Computer Aided Engineering (ME-603 (B)) - Unit 3 Short Notes

UNIT 3: Computer Aided Engineering Applications

A. TURBOMACHINERY ANALYSIS & DESIGN

1.0 Fundamental Concepts & Equations

Euler's Turbine Equation

• Definition: Relates the change in angular momentum of the fluid to the torque exerted on the rotor.

• Derivation: From moment of momentum principle for a steady flow through a turbomachine.

$$ \dot{W} = \dot{m} (U_2 V_{\theta 2} - U_1 V_{\theta 1}) $$

Where:

• $\dot{W}$ = Power transferred (W)

• $\dot{m}$ = Mass flow rate (kg/s)

• $U$ = Blade speed (m/s)

• $$\displaystyle V_{\theta} $$ = Tangential (whirl) component of absolute velocity (m/s)

• Subscripts 1 & 2 denote inlet and outlet.

• Significance for Reaction Turbines: For a reaction turbine ( Parsons stage), $$\displaystyle V_{\theta 1} = V_{\theta 2} $$ (symmetrical velocity diagram), simplifying to $$\displaystyle \dot{W} = \dot{m} U (V_{\theta 2} - V_{\theta 1}) $$.

• Energy Equation Interpretation: The Euler equation represents the ideal, isentropic work transfer per unit mass, assuming no losses between fluid and blades.

[!TIP] Exam often asks to derive Euler's equation from first principles. Remember the sign convention: work done by the fluid on the blades is positive for turbines.

Degree of Reaction (R)

• Definition: The ratio of the static enthalpy drop in the rotor blades to the total static enthalpy drop in the stage.

• Mathematical Expression:

$$ R = \frac{\text{Enthalpy drop in rotor}}{\text{Total stage enthalpy drop}} = \frac{h_1 - h_2}{h_0 - h_2} \quad \text{(for stage with nozzle + rotor)} $$

Alternatively, in terms of velocity diagram for symmetrical blading:

$$ R = \frac{1}{2} - \frac{(V_{\theta 2} - V_{\theta 1})}{2U \tan \beta_2} \quad \text{(for Parsons/reaction turbine)} $$

• 50% Reaction Turbine (Parsons Stage):

  • Rotor and stator blades are identical and symmetrical.

  • Velocity diagram is symmetrical: $$\displaystyle \alpha_1 = \beta_2 $$, $$\displaystyle \beta_1 = \alpha_2 $$.

  • Pressure drop occurs equally in fixed and moving blades.

  • Optimal for axial thrust balance.

• Application to Steam Turbines: High reaction (R > 0.5) stages are used in the low-pressure sections of large steam turbines to improve efficiency and reduce blade speed.

Velocity Diagrams

• Construction for Impulse Turbines (e.g., Curtis):

  1. Draw absolute velocity $$\displaystyle V_1 $$ at nozzle angle $$\displaystyle \alpha_1 $$.

  2. Draw blade speed $U$ horizontally.

  3. Relative velocity $$\displaystyle W_1 $$ is the vector difference $$\displaystyle V_1 - U $$.

  4. For frictionless, symmetrical blades: $$\displaystyle W_2 = W_1 $$, $$\displaystyle \beta_1 = \beta_2 $$.

  5. $$\displaystyle V_2 $$ is found by adding $U$ to $$\displaystyle W_2 $$.

  6. Key: $$\displaystyle V_1 >> U $$, large pressure drop in nozzle only.

• Construction for Reaction Turbines (Parsons Stage):

  1. $$\displaystyle V_1 $$ at $$\displaystyle \alpha_1 $$, $U$ horizontal.

  2. $$\displaystyle W_1 $$ such that $$\displaystyle \beta_1 $$ is designed for shockless entry.

  3. Pressure drop in rotor causes $$\displaystyle W_2 > W_1 $$ (acceleration).

  4. $$\displaystyle V_2 $$ at $$\displaystyle \alpha_2 = \beta_1 $$ (symmetry for 50% reaction).

  5. $$\displaystyle V_{\theta 1} = V_{\theta 2} $$, so Euler work is $$\displaystyle U(V_{\theta 2} - V_{\theta 1}) = 0 $$? No: For 50% reaction, $$\displaystyle V_{\theta 1} \neq V_{\theta 2} $$ unless $$\displaystyle \alpha_1 = \beta_2 $$. Standard derivation gives $$\displaystyle V_{\theta 2} - V_{\theta 1} = 2U \cos \alpha_1 $$ for symmetrical blading.

• Relationship (Steam vs. Hydro Turbines):

  • Steam Turbine: Absolute velocity changes significantly due to large pressure drop in nozzles/stators. $$\displaystyle V_1 \neq V_2 $$ generally.

  • Hydro Turbine (Pelton, Francis): Pressure drop occurs entirely in volute/casing (for reaction) or nozzle (for impulse). Velocity diagrams are simpler; for Pelton (impulse), $$\displaystyle V_1 $$ is jet velocity, $$\displaystyle W_1 = V_1 - U $$, $$\displaystyle W_2 \approx W_1 $$ (ideal), $$\displaystyle V_2 \approx V_1 - 2U\cos\beta_1 $$.

Dimensional Analysis (Buckingham Pi Theorem)

• Goal: Express efficiency $\eta$ as function of $\rho, \mu, \omega, D, Q$.

• Variables:

  • $\eta$: Efficiency (dimensionless) → Repeating variable.

  • $\rho$: Density ($$\displaystyle ML^{-3} $$)

  • $\mu$: Viscosity ($$\displaystyle ML^{-1}T^{-1} $$)

  • $\omega$: Angular speed ($$\displaystyle T^{-1} $$)

  • $D$: Diameter ($L$)

  • $Q$: Discharge ($$\displaystyle L^3T^{-1} $$)

• Steps:

  1. Total variables $$\displaystyle n=6 $$, fundamental dimensions $$\displaystyle k=3 $$ (M, L, T) → $\pi$ terms = $$\displaystyle n-k = 3 $$.

  2. Choose repeating variables: $\rho, \omega, D$ (cover M, L, T).

  3. Form $\pi$ terms for $\mu$ and $Q$:

     • $$\displaystyle \pi_1 = \mu / (\rho \omega D^2) $$ → Reynolds number inverse.

     • $$\displaystyle \pi_2 = Q / (\omega D^3) $$ → Flow coefficient $\phi$.

  4. Efficiency function:

$$ \eta = f\left( \frac{\rho \omega D^2}{\mu}, \frac{Q}{\omega D^3} \right) = f\left( Re, \phi \right) $$

• Significance: Allows performance testing of geometrically similar turbomachines at different scales/speeds by maintaining constant $\pi$ groups.

[!TIP] Common mistake: Forgetting that efficiency is dimensionless, so it becomes the dependent $\pi$ term. Always verify dimensions of each $\pi$ term is zero.

2.0 Steam Turbines

Compounding

• Velocity Compounding (Curtis Turbine):

  • Principle: High jet velocity from nozzle is compounded (divided) by multiple stages of moving blades on the same shaft (no intervening nozzles).

  • Construction: One nozzle → multiple (2-3) rotor blade rings on same drum.

  • Advantage: Reduces blade speed for given jet velocity, lowering centrifugal stress. Suitable for high-pressure stages.

  • Disadvantage: More complex, higher leakage losses.

• Pressure Compounding (Rateau Turbine):

  • Principle: Total pressure drop is divided into many small drops by alternating nozzles and moving blades (multiple stages).

  • Construction: Classic multi-stage turbine: Nozzle → Moving blades → Nozzle → Moving blades...

  • Advantage: Better efficiency at partial loads, lower exit velocities.

  • Disadvantage: Longer shaft, more bearings.

• Comparative Analysis:

  | Feature | Velocity Compounding (Curtis) | Pressure Compounding (Rateau) | |---------|-----------------------------|-----------------------------| | Pressure Drop | All in first nozzle | Distributed over stages | | Blade Speed | Lower for given $$\displaystyle V_1 $$ | Higher per stage | | Stages | Few (2-3) on one shaft | Many (10-20) | | Application | HP stages of large turbines | LP stages, industrial turbines | | Efficiency | Lower than pressure compounded | Higher, especially at part load |

Performance & Losses

• Major Losses:

  1. Nozzle Losses: Friction, shock, incomplete expansion.

  2. Blade Friction Losses: Skin friction on blade surfaces.

  3. Blade Exit Loss (Kinetic Energy Loss): $$\displaystyle V_2^2/2 $$ not recovered.

  4. Leakage Losses: Past blade tips, glands.

  5. Disc Friction Losses: Windage on rotating discs.

• Blade Efficiency ($$\displaystyle \eta_b $$) Optimization:

  • For impulse turbine with friction: $$\displaystyle \eta_b = \frac{2 U \cos \beta_2}{V_1} \left( \cos \alpha_1 - \frac{\rho}{2} \right) $$ where $$\displaystyle \rho = \frac{V_2}{V_1} $$ (velocity coefficient).

  • Condition for max $$\displaystyle \eta_b $$: $$\displaystyle U/V_1 = \frac{\cos \alpha_1}{2} $$ (for frictionless, $$\displaystyle \rho=1 $$).

• Stage Efficiency ($$\displaystyle \eta_{stage} $$): Product of nozzle efficiency $$\displaystyle \eta_n $$ and blade efficiency $$\displaystyle \eta_b $$.

• Overall Efficiency ($$\displaystyle \eta_{overall} $$): $$\displaystyle \eta_{overall} = \eta_{mech} \times \eta_{thermal} $$.

• Reheat Factor (RF):

  • Definition: Ratio of cumulative isentropic enthalpy drop to total isentropic enthalpy drop for the entire turbine.

$$ RF = \frac{\sum (h_i - h_{i+1})_s}{(h_{inlet} - h_{exit})_s} $$

• Cause of Multi-stage Efficiency Improvement: In multi-stage turbines, reheat (intermediate reheating of steam in the blade rows) reduces moisture content in later stages, improving blade efficiency. RF > 1. Typical RF = 1.03 to 1.08 for large turbines.

• Relation: $$\displaystyle \eta_{multi-stage} = \eta_{single-stage} \times RF $$.

Design Parameters

• Blade Inlet/Outlet Angles for Shockless Operation:

  • Condition: Relative velocity $$\displaystyle W_1 $$ must be tangent to blade inlet angle $$\displaystyle \beta_1 $$ → $$\displaystyle W_1 $$ direction = blade inlet direction.

  • For impulse turbine with symmetrical blades ($$\displaystyle \beta_1 = \beta_2 $$), shockless condition: $$\displaystyle \beta_1 = \tan^{-1}\left( \frac{U}{V_1 \cos \alpha_1} \right) $$.

• Blade Speed Optimization:

  • From blade efficiency formula, optimum $$\displaystyle U/V_1 = \cos \alpha_1 / 2 $$ for max efficiency.

  • Practical limit: $U$ limited by centrifugal stress $$\displaystyle \sigma \propto U^2 D $$.

• Axial Thrust Calculation:

  • Net axial force on blades: $$\displaystyle F_a = \dot{m} (V_{f1} - V_{f2}) + (p_1 A_1 - p_2 A_2) $$.

  • For impulse turbine with symmetrical blades and neglecting pressure forces: $$\displaystyle F_a = \dot{m} V_1 (\sin \alpha_1 - \sin \alpha_2) $$.

  • For reaction turbine: Pressure forces significant; must include $$\displaystyle p_1 A_1 - p_2 A_2 $$.

Governing

• Methods:

  1. Throttle Governing: Main steam valve throttled to control flow. Simple, used for small load changes.

  2. Nozzle Governing (Group Governing): Sets of nozzles turned on/off sequentially. Used in large turbines.

  3. Bypass Governing: Steam bypassed to condenser.

  4. Slide Valve Governing: Obsolete.

• Importance: Maintains constant speed under varying load, prevents overspeeding, protects turbine from stress during load fluctuations.

3.0 Hydraulic Turbines

Pelton Wheel

• Velocity Diagram & Bucket Design:

  • Single jet hits split bucket (double-cupped).

  • $$\displaystyle V_1 = $$ jet velocity, $$\displaystyle U = $$ bucket speed.

  • Ideal: $$\displaystyle V_2 \approx V_1 - 2U\cos\beta_1 $$; for $$\displaystyle \beta_1 \approx 0^\circ $$ (bucket shape), $$\displaystyle V_2 \approx V_1 - 2U $$.

  • Optimum $$\displaystyle U/V_1 = 0.5 $$ for max efficiency.

• Power Available at Nozzle:

$$ P_{avail} = \rho g Q H $$

Where $H$ = net head, $Q$ = discharge.

• Hydraulic Efficiency ($$\displaystyle \eta_h $$):

$$ \eta_h = \frac{\text{Power developed by runner}}{\text{Power available at nozzle}} = \frac{\dot{m} U (V_1 + V_2 \cos \beta_2)}{\rho g Q H} \approx \frac{2U(V_1 - U)}{V_1^2} \quad \text{(ideal)} $$

• Effect of Side Clearance Angle:

  • Bucket sides are not perfectly vertical; have clearance angle (typically $$\displaystyle 15^\circ-20^\circ $$) to prevent rubbing.

  • Causes escape velocity loss: some water escapes without transferring full momentum → reduces efficiency.

  • Larger clearance angle → lower efficiency.

Draft Tubes

• Necessity & Function:

  • Converts kinetic energy at runner exit to pressure head (pressure recovery).

  • Allows setting turbine above tailrace level → protects from flooding, facilitates maintenance.

  • Increases net head effectively: $$\displaystyle H_{net} = H_{gross} - h_f - h_{dt} $$, where $$\displaystyle h_{dt} $$ is draft tube head loss.

• Types:

  1. Conical Draft Tube: Simple, efficient, used for vertical shafts.

  2. Cylindrical Draft Tube: For low specific speed turbines.

  3. Elbow Draft Tube: For horizontal shafts, compact.

• Pressure Recovery: Based on Bernoulli: $$\displaystyle p_{exit} + \frac{1}{2}\rho V_3^2 = p_{tailrace} + \frac{1}{2}\rho V_4^2 + h_{loss} $$.

Cavitation

• Phenomenon: Formation and collapse of vapor bubbles in regions of local pressure below vapor pressure.

• Causes in Turbines:

  • High suction head (low pressure at runner inlet, especially for reaction turbines).

  • High flow velocity.

  • Inadequate NPSH (Net Positive Suction Head) available.

• Effects:

  • Pitting and erosion of blades (material loss).

  • Vibration, noise, loss of performance.

  • Reduced efficiency, eventual failure.

• Prevention Methods:

  1. Ensure NPSH_available > NPSH_required by design.

  2. Use cavitation-resistant materials (stainless steel, bronze).

  3. Optimize runner inlet design (larger diameter, lower speed).

  4. Install turbine below tailrace level (positive suction head).

Specific Speed ($$\displaystyle N_s $$)

• Definition: The speed of a geometrically similar turbine that would develop unit power (1 kW) under unit head (1 m).

• Derivation from similarity laws:

$$ P \propto N^2 D^5, \quad H \propto N^2 D^2 \quad \Rightarrow \quad N_s = \frac{N \sqrt{P}}{H^{5/4}} \quad \text{(metric units)} $$

Where $N$ = rpm, $P$ = kW, $H$ = m.

• Significance for Turbine Selection:

  • Low $$\displaystyle N_s $$ (0-30): Pelton wheel (impulse, high head, low flow).

  • Medium $$\displaystyle N_s $$ (30-300): Francis turbine (reaction, medium head/flow).

  • High $$\displaystyle N_s $$ (300-1000): Kaplan/Propeller (reaction, low head, high flow).

Efficiencies

• Hydraulic Efficiency ($$\displaystyle \eta_h $$): $$\displaystyle \frac{\text{Power delivered to runner}}{\text{Water power input}} $$.

• Mechanical Efficiency ($$\displaystyle \eta_m $$): $$\displaystyle \frac{\text{Shaft power}}{\text{Power delivered to runner}} $$ (bearings, gland losses).

• Overall Efficiency ($$\displaystyle \eta_o $$): $$\displaystyle \eta_o = \eta_h \times \eta_m $$.

• Manometric Head ($$\displaystyle H_m $$):

  • Definition: The head equivalent to the pressure rise produced by the pump/turbine, including losses.

  • For pumps: $$\displaystyle H_m = \frac{p_{out} - p_{in}}{\rho g} + \frac{V_2^2 - V_1^2}{2g} + (z_2 - z_1) $$.

  • Used to calculate pump head excluding velocity head differences.

4.0 Compressors

Axial Flow Compressor

• Vector Diagram Construction:

  1. Draw axial velocity $$\displaystyle V_f $$ (constant for design).

  2. Draw blade speed $U$ (increases with radius).

  3. Relative velocity $$\displaystyle W_1 $$ enters at angle $$\displaystyle \beta_1 $$ (determined by blade inlet angle).

  4. Absolute velocity $$\displaystyle V_1 $$ has components $$\displaystyle V_f $$ and $$\displaystyle V_{\theta 1} $$.

  5. In rotor, $$\displaystyle W_2 $$ is turned by blade angle $$\displaystyle \beta_2 $$.

  6. $$\displaystyle V_2 = W_2 + U $$.

  7. In stator, $$\displaystyle V_2 $$ is turned back to $$\displaystyle V_3 $$ with $$\displaystyle V_{f3} = V_f $$ for next stage.

• Surging: System instability at low flow rates. Flow separation on compressor blades → reversed flow → pressure drop → flow re-establishes → cycle repeats. Causes vibration, damage.

• Choking: Mass flow limit at high flow rates. Sonic velocity reached at blade throat ($$\displaystyle V_f / \sin \beta_{min} = a $$). Flow cannot increase further; pressure ratio drops.

• Stage Efficiency ($$\displaystyle \eta_{stage} $$): $$\displaystyle \eta_{stage} = \frac{\text{Isentropic work}}{\text{Actual work input}} = \frac{c_p T_1 \left[ (p_2/p_1)^{(\gamma-1)/\gamma} - 1 \right]}{c_p (T_2 - T_1)} $$.

• Overall Efficiency: $$\displaystyle \eta_{overall} = \frac{\text{Isentropic work for whole compressor}}{\text{Actual total work input}} $$.

• Polytropic Efficiency ($$\displaystyle \eta_p $$):

  • Definition: Efficiency of an infinitesimal stage; constant for all stages in a multi-stage compressor.

  • Significance: More accurate for comparing compressors of different pressure ratios; independent of pressure ratio.

  • Relation to Isentropic Efficiency:

$$ \eta_s = \frac{(r_p)^{(\gamma-1)/\gamma} - 1}{(r_p)^{(\gamma-1)/(\gamma \eta_p)} - 1} $$

Where $$\displaystyle r_p $$ = total pressure ratio.

Centrifugal Compressor

• Vector Diagram Construction:

  1. Inlet: $$\displaystyle V_1 $$ radial (if vaneless) or at angle (if with inlet guide vanes).

  2. $$\displaystyle U_1 $$ tangential at inlet radius $$\displaystyle r_1 $$.

  3. $$\displaystyle W_1 $$ relative velocity.

  4. In impeller, $$\displaystyle W_2 $$ at outlet radius $$\displaystyle r_2 $$, $$\displaystyle \beta_2 $$ is blade outlet angle.

  5. $$\displaystyle V_2 = U_2 + W_2 $$; has radial and tangential components.

  6. In diffuser, $$\displaystyle V_2 $$ slowed down, pressure increased.

• Comparison with Axial Flow:

  | Feature | Centrifugal | Axial Flow | |---------|-------------|------------| | Pressure Ratio per Stage | High (3-5:1) | Low (1.1-1.2:1) | | Flow Rate | Medium | High | | Efficiency | Slightly lower | Higher (for large capacity) | | Size/Weight | Compact | Long, slender | | Application | Medium capacity, high pressure | Large capacity, gas turbines |

General Compressor Analysis

• Positive Displacement Machines:

  • Traps fixed volume, displaces it to higher pressure.

  • Types: Reciprocating, rotary (vane, screw, lobe).

  • Advantage: High pressure at low flow, good for gases.

• Slip Factor ($\sigma$):

  • Definition: Ratio of actual whirl velocity at impeller outlet to ideal (no slip) whirl velocity.

$$ \sigma = \frac{V_{\theta 2, actual}}{V_{\theta 2, ideal}} = \frac{V_{\theta 2}}{U_2} \quad \text{(for radial entry)} $$

• Cause: Fluid viscosity, boundary layer, finite number of blades → deviation from ideal flow.

• Effect: Reduces pressure rise and efficiency. Stodola's slip factor: $$\displaystyle \sigma = 1 - \frac{\pi}{z} \frac{\sin \beta_2}{1 - m} $$ where $z$ = blades, $$\displaystyle m = r_1/r_2 $$.

5.0 Pumps & Power Transmission

Centrifugal vs Reciprocating Pumps

• Centrifugal Pump:

  • Advantages: Continuous flow, low maintenance, no valves, handles suspensions, high flow rates.

  • Disadvantages: Low suction head, efficiency drops at high pressure, priming needed.

  • Applications: Water supply, irrigation, chemical transfer.

• Reciprocating Pump:

  • Advantages: High pressure, high efficiency at high head, good suction lift, constant delivery (with air vessel).

  • Disadvantages: Pulsating flow, high maintenance, valves wear, not for viscous fluids.

  • Applications: High-pressure cleaning, oil pipeline, dosing.

Pump Analysis

• Specific Speed of Pumps ($$\displaystyle N_s $$):

  • Definition: Speed at which a geometrically similar pump would deliver 1 m³/s against 1 m head.

$$ N_s = \frac{N \sqrt{Q}}{H^{3/4}} \quad \text{(metric)} $$

Where $N$ = rpm, $Q$ = m³/s, $H$ = m.

• Significance: Predicts pump type and shape:

  • Low $$\displaystyle N_s $$ (< 500): Radial flow (centrifugal).

  • Medium $$\displaystyle N_s $$ (500-5000): Mixed flow.

  • High $$\displaystyle N_s $$ (> 5000): Axial flow.

• Manometric Head ($$\displaystyle H_m $$): See above under Hydraulic Turbines.

Fluid Power Devices

• Fluid Coupling:

  • Working Principle: Hydraulic connection between driving and driven members via fluid. No mechanical contact.

  • Components: Impeller (pump) on input shaft, runner (turbine) on output shaft, casing.

  • Slip ($s$): $$\displaystyle s = \frac{N_1 - N_2}{N_1} = 1 - \frac{T_2}{T_1} $$ (torque ratio).

  • Efficiency ($\eta$): $$\displaystyle \eta = \frac{T_2 \omega_2}{T_1 \omega_1} = \frac{N_2}{N_1} = 1 - s $$.

  • Application: Soft start, overload protection, vibration damping.

• Torque Converter:

  • Construction: Similar to coupling but with stator (fixed blades) between impeller and runner.

  • Operation: Stator redirects fluid flow from runner to impeller → torque multiplication.

  • Torque Ratio: $$\displaystyle TR = \frac{T_2}{T_1} > 1 $$ at low $$\displaystyle N_2/N_1 $$.

  • Efficiency: Lower than coupling due to stator losses; high at high speed ratios.

  • Application: Automatic transmissions, marine propulsion.

• Hydraulic Intensifier:

  • Principle: Uses low-pressure, high-volume fluid to drive a piston that pressurizes a smaller area → high pressure, low volume output.

  • Construction: Two concentric cylinders, large diameter piston (low pressure side) fixed to small diameter piston (high pressure side).

  • Application: Hydraulic presses, test rigs where high pressure needed from low-pressure source.

[!TIP] Torque converter vs fluid coupling: Stator is key differentiator. Converter multiplies torque; coupling only transmits.

B. PRODUCT DESIGN & COMPUTER AIDED MANUFACTURING

1.0 Product Development Framework

Product Life Cycle (PLC)

• Stages:

  1. Introduction: Low sales, high costs, negative profit. Marketing focus on awareness. Example: Electric vehicles (early 2010s).

  2. Growth: Rapid sales increase, profits rise, competition enters. Example: Smartphones (2010-2015).

  3. Maturity: Sales peak, market saturated, price wars, profit stabilizes/declines. Example: Basic mobile phones (2010s).

  4. Decline: Sales fall, profit erodes, product phased out. Example: DVD players.

• Strategic Implications:

  • Introduction: Invest in R&D, build brand.

  • Growth: Expand distribution, improve product.

  • Maturity: Cost reduction, product differentiation, find new markets.

  • Decline: Harvest or divest.

Product Strategy

• Elements:

  • Target market selection.

  • Product positioning.

  • Value proposition.

  • Roadmap.

• Resource Allocation Processes:

  • Portfolio management (BCG matrix).

  • Stage-gate process with funding per phase.

  • Cross-functional team budgeting.

• Organizational Policies:

  • New product development (NPD)流程.

  • IP protection.

  • Sustainability mandates.

Customer-Centric Design

• Importance: Ensures market acceptance, reduces redesign costs, builds loyalty.

• Methods for Obtaining Customer Input:

  • Surveys, focus groups, interviews.

  • Observation/ethnography.

  • User testing, beta programs.

  • Social media listening.

• Involving Customers:

  • Co-creation workshops.

  • Lead user innovation.

  • Crowdsourcing ideas.

Competitive Analysis

• Benchmarking Process:

  1. Identify key competitors.

  2. Select products/features to compare.

  3. Measure performance (price, quality, features).

  4. Analyze gaps.

  5. Set improvement targets.

• Rival Product Assessment Factors:

  • Price, quality, features, reliability, service, brand perception.

Innovation & Policy

• Role in Product Policy: Drives growth, competitive advantage, market leadership. Policy must encourage R&D, tolerate failure.

• Challenges in NPD:

  • Market uncertainty.

  • Technical risk.

  • Resource constraints.

  • Time-to-market pressure.

• Characteristics of Successful Development:

  • Clear market need.

  • Strong cross-functional teams.

  • Top management support.

  • Iterative prototyping.

2.0 Design Methodologies

Value Engineering (VE)

• Objectives: Improve value = Function / Cost. Not just cost cutting.

• Principles:

  • Function-focused.

  • Team approach (multi-disciplinary).

  • Creative thinking.

  • Systematic evaluation.

• Procedure (Job Plan):

  1. Information Phase: Gather data on function, cost, constraints.

  2. Speculation Phase: Brainstorm ways to achieve functions cheaper/better.

  3. Evaluation Phase: Rank ideas, select promising.

  4. Development Phase: Detailed analysis, cost estimates.

  5. Presentation Phase: Recommend to management.

• Example: Redesigning a bracket: Original solid steel → hollow with ribs → 40% weight saving, same strength.

Function Analysis System Technique (FAST)

• Detailed Methodology:

  • Basic Function (BF): What the product must do (verb + object). E.g., "transport fluid".

  • Secondary Functions (SF): How BF is achieved. E.g., "contain pressure", "minimize leakage".

  • Tertiary/Superfluous Functions: Unnecessary or over-designed features.

  • Diagram: Logic tree (IF-THEN) linking functions.

• Application in Automotive Systems:

  • BF: "Provide transportation".

  • SF: "Transfer power", "Support vehicle", "Steer", "Brake".

  • Can identify over-engineered components (e.g., excessive material in non-critical brackets).

• Handling Tertiary Functions: Identify and eliminate or reduce cost without affecting BF.

Creative Techniques

• Methods:

  • Brainstorming: Free idea generation, no criticism.

  • Synectics: Analogies, metaphors.

  • Mind Mapping: Visual association.

  • SCAMPER: Substitute, Combine, Adapt, Modify, Put to other uses, Eliminate, Reverse.

  • TRIZ: Systematic innovation based on patterns.

Design for X (DFX)

• DFM (Design for Manufacture): Design for easy/cheap manufacturing.

  • Minimize parts, standard materials, tolerances, avoid complex shapes.

• DFA (Design for Assembly): Design for easy/quick assembly.

  • Minimize parts, symmetrical parts, self-locating, reduce fasteners.

• DFMA Integration: Combine DFM & DFA; often done simultaneously. Tools: Boothroyd-Dewhurst method.

• DFE (Design for Environment): Minimize environmental impact.

  • Recyclable materials, reduce energy use, easy disassembly, non-toxic.

• Robust Design:

  • Principle: Design products insensitive to variation (noise factors).

  • Implementation: Use Taguchi methods: Orthogonal arrays, signal-to-noise ratios.

  • Challenges: Requires statistical expertise, more experiments, may increase initial cost.

3.0 Manufacturing-Driven Design

Process-Specific Guidelines

• Sand Casting:

  • Design Rules:

    • Avoid sharp corners (use fillets).

    • Draft angles (1-3° on vertical surfaces).

    • Uniform wall thickness to avoid shrinkage.

    • Avoid large flat surfaces (sagging).

    • Minimum section thickness: 3-5 mm.

• Die Casting vs Sand Casting:

  | Aspect | Die Casting | Sand Casting | |--------|-------------|--------------| | Mold | Metal (steel) | Sand (disposable) | | Pressure | High (700-1400 bar) | Low (gravity) | | Surface Finish | Excellent (1-2 μm) | Rough (25-200 μm) | | Dimensional Accuracy | High | Low | | Wall Thickness | Thin possible (0.5 mm) | Thicker (3+ mm) | | Production Rate | Very high | Low | | Cost | High tooling, low per part | Low tooling, high per part | | Design Consideration | Avoid undercuts, allow for ejector pins | More flexibility, draft angles critical |

• Non-Metallic Products:

  • Thermal: Consider CTE, thermal degradation, glass transition.

  • UV: Add stabilizers, select UV-resistant polymers.

  • Chemical: Select resistant polymers (PTFE, HDPE), avoid swelling.

Assembly Optimization

• Manual Assembly Guidelines:

  • Minimize parts count.

  • Symmetrical parts, no orientation required.

  • Use snap fits, self-locating features.

  • Reduce fasteners (use clips, adhesives).

  • Design for gravity-assisted assembly.

• Design for Disassembly:

  • Use standard fasteners.

  • Avoid permanent joints (adhesives, welding).

  • Modular design.

  • Mark material types for recycling.

Quality Considerations

• Injection-Molded Part Quality Factors:

  • Wall thickness uniformity.

  • Draft angles.

  • Gate location/design.

  • Cooling time.

  • Material drying.

  • Mold temperature.

• CAD/DFM Tools:

  • Moldflow analysis (flow, cooling, warpage).

  • Draft angle checks.

  • Thickness analysis.

  • Automatic DFM checks in CAD software.

4.0 Computer Aided Design & Prototyping

CAD Fundamentals

• 2D vs 3D Modeling:

  | 2D Drafting | 3D Modeling | |-------------|-------------| | Flat views (plan, elevation) | Solid/surface representation | | No volume/volume data | Full geometric data | | Manual projection | Automatic view generation | | Used for drawings only | Used for analysis, RP, manufacturing | | Role in Manufacturing Optimization: 3D models enable CNC programming, simulation, clash detection, RP directly.

Rapid Prototyping (RP)

• Five-Step Process:

  1. CAD Modeling: Create 3D model.

  2. Conversion to STL: Model triangulated to STL format.

  3. Slicing: RP software slices STL into layers.

  4. Part Construction: RP machine builds layer-by-layer.

  5. Post-Processing: Remove support, finish surface.

• Classification of Methods:

  1. Photopolymer (Vat Polymerization): SLA.

  2. Powder Bed Fusion: SLS, DMLS.

  3. Material Jetting: PolyJet.

  4. Material Extrusion: FDM.

  5. Sheet Lamination: LOM.

• Surface Finish Comparison:

  • SLA: Smooth (0.1-0.5 μm), requires post-cure.

  • SLS: Rough (50-100 μm), grainy (powder).

  • LOM: Stepped (layer lines visible), paper/wood texture.

• Powder Handling in SLS:

  • Powder is spread by roller, sintered by laser.

  • Un-sintered powder supports overhangs.

  • Post-process: Dig out part, bead blasting to remove powder.

  • Powder can be recycled (filtered, mixed with fresh).

• Applications in Design Validation:

  • Form/fit check.

  • Functional testing (limited).

  • Pattern for casting.

  • Visual aids.

Data Formats

• STL (Stereolithography):

  • Significance: De facto standard for RP. Represents surface as triangular mesh.

  • Limitations: No color, no texture, no solid info, faceted.

• Other Formats: OBJ (color/texture), 3MF (modern, includes support/material), STEP (for CAD exchange).

Simulation & Analysis

• Role: Virtual testing of designs (FEA, CFD, motion) before physical prototype.

• Validation for Production Processes:

  • Moldflow (injection molding).

  • Metal forming simulation.

  • Welding distortion.

  • Machining (CNC simulation).

5.0 Sustainability & Ergonomics

Eco-Design Principles (DFE)

• Impact on Design:

  • Material selection (recycled, renewable, non-toxic).

  • Energy efficiency during use.

  • Design for disassembly/recycling.

  • Minimize packaging.

  • Longevity/durability.

• Sustainable Product Examples:

  • Fairphone (modular, repairable).

  • Tesla (electric, battery recycling).

  • Patagonia (recycled polyester, repair program).

• Eco-Friendly Packaging:

  • Minimal material.

  • Biodegradable/compostable.

  • Reusable containers.

  • Right-size packaging.

Ergonomics

• Integration in Product Design:

  • User-centered design process.

  • Anthropometric data (percentiles).

  • Cognitive load reduction.

  • Safety (prevent RSI).

• Human Factors Considerations:

  • Physical: Reach, strength, posture.

  • Cognitive: Intuitive controls, feedback, error tolerance.

  • Sensory: Visibility, audibility, tactile feedback.

• Visual Design Elements & Concepts:

  • Color (coding, contrast).

  • Typography (readability).

  • Layout (grouping, hierarchy).

  • Icons (universal understanding).

  • Affordance (perceived function).

6.0 Power Transmission & Fluid Power (Industry Applications)

Power Transmitting Devices

• Industrial Applications Overview:

  • Belts/Pulleys: HVAC, conveyors, machine tools.

  • Chains/Sprockets: Motorcycles, bicycles, industrial machinery.

  • Gears: Automobiles, gearboxes, robotics.

  • Couplings: Pumps, compressors, generators.

• Selection Criteria:

  • Power/torque.

  • Speed ratio.

  • Center distance.

  • Shock load.

  • Environment (temperature, contamination).

  • Maintenance requirements.

Fluid Power Systems

• Hydraulic Press Calculations (Ram/Plunger):

  • Principle: Pascal's law: $$\displaystyle p = F/A $$.

  • Force Multiplication: $$\displaystyle F_2 = F_1 \times (A_2/A_1) $$.

  • Example: Ram diameter 200 mm, plunger 30 mm, load 3 kN.

$$ A_1 = \pi (0.03)^2/4 = 7.065 \times 10^{-4} \mathrm{m^2}, \quad A_2 = \pi (0.2)^2/4 = 3.142 \times 10^{-2} \mathrm{m^2} $$

$$ F_1 = F_2 \times (A_1/A_2) = 3000 \times (7.065 \times 10^{-4} / 3.142 \times 10^{-2}) = 67.5 \mathrm{~N} $$

• System Design Considerations:

  • Pump selection (flow, pressure).

  • Actuator sizing.

  • Valve selection (directional, pressure, flow control).

  • Accumulators (energy storage, shock absorption).

  • Filtration.

  • Heat dissipation.

  • Safety factors.

[!TIP] Hydraulic press problems are common. Always convert diameters to meters, compute areas, apply $$\displaystyle F_1/A_1 = F_2/A_2 $$.