Upload
kr-manu
View
271
Download
0
Embed Size (px)
Citation preview
8/20/2019 Engine Top Bracing.
1/32
Engine Top BracingEngine Top Bracing
8/20/2019 Engine Top Bracing.
2/32
Engine Top BracingEngine Top Bracing
Hull structure
Top bracing
Engine
8/20/2019 Engine Top Bracing.
3/32
Learning ObjectivesLearning Objectives
Understand the purpose of engine top bracing arrangementUnderstand the purpose of engine top bracing arrangement
Describe the mechanical top bracing arrangementDescribe the mechanical top bracing arrangement
Explain the functioning of mechanical top bracing arrangementExplain the functioning of mechanical top bracing arrangement
Describe the hydraulic top bracing arrangementDescribe the hydraulic top bracing arrangement
Explain the functioning of hydraulic top bracing arrangementExplain the functioning of hydraulic top bracing arrangement
Describe the periodic maintenance to be carried outDescribe the periodic maintenance to be carried out
8/20/2019 Engine Top Bracing.
4/32
OverviewOverview
Engine top bracings are used to connect upper end of the engineEngine top bracings are used to connect upper end of the engine
to a hull structure for damping lateral vibration generateto a hull structure for damping lateral vibration generated by slowd by slowspeed main enginesspeed main engines
Bracing bolts play an important role for satisfactory operatiBracing bolts play an important role for satisfactory operati
on ofon of
slow speed diesel enginesslow speed diesel engines
Prolonged running with slack bracing bolts may cause seriousProlonged running with slack bracing bolts may cause serious
vibration and damage to engine structurevibration and damage to engine structure
Proper maintenance of engine top bracing arrangement isProper maintenance of engine top bracing arrangement is
essential at regular intervals.essential at regular intervals.
8/20/2019 Engine Top Bracing.
5/32
Forces
Acting on
X-Head
Guides
Due to
Con-rod
Angularity
8/20/2019 Engine Top Bracing.
6/32
Guide Force MomentGuide Force Moment
Forces on the guides will cause the guide force moment betweenForces on the guides will cause the guide force moment between
guide shoe axis and c/shaft axisguide shoe axis and c/shaft axis
Guide force moments are caused by the gas force on the pistonsGuide force moments are caused by the gas force on the pistonsand by the inertia forcesand by the inertia forces
The moments may excite engine vibrations by moving the engineThe moments may excite engine vibrations by moving the engine
top athwart shipstop athwart ships
It may cause a rocking (excited by HIt may cause a rocking (excited by H--moment) or twistingmoment) or twisting
(excited by X(excited by X--moment) movement of the engine.moment) movement of the engine.
Engines with less than seven cylinders, this guide force momentEngines with less than seven cylinders, this guide force momenttends to rock the engine in transverse directiontends to rock the engine in transverse direction
Engines with seven cylinders or more, it tends to twist the engiEngines with seven cylinders or more, it tends to twist the enginene
8/20/2019 Engine Top Bracing.
7/32
8/20/2019 Engine Top Bracing.
8/32
Transverse Vibration of EngineTransverse Vibration of Engine
8/20/2019 Engine Top Bracing.
9/32
Transverse Vibration
Due to
Guide
Force
Moments
8/20/2019 Engine Top Bracing.
10/32
Engine Top BracingEngine Top Bracing
To counteract the impact of guide force momentTo counteract the impact of guide force moments
the installation of a set of top bracings isthe installation of a set of top bracings is
recommended between the upper gallery of therecommended between the upper gallery of the
main engine and the hull structure.main engine and the hull structure.
8/20/2019 Engine Top Bracing.
11/32
Top BracingTop Bracing
FunctionFunction
To detune lateral vibration of main engine by increasingTo detune lateral vibration of main engine by increasingthe natural frequency of engine vibrating system to suchthe natural frequency of engine vibrating system to such
an extent that resonance occurs above the runningan extent that resonance occurs above the running
range of engine speed.range of engine speed.
If vibration level due to guide force moment is low andIf vibration level due to guide force moment is low and
within acceptable limit, top bracing may be eliminated.within acceptable limit, top bracing may be eliminated.
Vibration level normally to be checked by measurementsVibration level normally to be checked by measurements
with and without top bracing during sea trial.with and without top bracing during sea trial.
8/20/2019 Engine Top Bracing.
12/32
Top Bracing ArrangementTop Bracing Arrangement
Mechanical Friction TypeMechanical Friction Type
Hydraulic TypeHydraulic Type
8/20/2019 Engine Top Bracing.
13/32
Top bracing is installed between
the engine's upper platformbrackets
Top bracing is normally placed onthe exhaust side of the engine
Top bracing can alternatively be
placed on the camshaft side
8/20/2019 Engine Top Bracing.
14/32
Mechanical Top Bracing Arrangement
8/20/2019 Engine Top Bracing.
15/32
Mechanical Top Bracing ArrangementMechanical Top Bracing Arrangement
8/20/2019 Engine Top Bracing.
16/32
8/20/2019 Engine Top Bracing.
17/32
Hydraulic Top BracingHydraulic Top Bracing The hydraulically adjustable top bracing is anThe hydraulically adjustable top bracing is an
alternative to the mechanical top bracingalternative to the mechanical top bracing
It is intended for application in vessels where hullIt is intended for application in vessels where hull
deflection is foreseen to exceed the usual leveldeflection is foreseen to exceed the usual level
oror
In cases where the detuning effect from the topIn cases where the detuning effect from the top
bracings is only required in part of the engine speedbracings is only required in part of the engine speed
range.range.
8/20/2019 Engine Top Bracing.
18/32
Hydraulic
top bracingarrangement
8/20/2019 Engine Top Bracing.
19/32
Hydraulic Cylinders And Pump Station
8/20/2019 Engine Top Bracing.
20/32
HydraulicHydraulic
TopTopBracingBracing
ArrangementArrangement
8/20/2019 Engine Top Bracing.
21/32
Hydraulic TopHydraulic Top
Bracing ArrangementBracing Arrangement
8/20/2019 Engine Top Bracing.
22/32
8/20/2019 Engine Top Bracing.
23/32
w
8/20/2019 Engine Top Bracing.
24/32
Hydraulic
Top-Bracing
8/20/2019 Engine Top Bracing.
25/32
Hydraulic TopHydraulic Top--BracingBracing
Working principleWorking principle
The hydraulic topThe hydraulic top--bracing consists of a singlebracing consists of a single--acting hydraulic cylinder andacting hydraulic cylinder anda hydraulic controla hydraulic control--unit mounted directly on the cylinder housing.unit mounted directly on the cylinder housing.
The topThe top--bracing is self bracing is self --adjusting, using the vibration energy emitted byadjusting, using the vibration energy emitted by
the engine.the engine.
When the engine is running, the unit builds up a pressure in proWhen the engine is running, the unit builds up a pressure in proportionportion
to the vibration level.to the vibration level.
This detunes the engineThis detunes the engine’’s natural frequencies and accordingly lowers the impact ofs natural frequencies and accordingly lowers the impact of
the vibrations.the vibrations.
When the engine is at standstill, the pressure is then released.When the engine is at standstill, the pressure is then released.
8/20/2019 Engine Top Bracing.
26/32
When the distance
between the hull and
engine increases, oil flows into the cylinder
under pressure from the
accumulator
Working Principle
8/20/2019 Engine Top Bracing.
27/32
When the distance between
hull and engine decreases,
a non return valve prevents
oil from flowing back to the
accumulator and the pressure
rises.
If the pressure reaches a preset
maximum value, a relief valve
allows the oil to flow back to
the accumulator, maintaining
the force on the engine and
hull structures below the
specified level.
Working Principle
8/20/2019 Engine Top Bracing.
28/32
The top-bracing is automatically
controlled by the RPM signal fromthe propulsion control-system.
The system is active as standardwhen the engine is running, but a
programmable switch makes itpossible to choose an RPM rangewithin which the top-bracing systemis active.
For service purposes, manual controlis also possible.
Operation
8/20/2019 Engine Top Bracing.
29/32
MaintenanceMaintenance
&&
InspectionInspection
8/20/2019 Engine Top Bracing.
30/32
Mechanical Top BracingMechanical Top Bracing Relative movements between top bracing andRelative movements between top bracing and
fastening plate to be checked with dial gaugefastening plate to be checked with dial gauge
Accordingly tightening of bracing bolt to be carriedAccordingly tightening of bracing bolt to be carried
out with specified torqueout with specified torque
Tightening to be checked with torque wrench orTightening to be checked with torque wrench or
by hydraulic tensioningby hydraulic tensioning
Checking should be carried out once or twice a year.Checking should be carried out once or twice a year.
8/20/2019 Engine Top Bracing.
31/32
If relative
movementlarger than
+/- 0.02 mm,
increase
tightening
torque
8/20/2019 Engine Top Bracing.
32/32
Hydraulic Top BracingHydraulic Top Bracing Oil pressure of the hydraulic cylinders are to beOil pressure of the hydraulic cylinders are to be
compared with each other at regular intervalscompared with each other at regular intervals
If one of the cylinders shows a considerable lowerIf one of the cylinders shows a considerable lower
pressure, the opposite hydraulic cylinder must bepressure, the opposite hydraulic cylinder must be
released of its pressure until the problem has beenreleased of its pressure until the problem has been
remediedremedied
Oil leakages to be checkedOil leakages to be checked
Hydraulic cylinder to be overhauled in case of leakageHydraulic cylinder to be overhauled in case of leakage