses a seismic array of an underwater earthquake simulation vibrostand. The seismic array comprises a seismic array pedestal arranged on a power base, and a deep pool arranged on the seismic array pedestal. Two vibrostand surfaces are arranged in the deep pool. The lower parts of the vibrostand surfaces are provided with a horizontal actuator, a vertical actuator and a guide device arranged via a hydrostatic back-up. One side of the deep pool is provided with a reaction wall, and the other side of the deep pool is provided with an oil transmission pipeline for connecting an oil pump station with an accumulator group. The inner side thereof is provided with a wave maker group. The bottom of the reaction wall and the lower part of the deep pool are respectively provided with manholes. According to the invention, the dynamic test on large engineering structure under the coupling excitation effect of waves, the water flow and the earthquake is realized. meanwhile, the coupling effect of multi-point and multi-dimensional earthquake and wave power is realized. The seismic array is long in period, large in displacement, good in high-frequency seismic property and higher in operability. The synchronous / asynchronous control of two vibrostands, the generation of waves and seawater, and the synchronous / asynchronous control of the vibrostand seismic array excitation are realized.

The invention discloses an earthquake simulation experience platform. The earthquake simulation experience platform comprises a vibration device and an earthquake simulation control system, wherein the vibration device comprises an experience platform, a first support platform, a second support platform and a base; a plurality of support springs are uniformly arranged between the experience platform and the first support platform; a vertical driving device is fixedly arranged between the first support platform and the second support platform, and consists of a servo motor, a ball screw and a telescopic rod; horizontal driving devices are fixedly arranged between the second support platform and the base, and are arranged at the same side; a slide block and slide rail mechanism is arranged between the second support platform and the base; the earthquake simulation control system utilizes a control cabinet which is fixedly arranged on the base; a PLC (programmable logic controller) is used for outputting corresponding data signals to the terminal servo motor via a frequency converter, so as to simulate the earthquake of different intensity. The earthquake simulation experience platform has the advantages that the structure is simple, the property is stable, and the accuracy is high; the real vibration effect during earthquake of different intensity can be simulated.

The invention discloses a plateau earthquake climatic environment simulating device and belongs to the technical field of testing equipment. The plateau earthquake climatic environment simulating device comprises a plateau earthquake simulating cabin equipped with two cabin layers and an earthquake simulating structure disposed in the plateau earthquake simulating cabin. The top cabin layer of the plateau earthquake simulating cabin is a plateau earthquake chamber and the bottom cabin layer of the plateau earthquake simulating cabin is an earthquake falling chamber. An air supply system, a spraying system, a temperature control system, a sunlight generator, an ice-making system, a mist-making system, and a noise system are disposed in the plateau earthquake simulating cabin. By means of the plateau earthquake simulating cabin and the earthquake simulating structure, the plateau earthquake climatic environment simulating device may simultaneously simulate a plateau, an earthquake, and various extreme climate environments formed by combining the plateau with the earthquake, enables a proofer to experience various plateau and earthquake extreme climates at one time, and solves a problem that a product in the prior art may just simulate a single climate so as to be high in experience cost and manufacture cost.

The invention discloses an earthquake simulating demonstration device which comprises a ground sight demonstration platform (1). A demonstration platform surface (2) is arranged on the ground sight demonstration platform. A cabin swaying device (3), an earth surface falling device (4) and a fault diastrophism device (5) are arranged on the demonstration platform surface (2). A guardrail (6) is arranged on one side of the demonstration platform (1) and a controlling platform (7) capable of controlling the cabin swaying device (3), the earth surface falling device (4) and the fault diastrophism device (5) is arranged on the guardrail (6). According to the earthquake simulating demonstration device, influences of the earthquake damages by earthquake origin, earthquake magnitude can be intuitively displayed, thus people can understand the earthquake clearly.

Provided is a 6-DOF earthquake simulation vibrating device, comprising a support platform; the support platform comprises a table top supporting an earthquake model; the table top is jointed by a plurality of motion units of a same structure; each motion unit can be independently perpendicular to the table top and move up and move; the support platform is supported on a second platform framework through a first platform framework and moves in a horizontal surface. The method employs the table top jointed by a plurality of motion units to provide local splitting up and down motion in a vertical direction, thereby directly performing local motion on the soil body of an earthquake model; through performing separation continuous motion on the model soil body, the model soil body can generate real cutting effects; in addition, the first platform framework and the second platform framework provide front, rear, left and right motion in a horizontal direction, thereby forming 6-DOF omnibearing earthquake simulation.

The invention discloses a simulation demonstrator of collapse earthquake, which aims at providing a collapse earthquake model which has a simple structure, can be automatically reset and used for repeatedly demonstrating. The simulation demonstrator is technically characterized in that the simulation demonstrator comprises a demonstrator and a driving device; the demonstrator comprises an operating console (16) and a ground sand table model (17) with collapse ground (18); the driving device is positioned below the collapse ground (18); and the driving device comprises a framework (12), a motor (1), a synchronizing wheel (2), a synchronous belt (14), a ball screw (4), a connecting plate (9), a sliding block connecting block (10) and a stainless steel shaft (11).

The invention provides an electro-hydraulic servo earthquake simulation vibrating table used for conducting the seismic simulation test. The earthquake simulation vibrating table comprises a processor and a control system. The processor executes a program module stored in a memory so as to realize the earthquake waveform reproduction. The reference input r(k) of seismic waves of the control system is tracked. A minimum variance estimator containing an electro-hydraulic servo vibrating table and a controlled object model of a geotechnical model are introduced. Meanwhile, a target function with an object output prediction square-error to be minimum is adopted to solve the output u(k) of the controller in the control system. therefore, the output y (k) of the seismic waves of an controlled object is realized.

The invention relates to an earthquake simulation vibrostand control method, which belongs to the technical field of structural experiment. According to the control method, a differential signal of anacceleration instruction signal and a differential signal of an acceleration feedback signal are obtained by virtue of differentiation, a difference between the displacement feedforward and feedbackis integrated to obtain a displacement error integral signal, summation is performed for the acceleration instruction differential signal, the acceleration feedback differential signal and the displacement error integral signal and the known three parameter instruction signal, thereby obtaining a composite multi-parameter control signal. Compared with the existing three-parameter control method, the acceleration feedback differential signal in the multi-parameter control algorithm can reduce the influence of system resonance frequency and can increase the system bandwidth; the acceleration instruction differential signal can increase the system frequency band and can improve the system high-frequency performance; and the displacement error integral signal can reduce a displacement static error of a multi-vibrostand system and can improve the low-frequency control performance of the system.

The invention discloses a double-hydraulic-motor drive type large-displacement earthquake shaking simulation device and method. The device comprises a shake table body and a shake controller. The shake table body comprises a first horizontal guide rail, a first coupler, a first hydraulic motor, a first electro-hydraulic servo valve, a second horizontal guide rail, a second hydraulic motor, a second electro-hydraulic servo valve, a second coupler, a third horizontal guide rail, a base, a motion table top, a first ball screw, a first bearing block, a second ball screw, a second bearing block, an acceleration sensor and a displacement sensor. According to the device and method, a combined drive type structure of hydraulic motors and ball screws is adopted, and therefore low-frequency response and large-displacement motion control characters of earthquake simulation tests can be achieved; meanwhile, the earthquake shaking simulation device can have larger anti-overturning torque by adopting the horizontal guide rail structure, and therefore stability and reliability of the shake device in the working process can be guaranteed.

The invention discloses a multiple climatic environment analogue device, belonging to the test apparatus technical field, and comprises a plateau boiler-plate, a sea boiler-plate and an earthquake simulation structure. The sea boiler-plate is fixed directly under the plateau boiler-plate; the plateau boiler-plate is internally provided with an air feed system, a spraying system, a temperature control system, a sunshine generator, an ice manufacturing system, a fog making system and a noise system; the sea boiler-plate is internally provided with an air feed system, a spraying system, a temperature control system, a seawater circulation system, an ocean wave generation device, a peculiar smell generating device and a noise system. The multiple climatic environment analogue device is provided with the plateau boiler-plate, the sea boiler-plate and the earthquake simulation structure, and can meanwhile stimulate various extreme climatic environments of plateau, sea, earthquake, etc., allow different experiencers to once experience various extreme climatic environments, and overcome the problems of high experience cost and high manufacture cost of only simulating a single climate in the prior art.

The invention discloses a modular construction method and system for a simulation scene of helicopter earthquake rescue, which relates to the general aviation / helicopter operation support field. According to the method, on the basis of characteristics, like intensity attenuation and house vulnerability, of the earthquake, the construction system is divided into seven modules, so that the modeling staff can construct an earthquake rescue simulation scene scientifically and reasonably without any professional earthquake knowledge. During the application process, construction is carried out based on the divided seven modules; all the modules are integrated according to steps and rules to obtain an earthquake simulation scene with a high reduction degree quickly. Moreover, because the system and method are especially used for the simulation scene of helicopter earthquake rescue training and the models are layered and simplified reasonably, the training effect can be guaranteed and the modeling time and cost can be saved.

The invention discloses a model test device for simulating instability failure of a rock-soil slope. The model test device comprises a test bin, a multifunctional mechanism, a water supply mechanism, an earthquake mechanism and a monitoring mechanism, a bottom plate mechanism is fixedly connected to the bottom of an inner cavity of the test bin, and a simulated rock-soil slope is placed on the bottom plate mechanism; the multifunctional mechanism comprises an air supply assembly, a pressurizing assembly and an angle adjusting assembly; the water supply mechanism comprises a water supply assembly, a gas supply assembly and a water outlet plate assembly which are communicated with the bottom plate mechanism, and the water outlet plate assembly is arranged at the top opening of the test bin; the earthquake mechanism comprises a base assembly and a vibration assembly, and the vibration assembly is used for sending earthquake simulation vibration to the base assembly; and the monitoring mechanism comprises an image assembly and a data sensing assembly, the image recording assembly and the data sensing assembly are electrically connected with a wireless transmission module, and the wireless transmission module is wirelessly connected with an operation terminal. According to the invention, simulation of factors such as rainfall, wind blowing, load, earthquake and the like on the rock-soil slope can be realized, and simulation data can be recorded and transmitted.

The invention discloses seismic simulation test equipment, and relates to the technical field of civil engineering indoor test equipment. The seismic simulation test equipment includes a pedestal, an upper platform is arranged in the pedestal, a bottom plate is arranged under the upper platform, support pillars are arranged in the positions of four corners of the bottom of the bottom plate, the positions of the bottom of the pedestal, which are corresponding to the support pillars, are provided with connecting ear plates, the bottom of the bottom plate is provided with a first vibrating motor and a second vibrating motor side by side, the upper side of the upper platform is provided with a vibrating table, the bottom of the vibrating table is movably connected through rivets with fixed connecting seats arranged in the positions of four corners at the upper side of the upper platform, the middle part and the top of the vibrating table are provided with a middle layer support plate and an upper layer support plate respectively, each of the middle layer support plate and the upper layer support plate is provided with a magnetic block, two sides of the pedestal are provided with a backboard and a camera respectively, a controller is arranged on the pedestal, and the controller is electrically connected with the first vibrating motor and the second vibrating motor. The seismic simulation test equipment is easy to operate, low in manufacturing cost and simple in principle, and is suitable for classroom teaching.

The invention relates to a seismic response simulation method for a heterogeneous hydrate reservoir. The method comprises the steps that the content, elasticity modulus and density of various mineralcomponents in a matrix framework, the elasticity modulus and density of hydrate, the elasticity modulus and density of formation water and reservoir porosity are obtained; establishing a non-uniform model of vertical change of hydrate stratum saturation and transverse change of stratum thickness, and obtaining a change rule of speed and attenuation of the sandstone stratum containing the natural gas hydrate along with frequency by utilizing the BISQ model; calculating the velocity dispersion characteristics of the underlying free gas stratum of the hydrate-containing stratum by using a White spotted saturation model; and based on a propagation matrix theory, calculating reflection waveforms of the heterogeneous hydrate stratum and the free gas stratum. The method comprises the following steps: establishing a non-uniform model of hydrate stratum saturation vertical change and stratum thickness transverse change; and calculating the seismic reflection waveform response of the non-uniformhydrate stratum through a rock physical model and a seismic simulation method based on a propagation matrix theory.

The invention relates to a model experiment apparatus for simulating ground long-term settlement due to overlapped tunnel operation in a high compact district under earthquake-rainfall effects, and belongs to the technical field of city underground engineering disaster prevention and disaster mitigation as well as ground settlement geological disaster. The model experiment apparatus comprises thefollowing components: a rainfall simulation system, an earthquake simulation system, a combined module system, an earth surface compact building system, soft soil, a lonestone group, a sensing system,a tunnel system, a conduction system, a vehicle vibration system, and a central control system. The apparatus can simulate influences due to long-term settlement of ground under extreme rainfall environment, earthquake disaster environment, and effects of rainfall environment, earthquake environment, and combination environments of rainfall and earthquake; the apparatus can simulate influences ofvehicle load vibration coupling effects at any positions during subway operation in a city high compact district on soil long-term settlement, and the apparatus has the characteristics of high environment simulation fidelity and experiment repeatability; the experiment is not limited by extreme environment, and has the characteristics of reliable data and high operationality.

The invention relates to a general waveform reproduction control method and device. The general waveform reproduction control method includes setting test parameters, performing target wave processing, estimating original transfer functions and adjusting order. The control device comprises a computer and a signal interface case. The computer is connected with the signal interface case through Ethernet electric signals and provided with a general seismic modeling control system. The signal interface case is used for connecting controller inner signals and inputting and outputting external hardware signals. The signal interface case integrates an acceleration signal conditioning board, a displacement signal conditioning board, a busbar clamping slot, a single board computer and a power supply module. The general seismic modeling control system comprises a test parameter setting unit, a target wave processing unit, a seismic waveform simulation unit and a signal analyzing unit. By the use of the control method, estimation accuracy of the system transfer functions within full spectrum band is high, and test steps are simplified. The control device is simple and reasonable in structural design and high in control accuracy and has fewer modules and complete signal analyzing and processing functions.