Every loading condition on a ship or workboat starts with one question: is the vessel stable enough to sail? The fastest first answer is the transverse metacentric height, GM. This post sets out the hydrostatic fundamentals behind it, shows how free surface in slack tanks erodes it, explains how the inclining experiment fixes the lightship KG, and works through a loading condition for a small cargo vessel. It ends with the first checks against the IMO 2008 Intact Stability Code. It is a screening method, not a substitute for a full stability booklet. It also sits alongside our wider overview of marine engineering and naval architecture . Fundamentals: KB, BM, KM, KG and GM A floating vessel is in equilibrium when weight equals buoyancy and both act along the same vertical line. Buoyancy is the resultant of hydrostatic pressure on the hull, a topic we cover in pressure and fluid statics . When the vessel heels through a small angle, the underwater shape changes, and the centre of buo...
It is defined as, "Laminar flow of viscous fluid in the space between two parallel plates (one of which is moving relative to the other)".
Flow is driven by:
Viscous drag force acting at the fluid.
Applied pressure gradient parallel to the plates.
Application are:
Hydro-static lubrication
Viscosity pumps
Turbine
Applied to Journal bearings (used in mechanical systems).
3. Steady, Incompressible & Laminar Flow in a Circular Tube
It is defined as, "Steady, incompressible and laminar flow through a straight circular tube of constant cross-section". It is also called Hagen-Poiseuille Flow.
Lubrication
Navier-stokes equation used to find out the velocity profile inside a bearing. There are 3 types of lubrication:
Full Film Lubrication ↦ Bearing surfaces are fully separated by a film of lubricant.
Boundary Lubrication ↦ Bearing surfaces physically come into contact.
Mixed Film Lubrication ↦ Combination of partial lubricant films and some asperity (roughness/difficult to endure) contact between the surfaces.
Full film lubrication is further divided into the following:
Hydrostatic ↦ Surfaces are separated by an externally pressurized lubricant.
Hydrodynamics ↦ Surfaces are separated by a dynamic film of lubricant.
Elastohydrodynamic ↦ Characterized by elastic deflections of the surfaces under very high pressures within the contact zone with an increase in viscosity of the fluid.
Hydrodynamic Lubrication
It is governed by Reynold's equation of Classical Lubrication Theory which came into existence by assuming:
Liquid flowing through thin region separated by 2 moving surfaces.
Pressure does not vary across the film.
Appropriate boundary conditions required for Reynold's equation solution.
Reynold's Equation
It is defined as, "Analysis of Momentum Transport and Continuity equations leads to a single elliptic DE".
Analysis served as a basis of designing hydrodynamically lubricated bearings.
Reynolds Number: Reynolds Number is the ratio of Inertial forces to the Viscous forces. By knowing this number, one can describe the flow whether the flow is laminar, turbulent or transitional flow. There are three possibilities of the range of Reynolds Number: If Reynolds number < 2100 or 2300 ⟺ Laminar Flow If Reynolds number > 4000 ⟺ Turbulent Flow If 2300 < Reynolds number < 4000 ⟺ Transitional Flow In case of different shapes other than circle, the formula for Reynolds Number remain the same however diameter involves in the formula become Hydraulic Diameter which is given by: For pipe: Critical Reynolds Number ⟾ The Reynolds number at which the flow becomes turbulent Re cr For different shapes, the hydraulic diameters are given by: Completely Filled Flow In Closed Channel: If pipe is is considered to filled completely with closed channel, then following are the conditions which...
Intersection Of Solids: Solids are obtained by the combination of of two or more basic solids. When two or more solids combine, a definite curve/line is seen at their intersection. This curve/line is called curve/line of intersection (COI / LOI) and it is the result of inter-penetration of solids. Applications Of Intersection Of Solids: Designing a sheet metal objects. Automobile Parts. Moulding patterns. Forged end of connecting road. Intersection of two contacting surface, etc. Inter-Penetration Of Solids: When one solids penetrates another solids then their surfaces intersect and at the junction of intersection a typical curve is formed, which remains common to both solids. This curve is called Curve of Intersection and it is a result of inter-penetration of solids. Cases Of Intersection Of Solids: First we need to discuss the general solution steps of how we draw intersection of solids diagram. So know, we are going to discuss the basic steps:...
Types Of Lines And Its Uses: There are three types of types on the basis of thickness and they are: Visible Lines ↝ It represents features that can be seen in the current view. Hidden Lines ↝ It represents features that cannot be seen in the current view. Center Line ↝ It represents symmetry, path of motion, centers of circles,, axis of asymmetrical parts. Dimension and Extension Lines ↝ It indicates the sizes and location of features on a drawing. Placement Of Dimension Lines: Dimension should be outside the view. Dimension should be applied to one view. Dimension should be placed in a view that shows the distance in its true length. Dimension lines should be placed, in general 10 mm (1/2 in) away from the outlines from the view. Parallel lines should be placed uniformly. Values should be midway (auto centered) between the arrow heads, except when a center-line interferes. Dime...
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