UPDA Mechanical cheat sheet

Order of obligation: public safety and welfare first, then client or employer, then the profession; record any conflict in writing.

Disclose a conflict of interest in writing before accepting an assignment, and withdraw if the conflict cannot be managed.

Sign and seal only drawings, calculations, and reports personally prepared or directly supervised.

Report a confirmed danger to life or property to the responsible authority when the employer fails to correct it.

Accept only work within your competence; engage a specialist and record the division of responsibility in writing.

Code precedence in Qatar: applicable local regulations and building code first, then contract-specified standards, then recognized international practice.

Retain design calculations, approved submittals, and as-built records for the project liability period and the period stated in the contract.

A gift, hospitality, or payment that could reasonably influence a design or approval decision is declined and disclosed.

Closed-system first law: Q minus W equals delta U; steady-flow: q minus w equals delta h plus delta KE plus delta PE.

Ideal gas: P v equals R T; c_p minus c_v equals R; polytropic work for n not equal to 1 is (P2V2 minus P1V1)/(1 minus n).

Carnot efficiency equals 1 minus T_L/T_H using absolute temperatures; no real cycle between the same reservoirs exceeds it.

Conduction q equals minus k A dT/dx; convection q equals h A (T_s minus T_infinity); radiation q equals epsilon sigma A (T_s^4 minus T_sur^4).

Heat exchanger duty equals U A F deltaT_lm; effectiveness equals actual heat transfer divided by maximum possible heat transfer.

Critical radius of cylindrical insulation r_c equals k/h; adding insulation increases heat loss while the outer radius is below r_c.

Entropy generation is zero for a reversible process and positive for any real process; a cycle cannot convert all heat to work.

Overall heat transfer coefficient for a plane wall: 1/U equals 1/h_i plus sum of t/k plus 1/h_o.

Continuity for steady flow: rho A V equals constant; for incompressible flow Q equals A1V1 equals A2V2.

Bernoulli along a streamline: P/gamma plus z plus V squared over 2g equals constant, with head losses subtracted between sections.

Reynolds number Re equals rho V D/mu; pipe flow is laminar below about 2300 and turbulent above about 4000.

Darcy-Weisbach head loss h_f equals f (L/D)(V squared/2g); friction factor f is read from the Moody chart using Re and relative roughness.

Pump total head equals (P2 minus P1)/gamma plus elevation change plus velocity head change plus system losses.

NPSH available equals (P_atm minus P_v)/gamma plus static suction head minus suction line losses; it must exceed NPSH required.

Pump affinity laws: Q proportional to N, H proportional to N squared, P proportional to N cubed at constant impeller diameter.

Hydrostatic force on a plane surface equals gamma times centroid depth times area; the center of pressure lies below the centroid.

Axial stress sigma equals P/A; strain epsilon equals delta/L; Hooke's law sigma equals E epsilon within the proportional limit.

Bending stress sigma equals M y/I, maximum at the outer fibre; shear stress tau equals VQ/(I t).

Euler buckling P_cr equals pi squared E I/(K L) squared; K is 0.5 fixed-fixed, 0.7 fixed-pinned, 1.0 pinned-pinned, 2.0 fixed-free.

Torsion of a circular shaft: tau equals T r/J; angle of twist theta equals T L/(J G).

Fully restrained axial member: sigma equals E alpha deltaT; thermal stress exists only when expansion is prevented.

Principal stresses from Mohr's circle: sigma_1,2 equals (sigma_x plus sigma_y)/2 plus or minus the square root of ((sigma_x minus sigma_y)/2) squared plus tau_xy squared.

Deflections of linear elastic beams are combined by superposition; check both strength and serviceability limits.

Combined axial and bending stress adds algebraically at the section fibre; check tension, compression, and buckling separately.

Shaft design under torsion: tau equals 16T/(pi d cubed); under combined bending and torsion use equivalent moment or equivalent torque.

Ball bearing life L10 equals (C/P) cubed in millions of revolutions; roller bearings use exponent 10/3.

Gear train ratio equals product of driven teeth divided by product of driving teeth; speed ratio is the inverse.

Bolt tightening torque T equals K F d, with K about 0.2 for dry steel threads; preload controls joint fatigue and leakage.

Fatigue criteria: Goodman and Soderberg lines are conservative; Gerber is less conservative; mean stress reduces allowable alternating stress.

Helical spring rate k equals G d to the fourth/(8 D cubed N), where d is wire diameter, D mean coil diameter, N active coils.

Design factor of safety equals material strength divided by applied stress; the required value depends on load uncertainty, consequence, and code.

Interference fits: the diametral interference must produce the required holding torque without exceeding the yield strength of either member.

Chvorinov rule: solidification time equals a constant times (volume/surface area) squared; a riser must freeze after the casting it feeds.

Welding heat input per unit length equals voltage times current divided by travel speed; higher heat input increases distortion and HAZ width.

Carbon equivalent CE equals C plus Mn/6 plus (Cr plus Mo plus V)/5 plus (Ni plus Cu)/15; high CE requires preheat and controlled cooling.

Taylor tool life: V T^n equals C; increasing cutting speed reduces tool life and raises temperature at the cutting edge.

Machining cutting speed is surface speed; feed is advance per revolution; depth of cut is radial engagement.

Annealing softens and relieves stress; normalizing refines grain; quenching hardens; tempering restores toughness after quenching.

Blanking and piercing clearance is a percentage of sheet thickness and depends on material; too little clearance causes edge tearing.

NDT methods: visual, dye penetrant, magnetic particle, ultrasonic, and radiographic, each limited by material and defect type.

Sensible coil load in watts is about 1.23 times air flow in L/s times the dry-bulb temperature difference in K.

Latent coil load in watts is about 3010 times air flow in L/s times the humidity ratio difference in kg/kg.

Chiller efficiency: COP equals 3.517 divided by kW/ton; a 0.6 kW/ton chiller has a COP of about 5.9.

Refrigeration cycle: evaporator absorbs heat at low pressure; compressor raises pressure; condenser rejects heat; expansion valve drops pressure.

Duct equal-friction method selects sizes so that total pressure loss per unit length is approximately constant along the run.

Outdoor air ventilation rate is set by ASHRAE 62.1 or the applicable Qatar code, using people-based and area-based components.

Fan and pump affinity laws apply to variable-speed drives: flow proportional to speed, pressure proportional to speed squared, power to speed cubed.

Air changes per hour equals supply volumetric flow divided by room volume; it is a check, not a substitute for load calculation.

PID output equals Kp e plus Ki integral of e dt plus Kd de/dt; integral action removes steady-state offset.

First-order system time constant tau reaches 63.2 percent of final value in one tau and about 95 percent in three tau.

Second-order response is set by damping ratio zeta and natural frequency omega_n; zeta below one gives overshoot.

Routh-Hurwitz, Bode gain margin, and phase margin test closed-loop stability; gain margin is the gain increase that causes instability.

Standard analog transmission is 4-20 mA; 4 mA is live zero, allowing detection of a broken wire.

A PLC scan cycle reads inputs, executes the program, then updates outputs; scan time must be shorter than the fastest process event.

Control valves are specified fail-closed or fail-open so that loss of air or power leaves the process in a safe condition.

RTDs are stable and accurate; thermocouples suit high temperature; thermistors are sensitive but limited in range.

Critical path is the longest path through the network; its total float is zero and it sets the minimum project duration.

Earned value: CV equals EV minus AC; SV equals EV minus PV; CPI equals EV/AC; SPI equals EV/PV.

ES and EF pass forward; LS and LF pass backward; total float equals LS minus ES or LF minus EF.

A change order requires documented scope, cost, and schedule impact before work proceeds.

Risk score equals probability times consequence; response options are avoid, transfer, mitigate, and accept.

Lump-sum contracts place quantity risk on the contractor; remeasured and cost-plus contracts allocate it differently.

A project baseline is the approved scope, schedule, and cost plan against which performance is measured; changes require formal approval.

Hierarchy of controls: elimination, substitution, engineering controls, administrative controls, then PPE as the last barrier.

Lockout/tagout isolates all hazardous energy, applies locks and tags, and verifies zero energy before maintenance.

Confined-space entry requires atmospheric testing for oxygen, flammables, and toxics, plus a permit, attendant, and rescue plan.

Fire triangle: fuel, oxygen, and ignition; removing any one prevents or extinguishes combustion.

Permit-to-work systems control hot work, confined-space entry, excavation, and energization.

QA covers process and system conformity; QC covers inspection and testing of the product or installation.

Noise exposure limit commonly used is 85 dBA over eight hours; higher levels require shorter exposure and hearing protection.

HAZOP examines deviations from design intent using guide words such as no, more, less, reverse, and other.