109 results about "Friction coefficient" patented technology

The invention discloses a double-force-control automatic compensation method and double-force-control grinding and polishing integrated device.According to the technical scheme, the double-force-control automatic compensation method comprises the steps that workpiece surface crystal orientation data are obtained through a diffraction pattern, and a crystal orientation distribution matrix is generated through denoising and clustering analysis; dividing a crystal orientation region and associating the friction coefficient, hardness and other mechanical properties; based on the material removal rate distribution matrix, a gradient algorithm is adopted to correct grinding tracks and cutting parameters of all areas, and a compensation track matrix is generated; and double-force-control feedback of normal force and tangential force is combined, the abrasive particle contact force and the feeding rate are dynamically adjusted, and a closed-loop compensation strategy is formed. Through crystal orientation partition optimization and double-force-control dynamic compensation, the problem that compensation is insufficient in the grinding process of the glass crystal is solved, and high-precision and self-adaptive surface machining is achieved.

The invention discloses a manipulator clamping force control method and device based on motor driving, and relates to the field of intelligent manipulators. Comprising the following steps that the mass of a to-be-clamped object is obtained, and basic friction force is calculated; collecting object shape characteristic parameters such as the maximum boundary length, the outer surface area and the volume, and calculating a shape influence coefficient; then, acquiring surface characteristic parameters such as average curvature, irregularity and projection area, calculating a surface concave-convex coefficient, and generating a shape complexity index in combination with the shape influence coefficient; then, acquiring material characteristic parameters such as hardness and elastic modulus, determining and correcting a basic friction coefficient, and calculating friction force; and finally, the instantaneous speed of the clamping task of the manipulator is obtained, the impact load is calculated, the basic friction force is corrected based on the parameters, the accurate clamping force is obtained, and therefore the accurate control over the clamping force of the manipulator is achieved. According to the method, the clamping effect and safety are improved, and the method is suitable for various clamping scenes.

When a sliding main bearing of a wind driven generator is under a heavy-load working condition, a lubricating oil film in a starting stage is not enough to form a complete fluid lubricating film, namely, a friction surface forms a boundary lubrication state, and friction in the stage seriously affects the service life of the bearing. In this way, a macroscopic model and a microscopic model are coupled, and a multi-scale model is verified through experiments. The macroscopic model is established based on an actual structure of a wind power main shaft sliding bearing, and is equivalent to a three-layer structure of a rigid bearing base, an elastic surface supporting layer and a main shaft; a three-layer microcosmic molecular model representing'main shaft-lubricating oil-elastic supporting layer 'is established by the microcosmic model facing the boundary lubrication state of a friction pair. Wherein the thickness of the supporting layer is changed by the macroscopic model, the components of the supporting layer material are changed by the microscopic model, the friction coefficient of the tribological interface under different supporting layer thicknesses and material components is analyzed through the macro-micro cross-scale analysis model, and the optimal thickness and the optimal material component proportion suitable for the service condition of the wind power main shaft sliding bearing are obtained.

The invention relates to the technical field of friction coefficient measuring devices, and discloses a device for testing the friction coefficient of an anti-skid coating of a cultivation work ship deck. Comprising a testing platform, a friction coefficient testing mechanism arranged below the testing platform, a driving mechanism arranged on the testing platform and used for driving the friction coefficient testing mechanism to horizontally move, and a partition assembly and a water spraying assembly arranged in the middle of the lower surface of the testing platform; through the arrangement of the high-pressure nozzles, in the moving process of the testing platform, high-pressure gas can automatically clean a deck testing area through the high-pressure nozzles, dust attached to the surface of a deck is effectively removed, manual pre-cleaning is not needed, the testing efficiency is remarkably improved, meanwhile, seawater is sprayed to the designated testing area through the water spraying assembly, and the testing efficiency is improved. The environment of the residual seawater on the deck in the actual operation of the cultivation work ship is accurately simulated, and the technical problems that an existing portable sliding friction instrument needs to be manually cleaned and cannot simulate the residual seawater environment are solved.

According to the precise cutting machining method and system for the soft material, firstly, the three-dimensional model and the cutting parameters of the material are obtained, the initial cutting track is generated, in the cutting process, material deformation is monitored in real time through the multi-sensor fusion technology, the cutting track and depth are adjusted through the dynamic compensation algorithm, and the cutting precision is improved. And meanwhile, a laser interference measurement system is adopted to track the position of a cutting tool, and micron-level precision is achieved through closed-loop feedback control. According to the method, pressure control and cutting depth adjustment are combined, a specific microstructure is created to achieve differential friction coefficients, in addition, the surface chemical composition is monitored through real-time spectrum analysis, and it is ensured that the preset surface characteristic requirement is met. The cutting track, depth and surface texture of the soft material can be accurately controlled, high-precision and customizable soft material machining is achieved, and key technical support is provided for intelligent machining in the fields of flexible electronics, bionic robots and the like.

The utility model relates to the technical field of drawing equipment, in particular to multi-pass wire drawing equipment. The equipment comprises a drawing cone pulley mechanism and a heating furnace, the drawing cone pulley mechanism comprises a cone pulley, and the surface of the cone pulley is divided into at least Z sections of areas in the axial direction of the cone pulley; wherein the surface roughness of each section of area is different, so that the surface friction coefficient of each section of area is different; the total drawing pass is M, and when M is larger than or equal to 2, Z is larger than or equal to 2 and smaller than or equal to M, so that at least one pass of wire drawing is conducted on each area. The drawing cone pulley solves the problem that due to the fact that the number of drawing passes is increased, the sliding coefficient difference between the first pass and the last pass is too large, and wires are broken, and the drawing efficiency of a single machine is remarkably improved.

The invention provides a self-adaptive grabbing system and method based on photoelectric sensing and material recognition. The system comprises a manipulator, a mechanical arm, a front-end processor and an upper computer controller. The manipulator is driven by a torque-adjustable motor, and an optical sensor module based on a photoelectric sensing principle is mounted on a fingertip of the manipulator; the optical sensor module is used for acquiring a texture grayscale image and sliding micro-displacement information of the surface of a grabbed object; the front-end processor is used for collecting data of the optical sensor module and transmitting the data to the upper computer controller; the upper computer controller recognizes the material of the object and matches the friction coefficient, the optimal clamping force increment is calculated according to the sliding micro-displacement information and the friction coefficient, and the motor is controlled to achieve self-adaptive grabbing. According to the system, the manipulator can be controlled to increase the clamping force in an optimal clamping force increment mode according to the sliding amplitude and the friction characteristic of the object, and self-adaptive stable grabbing of the object is achieved.

The invention provides a method for dynamically testing the shear-slip friction coefficient and fracture permeability of rock. The method comprises the following steps: S1, preparing an experimental test piece according to a preset size; s2, carrying out a shear-slip friction coefficient test experiment on the experiment test piece to obtain a shear experiment rock, and calculating to obtain a shear-slip friction coefficient; s3, performing a crack permeability test experiment on the shear experiment rock, and calculating to obtain the crack dynamic permeability; and S4, obtaining a test effect of the dynamic permeability of the crack according to the shear slip friction coefficient and the dynamic permeability of the crack. According to the invention, the shear slip friction coefficient of the rock can be more accurately tested, the dynamic permeability of the shear crack can be reflected, the influence of an unstable slip starting stage and fluctuating slip after the shear failure of the rock is eliminated, and the original permeability characteristic of the shear crack surface can be accurately reflected; the effect of comprehensively and universally testing the dynamic permeability of the crack is achieved.

A treadmill includes a walking board assembly, and a walking belt encircling the walking board assembly. The walking board assembly includes a support plate, a wear-resistant plate mounted on the support plate, and a wax layer mounted on the wear-resistant plate. The wear-resistant plate is made of wear-resistant material with a low friction coefficient. The wear-resistant plate has a bottom face abutting the top face of the support plate. The wear-resistant plate has a top face integrally formed with multiple grooves. The wear-resistant plate has a thickness less than that of the support plate. The wax layer is coated on and filled with the grooves of the wear-resistant plate. The wax layer has a coating height at least equal to the depth of each of the grooves.

The invention discloses a cylindricity detection device for mechanical shaft parts. The cylindricity detection device comprises a detection machine body which is provided with a unit for controlling a detection structure and a space for assembling a shaft body clamp, the shaft body clamp is connected to the upper surface of the detection machine body through a bolt and is used for clamping and fixing one end of the shaft body; the detection structure is connected to the upper surface of the detection machine body through bolts and located on the right side of the shaft body clamp; through the arrangement of the detection structure, scrap iron, dust and other sundries on the surface of a shaft can be effectively removed in the aspects of cleaning and lubricating, the friction coefficient of a probe and the shaft is reduced, abrasion of the probe to the probe is avoided, the detection structure can be adjusted at different height positions through the hydraulic effect, the time needed by position adjustment during detection is greatly shortened, and the detection efficiency is improved. The detection linkage and reliability are improved, meanwhile, a cylindricity detection piece can be assisted to execute comprehensive detection on different positions of the mechanical shaft from top to bottom, and a powerful guarantee is provided for obtaining high-quality detection data.

The non-slip member has, on at least a part of the surface of a base material made of an inorganic material, a protrusion region in which a plurality of protrusions are vertically provided, the protrusion region having a first direction and a second direction intersecting the first direction. The plurality of protrusions are periodically arranged in at least one of the first direction and the second direction, the average pitch of the plurality of protrusions in the first direction and / or the second direction is within the range of 20 nm or more and 1000 nm or less, and the static friction coefficient on the surface is 0.20 or more.

The present invention provides a method and system for optimizing the anti-skid performance of a sliding plate, which relates to the field of anti-skid detection technology. The method includes: setting an oblique groove on the upper contact surface of a test sliding plate; laying coarse sand in the oblique groove, fixing the lower contact surface of the test sliding plate to the ground, and placing a heavy object on the test sliding plate; applying traction and recording the critical traction; determining a friction coefficient function based on the critical traction, the particle size of the coarse sand, the angle of the oblique groove, and the weight of the heavy object; determining an optimized angle and an optimized particle size based on the friction coefficient function, the weight of the transported object, a first preset friction coefficient, and a second preset friction coefficient; and processing the sliding plate based on the optimized angle and the optimized particle size. According to the present invention, a friction coefficient function representing the relationship between the processing method and the anti-skid performance can be determined, and based on the friction coefficient function, an optimized processing method can be determined in combination with actual transportation needs to reduce the risk of the transported object slipping during transportation.

The invention provides a self-adaptive grabbing method based on tactile friction perception and an adjustable friction coefficient. The self-adaptive grabbing method is based on a grabbing mechanical arm with the adjustable friction coefficient. The surface, used for making contact with a grabbed object, of each finger is a friction surface with an adjustable friction coefficient, and a strain sensing module is embedded in the lower portion of each friction surface to detect the strain amount. The motor output is gradually increased, and meanwhile dynamic optimization of the minimum safe clamping force is conducted; the clamping static friction force Ff1 is obtained according to the motor output at the current moment in combination with the adjustable friction coefficient; a dependent variable epsilon is obtained and converted into a strain friction force Ff2, and a real-time friction force Ff is calculated; whether the minimum safe clamping force is obtained or not is judged according to the real-time friction force; and subsequently, the minimum safe clamping force is adopted for grabbing. According to the method, the minimum safe clamping force capable of overcoming the gravity of the workpiece can be dynamically adjusted, so that the vulnerable workpiece is protected to the greatest extent while reliable grabbing is ensured.

This invention discloses a method for obtaining the strength of a pillar considering friction factors, comprising: preparing rock samples with different aspect ratios and configuring contact surface materials with different tribological properties; determining the cohesion and friction coefficient of each contact surface material through shear testing, conducting compressive strength tests on rock samples with different contact surface materials to obtain rock sample strength data under different friction levels and aspect ratios; selecting a pillar strength calculation formula corresponding to the actual contact conditions between the pillar and the surrounding rock, calculating the strength of the target pillar under design conditions, and calculating the load on the pillar itself based on the pillar area bearing theory; calculating the pillar safety factor based on the pillar strength and the load, and optimizing the pillar design accordingly.

The utility model relates to the technical field of drawing equipment, in particular to a drawing cone pulley, a drawing cone pulley mechanism and multi-pass wire drawing equipment. The surface of the drawing cone pulley is divided into at least Z sections of areas along the axial direction; wherein the surface roughness of each section of area is different, so that the surface friction coefficient of each section of area is different; wherein the total drawing pass is M, and when M is larger than or equal to 2, Z is larger than or equal to 2 and smaller than or equal to M, so that at least one pass of wire drawing is conducted on each area. The drawing cone pulley solves the problem that due to the fact that the number of drawing passes is increased, the sliding coefficient difference between the first pass and the last pass is too large, and wires are broken, and the drawing efficiency of a single machine is remarkably improved.

A colorimetry device includes a support base having a support surface for supporting a measurement target and a carriage to which a colorimeter is detachably attached and that is configured to move in a first direction, which is a direction along the support surface, and in a second direction, which is a direction along the support surface and which intersects the first direction, the colorimeter being configured to measure color of the measurement target, wherein the carriage includes, on an inner wall of an accommodation section that accommodates the colorimeter, a contact surface that is in contact with a side surface of the colorimeter when the colorimeter is attached or detached and a friction coefficient μ1 between the contact surface and the side surface of the colorimeter is smaller than a friction coefficient μ2 between the housing of the carriage and the side surface of the colorimeter.

A carrier plate comprises a plate body with a bearing surface and an anti-skid pad with a preset friction coefficient, and the anti-skid pad is fixedly arranged on the bearing surface. The utility model further provides the jigsaw table. According to the carrying plate and the jigsaw table, the friction force between the carrying plate and a carried object is increased through the anti-skid pad, and therefore the problem that jigsaw patterns displace and even slip off due to external force is effectively solved.

The present application discloses a device for testing the coefficient of kinetic friction of a landslide, comprising an L-shaped bracket for supporting the entire testing device, a slide slidably arranged on the L-shaped bracket to maintain a preset tilt angle and serve as a slideway, the slide being a box structure with an upper opening; a sliding frame in contact with the slide and sliding on the slide; and a first timing trigger and a second timing trigger electrically connected to a main control unit arranged along the length direction of the slide, the main control unit being connected to a rechargeable lithium battery and a display screen for displaying the time taken by the sliding frame from the first timing trigger to the second timing trigger. The present application can flexibly replace different materials for multiple tests according to the test needs, the test operation is convenient, and the measurement data is accurate; at the same time, the set slide and sliding frame can adapt to the measurement of the coefficient of kinetic friction between materials of different materials and properties, with strong compatibility and a wide range of applications.

Disclosed are a friction and wear test system and a friction and wear test method. To reduce the error of measured friction coefficients, the friction and wear test system of the present disclosure includes a rotating shaft, a dynamic specimen mounting structure mounted on the rotating shaft, a first static specimen mounting structure, a first loading module for applying a preset loading force to the first static specimen during the test, and a second static specimen mounting structure arranged directly opposite to the first static specimen mounting structure in the axial direction of the rotating shaft. The second static specimen mounting structure is configured with a second loading module for applying a preset loading force pointing at the dynamic specimen to the second static specimen during the test, so as to at least partially counterbalance the force loaded on the dynamic specimen by the first static specimen during the test.

The invention relates to the technical field of friction coefficient testing, and provides a metal material high-temperature friction coefficient testing device which comprises a motion control system, a motion platform assembly, a heating system and a measuring system. The test piece made of a metal material and the sliding block are arranged on the motion platform assembly, and the sliding block is placed on the test piece; the heating system is used for heating and preserving heat of a test piece and a sliding block which are arranged on the motion platform assembly; the motion control system drives the motion platform assembly to drive the test piece to slide, so that the test piece slides relative to the sliding block; when the test piece and the sliding block slide relatively, the measuring system monitors data of force generated by the sliding block in real time through the force sensor, records a time-domain curve of the data and calculates the friction coefficient according to the time-domain curve. According to the scheme of the invention, the method can meet the temperature requirement of a metal material use environment, and can measure the static friction coefficient and the dynamic friction coefficient of the metal material in a high-temperature state.

The invention discloses a carrying system and photovoltaic preparation equipment. The carrying system comprises a manipulator, a detection module and a control module. The mechanical arm comprises a bearing part, the bearing part is provided with an open end, a closed end and a limiting piece, the open end and the closed end are oppositely arranged, and when a to-be-carried object is fed, the to-be-carried object enters the bearing part through the open end till making contact with the limiting piece; the first driving part drives the bearing part to move from the carrying starting point to the carrying ending point, so that the bearing part has displacement in the horizontal direction; the second driving part drives the bearing part to rotate around a rotating shaft, and the rotating shaft is perpendicular to the open end and / or the closed end; the detection device detects the acceleration of the to-be-carried object relative to the bearing part; the control module controls the first driving part and controls the second driving part according to the acceleration of the to-be-carried object relative to the bearing part, the mass of the to-be-carried object and the friction coefficient between the to-be-carried object and the contact face of the bearing part, so that the to-be-carried object slides reversely and returns to the position where the to-be-carried object makes contact with the limiting piece during feeding. The carrying efficiency is improved, and the position accuracy is improved.

The utility model relates to the technical field of radial drilling machines, in particular to a rocker arm and a radial drilling machine, which comprise a support component, the top of the support component is fixedly connected with a rocker arm component, the side surface of the rocker arm component is provided with a driving component, and the top of the support component is fixedly connected with a workbench component; movement of the lifting arm and the telescopic arm is achieved through movement of the hydraulic cylinders in the lifting arm and the telescopic arm, the hydraulic lifting process is stable, shaking and damage of objects can be reduced, large weight can be borne, the lifting device is suitable for lifting of heavy-load objects, accurate lifting position control can be achieved through a control system, and the lifting device is convenient to use and popularize. Various operation requirements are met, a plurality of belts can be loaded through the multi-wheel grooves formed in the rotating wheel and the transmission wheel, compared with a single-wheel-groove driving wheel, the rotating wheel and the transmission wheel serving as the multi-wheel-groove driving wheel have the advantages that the friction coefficient of the multi-wheel-groove driving wheel is large, and the rotating wheel and the transmission wheel of the multi-wheel-groove driving wheel can be used for preventing the driving wheel from losing rotating.

The present invention discloses a design method for porous arrangement of wall blowing for boundary layer drag reduction, which relates to the field of flow control of the aerodynamic performance of aircraft, and includes: S1. Obtain the friction coefficient of the surface of the aircraft that needs drag reduction; S2. On the wall where the blowing holes need to be arranged, divide the arrangement baseline of the wall blowing holes along the flow direction. For any one baseline j , calculate the friction coefficient difference by extracting the friction coefficient on the baseline j and the given number of blowing holes; S3. Determine the friction coefficient corresponding to the j th blowing hole on the baseline i ; S4. Obtain the physical coordinates of each blowing hole on the baseline j ; S5. Repeat S2-S4 until the arrangement of the blowing holes on each baseline is completed, and obtain the wall blowing holes with non-uniform layout. The present invention provides a design method for porous arrangement of wall blowing for boundary layer drag reduction. Compared with the traditional method, it makes full use of the synergistic control effect of porous wall blowing, and the overall drag reduction effect is significantly improved.

The invention relates to the technical field of profile rolling, and particularly discloses a flat-rolling ultrathin aluminum alloy profile rolling device which comprises rolling racks, and a profile pretreatment unit is fixedly arranged between the front faces of the two rolling racks through bolts; sectional material rolling units are symmetrically arranged on the upper portion and the lower portion between the two rolling racks, and auxiliary supporting assemblies are arranged on the two sectional material rolling units. Through the composite structure design of the working roller, the rolling quality is improved from three aspects: the flat roller and the convexity roller are adapted to the thickness control requirements of profiles with different widths; the nano ceramic coating strengthens the wear resistance of the roller surface; by means of the micro-nano rib and pit structure, on one hand, the contact area of the roller and the profile is reduced, the friction coefficient is reduced, drawing marks or wrinkles of the profile are avoided, and on the other hand, the pits are used for storing lubricating oil and containing aluminum skimmings to protect the surface of the profile. And meanwhile, the servo electric cylinder is matched with the adjusting frame, so that the distance between the rollers can be accurately adjusted to adapt to rolling of profiles with different thicknesses, and the rolling precision is guaranteed.

The present invention relates to the technical field of superlubricant friction and wear, and particularly to a PEEK-based superlubricant composite material, a preparation method and an application, including: performing surface texturing treatment on a PEEK workpiece and removing the heat-affected zone around the surface texture of the PEEK workpiece; preparing a fluoropolymer coating on the surface of the PEEK workpiece to cover the surface texture of the PEEK workpiece; drying and sintering the PEEK workpiece coated with the fluoropolymer coating to obtain a PEEK-based superlubricant composite material; wherein, the lubricating medium of the PEEK-based superlubricant composite material is pure glycerol. Through the synergistic effect of the surface texturing technology and the fluoropolymer coating, the present invention gives full play to the lubricating effect of the coating and the texture storage function, enabling PEEK to achieve stable superlubrication in one step under an atmospheric environment. It solves the problem in the prior art that the high friction coefficient of PEEK material results in the inability of PEEK material to achieve long-life stable superlubrication.

To provide a cleaning device that can uniformly and efficiently remove dirt attached to a rotating body, and can prevent the occurrence of abnormal images including mainly vertical black streaks over a long period.SOLUTION: A cleaning device has cleaning means 22b that is in contact with a surface of a rotating body 22a to clean the surface of the rotating body 22a. The cleaning means 22b is a roller member and has a foam layer 224 in contact with the surface of the rotating body 22a, and the surface of the foam layer 224 has a coefficient of static friction of 0.5 or more, which is measured by the Euler belt method.SELECTED DRAWING: Figure 4

The application discloses spliced self-lubricating polyether ether ketone three-layer composite plate and a preparation method thereof. The spliced self-lubricating polyether ether ketone three-layer composite plate comprises, from bottom to top, a metal base layer, a copper powder layer and a spliced self-lubricating layer connected in sequence. The spliced self-lubricating layer is composed of a plurality of wear-resistant PEEK pieces with good wear resistance and friction-reducing PEEK pieces with good friction-reducing performance arranged alternately. The friction-reducing PEEK pieces are designed to be arranged at an angle of 30-60 degrees with the horizontal direction, i.e. the friction-reducing PEEK pieces are arranged in an inclined strip shape between the wear-resistant PEEK pieces with good wear resistance. The structure design can form a complete self-lubricating friction-reducing layer during reciprocating movement of the composite plate, reduces the friction coefficient of the plate and a friction pair, and finally improves the wear resistance of the material.

The present application relates to the technical field of decompression products, and in particular to a decompression ring and a method for determining the thickness of self-lubricating material thereof. The method comprises the following steps: determining the surface material of the fixed inner ring or the movable outer ring made of non-self-lubricating material; determining the friction coefficient between the self-lubricating material and the surface material; determining the dialing pressure, the dialing frequency and the expected service life according to historical user data; determining the wear rate according to the friction coefficient and the dialing pressure; determining the number of rotations according to the dialing frequency and the expected service life, and then determining the calculated thickness according to the number of rotations and the wear rate; obtaining the expected thickness, and determining the reference thickness according to the expected thickness and the calculated thickness; adjusting the reference thickness according to the gap between the self-lubricating material and the fixed inner ring or the movable outer ring and the user experience threshold, and determining the final thickness. The present application can reduce the size of the decompression ring while ensuring its service life and improving user experience.

The application discloses a sliding vane, a compressor and a processing technology of the sliding vane. The sliding vane comprises a body; and a roller mounting groove is arranged on the body, wherein the roller mounting groove is provided with an inner concave curved surface which is adapted to the roller, the inner concave curved surface is an optimal arc curved surface, and the opening of the inner concave curved surface is outward and upward. The roller mounting groove is designed in a targeted manner, the optimal arc is greater than one-half of a circle, and the opening direction is inclined at a certain angle, so that the relative position of the roller is fixed, the roller does not deviate and does not fall out during the operation of the compressor, the roller can be better accommodated and fixed, the sealing performance of the compressor during the operation is improved, the friction coefficient between the sliding vane and the piston roller is reduced, and the energy efficiency ratio is improved.

The method for evaluating the fracture mechanics performance of the water-soaked brittle solid material of the present application comprises the following steps: 1. A group of cuboid brittle solid material samples are prepared, and the samples are immersed in water. After the immersion is completed, the samples with different immersion times are selected for weighing, and then the samples with different water contents are selected; 2. The samples with different water contents in step 1 are selected, and the relationship curve between the uniaxial compression stress and strain of the brittle solid material samples and the initial density of the micro-defects of the samples under different water contents are measured; 3. The samples with different water contents in step 1 are selected, and the sliding friction coefficients of the brittle solid material samples with different water contents are determined; 4. The brittle solid samples containing cracks are prepared, and the fracture toughness of the brittle solid material with different water contents is measured; and 5. Based on the above steps, the fracture strength of the brittle solid material samples under the action of different water contents after being soaked in water is determined.