Introduction to Turbulent Flows (Lecture Slides)

During my PhD studies, I worked on the Turbulent Flows. I prepared these lecture slides with the intention of teaching the subject in a post-graduate degree program. One reason of preparing my own material on the subject was that I wanted to include clear explanations, provide limitations of validity for various laws and adopt an easy to follow writing style. It can be said that all the notes or lecture slides available on the turbulent flows are not necessarily easy to understand. 

The second reason was that in Pakistan, I did not find a single university course that dealt with Turbulent Flows. Even the best Engineering universities were not offering this important course. It was therefore better to start a course with my personal course materials. The distinguishing feature of these particular slides/notes is that I have tried to provide  the "Limitations" of various theories, laws and assumptions which are sometimes neglected and thus lead to in inaccurate results.

Bangladesh As Pakistan's Taiwan : A Missed Opportunity

China's Taiwan

In January 2012, USA refused to supply Taiwan (formerly called Formosa) with the latest generation F-16C/D fighter jets. Press articles pointed out that the technical details of modern weapon systems were being leaked to the China [1]. Many high-level officials (even Generals) were found to be spying for China [1]. Apparently China claims the territory of Taiwan and they are not on good terms but some analysts have pointed out that it might not be what it seems.


After long years of warfare with the Communists, General Chiang Kia-shek took refuge in the island of Taiwan off the coast of the Mainland China with his left-over forces in 1949. Mainland China was taken over by the Communist People's Liberation Army (PLA) led by Mao Tse Tung. Mao Tse Tung was an aggressive Chinese leader, an expert in warfare. He fought with and defeated Nationalists led by General Chiang Kia Shek (till 1949), fought with Japanese occupation forces in China (1937-1945), invaded and captured Tibet (1950), sent troops to Korea to fight against US/Allied forces (1950-1952), fought a war with India (1962), acquired nuclear weapons, was ready to go to war with USSR (Russia) on one occasion and more. One thing he did not do was to recapture Taiwan. On occasions, military exercises were held near Taiwan and tensions rose high but a full-scale invasion did not happen.


In a bid to protect Taiwan from Communist China, West (USA and Europe) opened their arms to Taiwan. Latest military and industrial technology was provided to Taiwan in addition to its human resource development. The AIM-9B Sidewinder missile-equipped F-104 Starfighters of the Taiwanese Air Force symbolised the military aid of USA in early 1960s (just like Pakistan Air Force). Allegedly, these technical advances got transferred to the mainland China.  As the world knows it, China has become both the nuclear and space power, equalling the technical advacements of the west spanning over centuries. In short, what the analysts hinted to was that China profited from a "hostile Taiwan".

Pakistan's Taiwan

Nuclear Reactors and Tactical Nuclear Weapons of India and Pakistan : The Missing Links

Nuclear reactors are mainly used for three purposes, i.e., for generation of electricity, for naval propulsion and for production of Plutonium. All five internationally-recognised nuclear weapon states build their own nuclear reactors (all three types mentioned above). India and Pakistan claim to have nuclear weapons technology but still they have not built their own nuclear reactors capable of electricity generation or naval propulsion. Research and experimental reactors are not included in this study. It must be immediately added that India did modify the Canadian Pressurized Heavy Water Reactor (PHWR) design to increase its output. But for light water reactors, it still needs technical assistance.

Canada, Germany, Sweden and Switzerland do not possess nuclear weapons but they build their own nuclear reactors. It should be relatively easy for a nuclear weapons state to build these reactors. For both India and Pakistan, the right and logical route for advancement in the nuclear technology was to first work on indigenous nuclear reactors and then go towards weapons. Even now, they can share their know-how in the civil nuclear sector for mutual benefit.

After mastering nuclear weapons technology, Pakistan's establishment (Planning Commission) turned to the Thar Coal project. It was like, "We are done with the nuclear technology, now lets use coal". The nuclear expertise and infrastructure should have been employed for the generation of much needed electricity by building civil nuclear reactors. Lets see what happened in the developped countries.

Automobile Maintenance: Door lock Motor Repair

After décades of continuous operation, these electric door lock motors go bad mainly due to a torn rubber boot. The air gets inside and the grease is lost. Dirt can also accumulate on the slip rings of the dc motor, hindering its smooth operation. First remove the outer cover of the door from inside the vehicle.

Computer Power Supply Repair

If your notebook computer's power supply goes bad, then here is a tutorial for you. Remove the connecting wires from the box of power supply. The wires seldom get bad, its mostly something inside the plastic casing, which eventually has to be opened.

Fake Stealth Helicopter of The Abbottabad Raid 2011

On 2nd May 2011, a heli-borne force raided a compound in the Abbottabad city of Pakistan for the capture of Osama Bin Laden. After the raid, media showed some pictures of the tail unit of a crashed stealth helicopter (supposedly). Without any solid reason, it was stated that the crashed aircraft was a stealth version of the MH-60 BlackHawk helicopter. Two elements were readily evident from the photos. Firstly a shrouded tail rotor and secondly a forward-swept elevator (use google for images).

 

The 1971 India-Pakistan War : Betrayal or Blunders

If we study the military history of the India (Pre-1947), it would become evident that when faced with failure in war, we have always blamed betrayal and conspiracy instead of learning the right lessons. Be it the defeat of Siraj-Ud-dollah of Bengal (1757), the fall of Sultan Tipu (1799) or the Independence War (1857), we have always blamed triators instead of battleplans, strategy and bad Generalship. A good General should succeed in achieving his minimum objectives despite the risk of betrayal.

Agents, spies and informers are present on both sides and it is so since the time immemorial. From the engineering background, I would say that a General should have a "factor of safety" in his planning. Factor of safety is the extra protection against unforseen factors. To give an example, General Wellington can be quoted, who fought against the French Imperial Army during the Peninsular Wars (1807-1814). Despite the activity of embedded french informers, he succeeded in giving surprise to the French on several occasions.

Frequently-Mentioned Causes of Debacle

Automobile Maintenance: Engine Vacuum Leaks

When a road-going naturally-aspirated gasoline engine is idling, there is vacuum in the intake manifold. Vacuum is any pressure that is less than the ambient atmospheric pressure. Atmospheric pressure is expressed in different units and it varies with altitude. Therefore we usually reference it at sea level. At room temperature (20-25°C), atmospheric pressure is 14.7 psi or 760 mm Hg or 29.9 Inches of Mercury or 760 torr etc. Vacuum at engine idle exists due to the fact that the throttle is fully closed and the little air that gets past the throttle is sucked in by the cylinders. When the throttle is gradually opened, the pressure inside the intake manifold increases and nears the ambient atmospheric value.

In the start of the above paragraph, I used the term road-going vehicle because in some race engines, there may not be enough vacuum even at idle. The race engines use long-duration camshafts and the amount of vacuum in an engine depends on the design details of the camshaft(s) like the valve overlap angle.

Nuclear Testing in the South Asia

The five declared nuclear powers, i.e., USA, Russia, UK, France and China are also the only permanent members of the United Nations Security Council. This elite nuclear club also has the the privilege of veto. These powers have signed the nuclear Non-Proliferation Treaty (NPT), forbidding any technical assistance related to nuclear weapons to the non-nuclear states. 

India was a vast country with a big economy, huge population and a powerful military but without the nuclear power status. Also India had border disputes with China and it could not really confront China without becoming a nuclear power. The move for getting nuclear power status and possibly a permanent seat at UNSC was undertaken in May 1998 by doing a series of nuclear weapon tests. In turn, Pakistan replied with its own tests. The earlier Indian test of 1974 was declared as “peaceful nuclear test” and hence new tests were needed for demonstrating nuclear weapons capability. 

Automobile Maintenance: Engine Cooling System (Update)

This is an update to the former article on the engine cooling system : http://syed-imran-shah.blogspot.fr/2015/08/automobile-maintenance-engine-cooling.html

Coolant Expansion Tank

To make things clear, a schematic diagram of the expansion tank is given here. The internal tube is shown as a dashed line. Real pictures of this tube are also added. This tube has a bubble flare on one side to facilitate the entry of coolant and a bevel on the other side to facilitate the exit of the coolant. A rubber seal is also mounted on the tube for sealing of coolant and vapours.

Automobile Maintenance: Testing of Electrical Relays

This write-up concerns the general-purpose electrical relays. The specialized ones like timer relays etc are not discussed here.


For testing of electrical relays, one must first understand their function and working principle. Fucntion of a relay is to allow the use of a low-amperes circuit to control a high-amperes circuit. By control is implied switching on and switching off operation. The low-Amps circuit is the control side and high-Amps circuit is the feed side of the relay.


Many online videos suggest that if a relay clicks, then it is working. Clicks are an audio test at best and does not confirm if a relay is actually working. A click confirms that the control side of the relay is good but nothing can be said definitely about the feed side based on a clicking sound.

Automobile Maintenance: Identification of Electrical Relays

Here I am discussing a topic which is very important for automotive safety and yet is rarely discussed. This write-up concerns the general-purpose automotive electrical relays. The specialized ones like timer relays etc are not discussed here.

Electrical relays allow the use of a low-amperes circuit to control a high-amperes circuit. They can have either five or four terminals but mostly four of them are used. Ignoring the fifth terminal, a relay has two ground and two power connections. The low-Amps circuit is the control side and high-Amps circuit is the feed side of the relay. Looking at the specific positioning of the terminals, one would think that plugging-in of the relays is fool-proof and that they can only be inserted one way but in reality it is not the case.