laser ultrasonics

Laser ultrasonics

Laser-ultrasonics uses lasers to generate and detect ultrasonic waves. It is a non-contact technique used to measure materials thickness, detect flaws and carry out materials characterization. The basic components of a laser-ultrasonic system are a generation laser, a detection laser and a detector.

Contents

• 1Ultrasound generation by laser
• 2Ultrasound detection by laser
• 3Ultrasonic laser technique operation

Ultrasound generation by laser

The generation lasers are short pulse (from tens of nanoseconds to femtoseconds) and high peak power lasers. Common lasers used for ultrasound generation are solid state Q-Switched Nd:YAG and gas lasers (CO₂ or Excimers). The physical principle is of thermal expansion (also called thermoelastic regime) or ablation. In the thermoelastic regime, the ultrasound is generated by the sudden thermal expansion due to the heating of a tiny surface of the material by the laser pulse. If the laser power is sufficient to heat the surface above the material boiling point, some material is evaporated (typically some nanometres) and ultrasound is generated by the recoil effect of the expanding material evaporated. In the ablation regime, a plasma is often formed above the material surface and its expansion can make a substantial contribution to the ultrasonic generation. consequently the emissivity patterns and modal content are different for the two different mechanisms.

The frequency content of the generated ultrasound is partially determined by the frequency content of the laser pulses with shorter pulses giving higher frequencies. For very high frequency generation (up to 100sGHz) femtosecond lasers are used often in a pump-probe configuration with the detection system (see picosecond ultrasonics).

Historically, fundamental research into the nature of laser-ultrasonics was started in 1979, by Dewhurst and Palmer. They set up a new laboratory in the Department of Applied Physics, University of Hull. Dewhurst provided the laser-matter expertise and Palmer the ultrasound expertise. Investigations were directed towards the development of a scientific insight into physical processes converting laser-matter interaction into ultrasound. The studies were also aimed at assessing the characteristics of the ultrasound propagating from the near field into the far field. Importantly, quantitative measurements were performed between 1979 and 1982. In solids, the measurements included amplitudes of longitudinal and shear waves in absolute terms. Ultrasound generation by a laser pulse for both the thermoelastic regime and the transition to the plasma regime was examined. By comparing measurements with theoretical predictions, a description of the magnitude and direction of stresses leading to ultrasonic generation was presented for the first time. It led to the proposition that laser-generated ultrasound could be regarded as a standard acoustic source. Additionally, they showed that surface modification can sometimes be used to amplify the magnitude of ultrasonic signals.

Their research also included the first quantitative studies of laser induced Rayleigh waves, which can dominate ultrasonic surface waves. In studies beyond 1982, surface waves were shown to have a potential use in non-destructive testing. One type of investigation included surface–breaking crack depth estimations in metals, using artificial cracks. Crack sizing was demonstrated, using wideband laser-ultrasonics. Findings were first reported at a Royal Society meeting in London with detailed publications elsewhere.

Important features of laser ultrasonics were summarised in 1990.

Ultrasound detection by laser

For scientific investigations in the early 1980s, Michelson interferometers were exploited. They were capable of measuring ultrasonic signals quantitatively, in typical ranges of 20nm down to 5pm. They possessed a broadband frequency response, up to about 50MHz. Unfortunately, for good signals, they required samples that had polished surfaces. They suffered from serious sensitivity loss when used on rough industrial surfaces. A significant breakthrough for the application of laser ultrasonics came in 1986, when the first optical interferometer capable of reasonable detection sensitivity on rough industrial surfaces was demonstrated. Monchalin et al. at the National Research Council of Canada in Boucherville showed that a Fabry–Pérot interferometer system could assess optical speckle returning from rough surfaces. It provided the impetus for the translation of laser ultrasonics into industrial applications.

Today, ultrasound waves may be detected optically by a variety of techniques. Most techniques use continuous or long pulse (typically of tens of microseconds) lasers but some use short pulses to down convert very high frequencies to DC in a classic pump-probe configuration with the generation. Some techniques (notably conventional Fabry–Pérot detectors) require high frequency stability and this usually implies long coherence length. Common detection techniques include: interferometry (homodyne or heterodyneor Fabry–Pérot) and optical beam deflection (GCLAD) or knife edge detection.

With GCLAD,(Gas-coupled laser acoustic detection), a laser beam is passed through a region where one wants to measure or record the acoustic changes. The ultrasound waves create changes in the air's index of refraction. When the laser encounters these changes, the beam slightly deflects and displaces to a new course. This change is detected and converted to an electric signal by a custom-built photodetector. This enables high sensitivity detection of ultrasound on rough surfaces for frequencies up to 10 MHz.

In practice the choice of technique is often determined by the physical optics and the sample (surface) condition. Many techniques fail to work well on rough surfaces (e.g. simple interferometers) and there are many different schemes to overcome this problem. For instance, photorefractive crystals and four wave mixing are used in an interferometer to compensate for the effects of surface roughness. These techniques are usually expensive in terms of monetary cost and in terms of light budget (thus requiring more laser power to achieve the same signal to noise under ideal conditions).

At low to moderate frequencies (say < 1 GHz), the mechanism for detection is the movement of the surface of the sample. At high frequencies (say >1 GHz), other mechanisms may come into play (for instance modulation of the sample refractive index with stress).

Under ideal circumstances most detection techniques can be considered theoretically as interferometers and, as such, their ultimate sensitivities are all roughly equal. This is because, in all these techniques, interferometry is used to linearize the detection transfer function and when linearized, maximum sensitivity is achieved. Under these conditions, photon shot noise dominates the sensitivity and this is fundamental to all the optical detection techniques. However, the ultimate limit is determined by the phonon shot noise. Since the phonon frequency is many orders of magnitude lower than the photon frequency, the ultimate sensitivity of ultrasonic detection can be much higher. The usual method for increasing the sensitivity of optical detection is to use more optical power. However, the shot noise limited SNR is proportional to the square root of the total detection power. Thus, increasing optical power has limited effect, and damaging power levels are easily reached before achieving an adequate SNR. Consequently, optical detection frequent has lower SNR than non-optical contacting techniques. Optical generation (at least in the firmly thermodynamic regime) is proportional to the optical power used and it is generally more efficient to improve the generation rather than the detection (again the limit is the damage threshold).

Techniques like CHOTs (cheap optical transducers) can overcome the limit of optical detection sensitivity by passively amplifying the amplitude of vibration before optical detection and can result in an increase in sensitivity by several orders of magnitude.

Ultrasonic laser technique operation

Ultrasonic laser set-up

The "Laser Ultrasonic" technique is part of those measurement techniques known as "non-destructive techniques or NDT", that is, methods which do not change the state of measurand itself. Laser ultrasonics is a contactless ultrasonic inspection technique based on excitation and ultrasound measurement using two lasers. A laser pulse is directed onto the sample under test and the interaction with the surface generates an ultrasonic pulse that propagates through the material. The reading of the vibrations produced by the ultrasounds can be subsequently measured by the self-mixing vibrometer : the high performance of the instrument makes it suitable for an accurate measurement of the ultrasonic wave and therefore for a modeling of the characteristics of the sample. When the laser beam hits the surface of the material, its behavior may vary according to the power of the laser used. In the case of high power, there is a real "ablation" or "vaporization" of the material at the point of incidence between the laser and the surface: this causes the disappearance of a small portion of material and a small recall force, due to compression longitudinal, which would be the origin of the ultrasonic wave. This longitudinal wave tends to propagate in the normal direction to the surface of the material, regardless of the angle of incidence of the laser: this would allow to accurately estimate the thickness of the material, knowing the speed of propagation of the wave, without worrying about the angle of incidence. The use of a high power laser, with consequent vaporization of the material, is the optimal way to obtain an ultrasonic response from the object. However, to fall within the scope of non-destructive measurements, it is preferred to avoid this phenomenon by using low power lasers. In this case, the generation of ultrasound takes place thanks to the local overheating of the point of incidence of the laser: the cause of wave generation is now the thermal expansion of the material. In this way there is both the generation of waves longitudinal, similarly to the previous case, and the generation of transverse waves, whose angle with the normal direction to the surface depends on the material. After a few moments the thermal energy dissipates, leaving the surface intact: in this way the measurement is repeatable an infinite number of times (assuming the use of a material sufficiently resistant to thermal stresses) and non-destructive, as required in almost all areas of application of this technology. The movement of the object causes a shift in the phase of the signal, which cannot be identified directly by an optical receiver: to do this it is first necessary to transform the phase modulation into an amplitude modulation (in this case, in a modulation of luminous intensity ). Ultrasound detection can therefore be divided into 3 steps: the conversion from ultrasound to phase-modulated optical signal, the transition from phase modulation to amplitude and finally the reading of the amplitude modulated signal with consequent conversion into an electrical signal.

Industrial applications

Well established applications of laser-ultrasonics are composite inspections for the aerospace industry and on-line hot tube thickness measurements for the metallurgical industry  Optical generation and detection of ultrasound offers scanning techniques to produce ultrasonic images known as B- and C-scans, and for TOFD (time-of-flight-diffraction) studies. One of the first demonstrations on small defects (as small as 3mm x 3mm) in composites was demonstrated by Dewhurst and Shan in 1993, for which they were awarded an outstanding paper award by the American Society for Non-Destructive Testing in 1994. This was also the time when significant developments on composite examinations were developed from the National Research Council of Canada and elsewhere. A wide range of applications have since been described in the literature.

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Speed Control of AC Motors

Speed Control Methods Of Induction Motor

An induction motor is practically a constant speed motor that means, for the entire loading range, change in speed of the motor is quite small. Speed of a DC shunt motor can be varied very easily with good efficiency, but in case of Induction motors, speed reduction is accompanied by a corresponding loss of efficiency and poor power factor. As induction motors are widely being used, their speed control may be required in many applications. Different speed control methods of induction motor are explained below.

Induction Motor Speed Control from Stator Side

1. By Changing the Applied Voltage:

From the torque equation of induction motor,

Rotor resistance R₂ is constant and if slip s is small then (sX₂)² is so small that it can be neglected. Therefore, T ∝ sE₂² where E₂ is rotor induced emf and E₂ ∝ V
Thus, T ∝ sV², which means, if supplied voltage is decreased, the developed torque decreases. Hence, for providing the same load torque, the slip increases with decrease in voltage, and consequently, the speed decreases. This method is the easiest and cheapest, still rarely used, because

1. Large change in supply voltage is required for relatively small change in speed.
2. Large change in supply voltage will result in a large change in flux density, hence, this will disturb the magnetic conditions of the motor.

2. By Changing The Applied Frequency

Synchronous speed of the rotating magnetic field of an induction motor is given by,

Where, f = frequency of the supply and P = number of stator poles.
Hence, the synchronous speed changes with change in supply frequency. Actual speed of an induction motor is given as N = Ns (1 - s). However, this method is not widely used. It may be used where, the induction motor is supplied by a dedicated generator (so that frequency can be easily varied by changing the speed of prime mover). Also, at lower frequency, the motor current may become too high due to decreased reactance. And if the frequency is increased beyond the rated value, the maximum torque developed falls while the speed rises.

3. Constant V/F Control of Induction Motor

This is the most popular method for controlling the speed of an induction motor. As in above method, if the supply frequency is reduced keeping the rated supply voltage, the air gap flux will tend to saturate. This will cause excessive stator current and distortion of the stator flux wave. Therefore, the stator voltage should also be reduced in proportional to the frequency so as to maintain the air-gap flux constant. The magnitude of the stator flux is proportional to the ratio of the stator voltage and the frequency. Hence, if the ratio of voltage to frequency is kept constant, the flux remains constant. Also, by keeping V/F constant, the developed torque remains approximately constant. This method gives higher run-time efficiency. Therefore, majority of AC speed drives employ constant V/F method (or variable voltage, variable frequency method) for the speed control. Along with wide range of speed control, this method also offers 'soft start' capability.

4. Changing the Number of Stator Poles

From the above equation of synchronous speed, it can be seen that synchronous speed (and hence, running speed) can be changed by changing the number of stator poles. This method is generally used for squirrel cage induction motors, as squirrel cage rotor adapts itself for any number of stator poles. Change in stator poles is achieved by two or more independent stator windings wound for different number of poles in same slots.
For example, a stator is wound with two 3phase windings, one for 4 poles and other for 6 poles.
for supply frequency of 50 Hz
i) synchronous speed when 4 pole winding is connected, Ns = 120*50/4 = 1500 RPM
ii) synchronous speed when 6 pole winding is connected, Ns = 120*50/6 = 1000 RPM

Speed Control from Rotor Side:

1. Rotor Rheostat Control

This method is similar to that of armature rheostat control of DC shunt motor. But this method is only applicable to slip ring motors, as addition of external resistance in the rotor of squirrel cage motors is not possible.

2. Cascade Operation

In this method of speed control, two motors are used. Both are mounted on a same shaft so that both run at same speed. One motor is fed from a 3phase supply and the other motor is fed from the induced emf in first motor via slip-rings. The arrangement is as shown in following figure.

Motor A is called the main motor and motor B is called the auxiliary motor.
Let, N_s1 = frequency of motor A
       N_s2 = frequency of motor B
       P₁ = number of poles stator of motor A
       P₂ = number of stator poles of motor B
       N = speed of the set and same for both motors
       f = frequency of the supply

Now, slip of motor A, S₁ = (N_s1 - N) / N_s1.
frequency of the rotor induced emf in motor A,   f₁ = S₁f
Now, auxiliary motor B is supplied with the rotor induce emf

therefore,  N_s2 = (120f₁) / P₂  =  (120S₁f) / P₂.

Now putting the value of  S₁ = (N_s1 - N) / N_s1

At no load, speed of the auxiliary rotor is almost same as its synchronous speed.

i.e. N = N_s2.
from the above equations, it can be obtained that

With this method, four different speeds can be obtained
1. When only motor A works, corresponding speed = .Ns1 = 120f / P₁
2. When only motor B works, corresponding speed = Ns2 = 120f / P₂
3. If commulative cascading is done, speed of the set = N = 120f / (P₁ + P₂)
4. If differential cascading is done, speed of the set = N = 120f (P₁ - P₂)

3. By Injecting EMF In Rotor Circuit

In this method, speed of an induction motor is controlled by injecting a voltage in rotor circuit. It is necessary that voltage (emf) being injected must have same frequency as of the slip frequency. However, there is no restriction to the phase of injected emf. If we inject emf which is in opposite phase with the rotor induced emf, rotor resistance will be increased. If we inject emf which is in phase with the rotor induced emf, rotor resistance will decrease. Thus, by changing the phase of injected emf, speed can be controlled. The main advantage of this method is a wide rage of speed control (above normal as well as below normal) can be achieved. The emf can be injected by various methods such as Kramer system, Scherbius system etc.

CRUSHED STONES IN RAILWAY TRACK

                           CRUSHED STONES IN RAILWAY TRACK

The crushed stones you see alongside railroad tracks are what is known as ballast. Their purpose is to hold the wooden cross ties in place, which in turn hold the rails in place.

Think about the engineering challenge faced by running miles of narrow ribbons of steel track on top of the ground: they are subject to heat expansion and contraction, ground movement and vibration, precipitation build up from rough weather, and weed and plant growth from underneath. Now keep in mind that while 99% of the time they are just sitting there unburdened, the remaining 1% they are subject to moving loads as heavy as 1,000,000 pounds (the weight of a Union Pacific Big Boy locomotive and its tender).

Put all this together, and you have yourself a really, really interesting problem that was first solved nearly 200 years ago, and hasn't been improved since!
The answer is to start with the bare ground, and then build up a foundation to raise the track high enough so it won't get flooded. On top of the foundation, you deposit a load of crushed stone with sharp edges (the ballast). On top of the stone, you lay down (perpendicular to the direction of the track) a line of wooden beams on 19.5 inch centers, 8 1/2 feet long, 9 inches wide and 7 inches thick, weighing about 200 pounds...3,249 of them per mile. You then continue to dump crushed stone all around the beams, effectively locking them in place.
These beams are made of hardwood (usually oak or hickory), and impregnated with creosote

for weather protection. In the US we call them "cross ties" (or, colloquially, just "railroad ties"); in the UK they are known as "sleepers", in Portuguese, "dormentes". While 93% of ties in the US are still made of wood, heavily trafficked modern rail lines are increasingly trying alternatives, including composite plastic, steel and concrete. Next, you bring in hot rolled steel rails, historically 39' long in the US (because they were carried to the site in 40' gondola cars), but increasingly now 78', and lay them on top of the sleepers end to end. They used to be joined by bolting on an extra piece of steel across the joint, but today are usually continuously welded end-to-end.

It would seem that you could just nail them or bolt them down to the ties, but that doesn't work because of the non-trivial movement caused by heat expansion and contraction along the length of the rail. So instead, the rails are attached to the sleepers by clips or anchors, which hold them down but allow them to move longitudinally as they expand or contract.
So there you have it: a centuries old process that is extremely effective at facilitating the movement of people and material over thousands of miles...even though nothing is permanently attached to the ballast distributes the load of the ties (which in turn bear the load of the train on the track, held by clips) across the foundation, allows for ground movement, thermal expansion and weight variance, allow rain and snow to drain through the track, and inhibit the growth of weeds and vegetation that would quickly take over the track.

INFRARED AND THERMAL TESTING

Infrared and thermal testing

Infrared and thermal testing is one of many nondestructive testing techniques designated by the American Society for Nondestructive Testing (ASNT). Infrared thermography is the science of measuring and mapping surface temperatures.

"Infrared thermography, a nondestructive, remote sensing technique, has proved to be an effective, convenient, and economical method of testing concrete. It can detect internal voids, delaminations, and cracks in concrete structures such as bridge decks, highway pavements, garage floors, parking lot pavements, and building walls. As a testing technique, some of its most important qualities are that (1) it is accurate; (2) it is repeatable; (3) it need not inconvenience the public; and (4) it is economical."

An infrared thermographic scanning system can measure and view temperature patterns based upon temperature differences as small as a few hundredths of a degree Celsius. Infrared thermographic testing may be performed during day or night, depending on environmental conditions and the desired results.

All objects emit electromagnetic radiation of a wavelength dependent on the object's temperature. The frequency of the radiation is inversely proportional to the temperature. In infrared thermography, the radiation is detected and measured with infrared imagers (radiometers). The imagers contain an infrared detector that converts the emitting radiation into electrical signals that are displayed on a color or black and white computer display monitor.
A typical application for regularly available IR Thermographic equipment is looking for "hot spots" in electrical equipment, which illustrates high resistance areas in electrical circuits. These “hot spots” are usually measured in the range of 40 °C to 150 °C (70 to 270 °F) above ambient temperatures. But, when engineers use its patented proprietary systems to locate subsurface targets such as underground storage tanks (USTs), pipelines, pipeline leaks and their plumes, and in this project, hidden tunnels, we are looking for temperature patterns typically in the range of 0.01 °C to 1 °C above or below ambient temperatures.
After the thermal data is processed, it can be displayed on a monitor in multiple shades of gray scale or color. The colors displayed on the thermogram are arbitrarily set by the Thermographer to best illustrate the infrared data being analyzed.
In this roofing investigation application, infrared thermographic data was collected during daytime hours, on both sunny and rainy days. This data collection time allowed for solar heating of the roof, and any entrapped water within the roofing system, during the daylight hours. IR data was observed until the roof had sufficiently warmed to allow detection of the entrapped wet areas because of their ability to collect and store more heat than the dry insulated areas. The wet areas would also transfer the heat at a faster rate than the dry insulated roof areas. At this point in time, the wet areas showed up as warmer roof surface temperatures than the surrounding dry background areas of the roof. During the rainy day, with minimum solar loading, any entrapped leak plumes would become evident because of their cooler temperature as compared to the dry roof areas

An infrared thermographic scanning system measures surface temperatures only. But the surface temperatures that are measured on the surface of the ground, above a buried pipeline, are, to a great extent, dependent upon the subsurface conditions.

The subsurface configuration effects are based upon the theory that energy cannot be stopped from flowing from warmer to cooler areas, it can only be slowed down by the insulating effects of the material through which it is flowing. Various types of construction materials have different insulating abilities. In addition, differing types of pipeline defects have different insulating values.

Contents

• 1Background
• 2Pipeline testing

Background

There are three ways of transferring energy: 1) conduction; 2) convection; and 3) radiation. Good solid backfill should have the least resistance to conduction of energy and the convection gas radiation effects should be negligible. The various types of problems associated with soil erosion and poor backfill surrounding buried pipelines increase the insulating ability of the soil, by reducing the energy conduction properties, without substantially increasing the convection effects. This is because dead air spaces do not allow the formation of convection currents.

In order to have an energy flow, there must be an energy source. Since buried pipeline testing can involve large areas, the heat source has to be low cost and able to give the ground surface above the pipeline an even distribution of heat. The sun fulfills both of these requirements. The ground surface reacts, storing or transmitting the energy received.

Pipeline testing

For pipelines carrying fluids at temperatures above or below the ambient ground temperatures (i.e., steam, oil, liquefied gases, or chemicals), an alternative is to use the heat sinking ability of the earth to draw heat from the pipeline under test. The crucial point to remember is that the energy must be flowing through the ground and fluids.

Ground cover must be evaluated for temperature differentials (i.e., anomalies such as high grass or surface debris), as to how it may affect the surface condition of the test area. Of the three methods of energy transfer, radiation is the method that has the most profound effect upon the ability of the surface to transfer energy. The ability of a material to radiate energy is measured by the emissivity of the material. This is defined as the ability of the material to release energy as compared to a perfect blackbody radiator. This is strictly a surface property. It normally exhibits itself in higher values for rough surfaces and lower values for smooth surfaces. For example, rough concrete may have an emissivity of 0.95 while a shiny piece of tinfoil may have an emissivity of only 0.05. In practical terms, this means that when looking at large areas of ground cover, the engineer in charge of testing must be aware of differing surface textures caused by such things as broom roughed spots, tire rubber tracks, oil spots, loose sand and dirt on the surface and the height of grassy areas

CREATING A SIMPLE REVIT FAMILY

CREATING A SIMPLE REVIT FAMILY

In this first entry, we’ll run through the steps to create a simple parametric box using reference planes, dimensions and constraints, shared parameters to control the length, width and depth of the box and we’ll wrap up by creating a type catalog for our new family.

Step 1 – Creating a new family

Start by creating a new family using the GENERIC MODEL.RFT file.  Note the file extension: RFT is a Revit family template.  RFA files are the actual Revit family.

Step 2 – Adding Reference Planes

Reference planes are 2-dimensional guidelines used to control the 3D geometry of the family.  To create reference planes, from the CREATE ribbon, on the DATUM panel click REFERNECE PLANE (or type RP).  Now draw four reference planes in a clock-wise manner.  Don’t worry about their spacing.  We’ll fix that in the next step using dimensions to constrain the reference planes.

Step 3 – Adding dimensions, constraints and shared parameters

Next we’ll need to add dimensions to constrain the reference planes and then add shared parameters to control the reference planes so from the ANNOTATE ribbon, on the DIMENSION panel click ALIGNED.  Select the left reference plane, then the middle and finally the right reference plan.  Click EQ to make the reference planes equidistant.  Then create a second dimension string this time selecting only the left and right reference planes.  Repeat the process for the horizontal reference planes.

Step 4 – Creating an extrusion

With the reference planes dimensioned and constrained, it’s time to create a simple extrusion.  On the CREATE ribbon, find the FORMS panel and click EXTRUSION.  Notice there are 5 different types of forms you can create: Extrusion, Blend, Revolve, Sweep and Swept Blend.  For this exercise we’ll be using the simple extrusion form.

After clicking EXTRUSION, you will then be placed into sketch mode.  Select the RECTANGLE button and pick two points to create a rectangular shape for our simple box extrusion.  The exact placement doesn’t matter because we’ll be constraining the geometry to the reference planes, but place it within the reference planes.

Click the green check mark to complete the sketch and exit sketch mode.

Step 5 – Constraining the extrusion

Now that the extrusion is created, we need to constrain it to the outer-most reference planes.  The simplest and fastest way to do this is to use the ALIGN command.  Start the align command and select the top reference plane then select the top edge of the extrusion.  After the edge of the extrusion is aligned to the reference plane, click the padlock icon to lock the edge of the extrusion to the reference plane.  Repeat this for the remaining 3 sides of the extrusion.

Step 6 – Adding Shared Parameters

Select the overall horizontal dimension string and from the Options Bar select ADD PARAMETER from the LABEL drop-down.

The PARAMETER PROPERTIES dialog appears.  Select SHARED PARAMETER [1], click SELECT [2], select the 00_COMMON [3] category from the SHARED PARAMETERS dialog box, select BVH_LENGTH [4], click OK [5], choose whether this parameter should be a TYPE or INSTANCE [6], select which category you want the parameter to appear under in the Properties palette (you can simply use the default value) [7] (for this exercise, select the INSTANCE option so you can change the values on a per-instance basis), click OK [8].  Repeat this process for the vertical dimension string and use the BVH_WIDTH parameter.

After applying the shared parameters, the dimension strings should look like the ones below.

Now switch to an elevation view and repeat steps 2, 3, 5 & 6 to create a reference plane, dimension and add a parameter to control the depth of the cube.

When you load your new custom box family into a project and place a few instances of it, you can control the dimensions of each instance separately.  If you had selected the TYPE property for the shared parameters, you would only be able to control the dimensions of the box from the family’s

Save your new family.  Note: Depending on the complexity of the family, you may want to save it at regular intervals to avoid the risk of losing any work.

Step 7 – Flex your family

When you “flex” a family, you’re changing the values of the parameters to ensure it reacts the way you expect it to.  In some instances, you may see the dimension strings and reference planes change, but the geometry doesn’t move.  That’s because the geometry isn’t locked to the reference planes.  In a simple family such as the one we just created, not much can go wrong, but if something does go wrong, it’s rather easy to fix.

Flexing a family prior to using it becomes more critical when you have more complicated geometry and/or nested families that you want to control.

CIVIL ENGINEERING ABBREVIATION

CIVIL ENGINEERING ABBREVIATION:

The common abbreviation used in civil engineering are as following:

A.A.S.H.T.O – American Association of state highway Transport Official.

A.C.I – American Concrete Institute.

A.R.E.A – American Railway Engineering Association.

A.B – Anchor  Bolt Or Asbestos Board

AC – Asphalt Concrete

A.S.C – Allowable Stress of concrete.

A.S.T.M – American society for testing materials

AC – Asbestos cement.

AE – Assistant Engineer

APM – Assistant Project Manager

B.M – Benchmark

B.M – Bending moment.

BLK – Block Work

BOQ – Bill Of Quantities

BRW – Brick Retaining Wall

BWK – Brick Work

B.O.F – Bottom Of Foundation

BHK – Bedroom, Hall, Kitchen

C.I.Pipe – Cast iron pipe.

C.I.Sheet – Corrugated Iron sheet.

CL- Centre Line

CRW – Concrete Retaining Wall

CBW – Concrete Block Wall

CIP – Cast In Place

CMU – Concrete Masonry Unit

CJ – Construction Joint

CC – Centre To Centre

CC – Cement concrete.

CE – Chief Engineer

CP – Cement plaster.

CPM – Critical path method.

CS – Comparative statement.

D – Diameter

DL – Development Length

Dia – Diameter

DIM – Dimension

D.L – Dead load.

DPC – Damp proof course.

DPR – Daily Progress Report

DRG – Drawings

DWLS – Dowels

EJ – Expansion Joint

E.L – Environmental load.

EL – Existing Load

EGL – Existing ground level.

ELCB – Earth Leak Circuit Breaker

F.M – Fineness Modulus.

Ft – Foot Or Feet

FL – Floor Level

FGL – Formation ground level.

FOC – Factor Of Safety

GL – Ground Level

GL – Ground level.

GP – Ground plane.

HFL – Highest Flood Level.

HAC – High Alumina Cement

HP – Horizontal plane.

IOM – Inter Office Memo

ISI – Indian standard institute.

JE – Junior Engineer

JST – Joist

Kg  – Kilogram.

L.L – Live load.

LW – Light  Weight

LWC – light Weight Concrete

LC – Lime concrete.

M – Meter

MM – Millimeter.

MB – Measurement book.

MCB – Miniature Circuit Breaker

MEP – Mechanical Electrical Plumbing

MFL – Maximum Flood Level

MRC – Material Receipt Challan

MT – Metric Tonnes

N – Newton

NCF – Neat cement finishing.

OPC – Ordinary Portland Cement

OGL – Original ground level.

OSR – Open Soace Reservation Area

PC – Pile Cap

PC – Precast Concrete

PCC – Plain Cement Concrete

PERT – Programme Evaluation and Review Technique.

PL – Plinth level.

PM – Project Manager

PO – Purchase Order

PPE – Personal Protective Equipment

PPR – Poly Propylene Random.

PVC – Poly vinyl choloride .

PVC – Polyvinyl Chloride

PSF – Pound Per Square Foot

PSI – Pound Per Square Inch

PWD – Permanent Works Engineer

QC – Quality control

QS – Quantity Surveyor

RC – Reinforced Concrete

R.B.W – Reinforced brick work.

RBC – Reinforced Brick concrete.

RCC – Reinforced Cement Concrete

RMC – Ready Mixed Concrete concrete.

RL – Reduced level.

SCC – Self Compacting Concrete

STP – Sewage Treatment Plant

SRC – Sulphate Resisting Cement

SWG – Standard wire gauge.

TB – Tie Beam

TBM – Tunnel Boring Machine

TDS – Total Dissolved Solids

TOB – Top Of Beam

TMT – Thermo Mechanical Treatment

TOC – Top Of Concrete

TOW – Top Of Wall

U.S.C – Ultimate stress of concrete.

UPVC – Unplasticized Polyvinyl chloride.

USD – Ultimate strength design.

VP – Vertical plane.

W.C – Water closet.

WL – Working Level

W.S.D – Working stress Design

WO –  Work Order